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VAN NOSTRAND'S

ECLECTIC

Engineering Magazine

VOLUME XIX.

JULY-DECEMBER

1878.

NEW Y O R K :

D. VAN NOSTRAND, PUBLISHER. 23 Murray Street and 2? Warren Street (up stairs).

18 7 8.

3^, •• ■•/

A

V5

CONTENTS.

VOL. XIX.

Page.

Accidents to bridges 534

Accidents, prevention of 526

Accurate navigation 47

Action of brakes 251

Action of railway brakes 339

Addition to the British navy 93

Aeronautics 439

Air, compressed 466, 4S1

Air duct for mines 192

Air vs. water 424

Altenbnrg tunnel 4T4

American Institute of Mining En- gineers 88

American Society of Civil Engi- neers 88, 185,317, 471

American Society of Civil Engi- neers 563

Ammonia, distribution of 374

Ammunition expenditure 568

Analyses of Russian iron 279

Ancient land survey 429

Architect, studies of 419

Architectural cements 498

Armor-plate tests 190

Arnold Hague 458

Artificial fuel 544

Artificial marble 324

Artificial stone 96

Atmosphere 135

Aubois canal-lock. 85

Belgian Railway Co 2S0

Birmingham wire gauge 564

Buster steel 21

Boiler explosions 119

Boilers, use of zinc in 561

Book Notices :—

Adams, Charles F., Jr. Rail- roads—Their Origin and Problems 383

Bilgram, Hugo, M.E. Slide- Valve Gears 382

Bourne, John, C.E. Modern Engines 570

Brown, J. Croumbie. Plan- tations on the Sand Wastes of France— Journal of For- estry 94

Cain, Prof. Wm., A M., C.E. Maxi i.um Stresses in Framed Bridges 383

Caldwell, Geo. C, S.B., Ph.D. and A. A. Breneman, S.B. Chemical Practice 382

Carpenter, F. De Y. Geo- graphical Surveying. . . 287, 478

Comstock, Gen. C. B. Survey of the Northern and North- western Lakes, &c 570

Du Bois, A. Jay, C.E., Ph.D. Graphical Statics . . ....... 478

Du Bois, A. Jay. Graphical Statics 571

Du Moncel, Th. Electricite. 191

Fontaine, H. Electric Light- ing 384

Forrest, James, A. J. C. E. Proceedings of the Institu- tion of Civil Engineers 569

Fourier, Joseph. Theory of Heat 477

Frankland, E..D.C.L., F.R.S. Researches in Chemistry.. 569

Handbook of Inspectors of Nuisances 384

Hartley, W. Noel, F.R.S.E., F.S.C. Water, Air and Dis- infectants 191

Huntington, W. S. Road Master's Assistant 95

Institution of civil engineers 384

Jordan, D. S., Ph.D. of Vertebrate? 383

King, U.S.N. War Ships of P^urope 95

Kirkmau, M. M. Railway Service 2S7

Latham, B., F.G.S., C.E. Sanitary Engineering 384

Loring, A. E. Electro Tele- graph 477

MacDonald, .lames. Ameri- can Agriculture 3S4

Mammene, E. J. La Fabrica- tion du Sucre 95

Marey, E. J. La Methode Graphique dans la Sciences Experimentales 95

Millar, J. B., B.E. Descript- ive Geometry 190

Nicolls, W. J., C.E. Railway Builder 191

Pechar, J. Coal and Iron — 477

Prang's Alphabets 476

Proceedings of the Institution of Civil Engineers 95, 287

Page. Page.

Manual ; Canal-lock, Aubois 85

Cast steel, silicon in 550

Cause of blisters on " blister

steel" 21

Causes of accidents to bridges. . . 534

Cements, architectural 498

Changes in the earth's magnetism. 230

Cheap railway 186

Chilltd cast iron wheels 566

Chromium in alloys 565

Circular curves for railways 10

Civil engineer, studies of 419

Cleopatra's needle 263

Coal mines, ventilation of 369

Co-efficient of friction 519

Collapsing boat. 94

Compass in mining surveys 259

Composite armor-plates 286

Compre.-sed air 466, 431

Congress on civil engineering 377

Conservancy of rivers and streams 345

Continuous girders 553

Conversion of motion 433

Cord and pulley 395

Cotton powder or tonite 321

Report of Survey of Northern

Lakes 570 j Dangerous shunting operations.. 473

Riddell, Robert. The Artisan 569 Deducing formulae 360

Sadtler, S. P., A.M., Ph.D. ] Deep boring 310

Chemical Experimentation . 383 j Determination of Rocks 399

Different qualities of iron and

steel 564

Discharge of rainfall 22

Discharge of sewage 54S

Discussion on continuous girders 553

Distribution of ammonia 374

Don Pedro Segundo Railway 9

Drainage in Bombay 418

Drainage of Glasgow 112

Dynamometer 277

Dynamometer, new 560

Earth boring 310

Earth's magnetism 121, 230

Earthquake country, structuresin 271

Earthquakes and buildings 248

East India Railway Co 91

Education in France 2S7

Effect of river improvement 541

Elasticity of American wood 8

Electric fuse and heavy cannon.

Signal Office Report for 1877. 3S3 >

Skertchley, B. J., F. G. S. Outline of Physiography. . . 570 i

Smith, Edward, M.D., F.R.S. Manual for Health Officers. 3S3

Spretson, N. E. Treatise on Casting 477 '

Stanley, VV\ F. Mathematical Instruments 569 :

Thompson, W. P., C.E. Pat- ent Law 478 j

Thurston, Robert H., A.M., C.E. Growth of the Steam Engine 477

Tidy, Dr. M. Modern Chem- istry 569 ;

Treatise on Files and Rasps. 3S3

Trousset, Jules. Histoire de la Marine . 569

Voillet-le-Duc, E. Le Massif

du Mont Blanc 191 I Electricity for transmitting mo-

Warren, Maj.-Gen. G. K. Bridging the Mississippi River 570

Westcott, T. Life of John Fitch 383

Whitworth, Jos. Whitworth Papers 287

Wilson, Robert, A. J. C. E. Boiler and Factory Chim- neys 95

Wright, C. R. A. Metals .... 191

Wurtz, Ad. Dictionnaire du

Chimie 570

Boring on the Continent 310

tion 133

Engine economy 42

Engineering, sanitary 308

Engineers Club of Philadel- phia 83,471,563

Engineers, work of 183

Engines, air vs. water 424

English railways 566

Error in leveling 287

Experiments on he ghts of jets. . . 524 Experiments on railway brakes. . 519

Experiments on ship models 432

Explosion of a western river

steamer 206

Brake as a dynamometer 277 | Explosions, boiler 119

Brakes, action of 251, 339 Extension of the railway system. 473

Brakes, railway 519 '

Breech-loaders 93 I

Breech-loading artillery 94 '

Bricks and brick making 353 j

Bridges, framed 71, 146

Bridges, iron 134

Bridging the Mississippi and Mis- souri 281

Britannia bridge 256

Bronze age 502

Builders, railway 266

Building in India 240

Building material 254

Buildings and earthquakes 248

Fire engines 480

Fire-resisting flooring 192

Flow of solids 326

Food vs. fuel 245

Formul e, method of deducing.. 360

Foster testimonial fund 288

Foundations for bridges 282

Four dimensions 83

Framed bridges, stresses in 71, 146

Friction between a cord and pul- ley 395

Friction, co-efficient of 519

Fuel, artificial 544

1]

CONTENTS.

Page.

Fuel, gas as 39

Fuel in India 280

Garrett torpedo boat 381

Gas as fuel 39

Gatling guns 283

Gearing, laying out 312

Geographical surveying 52, 163

Geological relations of atmos- phere 1 35

Girder, continuous 553

Girders, strain of 115

Girders, strength of 134

Glasgow, drainage of 112

Glass cloth 479

Glass tumblers . , 41

Glycerine arrests decomposition. 438

Graphical statics 1, 97, 234

Great engineering feat 187

Gun carriages 93

Harbor improvements 193

Hardening wood pulleys 114

Health, public 183

Heat value of fuel 479

Heavy ordnance 189

Height of jets 479

Heights of jets, experiments on. . 524

Highways of Paris 567

Hoopes' & Townsend's Works.. 377

Horse vs. Steam engine 245

Hydrology of the Mississippi 211

Ice in Bombay 287

Importance of geological knowl- edge to engineers 480

Improvements of Charleston (S.

C.) harbor 193

Improvements of rivers 541

India, building in 240

Influence of the moon on the

earth's magnetism 121 |

Institute of Mechanical Engi- neers S9, 279

Internal stress in graphical sta- tics 1,97, 234

Iron and steel 459

Iron and steel, different qualities. 564 Iron and steel at Philadelphia... 279

Iron and steel for ships 105

Iron as a building material 254

Iron bridges 134

Iron, overstrain in 534

Iron pillars 360

Italian iron-clad 284

Japan,protection of river banks in 129 Jetties in Charleston (S. C.)

harbor 193

Jets, experiments on 524

Kutter's formula 390

Land survey, ancient 429

Larger wheels for cars 565

Lattice girders, strain of , . 115

Laying out gearing 312

Loading of heavy guns 284

London, provision for rain fall in 22

Long span railway bridges 92

Loss of a locomotive in quick- sand 288

Low jetties 193

Macadamized roads 568

Magnetic needle 413

Magnetism, earth's 121, 230

Manufacture of artificial fuel 544

xWanufacture of iron and steel . . 459 Manufacture of materials in India 240

Manufacture of steel 378

Marble, artificial 324

Mathematical science 402

Maximum stress in framed

bridges ..71, 146

Measuring the strain of lattice

girders 115

Mechanical conversion of motion 433

Metallurgy, ori gin of 502

Mines, ventilation of 369

Mining surveys, compass in 259

Mississippi, hydrology of 211

Momentum and vis viva 229

Monster ordnance 188

Page.

Mont Cenis tunnel 396

Moon's influence on the earth's

magnetism 121

Moose mine of Colorado 82

Mosandria, a new metal 359

Most ancient land survey 429

Motion, transmission of 133

Narrow gauge in Guatamala 473

Navigation, accurate 47

Needle, Cleopatra's 263

Needle, magnetic 413

New dynamometer 560

New explosive 284

New field gun 284

Newfoundland railway 567

New motor for Tram-cars 565

Orenburg and Central Asia 379

Origin ot metallurgy 502

Overstrain in iron 534

Palliser on projectiles 569

Paris exhibition, iron and steel at 459

Paris highways 567

Paris observatory 288

Paris, sewerage system of 124

Paris, street cleansing in 103

Pig iron of the United States ... 91 Pioneer and military railways. . 91

Planet Vulcan 479

Plates, steel 268

Population of the earth 572

Porphyry 399

Powder, cotton 321

Power, transmission 466, 481

Preservation of iron 90

Preservation of iron surfaces 36S

Prevention of railway accidents. 526

Programme of studies 419

Projectiles 96

Properties of iron and mild steel. 472 Proposed removal of Smith's

Is and 385

Protection from lightning 253

Protection of river banks in

Japan 129

Provision for rain fall in London 22

Public health 183

Public works in France 283

Pulley and cord 395

Purification of water 28

Queensland railways 474

Quick steaming 285

Railroads of the U. S. in 1877. ... 280

Railway accidents 474

Railway accidents 526

Railway across Newfoundland. . . 567

Railway brakes 339

Railway brakes, experiments on. 519

Railway builders 266

Railway empioves in India 473

Railway half-finished 379

Railway ticket system 566

Railways, circular curves for 10

Railways in Russia 566

Railways of the United Kingdom 566

Railway wheels 565

Rainfall in London 22

Rectangles ir scribed in a given

rectangle ., 532

Removal of Smith's Island 385

Rensselaer Polytechnic Institute. 384

Resistance of ships 432

River banks, protection of in

Japan 129

River improvement works 541

Rivers in Brazil 282

River, Mississippi 211

Rivers and streams 345

River steamer, explosion of 206

RiverThames 342

Riveted joints 268

Rocks, determination of 399

Rolling stock 266

Russian steamers 475

Sanitary engineering 308

Science, mathematical 402

Secular variations 413

Page.

Sewage, discharge cf 548

Sewage system of Paris 124

Sharpening files 368

Shell penetration 284

Ships models, experiments on 432

Ships, steel 274

Siemens-Martin metal 279

Silicon, influence on cast steel. .. 550

Six-inch breech-loader 190

Smith's Island, removal of . . . 3S5

Societe des Ingenieurs 317

Solids, flow of 326

Space of four dimensions 83

Stamp mill in Venezuela 390

Steam boiler explosions .... 119

Steam engine economy 42

Steamer, explosion of 20ft

Steamship accidents 526

Steam steering gear 475

Steam tramway engines 92

Steam vs. horsepower 245

Steel at the Paris exhibition 471

Steel, blisters on 21

Steel for ship-building 105

Steel for structural purposes 472

Steel, manufacture of 459

Steel plates 268

Steel ships 274

Steel vs.Iron 185

Steering of screw steamers 475

St. Gothard 379

St. Gothard railway 280, 474

Storm flood 96

Streams, conservancy of 345

Street cleansing in Paris 103

Strength of girders 134

Stresses in framed bridges — 71, 146

Stress, internal 1, 97, 284

Structures in earthquake regions. 271 Studies of the architect and en- gineer 419

Survey, ancient 429

Surveying, geographical 52, 163

Survey of silver mines 325

Surveys, mining 259

Sutro tunnel 282

System of drainage in Glasgow.. 112

Telephone in India 192

Telephones on the Central Pacific 233

Telescopic artillery sights 568

Temperature of the head 262

Testing of collapsing boats 432

Tests for diamonds 162

Thames 342

Thames torpedoes 94

Tide calculating machine 192

Tonite 321

Torpedo cases 93

Torpedo defenses 96

Torpedo depot ships 475

To pedo warfare 285

Tramways 318

Transmission of motion 133

Transmission of power 466, 481

Transportation car 186

Tunnel, Mont Cenis 396

Underground telegraph 96

Uniformity in sanitary engineer- ing... 308

University College, London 338

Variations of the needle 413

Venezuela, stamp mill in 390

Ventilation of coalmines 369

Ventilation of the Mont Cenis

tunnel 396

Vibration of wood 8

Victorian railways 379

Vis viva 229

Water engines vs. air engines. .. 424

Water, purification of 28

Water supply to a stamp mill 390

Wheels, chilled cast iron 566

Wheels, railway 565

Wire rope conveyance 567

Wire tramway 282

Wood, elasticity of 8

Wrought iron pillars 360

Zinc, use of in steam boilers 561

VAN NOSTRAND'S

ECLECTIC

ENGINEERING MAGAZINE.

NO. CXV -JULY, 1878 -VOL. XIX.

THE THEORY OF INTERNAL STRESS IN GRAPHICAL

STATICS.

By HENRY T. EDDY, C. E., Ph. D., University of Cincinnati.

Written for Van Nostrand's Magazine.

I.

Stress includes all action and reaction of bodies and parts of bodies by attrac- tion of gravitation, cohesion, electric repulsion, contact, etc., viewed espe- cially as distributed among the particles composing the body or bodies. Since action and reaction are necessarily equal, stress is included under the head of Statics, and it may be defined to be the equilibrium of distributed forces.

Internal stress may be defined as the action and reaction of molecular forces. Its treatment by analytic methods is necessarily encumbered by a mass of formulae which is perplexing to any ex- cept an expert mathematician. It is necessarily so encumbered, because the treatment consists in a comparison of the stresses acting upon planes in vari- ous directions, and such a comparison involves transformation of quadratic functions of two or three variables, so that the final expressions contain such a tedious array of direction cosines that even the mathematician dislikes to em- ploy them.

Now, since the whole difficulty really lies in the . unsuitability of Cartesian co- ordinates for expressing relations which are dependent upon the parallelogram of Vol. XIX.— No. 1—1

forces, and does not lie in the relations themselves, which are quite simple, and, which no doubt, can be made to appear so in quaternion or other suitable nota- tion; it has been thought by the writer that a presentation of the subject from a graphical stand point would put the entire investigation within the reach of any one who might wish to understand it, and would also be of assistance to those who might wish to read the analyt- ic investigation.

The treatment consists of two princi- pal parts: in the first part the inherent properties of stress are set forth and proved by a general line of reasoning which entirely avoids analysis, and which, it is hoped, will make them well understood; the second part deals with the problems which arise in treating stress. These problems are solved graphically, and if analytic expressions are given for these solutions, such ex- pressions will result from elementary considerations appearing in the graphi- cal solutions. The constructions by which the solutions are obtained are many of them taken from the works of the late Professor Rankine, who em- ployed them principally as illustrations,

VAN NOSTRAND'S ENGINEERING MAGAZINE.

and as auxiliary to his analytic investi- gations.

It is thus proposed to render the treatment of stress exclusively graphical, and by so doing to add a branch to the science of Graphical Statics, which has not heretofore been recognized as sus- ceptible of graphical treatment. It seems unnecessary to add a word as to the importance, not to say necessity, to the engineer of a knowledge of the theory of combined internal stress, since all correct designing presupposes such knowledge.

Stress on a Plane. — " If a body be conceived to be divided into two parts by an ideal plane traversing it in any direction, the force exerted between those two parts at the plane of division is an internal stress." — Rankine.

A State op Internal Stress is such a state that an internal stress is or may be exerted upon every plane passing through a point at which such a state exists.

It is assumed as a physical axiom that the stress upon an ideal plane of divi- sion which traverses any given point of a body, cannot change suddenly, either as to direction or magnitude, while that plane is gradually turned in any way about the given point. It is also as- sumed as axiomatic that the stress at any point upon a moving plane of divi- sion which undergoes no sudden changes of motion, cannot change suddenly either as to direction of amount. A sudden variation can only take place at a surface where there is a change of material.

GENERAL PROPERTIES OF PLANE STRESS.

We shall call that stress a plane stress which is parallel to a plane; e.g., let the plane of the paper be this plane and let the stress acting upon every ideal plane which is at right angles to the plane of the paper be parallel to the plane of the paper, then is such a stress a plane stress.

The obliquity of a stress is the angle included between the direction of the stress and a line perpendicular to the ideal plane it acts upon. This last plane we shall for brevity call the plane of action of the stress, and any line perpendicular to it, its normal. In plane

stress, the planes of action are shown by their traces on the plane of the paper, and then their normals, as well as their directions, the magnitudes of the stresses, and their obliquities are correctly rep- resented by lines in the plane of the paper.

The definition of stress which has been given is equivalent to the state- ment that stress is force distributed over an area in such wise as to be in equili- brium.

In order to measure stress it is neces- sary to express its amount per unit of area: this is called the intensity of the stress.

Stress, like force, can be resolved into components. An oblique stress can be resolved into a component perpendicular to its plane of action called the normal component, and a component along the plane called the tangential component or shear.

When the obliquity is zero, the entire stress is normal stress, and may be either a compression or a tension, i.e., a thrust or a pull. When the obliquity is +90°, the stress consists entirely of a tangen- tial stress or shear. If a compression be considered as a positive normal stress, it is possible to consider a normal tension as a stress whose obliquity is +180°, and the c bliquities of two shears having opposite signs, also differ by 180°.

Fig.l

Conjugate Stresses. — If in Fig. 1 any state of stress whatever exists at o, and xx be the direction of the stress on a plane of action whose trace is yy, then is yy the direction of the stress at o on the plane whose trace is xx. Stresses so related are said to be conjugate stresses.

For consider the effect of the stress upon a small prism of the body of which axa^aK is a right section. If the stress is uniform that acting upon «x«4 is equal and opposed to that acting upon a2as, and therefore the stress upon these faces of the prism are a pair of forces in equilibrium. Again, the stresses upon

INTERNAL STRESS IN GRAPHICAL STATICS.

3

the four faces form a system of forces which are in equilibrium, because the prism is unmoved by the forces acting upon it. But when a system of forces in equilibrium is removed from a sys- tem in equilibrium, the remaining forces are in equilibrium. Therefore the re- moval of the pair of stresses in equili- brium acting upon axa4 and a2as from the system of stresses acting upon the four faces, which are also in equilibrium, leaves the stresses upon axa2 and a3a4 in equilibrium. But if the stress is uni- form, the stresses on axa2 and a%ak must be parallel to yy, as otherwise a couple must result from these equal but not directly opposed stresses, which is in- consistent with equilibrium.

This proves the fact of conjugate stresses when the state of stress is uni- form: in case it varies, the prism can be taken so small that the stress is sensibly uniform in the space occupied by it, and the proposition is true for varying stress in case the prism be indefinitely dimin- ished, as may always be done.

Fiff. 2 /

JL

Tangential Stresses. — If in Fig. 2 the stress at o on the plane xx is in the direction xx, i.e. the stress at o on xx consists of a shear only; then there necessarily exists some other plane through o, as yy, on which the stress consists of a shear only, and the shear upon each of the planes xx and yy is of the same intensity, but of opposite sign.

For let a plane which initially coin- cides with xx revolve continuously through 180° about o, until it again co- incides with xx, the obliquity of the stress upon this revolving plane has changed gradually during the revolution through an angle of 360°, as we shall show.

Since the obliquity is the same in its final as in its initial position, the total change of obliquity during the revolu- tion is 0° or some multiple of 360°. It cannot be 0°, for suppose the shear to be due to a couple of forces parallel to xx,

having a positive moment; then if the plane be slightly revolved from its initial position in a plus direction, the stress upon it has a small normal com- ponent which would be of opposite sign if the pair of forces which cause it were reversed or changed in sign; or, what is equivalent to that, the sign of the small normal component would be reversed if the plane be slightly revolved from its initial position in a minus direction. Hence the plane xx, on which the stress is a shear alone, separates those planes through o on which the obliquity of the stress is greater than 90° from those on which it is less than 90°, i.e., those hav- ing a plus normal component from those having a minus normal component.

Since in revolving through +180° the plane must coincide, before it reaches its final position, with a plane which has made a slight minus rotation, it is evi- dent that the sign of the normal com- ponent changes at least once during a revolution of 180°. But a quantity can change sign only at zero or infinity, and since an infinite normal component is inadmissible, the normal component must vanish at least once during the proposed revolution. Hence the obliq- uity is changed by 360° or some multi- ple of 360° while the plane revolves 180°. In fact the normal component vanishes but once, and the obliquity changes by once 360° only, during the revolution.

It is not in every state of stress that there is a plane on which there is no stress except shear, but, as just shown, when there is one such plane xx there is necessarily another yy, and all planes through o and cutting the angles in which are hx and b3 have normal com- ponents of opposite sign from planes through o and cutting the angles in which are 52 and b4.

To show that the intensity of the shear on xx is the same as that on yy, consider a prism one unit long and having the indefinitely small right section byb2bzbA. Let the area of its upper or lower face be a^bjb^, that of its right or left face be a2 — b2bz, then als1 and aus2 are the total stresses on these respective faces if *j and s2 are the intensities of the respective shears per square unit. Let the angle xoy—i, then

a,s, . a„ sin. i

van nostrand's engineering magazine.

is the moment of the stresses on the

upper and lower faces of the prism, and

a2s2 . ax sin. i

is the moment of the stresses on the right and left faces; but since the prism is unmoved these moments are equal.

These stresses are at once seen to be of opposite sign.

Fig. 3

V

A

"* X

0

x *

Y

V

Tangential Components. — In Fig. 3 if xx and yy are any two planes at right angles to each other, then the intensity at o of the tangential component of the stress upon the plane xx is necessarily the same as that upon the plane yy, but these components are of opposite sign.

For the normal components acting upon the opposite faces of a right prism are .necessarily in equilibrium, and by a demonstration precisely like that just employed in connection with Fig. 2 it is seen that for equilibrium it is necessary and sufficient that the intensity of the tan- gential component on xx be numerically equal to that on yy, but of opposite sign.

State of Stress. — In a state of plane stress, the state at any point, as o, is completely defined, so that the intensity and obliquity of the stress on any plane traversing o can be determined, when the intensity and obliquity of the stress on any two given planes traversing that point are known.

For suppose in Fig. 4 that the intensi- ty and obliquity of the stress on the given planes xx and yy are known, to find that on any plane x'x' draw mn || x'x' then the indefinitely small prism one unit in length whose right section is mno, is held in equilibrium by the forces acting upon its three faces. The forces acting upon the faces om and

on are known in direction from the obliquities of the stresses, and, if px and py are the respective intensities of the known stresses, then the forces are om.px and on.py respectively. The re- sultant of these forces and the reaction which holds it in equilibrium, together constitute the stress acting on the face mn: this resultant divided by mn is the intensity of the stress on mn and its direction is that of the stress on mn or

x x .

Fig. 4

It should be noticed that the stress at o on two planes as xx and yy cannot be assumed at random, for such assumption would in general be inconsistent with the properties which we have shown every state of stress to possess. For in- stance we are not at liberty to assume the obliquities and intensities of the stresses on xx and yy such that when we compute these quantities for any plane x'x' and another plane y'y' at right angles to x'x' in the manner just indicated, it shall then appear that the tangential components are of unequal intensity or of the same sign. Or, again, we are not at liberty to so assume these stresses as to violate the principle of con- jugate stresses.

But in case the stresses assumed are conjugate, or consist of a pair of shears of equal intensity and different sign on any pair of planes, or in case any stresses are assumed on a pair of planes at right angles such that their tangential compo- nents are of equal intensity but different sign, we know that we have made a con- sistent assumption and the state of stress is possible and completely defined.

The state of stress is not completely defined when the stress upon a single plane is known, because there may be any amount of simple tension or com- pression along that plane added to the state of stress without changing either the intensity or obliquity of the stress on that plane.

INTERNAL STRESS IN GRAPHICAL STATICS.

Principal Stresses. — In any state of stress there is one pair of conjugate stresses at right angles to each other, i.e. there are two planes at right angles on which the stresses are normal only. Stresses so related are said to he princi- pal stresses.

It has been previously shown that if a plane be taken in any direction, and the direction of the stress acting on it be found, then these are the directions of a pair of conjugate stresses of which either may be taken as the plane of action and the other as the direction of the stress acting upon it.

Consider first the case in which the state of stress is defined by a pair of conjugate stresses of the same sign; i.e., the normal components of this pair of conjugate stresses are both compressions or both tensions.

It is seen that they are of opposite obliquities, and if a plane which initially coincides with one of these conjugate planes of action be continuously revolved until it finally coincides with the other, the obliquity must pass through all in- termediate values, one of which is 0°, and when the obliquity is 0° the tangential component of the stress vanishes. But as has been previously shown there is another plane at right angles to this which has the same tangential compo- nent; hence the stress is normal on this plane also.

Consider next the case in which the pair of conjugate stresses which define the state of stress are of opposite sign, i.e., the normal component on one plane is a compression and that on the other a tension.

In this case there is a plane in some intermediate position on which the stress is tangential only, for the normal com ponent cannot change sign except at zaro. It has been previously shown that in case there is one plane on which the stress is a shear only, there is another plane also on which the stress is a shear only, and that this second shear is of equal intensity with the first but of opposite sign. Let us consider then that the state of stress, in the case we are now treating, is defined by these oppo- site shears instead of the conjugate stresses at first considered.

Now let a plane which initially coin- cides with one of the planes of equal shear revolve continuously until it finally coincides with the other. The obliquity gradually changes from +90° to —90% during the revolution, hence at some intermediate point the obliquity is 0°; and since the tangential component has the same intensity on a plane at right angles to this, that is another plane on which the obliquity of the stress is also 0°.

We have now completely established the proposition respecting the existence of principal stresses which may be restated thus:

Any possible state of stress can be completely defined by a pair of normal stresses on two planes at right angles to each other.

As to the direction of these principal planes and stresses, it is easily seen from considerations of symmetry that in case the state of stress can be defined by equal and opposite shears on a pair of planes, that the principal planes bisect the angles between the planes of equal shear, for there is no reason why they should incline more to one than to the other. We have before shown that the planes of equal shear are planes of separation between those whose stresses have normal components of opposite sign: hence it appears that the principal stresses are of opposite sign in any state of stress which can be defined by a pair of equal and opposite shears on two planes.

It will be hereafter shown how the direction and magnitude of the principal stresses are related to any pair of con- jugate stresses.

For convenience of notation in discuss- ing plane stress let us denote compression by the sign +, and tension by the sign

Let us also call that state of stress which is defined by equal principal stresses of the same sign a fluid stress. A material fluid can actually sustain only a + fluid stress, but it is convenient to include both compression and tension under one head as fluid stress, the proper- ties of which we shall soon discuss.

Let us call a state of stress which is defined by unequal principal stresses of the same sign an oblique stress. This

6

VAN NOSTRAND'S ENGINEERING MAGAZINE.

may be taken to include fluid stress as the particular case in which the ine- quality is infinitesimal. In this state of stress there is no plane on which the stress is a shear only, and the normal component of the stress on any plane whatever has the same sign as that of the principal stresses.

Furthermore let us call that state of stress which is defined by a pair of shearing stresses of equal intensity and different sign on two planes at right angles to each other a right shearing stress. We shall have occasion immediately to discuss the properties of this kind of stress, but we may advan- tageously notice one of its properties in this connection. It has been seen pre- viously from considerations of symmetry that the principal stresses and planes which may be used to define this state of stress, bisect the angles between the planes of equal shear. Hence in right shearing stress the principal stresses make angles of 45° with the planes of equal shear. We can advance one step further by considering the symmetrical position of the planes of equal shear with respect to the principal stresses and show that the principal stresses in a state of right shearing stress are equal but of opposite sign.

We wish to call particular attention to fluid stress and to right shearing stress, as with them our subsequent discussions are to be chiefly concerned : they are the special cases in which the principal stresses are of equal intensities, in one case of the same sign, in the other case of different sign.

Let us call a state of stress which is defined by a pair of equal shearing stresses of opposite sign on planes not at right angles an oblique shear- ing stress. The principal stresses, which in this case are of unequal intensity and bisect the angles between the planes of equal shear, are of opposite sign. A right shearing stress may be taken as the particular case of oblique shearing in which the obliquity is in- finitesimal.

We may denote a state of stress as + or — according to the sign of its larger principal stress.

Fluid Stress. — In Fig. 5 let xx and yy be two planes at right angles, on

which the stress at o is normal, of equal intensity and of the same sign; then the stress on any plane, as x'x', traversing o is normal, of the same intensity and same sign as that on xx or yy.

For consider a prism a unit long and of infinitesimal cross section having the face mn \\ x'x\ then the forces fx and/^ 0 acting on the faces om and on are such that

fx'fyi: om : on.

Now nm=\/om2 + on*, and the result- ant force which the prism exerts against nm is

/= v/.'+Z, S .: fx:f::om: mn.

But fx -±-om is the intensity of the stress on xx and f-r-mn is the intensity of the stress on x'x', and these are equal. Also by similarity of triangles the result- ant f is perpendicular to mn.

Fig. 6

V

/v

\ 1

A /

\X \

\/

\V[

y\

/o "\

X

\ ^\a;/

X

/

y \

\r

Eight Shearing Stress. — In Fig. 6, let xx and yy be two planes at right angles to each other, on which the stress is normal, of equal intensity, but of opposite sign; then the stress on any plane, as ccV, traversing o is of the same intensity as that on xx and yy, but its obliquity is such that xx and yy respect- ively, bisect the angles between the direction rr of the resultant stress, and the plane of action x'x' and its normal

y'y'-

INTERNAL STRESS IN GRAPHICAL STATICS.

For, if the intensity of the stress on x'x' be computed in the same manner as in Fig. 5, the intensity is found to be the same as that On xx or yy, for the stresses to be combined are at right angles and are both of the same magnitude. The only difference between this case and that in Fig. 5 is this, that one of the component stresses, that one normal to yy say, has its sign the opposite of that in Fig. 5. In Fig. 5 the stress on x'x' was in the direction y'y', making a cer- tain angle yoy' with yy. In Fig. 6 the resultant stress on x'x' must then make an equal negative angle with yy, so that yor=yoy'. Hence the statement which has been made respecting right shearing stress is seen to be thus established.

Combination and Separation. — Any states of stress which coexist at the same point and have their principal stresses in the same directions xx and yy combine to form a single state of stress whose principal stresses are the sums of the re- spective principal stresses lying in the same directions xx and yy : and con- versely any state of stress can be separ- ated into several coexistent stresses by separating each of its two principal stresses into the same number of parts in any manner, and then grouping these parts as pairs of principal stresses in any manner whatever.

The truth of this statement is nec- essarily involved in the fact that stresses are forces distributed over areas, and that as a state of stress is only the grouping together of two necessarily related stresses, they must then necessarily fol- low the laws of the composition and resolution of forces.

For the sake of brevity, we shall use the following nomenclature of which the meaning will appear without further ex- planation.

The terras applied to forces and stresses are :

Compound,

Composition,

Component,

Resolve,

Resolution,

Resultant.

The terms applied to states of stress are :

Combine,

Combination,

Component state,

Separate,

Separation,

Resultant state.

Other states of stress can be combined besides those whose principal stresses coincide in direction, but the law of combination is less simple than that of the composition of forces; such combi- nations will be treated subsequently.

Component Stresses. — Any possible state of stress defined by principal stresses whose intensities are px and py on the planes xx and yy respect- ively is equivalent to a combination of the fluid stress whose intensity is ±i(Px + Py) on each of the planes xx and yy respectively, and the right shear- ing stress whose intensity is + -J ( px — py) on xx and — i(px — py) on yy.

For as has been shown, the resultant stress due to combining the fluid stress with the right shearing stress is found by compounding their principal stresses. Now the stress on xx is

i(p* +p ) + h{r*-Pv)=p*

and that on yy is

i(P* +Py)-i(P* ~Py )=Py and hence these systems of principal stresses are mutually equivalent

In case py = 0, the stress is complete- ly defined by the single principal stress px , which is a simple normal compression or tension on xx. Such a stress has been called a simple stress.

A fluid stress and a right shearing stress which have equal intensities com- bine to form a simple stress.

It is seen that the definition of a state of stress by its principal stresses, is a definition of it as a combination of two simple stresses which are perpendicu- lar to each other.

There are many other ways in which any state of stress can be separated into component stresses, though the separa- tion into a fluid stress and a right shear- ing stress has thus far proved more use- ful than any other, hence most of our graphical treatment will depend upon it. It may be noticed as an instance of a different separation, that it was shown that the tangential components of the stresses on any pair of planes xx and yy at right angles to each other are of equal intensity but opposite sign. These tangential components, then, together form a right shearing stress whose prin-

8

VAN NOSTRAND'S ENGINEERING MAGAZINE.

cipal planes and stresses x'x' and y'y' bisect the angles between xx and yy> while the normal components together define a state of stress whose principal stresses are, in general, of unequal in- tensity.

Hence any state of stress can be sepa- rated into component stresses one of

which is a right shearing stress on any two planes at right angles and a stress having those planes for its principal planes.

The fact of the existence of conjugate stresses points to still another kind of separation into component stresses.

THE MODULUS OF ELASTICITY IN SOME AMERICAN WOODS, AS DETERMINED BY VIBRATION.

By Dr. MAGNUS C. IHLSENG. Written for Van Nostrand's Magazine.

The importance of this factor, so necessary for construction, is sufficiently acknowledged to warrant the use or arrangement of new methods for its accurate determination. The various direct methods which are now employed are more or less elaborate, involving a large outlay in apparatus. We have, however, a more ready means for ascer- taining this value, one which is not usually resorted to, namely, by vibra- tion.

When any rod or solid body is rubbed by a resined woolen cloth in the direction of its axis, it is urged into longitudinal vibration and gives out a note of high pitch. The particles of the rod are excited by a force which acts along the direction of the fibres and they will move backward and forward, thus executing an oscillation. This vi- bratory movement of the particles pro- duces a pulse running through the en- tire length of the rod in a given time, and this motion continues while the exciting cause is acting, the velocity de- pending upon the structure of the ma- terial. The propagation of this vibra- tion, however, depends upon the elastic force of the molecules and not on the tension which is applied externally. The more elastic the body is the greater will be the rapidity of transmission. So, it is evident, that the rapidity of vibra- tion, or, in other words, the pitch of the note which the rod is sounding, depends upon the velocity with which this pulse is propagated. If, now, we ascertain the pitch of the note, by counting the

number of vibrations per second, we have determined the velocity of propa- gation by substitution in this simple formula :

v = 2 n.l, in which v is the velocity per second, and n the number of vibrations executed by the rod, whose length is I. The length may be two meters, the thickness about 20 mm. The specimen should be, of course, as free as possible from im- perfections.

To measure the rate of vibration of the rod, I employed a simple direct pro- cess, which has been fully detailed, hav- ing been read before the National Acad- emy of Sciences, Oct., 1877.

In brief, the modus operandi is this; the rod to be experimented upon is clamped in the center by a vise, one end being free, the other end having a small brass pen fastened to it. This brass pen is bent somewhat and rests upon a smoked glass plate. When the rod is set into vibration by rubbing it along the free end, by a resined woolen cloth, the glass plate is moved under the pen by means of a falling weight. A tun- ing fork of a known rate simultaneously registers its vibration on the plate; the two pens have now described two traces, the number of vibrations in each depend- ing on the ratio between the two notes of the rod and fork. Two parallel lines are drawn upon the plate, embracing a given period of time. The number of the waves in each of the two traees are then counted between these parallel lines, by means of a low power microscope.

MODULUS OF ELASTICITY IN AMERICAN WOODS.

9

In this manner, the rates of vibration of several rods were determined. By calculation, v was obtained, which by substitution in the following formula, gives us the the value for the coefficient of elasticity ;

(39.37041 XvY

9 v=the velocity of sound in meters as cal- culated above; g is the accelerating force of gravity; m is the weight of one cubic

inch of the substance, in pounds; the factor, 39.37041 is the number of inches in a meter.

The following table shows the results of the experiments upon the several varieties of wood. The degree of humidity of these specimens was not found as they were well seasoned and in the condition employed in commerce. The determinations are all average values of from ten to fifteen observa- tions :

Cypress

Poplar

<<

<<

tt

Shell bark Hickorv

White Pine .".

White Pine

White Ash

White Ash

White Holly

Mahogany

Black Walnut

Wild Cherry

Yellow Pine

Red Oak

White Oak

Specific Gravity.

.432 .482 .465 .417 .478 .476 .443 .425 .478 .922 .491 .432 .544 .541 .562 .540 .518 .693 .664 .650 .775

Length.

1.836 M

1.8384

1.83875

1.83672

1.650

83857

834

21236

114237

5505

8419

8426

8365

83826

3785

3491

37863

5601

0524

4947

4945

Number of Vibrations.

1033.53

1107.97

1050.93

1132.8

1187 3

1339.98

1418.

2041.8

2035.47

1279.5

1227.21

1165.94

1159.13

1326.58

1532.6

1734.1

1413 26

2030.83

1395.04

1443.93

Velocity per Second.

3797.2 M

4073.89

3864.79

4161.65

3918.14

4927.4

5201.2

4950.68

4650.4

4110.1

4713.4

4522.47

4282.44

4261.51

3657.4

4135.3

4780.7

4409.5

4274.5

4179.8

4316.5

Modulus of Elasticity, inch lbs.

901020 1157100 1004700 1044700 1061500 1710700 1733560 1506800 1496880 2253000 1577890 1278100 1443140 1421100 1087450 1335800 1712500 1949160 1754940 1644160 2090050

There have been few experiments upon the elasticity of woods by any similar methods of vibration. Wertheim,* who alone has any extended investigations upon this point, decides that the coeffi- cient obtained by vibration is greater than that from elongation, by abput a per cent. This he explained by assum- ing a slight increase of temperature as produced by the compression of the particles of the rod. More recent modi- fications, however, show that the heat disengaged in the transmission of this motion has little influence.

The advantages of the present method are evident, as the number of vibrations are directly registered, a process, which Weisbach, by the bye, considered im- practicable.! I have also shown in my

* Annalen der Chemie et Physique, Ser. Ill, T. 12, p. 385, and Comptes i endus, Tome 23. p. 663.

+ Weisbach, Mechanics' of Engineering, Coxe, Vol. I, p. 1077.

article, above alluded to, that this method gives results which are lower than those obtained from Kundt's air method, by one per cent, or more; thus, perhaps, bringing it nearer the truth. Moreover, the rod registers the same number of vibrations, within the limits of error, that is given by a standard tuning fork to which the rod has been brought into unison.

The Don Pedro Segundo Railway line has reached its highest point, an al- titude of 3550 ft., 225 miles from Rio de Janeiro, in traversing the gorge of Juan Ayres, in the Mantiqueira range, whose highest peak is Itatiaia, 8380 ft. in alti- tude. The Pyrenees range, in Goyaz, although not so towering in outline as the Mantiqueira range, has been found to be over 1000 ft. higher, and to be the high- est in Brazil — its real backbone, in fact.

10

van nostkand's engineering magazine.

CIRCULAR CURVES FOR RAILWAYS.

By Pkof. WM. M. THORNTON, University of Virginia. Written for Van Nostra:nd's Magazine. § 1. SIMPLE CURVES.

1. Setting out a circular curve:

The deflection angle of a circular curve is the angle subtended at any point of it by a chord one chain long. If this angle d be given and the tangent at the origin o, it is easy to set out such a curve. Plant the transit at o, set the vernier at zero, sight to t and clamp the lower motion. Release the upper mo- tion, deflect d to 01 and make 01 equal to one chain. Deflect d again to 02 and make 12 equal to one chain; and so on.

2. Elements of the curve:

3. Fundamental formulae:

It is obvious geometrically that DCT

D.- Whence the following formulae

sm.

D:

tan. T>—

The elements of such a curve are d, the deflection angle,

r s t D

radius,

semichord,

tangent,

total deflection.

Thus in the diagram CD = CD'=r, DD' = 2s, DN=S, DT=D'T=:*, TDD' =TD'D=D. All lengths are in chains of 100 links, all angles in minutes.

sin. d-

1 2r>

the last formula is a special case of the first. For when D=d, 25=1. These formulae are exact and afford the solution of all possible cases. In applying them to numerical examples it is most con- venient to throw them first into the logarithmic form, thus:

Jjr=l. 69897— L sin. d, Ls=Lr-f-L sin. D, Lz=Lr + Ltan.D.

The following example shows the most convenient order for conducting the computation:

d=lS\ D = 24° 19'

23.55

1.69897

L sin. d

8.32702

Lr

1.37195

L sin. D

9.61466

L tan. D

9.65501

Ls

0.98661

U

1.02690

9.70 10.64

The computations are sufficiently sim- ple. But as it would be necessary for the engineer to carry into the field a set of logarithmic tables and to interrupt his work to perform the computations, the approximate formulae in the follow- ing article have been devised. These

CIRCULAR CURVES FOR RAILWAYS.

11

reduce the necessary computations to a few easy divisions, by means of a small collection of tables.

4. Approximate formulae :

If x be expressed in circular measure

sin. x=x-

x x 6 +120

sin. x <

Remembering then that dis expressed in

minutes and that sin. d=—. we have

2r

, 5400 n\r d <

6.108002

The second member is less than -§- if J<521; that is if r>3.30. No greater curvature than this should be permitted in railway curves. Accordingly the formula

5400

nr

gives the value of d for a given r within a half minute in defect. It is therefore for railway practice as good as exact. Hence if we put

5400 m = = 1118.81:

7t

S=m sin. D, T=?n tan. D, we have the formulae

dr=m, ds=S, dt=T*

5. Tables:

The tables required for use with this method are a table for r with d as argu- ment, and tables for S T, with D as argument. Such tables arranged in a convenient form are appended to this article.

6. Short chords :

At the terminus of a curve it is fre- quently necessary to use a short chord to join it to the tangent. A short chord is also frequently used to complete a chain begun on the initial tangent. In either case the appropriate deflection angle is easily found. For if dx be the required angle, cx the length of the chord then

sin. dx = — 2r

But since dx is less than d we can put

7 dx

sm. dx=—

2m

.-. dx = dcx

7. Length of the curve:

The number of chords in the curve is obviously given by the formula

nd=T>

The fractional part of n if any will by the last article be the length of the short chord necessary to complete the curve* Thus in the example treated in (1, 3)

24°19/ n=— — T = 19.99: to

so that the curve consists practically of 20 chains. If £=112', D=31° 12'

n=16.7l

so that the curve consists of 16 chains and a short chord of 71 links, the deflec- tion angle for which is

dx = 112/X0.71 = 80/

8. Long chords:

Chords running two or more stations are often used to test the accuracy of the field work. If x be the number of sta- tions, cx the length of the chord

c~ = 2r sin. dx.

But

sin. dx:

m'

.-. dcx = 2Sdz-

Sdx is taken from the S— Table and cx found by an easy division:

9. Ordinates:

Intermediate points on the curve are fixed by means of ordinates or offsets normal to the chord.

12

VAN NOSTRAND7S ENGINEERING MAGAZINE.

If AB be the chord, PAI the normal to the chord, IQ the normal to the curve we may disregard the difference between PM, IQ and put PQ=y tne required ordinate. If therefore PA=a?

y{2r-y)=x{l-x)\

or since y is very small in comparison with r

y=

il-x)

2r

For the middle ordinate x=% and hence 1

2/o=

8r

For the quarter ordinates£=J and hence y^f yo. In terms of the deflection angle we have

2/0=0.00007274 d.

* For bending rails of length I the analo- gous formula is

yo ==0.00007274 dl\

10 Cant:

The centrifugal force acting on a mass m revolving in a circle of radius r feet,

with velocity v feet per second is — ;

the weight of the same mass is rag. The resultant of these forces must be normal to the road bed. Hence if G be the gauge, H the cant or superelevation of the outer rail both expressed in the same unit

H_^2

G~ gr

In practice the velocity is usually given in miles per hour V; and hence

3600 v = 5280 V,

<tfr=l7l887; #=32.1695;

••• l=^°

where q is a constant factor such that

Lq= 7.58999

For the ordinary gauge 4' 8^" we have for the cant in inches

H=0.00002198dV2.

* Reducing the coefficient to a continued fraction and calculating the convergents we find for the middle ordi- nate in links the practically exact and very simple formula

11 100* The side ordinates win be iT' Too' The formulse

are so simple that no tahle is needed.

or with a high degree of accuracy H_22Va d~ 106 The following table gives the values of 1000 — for equidistant values of V.

15

20

25

30

35

40

45

50

5

9

14

20

27

35

45

55

11. Field Problems:

The problems which arise in the field have been exhaustively treated by so many writers that it will be necessary simply to indicate the mode in which our formulse and tables are applied. The data are as follow:

A. The origin, the tangent there and the terminus.

Measure DD'=2S, TDD'=D. Then take S from the table. We shall then have

s d

and the curve is set out as in (1, 1)

B. The origin, the terminus and the curvature.

Measure DD' = 2S. Then S = ds; whence D from the S table. Set out DT)T=D and proced as in (1, 1)

C. The origin and both tangents.

1. Point of concourse of the tangents accessible:

Plant the transit at T and measure the exterior angle which is 2D ; measure also the tangent TD=£. Then having got T from the table we have

_ T D

d=Vn=~d

2. Point of concourse of the tangents inaccesssible

Set out and measure PQ and the

CIRCULAR CURVES FOR RAILWAYS.

13

Measure the exterior angle T: and take T from the table. Then

2D,

t—

~cV

D

angles P, Q. Or where this is impossible determine the no by a traverse. Then

2D = P + Q,

PT=PQ4-n-^-, = PQ.|^

^ sin 2D' ^ S2D

Z=PT-PD.

D. The curvature and both tangents: 1. Point of concourse accessible:

The first formula fixes D, the origin. 2. Point of concourse inaccessible: Set out and measure PQ and the angles P, Q. Then

2D=F + Q,

PT=PQ.

sin. Q

=PQ,

'2D

t:

n=—.

sin. 2D T

7r

D d> PD=PT-£.

The last formula fixes the origin. 12. Obstacles:

A. When the stations after x are no longer visible from 0.

The telescope being set on x clamp the vernier plate, remove the transit and plant at x. Siujht back to o by the lower motion and clamp. Reverse the tele- scope and release the vernier plate.

Bring the vernier back to zero and con- tinue setting out as from a new origin o' . B. When two stations b, c are visible from the origin o but the chord between them bo cannot be measured.

To fixe

(1) Measure the long chord oc.

(2) Measure the chord from second station back, ac.

the

(3) Range out bd-- 1.

:aZ>, and make dc

13. Corrections:

Having run a curve from a given tan- gent terminating in a certain tangent, it is required to determine a curve which will terminate in a parallel tangent.

(1) Without changing the origin. Since the deflection remains the same

the new terminus Q will lie in the pro- longation of DP where it cuts the parallel tangent. Fix Q and measure PQ. Then if s'=s + PQ

d'=-t

s

(2) Without changing the curvature: Set out PP parallel to the initial tan- gent, measure PQ and make DE=PQ.

14

VAN nostrand's engineering magazine.

Or measure the horizontal distance QR 14. To find the curvature of a eiven —h, between the tangents and make curve:

Make,,AB=BC=ED=l ch. and AE perpendicular to AC. Then tf=CAD=i CBD, J_ 1 r~CD~"2BE

§ 2. COMPOUND CURVES.

_ 1. When the tangents are on opposite sides of the chord which joins the termi- nal points of a railway curve and are equally inclined to it, a simple curve

CIRCULAR CURVES FOR RAILWAYS.

15

consisting of a single circular arc may be used to unite them. But when the angles of inclination are unequal a com- pound curve, consisting of two circular arcs with their curvatures, in the same direction and tangent to each other at their point of juncture must be used to write them.

2. Formulae:

Let A,A' denote the angles of inclination of the tangents to the chord.

2w denote the exterior angle be- tween them.

n,n' denote the length of the nor- mals.

D,D' denote the deflections of the arcs.

r,r' denote the radii.

d,d; denote the deflection angles.

2c denote the lengths of the chord.

Then it is obvious that

(1) 2a> = A + A' = 2D + 2D',

2{r—n){r,—n') cos. 2cof which is reducible to the form

(2) r sin. A-fV sin. A'= — cos.2w-f-c

or (2')

7YI C

Jsin. A'-f-c^'sin. A=— cos.2w + — dd\ c m

or (2")

7 m - \ d=— sin. A

c

COS. to

sin. A

sin. A'

A'H:

co and Then measure HAT=D and

A. One radius assumed:

1. Set out A'H so that HA'T' 2Sw

: d'

set out A'J to meet AJ in J making HA'J=D. Then set out the curves A J, A'J by the rules of § 1.

2. Having assumed r computed by equation (2") above and set out the two branches of the curve as in § 1.

B. One deflection assumed.

1. Having assumed D we have D'=w — D. Set out AJ, A'J to meet in J, making TAJ=D, T'A'J'=D' and then set out the curves AJ, A'J by the rules of § 1.

2. Having assumed D and found D' we compute the other elements of the arcs by the following formulae

sin. co

sin.(A'-D'),

sin. co

sin. (A-D),

dz

d'.

D

d'

It would be easy to show by means of equation (2) that the best conditions of curvature are obtained by making the common normal JCC perpendicular to the common chord AA'. That is, by making 2D = A, 2D' = A'. It is alto- gether possible, however, that the con- struction of the curve thus obtained may be attended with disadvantages whicn more than compensate its benefits.

16

VAN NOSTRAND'S ENGINEERING MAGAZINE.

§ 3. REVERSE CURVES.

1. When the tangents are on the same side of the chord which joins the termini neither a simple curve nor a compound curve can be used. We must have re- course to a curve composed of two cir- cular arcs tangent to each other at their junction with their curvatures in oppo- site directions.

2. Formulae:

Let A,A' denote the angles of inclination of the tangents to the chord.

2w denote the interior angle be- tween them.

n,n' denote the lengths of the nor- mals.

D,D' denote the deflections of the arcs.

r,r' denote the radii,

d,df denote the deflection angles.

2c denote the length of the chord. Then it is obvious that (1) 2w:=A-A/ = 2D-2D',

(r + r'y=(n-ry+(n' + r'y

— 2(?i— r)(n' + r') cos. 2«

which is reducible to the form

(2) r sin. A + r' sin. A'=c—

rr

or (2')

r sin. a)

7 m . . c sin. A d=— sin. A. ;

c _ r'

1 sin. A'

c

3. Solutions:

CIRCULAR CURVES FOR RAILWAYS.

17

A. One radius assumed:

1. Set out AH so that HAT=w, AH

= ~ and measure HAT' = D'. Then d

set out AJ to meet A'H in J so that

HAJ=D'. Then the curves A J, A' J

may he set out by the rules of § 1.

2. Having assumed rf compute d by equation 2') above, and then set out the two branches of the curve as in § 1.

B. One deflection assumed:

1. Having assumed D we have D'=D — id. Set out A J, A' J to meet in J, so that TAJ=D, T'A'J^D' and then set out the curves AJ, A'J by the rules of

§ l-

2. Having assumed D and found D' compute the other elements of the arcs by the following formulas:

sin. o)

sin. (A' + D')}

sin. (D+A).

d=

d' =

-?;

S' s"

d''

4. Special case:

When the tangents are parallel u) — o\ whence J lies in A A' and D = D'=A. The relation between the radii becomes />

sin. A Unless some specific reason forbids it

is best to make r=r'; hence

c , D d remembering that D=A

§ 4. SWITCHES AND FROGS.

1. The data in setting a frog are the length and travel of the switch and the number of the frog. The circular meas- ure of the switch angle is the quotient of the travel by the length. The circu- lar measure of Ihe frog angle is the reciprocal of its trade number.

2. Setting the frog:

In the diagram H is the heel of the switch, T the toe, F the point of the Vol. XIX.— No. 1—2

frog, TN" the travel, c the center of the main line, o the center of the turn out. OTC is therefore the switch angle, OFC the frog angle.

Let G denote the gauge. J denote the travel.

denote the circular measure of the

switch angle, denote the circular measure of the

frog angle, denote the radius of the main line, denote the radius of the outer rail of the turn out. d denote the deflection angle of the

main line. 6 denote the deflection angle of the outer rail of the turn out. If afi be two sides of a triangle in- cluding the very small angle x and c the third side, then very nearly

c*=(a-by + abx\

Apply this formula to the triangles TOC, FOC. We have for OO2 the equiv- alent expressions

(CT-OT)2 + OT.CT.pa

= (CF-OF)2 + OF.CF.?2,

... (CT-CF)(CT + CF-20T)

= OT(CF.q*-CT.p*).

Now GF=r-iG, CT=r + ^G-J, OT

=p; hence

(G-J)(2r-J-2i»)

=p[(r-iG)?-{r+iG-J)p']

18

VAN NOSTRAND'S ENGINEERING MAGAZINE.

But in comparison with r, G and J may be neglected; the equation becomes

2(G-J)(r-P)=rp(q*-p>)y

" d a~ 2(G- J) '

When the curvatures are in opposite directions we have simply to change the sign of d. When the main line is straight d=o. In any case it is simply

necessary to deduce 6, set out TF and make the point of concourse F.

3. Tables:

In the ordinary case J — 5", G=4' 8'^; whence

6— d=v(q*.— £>2), W=20025,7l.

The following tables give the values of vq*f vp2 for various frog numbers and switch lengths:

No. of frog. . . .

4 1251.6

5 801.0

6 556.3

7

8

9

10

11

12

vo2

408.7

312.9

247.2

200.3

165.5

139.1

Switch Length.

8

12

16

20

22

24

26

28

30

W)2

54.3

24.1

13.6

8.7

7.2

6.0

5.1

4.4

3.9

This table enables us to solve imme- diately any example that can occur.

(1) Given the original deflection angle 123', the switch length 26 feet, the frog number 9, then 6 — d—2^.2 — 5.1 = 242'; d=365'.

(2) Given the original deflection angle 94', the switch length 30 feet, the frcg number 6, then for a turn out on the convex side S + d— 556.3 — 3.9=552.4, tf=458'J.

Such are the " tedious and complicated calculations " which Trautwine dreads. [P.B. 404].

4. If the main line is straight the exact formulas are very simple. Their employment is however attended with no advantage.

H

If in the figure the frog distance TF=/, then since o=q—p, TFN=£

{',+p) ,=.JL-£„

sin. Uq-p)

f

2 sin. i (q-p) 5. Frog distance:

The first of these formulas gives the approximate result

2(G-J) / ' p + q

When G=4' b"|, J = 5" this gives for / in feet

103

f-U(pTq)

It would not be difficult to show that this formula is approximate in defect, the proportion of error being about

24

which in the most unfavorable case does not amount to more than 0,13 of one per cent. Accordingly it will be found that the values of / given in the following table are more precise than Trautwine's [P.B. 402] obtained it is presumed from an exact formula but by a more circuit- ous process :

(See Table on following page.)

§ 5. SYLLABUS OF FORMULAE.

1. Exact formulas:

Lr= 1.69897— L sin. d, Ls=I> + L sin. D, Ltf=Lr + L tan. D.

CIRCULAR CURVES FOR RAILWAYS.

19

1

4

5

6

7

8

9

10

11

12

8

284

340

392

440

485

526

564

600

634

12

301

366

426

483

537

589

637

683

727

16

311

380

445

508

568

626

681

751

785

20

317

389

458

524

589

651

710

768

824

22

319

392

462

530

566

660

722

781

839

24

321

395

466

536

603

668

731

793

852

26

323

397

470

540

609

675

740

803

864

28

324

399

473

544

614

682

747

811

874

30

325

401

475

548

618

687

754

819

883

This table gives the values of f to the nearest tenth of a foot

2. Approximate formulae:

dr=?n, ds=S, dt=T, d/i=D.

3. Deflection angle of a short chord:

dx = dcz

4. Long chord:

2Sda; a

5. Middle ordinate in links:

_8 d_ y°~ 11*100

6. Cant in inches; common gauge: 22f?Va

:20025.71.

H

106

7. Compound curves:

D+D'=1(A+A')=a>,

dsin. A' + d' sin. A=— cos.2w -f - dd\ c m

rf cos.2«>

j m . c'sin.A d—— sin. A. 7

l--sin.A'

c

8. Reverse curves:

D-D'=|(A-A')=",

d sin. A' + d' sin. A=-dd'-~ sin.2a>, m c

r' sin.2w

7 m . . c 'sin. A d— — sin. A.

c r' . A ,

1 sin. A'

c

1 9. Deflection angle of turnout from a curve:

°~2(G-J) +a For common gauge and travel 5 inches

7)1 § 6. EXAMPLES.

This section contains solved examples to illustrate the rules and processes of the method which has been explained. 1. Simple curve: — data, D=]8° 37^ d=2° 50'

1117 97

re=-m=Vo=6-57

The curve therefore consists of six complete chords and a short cord of 57 links whose deflection angle is 97°. The radius 10.11 is taken from the table And

y0=r-X 1.7=1.2

Finally from the S— table

37 S=531.2 + — X 28.4=548.7 bO

548.7

This or any other long chord may be used to test the precision of the field work.

2. Simple curve:— data, 5=10.32; d=V 47'

S = 107X10.32 = 1104.2 .'. D = 39°58'

20

VAN NOSTRAND' S ENGINEERING MAGAZINE.

44 22-— =22.41 107

r=16.37— -X7.4=16.07 5

y=TiX 1.07 = 0.8

3. Simple curve: — data, s= 8.42; D = ll 29'

29 S = 328.0 + — X29.4. 60

342.2

34^ 2 d= =40.63 say 40|

8.42

.-. 2s'=2 X

342.2

40|

16.83

689 40f

16.94

8

2/o"nxo'40§=0,3

It will be observed that the corrected chord 2s' falls 1 link short of the old chord. This variation is entirely admissi- ble and unavoidable with a transit that reads, as is usual, only to 20 seconds. 4. Simple curve: — data £=19.25, 2D = 48° 24'

12 T=765.3 + — X 36.2 = 772.5

60

19.25

1452 12

=36—:

40 40

36.30

y0=nxo.4=o.3

S = 699.1 +|X27.3 = 704.6

R— Table, Argument d,

n 704.6

2s= = 35.23.

20

5. Compound curve: — data 2c=8.43; 21°11/

A=14° 23'; A

Assume A=2D; then D = 7° ll'i D' = 10° 35'£

, 525X215.2

'4.215X316.0

:85

d'=

525X316.0

4.215X215.2

183

„=i!= = 5.09 „'=i= = 6..5.

85 183

6. Reverse curve: — data 2c = 11.28; = 16° 24'; A/=10° 42'

Assume

D = 15°; D' = l° 27';

fe4,0y.X^°=lU.5;

5,64X277,3

d'.

402.7X42.0

5.64X43.5

69

900

7.:

1 69

= — = 1.23

114.5

7. Tarn out: — c?=130'; no. of frog, 8; length of switch, 24.

vq*=312.9

^2=6.0

306.9

d=130.0

tf=437

The corresponding radii are 13.22 and 3.94. From a drawing made to scale the frog distance may be found approxi- mately. It is best however to determine the place of the frog by setting out the turnout.

0°

1°

2?

3°

4°

5°

6°

7°

8°

9°

0'

00

2865

1432

955

716

573

478

409

358

318

0'

5'

34377

2644

1375

929

702

564

471

404

354

315

5'

10'

17189

2456

1322

905

688

553

465

400

351

313

10'

15'

11459

2292

1273

981

674

546

458

395

347

310

15'

20'

8594

2144

1228

859

661

537

452

391

344

307

20'

25'

6875

2022

1186

838

649

529

446

386

340

304

25'

30'

5730

1910

1146

819

637

521

441

382

337

302

30'

35'

4911

1809

1109

799

625

513

435

378

334

299

35'

40'

4297

1719

1174

781

614

506

430

374

331

296

40'

45'

3820

1637

1042

764

603

498

424

370

327

294

45'

50'

3438

1563

1011

747

593

491

419

366

324

291

50'

55'

3125

1495

982

731

583

484

414

362

321

289

55'

0°

1°

2°

3°

4°

5°

6°

7°

8°

9°

21

S— Table, Argument D.

0

1

2

3

0

0.0

30.0

60.0

90.0 \

1

298.5

328.0

357.4

386.7 j

2

587.9

616.0

643.9

671.5 !

3

859.4

885.3

910.9

936.2 i

4

1104.9

1127.7

1150.1

1172.2 !

5

1316.7

1335.8

1354.5

1372.7

6

1488.6

1503.4

1517.6

1531.5 |

7

1615.2

1625.2

1634.7

1644.0

S

1692.7

1697.7

1702.1

1706.1 :

119.9

415.8

699.1

961.2

1194.0

1390.6

1544.9

1652.3

1709.4

6

149.8

444.9

726.4

985.9

1215.4

1408.0

1557.8

1660.8

1712.3

179.7 473.8 753.5 1010.3 1236.4 1425.0 1570.3 1667.8 1714.7

209 502 780 1034 1257, 1441, 1582, 1674

1716.5

8

9

239.2

268.9

531.2

559.6

807.0

833.3

1058.2

1081.7

1277.4

1297.2

1457.7

1473.4

1593.7

1604.7

1681.3

1687.3

1717.8

1718.6

T— Table, Argument D.

0

1

2

3

4

0

0.0

30.0

60.0

90.1

120.2

1

303.1

334.1

365.4

396.8

418.8

2

625.6

659.8

694.5

729.6

765.3

3

992.4

1032.8

1074.1

1116.2

1159.4

4

1442.3

1494.2

1547.7

1602.9

1659.9 !

5

2048.5

2122.6

2200.0

2281.0

2365.8

6

2977.1

3100.9

3232.7

3373.4

3524.2

7

4722.5

4992.0

5290.1

5622.1

5994.3

8

9748.1

10853.

12230.

13999.

16354.

150.4 460.6 801.5 1203.6 1718.9 2454.8 3686.1 6414.9 19647.

6

7

180.7

211.0

492.9

525.5

838.3

875.8

1248.8

1295 2 ,

1779.9

1843.2;

2548.3

2646.8s

3860.6

4049.5 j

6894.0

7445.3

34581 .

32797. !

i

s

241.6 585.5 913.9 1342.9 1909.0 2750.7 4254.3 8086.7 49222.

9

272.2 591.9 952.8 1391.9 1977.3 2860.7 4477.7 8842.8 78221 .

0 1 2 3 4 5 6 7 81

ON THE CAUSE OF THE BLISTERS ON "BLISTER STEEL.

By JOHN PERCY, M.D., F.R.S. Journal of the Iron and Steel Institute.

In the process of making steel, which is so largely practiced at Sheffield, bars of iron, usually of Swedish or Russian manufacture are embedded in charcoal powder, and kept heated to bright red- ness during about a week or ten days, according to the degree of carburization desired. Carbon is thereby imparted to the iron, and steel is the product. The bars operated upon are generally about 3 inches broad and £ of an inch thick. How the carbon finds its way even to the center of such bars is a question not yet satisfactorily solved, though it pos- sesses high scientific interest, and has been much discussed. It is not however my intention to consider that question on the present occasion; but to commu- nicate to the Institute experimental evi- dence as to the cause of the singular phenomenon which accompanies this process of converting iron into steel,

namely, the occurrence of blister-like protuberances on the surfaces of the | bars. This appearance is so characteris- | tic and so constant, that the name of i "blister-steel" is applied to such bars. I The protuberances are hollow, exactly ; like blisters, and vary much both in number and size: some are not larger ! than peas, while others may exceed an j inch in diameter, and they are always confined to the surfaces of the bars, for I have a specimen of " blister steel " in my collection, in which there is a single blister as large as a small hen's egg, pro- truding equally from each of the flat opposite surfaces of the bar.

With regard to the cause of these blisters there has been a difference of opinion. I will take the liberty of mak- ing the following quotation on the sub- ject from my volume on "Iron and Steel," published in 1864:— "They (i.e.

22

VAN NOSTRAND'S ENGINEERING MAGAZINE.

the blisters) appear to be due to inter- nal local irregularities and gaseous ex- pansion from within, while the iron was in a soft state from exposure to a high temperature. There is no doubt that all forged bars, for reasons previously assigned [and which I stated in consider- able detail], contain more or less inter- posed basic silicate of iron irregularly diffused throughout. Now, what should be the effect of the contact of carbon, at a high temperature, with particles of this silicate ? Most probably the re- duction of part of the protoxide of iron with the evolution of carbonic oxide, and if this be so, then it seems to me, the formation of blisters may be satis- factorily accounted for. Admitting this explanation to be correct, a bar, which has been ;made from molten malleable iron, should not blister during cementa- tion [the term used to designate the pro- cess in question of making steel]; and, should this prove to be the case, it» would not be difficult to prepare such a bar with particles of cinder [ferrous sili- cate] imbedded, and by subsequently ex- posing it in a converting furnace, ascer- tain positively whether blisters would occur only in places corresponding to the cinder."

It has, I think, been conclusively proved that all bar iron manufactured by charcoal finery processes, or by pud- dling, must contain, intermixed, some of the slag, which results from the conver- sion of pig iron into malleable iron by such processes, in which, let it be re- membered, the malleable iron is never actually melted. In the quotation which I have given I mentioned only ferrous silicate as constituting the slag; but I ought, also, to have included free oxide of iron, doubtless magnetic oxide. The bars converted at Sheffield are chiefly

Swedish, and are generally manufactured by the so-called Lancashire process.

On a visit to the great steel works of Messrs. Firth, at Sheffield in February last, Mr. Charles H. Firth was so good as to undertake, at my suggestion, to settle the question whether blistering would occur in the converting process in the case of a bar of iron which had been actually melted, and so freed from all intermixture of ferrous silicate, or mag- netic oxide of iron. The experiment was accordingly made, and with good effect, of confirming, and, I think I might almost say, establishing the cor- rectness of the explanation which I ven- tured to submit concerning the cause of the formation of the blisters. On the 9th of last May, Mr. Firth informed me that be had melted Swedish bar iron, and cast it into a flat ingot, which he had carburized in the converting furnace in the usual manner; and, at the same time, he forwarded to me a piece broken from the ingot, after conversion: this piece was about six inches long, three inches broad, and a little more than half an inch (exactly T7¥) thick; it showed a fracture at each end characteristic of converted steel, but there was not the slightest indication of a blister.

The other experiment, which 1 sug- gested, seems scarcely to be needed, namely, that of cementing a cast bar of malleable iron, in which bits of slag, or magnetic oxide of iron, had been imbed- ded. But should any one be willing to make such an experiment, probably the best way would be to cast an ingot of Swedish iron, drill a hole or two in it to the depth of about the center, insert a bit of slag in one hole, and a bit of mag- netic oxide of iron in another, then plug up the holes hermetically by a screw or otherwise, and convert in ordinary way.

THE STRUCTURAL PROVISION FOR THE DISCHARGES THE RAINFALL OF LONDON.

OF

From " The Builder.'

The serious damage and discomfort inflicted on so large an area of London by the rain of the night and morning of the 10th and 11th of April afforded a subject of very serious contemplation to

all who are engaged in building, or in dealing with that first duty of the archi- tect, the art of keeping houses dry. It is satisfactory to find that the first ac- count which was published of the burst-

PROVISION FOR THE RAINFALL OF LONDON.

23

ing of a main sewer in the Brixton-road has been subsequently contradicted, and that it was not to the failure of any por- tion of the Main Drainage works, in as far as their structural strength was con- cerned (that is to say, as a question of strength apart from the question of capacity), that so serious a misfortune is to be attributed. At the same time, it can hardly be argued that the inhabit- ants of a city like London ought to be exposed to those floods and watery dis- asters which have of late been but too common in the southern portion of the metropolis. Convulsions of nature, in- deed, may be beyond the forecast of hu- man wisdom to prevent or to render harmless. Thebursting of a water-spout, or the violent down-pour occasioned by a throw on a low-lying district a mass of tornado, may water that will for a time choke up the best engineering arrange- ments for outfall. The rain of the night of the 10th of April, however, was by no means of so altogether exceptional a kind as is called a meteoric phenomenon. It was heavy, continuous and prolonged, rather than sudden and violent. Its fall was stated at two inches in London streets (and as much as three inches at Green- wich) in about nineteen hours, a quantity which, while giving a quantity of 200 metric tons per acre, is not so great that it should overtax our means of dis- charge. Double the former depth of rainfall was gauged in some parts of England in the wet time some two years ago. At all events, it is an amount of rain for which experience tells us that we ought to provide, and the possible occurrence of which was distinctly re- ferred to by the engineer of the Main Drainage works as having been re- garded as possible. It would be a de- plorable outcome of the engineering science of the nineteenth century for us to be told that when two inches of rain falls within twenty-four hours, or when an east wind comes at the back of a high spring tide, the inhabitants of a large part of London are to resign themselves to partial submergence, with all the damage to property, as well as to health, involved in such a calamity. But unless the recent disaster be taken up by the public and by the press with rather more persistence, as well as with rather better information than was the case

with . regard to the last floods, little practical good will be derived from so costly a lesson.

The subject is so immediately con- nected with the primary structural and sanitary question of the proper method of securing an outfall for storm-water, that it may be instructive to glance at the physical features of London, imme- diately to the south of the Thames, and at the change in the course of the out- i flow of rainfall that has been effected by j the Main Drainage works. The river ! Thames, from the confluence of the I Wan die at Wandsworth to that of the j liavensbourne at Deptford, makes an irregular triple curve, or series of three loops, to the north, running at an ex- treme distance of as much as 2| miles from the chord of this compound arc. There are reasons for supposing that the ancient bed of the river took a more direct line than thai of the present channel. At all events, the whole area which we have described lies below, — some of it as much as sixteen feet below, — the contour line of ten feet above Trinity high -water mark of the year 1800, — a level which high tides now not unfrequently surmount. The ground was marsh, so recently as the Restora- tion; and is represented as such in an engraving of the entrance of King Charles II. into London, which exists in Mr. Gardner's remarkable collection of drawings, engravings, and other publica- tions illustrative of the history and architecture of the metropolis. Gradu- ally, as the progress of population covered this marshy site with building, the house-drainage became a source of more and more disquietude. The low- lying area above indicated covers as much as twenty square miles. It is in places as much as five feet or six feet below high- water mark. The sewers which, since the year 1815, were gradu- ally constructed so as to run mostly in an easterly direction, into the Thames, had but little fall, and, except at the period of low tide, were tide-locked and stagnant. After long-continued rain they became overcharged, and were unable to empty themselves during the short period of low water. Many days, therefore, often elapsed during which the rain accumulated, and the sewage was forced into the basements and eel-

24

VAN nostrand's engineering magazine.

lars, to the destruction of much valuable property, and to the great loss of health among the residents.

There is no doubt that a considerable benefit has been conferred on this dis- trict by the works of the main metro- politan drainage, even though these works have proved inadequate to the discharge of a steady rain like that of April 10th, 1878. It was the design of the works to arrest the torrent water before it descended into this low-lying district. For this purpose two lines of sewer were constructed, one approxi- mately parallel to the course of the river, and the other approaching the line of the first at an acute angle. The first, or main line, commences at Clap- ham, — the second, or branch, at Dulwich. Between them they drain an area of about twenty square miles, including Tooting, Streatham, Clapham, Brixton, Dulwich, Camberwell, Peckham, Nor- wood, Sydenham, and part of Greenwich.

It was stated in the original report as to these main sewers that they were of sufficient capacity to carry off all the flood-waters, so that they would be entirely intercepted from the low-lying districts, which were thus to be protected from floods. The falls of the main line are fifty-three feet, twenty-six feet, and nine feet per mile to the Effra sewer at the Brixton-road, and thence to the out- let 2^ feet per mile. The old course of the Effra fell into the Thames near Yauxhall Bridge. The diversion of this torrential channel so as to flow into the Thames at Deptford is in accordance with the principles of outfall drainage laid down and followed out by the Rennies, and by the most able and dis- tinguished engineers. But the combina- tion of a torrential diversion with a main sewerage drainage is another mat- ter. As a question of quantity alone, it is now manifest that the sectional area, varying from a barrel of seven feet in diameter to a section of ten feet six inches by ten feet six inches with a cir- cular crown and segmental sides and invert, is not adequate to the discharge of a quantity of rain which is not more than half of that which has been known to occur in some parts of the country, in twenty-four hours, within the last two years. The sectional area of a seven foot barrel is, say, forty square feet.

We may take that of the larger section as about eighty square feet. A fall of two inches of water, in twelve hours, over an area of twenty square miles, gives a flow of 2,085 cubic feet, or 13,000 gallons, per second, which would require a velocity of about sixteen miles per hour in order to be discharged through a culvert of the larger of the two sec- tions named, — a velocity which is practi- cally impossible. This calculation must be confronted with the fact that in pro- posing to turn the storm water of Lon- don into the main sewerage, the engi- neer considered that a rainfall of J inch per day, in excess of the maximum flow of the sewers, was all that had to be provided for. Sir J. Bazalgette, in his report on the Main Drainage system in March, 1865, stated with perfect truth that "there are, in almost every year, exceptional cases of heavy and violent rain storms, and these have measured one inch, and sometimes even two inches, in an hour." The maximum flow of sew- age is estimated, in the report cited, at a volume equal to that produced by a rainfall of 80.01 inch per hour, or, as above mentioned, 0.25 inch in twenty- four hours. As a rule, then, the area of the sewers has been doubled, in order to provide for an arbitrarily restricted quantity of rain, amounting to less than an eighth-part of that which was known occasionally to occur.

" But," the report continues, " excep- tional rain storms must be provided for, however rare this occurrence, or they would deluge the property on which they fell."

This brings us to the point of which the due appreciation is rendered so urgent by the disaster of the 10th of April. The question of the provision for storm-water, or excessive rainfall, is one of the most serious that can demand the attention of the architect or of the engi- neer, especially in the case of a large city. In those parts of the world where rain of from one inch to two inches or even more per hour, is not uncommon, the architect is compelled by necessity to look facts in the face, and to provide for the safe discharge of what would otherwise prove destructive floods. Thus in the south of Europe the streets, of the principal cities are so constructed that they offer ready and efficient channels

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for the torrents that spring up in formi- dable volumes after an hour or two of rain. In Turin, in Naples, and in other cities, the arrangements for this purpose are very effective. It is true that they are not complicated by being mixed up with the scavenger drainage of the cities. But that is the very point at issue. The question is, ought the rain- fall to be turned into the sewers ?

In cases where no regular artificial water supply is provided for a large collection of dwellings, but where the sewage of the houses is carried off by underground culverts, the utilization of the rain water, at least in part, for the flushing of the sewers is indispensable. That much may be freely admitted as necessary in the interests of sanitation. But one of the main objects in the sup- ply of a volume of water varying from twenty-five to forty gallons per head of the population per diem is to provide a regular and adequate amount of water carriage for the removal of the sewage. The most that can be said in favor of the admission of storm water into the sewers, as far as the sanitary service of the population is concerned, is that it will not materially affect the regularity of the daily discharge. With such a supply of water as we have named, there is no need for flushing at irregular and uncontrollable intervals. The two sys- tems are not only different, but incon- sistent. When rain is depended on for flushing, an arrangement is proper that differs materially from that which is suited to the discharge of a regular daily quantity of diluted sewage. When the latter is properly provided for, — when the inflow of the water runs through a well-devised system of pipes, and the outflow of the same water, bearing with it the refuse products of city life, is carried on through a proper series of pipes and culverts, any capricious excess of quantity, such as that arising from storms, only complicates matters. If, on the one hand, the sewers be provided so large as to deal with, not only the ordinary but the extraordinary rainfall, their dimensions must be so large as to cause an enormous expense. The figures above given will show that something like sixteen times the sectional area that is required for the daily regular service must be added to that section in order

to give anything approaching certitude as to dealing with storm water; although the occasions on which that section would be filled will be very rare.

We are not about to pronounce an ex cathedra opinion on a subject as to which different views are entertained by pro- fessional men of experience; nor do we wish to offer any criticism as to details of the existing arrangements. It is rather our object to elicit general princi- ples as to the truth of which debate is unnecessary; and to point out the prac- tical result of the application of these principles. Such, wTe conceive, is the useful and important function of the scientific press; and such the line which should divide the remarks of a public writer from the report of a consulting engineer.

It is certain that, in providing for the drainage of a town or city, one of three courses must be taken. Either the rain- fall and storm- water must be excluded from the sewers, or it must be accommo- dated by them, or there must be a more or less perfect combination of the two systems; that is to say, part of the rain will be, and part will not be, carried off by the sewers.

Of these three methods, the second, which is the simplest, is supposed to be excluded from consideration on account of its expense. In the case of London, for example, instead of being designed of a capacity, as at present, to carry off twice the maximum flow of sewage, the sewers, in order to be efficient under any stress of weather, must be of a size to carry off at least seventeen times that volume. Even this considerable addi- tional cost, however, is not the main difficulty. Sixteen times the discharging area of channel would not imply sixteen times the cost of construction, although it would no doubt involve 2^- times as much outlay, or even more. But the real difficulty, in the case of London, lies in the fact that the entire extra volume has to be pumped up for a height of 36 feet in order to enter the Thames. There is indeed, an outfall for storm water provided at Deptford, but there is, even at that point, a lift of 18 feet from the low-level sewer. If we take the smaller lift alone we still find that either the capacity of the pumping apparatus must be so arranged as to enable it to deal

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with a sixteen or seventeen fold quantity of water, on a sudden emergency, or that the enlarged sectional area given to the sewers would be of no value as a protec- tion to the district. Practically, there fore, the provision for the whole of the storm water by the sewers is pretty well out of the question.

If we take the opposite view, namely, that the storm water should be excluded from the closed system of water supply and of sewage we commence with the advantage of a diminution of cost, and better sewers as respects sewage alone. Both as regards the pumping appara- tus, half the actual provision would on that system have been adequate.

The question, however, would then have arisen. How to deal with the rain ? But this very question is no less import- ant, and, we must be allowed to say, is not brought much nearer to a satisfac- tory solution, under the adoption of the the present plan, which is one of a mixed character, accommodating a part of the rainfall in the ordinary sewers, and pro- viding (or rather as it seems not provid- ing) for the remainder by supplementary works.

It is well to observe that the suffering caused by the flood of the 11th of April is by no means confined to the district drained by the Metropolitan Board of Works. The area of the rainfall was limited. Although it rained during the night over large part, and probably over the whole, of the watershed basin of the Thames it was on approaching London that the traveler became aware of any- thing like a phenomenal rainfall. More rain fell on the north than on the south of London. The river Wey was not un- usually, full at the time when the rivers Colne and Brent were bringing down exceptionally high floods. The Medway also was greatly swollen. Thus, if we take the case of Brixton as one most fit to be examined, it is not to be thought that the diversion of the Effra is a sole cause of difficulty; although it may afford an unusually forcible illustration of the operation of the mixed system of outfall at present in vogue.

The principle of the existing works for the drainage of London is thus stated by Sir J. Bazalgette. " As it would not have been wise, or practicable, to have increased the size of the intercept-

ing sewers much beyond their present dimensions, in order to carry off rare and excessive thunderstorms, overflow weirs, to act as safety valves in times of storm have been constructed at the junctions of the intercepting sewers with the main valley lines. On such occasions the sur- plus water will be largely diluted, and after the intercepting sewers are filled, will flow over the weirs, and through their original channels into the Thames." How far this plan has been adhered to in the case of the Effra line of drainage we shall, perhaps, learn trom the report which Sir J. Bazalgette has been direct- ed to prepare. But the report of 1 v 65, from which we are quoting, says further, "The old Effra sewer, which fell into the river near Vauxhall Bridge, has been diverted, through this (the intercepting) sewer to a new outlet at Deptford, and the old line has been filled in and aban- doned." There seems to be some con- tradiction between these two passages of the report; and we are thus unable at the moment to ascertain how far the principle of allowing an overflow to take the course of the original outfall has been carried out in the case of the Brixton sewers.

Whatever be the arrangement in this particular instance, it is evident that the safety-valves provided have been entire- ly inadequate to carry off an amount of rain that may at any time descend on London. This, however, is, in our opin- ion, by no means the most important part of the question. It is one thing to have drainage that works very well on ordinary occasions, but that breaks down in a storm, and another matter to have a system that adds to the mischief of a storm that of a widespread pollution by sewage. The expression "the surplus waters will be largely diluted " contains the marrow of that to which we object on sanitary as well as on economical grounds. If a system of sewers is so constructed as to be capable of convey- ing only a fraction of an unusual rain fall, it ought to be the care of the engi- neer that no excess over that fraction should be allowed to enter the sewers. By entering in detail the contributory drains, sweeping them of their contents, filling the intercepting lines, and then overflowing not only through streets but through houses, the rain takes the most

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mischievous and disastrous course into which it can possibly be»turned.

We confess that this consideration has very great weight in inclining us to the opinion that, all things considered, econ- omy, as well as public health, would be consulted by the systematic exclusion of the rainfall from the sewers. It is certain that if the whole of the rain be turned into this channel of discharge, and if the latter proves at times totally inadequate to carry it off, — the worst kind of evil remains. The limitation of the ingress of the rain is a more difficult matter than its total exclusion.

The question then would arise, it may be urged, how to provide for the rain- fall? But this is the very question which is involved under the mixed sys- tem. The mixed system provides, let us say, for 364 days out of the year, but breaks down under a deluge on the 365th. Somehow or other we are bound to pro- vide for that exceptional 365th day. The question is, can we not most surely, most thoroughly, and most economically provide for the entire disharge of the rain whether normal or abnormal without turning it into the sewers ?

We prefer to put this question as a suggestion. We take it for granted that London has the right to claim an effec- tual protection from floods, whether arising from the Thames, or poured down from the surrounding water-shed. At the present moment there can be no doubt that the expenditure of nearly eleven million sterling in drainage and embankment works has placed large districts of London in a far worse posi- tion, when exceptional floods occur, than they were in fifty years ago. It is stat- ed in the report by Mr. Redman, to which we have before referred, that the height of the Thames floods has been increased by the Embankment on the north of the river. It is clear from the reports of the late disaster that the action of the southern drainage works has been such as to pollute the torrent water that overflowed streets and houses with sewage. These are results of a mixed system, which, to our minds, has a fatal flaw. It is that of being a fine weather system alone. Would it not be better to look foul weather in the face ? Would not a system that should provide specially for rainfall, whether it be 0.01

inch per hour or 0.25 inch per hour, fully and simply, without choking the sewers, or overpowering the pumping engines as soon as the lower dimension was much exceeded, be the most economical, as well as in all other respects the best.

For the discharge of rain, not by the sewers two modes are possible, — which of course, may be combined according to circumstances. One is the original method, which is capable of very admir- able management, of making the road- way form channels, or a channel, for the rain. The other is that of constructing special subways, for culverts, for that purpose. The city of Turin is subject to violent rain. Storm clouds collect over the Alps, and after two or three days of intense heat often burst in a sud- den deluge on the city. The violence of the rain is far greater than any to which we are accustomed in this country. But the architects and surveyors of Turin have made such provisions that the rain comes as a friend, not as a de- stroyer. The streets are carefully paved for the most part with broad lines of dressed stone for the wheels to run over and intermediate pitching for the horses, edged with raised footpaths, and pierced with gully-holes at certain appropriate points. It is by no means unusual to see from 2 inches to 3 inches of water running over one of the main streets of Turin after half an hour's rain. But all that follows is, that for so many min- utes a clear bright stream of that depth runs along the road. By the time that the storm has ceased, and pedestrians and carriages can venture forth from the shelter to which they were driven, the rain has run off as rapidly as it at first rose, and a clean street is all that remains to tell of the downfall.

In Naples more formidable torrents find their way through the city in storms, owing to the greater amount of catch- water area which intervenes between the city and the crest of the Apennines. The sirocco, a southern wind, brings a tropical fall of rain, not only over the city, but over the country for miles round. To protect the city there is a large intercepting fosse, or moat which is practicable as a road in dry weather but which becomes a veritable river in storms. Besides this, the streets are ar- ranged in accordance with the lie of the

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land, so as to carry off the water. In some places pavement, as in Turin, lead- ing to culverts at proper places, pre- vents any permanent inconvenience from the results of a tropical downpour. But in others and notably in the road leading into Naples from Caserta, a wide street dips gradually towards the center, in which is a paved open channel, dry, ex- cept in time of rain, and readily carrying off any moderate quantity of water. But when a sirocco deluge comes on, a vast body of water seeks this channel. The inclination of the sides of the streets is such as to allow the gradual widening as well as deepening of the torrent, in proportion to the exigencies of the mo- ment. In the utmost volume of the rain the sides of the street remain above the flood, and light iron bridges, under which it is easy to drive in fine weather, afford means of crossing to pedestrians when the central part of an important thoroughfare is converted from road into river.

The conditions of the Italian cities are far more severe, as regards liability to floods, than any that prevail in England. For that reason Italian architects have have been obliged to look flood in the face, and to provide for its ready dis- charge. For that reason no one in Naples or in Turin suffers any inconve-

nience from violent storms, beyond the risk of a wetting if he ventures out in them; for an umbrella is but a child's toy if opposed to an Alpine storm or to a sirocco shower. That similar arrange- ments might be introduced into the streets of London cannot be questioned by men of foreign experience. That by a thorough consideration of the worst possible case, the means of providing for the discharge of an inch of water in an hour, London might be rendered perfect- ly safe against a rain flood, will not be doubted by any who gives attention to the subject. That a due consideration of what is needful in extreme emergency would lead to a provision that would at all times be efficient, and that would take a great load off the whole system of sewerage and of pumping, is the thesis that we submit for consideration. As we must provide for the worst — under penalty of extraordinary loss — is it not better to do so in the first instance and at the same time to arrange for the dis- charge of all our rain water, whether it be an inch, or a hundredth of an inch, in an hour, without inflicting on the works of the sewerage a duty that may at any moment rise to the double of the neces- sity amount of work, and which, as soon as it exceeds that double, commences the work of disaster ?

THE PURIFICATION OF WATER.

By GUSTAV BISCHOF, F.C.S. From "Journal of the Society of Arts."

The subject which I have the honor to bring under your notice to-night is of a somewhat embarrassing magnitude, though it is my intention to confine my- self solely to the purification of water for sanitary purposes. It would be easy to lay before you a number of facts and conclusions bearing on the means by which this may be more or less effected, but it would be almost like building a house without foundations were I not first to attempt an understanding be- tween us, or, at least, to explain my views as to the nature of the work which a purifier of water has to perform.

Absolutely pure water, containing ex- clusively oxygen and hydrogen in the proportion in which they chemically combine to form water, is not known, even in our laboratories. The foreign matter in ordinary water is either gase- ous, mineral, or organic.

The gases which generally occur in water, namely, free oxygen, nitrogen and carbonic anhydride, ' are, in moderate quantities, not only harmless but even desirable. Oxygen and carbonic an- hydride render water sparkling and palatable. It is chiefly to them the so- called mineral waters owe their palata-

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bility, and they appear to have a bene- 1 ficial effect upon the digestive organs. | Other gases, such as sulphuretted hydro- ! gen, indicate organic impurities and are objectionable.

Whether hard or soft water be more conducive to health has not been defi- nitely settled, but probably a moderately hard water is more wholesome than either excessively hard or soft water.

Of greater consequence are the impuri- ties of organic origin, consisting of living or dead animal or vegetable mat- ter. These occur in water partially as solid particles in a state of suspension and partially in solution. Suspended impurities may be separated to a certain extent by mechanical filtration through sand, paper, or other materials. How- ever, even in the brightest water, solid bodies are frequently discovered under the microscope, or by passing an electric ray through the water, as I will by-and- bye illustrate experimentally. These microscopic solid bodies are extremely minute in their largest sizes, the smaller objects remaining probably unseen, even by the aid of our most powerful micro- scopes. They are, therefore, not unfre- quently considered amongst the matter which is in a state of solution. If these bodies are of an organized nature, we have in all probability to search amongst them for the virus which produces a number of the most disastrous diseases.

This naturally leads me to the germ theory. Whether and how far germs are at the root of disease, or whether the latter are due to common chemical agencies, is a much contested question. And yet it is a matter of considerable importance, upon which the decision hinges, whether we may depend upon the laws of chemistry in deciding any question relating to water supply, or whether this belongs more or less promi- nently to the physiologist. Being my- self a believer in the germ theory, I wish to lay before you a i'ew arguments, however incomplete they necessarily must be. We designate as contagia such parasitic infectious agencies as are transferable from one individual into the healthy body of another; there, we sup- pose, they multiply, when finding a favorable nidus, and produce a specific disease, similar to the one from which they originate, such as cholera or typhoid.

What evidence, then, tends to demon- strate the organized nature of these con- tagia? They have never been with cer- tainty isolated, no one has ever seen them, and yet, if we find that they are endowed with properties peculiar to living bodies, we can hardly evade the conclusion, that they themselves belong to a class of organisms. I think we shall agree that the property of producing their like by separation of part of their j body and of growing by assimilation of I extraneous matter, is peculiar to organized beings. Let us, then, see whether con- tagia exhibit any evidence of such prop- erties. Chauveau has proved experi- mentally that the virus of small-pox, sheep-pox, and glanders is independent of quantity. The minutest particle, such as can only be obtained by great dilution, produces the disease with apparently the same virulence as concentrated matter. j The remarkable epidemic of typhoid at i Lausanne (Switzerland) in 1872, is, on the other hand, a practical demonstra- | tion, amongst many others, that the | virus of typhoid produces fearful results I in a state of dilution, in which the dead- liest of the known chemical poisons would, as a matter of certainty, have had no effect whatever. Is it not proba- ble in the highest degree, that we have to account for that apparent independ- ence from quantity by a power of repro- duction and rapid self-multiplication ?

Again, the direct connection between cholera, or typhoid, and preceding cases of the same disease, has in so many in- stances been traced as to justify in my opinion the conclusion that nobody has ever been attacked by either of them, unless the specific virus had been trans- ferred to him originally from a person afflicted with the same disease. It is, of course, out of my power to substantiate this to-night, by detailing a great many instances, but I may suppose that most, if not all, of you are familiar wTith them. Such unvariable connection can scarcely be explained, except by assuming that the virus possesses the peculiarity of organized beings of self-reproduction, in other words, as Dr. Simon expresses it in one of his reports to the Privy Coun- cil, that contagia multiply, in case after case, their respective types, with a suc- cessivity as definite and identical as that of the highest order of animal or vegeta-

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ble life. Indeed, unless we assume this, we cannot understand the constant re- lation to a parent case and the total ab- sence of any de novo generation by chance or coincidence.

There are, further, numerous instances of epidemics which appear to prove al- most to demonstration that the virus of typhoid is peculiarly virulent, when gain- ing access to our milk supply. Similarly we have reason to believe, that the virus is more active, when passed into water largely contaminated with organic mat- ter, than when passed into comparatively pure water. This is at once explained, if we assume that the virus is capable of assimilating organic matter, in fact, of living upon it.

In cases of poisoning by known chemi- cal agencies on the other hand, say, by lead, the poison is not transferable from person to person; and whenever certain conditions are given, such as water of a certain composition passing through lead pipes, any person may, on drinking that water, be poisoned without any reference to a previous case. Small, but traceable, quantities of lead have frequently been found in the blood, liver, and other human organs, without any distinct in- jury to the system. Minute quantities of lead have sometimes been taken habitually for years, until the poison gradually accumulated to an extent suffi- cient to cause serious disorders, or even death. In his standard work on Hy- giene, the late Dr. Parkes says with ref- erence to this : — " On the whole it seems probable, that any quantity over l-20th of a grain (of lead) per gallon should be considered dangerous." Such poisons therefore are not independent of quan- tity; on the contrary, let me also remind you, some of the strongest chemical poisons, such as strychnine, arsenic, lead, copper, and morphia, are given in small quantities as remedies against various ailments. Thus there appears to exist a sharp and remarkable contrast between ordinary chemical poison and the virus of cholera, typhoid, and similar diseases.

Dead organic matter forms a large proportion of ordinary filth, and all kind of filth is more or less liable to contami- nate our water supplies. Those diseases, which are produced by common septic ferment, or by the ordinary putrefactive changes which dead organic matter un-

dergoes, are therefore of peculiar interest to us.

As far back as about the middle of last century, Albrecht von Haller de- monstrated that putrescent organic mat- ter in aqueous solution may be fatal, if injected into the veins of animals. The symptoms lie observed are, inflammation of the digestive organs, and disturbance of the nervous system. The animal heat is sometimes considerably in- creased, sometimes decreased. Panum succeeded in extracting a poison from putrid matter, which he describes as so- luble in water, insoluble in alcohol, and free from albuminous matter. It is not destroyed at a boiling heat, and acts ap- parently like ordinary chemical poisons, the virulence being proportionate to the quantity injected. Arnold Hiller, on the other hand, has recently extracted an al- buminous body from putrid meat by means of glycerine, which is precipitated and destroyed at a boiling heat, and so- luble in alcohol and acids. On being injected under the skin of a rabbit, the extract, in which Hiller failed to discover any organisms, showed no effect for several days. Then, apparently after the ordinary period of incubation, the symptoms of blood poisoning made their appearance until the rabbit died. The poison was reproduced in the body of the animal, and by transferring it from rabbit to rabbit, Hiller calculated that in the tenth generation 1- 120th of a drop of the original glycerine extract was sufficient to kill a rabbit in fifty-two hours. The symptoms were, fever, asthma, increased solution of the red blood corpuscles and diarrhoea. If Hil- ler's observation was conclusive as to the absence of organisms in the original ex- tract, common chemical poison would appear capable of producing effects which I have endeavored to show can only be attributed to living organisms. But I venture to suggest, that the ab- sence of the lowest forms of organic life, or their germs, can, at the present time at least, be hardly proved con- clusively, excepting by the absence of their ordinary visible effects, for there is certainly evidence of life beyond the power of our microscopes, and we can- not know what we might see if their magnifying power were increased ten or a hundred fold. The disastrous conse-

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quences which must be expected from the drinking of water, which is polluted by fermenting organic matter are, at any rate, illustrated by Hiller's experiments.

Upon what condition, then, does the wholesomeness, of a water supply de- pend ? I cannot answer this by simply classifying the different sources of sup- ply in one way or another, and laying down a rule that such and such sources are objectionable, or require purification, because those sources, which generally furnish an excellent supply, are some- times contaminated and vice versa. But water must always be looked upon with the more suspicion the greater its lia- bility to contamination by sewage, and more especially by human discharges, as these may carry with them the most dangerous specific seeds of disease. Thus, shallow well and river water are gen- erally most largely polluted, whilst at the same time they are very extensively used for water supply. If we find these two attributes, namely, extensive use and pollution combined, it is worth our attention to inquire somewhat more closely into the alleged danger arising from the use of rivers and shallow wells as sources of water supply.

Rivers are generally largely fed by polluted surface water from cultivated land, and by vast volumes of sewage and other polluting waste materials. In the Registrar General's returns we read from time to time that a variety of most disgusting matter may be traced in Thames water, not only at the intakes of the*several water companies in London, but even after filtration through sand, although the water is then mostly free from disagreeable smell or taste. From this we see that we cannot rely upon the outward appearance, the brightness, palatability, or absence of color and smell, in forming an opinion of the wholesomeness of a water.

The danger arising from the drinking of river water, especially in times of epidemics, is well illustrated by the ex- perience of Glasgow. The mortality there, per 10,000 of population, during the three cholera epidemics of 1832, 1847, and 1854, was respectively, 140, 106, and 119, or, on the average, 122. During this period the water supply was derived exclusively, or almost exclusive- ly, from the Clyde. Then followed the

epidemic of 1866, after, in the meantime, the Loch Katrine water had been intro- duced. What was the result? The mortality from cholera decreased from the average of 122 to only 1.6, or to less than one and a half per cent, of that figure. There is no showing that this can be attributed to any other cause than the abandonment of the Clyde as a source of water supply.

Do not believe that this is an excep- tional case. A glance at the map ap- pended to the Sixth Report of the Rivers Pollution Commission will show the in- finitely small area, which, excepting the Scotch Highlands, is covered by unpol- luted river basins.

I have not been able to lay hold of any experimental proof in favor of the hypothesis of self-purification, of at least our English rivers, by oxydation; but in the Sixth Report of the Rivers Pollution Commission we find rather the reverse. The dilution, to which sewage is being subjected in rivers, may be a safeguard, to some extent, against common filth; but if contagia be organized bodies or individuals, dilution offers, in all proba- bility, no protection against propagation of disease by their agency. This, I think, must be followed from the experi- ence gathered during the epidemic at Lausanne, to which I have already re- ferred, and from other instances. It fol- lows also, from a consideration of the extraordinary power of multiplication which, at any rate, some of the lowest forms of organic life exhibit. Thus, F. Cohn, a great authority on these matters, has calculated that one single bacterium might, within less than five days, fill up by its progeny the whole ocean, supposing they found a sufficiency of food.

The remarks about river water apply also more or less to shallow well water. A striking illustration of the dangerous character of this source of water supply was furnished by the epidemic of typhoid in Broad Street, London.

It is impossible, within the time at my disposal, to enter into any more particu- lars as to the different sources of water supply, but I wish to offer a few general observations on this point.

It is not sufficient that a water supply should be generally of a more or less satisfactory quality, nor that its average state should not give rise to any serious

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apprehensions. Otherwise, we would find ourselves unprepared and unpro- tected when the worst condition arrives, or when owing to the prevalence of epi- demics, more than ordinary precaution should be required. In illustration of this, I believe that at ordinary times there is no actual danger in drinking, almost throughout the year, the water supplied from the Thames to the greater part of London, if it is sufficiently filtered through sand. This must be accepted in the face of the comparatively low mor- tality we have. But now and then, especially in times of floods, the water deteriorates, sometimes very seriously, and we even read of excremental matter being then traced in it under the micro- scope. This is certainly quite serious enough; but I ask you, is there any guarantee whatever that, should London be visited by an epidemic, our experience would be any better than that of Glas- gow during the Clyde water period ? It would, therefore, certainly be a great boon could we here have a water supply as pure as that from Loch Katrine; but, as long as this appears impracticable, we ought at least to have some additional means beyond those at present employed of purifying Thames water during cer- tain periods of the year, and during epi- demics.

By-and-bye I will return to this point, but in the meantime let me direct your attention to some of the most prominent materials employed in the purification of water. Some have either exclusively or prominently a mechanical action, sepa- rating like a fine sieve the coarser parti- cles of suspended matter; others act chemically upon the foreign mineral or organic matter, and reduce the latter more or less to harmless constituents.

The organic matter retained by me- chanical purifiers must gradually under- go decomposition, and the water, in pass- ing through them, takes up more or less of the decomposing matter. It is thus intelligible that such a water may, physiologically speaking, be impurer, and may be less wholesome after, than before, filtration, should even chemical analysis indicate an improvement. To this class of materials belong mainly sand and wood charcoal, though the lat- ter for a very short time has also a slight chemical action. The more frequently

the materials are changed, and the more they are aerated during filtration, the more perfect will be their purifying action.

With the exception of animal char- coal and spongy iron, I have not been able to lay hold of any conclusive evi- dence of the efficiency of the materials proposed as chemical purifiers. They both have been extensively used in domestic filters.

The success of any material used for domestic filtration largely depends upon the arrangement of the filters in which they are used. These should be as easily manageable, and as simple in construc- tion, as is compatible with efficient work- ing. In insisting upon the former, let us not overlook the latter portion of this sentence. The remark that absolutely pure water is not known, even in our laboratories, sufficiently explains that the purification of water is not a simple or easy operation, the efficient perform- ance of which must be expected to give some little trouble. The easiest and simplest way is, after all, not to filter water at all, and it is but reasonable to expect that its purification should be in some ratio to the care we bestow upon it. We should, therefore, not be satisfied to leave the filter entirely to the care of servants, or even frequently without giving them any guidance how they are to manage it.

In all domestic filters easy access should be given to the user himself for cleaning and recharging, as it is indis- pensable that chemical purifiers should be renewed from time to time, and, as a rule, the more frequently they are re- newed the better. Instead of the re- newal, a cleansing of the material is sometimes recommended, by passing the water through the filter in the opposite direction to that ordinarily employed. By these means a passage may be opened for water through the filtering medium, however its pores had been clogged with filth, but the latter will never be removed efficiently. If any one doubt this, let me remind him of* the difficulty which we find in keeping even the smooth sur- face of our slate cisterns in a clean con- dition. The slimy deposit adheres most tenaciously, and must adhere still more tenaciously to a granular, mare or less porous, material. How often a material

THE PURIFICATION OF WATER.

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requires thus to be renewed depends, largely, upon the energy of its chemical action upon organic matter.

If these considerations are conclusive, I must condemn all filters in which the materials are enclosed between slabs, which are cemented into the filter case; as this, by not giving access to the con- tents, encourages the undue prolongation of their use. From, the same point of view, all materials are objectionable which, being in the form of porous slabs or balls, are not accessible throughout their mass. And, just in passing, let me warn you against the use of sponges, which, although excellent and convenient mechanical strainers, are truly a hotbed for the lower forms of organic life.

The water is passed through the ma- terials mostly downwards, sometimes up- wards, or laterally. There are, of course, advantages and disadvantages incidental to each of these methods, but I believe that, by downward filtration, under otherwise like conditions, the most per- fect purification is effected. The water, in passing through a granular material, upwards or laterally, has a tendency to force a passage through certain channels, wherever it finds the least resistance, without being uniformly disseminated through the material. Another defect of upward filtration is that the deposit of any filth, which mostly collects where the water enters the material, is ex- cluded from view, and even largely from our sense of smell, instead of being exposed and giving us warning. Down- ward filtration, whilst free from these disadvantages, renders filtering materials liable to choke, owing to their natural tendency to follow the course of the water.

A filter ought to yield as much water, in a given time, as can be efficiently puri- fied by the material, necessitating some arrangements for accurately regulating the flow of water. This arrangement ought, preferably, to be independent from any compression of the filtering medium, as, by simple compression, a satisfactory regulation cannot practi- cally be obtained, and should it even be obtained in the first instance, as the yield necessarily decreases at once as soon as any suspended matter is deposited from the water between the pores of the ma- terial.

Vol. XIX.— No. 1—3

The construction of domestic filters would, nevertheless, be comparatively easy, could one always depend upon a little common sense in their use. But it is necessary to guard, as far as possible, against ignorance and mischief, even at the risk of complication. A point fre- quently disregarded by the user is that portable filters should oe paced in a cool locality, free from any vitiated air, and the filter taps ought to be situated as conveniently as possible, so as to en- courage the use of filtered in preference to unfiltered water. If the unfiltered water supplying the filter be stored in cisterns, they should be kept clean, and have no connection with water-closets or drains.

These are the main points which have guided me in designing the different forms of spongy iron filters. The ordin- ary portable domestic filter consists of an inner, or spongy iron, vessel, resting in an outer case. The latter holds the "prepared sand," the regulator arrange- ment and the receptacle for filtered water. The unfiltered water is, in this form of filter, mostly supplied from a bottle, which is inverted into the uppei part of the inner vessel. After passing through the body of spongy iron, th^ water ascends through an overflow pipe. The object of this is to keep the spongy iron, when once wet, constantly under water, as otherwise, if alternately ex- posed to air and water, it is too rapidly oxidized.

On leaving the inner vessel the water contains a minute trace of iron in solu- tion, as carbonate or ferrous hydrate, which is separated by the prepared sand underneath. This consists generally of three layers, namely, commencing from the top, of pyrolusite, sand, and gravel. The former oxidizes the protocompounds of iron, rendering them insoluble, when they are mechanically retained by the sand underneath. Pyrolusite also has an oxidizing action upon ammonia, con- verting it more or less into nitric acid.

The regulator arrangement is under- neath the perforated bottom, on which the prepared sand rests. It consists of a tin tube, open at the inner and closed by serew caps at the outer end. The tube is cemented water-tight into the outer case, and a solid partition under the per- forated bottom referred to. It is provided

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with a perforation in its side, which forms the only communication between the up- per part of the filter and the receptacle for filtered water. The flow of water is thus controlled by the size of such per- foration. Should the perforation be- come choked, a wire brush may be in- troduced, after removing the screw cap and the tube cleaned. Thus, although the user has no access to the perforation allowing of his tampering with it, he has free access for cleaning. Another ad- vantage of the regulator arrangement, is that, when first starting a filter, the ma- terials may be rapidly washed without soiling the receptacle for filtered water. This is done by unscrewing the screw cap, when the water passes out through the outer opening of the tube, and not through the lateral perforation.

Various modifications had, of course, to be introduced into the construction of spongy iron filters, to suit a variety of requirements. Thus, when filters are supplied by a ball-cock from a constant supply, or from a cistern of sufficient capacity, the inner vessel is dispensed with, as the ball-cock secures the spongy iron remaining covered with water. This renders filters simpler and cheaper; and I incidentally remark that on this principle the larger sizes of filters, be- yond portable domestic filters, are fre- quently constructed.

As the action of spongy iron is de- pendent upon its remaining covered with water, whilst the materials which are employed in perhaps all other filters lose their purifying action very soon, unless they are run dry from time to time, so as to expose them to the air, the former is peculiarly suited for cistern filters.

Cistern filters are frequently con- structed with a top screwed on to the filter case by means of a flange and bolts, a U-shaped pipe passing down from this top to near the bottom of the cistern. This tube sometimes supplies the unfiltered water, or in some filters carries off the filtered water, when up- ward filtration is employed. This plan is defective, because it practically gives no access to the materials; and unless the top is jointed perfectly tight, the un- filtered water, with upward filtration, may be sucked in through the joint, without passing at all through the ma-

terials. This I remedied by loosely sur- rounding the filter case with a cylindri- cal mantle of zinc, which is closed at its top and open at the bottom. Supposing the filter case to be covered with water, and the mantle placed over the case, an air valve is then opened in the top of the mantle, when the air escapes, being re- placed by water. After screwing the valve on again, the filter is supplied with water by the syphon action taking place between the mantle and filter case and the column of filtered water, which passes down from the bottom of the filter to the lower parts of the building. These filters are supplied with a regu- lator arrangement on the same principle as ordinary domestic filters. The wash- ing of materials, on starting a filter, is easily accomplished by reversing two stop-cncks, one leading to the regulator, the other to a waste-pipe.

Another form of filter has been specially adapted for the use on board ships, the splashing of water, or shifting of the materials, consequent to the roll- ing of the ship, being prevented by suitable arrangements.

For the requirements in India and other colonies, a filter had to be con- structed combining lightness, easy and safe packing, easy management and cheapness. In this there is no inner ves- sel, the spongy iron being kept covered with water by the joint action of two tin tubes, one sliding loosely over the other. The outer tube reaches from the top of the filter to a well with perforated sides, which rests on a watertight parti- tion on the top of the receptacle for fil- tered water. The inner tube is closed at its base, reaching from the top of the spongy iron to some distance below the partition, through the center of which it passes. Within the receptacle for filtered water this tube is provided with a regu- lator similar to the one in the ordinary domestic filter. Thus the water is made to pass through the filtering materials, which rest on the water-tight partition, and the well enters the latter, ascends between the two tubes, and descends through the inner tube, whence it passes through the regulator opening to the re- ceptacle for filtered water. A perforated lid on the top of the materials is ar- ranged to be tied down during transport, to prevent shifting of the contents.

THE PURIFICATION OF WATER,

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Permit me now to explain briefly what spongy iron is, and to make a few sug- gestions as to its probable action as a purifier of water.

Spongy iron is metallic iron, which has been reduced from some oxide of iron without melting the product. I have tried various arrangements for the pro- duction of spongy iron, including the Siemens' revolving steel furnace, and believe that a reverberatory furnace of suitable construction is best adapted to the purpose. The weight of spongy iron is about 1 cwt. per cubic foot, or one quarter of that of ordinary iron which has been fused. Its more powerful puri- fying action, as compared with ordinary melted iron, is largely based on the fine state of division. But if we bear in mind certain properties of spongy platinum, we can easily understand that the difference is not solely due to the physical condition of the spongy ma- terial, which may have affinities differing from those of ordinary iron. This is at once indicated by its property of decom- posing water without the presence of an acid. Spongy iron also reduces nitrates and the carbonaceous and nitrogenous organic matter. Whilst it thus appears to have essentially a reducing action, there are also indications of an oxidizing process. Thus it appears that, under certain conditions, perhaps under the in- fluence of some oxide, resulting from the gradual oxidation of the metallic iron, the ammonia may disappear entirely, being probably converted into nitric acid.

I need not explain to the members of the Chemical Section, that spongy iron is most energetic in precipitating any lead or copper, but even to chemists it is a remarkable fact, that it should reduce the temporary hardness of water very considerably, and the permanent hard- ness slightly. I cannot offer any ex- planation of the latter reaction, but the former, the reduction of the temporal hardness, is probably due to the affinity of the first product of oxidation, or fer- rous hydrate, for the carbon anhydride, which is the solvent of the calcic carbon- ate. Ferrous carbonate is formed, and the calcic carbonate precipitated. From some reports, we shall presently see that this action was found to continue equally energetic for upwards of a year.

I have frequently been asked the question, what becomes of the organic impurities when filtering water through spongy iron. The reactions are of a complicated nature, and, up to the present moment, I can hardly give more than a few hints about them. .

In two successive papers, one read be- fore the Royal Society last year, the other recently, I have referred to a gas which I observed within the bulk of spongy iron, after it had been in use for some time. It is sometimes explosive, sometimes not. When ordinary water, snch as that supplied by the New River Company, had been passed through a filter for several months, I found this gas to contain a hydro-carbon. On the contrary, when leaving spongy iron in contact with distilled water for an equal length of time, I failed to detect either carbon or hydrogen in the gas. This apparently demonstrates that the carbon in the former case was a product of the; decomposition of organic matter.

It is likely that the nitrogen is, in the first instance at least, more or less con- verted into ammonia by filtration through spongy iron, but as ammonia is un- questionably at the same time produced in several other ways, I do not at present see how to furnish an experimental proof of that hypothesis.

Whether the ferrous hydrate formed by oxidation of the metallic iron has any decomposing action upon organic matter, is a question which I have not hitherto succeeded in answering. The final product of the oxidation is of course ferric hydrate. We know the destructive action of rust stains upon even such in- destructible organic matter as linen and cotton fibres. It was, therefore, to be expected, that ferric hydrate should take an active part in the separation of or- ganic matter from water. This led to the following experiments.

A glass bottle, tabulated at its base, was internally coated with a film of ferric hydrate, by filtering water through spongy iron, and then passing it into the bottle without previously separating the iron in solution. As soon as the bottle was nearly full, it was again emptied by a syphon arrangement, the soluble iron being thus oxidized and precipitated at the sides of the bottle. This was re- peated until a sufficient deposit had been

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VAN NOSTRAND'S ENGINEERING MAGAZINE.

obtained, showing the characteristic ap- pearance of ferric hydrate. The bottle thus prepared, after being filled with hay infusion, was stoppered, and left to stand for a couple of months, when the color of the film gradually darkened. The bottle was then emptied, rinsed with water, and left exposed to the air. After about a fortnight, the coating al- most regained its original yellowish- brown tint. It is thus evident that part of the oxygen had, in the first instance, been transferred from the ferric hydrate to the organic matter of the hay infusion. As any action would be much more energetic in the nascent state of the ferric compound, it became of interest to study more closely the re-actions which take place when passing water through the spongy material.

A tabulated glass vessel was filled with spongy iron. On allowing the water to pass through the vessel con- tinuously for a few days, each granule appeared coated with ferric hydrate. However, on stopping the passage of the water, the color of the material which re- mained covered with water soon became darker, having after a few days, almost its original appearance. I explain this by a reduction of the coating of ferric hydrate, by agency of the kernel of metallic iron in each granule, the pro- duct being some lower oxide, which in its turn is readily re-oxidized to ferric hydrate by the oxygen dissolved in water. Thus the spongy iron acts indi- rectly as the vehicle for conveying the atmospheric oxygen to organic matter and this continues for a long time, as on the very top I found still a considerable pro- portion of metallic iron, after passing water continuously through spongy iron for upwards of ten months. Thus there are reducing and oxidizing agencies con- stantly at work in the spongy iron filter, and the several oxides of iron are present in their nascent state.

In entering upon the chemical evi- dence of the efficiency of those agents which are employed or proposed as puri- fiers of water, I regret that there should be so little conclusive evidence concern- ing them, excepting as to animal char- coal and spongy iron. Whilst I cannot hesitate to lay before you the evidence of disinterested authorities, I am natural- ly reluctant to refer to my own experi-

ence in judging of the merits of other materials than spongy iron. There was lately a chance of enlarging our knowl- edge on this subject, when the Sanitary Institute of Great Britain arranged for a competitive examination of domestic filters in connection with their exhibition at Leamington. Unfortunately, only a few of those invited thought fit to sub- mit their filters to the trial, those repre- sented comprising animal charcoal, the peculiar shale which is employed in some filters, and spongy iron. The committee appointed by the institute to test the purifying power and other merits of the several filters consisted of Dr. Bostock Hill, of Birmingham, county analyst; Dr. George Wilson, of Leamington medical officer of health: and Professor Cameron, of Dublin. You are probably aware that the award " for general ex- cellence" of the Institute's medal was made to the spongy iron filter.

Important evidence on the same sub- ject, though also incomplete, owing to the unwillingness of most manufacturers to submit their filters, is to be found in the Sixth Report of the Rivers Pollution Commission, " On the Domestic Water Supply of Great Britain." There we find the result of fifteen pairs of analyses of Thames water, before and after filtra- tion through spongy iron, the testing being repeated about every fortnight. On comparing the average result of the two last pairs of samples with that of all samples, we find that, after the fil- ter had been in constant action for up- wards of eight months, the reduction of the important nitrogenous organic matter and of the hardness was still con- tinuing.

I may take it for granted that the con- clusions which have been drawn in the report from these analyses are known to you; they would, without doubt, have been still more satisfactory had not the spongy iron filter experimented upon been one of the very first ever made. Thus, it was of a somewhat crude con- struction, not provided with the regulator which has now become a feature of the filter: thus I account for a certain irreg- ularity in the analytical results.

Now, in the same report, there is also exhaustive evidence as to the merits of animal charcoal as a purifier of water. It is demonstrated, and I think we all

THE PURIFICATION OF WATER.

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are aware of this fact, that fresh animal charcoal removes not only a large pro- portion of the organic impurity, but also of the mineral matter. However, the report tells us the reduction of the hard- ness ceases in about a fortnight, the re- moval of organic matter continuing even after six months, though to a much less extent especially if the filter be much used. For this reason it was found necessary to renew the charcoal every six months, when used for the filtration of the comparatively pure water of the New River Company; whilst the water which is supplied from the Thames re- quires the renewal of the charcoal every three months. Unless this be done, we are told that myriads of minute worms are developed in the material, passing out with the filtered water. This state- ment sufficiently explains the final con- clusion, but the property of animal char- coal of favoring the growth of the low forms of organic life is a serious draw back to its use, as a filtering medium for potable waters.

The chemical, part of this evidence is more than corroborated by Mr. Byrne's experiments. He stated, in a paper read before the Institution of Civil Engineers in 1867, that on passing 12 gallons of moderately impure water through ani- mal charcoal, over 55 per cent, of the organic matters were removed from the first gallon, but that this declined so rapidly that, at the eighth gallon, organic matter was given back to the water. In the debate on Mr. Byrne's paper, Mr. Chapman stated that he actually recovered from the charcoal the amount of organic matter which had been pre- viously removed by it from a water. If we compare these statements with others which are more favorable to char- coal, we must, I think, conclude that under certain conditions, which are as yet not thoroughly understood, it ap- pears capable of giving more satisfac- tory results. Probably this depends largely upon the thorough burning, without alteration, of the physical struc- ture.

But, granted that there are no remains of half charred flesh or fat in the char- coal filter; that all organic matter has been destroyed by burning; even then we can explain the physiological results referred to in the report, namely, the lia-

bility of favoring the growth of the low forms of organic life. An intimate con- nection appears to exist between these and phosphorus, as is clearly demon- strated by the microscopic water test which has been proposed by Mr. Heisch. If a minute quantity of cane sugar be added to ordinary water, low organisms are developed in such enormous numbers, as to cause, in about twenty-four hours, an opalescence, ormilkiness. Dr. Frank- land has demonstrated that this is wholly or partially due to the minute trace of phosphorus contained in sugar, as he ob- tained a similar result by adding a variety of compounds of phosphorus in- stead of sugar. Is it then astonishing that animal charcoal, containing some seventy-five per cent, of calcic phosphate, which is by no means insoluble in water, should produce a like effect ?

If I have succeeded in demonstrating that fermenting organic matter is amongst the most objectionable impuri- ties in water, the preceding suggestions are worth our fullest attention, as the milkiness produced in water by sugar is unquestionably due to fermentation. But the objection to the use of animal char- coal as a filtering medium for portable water becomes still more serious, if we assume that some of the most disastrous epidemic disases are produced by low forms of organic life. Can we, in this case, a priori, maintain, that their growth may not also be favored by animal char- coal ? Chemical analysis is incompetent to deal with this question, for the living matter in water is by weight always in- significant, as compared with the dead organic matter. Analysis may, there- fore, show, after filtration, a considerable reduction of the total organic matter, and yet those living bodies may have enormously increased.

May I, in further support of this im- portant point, refer you to my researches, which you will find in the proceedings of the Royal Society ? With a view of testing the purifying action of spongy iron, physiologically, I left meat in con- tact for many months with ordinary water, or even hay infusion, both having been filtered through spongy iron. The meat remained fresh throughout, if no putrefactive agents had access to it, ex- cepting those that might have passed with the water or hay infusion through

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the filtering medium. Putrefactive agents were, therefore, absent from the filtered liquids. But on filtering the same kind of water as before, under otherwise precisely like conditions, through animal charcoal, the meat was putrid after a short time. It would of course have been useless to extend the latter experiment to hay infusion.

From these results we may draw im- portant practical conclusions. Ferment- ation or putrefaction are some of the most powerful agents in destroying or- ganic matter by converting it into a number of gaseous and other constitu- ents. If such fermentation be constantly at work within a filtering medium, we can understand what becomes of the or- ganic matter, should it even be only mechanically retained in a filter. But this is different in the spongy iron filter, looking at the preceding results. Putre- faction being unable to effect the elimi- nation of organic impurities, they must either accumulate or be got rid of by some such chemical agency as before suggested. A constant accumulation would necessarily soon result in a con- tamination of the filtered water, the lat- ter taking up organic matter from the filtering medium, as we found it stated in the case of animal charcoal. This be- ing contrary to all evidence, we must conclude that no such accumulation takes place, but that the organic impuri- ties are destroyed and rendered innocu- ous in the spongy iron filter, by at least as powerful chemical agents as fermenta- tion and putrefaction.

You are probably acquainted with the three reports in the Registrar General's returns for 18*76, 1877, and 1878, on the spongy irOn filter, and I might pass them over, did I not wish to draw your attention to the interesting result re- corded in the report for 1877, that even in times of flood, when the Thames was unusually loaded with organic impuri- ties of the most disgusting origin, its water was, after filtration through spongy iron, purified to such an extent as to surpass the Kent water, which, from its freedom from organic contamination, is justly considered the standard of purity. The organic carbon in the fil- tered Thames water was .038 in 100,000 parts, that in the Kent water .048. Both were equally free from organic nitrogen,

but the hardness of the filtered Thames water was less than one-third that of the Kent water. The filter had previously been in use for more than a year without change of materials. The ammonia in the filtered water was increased to .010. Referring to the correspondence on this subject in the early numbers of the Chemical News during the present year, I maintain, that we cannot draw from the presence of ammonia in such filtered water any inference, which might be more or less justified when analyzing a natural water that has not undergone any such artificial treatment.

By direction of the Under Secretary for War, a trial of filters was commenced at the Army Medical School, Netley, by the late Dr. Parkes, and completed about two years later by Dr. de Chau- mont. It was found that of all filters experimented upon, the spongy iron filter alone yielded water in which no living or moving organisms could be de- tected under the microscope.

A report strongly recommending spongy iron has also been recently made to the Prussian War Minister by the military authorities at Coblenz. It is based up- on experience with a large filter during an epidemic of typhoid amongst the gar- rison. A cop^ of the report has been promised to me, but as yet I have not received it.

Lastly, a report was made at the Somerset House laboratory, by request of the Secretary for India, which is throughout in favor of the spongy-iron filter.

I have devoted so much time to do- mestic purification of water, because, as a rule, it is more effective than that on a large scale before delivery of the water to the consumer. This hardly re- quires an explanation. Look at our city. Its daily requirement of water, in round figures, is 120 million gallons. Such an enormous quantity is not easily dealt with, moreover, only a small pro- portion is used for drinking and cooking. This consideration has lately led to the proposal of two distinct water supplies, one for drinking and cooking, and an- other for general use. We then might either have derived the former supply from unexceptionally pure sources, or we might have bestowed so much more care and expense upon the purification

THE PURIFICATION OF WATER.

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of the potable water. But although this apparently would have been a satis- factory solution of the question, I am afraid it is fraught with great difficulties indeed.

If that scheme had ever been carried out, the present water supply would, al- -most, as a matter of necessity, have been neglected, as its purity for flushing and the like is of no great consequence. The quantity of water for drinking and cook- ing alloted to each consumer by the pro- visions of the scheme was very liberal; but suppose the supply of pure water had ever failed, what would have been the consequence ? Again, I do not see how any householder could possibly have been prevented from using three or four times the quantity of pure water he was entitled to. The result must have been inevitably an insufficiency elsewhere. Now, in these cases, and if by negligence or obstinacy of servants the impure water were used for drinking, it would have been a most serious matter had our present supply deteriorated.

In view of the difficulty of purifying the whole water supply, or of branching off a separate supply for internal use, we would at once dismiss purification on the large scale as undesirable, and confine ourselves to domestic filtration, if not there again we found most serious objec- tions. We cannot expect, for the pres- ent at least, to reach with domestic fil- tration the poorer classes and we have not only an interest in their welfare as our " neighbors," but we are person- ally interested in it. However careful we may be to exclude disease from our houses, by providing a wholesome water,

disease may be spread to them from the houses of the poor.

This leads me to a practical suggestion. I take it for granted that in London, and the same holds good in many other localities, careful filtration through sand is sufficient almost throughout the year. Why, then, should not additional means of purification, say through spongy iron, or any other medium that may be found preferable, be held in readiness, to be used ouly in emergencies, such as floods, or during periods of epidemics ? The same spongy iron might thus be made to Jast at least five or six times longer than when continuously used, and the working expenses would be so considerably re- duced as to become insignificant. I be- lieve, that, with an efficient supervision of the water supply, this proposal might work very well, offering all reasonable guarantees.

A water which has never been polluted would certainly be preferable to one which, after contamination, is re-purified. But where is, with rare exceptions, water to be found which has never been polluted ? Deep-well waters and even spring waters are unquestionably more or less supplied by polluted surface water, which is purified by natural filtra- tion. If analysis, if the microscope, prove that artificial filtration is equally or even more effective, if the physiologi- cal character of both waters should prove the same, w7e may, I think, as safely rely upon artificial as upon natural filtra- tion, and more so upon the former, as the naturally purified water may fail, whilst artificial filtration may be carried out to almost any extent.

GAS AS FUEL.

By M. M. PATTISON MUIR.

From "Nature."

Attempts have been made from time to time to use gas as a means for heat- ing; these attempts have more frequently failed than succeeded, chiefly by reason of the mechanical difficulties to be over- come.

It is pretty generally agreed that, on account of the ease with which the sup- ply of a gaseous fuel can be regulated,

the completeness with which such a fuel can be burned, the comparative readi- ness with which cleanliness can be main- tained while using this fuel, and by rea- son of its high heating power, and for other reasons, gaseous fuel is to be much preferred to fuel in the solid form.

The most perfect gas for heating pur- poses would be that, the constituents of

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which should be all combustible, should be possessed of high thermal powers, and should produce, on burning, com- pounds of small specific heat. No gas which has yet been produced for use as fuel completely fulfills these conditions.

Common coal-gas contains such non- combustible bodies as carbon dioxide and nitrogen, and among the products of its combustion is water, a body of large specific heat, and also requiring a con- siderable amount of heat to convert it into vapor. The complete combustion of coal gas also necessitates a compara- tively large supply of air, and this, again, involves special mechanical appli- ances. Nevertheless, coal-gas has been proved to be, for certain purposes, a cheaper, more effective, and more easily managed fuel than eoal, wood, or other forms of solid heat-giving material.

That steam is decomposed by hot car- bon with the production of a gaseous mixture of considerable heating powers, has long been known, and several attempts have been made to utilize the products of this decomposition. These attempts have met with no great success on account of the cost of the plant re quired to work the manufacture and of the difficulties of the process. Long- continued experiments have, however, been carried on, and it would appear from a paper recently communicated to the Society of Arts by Mr. S. W. Davies, that these experiments have been crowned with a very fair measure of success.

The great difficulty was a mechanical one : it has been very simply overcome. Superheated steam is produced in a coil placed within a cylinder and is driven by its own tension in the form of a jet into the lower part of an anthracite fire. The jet of steam carries with it air sufficient to actively maintain the combustion of the anthracite; the gases issue at the top of the apparatus and pass into the mains. The fire is fed from the top by an arrangement which allows of the process being continuous. Water is forced into the coil under a pressure varying from fifteen lbs. to forty lbs. on the square inch. The whole apparatus is compact . and simple.

The products of the decomposition of steam by hot carbon are mainly hydrogen and carbon monoxide; traces of marsh

gas are also formed. Could these gases be produced free from admixed non- combustible bodies we should have a gas of very high heating powers. But the temperature of the glowing carbon must be maintained by the introduction of oxygen, that is, in practice, by the intro- duction of air. The problem how to in- troduce air sufficient to keep up vigorous combustion, and at the same time to maintain the decomposition of the steam, appears to have been satisfactorily solved; but the introduction of air means a lowering of the heating power of the gas produced, inasmuch as four volumes of nitrogen are brought in along with every volume of oxygen supplied. By passing the gas through a series of ves- sels containing hot carbon the nitrogen may be very much diminished in amount, and the heating power of the gas pro- portionally increased.

The gas produced by the decomposi- tion of steam by hot carbon always con- tains traces of carbon dioxide which is non-combustible; the amount of this compound may, however, be reduced to three or four per cent, by regulating the depth of the layer of hot carbon through which the gases pass, and by maintaining the temperature of that carbon at a high point. But the maintenance of a high temperature throughout a mass of carbon can be accomplished, under the condi- tions of the manufacture, only by intro- ducing a rapid current of air, which again means a dilution of the gas pro- duced.

If, therefore, means could be found for feeding the anthracite fire with oxygen, a gas of very high heating power might be produced. A supply of oxygen at a cheap rate is a great desideratum; the gas exists in practically unlimited quan- tity in the atmosphere, but an easy and successful method for separating it from the nitrogen with which it is there mixed is still only hoped for by the chemical manufacturer. Were a supply of oxy- gen forthcoming, mechanical difficulties would present themselves before it could be utilized in the production of " water gas." The introduction of too small an amount of oxygen would mean the non- decomposition of the whole of the steam and the cessation of the combustion of the anthracite; the introduction of too much oxygen would mean the produc-

GAS AS FUEL.

41

tion of carbon dioxide in considerable quantity. But by regulating the size of the steam jet and of the blast-pipe, these difficulties might probably be overcome.

As the gas is now produced all danger of explosion is removed.

The heating effect of the gas as at pres- ent manufactured is about one-fifth that of ordinary coal-gas, for equal volumes; but the cost of the gas is so much less than that of coal-gas, that a given amount of heating work may be done — according to the figures given in the paper referred to — by using the new gas, with a saving of from one-third to two-thirds of the expenditure which would be involved were coal-gas em- ployed.

Although the new gas is not perfectly adapted for the purposes for which it is to be used, yet there can be little doubt that we are now a step, and a very con- siderable step, nearer the final solution of the problem. Doubtless improved furnaces, and improved apparatus gen- erally for burning the improved fuel will be introduced.

The production of a cheap gaseous form of fuel is a great gain ; so also is the invention of a means whereby the large stores of anthracite coal in this and other countries can be utilized.

Of all the forms of carbon experi- mented with in the production of the new gas, anthracite was found the best. Anthracite is difficult to burn; the ordi- nary forms of furnace do not admit of such a complete oxidation as is required in order to maintain the combustion of anthracite. But the blast of air carried into the gas generator of the water-gas apparatus by the steam jet insures the presence of a large quantity of oxygen, and therefore the combustion of the anthracite. Whether a simpler means could not be adopted for the combustion of anthracite is a question worthy of consideration. That a steam jet can be thrown into an ordinary furnace charged with anthracite, and the combustion of the coal be thereby insured, has been shown to be possible. Nevertheless, the production of combustible gas from the anthracite is to be preferred, for many reasons, to the consumption of the solid fuel.

The fact that we shall soon probably be in a position to make use of our stores

of anthracite, is one of very considerable importance from an economic point of view. In possessing large quantities of anthracite we possess a valuable com- modity, but if we cannot realize a use for that commodity it ceases to be a source of wealth to us.

Further, large quantities of anthracite are known to exist in some of the British Colonies and in the United States; the utilization of these would mean an in- crease in the commercial enterprises owned by Englishmen abroad, or sup- ported by English capital; it would also probably imply an increase in the ton- nage of shipping, and would thus tend to increase our " international wealth."

Whether it be regarded from the point of view of the chemist, or of the econo- mist, the introduction of a cheap gase- ous fuel manufactured from anthracite, marks a point of no little importance in the advance of manufacturing industries.

The experiments detailed in the paper by Mr. Davies show that the new gas is especially adapted for use in cooking operations in large private establish- ments, in clubs, hotels, barracks, &c. It is known that cooking can be more cheaply and more rationally conducted with the aid of gaseous than of solid fuel; if the new fuel does all that it promises to do, judging from the actual trials already made, its introduction will be welcomed by the artistic cook no less than by the scientific chemist, and by the political economist.

Good strong blown glass tumblers are being delivered into English ports from America for 8d. per dozen, and good hexagonal and octagonal cut Dutch tumblers for 4s. 8d. per dozen. The above fact relating. to importation from the United States, from whence but re- cently nothing of the kind was exported, is illustrative of the keen competition in manufactures generally, and in particular shows the necessity for the abolition of the English glass blowers practice of working but four days per week, a practice maintained by the glass blowers' guild, and one which prevents the con- tinuous operation of the costly furnaces and plant in a glass works. A smaller profit on most English goods will have to be accepted in the near future.

42

VAN NOSTRAND'S ENGINEERING MAGAZINE,

STEAM ENGINE ECONOMY— A UNIFORM BASIS FOR

COMPARISON.

By CHAKLES E. EMERY, M. E. From the Transactions of the American Society of Civil Engineers, March, 18T8.

In writing a general report on the exhibits referred to the Judges of Group XX, Centennial Exhibition, the writer compared the facts available in regard to the economy of steam engines of various kinds, on the uniform basis that the boiler is capable of absorbing 10,000 heat units per pound of coal consumed. This corresponds to an evaporation of 8.99 pounds of water at 80 pounds pressure, 9.03 pounds at 60 pounds pressure, or 9.08 pounds at 40 pounds pressure from a temperature of 100° in each case. This evaporation is higher than is usually obtained, but has been so much exceeded in practice* that it is not considered too high for a basis of comparison. The basis moreover enables the duty of pumping engines and other steam machinery to be ascertained and expressed in a very ready and conven- ient manner. Ten thousand heat units per pound of coal is equivalent to one million heat units per 100 pounds of coal and as the duty of pumping engines is conventionally expressed in millions of foot pounds per 100 pounds of coal it follows on the basis presented that the number of foot pounds per heat unit rep- resents also the number of millions of foot pounds duty per 100 pounds of coal. The performance of all kinds of steam engines may be readily compared on this basis. The simplest application is in testing vacuum pumps, the duty of which may be readily ascertained by noting the height of lift, and the initial and final temperatures of the water lifted. All the heat of the steam not expended in work enters the water, and the work performed lifts the same water. The difference in temperature gives very nearly the number of heat-units imparted to each pound of water lifted, and each pound of water so heated is lifted a cer- tain number of feet high, so the result may be expressed readily in foot-pounds per heat-unit, which, as before stated, equals also, on the basis presented, the

number of millions of foot-pounds duty for 100 pounds of coal. For ordinary comparisons the number of millions duty equals the lift, divided by the difference between the initial and final tempera- tures of the water. For more accurate computations, the divisor should be in- creased by the number of heat-units ex- pended for work per pound of water lifted, which equals the height divided by 772. The height preferably should be calculated from the indications of a pressure-gauge at the bottom of the dis- charge-pipe, so as to include frictional resistances. If D = duty in foot-pounds per 100 pounds of coal, H = the height of lift per gauge, and t and T = the initial and final temperatures respective- ly, then

1,000,000 H

D:

T— 2-K0013 H.

* See examples at page 75 of the report referred to.

Arrangements have been made by the writer to use the same basis in testing pumping-engines, by discharging water from the hot wrell into the suction of the main pumps, and rioting with delicate thermometers the resulting increase of temperature of the water lifted

A vacuum-pump tested by the writer in 1871 gave a duty, on the above basis, of 4T\ millions; one tested by Mr. J. F. Flagg, at the Cincinnati Exhibition in 1875, reduced to the same basis, gave a maximum duty of 3-^ftj- millions. Several vacuum and steam pumps tested on this basis, at the suggestion of the writer about two years since, gave duties re- ported as high as 10,000,000 to 11,000,000, the very small steam-pumps doing no better apparently than the vacuum- pumps, which is by no means surprising. Elaborate experiments made with steam- pumps at the American Institute Exhibi- tion of 1867* showed that average-sized steam-pumps do not, on the average, utilize more than 50 per cent, of the in- dicated power in the steam- cylinders,

* See Report of Messrs. Holmes, Selden, and Emery, Judges, etc., Transactions American Institute, 186T-68.

STEAM ENGINE ECONOMY.

43

the remainder being* absorbed in the friction of the engine, but more particu- larly in the passage of the water through the pump. Again, all ordinary steam- pumps for miscellaneous uses require that the steam-cylinder shall have 3 to 4 times the area of the water-cylinder to give sufficient power when the steam is accidentally low; hence, as such pumps usually work against the atmospheric pressure, the net or effective pressure forms a small percentage of the total pressure, which, with the large extent of radiating surface exposed and the total absence of expansion, makes the expendi- ture of steam very large. One pump tested by the writer required 120 pounds weight of steam per indicated horse- power per hour, and it is believed that the cost will rarely fall below 60 pounds; and as only 50 per cent, of the indicated power is utilized, it may be safely stated that ordinary steam-pumps rarely require less than 120 pounds of steam per hour for each horse-power utilized in raising water, equivalent to a duty of only 15,000,000 foot pounds per 100 pounds of coal on the same basis adopted for the vacuum-pumps. With larger steam- pumps, particularly when they are pro- portioned for the work to be done, the duty will be materially increased.

Ten thousand heat units per pound of coal represent an ultimate efficiency of only (10,000X100-^14,500*=) 69 per cent, of the calorific value of anthracite coal, so that ordinarily more than (100 — 69 = ) 31 per cent, of the heat in the fuel is carried to waste up the chimney. A still greater loss is, however, experi- enced in utilizing the steam for the pur- pose of work in the engine. The mechanical equivalent of one heat-unit is 772 foot-pounds, which, on the basis referred to above, corresponds to a duty of 772 millions of foot-pounds per 100 pounds of coal. The most economical steam-engines, for instance pumping- engines of approved types, utilize in the steam-cylinder only about 130 millions, on the same basis, equivalent to an ulti- mate efficiency of (130X100-^-772=) 16.84 per cent, of the heat in the steam, and but (16.8-4X.69 = )11.62 per cent, of the calorific value of the fuel. The

principal reason for this is that the ex- haust steam necessarily carries to waste the heat required to maintain it in a vaporous state at the tension due to the back pressure. This, under the most favorable circumstances, forms the larger proportion of the total heat of the steam, and reduces the opportunities for secur- ing economy within small limits com- pared with the theoretical limit, although the differences between the performances of different engines are great when com- pared one with another.*

Means for securing economy in steam- engines may be divided into two classes, viz., those of a mechanical nature and those which influence the thermal con- ditions. As to the first, the necessity of securing tight pistons and valves, ample area of cylinder passages, reduced clear- ances, etc., are well understood, also the incidental advantages due to a certain degree of compression. Those of the second class act to reduce the cylinder condensation, and include high speeds of revolution, steam superheating, steam- jacketing, and the compounding of en- gines. High speed of revolution (which does not necessarily imply high piston speed, as generally understood) secures economy, by reducing the time in which the transfers of heat to and from the steam and inclosing walls must take place, f

Superheating the steam has experi- mentally proved effective for moderate rates of expansion, in wThich the original

* la view of discussions in progress at the date of writing on the proper details of a theoretically perfect steam-engin j, it is p oper to mention that in the year 186S the writer designed and partially constructed a non- exhausting experimental eugine in which the steam, after expansion in the cylinder, was to be circulated through another vessel, to withdraw the water due to the per- formance of work; the dry steam was then to be returned to the cyliuder and compressed, which it was expected would require less power than the expansion would fur- nish, aud sufficient steam only be received from the boiler to supply that condensed for work. A demonstra- tion of the correctness of the principle only wa,s intended, the power expected being so small that the experimental engiue was to be connected to another to keep it iu motion. Before the apparatus was completed the funds were diverted to objects of greater immediate necessity, and the subject is mentioned only as indkating'the general princi- ple upon which a theoretically perfect steam-engine may be constructed. See description of the apparatus in arti- cle on the " Theoretical Ste mi-Engine," Scientific Ameri- can Supplement, Aug. 18, 1S77. See also Prof. Thurston's calculations on a similar subject iu Journal of the Frank- lin Institute, Oct., Nov., and Dec, 1871.

• The calorific value of anthracite coal is usually con- sidered to be that of the carbon element or 14500 heat- units.

t The value of this saving was writer for the Novelty Iron Works,

determined by the . Mr. Horatio Allen, President, in the year 1868, and embodied in a series of tables showing the relative power and economy of differ- ent sizes of steam-engines, which tables were afterwards published Jby Prof. W P. Trowbridge, the former Vice- President of the company.

44

van nosteand's engineeking magazine.

temperature required to maintain the gaseous condition of the steam to the point of release was not too high to pre- vent proper lubrication. Mr. Geo. P. Dixwell, of Boston, Massachusetts, has applied a thermometer to a steam cylin- der, by inspection of which it is possible to regulate the temperature so as to pre- vent injury to the metal surfaces. The great difficulty is, however, to secure a permanent and reliable superheating ap- paratus. Steam-jacketing has to a limit- ed extent advantages of the same kind as superheating, and involves no serious difficulties in management. The jackets are most effective on long cylinders of small diameter. In experiments with United States Tevenue steamers, herein- after mentioned, the economy of a steam- jacket on a comparatively short cylinder was found to be eleven to twelve per cent.

Compound engines, in addition to ad- vantages of a mechanical nature, in bet- ter distributing the strains and rendering more uniform the rotative efforts, serve also to reduce cylinder condensation by the distribution of the differences of temperature between two cylinders. The radiation to and from the steam and its inclosing walls increases more rapidly than the difference in temperature, so that the aggregate loss, when the differ- ence of temperature is divided between two cylinders, is less than when it all occurs in a single cylinder*. Moreover, the heat imparted to the exhaust steam by the metal of the first cylinder is available for wTork in the second, and the low-pressure piston acts as a screen be- tween the high temperature in the small cylinder and the low temperature in the condenser.

It is still strenuously denied by many that greater economy can be secured with a compound engine than with a long-stroke single engine using the same steam pressure. There are coasting steamers of similar size running regularly in the United States using both types of engine, with, it is claimed, substantially the same results; but the boilers for the single engines are evidently the more economical, making an accurate com-

* See article by the writer in American Artizan, March 8th, 1871. See also this Magazine, for May, 1871.

parison impossible. Strictly compara- tive experiments have, however, been made by Chief Engineer C. H. Loring, U.S.N., and the writer with engines of different kinds in the steamers of the United States Revenue Marine, and by the writer with some of those of the United States Coast Survey.*

The revenue steamers were of the same size and the boilers \erj nearly identical. In one steamer was a compound engine with steam-jacketed cylinders; in another, a long-stroke, high -pressure condensing engine (cylinder not jacketed) ; in another, an ordinary low-pressure engine (cylinder not jacketed); and in still another, a high-pressure condensing en- gine with a jacketed cylinder. The com- pound engine showed a saving of 12 to 16 per cent, compared with the best per- formance of either single engine when operated at the same steam pressure. It is believed that substantially the same differences will be found in all cases when equally good engines of both types are compared. The performance of a short-stroke compound engine may be equaled or even excelled by that of a long-stroke single engine, on account simply of the difference in clearance spaces and the superior efficiency of the steam-jacket in the latter case, but by making the compound cylinders in the same form they should still show an ad- vantage. In practice, the economy of marine compound engines is greater than above mentioned, for the reason that the high steam pressure is better maintained with them by the engineers than when single cylinders are used with high rates of expansion, causing difficulties in man- agement.

The following table shows in line 1 the performance of one of the Leavitt compound beam pumping-engines, at Lawrence, Massachusetts, and in line 2 that of the engines of the Hush, one of the revenue steamers previously referred to :

* See article by the writer on " Compound and. Non- Compound Engines," Transactions American Society of Civil Engineers, vol. iii. p. 68, 1875; Journal of the Franklin Institute, Feb. and March, 1875 ; Engineering (London), Jan., Feb., and March, 1875; Proceedings of Institution of Civil Engineers (British), vol. xT. p. 292, and vol. xli. p. 296 ; also report of trial of United States reve- nue steamer Gallatin, Journal of the Franklin Institute, Feb., 1876, and vol. xxi., Engineering, 1876.

STEAM ENGINE ECONOMY.

45

6

a

.2

'oS

a

S3

o

o ft

h3

Pressure d to Large Under.

CO

8-i

H3 o ft

ej-l

O

™6

pa

ft

21

s

O

'■§1

O ft

O

Water per Indi Horse-Power Hour.

a

1*

ft ft <1

O

.2

p

5

5

03

o

C72

>

M

o

Mean referre

Cy

Inches.

Inches.

Inches.

Feet per Minute.

Pounds.

Pounds.

1

90

13.5

18

38

96

16.27

260.3

22.15

196.4

14.02

2

70

6.22

24

38

27

70.84

318 8

24.48

266.6

18.38

The comparison is very interesting. In both engines the larger cylinders are of the same diameter, but the difference in the duty for which the engines were designed required great differences in other proportions and in all the details of construction. In the pumping-engine for use on land there were no restrictions as to weight and space, so a compara- tively long stroke could be employed and the connections made through a beam. The marine engine had, how- ever, to be located in a small vessel, and was therefore directly connected and proportioned accordingly. Yet the long- stroke engine was run with so much ex- pansion and at so slow a speed as to de- velop less power than the smaller one, and the latter was less economical, on account of the lower steam pressure and rate of expansion and the relatively greater proportion of waste room in the cylinder, incident to the necessary use of ordinary slide-valves. The engine of the Hush was, however, more economical than the ordinary stationary compound engines used for manufacturing purposes, as the latter, according to published re- ports in the engineering journals, require the evaporation of not less than twenty pounds of water for each indicated horse-power. The Lawrence engine contains all well-known means for secur- ing maximum economy of steam, and it is probable that few if any engines are working with greater economy in respect to the indicated power. The perform- ance is, however, much below that given by calculation when all the conditions are taken into consideration, other than

the slight distortion of the theoretical indicator diagram found in practice and the important loss due to cylinder con- densation.

In an engine using a total pressure of (90 + 14.7 = ) 104.7 pounds, expanded 13.5 times in a cylinder, with clearances, etc., equal to .02 of the displacement, the calculated cost of one horse-power per hour, or 1,980,000 foot-pounds, should be only 8.12 pounds of water evaporated from the initial pressure, on the basis that the curve of expansion is hyper- bolic, and that the consumption of steam equals the volume at the initial pressure required to fill the cylinder to the point of suppression, plus that condensed for the 'total work. With a pressure of 100 pounds above the atmosphere, and an ex- pansion of twenty times, there should be required on same basis the evapora- tion of only 6.00 pounds of water per indicated horse-power per hour. It is probable that the practical results ob- tained with the latter pressure and ex- pansion would be little or no better than those from the Lawrence engine, on ac- count of the greater cylinder condensa- tion due to the increased expansion.

The above-calculated performances, and the practical results obtained with engines and other steam machinery of various kinds, is shown in the accom- panying table, in connection with the relative efficiencies obtained by consider- ing the heat units in the steam and the calorific value of the fuel. The table and a portion of the above are from the report previously mentioned and the references are to pages therein :

46

VAN NOSTRAND's ENGINEERING MAGAZINE.

Description.

a

<o

o

Si

OQ

2

a

<fl

53

a

u

X!

Ph

H

B

o

o3

<u

o

OQ

"o3

«

Comparative Results on Basis that 10,000 Heat-Units are imparted to Water per Pound of Coal. See pp. 21 and 115. § Calculations based on a Temperature of Feed of 100°.

IS

OO ^ ffl iTfafl

A

•^ o

§^

o3 o

a^ o

»^.-£

'3 Jo «a o <u

53 g *

PhS

«

&0 o3 a • ©

=4h a

■S* S ° a.SPn

fi5o

3^3

10 11 12

Calculated performance.

Maximum

Calculated performance (see page 120)

Calculated performance

Lawrence compound beam pumping-eneines

U.S. Revenue steamer Rush,* compound engine

U. S. Revenue steamer Galla- tin,* vertical cylinder with steam-jacket

U. S Revenue steamer Dex ter,* vertical cylinder with- out steam jacket

U. S. Revenue steamer Dal- las* vertical cylinder with- out steam-jacket

U. S. steamer Mackinaw, f in- clined cylinder without steam-jacket

U. S. steamer Mackinaw, steam superheated

Non condensing engine, with governor cut off:}: (st. jacket)

Non - condensing engines, regulated by throttle

100 90

89.4

69.2

67.2

67.1

32.0

49.0 52.0

81.7

20 13.5

13.7

6.22

4.19

3.49

3.13

2.2 3.2 5.0

6.005 8.122

14.019

18.384

21.48

23.905

26.945

30.306

22.725 25.482

772.0

295.2

218.6

126.7 97.03

1.00

.382 .283

.164

.126

83.08 i .108

74.66 66.91

59.16

78.83

69.81

30 to 45

.097

.087

.077

.102

.090

04 to. 06

.690

.264 .195

.113

.087

.074

.067

.060

.053

.070

.062

03 to. 04

13 14 15 16

17

Pumping- engines

Steam-pumps. Large size proportioned for the work to be done

Steam pumps. Small sizes for ordinary uses. See page 22 §

Vacuum-pumps. See page 21 §

Iujectors when used for lifting water not required to be heated. See page

30 to 110

15 to 30

8 to 15

3 to 10

2 to 5

* See references in foot-note, page 119, and page 44 of this No.

t See vol. ii, Isherwood's Experimental Researches in Steam Engineering, pp. 77-116.

t American Institute Reports, 1869-70, 1870-71.

§ General Keport of the Judges of Group XX, Philadelphia International Exhibition. Lippincott & Co., Phila.

ACCURATE NAVIGATION.

47

ACCURATE NAVIGATION.

By Captain MILLER. From " The Nautical Magazine."

There are many non-nautical critics, learned as well as unlearned, who take it for granted that navigation as a perfect science is always available to the navi- gator. They seem to think that under all circumstances he has simply to work out a few problems, which they suppose can be done at any time, and if done cor- rectly and properly applied must neces- sarily lead to infallible results. Not- withstanding the apparent blunders, the numerous casualties, and the pile of evi- dence to the contrary, that continually come to light through our Courts of In- quiry, these persons comment as flip- pantly on any particular case of casualty as though there were no reason why a ship should not arrive at her destination as accurately as a railway train, which, starting from one end of the kingdom, runs up to its terminus at the other within a foot of the platform.

Unfortunately for the value of these comments, there are no rails laid over the seas, and until this is actually achieved ships will continue to deviate from straight courses. As Nature is said to abhor a vacuum, so ships in their courses seem to abhor being kept to perfectly straight lines. All that science does for the navigator is to aid him occasionally; occasionally, I say, because science in her attendance on him is very whimsical, being present only when her assistance is least required, and invariably being absent when her assistance is most need- ed. When, for example, the navigator has the full use of vision and can see everywhere around him, when through having the use of this vision there is no risk of his running his ship into danger, and navigating her is comparatively an easy process, then science, with her brightest smiles, is always present, ready to overwhelm him with the tender of her innumerable problems to verify his posi- tion. But when, having to run for some iron bound coast, the weather thickens for some days previous to his reaching it, and wind and sea press and heave the ship an unknown amount from her track, when all is thick, dark, and dreary, and

vision altogether fails, when the ship may be said to be running through a sort of " valley of the shadow of death," where then is science with all her bright smiles and tenders of assistance ? These are the times when the navigator most needs her presence, but these are the times when she always absents herself, and leaves no other assistance, to aid him in his most difficult and delicate work, than that assuming and guessing old pilot called " dead reckoning."

I wonder why our ancestors called this old