TJ .^■ .0^ 'o ^ ,# c » "^ '• . I - ■>< C'^ ^^ .^^,%. '^. s ^ ^^ , ^- K ^ ^K, > ./ ■?/■ "^. M^' •^ <■ X ■» , 0^ ■^00^ % S^ *s- . >• ,0 %<.^^ -" o5' x^- '^... 'A -^c. A^' "-^c n, = ■^, .^v cO^^ ^'^^^:^^ ^<^^''?:s^. :, >^ c^'*" .^:^^% V ■■ X» ^ ^ ^'^■,.o.c/V'-^\^ ,. -j^-:^; *'-°o i^-; '^oo^ ^' r^J^^V / = -^!^' ■> VI ^V ^'t. 8 1 \ "^ \ V rf*« ■^ .=--■ * ,f^ -. .-.^^^ HA.ND-BOOK OF Land and Marine Endnes, INCLUDING THE MODELLING, CONSTRUCTION, RUNNING, AND MANAGEMENT OF LAND AND MARINE ENGINES AND BOILERS. lj)it| )((Itt$italimt3. BY STEPHEN ROPER, Ekgineer, Author of ' Roper's Catecliism of High Pressure or Non-Condejis«ig"5TigiT*^^' " Roper's Hand-Book of the Locomotive," ieje- ^'^' 0("j t^N^ PHILADELPHIA: CLAXTON, EEM8EN & HAFFELFINGER, 624, 626 & 628 MARKET STREET. 1875. Entered according to Act of Congress, in the year 1875, by STEPHEN ROPER, in the Office of the Librarian of Congress, at Washington. ^-^3- 5^ 6 ^•-J :)'' I, philad'a. fe<:^^^'^ J. FAGAN ELECTR0TYPER8, Seiheimer &, Moore, Printers- 501 Chestnut Street. TO THE ENGINEERS OF THE UNITED STATES, THIS BOOK " Steam Engineering is one of the noblest sciences that ever attracted the attention of manP 1* "A place for everything and everything In Its place."— See page 264. vi INTRODUCTION. n[^HE object of the writer in preparing this work has -L been to present to the practical engineer a book to which he can refer with confidence for information regard- ing every branch of his profession. Many of the books heretofore written on this subject are full of formulae for calculating questions that may arise in the engine-room ; but, as they are generally expressed in algebraical form, they are of little service to the majority of engineers ; for, however useful such formulae may be to the scientific, they can be of no practical value to men who do not fully understand them. It is also no less a fact that nearly all writers on the steam-engine deal more with the past than the present. This is to be regretted, for, however inter- esting the bygone records of steam engineering may be, as a history, they cannot instruct the engineer of the present day in the principles and practice of his profession. An experience of over thirty years with all kinds of engines and boilers enables the writer to fully comprehend the wants of the class for whom^. he writes, and what they can understand and employ. With this object in view, ' he has carefully investigated all the details of Land and Marine Engines and Boilers, taking up each subject singly, and excluding therefrom everything not directly connected with Steam Engineering. Particular attention has been given to the latest improvements in all classes of engines, vii Vlll INTRODUCTION. and to their proportions according to the best modern prac- tice, which will be found of special value to engineers, as nothing of the kind has heretofore been published. The book also contains ample instructions for setting up, lining, reversing, and setting the valves of all classes of engines, — subjects that have not, up to the present time, received that attention from writers on the steam-engine that their importance to engineers so justly merits. It also contains a complete Lexicon of Central, Mechanical, and Natural Forces, which will be found of great value to engineers, as scarcely anything of the kind that has heretofore been published, has been applicable to American practice. A large portion of the work is devoted to the examination and discussion of the principles of Hydro- and Thermo- dynamics, which include Air, Water, Heat, Combustion, Steam, Liquefaction, Dilatation of Gases, Molecular and Atomic Forces, Dynamic Equivalents, subjects with which the practical engineer should be fully conversant ; as to ignore the principles of any subject is similar to building a structure without knowing the strength of the foundation ; for it was only by a minute and careful analysis of the physical phenomena which convert heat into a motor force that the steam-engine has been brought to its present per- fection. The strength of materials, design, construction, care, and management of all classes of Steam-Boilers are also fully discussed. The writer candidly admits that the work may be found somewhat defective in language, but he firmly believes that it will be found perfectly accurate and reliable in all other respects. S. R CONTENTS. F(yr a full reference to the Contents in detail, see Index, page 583, PAGE Introduction . . .7 The Steam-engine . 21 Steam . .25 Table showing the Temperature and Weight of Steam at different Pressures from 1 Pound per Square Inch to 300 Pounds, and the Quantity of Steam produced from 1 Cubic Inch of Water, according to Pressure . 39 Working Steam expansively 43 Table of Hyperbolic Logarithms to be used in Connec- tion with the above Eule 48 Table showing the average Pressure of Steam upon the Piston throughout the Stroke, when Cut-off in the Cylinder from J to y\> commencing with 25 Pounds and advancing in 5 Pounds up to 75 Pounds Press- ure 49 Table showing the average Pressure of Steam upon the Piston throughout the Stroke, when Cut-off in the Cylinder from \ to J, commencing with 80 Pounds and advancing in 5 Pounds up to 130 Pounds Press- ure .... 50 Table of Multipliers by which to find the mean Pressure of Steam at various points of Cut-off. . . .51 High-pressure or Non-condensing Steam-engines . 54 Power of the Steam-engine 55 ix X CONTENTS. PAGE Foreign Terms and Units for Horse-power . . .59 Table of Factors 68 Waste in the Steam-engine 70 Design of Steam-engines 73 The Bed-plate 74 Cylinders 74 Table showing the proper Thickness for Steam-cylinders of different Diameters 75 Pistons . . 76 Piston-rings 77 Piston-springs. ,77 Steam-pistons 78 Solid Pistons . 78 Table of Piston Speeds for all Classes of Engines — Sta- tionary, Locomotive, and Marine . . . .79 Piston, Connecting-rod, and Crank Connection . 80 Table showing the Position of the Piston in the Cyl- inder at different Crank - angles, according to the length of Connecting-rod 81 Table showing Length of Stroke and Number of Revolu- tions for different Piston Speeds in Feet per Minute . 82 Piston-rods 83 Crank-pins 83 Table showing the Angular Position of the Crank-pin corresponding with the various Points in the Stroke which the Piston may occupy in the Cylinder . . 84 Steam-chests . .85 Valve-rods 85 Guides 85 Rock-shafts S6 Cross-heads S6 Steam-ports . .87 Table showing the Proper Area of Steam-ports for dif- ferent Piston Speeds 88 Slide-valves .89 Proportions of Slide-valves 93 CONTENTS. Xi PAGE Lap on the Slide-valve. . . . . , .93 Poppet ok Conical Valves . . . . . . 95 Table showing the Amount of "Lap" required for Slide- valves of Stationary Engines when the Steam is to be Worked expansively 97 Lead of the Slide-valve .97 Clearance . . .99 Compression < . . . 100 Friction of Slide-valves 100 Balanced Slide-valves 102 Fitting Slide-valves . . . . . . . 103 Slide-valve Connections ...... 103 Eccentrics , • . . .104 Eccentric- RODS 108 Cranks 109 Crank-shafts 114 Pillow-blocks, or Main Bearings .... 114 Fly-wheels . . . . . . . . . 115 Link-motion 116 Proportions of Steam-engines according to the BEST Modern Practice 121 Setting up Engines 127 Dead-centre 128 How TO PUT AN Engine in Line . . . . . 128 How TO Eeverse an Engine 131 Setting Valves 131 How TO set A Slide-valve 132 Setting out Piston Packing 134 Piston- and Valve-rod Packing 185 Cut-offs 138 Governors 139 The Huntoon Governor 140 The Allen Governor 142 The Cataract 145 Wright's High-pressure Engine 146 Hawkins and Dodge's High-pressure Engine . 147 Xll CONTENTS. PAGE Watts and Campbell's High-pressure Engine . . 148 The Buckeye High-pressure Engine . . . . 148 Wheelock's High-pressure Engine . . . .151 The Corliss High-pressure Engine . . . .151 Hampson and Whitehill's High-pressure Engine . 153 The Allen High-pressure Engine ... . .155 Woodruff & Beach's High-pressure Engine . . 156 Naylor's Vertical High-pressure Engine '. . 157 Williams' Vertical Three-cylinder High-press- ure Engine 158 Eoper's Caloric Engine 159 Haskins' Vertical High-pressure Engine . . 163 Massey's Rotary Engine . . . . . . 164 Portable Engines 166 How to balance Vertical Engines . . . . 166 Knocking in Engines 168 The Injector 169 Method of working the Self-adjusting Injector WHEN Required to Lift the Water . . . 172 Method of working the Adjustable Injector when Required TO Lift THE Water . . . . 173 Instructions for Setting up Injectors . . . 173 Temperature of Feed- water . . * . . .176 Table of Capacities of Injectors ..... 177 Temperature of Feed-water 177 Pumps 178 Steam-pumps 180 The Dayton Cam-pump 181 Directions for setting up Steam-pumps . . . 184 The Pulsom^ter 185 James Watt 187 Condensing, or Low-pressure Steam-engines . . 188 Explanation of the working Principles of the Condensing Engine 190 Horse-power of Condensing Engines . . . .191 The Vacuum 193 CONTENTS. Xlll PAGE Marine Steam-engines . . . . . . .197 Compound Engines 200 Direct- ACTING Engines 203 Balancing the Momentum of Direct-acting En- gines -- . . . 205 Oscillating Engines . 205 Trunk Engines . . 207 Geared Engines . . 207 Back-action Engines 208 Side-lever Engines 209 Beam Engines 209 Marine Beam Engine 211 Starting-gear for Marine Engines .... 215 Condensers . . . 216 Air-pumps 222 The Hydrometer, Salinometer, or Salt-gauge . 223 The Manometer , . . 224 The Barometer . . . . * . . . 225 Marine Engine Register, Clock, and Vacuum Gauge ..... ... 226 Steam-gauges 227 Glass Water-gauges . . . .... . 233 The Steam-engine Indicator 235 Method of Applying the Indicator .... 241 Form of Diagrams , 250 How TO keep the Indicator in Order . . . 252 The Dynamometer , . 254 The Engineer 256 Management of Land and Marine Engines . . 258 How TO PUT THE ENGINES IN A STEAMBOAT OR ShIP . 265 Screw-propellers 271 Negative Slip of the Screw-propeller . . . 274 Table of the Proper Proportions of Screw-propellers . 279 Measurement of the Screw-propeller . . . 279 How TO Line up a Propeller-shaft .... 282 Paddle-wheels 282 2 xiv CONTENTS. / PAGE Fluid Eesistance . 287 Signification of Signs used in Calculations . . . 291 Decimal . . .291 Decimal Equivalents of Inches, Feet, and Yards . . 292 Decimil Equivalents of Pounds and Ounces . . . 292 Useful Numbers in calculating Weights and Measures, etc. ... . ... . . .292 Decimal Equivalents to the "Fractional Parts of a Gallon or an Inch . . . . . . . . . 294 Units. . . . . 294 Theory OF the Steam-engine 298 Water 299 Table showing the Weight of Water . . . .805 Table showing the Weight of Water at different Tem- peratures .... . . . . . 305 Table showing the Boiling-point for Fresh Water at different Altitudes above Sea-level . . . . 306 Table showing the Weight of Water in Pipe of various Diameters 1 Foot in Length 307 Air 309 Table showing the Weight of the Atmosphere in Pounds, Avoirdupois, on 1 Square Inch, corre- sponding with different Heights of the Barometer, from 28 Inches to 31 Inches, varying by Tenths of an Inch * . . . . 311 Table showing the Expansion of Air by Heat, and the Increase in Bulk in Proportion to Increase of Tem- perature . . 312 The Thermometer 313 Comparative Scale of Centigrade, Fahrenheit, and Reaumer Thermometers 314 Elastic Fluids . . . . . . . . 320 Caloric 321 Heat 323 Latent Heat of Various Substances .... 331 Table of the Radiating Power of different Bodies . . 831 coiirrENTS. XV PAGE Table showing the Effects of Heat upon different Bodies .332 Combustion . . . 332 Composition of different Kinds of Anthracite Coal . 336 Table showing the Total Heat of Combustion of various Fuels . . .. .. . . . . . . 342 Table showing the Nature and Value of several Varie- ties of American Coal and Coke, as deduced from Ex- periments by Professor Johnson, for the United States Government ... . . . . . 34c Table showing some of the Prominent Qualities in the principal American Woods 344 Table showing the Kelative Properties of good Coke, Coal, and Wood. . . ... . . . / . . 344 Table of Temperatures required for the Ignition of dif- ferent Combustible Substances , . . . . 345 Gases . . . . 346 Steam-boilers 350 Steam-domes . . . . . , . , . . . . 353 Mud-drums 355 Setting Boilers 356 Expansion and Contraction of Boilers . . . 358 Testing Boilers . . . . . . . . 359 Neglect of Steam-boilers 362 Care and Management of Steam-boilers . . 363 Heating Surface . ..... . . 369 Kules for finding the Heating Surface of Steam- boilers .371 Evaporative Efficiency of Boilers . . . . 372 Horse-power of Boilers 375 Firing . . 378 Instructions for Firing . . . ... 382 EuLES for finding the Quantity of Water Boilers AND other Cylindrical Vessels are capable of Containing .... . . . . 386 LONGITUDINAI^ AN!) Cui^VILINEAR STRAINS . . .387 XVI CONTENTS. PAGE EuLES . . .388 Explanation of Tables of Boiler Pressures on FOLLOWING Pages 389 Table of safe Internal Pressures for Iron Boilers . .390 Table of safe Internal Pressures for Steel Boilers . . 394 Marine Boilers 399 Proportions of Heating Surface to Cylinder and Grate Surface of noted Ocean, River, and Ferry-boat Steamers 402 Setting Marine Boilers 404 Bedding Marine Boilers 405 Clothing Marine Boilers 405 Care of Marine Boilers 406 Repairing Steam-boilers . , . . . . 409 Tubes . . 410 Table of Superficial Areas of External Surfaces of Tubes of Various Lengths and> Diameters in Square Feet 413 Boiler Flues . . , . . . . . .417 Table of Squares of Thicknesses of Iron, and Constant Numbers to be used in finding the safe External Pressure for Boiler Flues . . . . . .419 Table of safe Working External Pressures on Flues 10 Feet long . . . ; 420 Table of safe Working External Pressures on Flues 20 Feet long . . . . . . . . .422 Table of Collapsing Pressure of Wrought-iron Boiler- flues J Inch thick . . .... . . 425 Table of Collapsing Pressure of Wrought-iron Boiler- flues y5^ Inch thick . . ... . .426 Table of Collapsing Pressure of Wrought-iron Boiler- flues I Inch thick 427 Table of Collapsing Pressure of Wrought-iron Boiler- flues yV Inch thick . 428 Boiler-heads 429 Safety- yalves 431 CONTENTS. XVll PAGE Table showing the Kise of Safety-valves, in Parts of an Inch, at different Pressures 433 Table of Comparison between Experimental Eesults and Theoretical Formulae 435 KuLES . . . . 437 Foaming 439 Incrustation in Steam-boilers . . . . .441 Internal and External Corrosion of Steam- boilers . . 449 Boiler Explosions 452 Comparative Strength, of Single -and Double- riveted Seams 461 Calking 464 Strength of the Stayed and Flat Surfaces . . 468 Definitions as applied to Boilers and Boiler Materials « . 469 Table deducted from Experiments on Iron Plates for Steam-boilers, by the Franklin Institute, Phila. . 470 Table showing the result of Experiments made on dif- ferent Brands of Boiler Iron at the Stevens Institute ofTechnology, Hoboken, N. J 471 Feed- WATER Heaters 472 Table showing the Units of Heat required to Convert One Pound of Water, at the Temperature of 32° Fah., into Steam at different Pressures .... 473 Steam-jackets 474 Loss OF Pressure in Cylinders induced by Long Steam-pipes . . 475 Priming in Steam-cylinders 476 Oils and Oiling 477 Table of Coefficients of Frictions between Plane Sur- faces . . 480 Grate-bars . 482 Chimneys . 483 Table showing the proper Diameter and Height of Chimney for any kind of Fuel. 484 2* B XVUl CONTENTS. PAGE Smoke . . , . 485 Mensuration of the Circle, Cylinder, Sphere, ETC 487 Central and Mechanical Forces and Defini- tions . . . . . , . . . . 490 The Circle 511 Table containing the Diameters, Circumferences, and Areas of Circles, and the Contents of each in Gallons, at 1 Foot in Depth. Utility of the Table 511 Logarithms 515 Table of Logarithms of Numbers from to 1000 . . 516 Hyperbolic Logarithms . . . . . . 517 Table of Hyperbolic Logarithms . . . . . 518 Table containing the Diameters, Circumferences, and Areas of Circles from yV of an Inch to 100 Inches, advancing by ^^ of an Inch up to 10 Inches, and by -J of an Inch from 10 Inches to 100 Inches . . . 521 Table of Squares, Cubes, and Square and Cube Eoots of all Numbers from 1 to 620 532 Table showing the Tensile Strength of various Qualities of Wrought-iron 547 Table showing the Actual Extension of Wrought-iron at various Temperatures 548 Table showing the Tensile Strength of various Qualities of Steel Plates 549 Table showing the Tensile Strength of various Qualities of Cast-iron ' . . . 549 Table showing the Weight of Boiler-plates 1 Foot Square, and from -^ to an Inch thick .... 551 Table showing the Weight of Square Bar-iron, from -| an Inch to 6 Inches Square, 1 Foot Long . . .551 .Table showing the Weight of Eound-iron from | an Inch to 6 Inches Diameter, 1 Foot Long . . . 552 Table showing the Weight of Cast-iron Balls from 3 to 13 Inches in Diameter 553 CONTENTS. XIX PAGE Table showing the Weight of Cast-iron Plates per Su- pa-ficial Feet as per Thickness 553 Table showing the Weight of Cast-iron Pipes, 1 Foot in Length, from J Inch to IJ Inches thick, and from 3 to 24 Inches Diameter 554 Table showing the Weight per Square Foot of Wrought- iron, Steel, Copper, and Brass 555 kules for finding the diameter and speed of Pulleys 558 Gearing 559 Belting . . . . . . . . . .561 Cement for making Steam-joints and Patching Steam-boilers . 568 Non-conductors for Steam-pipes and Steam-cyl- inders . . . . . r . . . 569 How TO Mark Engineers' or Machinists' Tools , 569 To Polish Brass . , 570 Solder ..... 570 Table showing Weight of different Materials. . . 571 Joints . 1 571 Steam-boiler Flue and Tube Cleaners . . . 573 The Invention and Improvement of the Steam- engine . . . . 574 HAE^D-BOOK OP LAND AND MAEINE ENGINES. THE STEAM-ENGINE "VrOTHING furnishes man with greater cause for con- Xi gratulation, and even an excusable pride, than the feats of that mighty impersonation of brute force and human intellect, — the steam-engine, the Hercules of the nineteenth century, — which, once launched into the world's arena, has gone forth "conquering and to con- quer," fulfilling its high destiny as a great civilizing agent, with an energy which no human arm can arrest and a rapidity which fills us with astonishment and admiration. It would be superfluous here to attempt to enumerate the benefits which the steam-engine has conferred upon mankind. It is a matter of universal knowledge that all branches of industry have, since its introduction into use, made most important advances through its aid, and every day's experience shows it constantly extending its bene- ficial influence to new and important purposes, and lending its powerful assistance to the further advance of civili- zation. 21 22 HAND-BOOK OF LAND AND MARINE ENGINES. When we consider what the introduction of the steam- engine has already done, we have the less difficulty in anticipating that this invention may yet be destined to achieve objects of whose magnitude and importance we can at present form but a faint idea. There are few manufacturing processes that have not been revolutionized, simplified, and extended during the last fifty years through the agency of the steam-engine ; but it is not alone in the large manufactory, the splendid steamer, and the rushing locomotive, that steam shows its usefulness, but also in our villages, cities, and towns, delving into the mines, driving the printing-press, helping all trades, and multiplying man's power a thousand -fold. Cities have sprung up under its magic touch, and on every side we see traces of the wonderful efiects produced by this king of motors and mighty agent of civilization. Then the independence of time, season, circumstance, and locality, in consequence of its not being influenced by flood, frost, winds, or drought, which mark the great superiority of this potent creation of engineering skill, and which, in its multiform applications and applicability, have invested it with an importance and an interest which success seems only to stimulate and render more intense, while its complexity of parts and diversity of combination offer a wide scope for the exercise of ingenuity, alike highly inviting to the theoretical and the practical mechanic. Although the civilization of almost every people han been more or less affected by the introduction of steam, the extent to which steam-power is used is comparatively unknown. The total number of steam-engines of all descriptions in the world, at the close of eighteen hundred and seventy-four, was estimated at two hundred and seven thousand six hundred and seventy-seven, representing power equal to sixteen million horse-power, which would HAND-BOOK OF LAND AND MARINE ENGINES. 23 be equivalent to the actual power of at least twenty-fJve millions of ordinary horses working night and day, or equal to the work of two hundred millions of men. Of this enormous steam-power the United States had three million nine hundred thousand horse-power, and Great Britain three million five hundred thousand. But it must not be supposed that the utilization of steam-powder in the various productive industries of the world is circumscrib- ing the area of manual labor or rendering it less remu- nerative than formerly; it is quite the reverse, as man profits, in some way, by every discovery in science ; and though the discovery may compel him to abandon his former methods, it will still be found that the material results are invariably in his favor. The steam-engine, even as a stationary power, is of recent origin ; and contemplating the phases which it has already -assumed, in connection with the general feeling that its energies have not yet been fully developed, it is not a matter of wonder that no other object in the entire range of human devices has so irresistibly arrogated to itself the devotion of the scientist and mechanic. 24 HAND-BOOK OF LAND AND MARINE ENGINES. 25 STEAM. Steam is the elastic fluid into which water is converted by the- continued application of heat. How singular that steam should have been among the motive agents of the most ancient idol- worship of Egypt, and that it should formerly have been employed with tre- mendous effect to delude men and lock them in ignorance, while it' now contributes so largely to enlighten and benefit mankind ! The instances of the early application of steam make us regret that detailed descriptions of the various and ingenious devices have not been preserved ; for while we condemn the contrivers of such as were used for the purpose of delusion, we cannot but admire the ingenuity which they displayed in exhibiting before a barbarous people their gods in the most imposing manner, and with such terrific efiect. The mechanical properties of vapop are similar to those of gases in general. The property which is most im- portant to be considered, in the case of steam, is the elastic pressure. When a vapor or gas is contained in a close vessel, the inner surface of the vessel will sustain a press- ure arising from the elasticity of the fluid. This pressure is produced by the mutual repulsion of the particles, which gives them a tendency to fly asunder, and causes the mass of the fluid to exert a force tending to burst any vessel within which it is confined. This pressure is uniformly diffused over every part of the sur- face of the vessel in which such a fluid is contained : it is to this quality that all the mechanical power of steam is due. Steam might be said to be the result of a combination of water with a certain amount of heat, and the expansive force of steam arises from the absence of cohesion between and among the particles of water. 3 2Q HAND-BOOK OF LAND AND MARINE ENGINES. Heat universally expands all matter within its influence, whether solid or fluid. But in a solid body it has the co- hesion of the particles to overcome ; and this so circum- scribes its effect, that in cast-iron, for instance, a rate of temperature above the freezing-point sufficient to melt it causes an extension of only about one-eighth of an inch in a foot. With water, however, a temperature of 212"^, or 180"^ above the freezing-point (and which is far from a red heat), converts it into steam of 1700 times its original bulk or volume. Steam cannot mix with air while its pressure exceeds that of the atmosphere ; and it is this property, with that which makes the condition of a body dependent on its temperature, that explains the condensing property of steam. In a cylinder once filled with steam of a pressure of 15 pounds or more to the square inch, all air is excluded ; now, as the existence of the steam depends on its temper- ature, by abstracting that temperature (which may be done by immersing the cylinder in cold water or cold air), the contained steam assumes the state due to the reduced temperature, and this state will be water. The latent op concealed heat of steam is one of the most noteworthy properties. The latent heat of steam, though showing no eflTect on the thermometer, may be as easily known as the sensible or perceivable heat. To show this property of steam by experiment, place an indefinite amount of water in a closed vessel, and let a pipe, proceeding from its upper part, communicate with another vessel, which should be open, and, for convenience of illustration, shall contain just 6i pounds of water at 32°, or just freezing. The pipe from the closed vessel must reach nearly to the bottom of the open one. By boiling the water contained in the first vessel until steam H AMD-BOOK OF LAND AND MARINE ENGINES. 27 enough has passed through the pipe to raise the water in the open vessel to the boiling-point (212° Fah.), we shall find the weight of the water contained by the latter to be 6? pounds. Now, this addition of one pound to its weight has resulted solely from the admission of steam to it ; and this pound of steam, therefore, retaining its own tempera- ture of 212^, has raised di pounds of water 180°, or an equivalent to 990°, and, including its own temperature, we have 1201°, which it must have possessed at first. The sum of the latent and sensible heat of steam is in all cases nearly constant, and does not vary much from 1200°. The elasticity of steam increases with an increase in the temperature applied, but not in the same ratio. If steam is generated from water at a, temperature which gives it the same pressure as the atmosphere, an additional temperature of 38° will give it the pressure of two atmos- pheres ; a still further addition of 42° gives it the tension of four atmospheres ; and with each successive addition of temperature of between 40° and 50° the pressure becomes doubled. An established relation must exist between the temper- ature and elasticity of steam ; in other words, water at 212° Fah. must be under the pressure of the steam natu- rally resulting from that temperature, and so at any other temperature. If this natural pressure on the surface of the water be removed without a corresponding reduction in the temper- ature, a violent ebullition of the water is the immediate result. Another result attending formation of steam is, that when an engine is in operation and working ofi* a proper supply of steam, the water level in the boiler artificially rises, and shows by the gauge-cocks a supply greater than that which really exists. 28 HAND-BOOK OF LAND AND MARINE ENGINES. As the pressure of steam is increased, the sensible heat is augmented, and the latent heat undergoes a cor- responding diminution, and vice versa. The sum of the sensible and latent heat is, in fact, a constant quantity ; the one being always increased at the expense of the other. It has been shown that in converting water at 32° of temperature, and under a pressure of 15 pounds per square inch, it was necessary iBrst to give it 180^ additional sen- sible heat, and afterwards 990° of latent heat, the total heat imparted to it being 1170°. Such, then, is the actual quantity of heat which must be imparted to ice-cold water to convert it into steam. The actual temperature to which water would be raised by the heat necessary to evaporate it, if its evaporation could be prevented by confining it in a close vessel, will be found by adding 82° to 1170°. It may, therefore, be stated that the heat necessary for the evaporation of ice-cold water is as much as would raise it to the temperature of 1202°, if its evaporation were prevented. If the temperature of red-hot iron be, as it is supposed, 800° or 900°, and that all bodies become incandescent at the same temperature, it follows that to evaporate water it is necessary to impart to it 400° more heat than would be sufficient to render it red-hot, if its evaporation were pre- vented. It has been asserted, in some scientific works, that by mere mechanical compression, steam will be converted into water. This is, however, an error ; since steam, in whatever state it may exist, must possess at least 212° of heat ; and as this quantity of heat is sufficient to maintain it in the vaporous form under whatever pressure it may be placed, it is clear that no compression or increase of pressure can diminish the actual quantity of heat con- HAND-BOOK OF LAND AND MARINE ENGINES. 29 tained in the steam, and it cannot, therefore, convert any portion of the steam into power. Steam, by mechanical pressure, if forced into a dimin- ished volume, will undergo an augmentation both of tem- perature and pressure, the increase of temperature being greater than the diminution of volume; in fact, any change of volume which it undergoes will be attended with the change of temperature and pressure indicated in the table on pages 39-43. The steam, after its volume has been changed, will as- sume exactly the pressure and temperature which it would have in the same volume if it were immediately evolved from water. Let us suppose a cubic inch of water converted into steam under a pressure of 15 pounds per square inch, and the temperature of 212°. Then let its volume be reduced by compression in the proportion of 1700 to 930. When so reduced, its pressure will be found to have risen from 15 pounds per square inch to 29 J pounds per square inch ; but this is exactly the state as to pressure, temperature, and density the steam would be in if it were immediately raised from water under the pressure of 29 J pounds per square inch. It appears, therefore, that in whatever man- ner, after evaporation, the density of steam be changed, whether by expansion or contraction, it will still remain the same as if it were immediately raided from water in its actual state. The circumstance which has given rise to the erroneous notion that mere mechanical compression will produce a condensation of steam, is that the vessel in which steam is contained must necessarily have the same temperature as the steam itself. Water while passing into steam suffers a great enlarge- ment of volume ; steam, on the other hand, in being con- 3* 80 HAND-BOOK OF LAND AND MARINE ENGINES. verted into water, undergoes a corresponding diminution of volume. It has been seen that a cubic inch of water, evaporated at the temperature of 212°, swells into 1700 cubic inches of steam. It follows, therefore, that if a closed vessel, containing 1700 cubic inches of steam, be exposed to cold sufficient to take from the steam all its latent heat, the steam will be reconverted into water, and will shrink into its original dimensions, and will leave the remainder of the vessel a vacuum. This property of steam has supplied the means, in practical mechanics, of obtaining that amount of me- chanical power which the properties of the atmosphere confer upon a vacuum. The temperature and pressure of steam produced by immediate evaporation, when it has received no heat save that which it takes from the water, have a fixed relation one to the other. If this relation was known and expressed by a mathe- matical formula, the temperature might always be inferred from the pressure, and vice versa. But physical science has not yet supplied any principle by which such a formula can be deduced from any known properties of liquids. The same difficulty which attends the establishment of a general formula expressing the relation between the temperatures and pressures of steam, also attends the de- termination of one expressing the relation between the pressure and augmented volume into which water expands by evaporation. In the preceding observations, steam has been considered as receiving no heat except that which it takes from the water during the process of evaporation ; the amount of heat of which, as has been shown, is 1170° more than the heat contained in ice-cold 'water. But steam, after having HAND-BOOK OF LAND AND MARINE ENGINES. 31 been formed from water by evaporation, may, like all other material substances, receive an accession of heat from any external source, and its temperature may therefore be ele- vated. If the steam to which such additional heat is imparted be so confined as to be incapable of enlarging its dimen- sions, the effect produced upon it by the increase of tem- perature will be an increase of pressure. But if, on the other hand, it be confined under a given pressure, with power to enlarge its volume, subject to the preservation of that pressure, as would be the case if it were contained in a cylinder under a movable piston loiaded with a given pressure, then the effect of the aug- mented temperature will be, not an increase of pressure, but an increase of volume ; and the increase of volume, in this latter case, will be in exactly the same proportion as the increase of pressure in the former case. These effects of elevated temperature are common, not only to the vapors of all liquids, but also to all permanent gases ; but, what i^ much more remarkable, the numerical amount of the augmentation of pressure or volume pro- duced by a given increase of temperature is the same for all vapors and gases. If the pi-essure which any gas or ' vapor would have, were it reduced to the temperature of melting ice, be expressed by 100,000, the pressure which it will receive for every degree of temperature by which it is raised will be expressed by 208 J, or what amounts to the same, the additional pressure produced by each degree of temperature will be the 480th part of its pressure at the temperature of melting ice. Steam which thus receives additional heat after its separation from the water from which it is evolved has been called superheated steam, to distinguish it from common steam, which is that usually employed in steam-engines. \ 82 HAND-BOOK OF LAND AND MARINE ENGINES. Steam of atmospheric pressure occupies 1669 times the volume of the water from which it is raised, and as a cubic foot of water weighs 62*4 pounds, a cubic foot of steam of atmospheric pressure weighs about '038 pound. In order to exert a pressure by its mere dead weight of 14*7 pounds per square inch, such steam of uniform density would have to stand at a height of 10 J miles — ^the velocity due to a fall from this height in 1888 feet per second, and this, accordingly, is the velocity with which steam of at- mospheric pressure enters a vacuum. And if the velocity of steam were inversely as its pressure, this would be the velocity of steam of every pressure in moving into a vacuum, since, so far as generating effluent velocity is concerned, the mere elasticity of a gas is inoperative. The effluent velocity of steam into the atmosphere or into steam of lower pressure, then, has to be carefully con- sidered in the treatment of steam-engines. In the follow- ing table, the pressure given in pounds above the atmos- phere is 0*3 pound less than the pressure employed in making the calculation : Pressure above Velocity of Escape Pressure above Velocity of Escape the Atmosphere. per Second. ^ the Atmosphere. per Second. Pounds. Feet. Pounds. Feet. 1 540 50 1,736 2 698 60 1,777 3 814 70 1,810 4 905 80 1,835 5 981 90 1,857 10 1,232 100 1,875 20 1,476 110 1,889 30 1,601 120 1,900 40 1,681 130 1,909 To saturated steam, or steam as it rises from the water HAND-BOOK OF LAND AND MARINE ENGINES. 83 from which it is generated, these calculations of course only apply. Whatever may be the pressure per square inch common to different conditions of steam, the effluent velocity will be inversely as the square root of the specific gravity of steam. If the steam be superheated, its specific gravity for a given pressure will be diminished, and its velocity of escape into the air or into a vacuum will be in- creased. If, on the contrary, the steam carry with it any suspended moisture, its specific gravity for a given press- ure will be increased and its velocity of escape diminished. A very important question will probably arise in the mind of the reader as to the amount of work that a given weight of steam is capable of performing. A pound of steam, of say 120 pounds pressure above that of the atmos- phere, is virtually a pound of water heated 1681 degrees above the absolute zero of a perfect gas thermometer, 1220° above Fahrenheit's zero, 1188 degrees above the freezing- point, or 1118° above the sensible temperature of steam of one pound absolute pressure per square inch, the lowest pressure at which a condensing-engine could be expected to work. Either of these total temperatures, multiplied by 772, will give the energy in foot-pounds theoretically due to the steam when worked down, say, into water of the corresponding temperature. But it must be remembered that, as a gas (to which steam in this case is necessarily compared) it would, upon the accepted law of expansion, only lose its elasticity at a temperature below the freezing-point. If we work down to 102°, the temperature of water from which steam of one pound total pressure would escape, w^e shall have an energy, for one pound weight of steam, of 863,096 foot- pounds ; and if 10 pounds of steam be evaporated from 102° by one pound of coal, giving'^ 8,630,960 foot-pounds per pound of coal, an engine working up to the full C 34 HAND-BOOK OF LAND AND MARINE ENGINES. power of the steam would require but |||§f g^ = 0*23 pound, or less than four oxtnces of coal per indicated horse- power per hour, an hourly horse-power being 33,000 X 60 = 1,980,000 foot-pounds. To obtain such a result, the steam must in the very act of doing work be reduced to one pound of water at 102"^. This, however, is quite a theoretical deduction, and noth- ing like it could, with our present knowledge, be approached in practice ; especially, as in expanding, the steam is con- stantly losing heat and liquefying in the very act of doing work, and thus losing pressure apart from the loss due to the apparent enlargement of volume. Superheated steam admits of losing a part of its heat without suffering partial condensation ; but common steam is always partially condensed, if any portion of heat be withdrawn from it. But it must be remembered, any additional arrangements for heating the steam can but complicate the machinery, and thus require increase of space, besides adding to the cost of the engine. But these objections are more serious in the case of the marine engine, the boilers of which are mostly fed with sea-water, strongly impregnated with various salts, and particularly with chloride of sodium. At the usual temperature of the steam used for working these engines, which is generally from 250° to 270°, the presence of this salt causes no in- convenience ; but when the steam is superheated, chemical decomposition ensues, and the chlorine thus set free attacks all the brass work of the engine with which it comes in contact, and the valves and valve-seats are speedily de- stroyed and the engine put out of order. But there can be no doubt whatever but that the use of superheated steam is more economical than that of ordinary saturated steam. In some of the scientific reports on this subject, it has been shown that there is a saving of HAKD-BOOK OF LAND AND MARINE ENGINES. 60 from 20 to 25 per cent, in the fuel consumed. This fact has induced inventors to turn their attention to the task of devising some practical appliances for producing steam in this superheated condition. Motion of Steam. — Steam, if unimpeded, moves with great velocity from one enclosure to another, under very- slight differences of pressure. The laws which regulate this movement, though apparently of a simple character, are not so easily reduced to exact formula as would seem desirable. All the rules, therefore, which are given, must be taken with due reserve and with important qualifica- tions. The conditions of the free motion of steam will be exhibited as nearly as science has been able to estimate them. These conditions are three: Steam may flow into a vacuum, or into the atmosphere, or into steam of less density. The conditions of its flow in all these cases are of course entirely different. In the middle case — that of its flow into the atmosphere — about 15 pounds of its total pressure go for nothing, being expended in overcoming the atmospheric resistance, and before the slightest motion of its own or impulse to any other body is possible. The law applicable to non-elastic fluids is the same as that which applies to gases and steam. Volume and Weight of Steam. — Seventy-five cubic feet of steam at a pressure of 140 pounds per square inch weigh 26 pounds. Five cubic feet of steam at a pressure of 75 pounds per square inch weigh 1 pound. One cubic foot of steam at a pressure of 15 pounds per square inch weighs .038 pound. Steam, at any given pressure, always stands at a certain temperature, which is termed the " temperature due to the pressure." Steam follows very nearly the same law that all other gaseous bodies are subject to in acquiring ad- 36 HAND-BOOK OF LAND AND MARINE ENGINES. ditional degrees of heat. The law is, briefly, as follows : That all gaseous bodies expand equally for equal additions of temperature ; and that the progressive rate of expan- sion is equal for equal increments of temperature. If two volumes of steam of the same weight be com- pared, we institute a comparison between their relative volumes; for, being of the same weight, they are pro- duced from the same quantity of water. The relative volume of steam being the absolute volume divided by the volume of water from which it was produced,. the ratio of any two relative volumes of steam is the same as the ratio of their absolute volumes. So also with steam held in contact with the water in the boiler, the same pressure exhibited by the gauge corresponds to the same temper- ature in the boiler, and the same temperature in the boiler will always give the same corresponding pressure of steam. Therefore, if we increase the temperature, we increase the pressure and density, and we, of course, get the greatest pressure and density that steam can have at that temper- ature. The table on page 39 shows that the saving of fuel is in proportion to the increase of pressure — the advantage of generating and using high-pressure steam is thereby made apparent. The table also shows that the last 10 pounds of additional pressure only require four degrees of heat to raise it ; whereas, the first 10 pounds of pressure above the atmosphere require 29 additional degrees of heat to raise it — a difference of 25 degrees. It also shows that at 212^ the total heat of steam is 11784°, which gives a difference of 966*1°. This heat, usually termed latent, is absorbed in performing the work of expanding the particles of water from the solid to the gaseous state. Now, suppose the water is evaporated at 60 pounds pressure, the steam will have a temperature of 307°, and a total heat of 1207°. If the feed has been HAND-BOOK OF LAND AND MARINE ENGINES. 37 38 HAND-BOOK OF LAND AND MARINE ENGINES. introduced at 60°, it is evident that 1147° of heat have been imparted. As the amount evaporated is inversely proportional to the quantity of heat required, we have 1147 -i- 966 = 1*2. Multiplying by this factor, the quantity evaporated at 60 pounds pressure from 60°, we obtain the amount that would be evaporated at 212° by the same quantity of fuel. By the same table will be seen the comparatively small increase of heat required to evaporate water at higher pressures. Suppose we take water evaporated at 45 pounds pressure from a feed temperature of 60°, then each pound of water will require 1202*7° — 60 = 1142*7° for its conversion into steam. If we take the pressure at 100 pounds, we shall have 1216*5 — 60 = 1156-5° as the quantity required. The difference between these two total quantities is only 13*8°, and is so small as to be scarcely worth considering. Leaving out of account the loss due to the slight reduc- tion of the conducting power of the material, the increased amount of heat required for the higher pressure will be only ^^^ of the total heat required at 60 pounds. The economy of using steam of a high pressure is clearly manifest when, at the same time, advantage is taken of the facilities it offers for working expansively in the cylinder. Theory has long since demonstrated the economical ad- vantages to be derived from the use of high steam press- ures combined with high grades of expansion in the cylinder. The practical difficulties that stood in the way having been gradually and successfully overcome, the re- sult has been the marked changes from the 7 pound and 10 pound pressures, so common forty years ago, to the pressures of from 80 pounds to 100 pounds, at present employed ; and the more general employment of the higher pressures will be demanded as the advantages of using steam expansively become more generally recognized. II HAND-BOOK OF LAND AND MARINE ENGINES. 39 TABLE SHOWING THE TEMPERATURE AND WEIGHT OF STEAM AT DIF- FERENT PRESSURES FROM 1 POUND PER SQUARE INCH TO 300 POUNDS, AND THE QUANTITY OF STEAM PRODUCED FROM 1 CUBIC INCH OF WATER, ACCORDING TO PRESSURE. al pressure square inch isured from a vacuum. II ll sible temper- re in Fahren- 3it degrees. III ative volume steam com- ed with wa- from which was raised. Ill II" . i-oir- 1 102.1 1144.5 .0030 20582 2 126.3 1151.7 .0058 10721 3 141.6 1156.6 .0085 7322 4 153.1 1160.1 .0112 5583 5 162.3 1162.9 .0138 4527 6 170.2 1165.3 .0163 3813 7 176.9 1167.3 .0189 3298 8 182.9 1169.2 .0214 2909 9 188.3 1170.8 .0239 2604 10 193.3 1172.3 .0264 2358 11 197.8 1173.7 .0289 2157 12 202.0 . 1175.0 .0314 1986 13 205.9 1176.2 .0338 1842 14 209.6 1177.3 .0362 1720 14.7 *"*0 212.0 1178.1 .0380 1642 15 .3 213.1 1178.4 .0387 1610 16 1.3 216.3 1179.4 .0411 1515 17 2.3 219.6 1180.3 .0435 1431 18 3.3 222.4 1181.2 .0459 1357 19 4.3 225.3 1182.1 .0483 1290 20 5.3 228.0 1182.9 .0507 1229 21 6.3 230.6 1183.7 .0531 1174 22 7.3 233.1 1184.5 .0555 1123 23 • 8.3 235.5 1185.2 .0580 1075 24 9.3 237.8 1185.9 .0601 1036 25 10.3 240.1 1186.6 .0625 996 26 11.3 242.3 1187.3 .0650 958 27 12.3 244.4 1187.8 .0673 926 28 13.3 246.4 1188.4 .0696 895 29 14.3 248.4 1189.1 .0719 866 30 15.3 250.4 1189.8 .0743 838 31 16.3 252.2 1190.4 .0766 813 40 HAND-BOOK OF LAND AND MARINE ENGINES. TABLE— ( Qontinued) . Total pressure per square inch measured from a vacuum. 1 • • if Sensible temper- ature in Fahren- heit degrees. m ill Relative volume of steam com- pared with wa- ter from which it was raised. 32 17.3 254.1 1190.9 .0789 789 33 18.3 255.9 1191.5 .0812 767 34 19.3 257.6 1192.0 .0835 746 35 20.3 259.3 1192.5 .0858 726 36 21.3 260.9 1193.0 .0881 707 37 22.3 262.6 1193.5 .0905 688 38 23.3 264.2 1194.0 .0929 671 39 24.3 265.8 1194.5 .0952 655 40 25.3 267.3 1194.9 .0974 640 41 26.3 268.7 1195.4 .0996 625 42 27.3 270.2 1195.8 .1020 611 43 28.3 271.6 1196.2 .1042 598 44 29.3 273.0 1196.6 .1065 595 45 30.3 274.4 1197.1 .1089 572 46 31.3 275.8 1197.5 .1111 561 47 32.3 277.1 1197.9 .1133 550 48 33.3 278.4 1198.3 .1156 539 49 34.3 279.7 1198.7 .1179 529 50 35.3 281.0 1199.1 .1202 518 51 36.3 282.3 1199.5 .1224 509 52 37.3 283.5 1199.9 .1246 500 53 38.3 284.7 1200.3 .1269 491 54 39.3 285.9 1200.6 .1291 482 55 40.3 287.1 1201.0 .1314 474 56 41.3 288.2 1201.3 .1336 466 57 42.3 289.3 1201.7 .1364 458 58 43.3 290.4 1202.0 .1380 451 59 44.3 291.6 1202.4 .1403 444 60 45.3 292.7 1202.7 .1425 437 61 46.3 293.8 1203.1 .1447 430 62 47.3 294.8 1203.4 .1469 424 63 48.3 295.9 1203.7 .1493 417 64 49.3 296.9 1204.0 .1516 411 65 50.3 298.0 1204.3 .1538 405 66 51.3 299.0 1204.6 .1560 399 67 52.3 300.0 1204.9 .1583 393 6S 53.3 300.9 1205.2 .1605 388 69 54.3 301.9 1205.5 .1627 383 HAND-BOOK OF LAND AND MARINE ENGINES. 41 TABLE--( Continued). al pressure square inch isured from a vacuum. Is sible temper- re in Fahren- eit degrees. ill ill go ative volume steam corn- ed with wa- from which was raised. g"c3 el's o , is f"^ 70 55.3 302.9 1205.8 .1648 378 71 56.3 303.9 1206.1 .1670 373 72 57.3 304.8 1206.3 .1692 368 73 58.3 305.7 1206.6 .1714 363 74 59.3 306.6 1206.9 .1736 359 75 60.3 307.5 1207.2 .1759 m 76 61.3 308.4 1207.4 .1782 349 77 62.3 309.3 1207.7 .1804 345 78 63.3 310.2 1208.0 .1826 341 79 64.3 311.1 1208.3 .1848 337 80 65.3 312.0 1208.5 .1869 333 81 66.3 312.8 1208.8 .1891 329 82 67.3 313.6 1209.1 .1913 325 83 68.3 314.5 1209.4 .1935 321 84 69.3 315.3 1209.6 .1957 318 85 70.3 316.1 1209.9 .1980 314 86 71.3 316.9 1210.1 .2002 311 S7 72.3 317.8 1210.4 .2024 308 88 73.3 318.6 1210.6 .2044 305 89 74.3 319.4 1210.9 .2067 301 90 75.3 320.2 1211.1 .2089 298 91 76.3 321.0 1211.3 .2111 295 92 77.3 321.7 1211.5 .2133 292 93 78.3 322.5 1211.8 ,2155 289 94 79.3 323.3 1212.0 .2176 286 95 80.3 324.1 1212.3 .2198 283 96 81.3 324.8 1212.5 .2219 281 97 82.3 825.6 1212.8 .2241 278 98 83.3 326.3 1213.0 .2263 275 99 84.3 327.1 1218.2 .2285 272 100 85.3 327.9 1213.4 .2307 270 101 86.3 328.5 1213.6 .2329 267 102 87.3 329.1 1213.8 .2351 265 103 88.3 329.9 1214.0 .2373 262 104 89.3 330.6 1214.2 .2393 260 105 90.3 331.3 1214.4 .2414 257 106 91.3 331.9 1214.6 .2435 255 107 92.3 332.6 1214.8 .2456 253 4* 42 HAND-BOOK OF LAND AND MARINE ENGINES, TABLE— (Continued). al pressure square inch isured from a vacuum. 03 Si ,d 2f sible temper- re in Fahren- eit degrees. d^l 0) ative volume steam com- ed with wa- from which was raised. £ ir e|o 'S d w'sl^" 108 93.3 333.3 1215.0 .2477 251 109 94.3 334.0 1215.3 .2499 249 110 95.3 334.6 1215.5 .2521 247 111 96.3 335.3 1215.7 .2543 245 112 97.3 336.0 1215.9 .2564 243 113 98.3 336.7 1216.1 .2586 241 114 99.3 337.4 1216.3 .2607 239 115 100.3 338.0 1216.5 .2628 237 116 101.3 338.6 1216.7 .2649 235 117 102.3 339.3 1216.9 .2674 233 118 103.3 339.9 1217.1 .2696 231 119 104.3 340.5 1217.3 .2738 229 120 105.3 341.1 1217.4 .2759 227 121 106.3 341.8 1217.6 .2780 225 122 107.3 342.4 1217.8 .2801 224 123 108.3 343.0 1218.0 .2822 222 124 109.3 343.6 1218.2 .2845 221 125 110.3 344.2 1218.4 .2867 219 126 111.3 344.8 1218.6 .2889 217 127 112.3 345.4 1218.8 .2911 215 128 113.3 346.0 1218.9 .2933 214 129 114.3 346.6 1219.1 .2955 212 130 115.3 347.2 1219.3 .2977 211 131 116.3 347.8 1219.5 .2999 209 132 117.3 348.3 1219.6 .3020 208 133 118.3 348.9 1219.8 .3040 206 134 119.3 349.5 1220.0 .3060 205 135 120.3 350.1 1220.2 .3080 203 136 121.3 350.6 1220.3 .3101 202 137 122.3 351.2 1220.5 .3121 200 138 123.3 351.8 1220.7 .3142 199 139 124.3 352.4 1220.9 .3162 198 140 125.3 352.9 1221.0 .3184 197 141 126.3 353.5 1221.2 .3206 195 142 127.3 354.0 1221.4 .3228 194 143 128.3 354.5 1221.6 .3258 193 144 129.3 355.0 1221.7 .3273 192 145 130.3 355.6 1221.9 .3294 190 HAND-BOOK OF LAND AND MARINE ENGINES. 43 TABLE— ( Concluded). Total pressure per square inch measured from a vacuum. 1^ Sensible temper- ature in Fahren- heit degrees. o ^ Relative volume of steam com- pared with wa- ter from which it was raised. 146 131.3 356.1 1222.0 .3315 189 • 147 132.3 356.7 1222.2 .3336 188 148 133.3 357.2 1222.3 .3357 187 149 134.3 357.8 1222.5 .3377 186 150 135.3 358.3 1222.7 .3397 184 155 140.3 361.0 1223.5 .3500 179 160 145.3 363.4 1224.2 .3607 174 165 150.3 366.0 1224.9 .3714 169 170 155.3 368.2 1225.7 .3821 164 175 160.3 370.8 1226.4 .3928 159 180 165.3 372.9 1227.1 .4035 155 185 170.3 375.3 1227.8 .4142 151 190 175.3 377.5 1228.5 .4250 148 195 180.3 379.7 1229.2 .4357 144 200 185.3 381.7 1229.8 .4464 141 210 195.3 386.0 1231.1 .4668 135 220 205.3 389.9 1232.8 .4872 129 230 215.3 393.8 1233.5 .5072 123 240 225.3 397.5 1234.6 .5270 119 250 235.3 401.1 1235.7 .5471 114 260 245.3 404.5 1236.8 .5670 110 270 255.3 407.9 1237.8 .5871 106 280 265.3 411.2 1238.8 .6070 102 290 275.3 414.4 1239.8 .6268 99 300 285.3 417.5 1240.7 .6469 96 WORKING STEAM EXPANSIVELY. There are two modes of applying the power of steam to the working cylinders of steam-engines, namely : One, allowing steam to flow from the boiler during the whole length of the stroke ; and the other, cutting it off from the boiler when the piston has travelled a determined distance — the great and paramount object of this last arrangement being a saving of fuel. 44 . HAND-BOOK OF LAND AND MARINE ENGINES. If steam be applied the full length of the stroke, the average pressure will be as the pressure per square inch upon the piston; but if the steam be cut off at half stroke, — suppose the pressure to be 65 pounds per inch when the pressure of the atmosphere is added, — there will be a mean equivalent, or average pressure, through- out the stroke of 55 pounds per square inch, being only 10 pounds less than the full pressure, or 16 per cent, of a loss in power, though half the former quantity of steam has only been used. This alone effects a saving of 34 per cent, in fuel, and shows the great benefit to be derived from expansion in one cylinder. If this principle be true, and its truth is undeniable, it is quite evident that the greatest economy will result from extending to their full limit the cylinders of steam-engines, and making them of sufficient capacity for this purpose ; though with the high-pressures, with which expansion is most available, they will require to be less than are usually made, to allow the engines to produce the maximum effect. The expansive property of steam is strictly mechani- cal, and is a property common to all fluids — air, gas, etc. It simply consists in this — that vapor of a given elastic force will expand to certain limits, and during the process of expansion will act on opposing bodies with a force gradually decreasing, causing a diminution of elastic power in an inverse ratio of the increase of volume, until it has reached the limits of its power, or is counterbalanced by the resistance of a surrounding medium. Thus, steam of any given pressure, expanded to twice its original bulk, will exert only one-half its original power. If a partial vacuum be formed on one side of a piston, its motion will be continued until the density of the steam on the other side be as low as that of the uncondensed vapor on the vacuum side of the piston. It is clear that HAND-BOOK OF LAND AND MARINE ENGINES. 45 the power which may be obtained by thus impelling a piston will be the average between the highest and the lowest pressure upon the piston. It must also be under- stood that it is a saving^ and not a gain, that thus results from expansion ; a power being made available which was before lost, by using the steam up to its last impelling force, and not allowing it to escape until the whole of that available force has been expended. This accounts for some engines using more fuel and steam than others, because the steam is not expanded to its utmost limit, in consequence of the steam not being cut off by the valve soon enough, or that the load on the engine is great, and requires the steam to be longer on the piston before it is cut off. If the load on the engine be such as to allow the steam to be cut off early, and to expand to its full available limits in the cylinder, then the most will have been made of it ; the highest pressure in the boiler will have been used upon the piston and down to the lowest point. Were atmospheric air compressed so as to exert a force of 20 pounds on the square inch, and were the supply to be continued throughout the stroke, an impulse would be given to the piston equal to 20 pounds to the square inch during the whole stroke ; but if the air was allowed to expand, the impulse would only be as the average, or 10 pounds. It will be evident that, if in the former case the air was suffered to depart from the cylinder at the same elasticity as that which it entered, we should lose the force which was necessary to compress it to its density ; while, by expanding it to its limits, we apply every part of that force. The main-spring of a watch actuates its machinery in this manner : an increasing effort is required to wind up the spring, and a decreasing impulse is given back to the 46 HAND-BOOK OF LAND AND MARINE ENGINES. machinery. But if, after the spring had partially un- coiled itself, it were then liberated, the force which wound it up to its last impelling point would be totally lost. So in the steam-engine ; if the steam be allowed to escape from the cylinder before its force is expanded to the lowest available pressure, the loss will be in proportion to the amount of the pressure not made available. A certain quantity of fuel is required to raise steam to a certain elasticity. If that steam be allowed, after hav- ing moved the piston, to escape into the atmosphere or condenser without having acted expansively, a portion of the fuel which was consumed to raise the steam up to that point of elasticity will have been lost. In one case, a given bulk of fuel would produce fifty ; in the other case, it would produce fifty, added to all the intermediates down to the lowest expansive force. By this it will be apparent that the advantages arising from expansion increase with the density of the steam. In round numbers, 65 pounds of high-pressure steam will perform more than seven times the duty of 25 pounds of low-pressure steam ; a fact greatly in favor of high-pressure steam and expansion. Expansion is, perhaps, the most extraordinary property of steam. The merit of the discovery is due to Horn- blower, who, in 1781, obtained a patent for the invention. The principle of expanding the steam in the condensing engine is the same as in the non-condensing engine, ex- cepting that the steam which exhausts into the atmosphere cannot expand below 15 pounds per square inch, because the exhaust is open to the pressure of the atmosphere in all cases. The resistance of the atmosphere (15 pounds) must be added to the pressure of steam above atmospheric pressure, when calculating the pressure of the expansion of steam upon the piston. HAND-BOOK OF LAND AND MARINE ENGINES. 47 Example. — Steam at 20 pounds pressure above the atmosphere upon the piston, cut off at one-fourth the stroke, will be 8 1 pounds at the termination of the stroke, as shown by the following calculation : 20 pounds added to 15 pounds, the pressure of the atmosphere, equal 35 pounds. This divided by four gives the quotient 81 pounds. Thus, 8f pounds is the pressure at the termina- tion of the stroke, or 6i pounds below atmospheric pressure. The tables on pages 49 and 50 show the average press- ure of steam upon the piston when cut off at any portion of the stroke, beginning at 25 pounds and advancing in 5 pounds up to 135 pounds per square inch, thereby enabling the engineer to determine, at any given pressure, the amount of expansion requisite for the full power to be obtained, and the saving thereby to be effected. In all cases the pressure of the atmosphere must be added to the pressure of the steam above' atmosphere, when reference is made to the table for the average throughout the stroke. Example. — 45 pounds of steam above atmosphere upon piston of a high-pressure engine, cut off at one-fourth of the length of the stroke. The average pressure through- out will be, allowing one pound for friction and back press- ure to force out the steam in the cylinder, 191 pounds. Thus: 45 pounds of steam cutoff at one-fourth the stroke, with 15 pounds added, make 60 pounds. Look for 60 on the top line of the table and J on the side. Trace that i to the figures under 60, and the average will be found to be 351 pounds. Take 16 pounds from 35 1 pounds for atmospheric pressure and friction, and there remain 19 i pounds, the available average pressure on the piston. Example. — 30 pounds cut off at one-third. Add 15 = 45. The average in the table will be 311 ; deduct 16 pounds, and there remain 15i pounds, the available average press- ure upon the piston. 48 HAND-BOOK 01^ LAND AND MARINE ENGINES. Another Example. — 15 pounds cut off at half-stroke. Add 15 = 30. The average in the table will be 25 J. Deduct 16 pounds, and 9i pounds remain, the available pressure. In these examples the steam in the cylinder has ex- panded to atmospheric pressure. In proportion to the pressure of the steam, the cut-off will have to be varied, if the steam is to be expanded to its full limit in the cylinder of a non-condensing engine ; that is, down to 15 pounds, or equal to the pressure of the atmosphere. Rule fop ascertaining the Amount of Benefit to be depived fpom wopking Steam expansively. — Divide the length of the stroke by the length of space into which steam is admitted ; find in the annexed table the hyper- bolic logarithm nearest to that of the quotient, to which add one. The sum is the ratio of gain. TABLE OF HYPERBOLIC LOGARITHMS TO BE USED IN CONNECTION WITH THE ABOVE RULE. No. Logarithm. .22314 No. Logarithm. 1.60943 No. Logarithm. 2.19722 1.25 5. 9. 1.5 .40546 5.25 1.65822 9.5 2.25129 1.75 .55961 d.d 1.70474 10. 2.30258 2. .69314 5.75 1.74919 11. 2.39789 2.25 .81093 6. 1.79175 12. 2.48490 2.5 .91629 6.25 1.83258 13. 2.56494 2.75 1.01160 6,5 1.87180 14. 2.63905 8. 1.09861 6.75 1.90954 15. 2.70805 3.25 1.17865 7. 1.94591 16. 2.77258 3.5 1.25276 7.25 i.98iao 17. 2.83321 3.75 1.32175 7.5 2.01490 18. 2.89037 4. 1.38629 7.75 2.04769 19. 2.94443 4.25 1.44691 8. 2.07944 20. 2.99573 4.5 1.50507 8.5 2.14006 21. S.04452 4.75 1.55814 22. 3.09104 'HAND-BOOK OF LAND AND MARINE ENGINES. 49 TABLE SHOWING THE AVERAGE PRESSURE OF THE STEAM UPON THE PISTON THROUGHOUT THE STROKE, WHEN CUT OFF IN THE CYLINDER FROM J TO -^^y COMMENCING WITH 25 POUNDS AND ADVANCING IN 5 POUNDS UP TO 75 POUNDS PRESSURE. Steam cut off in thQ Cylinder. jure Ie Pres L Pounds at the Commencement of the Stroke 25 30 35 40 45 50 55 60 65 1 70 75 Avera ge Pressure in Pounds upon the Piston. ■K- 17i 21 24} 28 31} 35 38} 42 45} 49 52} |- 23J 281 32t 37} 42 46| 51} 56} 61 65} 70} J 15 171 20t 231 26| 291 32| 35| 38f 41| 44| 1 - 21 25i 29^ 33f 38 42} 46} 50f 55 59} 63} 1 24 81f 332 38} 43} 48} 53 571 62} 67} 72} -^ 13 15} 18} 20| 23} 26 28} 31} 34 36} 39 1 19 23 26| 30J 39} 38} 42 46 491 53} 57} * 22} 26 3U 39} 40| 45} 49f 54} 581 63} 67f i 23f 29i 344 39 44 49 53J 58} 63} 68} 731 i Hi 14 16} 18} 20| 23} 25} 271 30} 32} 34f i 24i 29} 34} 39} 44} 49: 54 59 64 69 731 1 10} 12^ 14f 16f 18| 24 23} 25} .274 29} 3I2 f 16 19^- 22} 25i 28f 32 35} 38} 4l^ 45 48} f 19| 23| 27| 31} 35} 39} 43 47} 51^ 55} 59} f 22i 26f 31i 35} 40 442 49} 53} 57f 62} 664 23| 28} 33} 381 42| 47i- 52} 57} 62 66f 71} f 24i 29* 34* 39} 44} 49} 64} 59} 631 69} 74i 9} 111 13} 15} 17} 19} 21} 23 25 27 281 1 18} 22i 26 29J S3* 37 40f 44} 48} 52 55i 1 22i 27^ 32 36f 41} 45} 60j 55} 59| 64} 681 1 24J 291 34| 39^ 44} 49} 54} 59^ 64} 69} 74i J 8| 10} 12^, 14} 15f 171 19} 21} 23 24f 26| 1 13J 16} 19} 22} 25 271 30} 38^ 36 381 41t 1 20 24 28 32 36 40} 44- 48:- 52^ 56} 60} i 22 26i 30| 35} 39.^ 44 48} 52S 56^ 61t 66 ^ 24: 24^ 29 34 381 43| 48i 53- 58:- 63:- 68 72f 1 29| 34| 39f 44* 49i 54^ 59-,- 64^ 69} 74} r\ 7i- 9} 10| 12} 131 15} 16i 18} 20 21} 23 A 12.: 141 17} 19} 22 24^ 27 29} 31 1 34} 431 361 A 15} 181 21J 25 28 31} 34} 37} 40J 47 A 18| 21 f 25} 29} 32| 36} 40} 43f 47} 51 545 f\ 24t 28} 32} 36* 40i 44i 48| 62i 561 60f t\ 21 1 26i- 30* 35 39} 431 48 521 56| 61} 64| 65} A 23 '27} 32} 36J 41} 46 50f 55} 60 69} D GO HAND-BOOK OF LAND AND MARINE ENGINES. TABLE SHOWING THE AVERAGE PRESSURE OF STEAM UPON THE PISTON THROUGHOUT THE STROKE, WHEN CUT OFF IN THE CYLINDER FROM I TO I, COMMENCING WITH 80 POUNDS AND ADVANCING IN 5 POUNDS UP TO 130 POUNDS PRESSURE. Steam cut off in the Cylinder. Pressure in ] Pounds at the Commencement of the Stroke. , 80 85 90 95 100 105 110 115 120 125 130 i Iverag e Pres sure in Pounds upon the Piston. J 56 59} 63 66i 70 73 77} 80} 84 87} 91 f 75 79} 84^ 89 93| 98} 103 1071 112} 117 121| J 47| 50J 551 56f 59| 621 95^ 68} 71} 74} 77} ^ 67 1 72 76} 80} 84-1 89 73} 97} 101* 1051 110 J 77i 82 87 91| 96} 101} 106 111 115J 1201 125} - 41| 441- 47 49} 52} 54i 57:- 60 62* 65} 671 i 61i 65 69 721 76} 80} 84:- 88 91| 95| 99} f 72.} 77 81} 86 90} 95} 99i 104} 1081 113J 1171 78i 83 88 92i 97f 102f 107} 112} 117} 122} 127} i 37i 39} 41| 444 46} 48| 51 : 53} 55f 58 60| J 78| 83i 88f 93* 98} 103} 108: 113} 118} 123} 128 1 33^ 35i 37f 40 42 44 46; 48} 50} 52} 54* i 51} 54} 571 61 64} 67} 70i: 74 77} 80} 83} |- 63i 67i 71} 75} 79 83 87 91 94f 98f 102} 1 7U 75f 80 84} 89 93} 98 102J 1061 111}'115| 76} 81 85f 90i 95} 100} 105 1091 114} 119}124 79 84 89 93| 98| 103f 1081 113J 1181 123}, 128} 30| 32| 34* 36} 38} 40} 42f 442 46} 48 50 f 59i 63 66| 70j 74} 78 81f 85} 89 92f 96} 1 73- 78 82} 87} 91| 96} 101 105^ 110} 1141 119} i 79| 84i 89} 3lf 94- 99 104 109 114 119 124 1281 1 28;: 30- 33i 35} 37} 39 40f 42} 44} 46 442 474 55 57f 55} 58:- 84^ 61 63f 66f 69} 72} 1 64: 68:- 72^ 76:- 80} 88} 92} 96} 100} 104} ^ 70} 74f 79r ssi 88 92} 97 101} 105| 110} 114} 1 77l 82i 87.- 92: 97i 102 107 UIJ 116f 121} 126} Rule for finding the Mean op Average Pressure in a Cylinder. — Divide the length of the stroke, including the clearance at one end of the cylinder, by the distance, in- HAI^D-BOOK OF LAND AND MARINE ENGINES. 51 eluding the clearance at one end, that steam follows the piston before being cut off; the quotient will express the relative expansion the steam undergoes. Then find in the following table, in the expansion column, the number corresponding to this, and take the multiplier opposite to it, and multiply the full pressure of the steam per square inch, as it enters the cylinder, by it. TABLE OF MULTIPLIERS BY WHICH TO FIND THE MEAN PRESSURE OF STEAM AT VARIOUS POINTS OF CUT-OFF. Expansion. Multiplier. Expansion. Multiplier. Expansion. Multiplier. 1.0 1.000 3.4 .654 5.8 .479 1.1 .995 3.5 .644 5.9 .474 1.2 .985 3.6 .634 6. .470 1.3 .971 3.7 .624 6.1 .466 1.4 .955 3.8 .615 6.2 .462 1.5 .937 3.9 .605 6.3 .458 1.6 .919 4. .597 6.4 .454 1.7 .900 4.1 .588 6.5 .450 1.8 .882 4.2 .580 6.6 .446 1.9 .864 4.3 .572 6.7 .442 2. .847 4.4 .564 6.8 .438 2.1 .830 4.5 .556 6.9 .434 2.2 .813 4.6 .549 7. .430 2.3 .797 4.7 .542 7.1 .427 2.4 .781 4.8 .535 7.2 .423 2.5 .766 4.9 .528 7.3 .420 2.6 .752 5. .522 7.4 .417 2.7 .738 5.1 .516 7.5 .414 2.8 .725 5.2 .510 7.6 .411 2.9 .712 5.3 .504 7.7 .408 3. .700 5.4 .499 7.8 .405 3.1 .688 5.5 .494 7.9 .402 8.2 .676 5.6 .489 8. .399 3.3 .665 5.7 .484 52 HAND-BOOK OF LAND AND MARINE ENGINES. HAND-BOOK OF LAND AND MARINE ENGINES. 53 54 HAND-BOOK OF LAND AND MARINE ENGINES. HIGH-PRESSURE OR NON-CONDENSING STEAM- ENGINES. High-ppessupe, op non-condensing engines are those engines in which the steam, after its action on the piston, is permitted to escape into the atmosphere, and in which, therefore, the pressure of the outgoing steam must exceed the atmospheric pressure of 15 pounds to the square inch. In this class of engines are included all locomotive, fire, and nearly all stationary and river-boat engines, which, in turn, comprises a great variety of arrangements and designs known as vertical, beam, inclined, oscillating, trunk, horizontal, etc. If steam at 30 pounds to the square inch above atmo- spheric pressure, that is to say, 30 pounds on the steam- gauge, be applied to the piston of a high-pressure engine, it will exert a force equal to the pressure in the boiler above the atmosphere, providing there be sufficient room for the steam, and no obstacle to impede its free flow or lessen its pressure between the boiler and the cylinder; the other side of the piston being open to the atmosphere, and the steam having to overcome the atmospheric press- ure in its escape from the cylinder, 15 pounds from the total pressure of 45 pounds will be lost. Advantages of the High-pressupe Engine. — The prin- cipal advantages of the high-pressure engine are, its light- ness, moderate first cost, economy of space, and the facilities it affords for an increase of pressure and speed, should it become necessary ; hence, the high-pressure engine being lighter, more simple, compact, and less ex- pensive in construction, and also less complicated, requir- ing less skill to manage and less cost to repair, is more desirable for stationary, land, and river-boat purposes than the low-pressure engine. HAND-BOOK OF LAND AND MARINE ENGINES. 55 The high-pressure engine is also desirable in marine steamers on account of economy of room, weight, etc., though objectionable in consequence of its greater con- sumption of fuel. The causes which occasion this extra consumption of fuel are, first, the steam lost in over- coming the pressure of the atmosphere ; second, the loss of heat by radiation in consequence of high pressures and high temperatures; third, the loss occasioned by the escape of heat through the chimney. In the high-pressure engine, pressure and speed can be increased to any limit within the bounds of safety. Not so, however, in the case of the low-pressure, as, with extremely high pressures and correspondingly high temperatures, it would be impossible to condense the steam, and the result would be a loss of power, occasioned by back pressure resulting from an imperfect vacuum. For all steam-engines with cylinders less than 24 inches in diameter, the simple high-pressure or non-condensing engine is the most convenient and ecqnomical. POWER OF THE STEAM-ENGINE. The power which a steam-engine can furnish is generally expressed in " horse-power." It will, therefore, be of inter- est to engineers, and of special value to many, to have briefly stated what is meant by a " horse-power," and how it has happened that the power of a steam-engine is thus expressed in reference to that of horses. Prior to the introduction of the steam-engine, horses were very generally used to furnish power to perform various kinds of work, and especially the work of pump- ing water out of mines, raising coal, etc. For such pur- poses, several horses working together were required. Thus, to work the pumps of a certain mine, five, six, seven, or 56 HAND-BOOK OP LAND AND MARINE ENGINES. even twenty-five horses were found necessary. When it was proposed to substitute the new power of steam, the proposal naturally took the form of furnishing a steam- engine capable of doing the work of the number of horses used at the same time. Hence, naturally followed the usage of stating the number of horses which a particular engine was equal to, that is, its " horse-power." But as the two powers were only alike in their equal capacity to do the same w^ork, it became necessary to refer in both powers to some work of a similar character which could be made the basis of comparison. Of this character was the work of raising a weight perpendicularly. A certain number of horses could raise a certain weight, as of coal out of a mine, at a certain speed ; a steam- engine, of certain dimensions and supply of steam, could raise the same weight at the same speed. Thus, the weight raised at a known speed could be made the common meas- ure of the two powers. To use this common measure it was necessary to know what was the power of one horse in raising a weight at a known speed. By observation and experiment it was ascertained that, referring to the average of horses, the most advantageous speed for work was at the rate of two-and-a-half miles per hour — that, at that rate, he could work eight hours per day, raising perpendicularly from 100 to 150 pounds. The higher of these weights was taken by Watt, that is, 150 pounds at 2 J miles per hour. But this fact can be express- ed in another form : 2i miles per hour is 220 feet per minute ^ 2K X 5280 ^ 220). So, the power of a horse was taken at 150 pounds, raised perpendicularly, at the rate of 220 feet per minute. This also can be expressed in another form : The same power which will raise 150 pounds 220 feet high each minute, will raise HAND-BOOK OF LAND AND MARINE ENGINES. 57 300 pounds 110 feet high each minute. 3,000 " 11 " " 33,000 " 1 foot " For in each case the total work done is the same, viz., same number of pounds raised one foot in one minute. If it is clearly perceived that 33,000 pounds, raised at the rate of one foot high in a minute, is the equivalent of 150 pounds at the rate of 220 feet per minute (or 2J miles per hour), it will be fully understood how it is that 33,000 pounds, raised at the rate of one foot per minute, expresses the power of one horse, and has been taken as the standard measure of power. It has thus happened that the mode of designating the power of a steam-engine has been by " horse-power," and that one horse-power, expressed in pounds raised, is a power that raises 33,000 pounds one foot each minute. This unit of power is now universally received. Having a horse- power expressed in pounds raised, it was easy to state the power of a steam-engine in horse-power, which was done in the following manner : The force with which steam acts is usually expressed in its pressure in pounds on each square inch. The piston of a high-pressure steam-engine is under the action of the pressure, of steam from the boiler, on one side of the piston, and of the back action of the pressure due to the discharg- ing steam, on the other side. The difference between the two pressures is the effective pressure on the piston ; and the power developed by the motion of the piston, under this pressure, will be according to the number of square inches acted on and the speed per minute with which the piston is assumed to move. Thus, let the number of square inches in the surface of the piston of a steam-engine be 100, and the effective pressure on each square inch be 33 pounds, and the movement of the 5S HAND-BOOK OF LAND AND MARINE ENGINES. piston be at the rate of 200 feet per minute, then the total eifective pressure on the piston will be 100 X 33 = 3300 pounds, and the movement being 200 feet per minute, the piston will move with a power equal to raising 660,000 pounds one foot high each minute, (as 3300 X 200 = 660,- 000,) and as each 33,000 pounds raised one foot high is one-horse power, and ^^^ is 20, then the power of this en- gine is 20-horse power. If this power is used to do work, a part of it will be expended in overcoming the friction of the parts of the engine and of the machinery through which the power Is transmitted to perform the work. The calculation made refers to the total power developed by the movement of the piston under the pressure of steam. The number of feet moved by the piston each minute is known from the length of stroke of piston in feet, and number of revolutions of engine per minute, there being two strokes of the piston for each revolution of the engine. When these three facts are known, the power of an engine can be readily and accurately ascertained ; and it is evident that, without the knowledge of each of the facts, viz., square inches of piston, effective pressure on each square inch, and movement of piston per minute, the power can- not be known. But circumstances, especially those existing when the condensing-engine was introduced by Watt, led to assump- tions as to pressure per square inch and speed of piston which, though true at the time, have long since ceased to be true, and consequently the rules based on such assump- tions are entirely inapplicable, and when used must of necessity give false statements. With regard to how much is understood by a horse- power, there is in this country no question at all. Horses vary in their ability to endure protracted labor, and our standard may be more or less than the average of horses HAND-BOOK OF LAND AND MARINE ENGINES. 59 are able to do ; but that is of little importance. So long as the number of horse-power of an engine conveys a definite knowledge of its power, it is of little consequence what relation it sustains to the action of any particular class of animals. FOREIGN TERMS AND UNITS FOR HORSE-POWER. Countries. Terms. E|ig. translation. Units. English equivalent. English. French. German. Swedish. Russian. Horse-power. Force de cheval. Pferde-krafte. Hast-kraft. Syl-lochad. Horse-power Force-horse. Horse-force. Horse-force. Force-horse. 550 foot-pounds. 75 kilogr. metres. 513 Fuss-funde. 600Skalpund-fot. 550 Fyt-funt. 550 foot-pounds. 542.47 foot-pounds. 582.25 foot-pounds. 542.06 foot-pounds. 550 foot-pounds. The French apply the term force de cheval to a power capable of raising 4*5000 kilogrammes 1 metre high in 1 minute, which is equal to a force capable of raising 32,549 pounds 1 foot high in a minute, which is about ^^^ less than our unit of measure. Horse-power. Force de cheval. Horse-power. Force dQ cheval. 10 10.14 60 60.83 15 15.20 65 65.89 V 20 20.28 70 70.97 25 25.34 75 76.03 30 80.41 80 81.11 35 85.48 85 86.17 40 40.55 90 91.25 45 45.62 95 96.31 50 50.69 100 101.8856 55 55.75 In this country, and also in England, it has been usual to assign a certain horse-power for a high-pressure engine of certain dimensions ; thus, an engine having a cylinder 10 inches in diameter and 24 inches stroke of piston 60 HAND-BOOK OF LAND AND MARINE ENGINES. would be called a 25-horse-power engine, and so on with high-pressure engines of all dimensions. But it is utterly impossible to say what horse-power an engine of the above dimensions would be, unless we knew the effective pressure to be exerted against the piston, and also the speed at which the piston is intended to move. There are several kinds of horse-power referred to in connection with the steam-engine, — the " nominal," " indi- cated," " actual or net," " dynamometrical," and " com- mercial." The nominal horse-power is admitted to be a force capable of raising a weight of 33,000 pounds one foot high in one minute, or 150 pounds 220 feet high in the same length of time. The term '* nGminal horse-power/' as before stated, originated at the time of the discovery of the steam-engine, from the necessity which then arose for comparing its powers with those of the prevailing motor. The nominal horse-power was based on the general princi- ple of the age, which dealt with low pressures and slow piston speeds. These quantities have of late years been greatly increased, and the old formula, in consequence, has become of less importance as a true expression of relative capacity. Hence, the term nominal horse-power is in reality of itself nominal, as Watt, in order to have his engines give satisfaction, added some twenty-five per cent, to the real work of the best horses in Cornwall, But the term nominal horse-power implies the ability to do so much work in a certain period of time ; and, in order to have a proper idea of it, a unit of measure is also employed. This unit is called a horse-power, and, as before stated, is equal to 33,000 pounds raised through a space of one foot in one minute : it is the execution of 33,000 foot-pounds of work in one minute. Work is performed when a pressure is exerted upon a HAND-BOOK OF LAND AND MARINE ENGINES. 61 body, and the body is thereby moved through space. The unit of pressure is one pound, the unit of space one foot, and work is measured by a "foot-pound" as a unit. Thus, if a pressure of so many pounds be exerted through a space of so many feet, the number of pounds is multi- plied into the number of feet, and the product is the number of foot-pounds of work ; hence, if the stroke of a steam-engine be seven feet, and the pressure on each square inch of the piston be 22 pounds, the work done at each single stroke, for each square inch of the piston, will be 7 multiplied by 22, equal to 154 foot-pounds. Indicated Horse-power.— The indicated horse-power is obtained by multiplying together the mean effective press- ure nn the cylinder in pounds per square inch, the area of the piston in square inches, and the speed of the piston in feet per minute, and dividing the product by 33,000 ; and as the effective pressure on the piston is measured by an instrument called the indicator, the power calculated therefrom is called the indicated horse-power. Actual or Net Horse-power. — The actual or net horse- power expresses the total available power of an engine ; hence it equals the indicated horse-power less an amount expended in overcoming the friction. The latter has two components, viz., the power required to run the engine, de- tached from its load', at the normal speed, and that re- quired when it is connected with its load. For instance, if an engine is desired to drive 10 machines, each requir- ing 10-horse power, it should be of sufficient size to furnish 100 net horse-power ; but to produce this would require about 115 or/ 20 indicated horse-power. The net horse- power of an engine may be determined by subtracting from the indicated horse-power the power required to over- come the friction of the engine when in the regular per- formance of its duty. G 62 HAND-BOOK OF LAND AND MARINE ENGINES. Dynamometpical Horse-powep. — The dynamometrical horse-power is the net power of the engine after allowing for friction, etc., and this alone is the power with which users of steam-engines are concerned. Though not equal in point of accuracy to the indicator, the dynamometer gives the actual power of small engines near enough for all practical purposes ; but it cannot be conveniently ap- plied to large engines. Commercial Horse-powep. — The term commercial horse-power is not generally used, and, when used, has no definite meaning, as there is no recognized standard in use among engineers and manufacturers by which to buy and sell engines. Though the question has often been discussed, and its importance generally recognized, it has never been universally adopted, consequently, the nominal horse- power of a steam-engine means anything that the manu- facturer feels disposed to call it. It seems very strange that this should be so, as every civilized country has its standard of weights and measures, with strict laws com- pelling the observance of these standards in the various operations of trade. The public, also, are keenly alive to the importance of these regulations, and no purchaser is so unmindful of his own interests as not to insist on ob- taining the full weight of most articles for which he pays ; but steam-engines are almost universally bought and sold by a system of guess-work which would not for a mo- ment be tolerated, were it attempted to be practised in any other branch of trade. There is great need of some recognized standard that would designate the number of square inches in the cylinder, travel of piston in feet per minute, and average steam pressure through the length of stroke, that should constitute the commercial horse-power of engines, say, for instance, 4 square inches in the cylinder, a piston speed of 240 feet per minute, and an 1 HAND-BOOK OF LAND AND MARINE ENGINES. 63 average pressure of 40 pounds per square inch; such proportions would be capable of developing a horse-power in most ordinary high-pressure engines, without the neces- sity of excessive speed or undue straining. Small engines are generally more economical than large ones, where the steam pressures, points of cat-off, and power developed are the same ; for, although the smaller engine, at the same speed, would be less economical at the higher speed necessary to produce the same power, the gain due to high speed overbalances the loss due to the smaller size of cylinder. Engines too large for the work to be done are less eco- nomical than if proportionate to the power required ; for instance, an engine of 40-horse power doing the work of 20-horse power, and running at a high speed, the steam would necessarily have to be throttled down by the gov- ernor from, say, 60 or 70 pounds boiler pressure to 25 or 30 pounds on the piston, which would be a loss of nearly I in fuel, as the loss by atmospheric pressure in non-con- densing engines is equally as much for 25 pounds as for 100 pounds pressure. The steam necessary to drive a 40-horse power high- pressure engine with 7io load, would give more than 10- horse power in a small engine. The cylinder of any engine should be of sufficient size to give the full power required, leaving a reasonable margin for variation in pressure, and for recuperative power under sudden in- crease of load, and no larger. Large engines doing the work easily, and at a low pressure, are economical only when the speed is reduced in proportion to the work to be done. There are three conditions which influence the economy of non-condensing steam-engines : steam pressure, expan- sion, and speed of piston ; for it will be found, on selecting 64 HAND-BOOK OF LAND AND MARINE ENGINES. any particular horse-poweVy that the highest steam press- ures and revolutions and shortest points of cut-off are those which show the greatest economy of steam. When these three conditions are all favorable at the same time, the maximum economy is obtained ; but when one or more only is favorable, the results are so modified as often to appear contradictory. Effective Pressure against the Piston. — The character of the connections between the boiler and cylinder, their length, degree of protection, number of bends, shape of valves, etc., must all be considered in forming an estimate of the initial steam pressure in the cylinder; while the effective pressure will depend upon the point at which the steam is cut ofi*, and the freedom with which it exhausts ; as it has been fully demonstrated by experience that the efiective pressure against the piston in the cylinder of steam-engines, more particularly slide-valve engines, rarely, if ever, exceeds t of the boiler pressure, as the free flow of the steam from the boiler to the cylinder is obstructed by the action of the governor and affected by the character of the connection, as before stated, so that in calculating the horse-power of steam-engines, not more than t of the boiler pressure should be taken as the effective pressure in the cylinder. When comparing the relative merits of different en- gines, it is of more importance to steam users to look at the actual power an engine is capable of exerting, rather than at the stated nominal horse-power or size of cylinder ; as it is no uncommon thing with two engines of the same diameter of cylinder and the same general pro- portions, that one may be capable of developing much more power than the other, even with a less consumption of coal per actual horse-power. The nominal horse-power of a high-pressure engine, though never very definitely defined, should obviously HAND-BOOK OF LAND AND MARINE ENGINES. 65 hold the same relation to the actual power as that which obtains in the case of condensing engines, so that an en- gine of a given nominal power may be capable of perform- ing the same work, whether high pressure or condensing. But whether it does or not, the standard of a horse-power serves as a standard of comparison, and its utility as a unit of reference is not impaired, whether it represents the actual power of one horse or three, so long as the standard is universal. The following rule will be found very con- venient for those who may have occasion to estimate the horse-power of high-pressure or non-condensing steam- engines, as it is practical and correct. Rule fop finding the Hopse-power of Steam-engines. — Multiply the area of the piston by the average steam pressure per square inch ; multiply this product by the travel of piston in feet per minute ; divide this product by 33,000, and the quotient will be the horse-power. EXAMPLE I. Diameter of cylinder iu inches 10 10 Square of diameter of cylinder 100 Multiplied by the decimal .7854 Area of piston 78.54 inches. Boiler pressure, 60 pounds ; cut-off, i stroke, ] Average pressure in cylinder, 50 pounds;* V 45 lbs. 5 off for loss by condensation, etc., J 39270 31416 3534.30 Travel of piston in feet per minute f 250 Divide by 33,000)883575.00 26. horse-pow. * See Tables of Average Pressures, pages 49, 60. t To find the Travel of Piston in Feet per Minute. — Multiply the distance travelled for one stroke in inches by the whole number of strokes in inches, and divide by 12. ^ 6* E 66 HAND-BOOK OF LAND AND MARINE ENGINES. EXAMPLE II. Diameter of cylinder in inches 10 10 Square of diameter of cylinder 100 Multiplied by .7854 Area of piston 78.54 inches. Boiler pressure, 80 pounds ; cut-off, I stroke, ] Average pressure in cylinder, 47| pounds ; > 42.75 lbs. 5 off for loss by condensation, etc., J 39270 54978 15708 31416 3357.5850 Travel of piston in feet per minute, 300 Divided by 33,000)1007275.5000 30.* horse-power. EXAMPLE III. Diameter of cylinder in inches 20 20 Square of diameter of cylinder 400 Multiplied by .7854 Area of piston 314.1600 Boiler pressure, 60 pounds ; cut-off, | stroke, ) Average pressure in cylinder, 57 pounds ; V 52 lbs. 5 off for loss by condensation, etc., J 6283200 15708000 16336.3200 Travel of piston in feet per minute, 300 Divided by 33,000)4900896.0000 148.* horse-power. * In these examples, the fractional parts of a horse-power have been intentionally left out. HAITD-BOOK OF LAND AND MARINE ENGINES. 67 EXAMPLE IV. Diameter of cylinder in inches 20 20 Square of diameter of cylinder 400 Multiplied by 7854 Area of piston 314.1600 inches. Boiler pressure, 85 pounds ; cut-off, i stroke, | Average pressure in cylinder, 50 pounds; > 45 lbs. o off for loss by condensation, etc., J 15708000 12566400 14137.2000 Travel of piston in feet per minute 350 7068600000 424116000 Divided by 33,000)4948020.0000 149. horse-power. It will be seen from the foregoing examples, that any increase of pressure and piston speed makes a very notice- able difference in the power of the engine ; but this aug- mentation of power is not obtained without an increased quantity of steam in proportion to the increased pressure and speed, except where the steam is expanded to its lowest available limits. A high-pressure engine, for instance, working with 40 pounds steam above the atmospheric pressure upon the piston, cut off at one-third, and expanding the remainder of the stroke, the piston travelling 220 feet per minute, would only exert the power for which it was nominally calculated, independent of friction ; but take the same en- gine, and increase the speed from 220 to 440 feet per minute, — which is quite practicable, — the power of that engine would then be doubled, less the extra friction ; but double the quantity of steam would have been used. 68 HAND-BOOK OF LAND AND MARINE ENGINES. Suppose steam at 80 pounds pressure was introduced to the same cylinder, cut off at one-third and worked expan- sively, as in the first case, the power given out by the 80 pounds pressure would be less in proportion than that at 40 pounds, as the exhaust would be thrown away at about five times the pressure that it was at 40 pounds, and a portion of the useful effect of the steam would be lost, in consequence of its not being expanded to its full limit, the lost portion escaping into the atmosphere and exerting a corresponding back pressure on the piston. The following method will be found very convenient, as it somewhat abbreviates the rule used in the foregoing ex- amples for calculating the horse-power of a steam-engine. TABLE OF FACTOES. Diameter of Diameter of Cylinder in Factor. Cylinder in Factor. Inches. Inches. 8 .152 26 1.608 10 .238 30 2.142 12 .342 36 3.084 14 .466 40 3.808 16 .609 45 4.82 18 .771 48 5.483 20 .952 50 5.95 22 1.151 56 7.463 24 1.37 60 1 8.'568 Rule. — Multiply the factor of the given diameter of cylinder by the speed of piston in feet per minute (using all below hundreds as decimals) ; multiply the product by the average pressure in pounds per square inch. This last product will be the horse-power of the engine. HAND-BOOK OF LAND AND MAEINE ENGINES. 69 EXAMPLE. Diameter of cylinder, 12 inches, .342 2.40 Travel of piston per minute, 240 feet, 13680 684 Average pressure, 42 pounds, .82080 42 164160 328320 34.47360 horse-power. Bourne's Rule for ascertaining the nominal horse-power of a high-pressure steam-engine working about four times the usual speed. Multiply the square of the diameter of the cylinder by the pressure on the piston per square inch less a pound and a half, and by the cube root of the stroke in feet, and divide the product by 235. The quotient is the power of the high-speed engine in nominal horse-power. EXAMPLE. Diameter of cylinder, 20 20 400 sq. of diameter. Pressure per sq. in. 80 lbs., less 1^^ lbs., 78 J Stroke 36 inches = 3 feet, 31400 1.4422496 Divisor, 235)45286.6374400(192.7 n. h. p. Colbupn's Rule is to multiply the area of the piston, the pressure of steam per square inch, the number of revolu- tions per minute, and the length of stroke together ; divide the product by 33,000, and take /^ of the quotient. But Colburn's rule is not correct, as only one-half the piston speed is employed to get the power of the engine. In fact, neither Colburn's nor Bowen's rules are correct. 70 HAND-BOOK OF LAND AND MARINE ENGINES. WASTE IN THE STEAM-ENGINE. A pound of good coal, it is universally admitted, will liberate, during complete combustion, over 14,500 units of heat, each unit being equivalent to 772 foot-pounds. The mechanical equivalent of the heat developed by the com- bustion of a pound of coal is, therefore, say 14,500 X 772 = 11,000,000 foot-pounds. A horse-power is always as- sumed to be equal to 33,000 foot-pounds per minute, or 1,980,000 foot-pounds per hour. So, the combustion of each pound of coal per hour lib- erates heat enough to develop 11,000,000 -r- 1,980,000 = say 5-horse power ; and in a perfect steam-engine the con- sumption of coal would be about at the rate of one-fifth of a pound per hour for each horse-power developed. The greatest economy yet obtained in the best high- pressure engines may be taken at from 3 to 4 pounds of coal per indicated horse-power per hour ; but for ordinary high-pressure engines in this country and in England a consumption of from 7 to 9 pounds is quite common. In good modern high-pressure steam-engines the useful effect obtained from the work stored up in the fuel may be thus calculated : Lost through bad firing and incomplete combustion 10 per cent. Carried off by draft through chimney 30 " " Carried away in the exhaust steam 50 " " Utilized in motive power (indicated) 10 " " 100 The minor causes of loss in the steam-engine are radiation of heat from the boiler, steam-pipes, and cylinder, leakage and condensation ; but the great loss arises from the escape of the steam into the atmosphere with only a small portion of its heat utilized ; this of itself leads to a loss of from 40 to 60 per cent. ; a further loss of useful I HAND-BOOK OF LAXD ANp MAEINE EKGINES. 71 X o o (0 o X 3Q c 30 m O C H z o 72 HAND-BOOK OF LANP AND MARINE ENGINES. effect in the steam-engine ensues from a portion of the motive power actually developed being absorbed by fric- tion, the useful power of the engine being frequently reduced by this cause by from 10 to 15 per cent. The use of good material, good workmanship, thorough lubrication and cleanliness, it is true, go far to lessen the friction and increase the efficiency of steam-engines; so also the use of high-pressure steam, high rates of expan- sion, efficient feed-water heaters, non-conductors and steam- packing, is conducive to economy ; but what is needed to render the steam-engine what it should be, is complete combustion of the fuel in the furnace, the transfer of all the heat generated to the water in the boiler, the passage of the steam through the engine without the loss of heat, except such as is converted into motive power, the trans- mission of the remaining heat in the exhaust steam to the feed water, and the absence of friction in its working parts. In consequence of the enormous waste incurred in the use of the steam-engine, numerous attempts have been made to supersede steam as a prime mover, but as yet without success, as there are certain, difficulties connected with the employment of all other agents which have as yet proved insurmountable. In short, there is not at present on the horizon the faintest dawn of the appearance of any mode of generating force calculated to compete with, much less to supersede, the steam-engine. Electro-magnetism, from which, at one time, so much was expected, is now thoroughly understood to be a far more costly mode of obtaining power than the combus- tion of coal. Heat, electricity, magnetism, chemical affinity, force, are all equivalent to each other, according to ratios which are fixed and unalterable. The atomic weight of carbon is 6 ; that of zinc, 32. One pound of carbon HAND-BOOK OF LAl^D AND MARINE ENGINES. 73 will develop more heat, and consequently more force, than 6 pounds of zinc ; whilst, weight for weight, the cost of the former to the latter is as 1 to 50. The discovery of a new motor, even if such a thing should happen, would take a quarter of a century to replace the present arrangements ; and even then it would be the duty of the engineer and the inventor to strive to improve the modes of employing the agent we now pos- sess, and to inquire in w^hich direction further progress in its economical application would lead. That great improvements can and will be made in the economical working of the steam-engine, none can doubt, who have compared its theoretical capabilities with its present performances. DESIGN OF STEAM-ENGINES. The most valuable features of a steam-engine are strength, durability, simplicity, and economy ; therefore, in designing an engine, symmetry should be observed, in order that all the working parts may be accessible with- out any disarrangement of details ; lightness should also be adhered to as far as compatible with strength. The economical working of a steam-engine depends upon many things, — proportions of design, good work- manship, care in using the materials employed in its con- struction, and a skilful adjustment of the different parts ; as the resistance of every machine is increased or dimin- ished according to the harmony of proportions existing between its different principal parts. The wear of the shaft, the burden on the beam, the wear and tear of the cylinders and packing-rings, the weight borne by the guides in sustaining or directing the cross-head, should all be duly considered by the designing engineer. 7 74 HAND-BOOK OF LAND AND MARINE ENGINES. Steam-engines embrace a great variety of designs, viz., the vertical, inclined, inverted, beam, horizontal, side-lever, oscillating, trunk, steeple, etc. Those most generally used for stationary engines are the horizontal, vertical, and beam ; but there is no other form which stands the tests and meets the public wants as does the horizontal ; as an evidence of which, wherever steam-engines of great power are required, the horizontal style of engine is better liked than any other type. THE BED-PLATE. The bed, or bed-plate, should be cast in one piece when- ever the circumstance of design, construction, etc., will per- mit. The metal should be so distributed as to give it the necessary resisting strength without excessive weight, as it is not always the heaviest bed-plates that possess the greatest rigidity. CYLINDERS. The cylinder being one of the most important and ex- pensive parts of the steam-engine, in order to render it durable and reliable, it should be mathematically correct as to its inside diameter from end to end ; though, un- fortunately, this is not always the case. But there are several reasons which may be assigned as the cause of irregularities in the bore of steam cylinders, — the machine with which it is bored, the kind of tool used, speed of cutter, want of uniformity in the casting, etc. Experience has shown it to be advisable, when circum- stances will permit, to bore cylinders upright, taking out a heavy cut at first, and then bringing the interior of the cylinder, by successive cuts, to within ^^^ ^^ ^^ '^^^^ ^^ ^^^ required size ; the remaining portion should then be re- HAND-BOOK OF LAND AND MARINE ENGINES. 75 moved by a cutter which would be neither round nor diamond pointed, but a kind of combination of the two. It is not at all desirable that a cylinder when bored should present a dead smooth surface, as such surfaces in steam cylinders do not wear so well at the outset as those slightly ridged. This may be accounted for by the extent of surface to be worn down to a steam-tight bearing. Cylinders should never be removed from the bed-plate for the purpose of reboring, unless it be found impractica- ble to perform that operation while in its original position ; as, if the cylinder be out of line and the crank-pin be in line, the cylinder can be rebored in line with the crank- pin ; or if, as is often the case, the crank-pin be out of line with the cylinder, the pin can be removed and the hole in the crank rebored in accurate line with the cylinder. Of course, in such cases, it becomes necessary to have a new crank-pin. The thickness of steam cylinders cannot be deduced from any fixed rule which would be practical in all cases. For instance, a cylinder 6 inches in diameter should equal at least | of an inch in thickness ; whereas one 24 inches in diameter would be 1^ inches in thickness : the former equals -^q of the diameter, while the latter equals j^q of the diameter. TABLE SHOWING THE PROPER THICKNESS FOR STEAM CYLINDERS OF DIFFERENT DIAMETERS. Diam. of Cylinder. Thickness. Diam. of Cylinder. Thickness. 6 inch. 1 inch. 14 inch. 1 inch. 8 - 9 " 10 *' 11 ** 15 '* 17 ** 18 »* 19 ^* 1?" it :: 12 " H " 21 - If " 76 HAND-BOOK OF LAND AND MARINE ENGINES. The foregoing thicknesses include the proper allowance for reboring. But when the speed of the piston is intended to exceed 300 feet per minute, y'g of an inch should be added per 100 feet to the thickness given. The following table, however, is more in accordance with modern practice. Diam. of Cylinder. Thickness. Diam. of Cylinder. Thickness. 6 in. .440 18 in. 1.070 8 *' .545 20 ** 1.176 10 *' .650 22 ^* 1.280 12 '' .755 24 " 1.385 14 '' .860 26 *' 1.490 16 '* .965 28 " 1.595 30 *' 1.700 Rule for finding the required Diameter of Cylinder for an Engine of any given Horse-power ^ the Travel of Piston and available Pressure being decided upon, — Multiply 33,000 by the number of horse-power ; multiply the travel of piston in feet per minute by the available pressure in the cylin- der. Divide the first product by the second ; divide the quotient by the decimal "7854. The square root of the last quotient will be the required diameter of cylinder. PISTONS. The piston ranks next in importance to the cylinder, as the quantity of fuel consumed, the useful effect of the steam, the amount of power developed by the engine, etc., depend in a great measure on the character and condition of the piston. It is, therefore, not to be wondered at, that an immense amount of thought and mechanical skill has been devoted to its improvement, and that its condition is more frequently a source of loss and anxiety to owners of steam-engines, and annoyance to the engineer, than any other detail of the steam-engine. HAND-BOOK OF LAND AND MARINE ENGINES. 77 PISTON-RINGS. Piston-rings should be of a softer material than that of the cylinder, in order to prevent as far as possible the wear of the latter instead of the rings, as the expense of renewing them is trifling compared with that of reboring the cylinder. Cast-iron is very generally used, as it pos- sesses very many advantages for this purpose, among which are cheapness, durability, uniform expansion, and the ad- ditional advantage that it acquires a finer surface and generates less friction than any other material that may be used; although brass rings faced with Babbit-metal are very frequently used for the pistons of locomotives and marine engines. Piston-rings should be fitted so as to move freely between the flange of the piston-head and the follower-plate, in order that they may accommodate any inequality that may exist in the cylinder ; and as their edges are liable to corrode and become leaky, they should be frequently re- moved from the cylinder and faced-up in a lathe, and re- ground, and fitted to the flange and follower-plate. PISTON-SPRINGS. There is not, in the whole range of steam engineering, it may be safely said, a subject on which the inquiring engineer finds such a dearth of information as he does in regard to the proper amount of elasticity required for the elliptic springs so generally used in adjusting or setting out piston-packing. For, while some bear a slight resem- blance to, and possess some of the qualities of, an elliptic spring, others can be said to be nothing more than un- shapely pieces of steel. If any engineer wishes to test the elasticity of such springs, let him place the extreme points of one on two 78 HAND-BOOK OF LAND AND MARINE ENGINES. parallel pieces of iron, and place weights on it, and observe the enormous load it requires to deflect the spring even 3^^' of an inch in its centre ; this will enable him to form some idea of the amount of friction produced in steam cylinders by badly proportioned springs. Such springs, w^hen pressed against the packing-rings by means of set-screws, are as rigid as jack-screws, or solid blocks of iron, and possess no advantages over solid pistons, save that they can be read- justed to take up the wear. The pistons of large marine engines generally have lighter springs than many small engines, and are not packed so tight by many degrees pressure, in proportion to their areas, as some stationary engines. This may be accounted for by the fact, that pistons that would be per- fectly steam-tight under a pressure of 25 to 30 pounds to the square inch, would be apt to leak excessively under a pressure of from 80 to 100 pounds. STEAM-PISTONS. The chief merits of the steam-piston seem to consist in its diminished friction and first cost, as it can be more cheaply constructed than spring-pistons, and, after being once put in the cylinder, requires no further attention or adjustment on the part of the engineer; but it is claimed, by its opponents, that it is liable to leak, and wear the cyl- inder out of "true,'' in consequence of its being influenced by varying steam pressures. Nevertheless, the steam- piston, after encountering a good deal of prejudice, like many other innovations in steam engineering, is fast estab- lishing its merits with engineers and steam users. SOLID PISTONS. Solid pistons are sometimes used, and, when well de- signed and fitted, answer very well, as they have the ad- HAND-BOOK OF LAND AND MARINE ENGINES. 79 vantage of producing no friction ; but they are only prac- ticable in cases where the cylinder is of uniform bore all through, and the engine is perfectly in line. They have the disadvantage of not being adjustable when they become worn or leaky ; although there is one solid piston, " Bucks Patent," that can be adjusted to the cylinder more accu- rately than any spring-piston. The pistons of steam-hammeps are generally made solid, and are kept steam-tight by turning grooves around the head, into which narrow steel or wrought-iron rings are sprung, which adjust themselves to the form of the cyl- inder, it being the only kind of piston-head capable of resisting the immense jar to which the mass is subjected. The pistons of small steam-engines are frequently made in the same way, as they are found to be very cheap and convenient. TABLE OF PISTON SPEEDS FOR ALL CLASSES OF ENGINES — STATIONARY, LOCOMOTIVE, AND MARINE. Small Stationary Engines, 200 to 250 feet per minute. Average 225 " Large Stationary Engines, 275 to 350 " Average about 312 " Corliss Engines, 400 to 500 " Average 450 " Locomotives and Allen Engines, 600 to 800 " Average 700 " Engines of River Steamers, 400 to 500 " Average 450 " Engines of Ocean Steamers, 400 to 600 " Average 500 " 80 HAND-BOOK OF LAND AND MARINE ENGINES. PISTON, CONNECTING-ROD, AND CRANK CONNECTION. The annexed cut shows the position of the piston in the cylinder when the crank is at half stroke. It will be ob- served that the piston is ahead of its proper position throughout the forward stroke, and that it must of neces- sity lag behind its position on the return-stroke, and that the points of full power are not on exactly the opposite sides of the diameter of the circle described by the crank, and that a straight line passing through the centre of the crank-shaft cannot intersect both points. These irregu- larities, which are due to the influence of the crank and connecting-rod, entirely disappear at the end of each stroke. The crank of an engine moves six times as far while the piston is travelling the first inch of the stroke as while it is making the middle inch, and a little over twice as far while the piston is moving the second inch, and a trifle over li times as far while the piston moves the third inch, and the fourth inch less than I J times as far. The crank also travels less when the piston is making the last inch of the stroke than it does while it is making the first. An explanation of the objections formerly urged against the employment of the crank as a means of converting a reciprocating into a rotary motion, namely, that its leverage, and therefore its power, is so variable, will be found under the head of Cranks, page 109. HAND-BOOK OF LAND AND MARINE ENGINES. 81 TABLE SHOWING THE POSITION OF THE PISTON IN THE CYLINDER AT DIFFERENT CRANK ANGLES, ACCORDING TO THif LENGTH OF CON- NECTING-ROD. (For Back-action Engines, the words " Forward " and '* Return " must be reversed.) Length of Length of 1 Length of Conneeting-Rod Connecting-Rod Connecting-Rod 4 to 1 of Stroke. 4}4 to 1 of Stroke. 5 to 1 of Stroke. Piston Position in Cylinder. t . 'Ho- ^ V. . ej a> £ o 03^ t; '^ « o S <^' Deg. qM fe O 3^ k:M ^M Deg. ft Deg. ^±3 5 o s Deg. 1^ 5tt Deg. Deg. Deg. Deg. Deg. 0.125 =r| 37| 46:1 91 371 46} 8| 371 45f 7| 0.2 48 59^ llj 481 58f 10^ 48| 58i 9f 0.25 = J 54| 66| 12| 54| 66 Hi 55| 65f 10 0.3 60 73| 13 61 72| 111 61i 72 lOJ 0.333 =- i 64i 771 13f 64| 76i 12i 65| 76} 10^ 0.375 = 1 QSi 82f 13J 691 82 12J 70} 81f 114 0.4 71f 85f 13J 72f 84f 12i 73 84} 11} 0.45 77i 91J l4i 781 901 12^ 781 90 111 0.5-:J 821 97- 14} 83f 96} 12J 84f 951 Hi 0.55 88^ 102| 14i 891 lOli 12J 90 lOlf 111 0.6 94| 108} 13i 951 107| 12J 95f 107 11} 0.625 = f 97} lllj 13i 98 110^ 12J 98| 1091 IH 0.65 100} 1138 13| 1011 113^ 12i 101| 1121 lOi 0.666 = f 102| llSf 13f 1031 1154 12* 103f 114| 101 0.68 104 1171 13| 104f 116i 12 105i 116} 10| 0.7 1061 1191 13 107f 119 111 108 118J 10| 0.71 107i 120i 121 108f 120} 111 109f 1191 101 0.73 llOJ 123} 12| 111} 1221 Hi 112 122i lOJ 0.75 = f 113} 1251 12| 114 125i ni 114| 1241 10 0.76 1141 1261 12i 1151 1261 11 116i 125J 9| 0.77 1161 117| 1281 12 116i 1271 lOf 117^ 127} 9| 0.78 1291 llf 118f 1281 10^ 119 128^ 9^ 0.79 1198 1301 111 119J 130} lOf 120 J 129f 9} 0.8 120^ 132 Hi 121} 131i lOi 1211 13H 9} 0.81 122i 1231 133} iH 122| 132| 10 123J 132J 9 0.82 1341 11 1241 134} 91 125 133| 8f 0.83 125f 136 lOf 126 135| 91 126f 135J 8| 0.84 127 137J 10^ 1271 137 91 128} 136t 8^ 0.85 1281 138J m 1291 138J 9J 130 138} 8} 0.86 130i 1401 n 131} 140 8f 131 1 1391 84 0.87 132| 142 9| 133 141f 8t 133| 141r 71 0.875 = 1 133}142f 9-^ 133| 1421 8i 134i 142J 71 F 82 HAND-BOOK OF LAND AND MARINE ENGINES. i o to CO CO lO o l-^ QO O "^ 00 rt^ O 1^ Tfi r-H C5 1^ lO T-H O 05 00 1^ I--. O O O lO rfi -^ "^ OO CO CO CD CO COOCOOOOOC^OG^OOiOClOOOO-^ r-ioa50oi^ocooo'^'^rr'!rcococo CD CO COtOOOOfMrt^OOcoOOCCOOOiOOO^M oa50ooDi^':ooto^'^'OcOOvOOcDo:)OOO^CO — o Oc:'OOi-^ooi040Trirt<'^cococococo o C5D 03 o CO cOTt'CDO(M:OT-(r^coOt-oco»-'050o O500 1— 1--=X5O»OtJHt}it^C000C0C0(M-0rH00OTt<(NO00l^ C500l--COCD>O'^'^'^C0C0C0C0C0(MC^ O CO cOOO^LOOO0 1--TtiCOCOCOCO(MC^(?qc^l o c>q 0sD AND MARINE ENGINES, 159 downward stroke, the steam -port in it overlaps a port formed in the side of the cylinder, and steam then passes to the top of another of the cylinders. When, on the other hand, the piston has reached about one -half its return- stroke, it uncovers the port in the «ide of its cylinder, and allows the steam to escape from the cylinder, into which it was previously admitted, into a casing round the crank- shaft, from which the exhaust-steam is taken either to a condenser or to the air, as the case may be. The advantages claimed for this class of engines are cheapness, simplicity of construction, fewness of parts, and an almost unlimited speed. But while it may be admitted that the w^hole arrangement is simple and compact; yet it is difficult to see what advantage can be gained by its use, over that of the double-acting arrangement, as, when the cylinders become worn or the pistons leaky, they involve the expense of reboring three cylinders, or readjusting three pistons ; for, unless they are perfectly steam-tight, they must continue to be a great source of annoyance. ROPER'S CALORIC ENGINE. The cut on p. 324 gives an elevation of Roper's* caloric en- gine, showing the valves, valve-gearing piston, cylinder, air- pump, beam, and fly- and band-wheels. The cut on p. 325 shows a vertical section of the same, in which No. 1 rep- resents the piston, on the top of which is fastened a leather packing; 2, the piston-drum, made sufficiently long to keep the packing from the fire ; 3, a lining of asbestos filled in between the shell and the sheet-iron lining w^hich surrounds the fire-brick ; 4, the brick lining of the fire- box ; 5, the outer shell of the engine ; 6, an iron ring to fasten the packing to the piston-head. - The writer is not the inventor. 160 HAND-BOOK OF LAND AND MARINE ENGINES. To start the engine, it is only necessary to turn the fly-wheel half a revolution, in order to give the plunger of the air-pump an upward motion, when the cold air is drawn in at the opening, A; on the return of the plunger, the valve, B, closes, and the air is forced into the engine through the check-valve, D. If the lower damper, E, is open, and the upper damper, H, is closed, all the air will enter the fire-chamber under the grate, F, and pass through the fire. If the upper damper, H, is open, and the lower damper, E, is closed, as they should always be after the fire is in good condition, the air all passes over the fire. The expansion takes place in the fire-box, and, the d9ors being closed air-tight, the air remains under pressure until, by the eccentric motion communicated to the valve-toes, the inlet poppet-valve is opened, which allows the com- pressed air to pass into the cylinder, which forces the piston up; its place in the fire-chamber being supplied with cold air at the same instant by the downward movement of the air-pump plunger. At this moment, by the same motion, the outlet or ex- haust-valve is opened, and the inlet-valve closed. The force of the balance-wheel and the weight of the piston bring the piston back ; and the expanded air, returning by the same passage, finds the inlet-valve closed and the out- let or exhaust-valve opened, and is discharged through the funnel or chimney. Many of the mechanical difficulties heretofore expe- rienced in the employment of this class of motors seem to have been successfully overcome in this engine ; but still there are natural difliculties which neither chemistry nor mechanical science have been able to remove up to the present time, nor is it at all likely that they ever will be. The first great drawback to the use of heated air is the HAKD-BOOK OF LAND AND MARINE ENGINES. 161 14* 162 HAND-BOOK OF LAND AND MARINE ENGINES. small amount of its expansion. Water expands 1700 times; so that to obtain a volume of expansion of 1 cubic foot, it is only necessary to force into the boiler 1 cubic inch of water. Now, could air be obtained in any simi- larly condensed and manageable form, yet retaining its present small capacity for heat, it would stand on a totally different footing from that which it actually occupies. Even at 568°, (which is probably above the temper- ature at which it could be practically used with advantage in a cylinder with air-tight piston,) its volume is only double what it is at GO"^ ; consequently, for every volume of heated and expanded air which develops power as it escapes, half a volume of cold air must be forced into the reservoir where the heating and expansion are accom- plished. This operation at once consumes half the theoretic power of the engine, plus the friction of the supply cyl- inder with its valves and appendages, and increases its consumption of heat for duty to considerably more than double that of the steam-engine. The second great disadvantage under which an air- engine labors may be said to be included in the first. It is this : that the small degree of tension it is possible to employ, from the limit placed by the question of temper- ature, not only virtually precludes the employment of the principle of working expansively to any extent, but also entails the necessity of employing cylinders of an enormous and unwieldy size in proportion to the power obtained. By cutting oJff the steam when the piston of a steam- engine has made | of the stroke, its duty may be in- creased more than threefold, reducing the consumption of fuel to 33 per cent. Now, suppose expansion be carried sufficiently far in the air-engine to reduce its consumption of fuel to 33 per HAND-BOOK OF LAND AND MABINE ENGINES. 163 cent., thus placing it on an equality with the steam-engine, with regard to the consumption of fuel in proportion to the amount of pressure exerted on the piston, the steam- engine would still possess an immense advantage over the air-engine in practical utility and convenience on account of the huge bulk of the latter. An air-engine capable of developing power equal to that of a steam-engine would require a working cylinder with an area from 20 to 50 times greater than that of the steam cylinder, together with an air-pump of at least two- thirds the area of the working cylinder. Nevertheless, the caloric engine, in its present improved form, has for some years past been successfully employed as a hoisting-engine in stores and warehouses, and also as a pumping-engine at railway stations, hotels, and country residences. It is also desirable for yachts and agricul- tural purposes, on account of its simplicity and freedom from explosion. HASKIN'S VERTICAL HIGH-PRESSURE ENGINE.* This engine possesses some very excellent features, such as graceful design, compact, simple and perfect mechanism. The conical upright frame is bolted firmly to a base of considerable area, which in turn is bolted to the founda- tion ; the cylinder and steam-chest are neatly lagged and banded with brass. The openings to receive the brasses in the stub-ends of the connecting-rod are cut out of the solid forging ; the cranks are perfectly counterbalanced ; the crank-pin, cross-head wrist, piston-rod, valve-stem, etc., are all made of cast steel ; the bearing surfaces are univer- sally large, which prevents the possibility of rapid wear or excessive heating at any speed to which they may be sub- jected. The cross-head guides and pillow-block are cast * See page 308. 164 HAI^B-BOOK OF LAND AND MARINE ENGINES. with the frame, so that they cannot become loose or out of line. The guides have concave surfaces for the cross- head to slide against. In fact, these engines are noted for their splendid proportions, compactness, and economy. Their speed is regulated by the Waters and Crowther's governor. MASSEY'S ROTARY ENGINE * It has been far more frequently the fortune of inventors of rotary engines to fail than to succeed. So frequently, indeed, and from so many various causes, has this been the case, that most engineers adhere to the opinion that the reciprocating engine can never enter into successful competition with the rotary, much less prove a formidable rival. And it is true that until quite recently no rotary engine had been produced that could approach in economy of power the best types of reciprocating engines. This might be attributed to the large amount of clearance, and to the great friction on the journals and packing, and also the leakage caused by wear. But the difficulties heretofore experienced in the con- struction and use of the rotary engine — that of keeping them thoroughly steam-tight without undue friction, and that of working steam expansively with a variable cut-off, and without undue clearance — have, it is claimed by the inventor of this engine, been successfully overcome. The advantages claimed for the rotary over the recipro- cating engine are cheapness, lightness, simplicity of parts, compactness, and occupying only a minimum -of floor space. The rotary engine, in consequence of its prompt reversing and capability of holding the load, is especially adapted as a bolster for mines and elevators. Besides, it is well suited for working the steering-gear of vessels. The rotary engine is desirable for locomotive, marine, * See page 333. HAND-BOOK OF LAND AND MARINE ENGINES, 165 ■m 166 HAND-BOOK OF LAND AND MARINE ENGINES. and stationary purposes, as, when well constructed, one rotary engine can be made to do the work of two recipro- cating engines, for in the rotary there are no dead centres or variations in leverage, etc. But still the question, as to what extent the rotary engine can cope with the rotative engine of corresponding power in economical use of steam alone, cannot at present be determined with accuracy, but must be left for future decision. PORTABLE ENGINES. By a portable engine is meant a steam-engine so arranged that it may be carried with facility from place to place entire, in a condition for use, either on wheels of its own, or upon a wagon or other conveyance. It differs from a stationary steam-engine in that the boiler and the engine, with all intermediate and subsidiary parts, are connected together in a compact manner, so as to require no other than their mutual support. While in the stationary engine, the boiler requires a foundation and setting of its own, the engine requires a separate foundation, generally with a detached support for the back end of the main shaft ; and not unfrequently the force-pump is apart from the engine, requiring also its independent foundation and source of motion. ^ HOW TO BALANCE VERTICAL ENGINES. When a vertical engine runs slow, the weight of the piston and piston-rod, cross-head, connecting-rod, and crank-pin must be counterbalanced, so that it will stand still in. any position ; but when the speed is very high, it will be only necessary to counterbalance such parts as revolve round the centre of the shaft, the crank-pin, the stub-end, and half the connecting-rod. Very accurate counterbalances must in all cases be determined by trial and experiment. HAND-BOOK OF LAND AND MARINE ENGINES. 167 KNOCKING IN ENGINES. The causes of knocking in engines are very numerous, and while some of them will yield to an industrious and careful search, others will prove a puzzle alike to the engineer and the expert. Instances are not uncommon where weeks have been devoted, and engines taken all apart and put together again, to find the cause of a knock, when perhaps it was finally discovered to be caused by a loose crank-pin or key in a fly-wheel. Knocking, in many instances, arises from looseness in the boxes and joints, which strike each other whenever their motion is arrested. Knocking arising from this cause can be easily remedied by taking up the lost mo- tion. In many instances, shoulders become worn in the cylinder in consequence of the piston-rings not overlap- ping the counter-bore at each end of the stroke. In such cases any adjustment of the piston-packing or keys fs gen- erally followed by a knock in the engine. The most prac- ticable remedy for knocking arising from this cause would be to rebore the cylinder. Knocking is caused in some cases by steam being ad- mitted to the cylinder too late to take up the lost motion when the crank is passing the centre; while in others, in consequence of excessive lead, the steam is admitted too soon and too rapidly, which produces excessive cushioning, and causes the engine to thump. Engines frequently knock in consequence of the exhaust opening too late and closing too soon. The whereabouts of knocks arising from this cause are generally the most difficult to determine; and it not unfrequently happens that, after all ordinary means have been resorted to in vain, the indicator has to be applied in order to determine the precise location of the knock. 168 HAND-BOOK OF LAND AND MARINE ENGINES. Engines out of line generally knock sideways at certain points of the stroke. The knocking heard in cylinders may be produced by a loose follower-plate or piston-rod ; while the noise in steam-chests is generally due to lost motion in the valve connections. Engines in very good condition sometimes knock in consequence of the packing being too hard or too tight around the piston-rod. There are a hundred other causes of knocking which the indus- trious engineer will be called upon to discover, and while most of them, as before stated, will yield to an easy search, some will try him severely. In fact, to discover knocks, he must see with his ears and hear with his eyes, THE INJECTOR. Of all the inventions of the mechanic and the scientist, nothing seemed to the uneducated to approximate so nearly to perpetual motion as the instrument now in general use as a boiler-feeder on locomotives and station- ary engines, and known as the injector, and which, from common use, no longer excites the wonder even of those who do not understand its mode of operation. It consists of a slender tube, through which steam from the boiler passes to another or inner tube, concentric with the first. The latter tube conducts a current of water from a pipe into the body of the injector. Opposite the mouth of this second tube, and detached from it, is a third fixed tube, open at the one end, facing the water supply-pipe and leading from the injector to the boiler. When the instrument is ready for use, the steam and water supply-pipes being fitted with stop- valves, and the feed-pipe to the boiler with a check-valve, by simply opening the steam-valve steam enters the small steam- pipe and rushes out at its extremity, picking up the whole stream of water, leaps across the open space with a HAND-BOOK OF LAND AND MARINE ENGINES. 169 15 170 HAND-BOOK OF LAND AND MARINE ENGINES. loud hissing noise, and plunges with its burden of -water into the open end of the feed-pipe at a tremendous velocity. Thus it will be seen that the steam that was admitted to the injector from the boiler returns to the boiler, carry- ing with it more than twenty times its weight of water. Not a drop of water is lost — not a particle of steam wasted. The principle on which the injector acts is that which was discovered by Venturi, in the beginning of the pres- ent century, and is known or designated as the lateral action of fluids. The action is somewhat identical to that of the steam-jet in locomotive boilers, — steam being ad- mitted to the inner tube of the injector, and the central conical valve being withdrawn, the steam escapes in a jet, near th6 top of the inlet water-pipe. If the level of the water be below the injector, the escaping jet of steam, by its superficial action (or friction) upon the air around it, forms a partial vacuum in the inlet- pipe, and the water then rises in virtue of the external pressure of the atmosphere. Once risen to the jet, the water is acted upon by the steam in the same manner as the air had been seized and acted upon in first forming the partial vacuum into which the water rose. The velocity with which steam flows into the atmosphere at a pressure of 60 pounds to the square inch is about 1700 feet per second. Now let us suppose that steam is issuing with the full velocity due to the pressure in the boiler, through a pipe an' inch in area, — the steam is condensed into water at the nozzle of the injector, without suflfering any change in its velocity. From this cause its bulk will be reduced, say 1000, and therefore its area of cross-sec- tion — the velocity being constant — will experience a similar reduction. It will then be able to enter the boiler again by an orifice jo^o o^^i P^^^ <^f tl^at by which it escaped, HAND-BOOK OF LAND AND MARINE ENGINES. 171 172 HAND-BOOK OF LAND AND MARINE ENGINES. Now it will be seen that the total force expended by the steam through the pipe, on the area of an inch, in expel- ling the steam jet, was concentrated upon the area jo^oo^b of an inch, and therefore was greatly superior to the oppos- ing pressure exerted upon the diminished area. The injector, as a boiler-feeder, has the advantage of occupying but little space, and can be set in almost any position ; is free from that objectionable knocking so com- mon in pumps where they work against pressure ; is not liable to get out of order; requires no belt, oil, or packing, and obviates the necessity, under many circumstances, of running the engine for the purpose of pumping water into the boiler. It is also of great value on locomotives in cases where the train is detained on the road or at rail- way stations. METHOD OF WORKING THE SELF-ADJUSTING IN- JECTOR WHEN REQUIRED TO LIFT THE WATER. 1st. See that steam-plug, B (see cut on page 171), is closed down, and waste-valve stem, K, is raised. 2d. Admit steam from boiler to injector slowly, which should cause the water to flow from pipe, P. 3d. Turn up the steam-plug, B, until the waste- valve, K, can be closed without causing the injector to cease working. 4th. Turn the steam-plug, B, up to increase the delivery, and down to decrease it. When the water flows to the injector, it can be started and stopped without closing down the steam-plug, B. A failure to work will always be indicated by an escape of steam and water from the waste-check, C, between water- supply and waste-pipe. HAND-BOOK OF LAND AND MARINE ENGINES. 173 METHOD OF WORKINa THE ADJUSTABLE INJECTOR WHEN REQUIRED TO LIFT THE WATER. 1st. Screw in steam-spindle. 2d. Turn handle on side of injector, so that pointed end will be towards boiler end pf injector. 8d. Turn on the water, if it is supplied under pressure. 4th. Open wide the steam-valve, so as to give full head of steam. 5th. Screw steam-spindle out all the way. 6th. Turn pointed handle on side of injector until dis- charge from overflow stops. 7th. To reduce quantity of water discharged, screw in steam-spindle, and stop any discharge at overflow by ad- justing pointed handle. When the instrument has been set to feed a proper amount, it may be stopped and started by opening the water-cock and steam-valve, without moving the steam- spindle or pointed handle on the injector, provided the water flows to it. If the water is lifted from a tank or well, follow instructions as given above. INSTRUCTIONS FOR SETTING UP INJECTORS. It is of the utmost importance that great care be taken in setting all kinds of injectors ; and there are some par- ticulars that may be mentioned as holding in common with all kinds of injectors. All pipes, whether steam, water-supply, or delivery, must be of the same internal diameter as the hole in the cor- responding branch of each injector, and as short and straight as practicable. When floating particles of wood or other matter are liable to be in the supply-water, place a wire screen over the receiving end of water-supply pipe, taking care to have 15* 174 HAND-BOOK OF LAND AND MARINE ENGINES. HAND-BOOK OF LAND AND MARINE ENGINES. 175 the meshes as small as the smallest opening in the deliv- ery-tube, and the total area of meshes much greater than the area of water-supply pipe, to compensate for the closing of some of them by deposit. The steam should be taken from the highest part of the boiler, to avoid priming, but should not be attached to the steam-pipe leading to an engine, unless this pipe is large ; sudden variations in pressure may break the jet in the adjustable injectors, and would produce a constant move- ment of the piston in the self-adjusting. When any injector, capable of raising water, is set so as to lift the water, care must be taken to have the pipes very tight, so as not to draw air; and it is of importance that in any arrangement of the instrument, the water-supply should be unmixed with air, which will cause a sputtering sound, and is liable to break the jet. If the water is not lifted by the injector, but flows to it from a tank or hydrant, there should be a cock in the water-supply pipe. There must always be a stop-valve or cock in the steam- pipe between the steam space in boiler and injector, and a check-valve between the water space of boiler and the injector. After all the pipes are properly connected to the in- jector and boiler, and before admitting steam to the in- jector, it should be disconnected again from the pipes at the three union joints, and the steam and water should be allowed to flow through the pipes, to remove any red lead, or scale, and other solids from the interior of the pipes. This precaution will avoid trouble at first starting, which otherwise is liable to occur. In addition to the above, certain precautions must be taken in setting the self-adjustable injector. There must be in the water-supply pipe an alarm check- valve, with 176 HAND-BOOK OF LAND AND MARINE ENGINES. waste-check attached ; and, when fed with water under pressure, any considerable pressure in the water-supply pipe must be avoided. But when unavoidable, and the pressure in the supply-pipe is too great, a regulating stop- valve must be used. In determining the position of an injector, it must be borne in mind that the instrument may be placed verti- cally, horizontally, or at any angle, as most convenient. In some cases, when used without steam-spindle, it may be found convenient to place it upside down. For locomotives, the injector should be placed in pref- erence on the right-hand side of the engine, in the most convenient position for being operated. When placed so low down that the water from the tank will at all times flow to it, the instrument is more readily started, for in such case the regulation for quantity can be made by the steam -spindle, which afterwards need not be moved, but the instrument can be started by merely turning on the water from the tank, opening the starting-valve at the boiler, and closing the waste-valve. TEMPERATURE OP FEED-WATER. Maximum temperature of feed admissible at different pressures of steam. Pressure of steam, lbs. per sq. in., 10, 20, 30, 40, 50, 100. Temperature of feed, Fahrenheit, 148°, 138°, 130°, 124°, 120°, 110°. HAND-BOOK OF LAND AND MARINE ENGINES. 177 H»^ Ti 2 is 52. ft 2 ^ tzi to H-k H—' h-i h-* 1— ' OOooif^toO':ooo^05C;ii45»'Coto CO 12. cs COCOOitOtOtOtOtOu-'l-^i-'l-^ »,^^^,s^^^r^^:;r:;p C00iOCnC0C0 0C4i^l--i0C0TC0h-' OC' p p H-* ^ 0:) CC- CO k;^ CO ^ 05 00 be CO h^ii^ to 00 to to hl^ en Ci "tO CO c 0' CD CD K p CD »-< CD >-i w c i CO OOOOiO^CObOtOI— 't— ' H^tOCTiCOOO-iOCitOCDCJiCOtO pCaj-'H-pCOpitOCoptOph-*^ bi J;^ * bo CO * ^ 05 cn bi CD Oi Or Oi >i^ g ooo-4:^tOtO^H-»H^ ^OtOO^tOCOCOOCf^O-^k^tOh^ cOnJ^kfi-H-COCO^^COrf^^tOOikli-O cobo?-^coc5^b.b5fcobocobobi'H;:^ to 05 Ci 05 to Oi >4:^H|:^0O0C 4^ t0000054^COtOtOt-»H- cOCOCnH-^tOCOCOOtO^^JCOCiH- *h{^ ^ ;^ CO kt:^ 05 bo *hf^ CO CO to CO H-» GO 00 kj:^ to 00 to CO^OtOCn coo OOOirf^COtOtOi-'t-^ CO00OiOi0C0COi^--O:)f-^Q0Oit0H^ p rf^ p K^ h^ CO p CO to p to to 00 >-i bi-^'-JrtotocscotobiOH^K-'H-'bo (^ h- to -— '►-' ^4^OC0k--Cn00t0^?b0000Tt-0K-i p p 00 h-* p CO p p to p ; ' to * bi H-i * CO to H-' CO GO bi hf^ CO I-' CO 00 t-^ CO ^1 H- 1— » 4i-tOCO-aCnCOCOtOK-i-i COH-'OTCOCO^IOCOOOCOCOO^CO^-' CO4i^COH-*00COtO00tOCOtO0Ci--CO CO bi t-o H-* bo bi to bo h^ co rf^^ bi to C: ^ 00 00 -, shows the varying pressure of the steam. HAND-BOOK OF LAND AND MAKINE ENGINES. 241 The common errops in communicating motion to the paper are of two kinds, — those which arise out oF the movements employed, and those which, when the move- ments are correct, are occasioned by a high velocity of the parts ; but with pro|)er care these may all be avoided. Errors in the motion of the pencil are of a more serious nature. The spring may be accurate, but its unavoidable length and weakness, and its weight, joined to that of the piston and other attached parts, and the distance through which these must move, in order that the indications may be on a scale of sufficient magnijtude, render it almost im- possible to obtain, from engines which run at a high speed, correct diagrams. METHOD OF APPLYING THE INDICATOR. When it is practicable, diagrams should be taken from each end of the cylinder. The assumption made, that if the valves are set equal, the diagram from one end will be like that from the other, will be shown by this instru- ment to be erroneous, as It often occurs that there is a dif- ference in the length of the steam passages, and in the lead, or the amount of opening, or the point of closing. These, and many other causes, will make a difference in the diagrams obtained from the opposite sides of the piston. The indicator sliould be fixed close to the cylinder, especially on engines working at high speeds ; and if pipes must be used, they should not be smaller than half an inch in diameter. On vertical cylinders, for the upper end, the indicator- cock is usually screwed into the head, where the oil-cup is set, it being removed for the purpose. For the lower end, it is necessary to drill into the side of the cylinder at a convenient point in the space between the cylinder-head 21 Q 242 HAND-BOOK OF LAND AND MARINE ENGINES. and the piston, when the crank is at the centre, and screw in a short bent pipe, with a socket on the end to receive the indicator-cock. Fop horizontal cylinders, the best place for the indi- cator is on the top or upper side, at each end ; if it cannot be placed there, bent pipes may be screwed into the heads or into the side of the cylinder. The indicator should never be set to communicate with the port passages, as the current of steam passing the end of the pipes has a ten- dency to reduce the pressure in the instrument. On oscillating cylinders, care must be taken to set the instrument in such a position that the motion of the cyl- inder will not have the effect to throw the pencil to and from the paper. Proper Points from which to derive the Motion. — This may be taken from any part of the engine which has a motion coincident with that of the piston. For a beam- engine, a point on the beam, or beam-centre, will give the proper motion ; but care must be taken that the cord be so led off that, when the engine is on the half-stroke, it will be at right angles to whatever gives it motion. For horizontal and vertical engines, the motion of the paper is generally taken from the cross-head. For oscillating engines, the motion may be taken from the brasses at the end of the piston-rod. Facts to be recorded when Diagrams are taken. — The form of engine, whether single or double. Length of stroke, diameter 0/ cylinder, and number of strokes per minute. The size of the ports, the kind of valve employed, the lap and lead of the valve, and the exhaust-lead. The amount of the waste-room, in clearance and pass- ages. The pressure of steam in the boiler, the diameter and length of the steam-pipe, and the point of cut-off. HAND-BOOK OF LAND AND MAEINE ENGINES. 243 ^^'Fop locomotives, the diameter of the driving-wheels, aiid the size of the exhaust-nozzle, the weight of the train, and the gradient, or curve. Fop condensing engines, the vacuum by the gauge, the kind of condenser employed, the quantity of water used for one stroke of the engine, its temperature and that of the discharge, the size of the air-pump and length of its stroke, whether single- or double-acting ; and, if driven in- dependently of the engine, the number of its strokes per minute, and the height of the barometer. The description of boiler used, the temperature of the feed-water, the consumption of fuel and of water per hour, and whether the boilers, pipes, and engine are protected from loss by radiation, and if so, to what extent. Obsepvations on the Chapactep of the Diagpam, — If the expansion corner is much cut away, the engine is' working to a proportionate extent expansively. If the eduction corners are much cut away or slanted, the exhaust-passages are too small. If the lead corner is much slanted off, then the lead given to the engine is great ; the steam side of the valve is opened before the end of the stroke, or the exhaust-passage is shut too soon, which causes compression. In some cases the vapor may be compressed beyond the pressure of the steam, and cause the line of the diagram ' to form a loop above tjie steam line at the starting corner. If the starting corner is slanted much, then the steam is not admitted sufficiently early. Every change in the engine which diminishes the area of the diagram, by the rounding of its corners, diminishes the power of every strokeflbr the space enclosed in the pencil line exactly represents the power of a stroke of the engine, with the exception of the lead corner, — lead being efficacious in the working of the engine. k 244 HAND-BOOK OF LAND AND MARINE .ENGINES. How to Compute a Diagram. — Set down the length of the spaces formed by the vertical lines from the base, in measurements of a scale accompanying the indicator, and (m which a tenth of an inch usually represents a pound of pressure ; add up the total length of all the spaces, and divide by the number of spaces, which will give the mean length, or the mean pressure upon the piston in pounds per square inch. How to Calculate the Power the Engine is exerting when Ihe Diagram is taken. — Multiply the area of the piston by the mean pressure, as shown by the diagram ; multiply the product by the speed of the piston in feet per minute, and divide by 33,000. The quotient will be the indicated horse-power. Utility of the Indicator to Owners of Steam-Engines and Factories. — Disputes frequently arise between parties letting power and their tenants, in consequence of the latter using more power than that specified in the contract, and the price of which was fixed in the first place at so much per horse-power. Under such circumstances the question will arise, How much power is each tenant using? The only way to determine this accurately is by means of an indicator. Method of Determining how much Power each Tenant is actually using. — Throw off all the belts except the main or driving-belt, and take a set of diagj-ams from the engine, with no load on except the shafting ; then throw on the machinery of tenant No. 1, and take another set, and so on until all the machinery that is driven by the engine is in motion. Each set of diagrams will show the amount of power that each tenant is using, and by adding them together, they will show the aggregate work that the engine is performing. But, on the whole, it will be found to be less than would HAND-BOOK OF LAND AND MARINE ENGINES. 245 be shown by one set of diagrams taken with all the ma- chinery on. This arises from the fact that the friction of the engine and machinery decreases as the power required decreases. Diagram No. 4 was taken from an engine in very good 21* 246 HAND-BOOK OF LAND AND MARINE ENGINES. condition. The dotted line from E to F shows the boiler pressure, and from F to G, the theoretical curve. The line P, P, is the atmospheric line. The valve opens just as the crank is passing the centre ; and at the commencement of the stroke, the pressure of steam on the piston, S, ap- proaches close to the boiler pressure ; but, as the piston quickens its motion, the pressure urging it forward gradu- ally decrease^ to the point of cut-off, R, and from R to G the actual expansion curve approaches very closely to the theoretical curve. At G, the exhaust-valve opens, and the pressure drops to 1| pounds, which is steadily maintained until the piston reaches y, when the exhaust- valve closes, and the remaining steam in the cylinder is compressed until the crank reaches the dead centre, when the valve opens and another stroke is commenced. The line from i to y is called the line of counter-pressure, while the line from 2/ to ^ is the line of compression. Diagram No. 5 was taken from an engine that thumped badly from the first time it was started up, and after every other means were resortejd to to discover the cause of the knocking, the indicator was placed on the engine, and the diagram dotted line was obtained; by this in- formation the error was discovered and corrected. The engine then worked well, and gave the diagram shown by the full line on same cut. Diagram No. 6 was taken from a high-pressure engine working at a piston speed of 80 revolutions per minute. The lost power of this engine was found to be 20 horse- power, arising from back pressure, which was caused hy a weight on the exhaust-valve, placed there for the pur- pose of forcing the exhaust through a tank and 100 feet of inch pipe. HAND-BOOK OF LAND AND MARINE ENGINES. 247 The steam-gauge com pared with the indicator was found to be correct ; and it was also found that there was a loss of^l7 pounds per square inch between the boiler and the 248 HAND-BOOK OF LAND AND MAEINE ENGINES. cylinder, in consequence of the imperfect action of the governor. m Diagram No. 7 was taken from an engine that was sup- posed to be all right, but, on applying the indicator, it was HAND-BOOK OF LAND AND MARINE ENGINES. 249 found that the steam that should have been admitted at C, was not admitted until the piston had advanced to D, more than one-eighth of the stroke; the valves were reset by the indicator, after which Diagram No. 8 was taken, which shows that it lacks very little of being perfect. 250 HAND-BOOK OF LAND AND MARINE ENGINES. Diagram No. 9 was transferred from a card, taken from a Buckeye engine. Diam. of cylinder, 10 ; stroke, 18 ; rev., 170. Steam pressure, per gauge, 84 lbs. ; initial pressure above air-line, 82 ; terminal vacuum, 18 ; main effective pressure, 30| ; clearance, 2i per cent, of stroke; cushion, 8J; water per hour, per horse-power, 19 j^^^. Diagram No. 9, FORM OF DIAGRAMS. Were all engines constructed in the best possible pro- portion of valves, steam-passages, etc., and run at the proper speed for such proportion, and were the valves and pistons always tight, the same allowance made for clearance of piston, and no condensation of steam allowed in the cylinder, general rules might be given for the shape of diagrams from condensing and non-condensing engines, for each different pressure of steam and grada- tion of expansion. Thus, if steam were admitted freely from the boiler to the cylinder of a high-pressure engine during the whole stroke of the piston, the diagram should be nearly a parallelogram ; the upper line of which would represent HAIxD-BOOK OF LAND AND MARINE ENGINES. 251 the pressure of the steam on one side of the piston, and the lower that of the exhaust steam on. the other side, and the ends of it would be described while the piston of the indicator was passing from one end of the cylinder to the other. Three of the corners of such a diagram might, as a general thing, be quite well-defined angles; but the fourth — that which is produced while the piston of the indicator is passing from the steam line to the exhaust — must be more or less curved, unless the engine was going very slow, or the ports extraordinarily large, as the con- tents of the cylinder of the engine must be discharged during the time this line is being described. Diagrams from condensing engines differ from those produced by non-condensing engines in the fact that in the latter the lower line, instead of being a little above atmospheric pressure, approaches nearly to that of perfect vacuum ; and, as the steam has to be condensed while the pencil is tracing the exhaust line, it is still more difficult, with such engines, to produce in the lines well-defined angles. There is also more or less of a curve produced at the termination of the vacuum line, owing either to the lead of the valves, or the compression of vapor as the valve approaches its seat. But nearly the whole of the area of the diagram lost from want of sharpness in the several parts, or their de- parture from right angles, except when it is the result of expansion, represents so much capacity of the engine for which there has been an expenditure of steam, and for which there has been no other consideration exchanged than the relief to the engine from the effects of the greater percussion produced by a more instantaneous charge of the force acting upon the piston. To produce a diagram with well-defined angles, it is evident that the pressure upon the piston of the engine must be changed from one side to the other, nearly or so far as tlio 252 HAND-BOOK OF LAND AND MARINE ENGINES. ♦ usual diagram would show, quite instantaneously — a usage that few large engines would be able to stand. While economy of fuel, therefore, requires well-defined angles, the stability of the engine, or economy of repairs, must direct how nearly they may be allowed to approach them. In designating the quality of vacuum formed under the piston, there are two elements affecting it which ought to be noticed, viz.: the weight of the atmosphere, and the temperature of the water in the condenser at the time the diagram was made. For if the barometer stands at only 28 inches, 30" of mercury being equivalent to 14*7 pounds, 13*7 pounds would be a perfect vacuum ; and if the water in the condenser be at a temperature of 130^, its vapor will form a resistance of 2*17 pounds ; therefore the lowest attainable vacuum would be but 13*7 — 2'17=11'53 pounds ; whereas, if the barometer stood at 31", a perfect vacuum would be 15*2 ; and if the water was but 100°, its vapor would give a resistance of only '9, and consequently the highest attainable vacuum would be 15*2 — 7=14*3 pounds, making a difference of 2*77 pounds. The vacuum shown by the indicator will generally vary from that shown by the vacuum-gauge, when it is con- structed with a glass tube, hermetically sealed at the top ; for such gauges are designed to show the variation from a perfect vacuum, without reference to the weight of the atmosphere; but the vacuum shown by the indicator is affected by all its variations. HOW TO KEEP THE INDICATOR IN ORDER. After the indicator has been used, and before putting it away, it should be taken apart and carefully cleaned and dried, to prevent injury to the springs, and to keep the dust and dirt from scratching the cylinder and piston ; and, before using it again, the cylinder and piston, and the axis HAND-BOOK OF LAND AND MARINE ENGINES. 253 22 'lunnDB/v 'Ui«9JS 254 HAND-BOOK OF LAND AND MARINE ENGINES. of the paper cylinder, should be lubricated with some clean oil. If, in the use of the indicator, the cylinder or piston should be cut or scratched, so as to interfere with the freedom of its motion, they should be delicately scraped and burnished, or ground with some nicely prepared polish- ing powder or tripoli. THE DYNAMOMETER. The dynamometer is frequently employed instead of the indicator to measure the power transmitted from the engine to the machinery. In using the dynamometer, it is necessary to have the driving-pulley or band-wheel of the engine loose on the shaft, in order that it may move around freely. It is then connected by the springs of the dyna- mometer to a clamp, bolted firmly to the shaft, so that the strain on the band-wheel will cause it to turn on the shaft and act on the springs, producing a push or pull ; consequently, for every revolution the engine makes, an amount of power will be exerted which will be repre- sented by the strain, in pounds, on the springs connecting the driving-pulley to the clamp on the shaft. This strain multiplied by the number of feet through which the mechanism passes, and this number of foot- pounds multiplied by the revolutions per minute and divided by 33,000, will show the amount of work, in horse- power, that the engine is performing. To ascertain the power exerted by the engine of a screw- vessel, the thrust of the screw is made to bear upon the fulcrum of a lever of the second class, by receiving the force near the fulcrum ; and having a long arm for the weight, the force exerted by the screw is thus decreased in a great and easily ascertained ratio, somewhat after the manner by which, in the weighing-machine, a small weight in the machine-house balances a considerable one on the platform. HAND-BOOK OF LAKD AND MARINE ENGINES. 255 Machinery very rarely transmits power uniformly from one locality to another ; which is particularly the case with the ordinary steam-engine, as the storage and delivery of work by a fly-wheel causes an irregularity in the power transmitted which can be measured by the dynamometer. But the dynamometer is best adapted for measuring the force of pulling a load on a road, a boat on a canal, or of towing a ship. The force in pounds indicated by the dynamometer, multiplied by the velocity in feet per second, will be the power in effect, which divided by 550 will give the horse-power in operation. The force driving a paddle-wheel is frequently measured by a dynamometer placed on shore, a rope being carried from the vessel and fastened to the dynamometer, when the engines are set to work, and their tractive force ascertained precisely as in the last case. The use of the dynamometer has greatly furthered the mechanical improvement of screw-engines by affording facilities to estimate the thrust of the screw, and thus ascertain if any large amount of force is being wasted. Rule joT finding the Dynamometrical or Effective Horse- power of a Marine Engine, — Having found (by the dyna- mometer) the number of pounds pressure exerted by the screw-shaft, multiply it by the speed of the ship in knots, and the product by 6080 (the number of feet in a knot) ; then divide the result by 60 (the number of minutes in an hour) and by 33,000, and the quotient will be the horse-power. Another Rule. — Multiply the number of pounds press- ure by the speed of the ship in knots, as before, and this product by '00307 ; the product will be the horse-power. 2o(j HA]S"D-BOOK OF LAND AND MARINE ENGINES. THE ENGINEER. The skilful and practical engineer is a very important man, either in a manufacturing establishment, on a loco- motive, or on a steamship. And it can be safely said, that there are as many instances of genuine worth and ability to be found among engineers as in any other trade or profession — men who from small beginnings have worked themselves up to important positions, and have, by their intelligence and capability, not only won the respect of their employers, but of all with whom they have come in contact. Unfortunately, this is not so with all, as engineers are fre- quently met with who claim to know everything mentioned to them, and that they knew all about it long ago, or that they had a hand in originating the idea themselves. There is also a great tendency among persons having charge of steam-machinery, to look upon steam as some- thing very mysterious; and this tendency is not always confined to engineers who have the immediate charge of steam-engines and steam-boilers, but among those who, from ability or some other influence, occupy higher posi- tions. Now an engineer should be sure that his views are correct before putting them forth, and he should also be modest in expressing them, especially in the presence of his superiors. He may be able to teach others in his pro- fession, but in communicating his views, he should avoid making them feel that he assumes any superior knowledge. Men of superior ability generally prefer to show by their work what they know, and if a reason is asked for this or that, they are always ready with a clear and concise answer. The opportunities in this country for young engineers to rise are equalled in no other country in the world ; for this reason they should improve every opportunity to HAND-BOOK OF LAND AND MARINE ENGINES. 257 qualify themselves for the responsible duties of their call- ing, as it is only by slow and careful study that they can arrive at the logical conclusions so essential to success in their profession. They must remember that it is not through inspiration that the expert attains more accurate results than the novice ; yet perhaps the former was once more awkward and rude in science than the latter, and only obtained his superiority and skill by close study and investigation. It frequently occurs, however, that the expert in engineering, as in all other professions, is only an expert in name. Fop this reason there is a strong prejudice in favor of those who are known to be practical men, in distinction from those who are called theoretical engineers. The practical engineer is understood to be one who relies entirely upon the information he has gained by his personal experience, while the so-called theoretical en- gineer is willing to accept the facts established by others, when they are well authenticated, and uses them to increase his knowledge. It is hardly necessary to state that of two men, each having the same natural intelligence, the one who employs his intellect, and adds the result of his studies to the knowledge that he has gained by experience, will in general be much the abler engineer of the two. It is true, that if he relies entirely upon theory untested by experiment, his views will be of little value, since that theory only is correct which takes account of all the conditions that occur in practice. The very nature of sea service calls for superior intelli- gence in those on whom depend the care and management of a ship's machinery, on account of the very serious nature of the results which may accrue from a failure of the power in an emergency. Engineers should, therefore, prepare themselves for any casualty that may arise, by consider- 22^ R 258 HAND-BOOK OF LAND AND MARINE ENGINES. ing possible cases of derangement, and deciding in what way they would act should certain accidents occur. The course to be pursued must have reference to particular engines, and no general rules can therefore be given ; but every marine engineer should decide on certain measures to be pursued in the emergencies in which he may be called upon to act, and where everything may depend upon his energy and decision. When engineers, or any other class of mechanics, fail to improve or qualify themselves to discharge the duties of their respective callings with ability and honor to them- selves, their trade is sure to degenerate, until, from being a profession or a science, it falls into the hands of incom- petents, and ceases to be anything more than a mere occu- pation. Ignorance among any class of mechanics is a great misfortune, but it is particularly so in the case of engineers. MANAGEMENT OP LAND AND MARINE ENGINES. Extensive as is the literature connected with the steam- engine, there is very little in print in relation to the prac- tical management of steam machinery. It is not difficult to discover the reason for this omission. The practical details are so varied, for the different cases that may arise, that it is almost impossible to classify them. Among the most important duties of a marine engineer are, the proper adjustment of the different parts of the machinery, and to see that they are neither too tight nor too slack, and that none of them becomes injured from heating. In the generality of marine engines, the bearing most apt to heat is the crank-pin ; but much depends on the proportions of the parts, which differ in different en- gines. But, as in most engines the crank-pin can be touched with the hand at each revolution, there can be but little excuse for allowing any serious heating at that point. HAND-BOOK OF LAND AND MARIKE ENGINES. 259 In cases of extreme heating of the crank-pin, it is tisual to slack up on the keys, and lubricate the parts in contact with a mixture of sulphur and oil, or tallow, lead filings, or quicksilver ; but it sometimes becomes necessary to cool the heated parts with cold water applied by means of a hose communicating with the deck-pumps. Such ex- treme heating rarely occurs, except when the keys are too tightly driven, or the regular supply of oil neglected. When pillow-blocks, or main bearings, become trouble- some from heating, the annoyance, in a majority of cases, can be remedied by mixing a quantity of Bath brick-dust with water, and running it through the holes in the caps when the engine is in motion, as it has a tendency to smooth off the surfaces in contact, and bring them to a solid bearing. In cases where heating of the heavy revolv- ing parts is induced by grit, or such foreign substances as are frequently found in inferior qualities of oil, the diffi- culty may be removed by using a strong solution of pot- ash, or concentrated lye, on the parts affected while they are in motion. They should be thoroughly lubricated immediately after the solution is applied. Looseness in any of the revolving parts generally manifests itself by a knock ; but the keys of the parts that only vibrate may drop out and cause serious damage, with- out giving any warning ; for this reason, when the keys are properly adjusted, the set-screws should be screwed up sufficiently tight to prevent the possibility of the key moving backward or forward. Generally speaking, keys have a tendency to work further in, which frequently causes serious heating before the engineer is aware of it. While the vessel is in port, the bonnets and casings of the steam -chest should be removed for the purpose of examining the valves, faces, and seats, and if any hard or cut places be found they should be carefully scraped and 260 HAND-BOOK OF LAND AND MARINE ENGINES. refitted. The crank should then be placed on the top and bottom centres, with the go-ahead gear in position, in order to see whether the valves open and close at the right time, or if they have the proper amount of lead. The piston should frequently be removed from the cyl- inder, and the faces of the rings, where they form the joints with the flange of the piston-head and the follower- plate, reground and fitted, and the spring packing re- adjusted. The tightness of the piston should also be proved, by admitting steam above or below it, and open- ing the indicator's cocks on either side, to see if any steam escapes ; in such cases, the injector-cocks should be slightly opened an instant, to withdraw any steam that may have collected on the opposite side of the piston, so that the passage of any steam may be more readily perceived. The tightness of most parts of the engine may be tested in this way without moving it more than half a stroke. The link-motion should next receive special attention, for the purpose of ascertaining if the link, link-block, link- pins, eccentric - straps or rods, need readjustment or re- pairs. The screw-shaft should also be carefully examined, to determine if lining-up is required, or if the gland or any part has become badly worn or seriously cut. The air-pump cover should then be lifted, and the bucket withdrawn, for the purpose of ascertaining if the foot-valves are in good order. The condenser should also be proved, which can be done by taking oflT the door or doors, and filling it with cold water ; and should any leak be discovered, the tube or tubes should be removed and repaired or replaced with new ones. Every engineer should make himself perfectly familiar and conversant with all the details of the surface condenser. The state of the vacuum will be shown by the vacuum- gauge attached to the condenser ; and if it be imperfect, HAND-BOOK OF LAKD AKD MARINE ENGINES. 261 the cause must be ascertained and the fault corrected. If the hot - well be much more than blood - warm, more injection water must be admitted ; and if the vacuum is still imperfect, there must be some air leak, which the en- gineer must endeavor to discover. Very often the fault will be found to lie in the valve or cylinder cover, which must then be screwed down more firmly, or in the faucet- joint of the eduction-pipe, the gland of which will require to be tightened, or the leaking part puttied up. The cyl- inder and valve stuffing-boxes may at the same time be supplied afresh with tallow, and the door of the con- denser examined. The joints of the parts communicating with the condenser are usually tried with a candle, the vacuum sucking in the flame if the joint be faulty. When a leakage of air into the condenser, or its con- nections, has been discovered, it may be stopped tempo- rarily by calking in spun -yarn, or driving in thin fine wedges ; if the leakage be into the condenser, it is some- times convenient to allow water to be injected through the orifice, by which means little harm is done. In several cases where, during a long voyage, the bottom of the con- denser has become leaky by corrosion, (often induced by galvanic action with the copper bolts of the ship's bot- tom, as well as the brass foot-valve, etc.,) a water-tight crank has been constructed at sea between the side keelsons. By this means, the condenser and air-pump are submerged in a kind of well constantly replenished with cold water from the sea, which, forcing its way through the leaks by the pressure of the atmosphere, shares with the proper injec- tion water the duty of condensing the steam — the injec- tion-cock orifice being partially closed in proportion to the extent of the leakage through the bottom. When the vessel is laboring in a heavy sea, the supply of injection water should be diminished; for in such cases, 262 HAND-BOOK OF LAND AND MARINE ENGINES. where the speed of the engines is subject to great and con- stant fluctuations, depending upon the greater or less sub- mersion of the wheels or screw-propeller, the condenser is liable to become choked with water, thereby causing the engines to stop. The effect of working the engines with a stinted supply of condensing water is, of course, that the condensers will become hot, and the vacuum will be dimin- ished ; but this is a minor evil in comparison with endan- gering the machinery by subjecting it to too severe a strain. Cape must be taken, when the engines make a tempo- rary stoppage, that the injection -cock or air-pump does not leak, and allow the condenser to fill with water, which causes much trouble and delay in starting the engines again ; so, should this be apprehended, the sea-cock must also be closed at the same time with the injection-cock. When a stationary engine is stopped, even for a short time, the cylinder drip-cocks should be immediately opened, in order to allow the water of condensation to escape. They should not be closed until after the engine has been started. Before starting any engine, if it has been stand- ing still for some time, the cylinder should be warmed by admitting steam, and working the engine back and forth with the starting-bar. This is a necessary precaution against the dangers arising from an accumulation of water in the cylinder induced by the steam coming in contact with the cold iron. The oil OP tallow intended to lubricate the cylinder and valves should not be admitted until after the engine has been in motion and the drip-cocks closed ; as, other- wise, instead of being returned with the exhaust, and lubricating the rubbing surfaces, a portion of it would be driven out with the water of condensation, and lost. In setting up, repairing, or driving the keys of steam- engines, a soft hammer or piece of hard wood should HAND-BOOK OF LAND AND MARINE ENGINES. 263 invariably be used to drive the parts fast together. But, in the absence of either, a piece of sheet copper or brass should be interposed between the face of the hammer and the part to be driven. Any engineer can make himself a soft hammer by cutting a hole, for the handle, through a piece of brass or copper tube about two inches in diameter and four or five inches long, and, after inserting the handle, filling the tube with Babbit-metal or lead. Raising Steam and Getting under Way. — The first duty of the engineer, preparatory to getting under way, is to fill the boilers with water to the upper gauge-cock. If they be located in the hold, it will be only neces- sary to open the blow-cock, and the water will flow into the boilers through the bottom of the vessel, otherwise it will be necessary to fill them by the hand force-pump ; although donkey-pumps having separate boilers are most frequently used for that purpose. The next step is to start the fires, which should be allowed to burn slowly, in order that all parts of the boiler may expand uniformly, and the safety-valve be kept open for the purpose of allowing the air to escape from the boilers. As soon, however, as steam begins to escape through the safety-valves, they should be immedi- ately closed, for then the air is all expelled, an atmosphere of steam having taken its place. When the steam-gauge shows any excess of pressure over the atmosphere, the valves may be raised, and steam allowed to flow into the cylinder and through all the pipes ; this expels the air and warms the cylinder, and prevents the condensation of steam when the engine is started. When sufficient steam is shown by the gauge to work the air-pump and produce a vacuum, say 6 or 6 pounds, the injection-cocks should be opened a little, and the ec- centric-hook unshipped, and the valves moved back and 264 HAND-BOOK OF LAND AND MARINE ENGINES. forth with the starting-bar or the link, as the case may be, in order to produce a reciprocating motion in the piston. The engine should then be " turned over " two or three times for the purpose of seeing if everything is all right. If everything is found to be in perfect order, the engine is stopped, the oil-cups filled, and all the rubbing and revolving surfaces thoroughly lubricated ; then the vessel will be ready to proceed on her voyage. When it becomes necessary to stop the engine, the steam is first shut oif, or nearly so ; the supply of injection water diminished, the eccentric-catch unhooked, and the valves worked by hand ; the damper in the chimney should also be closed, and the furnace-doors opened. To back an engine, where only one eccentric is used, the steam is first shut ofi*, the eccentric-hook thrown out of gear, and steam admitted to the opposite end of the cylinder by means of the starting-bar. If the link be employed, it is only necessary to shift it to the backward motion. Every ocean steamer should carry a liberal supply of duplicates of the parts that would be most likely, in case of breakage, to disable the engine. They should also have a good supply of bolts, nuts, and washers, packing- solder, charcoal, portable forges, hammers, wrenches, spanners, screw- and monkey-jacks, ratchets and ratchet- drills, cold chisels, key-sets, files, reamers, pinch-bars, straight edges, T squares, brass-sheaved blocks, and all such tools as would be likely to be called into play in any emergency, which should be hung up or stored in con- spicuous, convenient, and accessible places, for, unless this be done, they are liable to become mislaid or eaten up with rust, as neglect generally follows their stowage in unfre- quented or obscure places.* * See page vi. HAND-BOOK OF LAND AND MAEINE ENGINES. 265 HOW TO PUT THE ENGINES IN A STEAM-BOAT OR SHIP. The art of placing engines in ships is more a piece of plain common sense than any other feat in engineering ; consequently, every engineer that engages in such an un- dertaking must settle a mode of procedure for himself, as it would be impossible to give any general instructions for such work that would meet all the requirements of the varying circumstances of each individual case. But as the subject is one of great interest and importance to engineers, it may not be out of place to offer some general observations upon it, together with specific directions in such particulars as seem to require them ; the most prac- tical mode of procedure being as follows : The first business of the engineer is to ascertain the precise beam centre of the boat. He then erects perpen- dicular straight-edges towards each end of the boat, suffi- ciently far apart to clear the cylinder at one end and the shaft and crank at the other. These straight-edges must rise strictly perpendicular to the side level of the boat, be- cause they are to serve as a guide in establishing the sidewise centre lines of the cylinder, gallows frame, walking-beam, and main connecting-rod ; and, indeed, must be kept in view in the whole operation of placing the engine in the boat. The manner of placing a straight-edge in its true posi- tion is, to rest the lower end upon the centre keelson, in such position that one side of the piece forming the straight-edge shall be exactly in the beam centre of the boat. To carry up the straight-edge in strict perpendicu- lar from this centre, a straight-edge must be laid also across the boat, at the level of the deck, resting in an exact horizontal position by means of blocks placed under each end, at the sides of the boat. The exact position of 23 266 HAND-BOOK OF LAND AND MARINE ENGINES. the perpendicular straight-edge may now be ascertained, either by means of a T square or by measuring from the outside of the hull towards the centre. Having found the position of one perpendicular straight- edge by the means described, the second will of course be fixed in an exact relative position to the first. The proper height of the gallows frame, where the pillow-block rests upon it, must now be measured from the flooring of the boat upon which the engine keelsons rest. This height must always be specified in the working drawings of the engine, to which reference must be had ; and having been measured on either side, that side of the gallows frame must be cut oS* at the proper point to receive the beam pillow-block. A T square applied to the side that has thus been cut off will indicate the point of cutting off the other side of the gallows frame, bringing both sides to exactly the same height. In applying the T square for this purpose, care should be taken to keep the long or per- pendicular arm of the square in exact line with the per- pendicular straight-edges above mentioned. The beam pillow-blocks can now be placed in their positions, precaution being taken to see that these blocks are of equal dimensions from the point resting upon the gallows frame to the centre of the journal, any difference to be obviated by the variation of the height of either side of the gallows frame from the exact point heretofore reached. A beam main centre piece of wood must next be made of the same dimensions as the beam centre itself. This wooden beam main centre piece must be placed in the journals of the beam pillow-blocks. The middle of this centre piece, measured from each journal, and indi- cating the beam centre of the working-beam, must be marked upon it, either by the person turning it or by the engineer himself, usually by the former. HAND-BOOK OF LAND AND MARINE ENGINES. 267 A piece of small cord, of very perfect manufacture and very strong (catgut is generally used), must now be em- ployed, stretched from one straight-edge to the other. A short straight-edge may also be fastened, with screws, to the wooden centre piece, exactly at the middle thereof, indicating the beam centre of the working-beam. This centre line must correspond with the catgut line drawn from the two straight-edges. The wooden centre piece should be brought to rest in exact right angles to the several centre lines of the working-beam ; that is, in right angle to the horizontal, perpendicular, and beam centres of the working-beam, as heretofore ascertained and described. Having described the manner of ascertaining the various points to be considered in fixing the beam pillow- blocks in their places, the work becomes merely mechanical, and will be accomplished by such means as suggest them- selves to the engineer; which done, the beam pillow-blocks may be permanently bolted to the top of the gallows frame. The laying of the bed-plate is the next object to receive the attention of the engineer. The bed-plate is laid on two oak planks, which may easily be adjusted to accom- modate the variations in the bed-plate. The planking which lies on the engine keelson, and comes in immediate contact with the bed-plate, should be adjusted as nearly as possible to its proper position. This may be done with the use of a T square. The exact centre of the steam-cylinder must now be taken into consideration, and, keeping that point in view, the bed-plate can now be placed upon the planking prepared, as above referred to, for its reception. The centre points where the condenser and air-pump rest upon the bed-plate must now be accurately ascer- tained, and again the T square must be employed to lay the bed-plate true in every direction. This being accom- plished, a line must be stretched from the two upright straight-ed^es before described, and the air-pump and con- 268 HAND-BOOK OF LAKD AND MARINE ENGINES. denser centres must be in accordance with this line. Now fix the true perpendicular centre line of the gallows frame, and measure from that line to the centre line of the cyl- inder, as established in the working drawing. This will settle the exact position of the bed-plate. The relative positions of the beam centre, as indi- cated by the cord drawn from the two upright straight- edges, and of transverse centres of the cylinder, con- denser, and air-pump, must be indicated by marks with a chisel upon the ends and sides of the bed- plate flanges, preparatory to the removal of the cord when the condenser is placed in position. Before doing this, however, four marks on the upper and lower flanges of the condenser must be made with a chisel, at right angles to each other, corresponding w4th the centre of the condenser. This centre is ascertained by means of a wooden cross placed in the condenser, the arms of the cross fitting closely to its inside diameter. The same marks, by the same process, must also be made on the upper and lower flanges of the steam-cylinder. The condenser may now be fitted to its place, care being taken to bring the centre at the top in exact posi- tion, measuring from the centre line of the gallows frame as before,' and in accordance with the line drawn from the two straight-edges ; in other words, that the centre line of the condenser is in exact perpendicular. The work of fitting the condenser to the bed-plate must, of course, be performed upon the " chipping-strips " in the lower flange of the condenser ; and when perfected, the condenser may be permanently bolted to its place. The cylinder bottom is always bolted to the cylinder, and when thus joined, the two are placed together upon the condenser. The marks upon the outside of the flanges will assist in bringing the lower part of the cylinder to its 43xact centre point. The cylinder must now be fitted to its HAND-BOOK OF LAND AND MARINE ENGINES. 269 place, care being taken, as in the case of the condenser, to maintain the perpendicular of its centre, the same rules governing both cases. The slides fop the cross-head must next be fitted to their places. To this end, a wooden cross must be placed in the lower extremity of the cylinder, the arms fitting closely to its inside diameter. A temporary platform, near the top of the gallows frame, must now be employed, to which a cord should be stretched from the centre point of the cylinder marked on the wooden cross in the cylinder. This cord should indicate a continuation of the true per- pendicular centre line of the cylinder, for the purpose of fixing the true position of the slides. In fixing the posi- tion of the slides, a wooden piece may be employed to represent the cross-head, with a point in the centre to show where the continuation of the centre line of the cyl- inder should pass ; and when the slides are accurately set, they should be bolted to the flanges of the cylinder. A brace must now be fitted to the upper flanges of the slides, to retain them in their proper position. And braces should be extended from the slides to the gallows frame. There should also be a diagonal cross-brace connecting the flanges of the slides with the other side of the gallows frame. Four more braces, two on each side, must be extended di- rectly from the slides to the gallows frame. All these braces must be bolted to the flanges of th^e slides and to the gallows frame. The piston, with piston-rod and the cylinder cover, may now be put in their places^ and then the cross-head put in its place and fastened to the piston. The working-beam, also, may be laid in the beam pillow-block journals. The setting of the main shaft and out-port pillow- blocks is the next work in order. A cord must be ex- tended, indicating the centres of these pillow-blocks. 23* 270 HA:^rD-BOOK of land and marine engines. These centres are to be ascertained by measuring the height, on the working drawings, from the top of the floor- . ing of the hull to the centre of the shaft, then drawing a horizontal line with a cord from the straight-edge to the perpendicular centre of the gallows frame at the height of the main shaft. A line must now be drawn perpendicu- larly through the centre of the shaft, parallel, in every direction, with the centre line of the cylinder, when a T square can be employed in determining the centre line of the main shaft, to be indicated by a cord drawn from one out-port pillow-block to the other ; the actual height, as well as the distance from the centre of the gallows frame, having been, as previously stated, ascertained by measur- ing the height, in the working drawing, from the flooring of the boat, and in using the T square, to see that this line is in strict right angle to the cord drawn from the' straight edge to the centre of the gallows frame, and also in right angle to the perpendicular line parallel to the centre of the cylinder. The placing of the main and out -port pillow-blocks must now be proceeded with. The engineer must measure the distance from the centre of the journals to the lower edges of the pillow-blocks, to ascertain the exact height of the resting-places of them above the flooring of the boat, when he will cut the timbers accordingly, with a view to the exact height of the centre of the shaft, fitting these timbers to the lower sides of the pillow-blocks. The centres of the journals of the out-port pillow- blocks must always be slightlj^ higher than the centre of the journal of the main pillow-blocks, on account of the great weight of the paddle-wheels, and the fact that the sides of the boat will yield more than the centre to the weight of the engine. If the two parts of the shaft, as usually employed in river -boats, lie perfectly true, the HAND-BOOK OF LAND AND MARINE ENGINES. 271 cranks will show no variation in their distances from each other at any point in their revolution. In placing the air-pump in its seat, reference must be had to the working drawing, following the centre points, etc., as there laid down, subject, of course, to the forma- tion of the bed-plate. Mechanically, the operation is pre- cisely the same as in placing the condenser and cylinder. It is well to fasten a piece forming a straight - edge along the engine keelson, the upper or straight-edge of this piece to be in strict right angle to the perpendicular centre line of the cylinder ; with the aid of a T square, this straight- edge will supply the place of the perpendicular straight- edges before described, in case their removal should be- come necessary from any cause. The bed -plate is laid upon a mixture of white and red lead spread carefully over the oak planks which come in immediate connection with the bed-plate. The object of this mixture of paint is to fill up all the crevices or imper- fections of any character which may exist, either in the surface of the bed-plate itself or in the planking, causing the bed-plate to receive equal and substantial support in all its parts. The same process must be followed in laying the main and beam pillow-blocks ; these important parts of tne engine frequently having been broken in conse- quence of not being set firmly and accurately in their places. A layer of red lead is also employed to secure a perfectly tight joint between the condenser and bed-plate, after which a rust cement, composed of cast-iron turnings, pulverized sal-ammoniac, and flour of eulphur is calked into the joint to render it perfectly air-, steam-, and water-tight. SCREW-PROPEI.LERS. The screw- propeller, so commonly applied to the pro- pulsion of vessels, consists of two, three, or four helical 272 HAND-BOOK OF LAND AND MARINE ENGINES. or twisted blades, set upon a shaft or axis, revolving be- neath the water at the stern. The shaft where it protrudes through the stern of the vessel is surrounded by astuflSng- Screw-Propeller, HAND-BOOK OF LAND AND MARINE ENGINES. 273 box, containing hemp packing, whereby the entrance of the water into the vessel is prevented, and the extremity of the shaft in the rear of the screw is supported in a socket or bearing attached to the rudder-post. This part rests upon the keel, and from it the rudder is suspended. The screw revolves in that thin part of the stern of the ship which is called the dead wood, in which a hole of suitable dimensions is cut for its reception ;. and the thrust or forward pressure caused by the action of the screw upon the water is transmitted to some point within the vessel which can be amply lubricated. It is the thrust of the shaft which is operative in propelling the vessel, and the amount of this thrust can be measured by means of a dyn- amometer applied to the end of the shaft within the vessel. The diameter of the screw is the diameter of the circle described by the arms ; and the length of the screw is the length which the arms occupy upon the revolving shaft. If a string be wound spirally upon a cylinder, it will form a screw of one thread ; if two strings be wound upon a cylinder with equal spaces between them, they will form a screw of two threads ; three strings similarly wound will form a screw of three threads, and so of any other number. If, instead of strings, flat blades be wound edgewise around the cylinder, and each blade has one of its edges attached to the cylinder by welding, soldering, or other- wise, then, if a slice be cut off the end of the cylinder, there will be only one piece of blade attached to that slice, if the screw be of one thread ; two pieces of blade, if the screw be of two threads ; three pieces of blade, if the screw be of three threads, and so of any number. The number of blades, therefore, of any screw determines the number of threads of which it is composed, and this indication equally holds however thin the slice cut off the end of the screw may be. S 274 HAND-BOOK OF LAND AND MARINE ENGINES. The pitch of a screw is the distance measured in the direction of the axis between any one thread and the same thread at the point where it completes its next con- volution. Thus, a spiral staircase is a single-threaded screw, and the pitch of such a screw is the vertical distance from any one step to the step immediately overhead. Ordinary screw-propellers are not made nearly so long as what answers to a whole convolution ; and in speaking of their pitch, therefore, it is necessary to imagine the screw to be continued through a whole convolution at the same angle of inclination with which it was begun. Of this whole convolution any given proportion may be em- ployed as a propeller, and the length of a screw, therefore, cannot be determined from the pitch, neither can the pitch be determined from the length. The form of screw most frequently employed in this country is a screw of two blades or threads, sometimes three or four blades are used. The pitch of the screw is not made less than its diameter, sometimes nearly twice the diameter, and in some instances over twice the diameter of the screw. The length of the screw is usually made equal to one-sixth of the pitch. The thrusting of the screw is measured by the area of the circle described by the arms, which is termed the area of the screw-disk. The screw-disk has generally about one square foot of area for every 2 J or 3 square feet in the immersed trans- verse section of the vessel. NEGATIVE SLIP OP THE SCREW-PROPELLER. By " slip " is meant the difference between the actual advance of the propeller through the water and the ad- vance which would be accomplished, if there were no recession of the water produced by the pressure of the propelling surface. HAND-BOOK OF LAND AND MARINE ENGINES. 275 A screw of 10 feet, if working in a stationary nut, would advance 10 feet for every revolution it performed ; but when such a screw acts in the water, it may only ad- vance 9 feet or less for every revolution — the water being, during the same time, pressed back one foot, from its inertia being inadequate to resist the moving force. In such a casej the slip is said to be 1 foot in 10, or 10 per cent. With every kind of propeller which acts upon water, there must be a certain amount of slip, for any force, however small, will overcome the inertia of the water to a certain extent ; but, by so proportioning the propelling apparatus that it will lay bold of a large quantity of water, the backward motion of the water will be small relatively with the forward motion of the vessel ; or, in other words, the slip will be reduced to an inconsiderable amount. One of the most remarkable phenomena connected with the action of the screw is, that under some circum- stances its apparent progress through the water is not only as great as that of the ship, but greater. In some of the early experiments with the screw, when the vessel was proceeding under the joint action of steam and sails, it was found that the progress made by the vessel through the water was greater than if the screw worked in a solid nut. It was from this inferred that the ship must be over- running the screw; yet it was plain that this could not be the case, as the engine was travelling at the usual speed; but investigation of the subject explains the phenomena, and ascribes it to the fact of the screw work- ing in a column of water which follows the ship, instead of in the stationary water of the sea. When a strong current of water runs through the arches of a bridge, the water may be observed to curl 276 HAND-BOOK OF LAND AND MAHINE ENGINES. around those ends of the piers which stand lowest in the stream ; and if a chip of wood be thrown into that spot, it will not be carried off by the stream, but will remain at rest, showing that the water is not in motion in that place. Now, suppose a screw to be placed in this stationary- water, it will be obvious that any movement of rotation given to it will produce some thrust upon the screw-shaft ; whereas, if the screw were placed in the stream, it would require to revolve faster than the stream runs, before any thrust upon the screw^shaft could be produced. Now, suppose the pier to be a ship, the other circum- stances specified will not be altered thereby; and it is conceivable, that a screw acting in this dead water might aid the vessel to stem the current, even though the screw moved with less velocity than that of the current itself. That the screw will exert some peaching force upon this dead water, even with any speed of rotation, is ob- vious enough ; but whether, with a speed inferior to that of the stream, it will produce a sufficient thrust to enable the vessel to stem the current, will depend very much upon the shape of the vessel and the dimensions of the screw employed. If the pitch be fine, and the number of revolutions answering to a given speed of vessel be great, there will be a tendency to pile up the water at the stern, owing to the adhesion of the water to the rapidly revolving blades, and the consequent acquisition of a considerable centrifugal force by the water. When this action occurs, the vessel will be forced forward, to some extent, by the hydrostatic pressure produced by the elevation of the water at the stern, and this pressure will aid the thrust of the screw\ If, then, by such an arrangement, a vessel could be made to stem a current, she could obviously, under like condi- tions, be made to move through still water. HAND-BOOK OF LAND AND MARINE ENGINES. 277 All vessels carry a cftirrent in their wake which answers to the dead water in the case of the bridge ; and if a screw acts in this current, then the apparent slip will be positive or negative, just as the real slip, or the velocity of the current, may preponderate. In every case, the screw must have some slip relatively with the water in which it acts ; but if that water has itself a forward motion, the result cannot be the same as if the water were stationary, and it will be necessary to reckon the forward motion of the current as well as the forward motion of the slip. Thus, if the peal slip of the screw be three miles an hour, and the following current runs at the rate of three miles an hour after the ship, then there will appear to be no slip, if the comparison be made with the open ocean on each side of the vessel ; or' there will appear to be a negative slip, as it is termed, of one mile an hour, if the following current runs at the rate of four miles an hour. The whole perplexity vanishes, if we consider that a cur- rent follows the ship at a rate which may be greater or less than the slip of the screw. This current is confined to the water very close to the ship, so that a log, whether of the ordinary or the patent kind, will not take cognizance of it if thrown over the stern. The centrifugal action of the screw, it appears not improbable, besides piling up the water at the stern, and thus forcing the vessel on with a velocity which may be greater than that of the screw, also causes a current of water to flow radially from the centre of the screw to its circumference ; and this stream of water, by intervening between the surface of the screw and the nut of water in which it works, may assist in making the vessel travel faster than the screw itself. In all screw-vessels, the slip is greater than is generally supposed ; for in all of them there is a following current 24 278 HAND-BOOK OF LAND AND MARINE ENGINES. in which the screw works ; and as, in some cases, the cur- rent conspires to make the apparent slip to disappear alto- gether, so it will, in every case, reduce the visible slip to a less amount than the real slip, and it is the real slip w^hich it concerns us to determine. There is no benefit derived from the existence of a following current in screw ' vessels, for to produce the current requires a large ex- penditure of power; and in screws so proportioned as to produce a negative slip, a poorer performance has been obtained than in cases in which screws producing an ap- parent slip of 10 to 20 per cent, have been employed. The Screw as compared with the Paddle. — Under favorable circumstances, there is but little diiference be- tween screws and paddles. In running before the wind the paddle has the advantage ; but when the wind is ahead, it is not so, for the wind acts on the paddle-boxes, which offer great resistance and retard the ship. The superiority of the screw is shown in long voyages ; for, whereas the lightening of the ship proves detrimental to the paddle, it cannot be so to the screw, the screw being more deeply immersed. The screw requires deeper water than the pad- dle. In ships of war, the screw gives a clear broadside, while the paddles occupy room that should be devoted to the guns. The vibration of ships propelled by the screw is greater than in those using the paddle, though the latter roll more in stormy weather. Twin Screws. — Twin screws are simply two screws, one on each side of the rudder, instead of one screw in the dead wood in front of the rudder. One screw turns to the right and the other to the left. It is claimed for this arrangement, that the ship can be very quickly turned within a small space. Two-bladed screws are claimed to be more efficient than those with three or four blades, but repeated experi- HAND-BOOK OF LAND AND MARINE ENGINES. 279 ments have shown that, in point of efficiency, there is very little difference between them. . Two-bladed screws should be made with a shorter pitch than those having three or four blades. TABLE OF THE PROPER PROPORTIONS OF SCREW-PROPELLERS. Screws of Two Blades. Screws of Four Blades. Screws of Six Blades. Ratio of Fraction Ratio of Fraction Ratio of Fraction Pitch to of Pitch to of Pitch to of Diameter. Pitch. Diameter. Pitch. Diameter. Pitch. 1.006 0.454 1.342 0.454 1.677 0.794 1.069 0.428 1.425 0.428 1.771 0.749 1.135 0.402 1.513 0.402 1.891 0.703 1.205 0.378 1.607 0.378 2.009 0.661 1.279 0.355 1.705 0.355 2.131 0.621 1.357 0.334 1.810 0.334 2.262 0.585 1.450 0.313 1.933 0.313 2.416 0.548 1.560 0.294 2.080 0.294 2.600 0.515 1.682 0.275 2.243 0.275 2.804 0.481 MEASUREMENT OF THE SCREW-PROPELLER. The surface of a screw-propellep is the same as would be generated by a line revolving around ' a cylinder, through the axis of which it passes, and at the same time advancing along the axis. In this way the under or back surfaces of the blade may be supposed to be formed, and then the proper thickness is put on, so as to make the front or entering surfaces. All measurements of a blade should, of course, be made on the back surface. It will be evident, from the explan- ation of the manner in which the surface of a blade is formed, that by varying the shape of the generating line, or at the rate of its motion along the axis, very different forms of blades can be produced. The pitch of a screw is the distance the generating line moves in the direction of 280 HAJSD-BOOK OF LAND AND MARINE ENGINES. the axis while it is making one revolution around the cylinder. It is evident from this that the pitch of the screw may- be constant throughout, or it may vary from forward to after part of the blade, or from, hub to periphery, accord- ing to the rate of motion of the generatmg line in an axial direction, and its angle of inclination to the axis. Hence, in measuring a screw-propeller, it will be necessary to de- termine the pitch at a number of points, for the purpose of ascertaining whether it is variable or constant. Every point in the generating line describes a curve which is called a helix. If measurements are taken along one of these helices, they will show whether the pitch varies from forward to after part of the blade, and meas- urements on corresponding points of different helices will indicate whether or not the pitch is constant from hub to periphery. As a general thing, the hub of a screw-pro- peller is faced off at the ends, and the blades do not over- hang a plane passing through this face. If necessary, however, a faced surface can be fitted to the hub, and made thick enough for its plane to clear the blades. Provide a straight-edge a little longer than the radius of the propeller, and secure cleats to it at every foot of its length for large wheels, and from six to nine inches apart for small wheels. These cleats are intended to serv^e as guides for a rule, so that measurements can be made with accuracy at right angles to the straight-edge. Secure to the end of the hub a piece of paper on which the centre of the hub is marked, and the circumference is divided into any number of equal parts. Then place the straight-edge on the end of the hub, bringing a mark near its end to the centre of the hub, and making its direction coincide with a division of the circumference. Measure the perpendicular distance from HAND-BOOK OF LAND AND MARINE ENGINES. 281 the straight-edge to the surface of the blade at each one of the cleats ; then move the straight-edge to coincide with the next division of the circumference, and again take measurements. Suppose that the circumference of the hub be divided into thirty-two equal parts, and that the measurements from the straight-edge to the blade, taken at each cleat, are each six inches, then move the straight-edge to the next position, and suppose that the measurements are each fourteen inches. This shows that the generatrix, in one thirty-second of a revolution, has advanced eight inches in an axial direction ; consequently, the pitch is thirty-two times as much, or twenty-one feet and four inches. If measurements taken as successive divisions of the circumference give a successive increase of eight inches for each division, it shows that the propeller is a true screw with a pitch of twenty-one feet and four inches. It will be observed that the measurements made at one cleat in different positions of the straight-edge give deter- mination for the pitch at different points of the sstme helix, and therefore show whether the pitch varies from forward to after part of the blade. The measurements taken at different cleats, in successive positions of the straight-edge, show the pitch at corresponding points of different helices, and indicate whether the pitch varies from hub to peri- phery. The method here described is one of the simplest and most accurate that can be given for determining the pitch of a screw-propeller. The other measurements — the di- ameter of screw, length of blade, dimensions of hub, and fraction of pitch employed — are so simple as to need no explanation. 24* 282 HAND-BOOK OF LAND AND MARINE ENGINES. HOW TO LINE UP A PROPELLER-SHAFT. Put two straight-edges on the slides, one at each end; run a line through their centre points, and continue it be- yond the shaft. Set a T square on one of the straight- edges, making one edge of the blade cut the centre point. Then erect a perpendicular, at the centre of the shaft to the line previously run, by looking it out of wind with the edge of the T square, or arranging it so that, when viewed from a distance, it covers the edge of the T square for the whole length. Then disconnect the crank from the rod, and swing it on the centre and half-centre, and measure the distances on its face and the two lines. If they vary at different points, the shaft is not in line, and must be ad- justed until the distances are the same from all points of the revolution. Radial Wheel. PADDLE-WHEELS. Paddle-wheels consist of two large wheels moving on the end of the engine-shaft. They are made by attaching arms to the centres on the shaft and to two large rings, on HAND-BOOK OF LAND AND MARINE ENGINES. 283 which are bolted the paddles or floats. As they are turned round, the resistance offered to them by the water causes the vessel to move, acting precisely on the same principle as a boat-oar ; by them the inertia of the water is made a means of locomotion. In using this appliance as a motive-power, its advan- tage greatly depends upon the amount of immersion. When the water approaches the centre, or reaches above, it is obvious the greatest waste of power will ensue. It is quite as obvious that the greater the diameter of the wheel the greater the leverage, and the greater is the effect obtained. There are various kinds of paddle-wheels, such as the ordinary radial, the cycloidal, and the feathering. The Ordinary Radial Wheel. — This wheel has the floats fixed on the radial arms. In this arrangement the floats enter the water with the whole of their faces pre- sented to it; the same action takes place as they come out. From this arises a great loss of power, for they should evidently offer the greatest resistance to the water when at their lowest point, and none when entering or leaving. From this cause, and the yielding of the water, the ship does not move as fast as the wheel. The loss is called slip, and is generally allowed to be from 10 to 20 per cent. Cycloidal Wheels. — To obviate the difficulties and dis- advantages of the ordinary radial wheel, the cycloidal was advocated. Its peculiarity consists in dividing the float into two strips longitudinally. The strip farthest from the centre is behind the radius, and the other in front of it. The intention of this arrangement is, that the floats may meet the water with more uniformity. It is a very good form of wheel for large vessels. In order that the floats may enter and leave the water with the least possi- ble resistance, they should enter in a tangential direction 284 HAND-BOOK OF LAND AND MARINE ENGINES* to the curve which is being described by any point in the wheel. This is what is known as the cycloidal curve. Feathering Wheel. The Feathering Wheel. — In the feathering wheel the floats are governed by mechanism, which causes them to enter and leave the water in a position perpendicular to the direction of their motion. By this arrangement they offer the greatest resistance at the lowest point ; the floats are in fact at right angles to the surface of the water when immersed. In the feathering wheel, as each float is always perpen- dicular to the water, they progress with the same horizon- tal velocity, therefore the point of maximum resistance or centre of pressure must be in a line passing longitudinally along the centre of the float. But in the radial wheel this cannot be the case, for the outside edge of the float moves much faster than the inside ; the point where these two average each other is taken at a distance of one-third the depth of the board from the outer edge. Although the feathering wheel produces more useful HAND-BOOK OF LAND AND MARINE ENGINES. 285 effect with the same application of power than the radial wheel, there are many practical objections to its use, the most prominent of which are, the increased first cost, the excessive weight, and the frequent overhauling that they require. The Manley Paddle-Wheel. — This wheel has only five or six floats, each of which is secured to a rock-shaft, to which a crank is attached. The feathering mechanism is a frame eccentric to the main shaft, connected with each of the cranks by an arm. Each float is secured to the rock-shaft below the centre, so as to divide the pressure on the float equally between the feathering mechanism and the adjacent side frame of the wheel. It is the first machine for marine propulsion which, by its action' and application of power, has imitated the Indian's paddle, and has conformed to the first great principle necessary to be observed in propelling a vessel through the water, by obtaining the proper resistance for the power upon the water. Manley Paddle-Wheel. 286 HAND-BOOK OF LAND AND MARINE ENGINES. This wheel does for the steam-ship what the Indian's paddle does for his boat, and even in greater perfection. It drops a paddle into undisturbed water, forces it back- ward or forward, as the case may be, in a direction exactly- perpendicular to the line of flotation, and, as it is being withdrawn from the water, another paddle is entering far ahead and grasping resistance entirely unused by the pre- ceding paddle. The operation is certain and constant while the power is applied. Immersion of Paddles. — The great difiiculty with paddle-wheels is to secure a proper immersion. As the ship proceeds on its voyage and consumes its store of coal, the vessel becomes lighter, and, consequently, its draught of water decreases. Therefore, supposing a paddle is properly immersed at the commencement of a voyage, it will be nearly out of the water at the end. At the com- mencement of a voyage the paddle must be too deeply immersed, at the middle the proper immersion will per- haps be attained, while there will be too little towards the end of the voyage. Disconnecting Paddle- Wheels. — In some instances, when the wind is fair and the ship is under canvas, the paddle-wheels are disconnected from the engine, and allowed to revolve on their bearings. Several contriv- ances, which it is unnecessary to mention here, have been introduced to accomplish this object. The paddle-shafty where it passes through the vessel's side, is usually surrounded with a lead stuffing-box, which will yield if the end of the shaft falls. This stufiing-box prevents leakage into the ship from the paddle-wheels ; but it is expedient, as a further precaution, to have a small tank on the ship's side a little below the stufiing-box, with a pipe leading down to the bilge, to catch and conduct away any water that may enter. HAND-BOOK OF LAND AND MARINE ENGINES. 287 FLUID RESISTANCE. The scientific investigation of bodies in moving through a fluid is still involved in much obscurity, from the want of independent research on the part of the various authors who have undertaken the elucidation of the subject ; and the mistakes incidental to the researches of Newton, and other eminent philosophers, have overrun various depart- ments of physical science, and are now found most difficult of eradication. The circumstances in connection make it expedient to investigate the matter in a practical way, and to illustrate a few of the leading principles of mechanics which relate to this question. Mechanical power is pressure acting through space; and the amount of mechanical power developed by any combination is measurable by the amount of the pressure multiplied by the amount of space through which the pressure acts. A pressure of 10 pounds acting through a space of 1 foot represents the same amount of mechanical power as a pressure of 1 pound acting through a space of 10 feet ; and 10 pounds gravitating through 1 foot, or 1 pound gravitating through 10 feet, represent ten times the amount of mechanical power due to the gravitation of 1 pound through 1 foot. In the same way, 1000 pounds gravitating through 1 foot is equivalent to 1 pound gravitating through 1000 feet, and, in general terms, the weight or pressure multi- plied by the space through which it acts represents the power universally. If, therefore, a body falls freely through space by the operation of gravity, since it parts with none of its power during its descent, the whole power must be accumulated in the falling body in the shape of momentum; and, at the instant of reaching the ground, the body must have such an amount of mechanical power 288 HAND-BOOK OF LAND AND MARINE ENGINES. stored up in it, as would suffice to carry it up again to the position from which it fell, if the power were directed to the accomplishment of that object. The amount of mechanical power, therefore, in any moving body, is measurable by the weight of the body multiplied by the space through which it must have fallen by gravity, to acquire the velocity it possesses ; and this fundamental law, if distinctly apprehended, and kept con- stantly in recollection, will insure exemption from the fallacies which prevail so generally among authors in ref- erence to such subjects. In Newton's " Second Law of Motion," it is» maintained that "the change or alteration of motion, produced in a body by the action of any external force, is always proportional to that force," from whence it is inferred, that to produce twice the quantity of motion in a body, will require just twice the power; and this is the doctrine maintained by Kobinson in his " Mechanical Philosophy," and by Hutton, Gregory, and most other English authors who have undertaken to illus- trate such questions. Nevertheless, there is no doubt whatever that this doc- trine, is altogether erroneous, as was shown by Leibnitz at the time of its promulgation, and subsequently by Smea- ton, who, by a series of carefully executed experiments, proved very clearly that, to double the velocity of a moving body, it required four times the amount of mechanical power that was necessary to put it into motion at first ; and consequently, that the momentum of moving bodies of the same weight varies as the squares of their respective velocities. ^ The soundness of this conclusion is made manifest by a reference to the law of falling bodies, by which it will be found that it is necessary a body should fall through four times the height to double its ultimate speed ; nine HAND-BOOK OF LAND AND MARINE ENGINES. 289 times the height, to treble its ultimate speed, and so on ; showing that the height, and therefore the power exerted in creating the motion, must be as the square of the ulti- mate speed ; and consequently, that the ultimate velocities of all falling bodies will be as the square roots of the heights from which they have respectively descended. In the case of two bodies of equal weight, therefore, moving in space, but of which one moves with twice the velocity of the other, the faster will have four times the amount of mechanical power stored up in it that is possessed by the slower ; for it must have fallen from four times the height, to acquire its doubled velocity ; and the relative quantities of powier capable of being exerted by bodies of the same weight are measurable in all cases by the spaces through which the weight or pressure acts. A cannon-ball moving with a velocity of 2000 feet a second, has four times the momentum of a cannon-ball of equal weight movj^ng with a velocity of 1000 feet a second ; and every particle of a stream of water moving with a velocity of 10 miles an hour has four times the momentum of every particle of a stream of water with a velocity of five miles an hour. Every particle of the faster stream, therefore, will exert four times the efiect in impelling any body on which it impinges, that is exerted by every particle of the slower stream. But in the faster stream not only will every particle impinge with four times the force, but there will be twice the number of particles impinging in a given time, and a quadrupled force for each particle ; and twice the number of particles striking in a given time gives an effect eight times greater, in a given time, with a doubled velocity of the stream. Accordingly, it is found that in a water- or wind-mill, when the velocity of the current is doubled, the power ex- erted is about eight times greater than before ; and it is 25 T 290 HAND-BOOK OF LAND AND MARINE ENGINES. also found that a steam-vessel, to realize a double velocity, requires about eight times the amount of power. But these results, it is obvious, have reference, not merely to the in- creased velocity of the particles of matter, but to the large number of them brought into operation ; and any given quantity of water, if flowing with a doubled velocity, would only exert four times the power exerted before. In the same manner, a steam-vessel, to accomplish any given voyage in half the time, would require four times the quantity of coal previously consumed ; for although eight times the quantity of coal would be consumed per hour, yet only half the number of hours would be occupied in accomplishing the distance. The number of particles of water to be displaced by a vessel in performing any given voyage is the same, what- ever the velocity of the vessel may be ; but the number of particles displaced in the hour differs with every dif- ferent velocity, and the power expended must consequently vary in a corresponding proportion. It may, hence, be asserted generally, that the power or dimension of an engine necessary to propel a vessel increases nearly as the cube of the velocity required to be attained ; but the consumption of fuel will only increase in about the ratio of the square of the velocity, looking to the number of miles of distance actually performed by a steamship. In order to be able to calculate the absolute amount of power required to produce a given effect, it is necessary to be acquainted with the laws which govern the resistance of fluids to the motion of solid bodies in them, which are generally admitted to be based on the following theorem. If a plain surface move at a given velocity through a fluid at rest, in a direction perpendicular to itself, the re- sistance is proportional to the density of the fluid, and to the square of the velocity of the plane. HAND-BOOK OF LAND AND MARINE ENGINES. 291 SIGNIFICATION OF SIGNS USED IN CALCULATIONS. = signifies Equality, • as 3 added to 2 = 5. + " Addition, "4 + 2 = 6. — " Subtraction, " 7 — 4 = 3. X " Multiplication, " 6 X 2 = 12. -T- " Division, " 16 ~- 4 = 4. I 11 I Proportion, " 2 is to 3, so is 4 to 6. s/ " Square Root, " n/ = 4. y/ " Cube Root, " 4^64 = 4. 32 u 3 is to be squared, " 3^ = 9. 33 « 3 is to be cubed, " 3^ = 27. 2 + 5x4= 28^signifie3 that two, three, or more num- bers are to be taken together, as 2 + 5 = 7, and 4 times 7 = 28. V5' — 3^ = 4 signifies that 3 squared taken from 5 squared. and the square root extracted = 4. v'lO X 6 = 1*587 signifies that where 10 is multiplied by 15 6 and divided by ^15, the cube root of the quotient = 1*587. DECIMAL. Decimal Apithmetic is of Hindoo origin, and was introduced into Arabia about one thousand years ago, from whence it spread throughout Europe and the entire civilized world. The base, 10, originated from the ten fingers, which were used for counting before characters were formed to denote numbers. The base, 10, admits of only one binary division, which gives the prime number 5 without fraction. The trinary divisions give an endless number of decimals. Decimal Fractions are fractions in which the denomina- tor is a unit or 1 with ciphers annexed, in which case 292 HAND-BOOK OF LAND AND MARINE ENGINES. they are commonly expressed by writing the numerator only with a point before it, by which it is separated from whole numbers ; thus, '5, which denotes five-tenths, j% ; •25, that is, j%%. DECIMAL EQUIVALENTS OF INCHES, FEET, AND YAKDS. Fractions of an Inch. I ■ 1 inch- Decimals of an Inch. •0625 : •125 •1875 : •25 •3125 : •375 •4375 : •5 •5625 : •625 •6875 : •75 •8125 : •875 •9375 : 1-00 Decimals of a Foot. •00521 •01041 •01562 •02083 •02604 •03125 •03645 •04166 •04688 •05208 •05729 •06250 •06771 •07291 •07812 •08333 Inch. Feet. Yards. 1 = -0833 = ■0277 2 = •1666 = •0555 3 = •25 = •0833 4 = •3333 =z •nil 5 = •4166 = •1389 6 = •5 = •1666 7 = •5833 — •1944 8 = •6666 =• •2222 9 = •75 = •25 10 = •8333 — •2778 11 = •9166 = •3055 12 :rrr 1-000 = •3333 DECIMAL EQUIVALENTS OF POUNDS AND OUNCES. Oz. i 1* 2i Lbs. •015625 •03125 •046875 •0625 •09375 •125 •15625 Oz. Lbs. 3 ^1875 31 -21875 4 -25 41 -28125 5 ^3125 51 ^34375 6 -373 Oz. Lbs. 61 ^40625 7 71 -4375 •46875 8^ -5 81 ^53125 •5625 •59375 Oz. Lbs. . 10 •625 lOi •65625 11 •6875 ^H •71876 12 •75 12i •78125 13 •8125 Oz. Lbs. m -84375 u •875 ^H •90625 15 •9375 15J •96875 16 I- USEFUL NUMBEKS IN CALCULATING WEIGHTS AND MEASUKES, ETC. Feet multiplied by .00019 equals miles. Yards ' ** -0006 ** miles. Links " -22 « yards. HAND-BOOK OF LAND AND MARINE ENGINES. 293 Links multiplied by -66 e qual .8 feet. Feet (( 1-5 <( links. Square inches (( •007 (( square feet. Circular inches ^ 3 's ^ S'^ P> Si^ td o ^s 03 2 S u rj CS fin a 44.69 25 21.62 25 23.80 25 22.43 25 32.36 25 25 27.00 25 24.63 23 25.25 25 19.04 23 18.68 23 §1 S'2 <^ o 4496 3821 3254 3254 3236 2700 2463 2333 1904 1868 1.00 0.81 0.71 0.69 0.65 0.57 0.54 0.52 0.43 0.42 TABLE SHOWING THE RELATIVE PROPERTIES OF GOOD COKE, COAL, AND WOOD. Name of Fuel. "o a u 3 o SI 1 1 xi o u bo .2 d 1 « O ft O CD Si o « r O A 11 li a a IP Is o fi 2 ill |g.S '3 o §1 Coke 63 80 30 4300 4000 2800 95 88 20 80 44 107 28 51 21 22.4 32.0 16 13 10 60 8i 6 ^ 100 71 29 Coal Wood HAND-BOOK OF LAISTD AND MARINE ENGINES. 345 TABLE OF TEMPERATURES REQUIRED FOR THE IGNITION OF DIFFERENT COMBUSTIBLE SUBSTANCES. Substances. Temperature of Ignition. Remarks. Phosphorus 140° Melts at 110^. Bisulphide of carbon vapor 300° 374° Melts at 130°. Used in percussion caps. Fulminating Powder Fulminate of Mercury ... 392° According to Legue and Champion. Equal parts of chlorate of potash and sulphur. 395° Sulphur 400° Melts, 280^; boils, 850°. Gun-cotton 428° According to Legue and Champion. Nitro-glycerine 494° a a a Rifl,e-powder 550° 563° (( (( (< a (t ti Gunpowder, coarse Picrate of mercury, lead or iron 565° H (( kl Picrate powder for tor- pedoes 570° a a a Picrate powder for mus- kets 576° (( It n Charcoal, the most in- flammable willow used for gunpowder 580° According to Pelouse and Fremy. Charcoal made by distill- ing wood at 500° 660° (( (( (( Charcoal made at 600°.... 700° i( (( n iPicrate powder for can- non 716° 800° Very dry wood, pine ** *' *' oak 900° Charcoal made at 800°.... 900° It will be seen by the above table that the most com- bustible substances generally considered very dangerous, will only ignite by heat alone at a high temperature, so that for their prompt ignition it requires the actual contact of a spark. 346 HAND-BOOK OF LAND AND MARINE ENGINES. GASES. All substances, whether animal, vegetable, or mineral, consisting of carbon, hydrogen, and oxygen, when exposed to a red heat, produce various inflammable elastic fluids, capable of furnishing artificial light. We perceive the evolution of this elastic fluid during the combustion of coal in a common fire. Bituminous coal, when heated to a certain degree, swells and kindles, and frequently emits remarkably bright streams of flame, and after a certain period these appear- ances cease, and the coal glows with a red light. The flame produced from coal, oil, wax, tallow, or other bodies which are composed of carbon and hydrogen, pro- ceeds from the production of carburetted hydrogen gas, evolved froM the combustible body when in an ignited state. If coal, instead of being burnt in the way now stated, is submitted to a temperature of ignition in close vessels, all its immediate constituent parts may be collected. The bituminous part is distilled over in the form of coal-tar, etc., and a large quantity of an aqueous fluid is disengaged at the same time, mixed with a portion of essential oil and various ammoniacal salts. A large quantity of carburetted hydrogen, carbonic oxide, carbonic acid, and sulphuretted hydrogen also make their appearance, together with small quantities of cyan- ogen, nitrogen, and free hydrogen ; and the fixed base of the coal alone remains behind in the distillatory apparatus in the form of a carbonaceous substance called coke. An analysis of coal is thus ,efiected by the process of destructive distillation. Hydrogen. — Hydrogen is the lightest of all known gases, its specific gravity being only 0*06896. This gas is colorless, and, when perfectly pure, inodorous. It has a HAND-BOOK OF LAND AND MARINE ENGINES. 347 powerful affinity for oxygen, and is therefore eminently combustible. Intense heat is developed by the combus- tion of hydrogen in oxygen gas, and but little light. Carbon. — Carbon is well known under the form of coke, charcoal, lamp-black, etc. It is one of the principal constituents of all varieties of coal, and is the basis of the illuminating gases. It is a colorless and inodorous gas, rather lighter than common air, having a specific gravity of 0*9727, is sparingly absorbed by water, and does not precipitate lime-water. It is inflammable, burning with a beautiful blue flame ; the product of its combustion is car- bonic acid. Carbon unites with hydrogen in many proportions, and many of these compounds are produced during the dis- tillation of coal ; but the only two of importance are car- buretted hydrogen and defiant gas. Carburetted Hydrogen. — Carburetted hydrogen is abundantly formed in nature, in stagnant pools, ditches, etc., wherever vegetables are undergoing the process of putrefaction ; it also forms the greater part of the gas ob- tained from coal. Carburetted hydrogen consists of 100 volumes of vapor of carbon, and 200 of hydrogen. It is colorless and almost inodorous ; it is not dissolved to any extent by water, and is much lighter than atmospheric air, its density being 0*5594. It is very inflammable, burning with a strong yellow flame. The products of its combustion are carbonic acid and water. Carburetted hydrogen, or coal-gas, when freed from the obnoxious foreign gases, may be propelled in streams out of smair apertures, which, when lighted, form jets of flame, which are called gas-lights. defiant Gas. — defiant gas is a product of the distilla- tion of oil, resin, and also of coal, when the process is well conducted. It is colorless, tasteless, and without smell 348 HAND-BOOK OF LAND AND MARINE ENGINES. when pure. Water dissolves about one-eighth of its ^ulk of this gas. It is formed of two volumes of hydrogen, and two of the vapor of carbon condensed into one volume. Olefiant gas burns with an intense white light, and requires a larger portion of oxygen for its combustion, one volume of the gas requiring not less than three volumes of pure oxygen, or fifteen volumes of atmospheric air for decomposition. The products of the combustion are water and carbonic acid. Nitrogen. — Nitrogen is one of the constituents of coal. It has the properties of extinguishing burning bodies, and is not absorbed by water ; its specific gravity is 0.9760, being lighter than common air, in which it forms a con- stituent part. Liquefaction of Gases. — Many of the gases have already been brought into the liquid state by the conjoint agency of cold and compression, and all of them are probably sus- ceptible of a similar reduction by the use of means suffi- ciently powerful for the required end. They must consequently be regarded as the superheated steams or vapors of the liquids into which they are com- pressed. Comppession and Dilatation of Gases. — When a gas or vapor is compressed into half its original bulk, its press- ure is double ; when compressed into a third of its original bulk, its pressure is treble ; when compressed into a fourth of its original bulk, its pressure is quadrupled ; and gen- erally the pressure varies inversely as the bulk into which the gas is compressed. So in like manner if the volume be doubled, the press- ure is made one-half of what it was before — the pressure being in every case reckoned from 0, or from a perfect vacuum. Thus, if we take the average pressure of the atmosphere HAND-BOOK OF LAND AND MARINE ENGINES. 349 at 14*7 pounds on the square inch, a cubic foot of air, if suffered to expand into twice its bulk by being placed in a vacuum measuring two cubic feet, will have a pressure of 7 '35 pounds above a perfect vacuum, and also of 7*35 pounds below the atmospheric pressure ; whereas, if the cubic foot be compressed into a space of half a cubic foot, the pressure will become 29*4 pounds above a perfect vac- uum, and 14*7 pounds above the atmospheric pressure. The specific gravity of any one gas to that of another will not exactly conform to the same ratio under different degrees of heat, and other pressures of the atmosphere. Water, as before stated, is composed of two gases, oxy- gen and hydrogen — the weight of a cubic foot of hydrogen being '005592 pounds, and of half a cubic foot of oxygen '0044628 pounds avoirdupois. One cubic foot of hydro- gen and half a cubic foot of oxygen combined form one cubic foot of steam. One cubic foot of steam, therefore, which results from the union of these gases, must weigh •05022 pounds. A Gang of Steam-Boilers. 30 850 HAND-BOOK OF LAND AND MARINE ENGINES. STEAM-BOILERS. Since the introduction of steam as a motive power, a great variety of boilers have been designed, tried, and abandoned ; while many others, having little or no merit as steam generators, have their advocates, and are still con- tinued in use. Under such circumstances, it is not sur- prising that quite a variety of opinions are held on the subject. This difference of opinion relates not only to the form of boilers best adapted to supply the greatest quan- tity of steam with the least expenditure of fuel, but also to the dimensions or capacity suitable for an engine of a given number of horse-power ; the mere arithmetic of the question remaining up to this day unsettled. In designing a steam-boiler, there are many important points to be considered, such as cost, proper materials, strength to bear the intended pressure, quantity of steam to be furnished in a given time, space occupied, weight, circulation of water, water room, facilities for cleaning and repairing, steam room, heating and grate surface, area through flues, etc. The three most important objects to be attained in the design, construction, and use of steam-boilers are, "safety," " durability," and " economy." To insure " safety," it is necessary that the boiler should be designed in accordance with true mechanical principles, avoiding as much as pos- sible ther evils of unnatural strains and unequal expansion and contraction ; due regard must also be paid to the quality of the material and character of the workmanship employed in its construction. We have no data by which to establish the general " du- rability " of any class of steam-boilers, but experience has shown, in all individual cases, that the durability of a steam- boiler depends on the quality of the material and the character of the workmanship used in its construction, the facilities afforded for cleaning, repairing, and renewal of HAND-BOOK OF LAKD AND MARINE ENGINES. 351 any of its parts, and also the care and management after being put in use. "Economy" in the generation of steam depends to a certain extent on the character or quality of the metal of which the boiler is made ; as it is a well known fact, that the thicker the iron, and the poorer its conducting qualities, the greater will be the loss of heat ; when by using a superior quality of iron, one whose tensile strength and conducting powers are both very great, we lessen the resistance to the passage of the heat from the furnace to the water and greatly increase the economy of the boiler. Cylinder Boiler. It is also well known to engineers that some qualities of iron are two and a half times stronger than others ; con- sequently, if a boiler be made of the poorer iron, that would be as strong as J inch of the best iron, it would be necessary to use plates I of an inch thick. Even then the heavy boiler would be weaker than the light one, from the fact that the heavy plates would sustain greater injury in the making. In point of economy and durability, the light boiler would be far superior to the heavy one. Cylinder Boilers. — The plain cylinder boiler, one of the earliest forms of steam-generators, and, until quite recently, the one most extensively used, is fast passing out of use, particularly in localities where space is limited and fuel expensive. Its advantages were its lightness and moder- 352 HAND-BOOK OF LAND AND MARINE ENGINES. ate first cost, and that it afforded better facilities for clean- ing, repairing, or the renewal of any of its parts than any Other type of boiler. It also possessed peculiar advan- tages for rolling-mill and blast-furnace purposes, as it re- quired less care, and was least dangerous on account of the great body of water it contained. Its disadvantages were its extreme length and wastefulness of fuel. Flue Boiler, Flue Boilers. — The advantages of this type of boilers over the former are, that it occupies less space, requires less fuel, and steams better in consequence of its extra heating surface. Like the cylinder, it is a favorite for roll- ing-mill and blast-furnace purposes, as it affords facilities for return draught ; but it has the disadvantages of extra weight, consequently, increased first cost, and that it is more difBcult to clean or repair. It also requires more care on account of the liability of the fliues to become overheated and collapse in case the regular supply of water should be neglected. Tubular Boiler. — This type of boiler possesses many advantages, in an economical point of view, over either the cylinder or flue, as it occupies less space, requires less fuel to evaporate a certain quantity of water in a given time, and, in consequence of the small diameter of the tubes, its lia- bility to collapse is entirely obviated. But it has the dis- advantage of requiring more care than either of the former, HAND-BOOK OF LAND AND MARINE ENGINES. 353 and is almost impossible to clean or repair. The double- deck boiler, a combination of the cylinder and tubular, is a very safe and economical type of boiler, as it occupies less floor space than either the cylinder, flue, or single tubular. It also presents an immense amount of heating surface, and, in consequence of the great body of water it ^contains, obviates the danger of the water becoming low, excepting in cases of extreme neglect. Tubular Boiler. Locomotive Boilers. — This kind of boiler, though not in very general use for stationary purposes, when well pro- portioned for its work, is very economical, as it occupies but little space, presents an immense amount of heating surface, steams very rapidly, and, when well constructed, is compact and powerful. Its great disadvantages arise from the complication of its parts, which makes it ex- tremely difiicult to clean or repair, consequently, it is liable to burn out; besides, as the water space is limited, it requires special care and attention. STEAM-DOMES. The advantages claimed to be derived from the steam- dome are, that it acts as a steam reservoir, and also an anti-primer, in consequence of being further removed from the water than any other part of the boiler, ♦hich is true 30^ X 354 HAND-BOOK OF LAND AND MARINE ENGINES. to a certain extent ; but as regards its advantages as a steam reservoir, it can easily be shown that an ordinary sized steam-dome adds very little to the steam room of a boiler. Fop instance, a boiler 48 inches in diameter and 20 feet long would contain 251 cubic feet of space ; if we take | of that as water space, we will have left about 63 cubic feet for steam room. Now suppose we take a steam-dome 24 inches in diameter and 2 feet high, we gain only 6 cubic feet of steam room, or about enough of steam to fill the cylinder of an engine 12 inches in diameter and 24 inch stroke, and about 5 times, even if worked expan- sively. Now, with respect to its advantages as an anti-primer, it appears to be taken for granted that the higher the point at which the steam is taken from the boiler, the drier it is likely to be ; but the cooling effect on the steam, by domes of large diameter exposed to the atmosphere, seems to be entirely lost sight of, as it is a well-known fact that, when an engine is at work, the steam rushes into and through the dome with great velocity, and in its pass- age is liable not only to take with it a great quantity of water, but have its temperature lowered by coming in contact with so much surface exposed to the action of the atmosphere. It frequently happens that the steam taken from a dome is more wet than that in any other part of the boiler. The pesepvoir of powep in a boilep is not so much in the steam as in the heated water. With a working press- ure of 60 pounds, each cubic foot of steam in the boiler will produce only 4*65 cubic feet of steam at atmospheric pressure ; but 1 cubic foot of water in the boiler will pro- duce nearly 35 times that amount, for at 60 pounds press- ure the temperature of the water is 307*5°, or 95*5° above the boiling-point at atmospheric pressure ; and, as every HAND-BOOK OF LAND AND MAKINE ENGINES. oOO degree of heat added to water already at 212° may be taken as competent to generate 1*7 cubic feet of steam, 95*5° will produce 162*35° cubic feet, or nearly 36 times as much as 1 cubic foot of steam at 60 pounds pressure. It will be seen from the above, that, notwithstanding the general opinion that the presence of a steam-dome is essential for obtaining dry steam and as a remedy for priming, it should be regarded as not only a useless and expensive appendage to a boiler, but a source of real weakness and danger ; the practice of cutting a dome-hole in the shell of a boiler, without providing for the weaken- ing of the plate by some other means, should be looked upon as a very mischievous and dangerous practice. When it becomes necessary to have a dome, as in case of limited steam room, or where the arrangement of the tubes or flues is such as to make it necessary to carry the ' water high in the boiler, the hole in the plate under the dome should not be cut larger than sufficient to allow a free escape of the steam from the boiler to the dome, or to admit of a convenient adjustment of the dome-braces. MUD-DRUMS. When we consider the short life of the mud-drum, which rarely exceeds six or seven years, and also the ex- pense of removing it and replacing it with a new one, its use in any case becomes a question of doubtful economy. Steam users and engineers for a long time entertained the belief that mud-drums were beneficial, inasmuch as they imparted extra heat to the feed-water, and retained the mud that would otherwise have been carried iuto the boiler. Experience, however, has shown this to be a grave error, as mud^drums impart very little heat to the feed- water, and retain nothing but the earthy matter which is held in suspension in the water, while all the destructive 356 HAND-BOOK OF LAND AND MARINE ENGINES. carbonates that are held in solution are carried into the boiler. A good deal has been said and written, and many theories advanced, to account for the pitting, or honey- combing, of mud-drums, but the mysterious manner in Mud-DrumSi which it occurs, and its peculiar character, have not as yet been fully explained, as scientific men are still unable to assign even a plausible cause. But the most probable cause for this singular pitting or rotting away might be assigned to the location of the drum, as it receives nearly all the heat imparted to it on the upper side, with not enough on the lower side to keep the iron perfectly dry and prevent the rusting away of the plates and rivet- heads. SETTING BOILERS. In " setting " or *' putting in " boilers, as it is sometimes called, all the surface possible should be exposed to the ac- tion of the heat of the fire,-^not only that the heat may be thus more completely absorbed, but that a more equal ex- pansion and contraction of the structure may be obtained. And in cases where convenience serves, it will be found ad- vantageous to return the draught through a brick flue over the top of the boiler, in order to equalize the heat and, consequently, the expansion ; and although this arrange- HAND-BOOK OF LAi^TD AND MARINE ENGINES. 357 ment does not facilitate the generation of steam, yet fuel will be saved by a more complete application of the heat, and the prevention of radiation from the upper part of the boiler. Convenient openings should be arranged in the brick- work to facilitate the cleaning of the boiler on the outside, as that part of the shell exposed to the action of the draught is liable to become permanently coated with soot and ashes, rendering a great portion of the heating surface nearly worthless ; the dijflaculty experienced in removing these non-conductors from the under side of the boiler generally arises from an improper arrangement at the time of set- ting, and a want of space. Boilers should be set with as little brickwork in con- tact with the shell as practicable. No mortar should be used where it can come in contact with the plates, but fire-clay should be used instead for the whole setting of the boiler. Long Boilers are often hung by means of loops riveted to the top of the boiler, and connected to cross-beams and. arches, resting on masonry above the boiler, by means of hangers. This is a very mischievous arrangement, unless turn-buckles, or some other contrivance, are used to main- tain a regular strain on all the hangers, as long boilers ex- posed to an excessive heat are apt to lengthen on the lower side and relieve the end hangers of any weight ; con- sequently, the whole strain is transmitted to the central hanger, which has a tendency to draw the boiler out of shape, which, in many instances, induces excessive leak- age, rupture, and eventually explosion. The most permanent practical method of setting boilers is to rivet cast-iron brackets or knees to their ends and centre, about 12 feet apart, resting on brick piers, as by that arrangement one end can settle without injuriously 853 HAND-BOOK OF LAND AND MABINE ENGINES. affecting the other. These brackets, in some instances, rest on small rolls arranged in a flanged seat, in order to prevent the piers from being forced out when the boiler expands. All boilers should be set with an incline of not less than 1 inch in 20 feet to the end in which the blow-off is situ- ated, in order that the water may run out by its own gravity. The blow-off should be located in the back or coldest end, as the mud and deposits always seek that part where the boiling currents are least violent. EXPANSION AND CONTRACTION OP BOILERS. A great difficulty to be contended with in the manage- ment and working of steam-boilers arises from the un- equal expansion and contraction of parts of the structure. In some instances these are so great as to be the cause of more " wear and tear " than any other condition to which the boiler is subjected ; consequently, in raising steam on new boilers, or those that have been blown out and allowed to cool down, great care should be taken in allowing the fire to burn moderately, as otherwise the boiler may be seriously weakened, if not permanently injured; more par- ticularly so in the case of flue and tubular boilers, as the flues or tubes, being exposed to the direct action of the fire, and generally of a thinner material than the shell, expand much quicker, and, as a result, the ends of the boiler are forced outward, and the whole structure ex- posed to an enormous strain. When the flues of boilers are placed nearer to the bottom than to the top, the strain, from unequal expansion and contraction, is often such that the plates of the under part of the outer shell are torn or broken ; and, in other cases, leakages take place in positions where they are most difficult to discover. HAND-BOOK OF LAND AND MARINE ENGINES. 359 When a boiler is set with only a small portion of its bottom exposed to the heat, and a great portion of the structure exposed to the atmosphere, as is the common practice, a powerful action is left at full liberty to work out most injurious results. The heat will expand that portion of the boiler to which it is applied ; while the other portion exposed to the cold atmosphere will con- tract. Thus the two forces are left to exert their respect- ive powers against each other, tending to tear the boiler asunder by means almost imperceptible. A boiler under steam is often strained, especially in a longitudinal direction, more by the greater dilation of the tubes compared with the shell, or by the unequal expan- sion of the top and bottom of the shell, than by the actual steam pressure. The persistent leakage often experienced at the seams, along the bottom of horizontal internally fired boilers, might in most cases be ascribed to the dif- ference in temperature of the water and steam at the bot- tom and top of the boiler ; but in some cases the leakage is principally caused by the longitudinal straining of the bottom of the shell, due to the greater expansion of the tubes, especially when the firing is forced in getting up steam after the boiler has been at rest. As this straining would not take place in testing the boiler by hydraulic pressure in the usual manner, this leakage would not be produced. It follows, from the above considerations, that a hydraulic test might fail to indicate weakness which would be produced and made ap- parent by steam pressure. TESTING BOILERS. Experience has shown that, let a boiler be ever so care- fully designed and constructed, there will still remain an element of doubt as to its actual strength, since the 360 HAND-BOOK OF LAND AND MARINE ENGINES. material may have sustained injuries in the process of construction which may have escaped detection. In the case of a new boiler, even by a first-rate manu- facturer, to say nothing of original and hidden flaws in the plates and castings, there is always a possibility of defects, such as bad welding, careless riveting, plates burnt in flanging or cracked in bending, and many other defects that may be traced to reckless negligence or want of skill ; consequently, the only means we have of ascertaining, with any degree of certainty, the safety of a boiler is by the application of cold water pressure, as many cases of dangerous defects, which the strictest scrutiny of the practical boiler-maker failed to detect, have been brought to light by means of the hydraulic test. There are many forms of boilers which do not admit of anything like a proper examination, as, for instance, tubular boilers, in which the shell of the boiler is filled with tubes nearly to the water line ; also many forms of marine boilers, whose construction is so irregular and complicated as to defy even an approximate calculation of their strength or condition. With regard to the various modes of testing by hy- draulic pressure, that commonly adopted is to pump water in until the desired pressure be reached. The condition of the joints and rivets is then looked to, and any very conspicuous distortion, leak, or defect marked ; and in cases of permanent distortion or flattening of tubes or flues, the injured parts should be immediately removed and repaired or renewed, as the injury to the tube or flue is liable to be aggravated by subsequent tests, and eventually result in rupture or collapse. Some advocate the method of marking the leaky joints while the pressure is on, and then lowering the pressure for the purpose of calking ; this is decidedly wrong. Boilers should never be calked while under steam HAND-BOOK OF LAND AND MARINE ENGINES. 361 or water pressure, however light, as the jarring induced by the calking is liable to spring the seams, and cause fresh leakage in different parts of the boiler. Some recommend the employment of hot water for test- ing boilers, as it assimilates, more than cold water, the conditions under which the boiler is placed when at work. But the \yater for test should never be more than moder- ately warm, as the hydraulic test is comparatively worth- less without a thorough examination of the boiler at the same time ; and it is impossible to do so in cases where hot water is used, in consequence of the presence of so much heat under and around the boiler. In some cases, the plan has been adopted of filling the boiler with water, closing every outlet, and putting fire to it. As water expands about -^-^ in volume in rising from 60° to 212°, the rise of temperature as the water becomes heated will cause a corresponding increase of pressure, and, from the regularity with which the pressure rises, any leak that may occur in the boiler will be easily noticed by the jerks or starts of the steam-gauge hand. But the wisdom of this method is extremely doubtful, as it involves a certain amount of danger, and prevents the possibility of examining the boiler in the parts most likely to be affected during the test. In whatever manner a boilep is tested, great care should be taken to obtain the exact amount of pressure employed, for the reason that safety-valves are very often unreliable, particularly so when water pressure is used, and spring- gauges are not always to be trusted under such circum- stances ; in all cases, when the cold water test is applied, two gauges should be used ; for, although a boiler cannot explode under the hydr&ulic test, yet many serious accidents have occurred by boilers giving way under such circum- stances. 31 362 HAND-BOOK OF LAND AND MARINE ENGINES. The hydraulic test meets with opposition from some engineers on the ground that it does not tell the actual strength of the boiler; but the same objection might be urged against the steam and expansion tests, as there is no accurate method of ascertaining the. strength of a boiler but to burst it. The hydraulic test is not meant for per- fectly sound boilers, but for the detection of weaknesses in certain parts, and is generally successful for that purpose, if well conducted. The injuries arising from an excessive application of the hydraulic test are most likely to occur to flue boilers, as, whenever flues subjected to external pressure depart from the true cylindrical form, or form of greatest resistance, they are liable to collapse, even under very low pressure. Sound Test. — The sound test is generally applied to all accessible parts of the boiler, such as the upper part of the shell, crown-sheet, crown-bars, angle iron, and braces, which is done by tapping the parts to be tested lightly with a small steel hammer. The experienced boiler-maker or inspector can easily tell, by the eff*ect of the sound on the ear, whether the part subjected to the blow is sound or not. But whether by sound, expansion, or hydraulic press- ure, the testing of boilers requires the utmost care and ex- perience, and should never be applied to any boiler unless all the conditions are fully understood, such as the di- ameter, age and condition, character of seams, etc.; nor even then, except by persons who fully comprehend the object and efiect of the test. NEGLECT OP STEAM-BOILERS. Perhaps no appliances connected with factories, and other places where power is used, ate more sadly neglected than steam-boilers, and nothing can be more surprising than this fact, when we consider the important part they HAND-BOOK OF LAND AND MARINE ENGINES. 363 occupy in the manufacturing arts. It would be difficult to assign any reasonable cause for this neglect, except that it may arise from the fact that nearly the whole attention of builders and leading engineers has been concentrated on the improvement and perfection of the steam-engine ; and the practical engineer, following the example set by the leaders, generally devotes all his attention to the engine. In the majority of cases boilers are not cleaned half as often as they should be. When the water is hard, and scale accumulates on the sides or flues of the boiler, solvents are very often resorted to to remove the scale. After the scale has been thrown down, it accumulates on the bottom of the boiler, and, if not removed at once, it becomes con- glomerated; forms a heavy coating ; and if the boiler is ex- ternally fired, the bottom is liable to be burned through. The yearly report of the Hartford Steam-Boiler Inspec- tion and Insurance Company shows that nearly half of the whole number of defective boilers became so on account of incrustation and deposit of sediment ; and, strange as it may seem, there were 40 per cent, more dangerous cases from the deposit of sediment than from incrustation and scale. The same report further shows that more than one- half the defective boilers from other causes are due to care- less and incompetent management, proving clearly that a large number of cases from which explosions might be expected may be traced to a direct cause. CARE AND MANAGEMENT OF STEAM-BOILERS. Familiarity with steam machinery, more especially with boilers, is apt to beget a confidence in the ignorant which is not founded on a knowledge of the dangers by which they are continually surrounded, but is the offspring of conceit and folly; while contact with steam, and a thorough ele- mentary knowledge of its constituents, theory, and action, 364 HAND-BOOK OF LAND AND MARINE ENGINES. only incline the intelligent engineer and fireman to be more cautious and energetic in the discharge of their duty. As the boiler is the source of power, and the place where the power to be applied is first generated, and also the source from which the most dangerous consequences may arise from neglect or ignorance, it should attract the special attention of the engineer, as, from the hour it is set to work, it is acted upon by destroying forces, more or less uncontrollable in their work of destruction. These forces may be distinguished as chemical and me- chanical. In most cases they operate independently, yet they are frequently found acting conjointly in bringing about the destruction of the boiler, which will be more or less rapid according to circumstances, care, management, etc. One of the most common causes of deterioration in steam-boilers, and also leakage of the seams and under side and at the junctions of the tube* and tube-sheets, is the reckless practice of blowing out the boiler while still hot, and filling it again with cold water. Under such cir- cumstances, the contraction of the crown-sheet, tube-sheets, and tubes is so rapid and unequal, that, if persisted in, it eventually results in the ruin of the boiler. Boilers should never be filled with cold water while they are hot, as it has a very injurious effect, causing severe con- traction of the seams and stays, which very often induces fracture of stays or leakage in the seams and tubes. Many boilers, well constructed and of good material, have been ruined by being blown out under a high press- ure of steam, and then suddenly filled with cold water. The tubes of boilers being generally of thinner material than the shell, consequently cool and contract sooner ; for this reason, the boiler should never be filled with cold water while the tubes are hot. The boiler should always be allowed to stand for several HAND-BOOK OP LAND AND MARINE ENGINES. 365 hours, or until it is cold, before the water is run out ; the de- posit of mud and scale will then be found to be quite soft, and can be easily washed out with a hose from all acces- sible parts. There seems to be an impression on the minds of some engineers that blowing out a boiler under pressure has a tendency to remove the deposits of mud from the boiler » but experience has shown this to be a very grave mistake. Tubes and flues should be frequently swept out, at least once a week. This can be done, in either land or marine boilers, while the engine is in motion, by covering the fire in the furnace, either in front of or under the tubes to be cleaned, with a thick layer of fresh coal, and cleaning one set of tubes at a time. Accumulations of salt frequently occur in the tubes of marine boilers, which are induced by leakage of the tubes or tube-sheet ; such accumulations should be removed as soon as discovered, and the tube thoroughly swept, or, if need be, bored out with a steel scraper, in order to prevent the part from becoming burnt through. It frequently becomes necessary to direct a steam-jet on the deposit before it can be effectu- ally removed. Tubes frequently become leaky in consequence of becoming split, or their ends at the tube-sheet being burned off. In the former case they have, of necessity, to be plugged, which can be done effectually by driving pine plugs solid into their ends ; although, in some cases, it becomes necessary to run a long bolt through the inside of the tube, with a flange and packing at each end ; in the latter case, they can be made tight by means of wrought-iron ferrules. When two op more boilers are connected by feed- pipes, the stop-valves on each should be shut off every night, or whenever they are not working, as the water is 31^ 366 HAND-BOOK OF LAND AND MARINE ENGINES. liable to escape from one to the other, on account of variation in the pressures; and, as a consequence, when the water in one is up to, or even above, the proper level, the tubes or flues in the other are very often bare of water. It is no uncommon thing in factories to have two boilers for the same engine, in order that one may be out of use while the other is working ; but, while this is an accommo- dation, it is not always economy, as boilers wear out faster when not in use, by oxidizing and corroding, than if moderately worked. It will be found more economical to work with extra boiler room than to have one or more standing. It will also tend to prevent priming. The furnaces will be more economically worked with a thick fire than with a thin one, by allowing the heat to accumu- late, thereby maintaining a high temperature in the furnace with slow combustion. The furnace door should never be allowed to remain open longer than a sufficient time to clean and replenish the fire, as the contraction of the tubes and flues, induced by the cooling down of the furnace, has a very mischiev- ous eflTect on all parts of the boiler exposed to the cold draught, more particularly so when the fire is thin, and the temperature in the furnace is of a high degree. The feed -water should be sent into the boiler as hot as possible, as, if it be forced in at a low temperature, it will impinge on that portion of the boiler with which it comes in contact, and, as a result of the continual expansion and contraction induced by the varying temperature of the water, the boiler is liable to crack and become leaky. Where economy of fuel is no object, as is often the case at coal-mines, saw-mills, and wood-working establish- ments, a very inexpensive way of averting the disastrous eflfects of pumping cold water into boilers is to introduce HAND-BOOK OF LAND AND MAKINE ENGINES. 867 the feed-pipe into the back end of the boiler, cawying it forward about three-quarters the length of the boiler, and then returning it to the back end where the water is discharged into the boiler. By this arrange- ment the water will have . ^ 1 . Heater Pipe. a temperature nearly equal to that of the w^ater in the boiler when discharged from the pipe. If, from neglect op any other cause, the water in the boiler should become dangerously low, the fire-doors and damper should be immediately thrown open for the pur- pose of admitting the cold air to the heated plates, and the fire withdrawn as soon as possible. Under such circum- stances, no attempt should be made to introduce cold water into the boiler, as it might be attended with the most dis- astrous results. Nor should the safety-valve be tampered with, as any moving of the safety-valve under such cir- cumstances would have a tendency to cause violent agita- tion or foaming of the water over the hot plates, which would have the effect of generating more steam than the Safety-valve could discharge, and most likely result in an explosion. Every boiler should be furnished with a safety-valve of sufficient capacity to prevent the steam from getting to a higher pressure than that considered safe, and the length of the lever should be as short as possible, in order that the pressure may not be increased with the same weight. The safety-valve should always be moved before the fire is started to get up steam, in order to ascertain if it is in good working order. It should also be raised whenever the boiler is being filled with cold water, so as to allow the air to escape, as air has a tendency to retard the influx of the water, and also to occupy the steam room when 368 HAND-BOOK OF LAND AND MARINE ENGINES. steam is»raised. Air also interferes with the uniform ex- pansion of the boiler. The safety-valve should be kept open until the steam commences to escape. All new boilers should be thoroughly examined before being filled with water, in order to ascertain if there are any tools, wood, lamps, greasy waste, etc., left behind by the boiler-makers, that would be liable to be carried into the connections, or cause the boiler to foam. In getting up steam in boilers just filled with cold water, or that have been out of use for sometime, the fire should be allowed to burn moderately at first, in order to admit of the slow and uniform expansion of all parts of the boiler ; as, when the fire is allowed to burn rapidly from the first start, some parts become expanded to their utmost limits, while others are as yet nearly cold, thereby expos- ing the boiler to those fearful strains induced by unequal expansion and contraction, resulting, as they always do, in leakage, fracture, and sagging of the shell and flues. In all cases, the engineer, or the person having charge, should ascertain with certainty the height of the water in the boiler before opening the draught or starting the fire, as any neglect to do so might be productive of great danger and inconvenience. When boilers are laid up, or out of use, even if it be for a few days, they should be opened, cleaned, and thor- oughly examined, in order to ascertain if any of the stays or braces have become loose or slack, or disconnected. Before being closed up, all gaskets for man- and hand- holes, and grummets for mud-holes, should be painted with a coating of black lead, in order to protect their seats from deterioration, induced by the chemical action of the sulphur in the gum packing, now so universally used for the joints of steam-boilers. In view of tjie above enumerated evils that so silently HAND-BOOK OF LAND AND MARINE ENGINES. 869 and persistently affect the durability of steam-boilers, the question might naturally be asked, " What guarantee of safety have steam users and the public against disastrous explosions ? " The answer would be, that safety does not depend so much on the strength of boilers as it does on their care and management, from the fact that a thorough knowledge of their condition enables intelligent engineers to avoid numerous causes and remedy many defects that would ultimately lead to destruction. HEATING SURFACE. The evaporative power of a boiler mainly depends upon the efficiency of its heating surface, whose duty it is to transfer the heat from the products of combustion with- out to the water within. The heat is communicated to the transmitting surface in two different ways, — by radiation and by contact ; and from two or three different hot masses in the furnace, viz., the solid incandescent fuel, the flame, and the hot gases produced by combustion. Beyond the furnace-bridge or tube-plate, the heat is imparted by contact and radiation from tl^e flame and gases only. The amount of heat transmitted by radiation from one body to another diminishes as the square of the distance between the bodies increases. The effect on any surface is also diminished by any increase in the inclination at which the rays fall upon it. The radiation from solid incandescent fuel is greater than from flame, whilst transparent hot gases scarcely radiate any heat at all. The more intense the contact heat of the flame by thorough mixture with the air, the less is the heat by radiation. Conduction is the transfer of heat either between the particles of the same body, or between the parts of dif- Y 870 HAND-BOOK OF LAND AND MARINE ENGINES. » ferent bodies in contact, and it is distinguished respectively as internal and external conduction. The rate at which the former takes place in metal plates is very much greater than the latter, where the heat passes from the hot mass to the plates, and from these again to the water. The efficiency of any heating surface may be defined as the proportion borne by the amount of heat it transmits to the whole amount available for transmission. Aflat, horizontal surface, not too far above the layer of fuel, is usually considered to be the most favorable for raising steam. By being made concave to the fire, it has, however, the further advantages of being still better adapted for receiving the radiant heat ; of facilitating the access of fresh supplies of water to replace the heated ascending particles, and thereby promoting the circula- tion ; of boiling off the matters deposited from the water, and so preventing incrustation ; and of being stronger, and in some cases more durable. Next in efficiency to the flat surface with the water above, comes the sloping surface surrounding the fire, which is superior to one in a vertical position, as it receives the rays of heat at a more favorable angle, and allows the steam bubbles to escape more freely. The value of horizontal surfaces beneath the fire is not worthy of consideration as heating surface. In externally fired boilers the heating surface is usually convex to the fire. This is, by many, regarded as inferior to a concave surface, probably because it is not so well adapted for directly receiving the radiant heat from the fire, and does not^fppear to ofl^er an equal facility for circulation. The results obtained from this description of surface in actual work do not appear to verify this con- clusion. The inferior evaporative power usually alleged of the ordinary externally fired boiler is, in a great measure, due to the waste of heat in the furnace. HAXD-BOOK OF LAXD AND MARINE ENGINES. 371 RULES FOR FINDING THE HEATING SURFACE OF STEAM-BOILERS. Rule for Locomotive op Fire-box Boilers. — Multiply the length of the furnace-plates in inches by their height above the grate in inches ; multiply the width of *the ends in inches by their height in inches ; also, the length of the crown-sheet in inches by its width in inches ; multiply the combined circumference of all the tubes in inches by their length in inches ; from the sum of the four products subtract the combined area of all the tubes and the fire- door ; divide the remainder by 144, and the quotient will be the number of square feet of heating surface. Rule fop Flue Boilers. — Multiply | of the circum- ference of the shell in inches by its length in inches ; multiply the combined circumference of all the flues in . inches by their length in inches; divide the sum of these two products by 144, and the quotient will be the number of square feet of heating surface. Rule fop Cylindep Boileps. — Multiply! of the circum- ference in inches by its length in inches; add to this product the area of one end ; divide this sum by 144, and the quotient will be the number of square feet of heating surface. Rule fop Tubulap Boileps. — Multiply | of the circum- ference of the shell in inches by its length in inches ; multi- ply the combined circumference of all the tubes by their length in inches. To the sum of these two products add | the area of both tube-sheets ; from this sum subtract twice the combined area of all the tubes ; mvide the remainder by 144, and the quotient will be the number of square feet of heating surface. 372 HAND-BOOK OF LAND AND MARINE ENGINES. EVAPORATIVE EFFICIENCY OF BOILERS. The evaporative efficiency of a given amount of heat- ing surface depends upon the time allowed for the trans- mission of heat through it, or for the contact of the hot gases. The greater their velocity, the less time they have to impart their heat to the plates or tubes where the length of the surface is constant. The velocity through a tube may be increased either by reducing its area, the total quantity of gases passing through remaining con- stant, or by increasing their draught, and so causing a greater amount of gases to pass through in a given time, the area of the tube remaining unaltered. When the heating surface consists chiefly of tubes, as in the locomotive type of boiler, the collective area of the tubes may be diminished without decreasing the extent of heating surface, since the sectional area varies as the square of the diameter, whilst the surface measured by the circumference diminishes simply as the diameter. With the gases passing at the same velocity through two tubes whose diameters are as 1 : 2, the latter will be traversed in a given time by four times the quantity of gases, and will have only twice the surface to absorb the heat. Therefore, to obtain the same evaporative economy as in the small tube, we must double the length of the largar, or, generally speaking, the proportion between diameter and length of a tube is constant for the same evaporative efficiency. When an increased quantity of gases of the same density pass through a tube in a given time, although there will be a greater absorption of heat, there will still be a loss by the increased amount of heat remaining in the escap- ing gases ; and in order to preserve the same economy, or in order that the heat of .the escaping gases shall remain constant, the length of the tube must be increased in HAXD BOOK OF LAND AND MARINE ENGINES. 373 proportion to the increased quantity of gases passed through. When we consider the heat to be imparted to the tube surface by radiation, which, however slight, is probably the principal mode of transfer in vertical and other long tubes, where the convection among the particles of gas cannot be supposed to take place to any great extent, we n\ay assume the heat to be concentrated in the axis of the tube, whence we find the quantity of heat received in a given time by the surface from radiation will be inversely as the square of the diameter. By doubling the diameter we shall have four times the quantity of gases passed through, and the quantity of heat received in a given time will be only one-quarter of ^vhat it was before, owing to the increase of distance. The surface being, however, twice as great, the absorp- tion per unit of length becomes equal to the original. Therefore, in order to bring the evaporative efficiency up to the original, we must double the length of tube, or generally we must increase the heating surface as the square of the diameter, in order to obtain the same evapo- rative efficiency from radiation when increasing the diam- eter of a tube. But if we reduce the diameter to one-half, we increase the absorbing power fourfold per unit of surface; the heating surface being, however, reduced to one-half, the evaporative power of the tube will be only doubled, whence the tube may be reduced to one-half the original length and still retain the same evaporative efficiency, or, the length remaining unaltered, the quantity of gases passing through should be doubled to maintain the same tempera- ture at the escaping end, or, as before, the efficiency of each square foot of heating surface increases inversely as the square of the diameter. 32 374 HAND-BOOK OF LAND AND MARINE ENGINES. The evaporative efficiency of a square foot of heating surface varies in different classes of boilers, as well as in the same boiler under different conditions ; in consequence of this there is considerable difficulty in determining the precise area of heating surface necessary for the produc- tion of a given amount of steam in a given time. For a given description of boiler, it is evident the evaporative efficiency will mainly depend upon the ratio between the quantity of coal consumed and the extent of heating surface, as well as the quality of the fuel and the manner in which it is burned. The easiest method, and consequently the one most frequently adopted, is to measure the quantity of water by th*e difference of its height in the glass gauge at the beginning and end of the experiment. But this method is very uncertain, as there can be but little doubt that in many boilers the surface of the water is not level, but is generally higher over the furnace, where the greatest ebul- lition takes places; the difference in the height at any time will greatly depend on the intensity of the firing. Meters are frequently employed for measuring the quan- tity of water that enters a boiler in a given time ; but, like all other contrivances resorted to for that purpose, they are not always reliable. The only sure method of ascer- taining the quantity of water evaporated is by actual meas- urement with a cistern or vessel whose cubic contents are accurately known. The quantity of water in the boiler before and after the trial should be measured at the same temperature, which should not exceed 212°, to insure accuracy. But even when the amount of water introduced, and the quantity passed off from the boiler, are accurately ascer- tained, there yet remains a doubt as to how much has been , actually evaporated, and how much may have passed off HAND-BOOK OF LAND AND MARINE ENGINES. 375 in priming, as there are very few boilers that do not prime more or less, and the quantity of water passed off in this manner is sometimes very considerable, and often fur- nishes boiler-makers, and more particularly manufacturers of patent boilers, an opportunity to delude steam users with the belief that their boilers are capable of evapora- ting 14 or 15 pounds of water to 1 pound of ordinary coal. In fact, unless the amount of water passed over with the steam by priming, when working under pr(3ssure, can be accurately ascertained,' it is utterly impossible to deter-, mine the evaporative capacity of the boiler. HORSE-POWER OP BOILERS. It must be admitted that the manner in which the power of a boiler is usually calculated is far from satisfac- tory. As it has long been the custom to estimate boilers by their real or nominal horse-power, and the nominal horse-power of engines is usually based upon the diameter of the cylinder, without regard to other conditions, so in boilers the nominal standard of power is estimated by their size, without regarding the pressure of steam, the efficiency of heating surface, size of grate, rate of combustion, qual- ity of fuel, etc. At the present time, it might be said that there is no received rule for estimating the power of a steam-boiler ; that is to say, no rule generally recognized by the trade. As it has long been a custom in England to estimate the horse -power of boilers for stationary enghies by their length, regardless of the diameter and other conditions, if we turn to marine engines, we find some makers esti- mating their power entirely by the grate surface; but while one maker divides his grate area by '8 and calls the result the horse-power, another uses '75, and another uses -5. Thus, a boiler with 100 square feet of grate sur- 376 HAND-BOOK OF LAND AND MARINE ENGINES. face maybe called 125-, 133-, or 200-horse power. Others, again, neglect grate surface altogether and go by heating surface, and anything between 12 and 25 feet is said by different makers to represent a horse-power. In view of the foregoing facts, it is very desirable that, in purchasing boilers, some understanding should be estab- lished as to the quantity of steam they are capable of fur- nishing in a given time. An idea has been very generally entertained by boiler- makers and boiler dealers that it would be impossible to lay down any rule that would apply to all classes and varieties of boilers ; but this seems quite improbable, as there should be no great difficulty in dividing boilers into different classes, and establishing, as a rule, the number of square feet of heating surface, steam room, water space, and grate surface that would form a standard of horse- power for each class. And although it might be somewhat difficult to estab- lish a standard that would apply with strict accuracy to all classes of boilers, still it might be made approxi- mately so. Certain vague notions have long existed among engi- neers and steam users that, in adjusting the dimensions of steam-boilers, it is better to have them larger than is absolutely necessary, consequently, it has grown into a custom to recommend a 15-horse power boiler for a 10- horse power engine, a 25-horse power boiler for a 20-horse power engine, and so on. This pule works well for the seller, but it does not always work both ways, as boiler-makers very often de- ceive purchasers in the extent of heating surface that they ought to receive, such misrepresentations giving rise to general distrust, disappointment, and dissatisfaction be- tween manufacturers and purchasers. It seems rather HAND-BOOK OF LAND AND MARINE ENGINES. 377 singular that all the ordinary methods of trade should be changed when the question becomes one of the purchase or sale of a steam-boiler. The rule most common in use In this country, if it might be called a rule, for determining the horse-power of steam-boilers, is to estimate the entire heating surface, and give an allowance for a horse-power; for cylinder boilers, 14 square feet of heating surface, and 1 square foot of grate surface; for flue boilers, 15 square feet of heating surface, and | of a square foot of grate surface ; and for tubular boilers, 15 to 16 square feet of heating surface, and J of a square foot of grate surface. A more liberal allowance of grate surface for the flue and tubular boilers would give more satisfactory results, as, when the grate surface is limited, the fuel has neces- sarily to be exposed to a sharp draught, which induces a great loss of the heated gases, as they are carried into the chimney without having sufficient time to impart their heat to the flues and tubes. EXAMPLE. Diameter of boiler, 48 inches. Length " " 11 feet. 46 3-inch tubes. 3 )1507968 circumference of shell. 50-2656 2 100-5312 132 length in inches. 2010624 3015936 1005312 13270*1184 sq. in. heating surface in shell. 32^ 378 HAND-BOOK OF LAND AND MAKINE ENGINES. 9*4248 circumference of 1 tube. 565488 376992 433-5408 132 8670816 13006224 43354 08 57227*3856 sq. in. heating surface in tubes. 3) 1809*5616 area of 1 tube-sheet. 603-1872 2 1206-3744 2 2412*7488 sq. in. heating surface in tube-sheets. 7*0686 area of 1 tube. 46 424116 282744 325*1556 area of tubes. 2 650-3112 13270-1184 57227*3856 2412*7488 72910*2528 650*3112 144)72259*94'16 total heating surface in sq. in. 16)501*8 sq. ft. of heating surface. 31* horse-power. Grate surface required, 15^ square feet. FIRING. Firing, like engineerirrg, ought to be recognized as a profession, and none but intelligent men, who can appre- ciate the importance of their position, should be placed in HAND-BOOK OF LAND AND MARINE ENGINES. 379 charge of the coal pile ; as it is a well-known fact that when the engineer has done all he can to attain economy in the steam-engine, much of the result still remains in the hands of the fireman. The use of a more improved class of steam-engines involves the necessity of employing more skilful and careful attendants ; not that the work is more difficult, as less coal has to be thrown into the furnace, but because a careless or unskilful fireman can counteract all the in- genuity displayed in the improvement, construction, and management of the engine. Consequently, every engineer should be required to pre- pare himself for the duties of his profession by com- mencing as a fireman ; otherwise, how can he be expected to be able to instruct his fireman in the manner of firing best calculated to insure the most satisfactory and eco- nomical results? Clean grate-bars, with an even distribution of the fuel in the furnace, the exercise of judgment in the quantity of air admitted, and the regulation of the draught, are the main points to be attended to ; and although they require the exercise of skill and intelligence, they cannot be said to involve an unreasonable amount of either labor or vigilance. Even with the best coal and most careful firing, a quantity of the coal falls through the fire-bars either as unburnt coal or ashes. Another portion goes up the chimney, unconsumed, in the form of smoke and soot ; and a further quantity, half consumed, in the form of carbonic oxide. The loss from these causes may amount to from 2 to 20 per cent. It all arises from wrongly con- structed furnaces and bad firing, and can nearly all be avoided. Most coal contains a greater or less quantity of moist- 380 HAND-BOOK OF LAND AND MARINE ENGINES. ure, and the evaporation of this moisture causes the first loss of heat. Kadiation from the furnace causes a further loss. But the great causes of loss are the admission into the furnace of a large quantity of useless air and inert gases, and the escape of these, with the actual products of combustion, up the chimney, at a very much higher temperature than that at which they entered the furnace. Aip is composed of about one-third oxygen and two- thirds nitrogen. The oxygen only is required to effect the combustion of the fuel, and the useless nitrogen merely abstracts heat from the combustibles, and lowers the temperature of the furnace. About 12 pounds of air contain sufficient oxygen to effect the combustion of 1 pound of coal, but, owing to the difficulty of bringing the carbon into contact with the oxygen, the quantity actually required to pass through the furnace is from 18 to 24 pounds of air per pound of coal burnt. The surplus air passes out unburnt, and its presence in the furnace lowers the temperature subsisting there, and abstracts a portion of the heat generated. As the whole of the aip enters the furnace at about 60° Fah., and the unconsumed air and products of combus- tion leave the flues at from 400° Fah. to 800° Fah., the total loss from these causes is from 20 to 50 per cent. Each pound of good coal burnt is theoretically capable of evaporating about 15 pounds of water; in good practice it evaporates but 9 or 10 pounds, and in ordinary practice but 6 or 8 pounds of water. There are difficulties in the way of abstracting all the heat from the furnace gases ; first, because, with natural or chimney draught, the gases require to pass into the chimney at not less than 500° Fah., in order to maintain the draught,; and secondly, because the transmission of heat from the gases to the water, when the difference of their HAND-BOOK OF LAND AND MARINE ENGINES. 381 temperatures is small, is so slow that an enormous exten- sion of the surface in contact with them becomes necessary in order to effect it. But by having energetic combustion and a high tempera- ture in the furnace, the quantity of air actually required may be much reduced; by suitable arrangements for admitting air and feeding coal into the furnace, the proportions of each may be suitably adjusted to each other ; and by a liberal allowance of properly disposed heating surface, the temperature of the reduced quantity of furnace gases may be reduced to that simply necessary to produce a draught in a furnace with natural draught, or to about 400^ Fah., or less, in a furnace where the draught is obtained from a steam jet or fan. There have not been, heretofore, that attention and thought devoted to the examination of the subject of the economy of fuel which the magnitude of the interest in- volved and its importance in a national point of view render it worthy of. The saving of one pound of water per horse-power per hour for ten hours a day, providing the engine is 100 -horse power, and assuming that the boiler evaporates 7 pounds of water per pound of coal, would make a saving of 1000 pounds of water per day, which would require the consumption of 143 pounds of coal per day, or 22^ tons a year, the cost of which would be, at the ordinary price of coal, over $125. The methods most in vogue for the consumption of all kinds of fuel are those which gradually developed them- selves, as necessity dictated, to the untutored intellect of uncultivated men, and which, however creditable to the men that devised them, inasmuch as they availed them- selves of all the sources of information ivithin their reach, are nevertheless a reproach to the more advanced knowl- edge of physical and mechanical science enjoyed by the present generation. 382 HAND-BOOK OF LAND AND MARINE ENGINES. INSTRUCTIONS FOR FIRING. In estimating the relative merits of different steam- engines, it is generally assumed that the fuel is burned under conditions with which the men who supply coal to the furnaces have nothing whatever to do, — in short, that any man who can throw coal on a fire and keep his bars clean must be as good as any other man who can do apparently the same thing. But this conclusion is totally erroneous, as it is within the experience of nearly every engineer and steam user that many engines now in operation throughout the country consume twice as much fuel, per horse-power, as is required in those that are more economically managed. When a boiler is of sufficient capacity to generate the necessary amount of steam without urging the fires, it will be found most advantageous to carry a thick bed of coal on the grates, as, when the coal can be burned in large quantities and with a moderate draught, the heat is more generally utilized than if the^ coal is burned in small quantities and with a sharp draught. Fop stationary boilers the fuel should not be less than from three to four inches thick on the grate. For marine boilers, if anthracite coal be used, from 5 to 6 ; if bitumi- nous, from 6 to 8 inches. Of course, the thickness of the fire must be governed by the character of the fuel and quantity of steam required. Before starting a fresh fire in the furnace, a thin layer of coal should be scattered over the grate ; most of the kindling, whether shavings, oily-waste, or paper, should be placed on the ends of the bars next the door, and then covered with a uniform layer of wood. This is a necessary precaution, as, when the fuel fails to ignite at the front at HAND-BOOK OF LAND AND MARINE ENGINES. 383 first, it generally takes a long time before the fire burns through. When the coal is in large lumps, so that the spaces between them are of considerable size, the depth may be greater than where the coal is small and lies compactly ; and where the draught is very strong, so that the air passes with great velocity over and through the fuel, there is not time for the carbonic acid to combine with and carry off the products of combustion, and consequently a bed of greater depth may with propriety be used. When very large coal is used, it will be found of im- mense advantage to mix it with some small coal ; more particularly so, when the draught is strong, as such an ar- rangement forms a resisting barrier to the currents of cold air that would otherwise pass through the interstices between the lumps, and render the combustion more perfect. When an increasing quantity of steam is wanted, the average thickness or quantity of fuel on the grate must not be increased, but rather diminished, and supplied in smaller quantities and more frequently. As soon, how- ever, as the supply of steam exceeds the demand, the coal may again be supplied in larger quantities at a time. In firing up, the coal should be scattered evenly over the grate, but thinner at the front near the dead-plate than at the middle or back, and no portion of the grate should ever be left uncovered. When it becomes necessary to replenish the fire, it should be done as quickly as possible, as, when the damper and the fire-door are both open at the same time, the current of cold air passing through the furnace above the fuel not only reduces the temperature in the furnace, but has a tendency to injure the boiler. There should in all cases be ample fire in the furnace, 384 HAND-BOOK OF LAND AND MARINE ENGINES. an extra quantity of water in the boiler, and a full head of steam, before any attempt is made to clean the fire; then the damper should be opened to its full limit, in order that the heated gases and dust may pass into the flue ; and, if there be more than one fire, one only should be cleaned at a time, and allowed to become thoroughly kindled before the next one is cleaned. The fire should never be allowed to become low for the purpose of making it more easy to clean, as, in consequence of the small quantity of fire in the furnace after cleaning, it would have a tendency to go nearly out, which is often attended with great loss and inconvenience. It is always best to have a good fire, then close the damper and open the furnace door, in order to take the white glare ofi* the fire before commencing to clean it ; the damper should then be reopened to its full extent and all the live fire pushed back to the bridge, without disturbing any of the ashes or cinders ; the latter should then be drawn out, and the fire that was pushed back, drawn forward to one side, and the ashes and cinders that remain near the bridge removed. The fire should then be distributed evenly over the grate, all the cinde»s and clinkers that remain picked out, and the fire covered with a thin layer of fresh coal, care being taken to waste none of the com- bustible fuel. Before commencing to clean the fire, it is always advis- able for the fireman to place a piece of scantling a short distance in front of the furnace, in order to protect his feet from the hot cinders as they fall out. In cleaning the fires of locomotive, marine, or other fire-box boilers, water should not be thrown in the ash-pit, as the lye formed from the wet ashes has a tendency to corrode and destroy the fire-box and water-legs. The fire should never be disturbed so long as any HAI^D-BOOK OF LAND AND MARINE ENGINES. 385 light shines through the grate into the ash-pit, unless the boiler fails to furnish the necessary amount of steam. Even then it is better, if anthracite coal be the fuel, to shed out the ashes from the bottom through the grate with a thin hooked poker; but if bituminous coal be used, it requires frequent breaking up, in order to allow the air to intensify the combustion. When broken up, it should always be pushed back to\vard the bridge, and the fresh fuel supplied in the front and allowed to coke. The smaller the quan- tity supplied at a time, and the more attention paid to its distribution and regulation, the more perfect will be the combustion and the more intense the heat. If, from neglect or any other cause, the fire should become very low or the grate partly stripped, it should not be poked or disturbed, as that would have a tendency to put it entirely out ; but wood, shavings, saw-dust, greasy waste, or some other combustible substance, should be thrown on the bare places, and, after being covered with a thin layer of coal, the damper opened to its full extent. If strict attention be paid to the regulation of the furnace, and coal applied to only one side of the fire at a time, nearly all the smoke can be consumed and quite a saving in fuel efiected. Fresh coal, should never be sup- plied except when absolutely necessary, and even then only in small quantities and at such places as are most aSected by the draught, as it is a common error, with inex- perienced firemen, to continually supply coal to the furnace, which eventually becomes choked, and the combustion of the fuel rendered imperfect. The regulation of the draught should receive particular attention, as air costs nothing, while fuel is quite expensive; therefore none of the latter should be allowed to pass out of the furnace without being fully utilized. The ash-pit and front of the furnace should at all times be kept free 33 Z 886 HAND-BOOK OF LAND AND MARINE ENGINES. from dirt, ashes, and cinders, as such accumulations have not only the effect of diminishing the cubic contents of the space under the furnace, but also of obstructing the free flow of air through the grate-bars, so essential to the per- fect combustion of the fuel. It is a well-known fact, that much of the waste attributed to the steam-engine occurs in the furnace, and while some of it may be unavoidable, a great portion of it, neverthe- less, is due to bad firing, which is the result of ignorance, carelessnes, or inattention. RULES FOR FINDING THE QUANTITY OF WATER BOILERS AND OTHER CYLINDRICAL VESSELS ARE CAPABLE OF CONTAINING. Rule for Cylinder Boilers. — Multiply the area of. the head in inches by the length in inches, and divide the pro- duct by 1728 ; the quotient will be the number of cubic feet of water the boiler will contain. EXAMPLE. Diameter of head, 36 inches. Area '' '* 1017-87 '* Length of boiler, 20 feet, or 240 inches. 1017-87 240 ^ / 4071480 203674 ^J^ 1728 )244288-80 'J^ 141-37 cubic feet. " ^' Rule for Flue Boilers. — Multiply the area of head in inches by the length of the shell in inches ; multiply the combined area of the flues in inches by their length in inches ; subtract this product from the first and divide the HAND-BOOK OF LAND AND MARINE ENGINES. 387 remainder by 1728 ; the quotient will be the number of cubic feet of water the boiler will contain. fiule.— To find theRequisite Quantity of Water for a Steam- loiler. — Add 15 to the pressure of steam per square inch; divide the sum by 18 ; multiply the quotient by '24 ; the product will be the quantity in U. S. gallons per minute for each horse-power. [{\x\b,—To find the Required Height of a Column of Water to supply a Steam-boiler against any given Pressure of Steam, — Multiply the boiler pressure in pounds per square inch by 2-5 ; the product will be the required height in feet above the surface of the water in the boiler. Another RulOa — To find the Requisite Quantity of Water for a steam-boiler,— -When the number of pounds of coal consumed per hour can be ascertained, divide it by 7*5, and the quotient will be the required quantity of water in cubic feet per hour. LONGITUDINAL AND CURVILINEAR STRAINS. The force tending to rupture a oylincler along the curved sides depends upon the diameter of the cylinder and pressure of steam ; and we may regard, hence, the total pressure sustained by the sides to be equal to the di- ameter X pressure per unit of surface X length of cyl- inder, neglecting any support derivable from the heads, which, in practice, depends on the length. It must be understood that the strain on a boiler sub- jected to internal pressure transversely, is exactly double what it is longitudinally, or in other words, the strain on the longitudinal seams is double that on the curvilinear. And no matter what the diameter of a boiler may be, the transverse pressure tending to tear it asunder will always be double the pressure exerted on the curvilinear seams. 388 HAND-BOOK OF LAND AND MARINE ENGINES. RULES. Rule joT finding Safe Working Pressure of Iron Boilers, — Multiply the thickuess of the iron by '56 if single riveted, and '70 if double riveted ; multiply this product by 10,000 (safe load) ; then divide this last product by the external radius (less thickness of iron) : the quotient will be the safe working pressure in pounds per square inch. EXAMPLE. Diameter of boiler... 42 inches. 2)42 21 external radius. •375 20*625 internal radius. Thickness of iron | = "375 •56 single riveted. 2250 1875 •21000 10000 safe load. 20-625) 2100-00000 101*81 pounds safe working press. In the above rule, 50,000 pounds per square inch are taken as the tensile strength of boiler iron, and one-fifth of that, or 10,000, as the safe load. Hence five times the safe working pressure, or 50,000 pounds, would be the burst- ing pressure. Rule for finding the Safe Working Pressure of Steel Boilers. — Multiply the thickness of steel by '56 if single riveted, and '70 if double riveted ; multiply this product by 16,000 (safe load) ; then divide this last product by the external radius (less thickness of steel) : the quotient will be the safe working pressure in pounds per square inch. HAND-BOOK OF LAND AND MARINE ENGINES. 389 EXAMPLE. Diameter of boiler 44 inches. Thickness of steel J inch. 2)44 22 external radius. '25 21'75 internal radius. Thickness of steel ^ =^ '25 •70 double riveted. 1750 16000 1050000 175 21'75) 2800-000 128*73 safe working pressure. 80,000 being taken, in the above rule, as the tensile strength of steel, and one-fifth of that, or 16,000, as the safe load. Hence 80,000 would be the bursting pressure. Rule for finding the Aggregate Strain caused by the Press- ure of Steam on the Shells of Steam-boilers. — Multiply the circumference in inches by the length in inches ; multiply this product by the pressure in pounds per square inch. The result will be the aggregate pressure on the shell of the boiler. EXAMPLE. Diameter of boiler 42 inches. Circumference of boiler 131*9472 " Length " 10 ft, or 120 ^' Pressure " 125 pounds. 131-9472 X 120 X 125 = 1,979,208 pounds -- 2000 = 989 tons. EXPLANATION OP TABLES OP BOILER PRESSURES ON POLLOWING PAGES. The figures |, 00, 0, 1, etc., in the horizontal column on the top of the tables on pages 390, 391, 392, 393, 394, 395, 396, and 397, represent the number of the iron or steel. 33* 390 HAND-BOOK OF LAND AND MARINE ENGINES. The decimals in the second horizontal column are equal to the fractional parts of inches in the third column. The vertical column on the left-hand side represents the diameter of the boiler in inches. All the other columns represent pounds pressure. Example. — 24-inch diameter, f steel, 289*03 pounds per square inch. TABLE OF SAFE INTERNAIi PRESSURES FOR IRON BOILERS. Birmingham Wire I f 00 1 2 Gauge. Thickness of Ironi .375 1 .358 1 Scant. .340 .300 .284 Dia. lbs. per lbs. j>eT lbs. per lbs. per lbs. per In. sq. in. sq. in. sq. in. sq. in. sq. m. External 24 180.65 172.20 163.29 143.59 135.75 Diameter. 26 166.34 158.58 150.39 132.28 125.08 28 154.13 146.96 139.38 122.63 115.95 30 143.59 136.92 129.88 114.29 108.07 32 134.40 128.17 121.58 107.01 101.20 34 126.31 120.47 114.29 100.60 95.14 86 119.15 113.64 107.81 94.92 89.77 38 112.75 107.54 102.04 89.84 84.98 40 107.01 102.07 96.85 85.28 80.67 42 101.81 97.12 92.11 81.16 76.77 Longitudinal 44 97.11 92.63 87.90 77.42 73.24 Seams, 46 92.82 88.54 84.02 74.01 70.01 Sin^e 48 88.89 84.80 80.47 70.89 67.06 Kiveted. 50 85.28 81.36 77.21 68.02 64.35 52 81.95 78.18 • 74.20 65.37 61.84 54 78.87 75.25 71.42 62.92 59.53 56 76.02 72.53 68.84 60.65 57.38 58 73.36 70.00 66.43 58.54 55.38 60 70.89 67.63 64.19 56.57 53.52 62 68.57 65.43 62.10 54.72 51.78 64 66.40 63.36 60.14 58.00 50.15 m 64.37 61.42 58.30 51.33 48.61 68 62.45 59.59 56.57 49.85 47.17 70 60.65 57.87 54.93 48.41 45.81 72 58.95 56.25 53.39 47.06 44.53 74 57.34 54.71 51.94 45.78 43.32 76 55.81 53.26 50.56 44.56 42.17 78 54.37 51.88 49.25 43.41 41.08 80 53.00 50.57 48.01 42.32 40.04 , HAND-BOOK OF LAND AND MARINE ENGINES. 391 T A B L 'Ei'^iConiimied) OF SAFE INTERNAL PRESSURES FOR IRON BOILERS. Birmingham Wire Gauge. 3 4 5 6 7 8 Thickness .^59 .238 .220 .203 .180 .165 of Iron. i Full. } Scant. A /^Full. g^Scant A Full. Dia. lbs. per lbs. per lbs. per lbs. per lbs. per lbs. per In. sq. in. sq. in. sq. m. sq. in. sq. in. sq. in. External 24 123.53 113.31 104.58 96.36 85.28 78.07 Diameter. 26 113.84 104.44 96.40 88.83 78.63 71.99 28 105.55 96.85 89.40 82.39 72.94 66.79 30 98.39 90.29 83.36 76.83 68.02 62.29 32 92.14 84.56 78.07 71.96 63.72 58.35 34 86.64 79.51 73.42 67.68 59.93 54.89 36 81.75 75.04 69.29 63.88 56.57 51.81 38 77.39 71.04 65.60 60.48 53.56 49.06 40 73.47 67.44 62.29 57.42 50.86 46.58 42 69.93 64.19 59.29 54.66 48.41 44.35 44 66.71 61.24 56.57 52.15 46.20 42.32 Long. 46 63.78 58.55 54.08 49.87 44.17 40.46 Seams, 48 61.09 56.09 51.81 47.77 42.32 38.77 Single 60 58.62 53.82 49.72 45.84 40.61 37.21 Eiveted. 52 56.35 51.74 47.79 44.07 39.04 35.77 54 54.24 49.80 46.00 42.42 37.58 34.43 56 52.28 48.01 44.35 40.90 36.23 33.20 .-, 58 50.46 46.34 42.81 39.48 34.98 32.04 f: 60 48.77 44.78 41.37 38.15 33.80 30.97 62 47.18 43.33 40.03 36.91 32.71 29.97 64 45.69 41.96 38.77 35.75 31.68 29.02 m 44.30 40.68 37.58 34.66 30.71 28.14 68 42.99 39.48 36.47 33.64 29.80 27.31 70 41.75 38.34 35.42 32.67 28.95 26.53 If 72 40.58 37.27 34.43 31.76 28.14 25.78 '• 74 39.48 36.25 33.50 30.89 27.38 25.08 76 38.43 35.29 32.61 30.08 26.65 24.42 78 37.44 34.38 31.77 29.30 25.96 23.79 80 36.49 33.52 30.97 28.56 25.31 23.20 B92 HAND-BOOK OF LAND AND MARINE ENGINES. TABLE — (Continued) OF SAFE INTERNAL PRESSURES FOR IRON BOILERS. Birmingham Wire Gauge. 1 00 1 2 Thickness of Iron. .375 1 .358 1 Scant. ^^ .340 a .300 .284 Dia. lbs. per lbs. per lbs. per lbs. per lbs. per In. sq. in. sq. m. sq. in. sq. m. sq. in. External 24 225.81 215.26 204.12 179.49 169.67 Diameter. 26 207.93 198,23 187.91 165.35 156.34 28 192.66 183.70 174.23 153.28 144.94 30 179.49 171.15 162.35 142.86 135.09 32 168.00 160.21 151.98 133.76 126.49 34 157.89 150.58 142.86 125.75 118.93 36 148.94 142.05 134.77 118.64 112.21 38 140.94 134.43 127.55 112.30 106.22 40 133.76 127.58 121.06 106.60 100.83 Longitudinal 42 127.27 121.40 115.20 101.45 95.96 Seams, 44 121.39 115.79 109.88 96.77 91.55 Double 46 116.02 110.68 105.03 92.51 87.52 Kiveted, 48 111.11 106.00 100.59 88.61 83.83 Curvilinear 50 106.19 101.70 96,51 85.02 80.43 Seams, 52 102.44 97.73 92.75 81.71 77.33 Single 54 98.59 94.10 89.27 78.69 74.41 Eiveted. 56 95.02 90.66 86.04 75.81 71.73 58 91.70 87.49 83.04 73.17 69.23 60 88.61 84.54 80.24 70.71 66.90 62 85.71 81.78 77.63 68.40 64.72 64 83.00 79.17 75.17 66.25 62.68 66 80.46 76.78 72.87 64.22 60.77 68 78.07 74.47 70.71 62,31 58.96 70 75.81 72.34 68.67 60.52 67.26 72 73.68 70.31 66.74 58.82 55.66 74 71.67 68.39 64.92 57.22 54.15 76 69.77 66.60 63.19 55.70 52.77 78 67.96 64.85 61.56 54.26 51.35 80 66.25 63.22 60.01 52.90 60.06 HAND-BOOK OF LAND AND MARINE ENGINES. 393 TABLE- (Continued) OF SAFE INTERNAL PRESSURES FOR IRON BOILERS. Birmingham Wire Gauge. 3 4 5 6 7 8 Thickness .259 .238 .220 .203 .180 .165 of Iron. i Full. J Scant. 3V lbs. per 3% Full. 3%Scant /^Full Dia. lbs. per lbs. per lbs. pet lbs. per lbs. per In. sq. in. sq. in. sq. in. sq. in. sq. in. sq. in. External 24 154.42 141.64 130.73 120.45 106.60 97.59 Diameter. 26 142.30 130.54 120.50 111.04 98.21 89.99 28 131.94 121.06 111.76 102.99 91.17 83.48 30 122.99 112.86 104.19 96.03 85.02 77.86 32 116.32 105.70 97.59 89.95 79.65 72.94 34 108.30 99.39 91.78 84.60 74.91 68.61 36 102.19 93.80 86.61 79.84 70.71 64.76 38 96.74 88.80 82.00 75.60 66.95 61.32 40 91.84 84.30 77.86 71.78 63.57 58.23 42 87.41 80.24 74.11 68.33 60.52 55.44 44 83.39 76.56 70.71 65.19 57.75 52.90 Long. 46 79.72 73.19 67.60 62.33 55.22 50.58 Seams, 48 76.37 70.11 64.76 59.71 52.90 48.46 Double 50 73.28 67.28 62.11 57.31 50.77 46.51 Kiveted. 52 70.43 64.67 59.74 55.08 48.80 44.71 Curvil. 54 67.80 62.25 57.51 53.40 46.98 43.04 Seams, 56 65.35 60.01 65.44 51.12 45.29 41.50 Single 58 63.07 57.92 53.51 49.35 43.72 40.06 Kiveted. 60 60.96 55.98 51.71 47.69 42.25 38.71 62 58.98 54.16 50.03 46.14 40.88 37.46 64 57.12 52.45 48.46 44.69 39.60 36.28 66 55.37 50.85 46.98 43.33 38.39 35.18 68 53.73 49.35 45.59 42.05 37.26 34.14 70 52.19 47.93 44.28 40.84 36.19 33.16 72 50.73 46.59 43.04 39.70 35.18 32.23 74 49.35 45.32 41.87 38.62 34.22 31.36 76 48.04 44.11 40.76 37.60 33.32 30.53 78 46.80 42.98 39.71 36.63 32.46 29.74 80 45.62 41.90 38.71 35.71 31.64 28.99 394 HAND-BOOK OF LAND AND MARINE ENGINES. T A B L lE^i—iCkmtinued) OP SAFE INTERNAL PRESSURES FOR STEEL BOILERS. Birmingham Wire 3 00 1 2 Gauge. f Thickness of Steel. .375 1 .358 f Scant. .340 .300 .284 Dia. lbs. per lbs. per lbs. per lbs. per lbs. per In. sq. m. sq. m. sq. ID. sq. in. sq. in. External 24 289.03 275.52 261.26 229.74 217.19 Diameter. 26 266.13 253.73 240.31 211.65 200.08 28 246.66 235.13 223.01 196.20 185.45 30 229.74 219.00 207.80 182.85 172.99 32 215.04 205.06 194.15 171.21 161.91 34 202.10 192.74 182.85 160.95 152.22 36 190.63 181.82 172.50 151.86 143.23 38 180.40 172.06 163.25 143.74 135.96 Longitudinal 40 171.21 163.30 154.95 136.44 129.06 Seams, 42 162.90 155.39 147.45 129.85 122.83 Single 44 155.37 148.21 140.66 123.87 117.17 Kiveted. 46 148.50 141.66 134.43 118.41 112.01 48 142.22 135.67 128.75 113.41 107.29 50 136.44 130.17 123.53 108.82 100.03 52 131.12 125.09 118.72 104.59 98.95 54 126.19 . 120.39 114.26 100.67 95.24 56 121.62 116.04 110.13 97.03 91.81 58 117.37 111.99 106.29 93.65 88.61 60 113.41 108.21 102.71 90.50 85.63 62 109.71 104.68 99.36 87.55 82.89 64 106.24 101.37 96.22 84.79 80.23 66 102.98 98.26 93.27 82.20 77.77 68 99,92 95.34 . 90.32 79.76 75.47 70 97.03 92.59 87.89 77.43 73.29 72 94.31 89.99 85.42 75.29 71.24 74 91.74 87.81 83.09 73.24 69.30 76 89.30 85.21 80.89 71.29 67.46 78 86.99 83.01 78.79 69.45 65.72 80 84.79 80.91 76.81 67.70 64.07 HAND-BOOK OF LAND AND MARINE ENGINES. 395 TABLE — (Continued) OF SAFE INTERNAL PRESSURES FOR STEEL BOILERS. Birmingham Wire Gauge. 3 4 5 6 7 8 Thickness .259 .238 .220 .203 .180 .165 of Steel. i Full. i Scant. A A Full. Y^Scant A Full. Dia. lbs. per lbs. per lbs. per lbs. per lbs. per lbs. per IiV sq. in. sq. in. sq. in. sq. in. sq. in. sq. in. External 24 197.63 181.13 167.33 154.18 136.44 124.91 Diameter. 26 182.13 167.09 154.24 142.13 125.80 115.10 28 168.88 154.95 143.04 131.83 116.70 106.85 30 157.42 144.45 133.36 122.92 108.82 99.65 32 147.42 135.29 124.91 115.14 101.94 93.36 34 138.60 127.22 117.47 108.28 95.88 87.81 36 130.80 120.05 110.86 102.20 90.50 82.89 Long. 38 123.82 113.65 104.96 96.76 85.69 78.49 Seams, 40 117.55 107.90 99.65 91.81 81.37 74.53 Single 42 111.40 102.71 94.85 87.45 77.46 70.95 Kiveted. 44 106.71 97.99 90.50 83.44 73.91 67.70 46 102.04 93.68 86.53 79.78 70.67 64.74 48 97.74 89.74 82.89 76.43 67.70 62.02 50 93.07 86.11 79.54 73.35 64.97 59.12 52 90.15 82.77 76.46 70.50 62.45 57.22 54 86.78 79.68 73.60 67.87 60.13 55.09 56 83.65 76.09 70.95 65.43 57.97 53.11 58 80.74 74.14 68.49 63.16 55.96 51.27 60 78.02 71.62 66.19 61.07 54.04 49.55 62 75.49 69.32 64.04 59.06 52.32 47.94 64 73.11 67.13 62.02 57.20 50.68 46.43 m 70.88 65.09 60.13 55.45 49.14 45.02 68 68.77 63.16 58.35 53.52 47.68 43.69 70 66.79 61.28 56.67 52.27 46.31 42.44 72 64.92 59.76 55.09 50.81 45.02 41.25 74 63.16 58.00 53.59 49.43 43.80 40.13 76 61.48 56.47 52.17 48.12 42.64 39.07 78 59.90 55.01 50.83 46.88- 41.54 38.06 80 58.39 53.63 49.55 45.65 40.50 37.11 396 HAKD-BOOK OF LAND AND MARINE ENGINES. T A B Li E — (Continued) OF SAFE INTERNAL PRESSURES FOR STEEL BOILERS. Birmingham Wire f 00 1 2 Gauge. Thickness of Steel. .375 f .358 1 Scant. .340 .300 .284 Dia. lbs. per lbs. per lbs. per lbs. per lbs. per In. sq. in. sq. in. sq. m. sq. in. sq. in. External 24 361.29 344.40 326.58 287.23 271.49 Diameter. 26 332.67 317.24 300.78 264.56 250.14 28 308.25 293.91 278.77 237.95 231.90 30 287.18 273.48 259.75 228.57 216.14 32 268.80 256.34 243.16 214.01 202.39 34 252.63 240.93 228.57 201.19 190.28 36 238.24 227.27 215.62 189.83 179.54 Longitudinal 38 225.50 215.08 204.07 179.67 169.95 Seams, 40 214.01 204.13 193.69 170.55 161.28 Double 42 203.63 194.24 184.31 162.31 153.54 Riveted. 44 194.21 185.26 175.80 154.83 146.47 Curvilinear 46 181.21 177.08 168.04 148.01 140.02 Seams, 48 177.77 169.55 160.94 141.77 134.12 Single 50 170.55 162.71 154.41 136.03 128.69 Riveted. 52 163.90 156.40 148.01 130.73 123.68 54 157.74 150.49 142.83 125.84 119.05 56 . 152.03 145.05 137.61 121.29 114.76 58 146.72 139.99 132.86 117.01 110.76 60 141.77 135.26 128.38 113.13 107.03 62 137.14 130.85 124.20 109.44 103.55 64 132.80 126.74 120.27 105.99 100.29 66 128.73 122.83 116.53 102.75 97.22 68 124.90 119.18 113.13 99.70 94.34 70 121.29 115.74 109.86 96.85 91.62 72 117.89 112.49 106.78 94.11 89.05 74 114.67 109.42 103.87 91.55 86.63 76 111.62 106.51 101.11 89.12. 84.33 78 108.73 103.76 98.49 86.72 82.15 80 105.99 101.14 96.01 84.63 80.08 HAND-BOOK OF LAND AND MARINE ENGINES. 897 T A B L E — ( Concluded) OF SAFE INTERNAL PRESSURES FOR STEEL BOILERS. Birmingham Wire Gauge. 3 4 5 6 7 8 Thickness .259 .238 .220 .203 .180 .165 of Steel. i Full. J Scant. A A Full. ■j^Scant A Full. Dia. lbs. per lbs. per lbs. per sq. in. lbs. per lbs. per lbs. per sq. In. In. sq. in. sq. m. sq. m. sq. in. External 24 247.06 226.62 209.16 192.72 175.63 156.14 Diameter. 26 227.67 208.87 192.80 177.66 157.25 143.98 28 211.10 193.69 178.80 164.78 145.87 133.57 30 196.78 180.57 166.71 153.65 136.03 124.57 32 184.28 169.75 156.14 143.92 127.43 116.70 Long. 34 173.27 159.06 146.84 135.35 119.85 109.77 Seams, 36 163.50 150.07 138.58 127.75 113.13 103.61 Single 38 154.73 142.07 131.20 120.95 107.12 98.11 Eiveted. 40 146.94 134.88 124.57 114.84 101.71 93.16 Curvil. 42 139.85 128.38 118.57 109.32 96.82 88.69 Seams, 44 133.42 122.48 113.13 104.30 92.39 84.64 Single 46 127.55 117.10 108.16 99.73 88.34 80.92 Eiveted. 48 122.18 112.17 103.61 95.54 84.63 ' 77.53 50 117.24 107.64 99.43 91.68 81.22 74.41 52 112.69 103.43 95.53 88.13 78.07 71.53 54 108.47 99.60 92.00 84.84 75.16 68.86 56 104.56 96.01 88.69 81.79 72.46 66.39 58 100.92 92.67 85.61 78.95 69.95 64.08 60 97.53 89.66 82.74 76.26 67.60 61.60 62 94.36 86.65 80.11 73.17 65.44 59.93 64 91.38 83.98 77.53 71.52 63.35 58.04 66 88.59 81.36 75.16 69.32 61.42 56.28 68 85.97 78.95 72.94 67.23 59.60 54.61 70 83.49 76.68 70.84 65.34 57.89 53.05 72 81.16 74.53 68.86 63.51 56.28 51.56 74 78.95 72.50 66.72 61.78 54.75 50.16 76 76.86 70.58 65.21 60.15 53.30 48.84 78 74.87 68.76 63.52 58.60 51.93 47.58 80 72.99 66.96 61.94 57.12 50.62 46.39 34 398 HAND-BOOK OF LAND AND MARINE ENGINES. HAND-BOOK OF LAND AND MARINE ENGINES. 399 MARINE BOILERS. There is now, as there always has been, a great diversity of opinion among engineers in regard to the true principles upon which to design a marine boiler which shall produce the greatest effect with the least stowage, first cost and subsequent labor, and fuel. But experience has shown that the best that can be done is to determine which of these considerations shall have the least weight, and to 'be governed accordingly, looking, as a guide, to practice rather than any assumed theoretical principles. For land purposes, there is hardly any limit to the size or weight of a boiler except first cost ; it is easy, therefore, to design and construct one with sufficient heating ^rface, water space, and steam room. But in designing a marine boiler the case is quite different, as the designer is restricted both in room and weight ; for if the vessel be occupied or loaded down with boilers, it detracts from the room and capacity that should be devoted to other purposes. Marine boilers are of necessity either flue or tubular, since the flame must be within the shell of the boiler ; but in this arrangement they are almost as various as the makers. The large flue is preferable because less liable to choke with soot, ashes, cinders, or salt which may come from leakage. But in situations which restrict length, height, and width of boiler, the only method of producing in a flue boiler such extent of fire surface as will extract all the heat capable of being used to advantage in generating steam, is to reduce the size and multiply the number of flues. The most ordinary forms of marine boilers are the hori- zontal and vertical ; and, so far as efficiency is concerned, there does not appear to be any great difference between 400 HAND-BOOK OF LAND AND MARINE ENGINES. them where equal surfaces are presented to the action of the fire ; but there are many things, particularly in sea- going steamers, to be considered, and for them that boiler is the best which gives equal effect, occupies the least space, and affords the best facilities for cleaning and repairs. A certain proportion between the area of the grate and the total heating surface has been found productive of the best results, with a given description of fuel; but any alteration in the quality of the fuel used will be found to a'ffect this result materially. Consequently, no general rule can be laid down for the design of marine boilers that will answer for all kinds of fuel, nor is it at all likely that any one form will ever fulfil all the varied conditions under which such boilers may be placed. A considepation of great importance in the construc- tion of marine boilers is their capacity to contain water and steam. This, of course, depends upon the size of the boiler and the proportion of space occupied by flues or tubes, as, if the space within it be nearly filled with flues, there can be but little room left for water. In fixing on the proper capacity of the water-space of a marine boiler, there are not such peculiar difliculties as in the case of the steam-chamber, and any one at a first view of the matter would say, as many do without suflS- cient consideration, that there cannot be too little water, provided the boiler is filled to the proper height ; for it is quite obvious the smaller the quantity of water the less will be the expenditure of the fuel during the first getting up of the steam after each stoppage of the engine. It is, however, not the "getting up " the steam, but the keeping it up, that ought to be -considered of most consequence. It is a prevailing opinion that, after the steam is once got up, there is no material difference between keeping a large HAND-BOOK OF LAND AND MARINE ENGINES. 401 quantity of water boiling and a small quantity, provided the escape of heat is prevented by sufficiently clothing the boiler with non-conducting substances ; but on this subject engineers differ. Why practical men should differ in opinion on so plain a matter is unaccountable. The quantity of water carried must exceed that of the evaporation in a given time, in order that the supply of feed-water may not greatly reduce the temperature of the water in the boiler and check the formation of steam. There must in all cases be a sufficient height of water in the boiler to prevent the flues or crown-sheet from becom- ing bare in case the supply of feed-water be neglected, or the vessel pitches in a rough sea. Steam room is understood to be the space in the shell of the boiler above the level of the water, and in marine boilers should be from ten to twelve times the capacity of the cylinder of the engine. This proportion has of necessity a very narrow limit of variation, as, if the steam room be less than the above proportions, at every stroke of the engine the pressure of steam on the surface of the water is liable to be reduced to such an extent as to produce violent ebullition or foaming. When boilers are sq constructed that steam cannot be taken off above the level of the water without the danger of working water into the steam-cylinder, it be- comes necessary to resort to the expedient of attaching a steam-dome to the boiler. This steam-dome is constructed either inside or around the smoke-pipe, which, though not adding much to the cubic capacity of the steam room, has the effect of superheating the steam, or imparting to it an extra heat, which greatly increases its expansive force and renders it less liable to condense in the passages between the boiler and the cylinder. 34^ 2A 402 HAND-BOOK OF LAND AND MARINE ENGINES. PKOPOETIONS OF HEATING SUKFACE TO CYLINDER AND GRATE SURFACE OF NOTED OCEAN, RIVER, AND FERRY-BOAT STEAMERS. ■fe^ '33 tM -M O . CO O Tfl Tt< CO iC -<* CO (M T-l o t^ O CO CO o:) (N CO "^* "*' Tli 'rti lO (M QO lO rH t-- rl^ (M O OS 00 CO O l^ O CC 00 (M O CO O C^ lO 00 rH CO CO ^ ^ ■^ lO rH (M CO "<*H lO lO O CO rH 05 i>- O CO C5 C^ T^^ l^ O CO CO* Tii T}? TJH iC CO tH . o CO CO Tji ''^ T}H td O CO i-H CO C. O CO to 00 CO* CO "^J^ ""ii Tji ^ Tj< rH CO CO CO O 1-* ''t* o r~ "^ •— • -^ t^ O C. Tji Tji Tfi* to to to t- CD tO rtl Tj^ CO "^ CO 00 O (M "* rH rti 1-. rH '^J^ t>. 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