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LESSONS AND PRACTICAL NOTES 
 
 ON 
 
 STEAM, 
 
 
 
 THE STEAM ENGINE, PROPELLERS, 
 
 ETC., ETC., 
 
 oaitg (Enpmrs, Jstttknts, aiUt 
 
 BY THE LATE 
 
 W. H. KING, U. S. N. 
 
 REVISED BY 
 
 CHIEF ENGINEER J. W. KING, U. S. N. 
 
 [NINETEENTH EDITIO\, ENLARGED.] 
 
 D. VAN NOSTKANI), Publisher, 
 
 23 MTJKRAY STBEET & 27 WAKBEN STBEET. 
 1879, 
 
- * 
 
 
 Entered, according to Act of Congress, in the year 1860, 
 
 BY J. W. KIXG : 
 
 In the Clerk's Office of the District Court of the United States for the Southern District of 
 
 New York. 
 
CONTENTS. 
 
 INTRODUCTION, PAGE 6. 
 CHAPTER I. 
 
 STEAM. 
 
 Steam, 7. Mechanical Effect, 9. Expansion of Steam, 12. Table of Hyperbolic 
 Logarithms, 14. Back Pressure, 16. Gain by Expanded Steam, 18. 
 
 EXPANSION VALVES. 
 
 Sickel's, 19. Stevens', 22. Allen & Wells', 23. 
 
 SLIDE CUT-OFFS. 
 
 Explanation, 24. Gridiron Valve, 26. W abash Valve, 29. 
 
 OTHER KINDS OF VALVES. 
 
 Double Poppet, 30. Single Poppet, 81. Hornblower's, 32. Box Valve, 33- 
 Equilibrium Slide, 34. Double Slide Valve, 34. Piston Valve, 35. Long 
 D Slide, 36. Short D Slide, 37. Worthington Pump Valve, 38. Pitts- 
 burg Cam, 39. 
 
 CHAPTER II. 
 
 "THE INDICATOR AND INDICATOR DIAGRAMS. 
 
 The Indicator, 41. Cylinder Diagrams, 44. Air-pump Diagrams, 56. Power 
 Required to Work the Air-pump, 60. 
 
 CHAPTER HI. 
 
 THE HYDROMETER. 
 
 The Hydrometer, 62. Loss by Blowing-off, 64. Gain by the Use of Heaters, 
 68. Injection Water, 71. Evaporation, 72. Steam and Vacuum Gauges, 75. 
 
4 CONTENTS. 
 
 CHAPTER IV. 
 
 CAUSALTIES, ETC. 
 
 Broken Eccentric, 79. Leaking Vessel, 79. Irregular Feed, 80. Foaming, 8L 
 Hot Condenser, 83. Getting Under Way, 85. Coming into Port, 86. 
 Scaling Boilers, 88. On Coming to Anchor, etc., 89. Management of 
 Fires, 90. Patching Boilers, 93. Sweeping Flues, 95. Ash Pits, 95. 
 Smoke-pipe Stays, 96. Grate Bars, &c., 96. Broken Air-pump, 97. Bro- 
 ken Cylinder-head, 98. Selection of Coal, 98. Safety Valve, 99. 
 
 CHAPTER V. 
 
 MISCELLANEOUS. 
 
 Theory of the Paddle Wheel, 101. Centre of Pressure, 114. Screw Propeller,, 
 116. Altering the Pitch, 132. Parallel Motion, 133. Strength of Mate- 
 rials, 136. Surface Condensers, 141. Cylindrical Boilers, 145. Boiler 
 Explosions, 148. Horse Power, 150. Vibration of Beams, 152. Marine 
 Economy, 154. Limit to Expansion, 155. The Proper Lift for a Valve, 
 155. Temperature of Condenser, 156. 
 
 CHAPTER VI. 
 
 WESTERN RIVER BOAT ENGINE. 
 
 Western River High-Pressure Engine, 159. Side Elevation, 159. End View,, 
 160. Explanations of Diagrams, 160. Hartuper's Lifter, 165. Stern Wheel 
 Boats, 167. Dimensions and Proportions of the Magnolia, 169. 
 
 CHAPTER VII. 
 
 BOILERS, ETC. 
 
 Water-Tube Boiler, 172. Horizontal Fire Tube, 173. Extracts from Report of 
 Experiments made to Determine the Relative Efficiency of the Two Boilers, 
 174. Western River Boilers, 179. Boiler Flues, 184. Riveting, 186. Su- 
 perheated Steam, 189. Draft, 191. 
 
 APPENDIX. 
 
 MATERIALS. 
 
 How to Test Iron, 194. Cast Iron, 195. Malleable Iron, 198. Steel, 202. Te- 
 nacity of Metals, 206. Transverse Strength, 206. Resistance to Torsion, 
 207. Results of Repeated Heating Bar Iron, 207. Strength of Joints of 
 Boiler Plates, 209. 
 
 THE ELEMENTS OP MACHINERY. 
 
 Motion, 211. Application of Power, 212. The Lever, 215. Inclined Plane, 217. 
 Wheel and Axle, 219. Pulley, 219. Screw, 223. Wedge, 224. Centre 
 of Gravity, 225. Centre of Pressure, 225 Gravity, 225. Displacement of 
 Fluids, 227. Table of Pressure, Temperature, and Volume of Steam, 228. 
 
INTKODUCTION. 
 
 WHITING a book and then apologizing for having 
 written it, is hardly in accordance with our convic- 
 tions ; but considering, nevertheless, the eminent tal- 
 ent which has preceded us upon the subject we have 
 taken up, a few remarks of explanation may not be 
 out of place. Books heretofore appearing on the 
 steam engine, have been of two classes, or the work 
 itself has been divided into two parts the one for the 
 theorist, the other for the practical man. In the one 
 case long mathematical formulas have been produced, 
 and in the other nothing but simple rules. The prac- 
 tical man, therefore, who has not had the advantage 
 o.f a mathematical education, has nothing presented to 
 him but the bare rules, which he is compelled wholly 
 to reject, or take entirely upon trust. Besides, these 
 works extend over numerous volumes, the study of 
 which involve much time, labor, and expense, and 
 which usually disheartens the practical man before he 
 has made much progress. Having had many of these 
 difficulties to surmount in our earlier studies of the 
 steam engine, we were led to the course of keeping a 
 Steam Journal, in which we noted, from time to time, 
 as we progressed, whatever we thought important, and 
 was made clear to our mind ; and this course we would 
 also recommend the young student ; for, however well 
 
6 INTRODUCTION. 
 
 " it may be to study books containing other mens 1 
 : t}iought% 5^hen ;we write we are led to the habit of 
 thinking fo biirselves, which is of the highest impor- 
 
 : :t^^fe*;^aq4,^b^ l X^pi n g a journal, we have also the 
 very great advantage of having always at our com- 
 mand, in a condensed form, those things which are the 
 more important, and which can be referred to at any 
 time. 
 
 Much of the present work has been taken from the 
 Author's Journal, and the remainder has been sup- 
 plied, from time to time, as he found leisure from his 
 hours of business. 
 
 Our object has not been so much to supply want- 
 ing information, as to direct the student into the habit 
 of thinking and reasoning for himself on those subjects 
 which may be presented for his consideration, and 
 which, in order that he may become eminent in his 
 profession, he must thoroughly understand. It is not 
 sufficient to assert that Newton said this, or somebody 
 else said that. The reasons why they said it, and the 
 fundamental principles upon which they based their 
 conclusions, are necessary to be understood, in order 
 to have a clear understanding of the subject ; and if 
 we have succeeded in making any thing more clear, 
 or in rendering any service to that class of persons 
 who are eagerly seeking for information, but who re- 
 quire some assistance to direct them in the proper 
 channel, our only object in launching this, our little 
 bark, on the troubled sea of authorship, is fully accom- 
 plished, conscious all the while, however, of the many 
 imperfections it contains. 
 
LESSONS AND PRACTICAL NOTES. 
 
 CHAPTER I. 
 
 STEAM. 
 
 STEAM is a thin, elastic, invisible fluid, generated 
 by the application of heat to any liquid, usually water. 
 That, however, which is generated while the water 
 is in a state of ebullition, is alone generally termed 
 steam, while that which is formed while the surface of 
 the water is quiescent, is denominated vapor a dis- 
 tinction, to our mind, without much difference. 
 
 The mean pressure of the atmosphere- at the sur- 
 face* of the ocean is equal to 14.7 pounds per square 
 inch, or is equivalent in pressure to a column of mer- 
 cury 29.9212 inches in height. Under this pressure, 
 fresh water boils at a temperature of 212 Fahrenheit. 
 
 The 212 is, however, not the total number of de- 
 grees in the steam, but simply that which is indicated 
 by the thermometer, and which is termed sensible 
 heat ; for we all know that to raise water from the 
 freezing to the boiling point requires a certain time, 
 and a certain amount of fuel; and we know further, 
 that when the water commences to boil, it does not all 
 evaporate at once, but that the evaporation goes on 
 
8 STEAM. 
 
 gradually, and the time, and hence the fuel required 
 to evaporate it, is much greater than that required to 
 raise it from the freezing to the boiling point. This 
 extra heat must have gone off somewhere, and must 
 be in the steam, but as it is not indicated by the ther- 
 mometer, it is termed latent heat. When the steam is 
 reconverted into water, the latent heat becomes again 
 sensible, which is evidenced by the large amount of 
 water required to condense a small amount in the 
 shape of steam. The precise ratio the one bears to 
 the other shows the latent, compared with the sensible 
 heat. 
 
 The subject of latent heat has been one of unusual 
 interest, ever since the invention of the steam engine, 
 and numerous theories have been advanced, and nu- 
 merous experiments made some of them not very 
 carefully in order to determine the exact law it fol- 
 lowed ; but none, up to Regnault's time, seem to have 
 settled the subject satisfactorily. Some maintained 
 that the latent heat of steam was a constant quantity, 
 some that the sum of sensible and latent heat was a 
 constant quantity, and that quantity was 1202 Fahr- 
 enheit. This was the most popular theory, and was 
 the one generally adopted by engineers. Others, 
 again, maintained that neither the sensible, latent, nor 
 sum of the sensible and latent heats, were a constant 
 quantity, but that they all varied. The exact ratio, 
 however, in which they varied was not established 
 until Regnault undertook his able series of experi- 
 ments at the instigation of the French Government. 
 These are the latest and most reliable experiments, 
 and we subjoin, therefore, a table compiled from his 
 labors, which we earnestly recommend to the attention 
 of the reader. 
 
MECHANICAL EFFECT. 
 
 REGNAULT'S EXPERIMENTS. 
 
 Degrees of heat contained in saturated steam, in Fahrenheit degrees 
 of heat and English inches. 
 
 J .l~ 
 
 
 c;5 ^~ 
 
 2 d-2 '^.-' 
 
 
 j 
 
 *o ^.2 
 
 Corresponding elastic 
 
 i ! g H 
 
 *S ft : 
 
 Corresponding elastic 
 
 2'S e^ 
 
 2 *.|1 
 
 force 
 
 sjf 
 
 8 S3 
 
 force 
 
 f-ll^ 
 
 Sl>.3 
 
 
 a_^J3 
 
 5 1 *j,g 
 
 
 C3 r-( xa T rl 
 
 p,s g^l 
 
 In 
 
 In Atmo- 
 
 3~J* 
 
 ||g| 
 
 In 
 
 In Atmo- 
 
 ffjl 
 
 !l<s 
 
 Inches. 
 
 spheres. 
 
 ii 
 
 I 1 !* 5 
 
 Inches. 
 
 spheres. 
 
 II b 
 
 Fah. 
 
 
 
 
 
 
 
 
 32 
 
 0.1811 
 
 0.006 
 
 1123.70 
 
 248 
 
 58.7116 
 
 1.962 
 
 1189.58 
 
 50 
 
 0.3606 
 
 0.012 
 
 1129.10 
 
 266 
 
 79.9321 
 
 2.671 
 
 1194.98 
 
 68 
 
 0.6846 
 
 0.023 
 
 1134.68 
 
 284 
 
 106.9930 
 
 3.576 
 
 1200.56 
 
 86 
 
 1.2421 
 
 0.042 
 
 1140.16 
 
 302 
 
 140.9930 
 
 4.712 
 
 1205.96 
 
 104 
 
 2.1618 
 
 0.072 
 
 1145.66 
 
 320 
 
 183.1342 
 
 6.120 
 
 1211.54 
 
 122 
 
 3.6212 
 
 0.121 
 
 1151.06 
 
 338 
 
 234.7105 
 
 7.844 
 
 1216.94 
 
 140 
 
 5.8578 
 
 0.196 
 
 1156.64 
 
 356 
 
 297.1013 
 
 9.929 
 
 1222.52 
 
 158 
 
 9.1767 
 
 0.306 
 
 1162.04 
 
 374 
 
 371.7590 
 
 12.425 
 
 1227.92 
 
 176 
 
 13.9621 
 
 0.466 
 
 1167.62 
 
 392 
 
 460.1943 
 
 15.380 
 
 1233.50 
 
 194 
 
 20.6869 
 
 0.691 
 
 1173.02 
 
 410 
 
 560.9673 
 
 18.848 
 
 1238.90 
 
 212 
 
 29.9212 
 
 1.000 
 
 1178.60 
 
 428 
 
 684.6584 
 
 22.882 
 
 1244.48 
 
 230 
 
 42.3374 
 
 1.415 
 
 1184.00 
 
 446 
 
 823.8723 
 
 27.535 
 
 1249.88 
 
 FIG. 1. 
 
 MECHANICAL EFFECT. 
 
 We will now take into consideration the mechani- 
 cal effect of steam, and a common-place demonstration 
 will serve our purpose. 
 
 Suppose a cylinder, A, Fig. 
 1, to be one square inch in 
 area of cross section, and fitted 
 with a steam tight piston, at- 
 tached by means of a flexible 
 cord to the weight <5, which is 
 of sufficient size to balance the 
 weight of the piston, and all 
 the parts to work without 
 friction. Now suppose a quan- 
 tity of water, equal to one 
 
 6 
 
 O 
 
 cubic inch, to be placed in the bottom of this cylinder, 
 
10 MECHANICAL EFFECT. 
 
 and a fire to be lighted under it. The temperature 
 of the water will gradually rise until it attains 212% 
 when it will commence to boil, and the piston will 
 soon begin, and continue to rise if the cylinder be 
 long enough until it obtains a height of 1700 inches 
 from the base. This 1700 is the volume of steam at 
 atmospheric pressure, the water being 1, from which it 
 is generated. If, now, we suppose to be added to the 
 weight, #, another weight equal to the pressure of the 
 atmosphere or a fraction less, so that motion may en- 
 sue and the steam under the piston to be condensed, 
 the piston will return to the bottom of the cylinder 
 by the pressure of the atmosphere, through a space 
 of 1700 inches, and will have raised the extra weight of 
 14.7 Ibs. appended to <5, up that distance. Hence this 
 cubic inch of water, by its evaporation, produced a 
 mechanical effect of raising 14.7 pounds through a 
 space of 1700 inches = (14.7 X 1700) = 24,990 pounds 
 through one inch. 
 
 Let us now take another cylinder, B, Fig. 2, similar 
 in every respect to A, excepting that the piston has a 
 weight laid upon it equal to the pressure of the atmo- 
 sphere, viz., 14.7 pounds, and suppose a fire to be 
 lighted under this cylinder. The water, as in the 
 other case, will be heated up to the boiling point, 
 which, in this case, will be 250, corresponding to the 
 pressure of two atmospheres when it will commence 
 to evaporate, and the piston will rise until it obtains a 
 height of 900 inches from the base, this being the 
 volume of steam under the pressure of two atmo- 
 spheres, water being 1. If, now, we suppose this pis- 
 ton to be fixed where it is, the weight removed from 
 the top of it and applied to e, then the steam condensed 
 toe. piston unfixed, it will return to the bottom of 
 
MECHANICAL EFFECT. 11 
 
 the cylinder, raising the weight applied to c, up a dis- 
 tance of 900 inches. Now, then, since the weight of 
 14.7 Ibs. was first raised 900 inches on the top of the 
 piston, and afterwards raised the same distance by be- 
 ing attached to e, the total distance moved = (900 X 2) 
 = 1800 inches, which is equal to (14.7 X 1800) = 26460 
 pounds raised one inch. The difference, therefore, be- 
 tween the work done in the first and second case 
 (26460 24990) = 1470 Ibs. raised one inch high, 
 which is 5.88 per cent, of the first number. If this 
 extra work was obtained without any extra fuel, which 
 would be the case were the total heat in steam at all 
 temperatures a constant quantity, it would be all gain, 
 but as such is .not the case, and as more heat is required 
 in the latter than in the former case, we will see what 
 this amounts to, and the difference between this loss 
 and the other gain will show the true gain. In the 
 first instance, it will be seen that the total heat in the 
 steam was 1178.6, and in the second, 1190; hence, 
 supposing the water in both cases to be at a tempera- 
 ture of 100 before the fires are lighted which is 
 about the temperature at which water is fed into ma- 
 rine boilers there would be required in the latter 
 case (1190- 100) = 1090 from the fuel, and in the 
 former case (1178.6 100) = 1078.6 from the fuel; 
 difference 11.4, which is 1.057 per cent, of 1078.6. 
 
 The extra fuel, therefore, required under the pres- 
 sure of two atmospheres is 1.057 per cent., and the 
 extra work done is 5.88 per cent., leaving a gain of 
 4.823 per cent. 
 
 In the same way we could ascertain what the gain 
 would be at any other pressure, either higher or lower; 
 but these examples suffice to show that the higher the 
 pressure of the steam, the greater is the mechanical 
 
12 EXPANSION OF STEAM. 
 
 effect with the same amount of fuel, but the gain is 
 small, and in practice, therefore, where great accuracy 
 is not required, it is neglected altogether. 
 
 Starting, therefore, from the assumption that the 
 mechanical effect performed by the same amount of 
 fuel is the same, no matter what the pressure may be 
 under which the steam is generated, we shall proceed 
 to the study of the 
 
 EXPANSION OF STEAM. 
 
 Opening a communication with the cylinder and 
 shutting it off again before the piston arrives at the 
 end of the stroke is called expansion of steam, or work- 
 ing steam expansively. Thus, supposing steam to be 
 admitted into the cylinder until the piston arrives at 
 half stroke, and the communication then to be shut off, 
 the steam already in the cylinder, by its expansion, 
 will force the piston to the end of the stroke ; by 
 which arrangement we gain all the work performed 
 after the steam is cut-off. 
 
 Take, for instance, a cylinder, A, Fig. 3, 
 two units in length, one unit in area of 
 cross section, and an initial pressure of 1, 
 the work performed during the first half 
 stroke, i. e., while the piston travels from 
 b to 0, will be 1 x 1 X 1 (area x pressure 
 X distance travelled ==) 1, and the work 
 j performed during the latter half stroke = 
 1 X .69 X 1 = .69, the total work, there- 
 
 fore, performed throughout the stroke 
 
 1-69 = 1.69. Now, if the steam, instead of be- 
 ing expanded from c to d, had been exhausted at <?, the 
 total work performed would have been only 1 instead 
 
EXPANSION OF STEAM. 13 
 
 of 1.69, and the quantity of steam would have been the 
 same, hence we see that by cutting off at one half the 
 same steam performs 69 per cent, more work. This 69 
 per cent, is what is termed the gain in cutting off, but it 
 does not, however, represent the saving in fuel, as we 
 will show presently ; but before proceeding to illus- 
 trate that subject we will explain to the student, from 
 what source we derive this 69. 
 
 Marriotte's law of gases is, that the spaces occupied 
 are inversely as the pressures. That is to say, if steam 
 of 20 pounds pressure per square inch, be allowed to 
 expand into double the space, the pressure will be 
 10 Ibs. ; if triple, 6-J Ibs. ; if four times, 5 Ibs. ; if five 
 times, 4 Ibs., and so on. This theory would be liter- 
 ally correct did the temperatures remain constant ; but 
 as the temperature of all gases becomes reduced by ex- 
 pansion, the law does not hold good ; nevertheless, in 
 the steam engine, where there are so many extraneous 
 circumstances which practically affect all calculations 
 appertaining to the same, it is considered all that is 
 ever required, and from its extreme simplicity is uni- 
 versally adopted. 
 
 From this law the pressure can be 
 ascertained approximately by dividing 
 the cylinder into a number of equal 
 parts, say eight, ascertaining the pres- 
 sure at each of those points, and taking 
 the mean. If the initial pressure, as 
 before, be supposed to be unity, the 
 pressure at each of the first four divi- 
 sions cutting off at half stroke will be 
 1 ; at the fifth division (A = ) .8 ; at the 
 6th (-1) = .6666; at the Yth (| =) .5714; 
 at the 8th (=),. 5; the mean pressure, therefore, by 
 
 .5714 
 .5000 
 
 .6345 
 
14 
 
 TABLE OF HYPERBOLIC LOGARITHMS. 
 
 this process, after the steam is cut off = .6845, and the 
 mean pressure before it is cut off = 1, the mean, there- 
 fore, throughout the stroke ( ~^~~ r) .8172. 
 
 This, however, is only an approximation, and in order 
 to arrive at any degree of accuracy, the divisions would 
 have to be very numerous, which would render the 
 operation tedious and lengthy. Fortunately, however, 
 we can dispense with this part of the calculation alto- 
 gether, for the Naperian or Hyperbolic logarithms, as 
 set forth in the following table, furnish to our hand 
 the ratios of pressures : 
 
 TABLE OF HYPERBOLIC LOGARITHMS. 
 
 1 
 
 c 
 
 lg> 
 
 1 
 
 P 
 
 o 
 
 }i 
 
 1 
 
 o 
 
 It 
 
 1 
 
 
 
 .2 
 
 || 
 
 | 
 I 
 
 p 
 
 1 
 
 IH 
 
 J? 
 
 w 
 
 to 
 
 w 
 
 to 
 
 i 
 
 to 
 
 W 
 
 
 ft 
 
 1.05 
 
 .049 
 
 3.05 
 
 1.115 
 
 5.05 
 
 1.619 
 
 7.05 
 
 1.953 
 
 9.05 
 
 2.203 
 
 1.1 
 
 .095 
 
 3.1 
 
 1.131 
 
 5.1 
 
 1.629 
 
 7.1 
 
 1.960 
 
 9.1 
 
 2.208 
 
 1.15 
 
 .140 
 
 3.15 
 
 1.147 
 
 5.15 
 
 1.639 
 
 7.15 
 
 1.967 
 
 9.15 
 
 2.214 
 
 1.2 
 
 .182 
 
 ! 3.2 
 
 1.163 
 
 5.2 
 
 1.649 
 
 7.2 
 
 1.974 
 
 9.2 
 
 2.219 
 
 1.25 
 
 .223 
 
 i 3.25 
 
 1.179 
 
 5.25 
 
 1.658 
 
 7.25 
 
 1.981 
 
 9.25 
 
 2.225 
 
 1.3 
 
 .262 
 
 i 3.3 
 
 1.194 
 
 5.3 
 
 1.668 
 
 7.3 
 
 1.988 
 
 9.3 
 
 2.230 
 
 1.35 
 
 .300 
 
 1 3.35 
 
 1.209 
 
 5.35 
 
 1.677 
 
 7.35 
 
 1.995 
 
 9.35 
 
 2.235 
 
 1.4 
 
 .336 
 
 1 3.4 
 
 1.224 
 
 5.4 
 
 1.686 
 
 7.4 
 
 2.001 
 
 9.4 
 
 2.241 
 
 1.45 
 
 .372 
 
 i 3.45 
 
 1.238 
 
 5.45 
 
 1.696 
 
 7.45 
 
 2.008 
 
 9.45 
 
 2.246 
 
 1.5 
 
 .405 
 
 3.5 
 
 1.253 
 
 5.5 
 
 1.705 
 
 7.5 
 
 2.015 
 
 9.5 
 
 2.251 
 
 1.55 
 
 .438 
 
 3.55 
 
 1.267 
 
 5.55 
 
 1.714 
 
 7.55 
 
 2.022 
 
 9.55 
 
 2.257 
 
 1.6 
 
 .470 
 
 3.6 
 
 1.281 
 
 5.6 
 
 1.723 
 
 7.6 
 
 2.028 
 
 9.6 
 
 2.262 
 
 1.65 
 
 .500 
 
 3.65 
 
 1.295 
 
 5.65 
 
 1.732 
 
 7.65 
 
 2.035 
 
 9.65 
 
 2.267 
 
 1.7 
 
 .531 
 
 3.7 
 
 1.308 : 
 
 5.7 
 
 1.740 
 
 7.7 
 
 2.041 
 
 9.7 
 
 2.272 
 
 1.75 
 
 .560 
 
 3.75 
 
 1.322 I 
 
 5.75 
 
 1.749 
 
 7.75 
 
 2.048 
 
 9.75 
 
 2.277 
 
 1.8 
 
 .588 
 
 3.8 
 
 1.335 
 
 5.8 
 
 1.758 
 
 7.8 
 
 2.054 
 
 9.8 
 
 2.282 
 
 1.85 
 
 .615 
 
 3.85 
 
 1.348 ! 
 
 5.85 
 
 1.766 
 
 7.85 
 
 2.061 
 
 9.85 
 
 2.287 
 
 1.9 
 
 .642 
 
 3.9 
 
 1.361 | 
 
 5.9 
 
 1.775 
 
 7.9 
 
 2.067 
 
 9.9 
 
 2.293 
 
 1.95 
 
 .668 
 
 3.95 
 
 1.374 1 
 
 5.95 
 
 1.783 
 
 7.95 
 
 2.073 
 
 9.95 
 
 2.298 
 
 2. 
 
 .693 
 
 4. ' 
 
 1.386 
 
 6. 
 
 1-792 
 
 8. 
 
 2.079 
 
 10 
 
 2.303 
 
 2.05 
 
 .718 
 
 4.05 
 
 1.399 ! 
 
 6.05 
 
 1.800 
 
 8.05 
 
 2.086 
 
 15. 
 
 2.708 
 
 2.1 
 
 .742 
 
 4.1 
 
 1.411 
 
 6.1 
 
 1.808 
 
 8.1 
 
 2.092 
 
 20. 
 
 2.996 
 
 2.15 
 
 .765 
 
 4.15 
 
 1.423 
 
 6.15 
 
 1.816 
 
 8.15 
 
 2.098 
 
 25. 
 
 3.219 
 
 2.2 
 
 .788 
 
 4.2 
 
 1.435 
 
 6.2 
 
 1.824 
 
 8.2 
 
 2.104 
 
 30. 
 
 3.401 
 
 2.25 
 
 .811 
 
 4.25 
 
 1.447 
 
 6.25 
 
 1.833 
 
 8.25 
 
 2.110 1 
 
 35. 
 
 3.555 
 
 2.3 
 
 .833 
 
 4.3 
 
 1.459 
 
 6.3 
 
 1.841 
 
 8.3 
 
 2.116 j 
 
 40. 
 
 3.689 
 
 2.35 
 
 .854 
 
 4.35 
 
 1.470 
 
 6.35 
 
 1.848 
 
 8.35 
 
 2.122 
 
 45. 
 
 3.807 
 
 2.4 
 
 .875 
 
 4.4 
 
 1.482 
 
 6.4 
 
 1.856 
 
 8.4 
 
 2.128 
 
 50. 
 
 3.912 
 
 2.45 
 
 .896 
 
 4.45 
 
 1.493 
 
 6.45 
 
 1.864 
 
 8.45 
 
 2.134 
 
 55. 
 
 4.007 
 
 2.5 
 
 .916 
 
 4.5 
 
 1.504 
 
 6.5 
 
 1.872 
 
 8.5 
 
 2.140 
 
 60. 
 
 4.094 
 
 2.55 
 
 .936 
 
 4.55 
 
 1.515 
 
 6.55 
 
 1.879 
 
 8.55 
 
 2.146 ! 
 
 65. 
 
 4.174 
 
 2.6 
 
 .956 
 
 4.6 
 
 1.526 
 
 6.6 
 
 1.887 
 
 8.6 
 
 2.152 
 
 70. 
 
 4.248 
 
 2.65 
 
 .975 
 
 4.65 
 
 1.537 
 
 6.65 
 
 1.895 
 
 8.65 
 
 2.158 j 
 
 75. 
 
 4.317 
 
 2.7 
 
 .993 
 
 4.7 
 
 1.548 
 
 6.7 
 
 1.902 
 
 8.7 
 
 2.163 
 
 80. 
 
 4.382 
 
 2.75 
 
 1.012 
 
 4.75 
 
 1.558 
 
 6.75 
 
 1.910 
 
 8.75 
 
 2. 169 
 
 85. 
 
 4.443 
 
 2.8 
 
 1.032 
 
 4.8 
 
 1.569 
 
 6.8 
 
 1.917 
 
 8.8 
 
 2.175 
 
 90. 
 
 4.500 
 
 2.85 
 
 1.047 
 
 4.85 
 
 1.579 
 
 6.85 
 
 1.924 
 
 8.85 
 
 2.180 
 
 95. 
 
 4.554 
 
 2.9 
 
 1.065 
 
 4.9 
 
 1.589 
 
 6.9 
 
 1.931 
 
 8.9 
 
 2.186 
 
 100. 
 
 4.605 
 
 2.95 
 
 1.082 
 
 4.95 
 
 1.599 
 
 6.95 
 
 1.939 
 
 8.95 
 
 2.192 
 
 1000. 
 
 6.908 
 
 3. 
 
 1.099 
 
 5. 
 
 1.609 
 
 7. 
 
 1.946 1 
 
 9. 
 
 2.197 
 
 0000. 
 
 9.210 
 
EXPANSION OF STEAM. 
 
 15 
 
 FIG. 5. 
 
 [ 
 
 a 
 
 3 
 
 4 
 5 
 6 
 
 7 
 
 C c- D 
 
 The hyperbolic logarithm of any number can be 
 found by multiplying the common logarithm by 
 2,30258509. 
 
 From the nature of hyperbolic logarithms they are 
 thus very useful in working steam, expansively. 
 
 Let the Line A, B, Fig. 5, represent 
 the pressure of steam which we will as- 
 sume to be unity at the time the cut-off 
 valve closes ; C, D, half the length of A, 
 B, and the line A, C, a hyperbolic curve, 
 .69+ from the table gives the mean length 
 of all the ordinates, 1, 2, 3, 4, &c., which 
 before we had to arrive at by approxima- 
 tion. If the cut-off valve, instead of closing 
 at half stroke, had closed at some other 
 point, say, when the piston had traveled 
 only one-fourth its distance, C, D, would be one-fourth 
 of #, 5, and the curve A, C, would have extended from 
 a to <?,' giving 1.38+ as a mean of all the ordinates 
 below a, b. 
 
 All we require then in working examples in ex- 
 pansion of steam, according to Marriotte's law, is to 
 know the initial pressure and point of cutting off, from 
 which we can deduce the mean pressure, pressure at 
 the end of the stroke, percentage of gain, &c., by 
 having before us a table of hyperbolic logarithms; 
 but if it be required to make such calculations, when a 
 table of this kind is not come-at-able, it can be done in 
 the manner we have previously shown. 
 
 EXAMPLE 1st. Suppose you have a cylinder in 
 which you are using steam of 20 pounds pressure per 
 square inch, inclusive of the atmosphere, and cut off at 
 half stroke, what is the mean pressure, pressure at the 
 
 end of the stroke, and per centage of gain. 
 2 
 
16 BACK PRESSURE. 
 
 Ans. 1st. From the foregoing considerations we 
 know that had the pressure of steam been 1 pound in- 
 stead of 20, all we would have to do would be to take 
 .69314 out of the table, add 1 to it and divide by 2 ; 
 therefore to find the mean pressure we have this rule : 
 As the number of times the steam is expanded, is to the 
 hyperbolic logarithm of that number plus 1, so is the 
 initial to the mean pressure, hence 2 : 1.69314::20: 
 16.9314lbs. mean pressure. 
 
 Ans. 2d. 20-f-2 = 10 Ibs. pressure at the end of the 
 stroke. 
 
 Ans. 3J. Work performed before expansion, 1. 
 after expansion, .69314. Therefore 1 : .69314 : : 100 : 
 69.314 per cent, gain by cutting off at half stroke. 
 
 BACK PRESSURE. 
 
 Inasmuch as it is impossible in practice to obtain 
 a perfect vacuum, there is always a certain amount of 
 steam in the cylinder opposed to the motion of the 
 piston, and this is termed back pressure. Suppose for 
 example, there was in the above instance 4 Ibs. per 
 square inch back pressure, the mean effective, or un- 
 balanced pressure, would be 16.9314412.9314 Ibs., 
 and the unbalanced pressure at the end of the stroke 
 would be 104=6 Ibs. 
 
 EXAMPLE 2d. Suppose the steam in example 1st 
 had been cut off at a \ from commencement of stroke, 
 what would have been the mean pressure, pressure at 
 the end, and percentage of gain in that case ? Also 
 the mean unbalanced pressure, and unbalanced pressure 
 at the end, the back pressure being 4 Ibs per square 
 inch? 
 
BACK PRESSURE. 17 
 
 Ans. 1st. 4 : 2.38629 : : 20 : 11.93145 Ibs. mean pres- 
 sure. 
 
 Ans. %d. 20 ~ 4 = 5 Ibs. pressure at the end. 
 
 Ana. 3d. 1 : 1.38629 : : 100 : 138.629 per cent. 
 
 Ans. 4:tk. 11.93145 4 Y.93145 mean unbalanced 
 pressure. 
 
 Ans. 5th. 54 1 Ib. unbalanced pressure at the 
 end. 
 
 It is useless hereto multiply examples ; those already 
 given we consider sufficient to give the student a clear 
 understanding of the manner in which these calcula- 
 tions are made, but we would recommend him to make 
 a number of others for himself, and work them out so 
 as to render himself the more familiar and ready with 
 the modus operandi. 
 
 "We come now to the percentage of gain of fuel by 
 using steam expansively. It has been previously 
 shown that when the steam is cut off at one half, the 
 work done before expansion takes place being repre- 
 sented by 1, the work done afterwards is .69 ; the total 
 work therefore performed is 1.69 ; now had not the 
 cut-off valve closed at all, the total work performed 
 would have been 2. Hence by this operation we have 
 the power of the engine reduced from 2 to 1.69. It is 
 therefore necessary to increase the initial pressure of 
 steam to make up this decreased power ; and keeping 
 in view Marriotte's law, we will let this pressure be 
 represented by x ; hence 2 : 1.69 : : x : .845 a?, the mean 
 pressure. It is manifest that the mean pressure in this 
 case must be the same as if the steam followed full 
 stroke, in order that the powers may be the same; 
 consequently 
 
 .845 x = 1 Ib. 
 
 x = 1.18 Ib. initial pressure. 
 
18 GAIN BY EXPANDED STEAM. 
 
 But only half a cylinder full of this steam is used to 
 every full cylinder of the other, consequently the dif- 
 ference between 1.18-^2 and 1, equals the saving, 
 which is 41 per cent. 
 
 To ascertain the saving of steam at any other point 
 of cutting off, take the hyperbolic log. of 3, 4, 5, 6, 
 <fec. as the cutting-off point may be -i-, J, -i-, -J-, &c., and 
 proceed in the same manner, or, in other words, divide 
 the whole length of the stroke by the portion traveled 
 before the steam is cut off; take the hyperbolic log. of 
 the quotient and proceed as above. 
 
 The 41 per cent, in the above example, is the 
 saving in steam that is to say, should a steamer, 
 using steam full stroke, perform a certain distance 
 in a certain time, cut the steam off at half-stroke r 
 and increase the initial pressure in the ratio of 1 
 to 1.18, she would perform the same distance in the 
 same time with 41 per cent, less steam. Not 41 per 
 cent, less coals put into the furnaces, but 41 per cent, 
 of that which reaches the cylinders minus the loss 
 from condensation due to expansion, i. e. that por- 
 tion of the fuel not combustible, and that portion pass- 
 ing out of the chimney in the shape of heat to produce 
 draft, together with the loss from radiation and con- 
 densation before the steam reachers the cylinders must 
 first be deducted. When this is done it will be found 
 that the actual saving will be reduced to less than 20 
 per cent., which is about the real saving of fuel in 
 practice cutting off at half stroke, and pro rata for any 
 other point varying somewhat according to better or 
 worse constructions. Any engineer can satisfy himself 
 on this point by using his steam with and without ex- 
 pansion for a sufficient given time, carefully weighing 
 all the coals and recording all the data. 
 
EXPANSION VALVES. 
 
 19 
 
 This should not therefore be confounded with the 
 69 per cent., which is theoretically the increased work 
 performed by the same steam over what it would have 
 performed had it not been cut off at all. 
 
 EXPANSION VALVES. 
 
 There are a variety of expansion valves and arrange- 
 ments for cutting off steam ; the principles operating 
 the more important of which we will now proceed to 
 examine. The following diagrams or sketches will 
 serve our purpose. We shall simply explain the lead- 
 ing features of each, in order to give an understanding 
 of the principles that govern them, leaving the student 
 to suggest for himself the 
 alterations in the mechani- 
 cal arrangement to adapt 
 them to different types 
 and arrangements of en- 
 gines. 
 
 Figure 1 is a diagram 
 of Sickel's momentarily 
 adjustable cut-off, in which 
 A, A, is the steam valve 
 of the double poppet con- 
 struction ; B, B, valve 
 stem ; C, dash-pot, filled 
 with water up to the line d 
 1, 2; D, plunger, fitting 
 in the dash-pot ; E, stuf- 
 fing-box, which is packed 
 air and water-tight; x, 
 hole in the bottom of the 
 plunger D, to allow the 
 water to enter when the plunger strikes it; J, a 
 
20 EXPANSION VALVES. 
 
 rod communicating motion to the wiper F, which 
 trips the valve ; A, a rod receiving motion from the 
 air-pump beam or any other part having motion coin- 
 cident with that of the piston. The motion of h is 
 communicated through the vertical rod, having c as a 
 fixed centre to , and thence to the wiper F. The 
 manner in which this cut-off operates is this: The 
 valve stem, instead of being permanently attached to 
 the lifting rod, is secured to it by a clutch and spring. 
 The valve is lifted by the eccentric, (operating as in 
 other cases,) but before it reaches its seat again, the 
 wiper F, which vibrates back and forth, strikes the 
 clutch, and detaches the valve from the lifter; the 
 valve then, from the action of gravity, would fall, and 
 strike its seat with a heavy blow ; to prevent which, 
 and allow the valve at the same time to fall quickly, 
 it is attached to the plunger D, working in the dash- 
 pot C. By this arrangement, before the valve reaches 
 its seat, the plunger D strikes upon the water in the 
 lower part of the dash-pot C, which is called the secon- 
 dary reservoir, and thereby allows the valve to close 
 without slamming, the water escaping into the cavity #, 
 and also around the plunger, into the upper or primary 
 reservoir. The plunger D, being hollow, small holes 
 are bored into it in the vicinity of the line 1, 2, to 
 allow the water to escape into it also. 
 
 We see that the cutting-off is effected by the wiper 
 F tripping the valve ; the sooner therefore the valve 
 is tripped, the sooner the steam will be cut off. Now 
 the manner in which this is made an adjustable cut-off, 
 is accomplished by moving the handle f backward or 
 forward on the arc <7, which will move the centre c to 
 one side or the other of its present position, the center e 
 remaining constantly fixed, and therefore giving the 
 
EXPANSION VALVES. 21 
 
 wiper F a greater or less distance to travel before 
 striking the clutch. By this means the cutting-off 
 point can be varied for any part of the stroke. The 
 handle /can be put in such a position that the valve 
 will not be tripped at all, or it can be placed so that 
 the valve will not lift at all, being exactly in the ver- 
 tical position when the lifter commences to rise. The 
 engine can be thus stopped by this cut-off. For the 
 other end of the cylinder there is another dash-pot, 
 &c., similar to the one described, the wiper being ope- 
 rated by a rod similar to , attached to the center d. 
 
 Should there be too much water in the dash-pot, 
 the valve will not seat quickly, but " hang," as it is 
 technically termed. At a there is a cock for the pur- 
 pose of supplying it with water. Attached to the 
 dash-pot, there is usually another cock or valve for 
 the purpose of letting out any superfluous water. In- 
 sufficient water is evidenced by the slamming of the 
 valve. 
 
 This cut-off was formerly made without the wiper 
 F, there being used instead a sliding cam, shaped 
 something like this < . As the valve rose up, the 
 clutch struck the bevel on this cam, which forced the 
 clutch out of its position, and allowed the valve to fall. 
 With this arrangement, however, it will be seen that 
 the valve must trip while it is rising, and as it is at its 
 highest position when the piston is about half stroke, it 
 cannot be possible to cut off by this mode longer than 
 half stroke ; but with the arrangement of the wiper, it 
 will be seen, inasmuch as it vibrates back and forth, 
 that the valve can be just as well tripped on its descent 
 as when rising, and this is the reason why it was sub- 
 stituted for the cam. 
 
 " Stevens" The next cut-off that we shall take 
 
22 
 
 EXPANSION VALVES. 
 
 FIG. 2. 
 
 s into consideration is Stevens's, a diagram of which is 
 shown in figure 2. A A are the steam toes ; B B, 
 the steam-lifting toes ; D, rock-shaft arms ; C C, the 
 valves ; #, pin in rock-shaft 
 arm for eccentric hook. The 
 manner in which this is 
 made an adjustable cut-off, 
 is by raising or lowering the 
 toes A A, thereby giving 
 them more or less lost mo- 
 tion. In the position in 
 which they are shown in the 
 diagram, it will be seen that 
 they will have to travel a 
 considerable distance before 
 touching the toes B, B, and 
 as the piston is in motion 
 during this time; and the 
 steam valve closed, the 
 steam will be acting expan- 
 sively. If the end of the toes A A be dropped lower 
 down, the steam will be cut off shorter ; if raised higher 
 up, longer. By dropping the toes down, however, we 
 diminish the lift of the valve, and also alter the lead. 
 To retain the one, we raise the pin a in the rock-shaft 
 arm, and the other we turn the eccentric a little ahead. 
 To alter the point of cut-off, therefore, while the engine 
 is in motion, so as to cut off shorter, we have first to 
 drop the toes A A, then raise the pin a, and set the ec- 
 centric ahead. To cut off longer, reverse the operation. 
 The number of things required to be altered in 
 changing the point of cutting-off is a very great objec- 
 tion to this arrangement. In practice it has seldom 
 been accomplished without stopping the engine. 
 
EXPANSION VALVES. 
 
 23 
 
 Allen and Wells. This cut-off is represented by 
 sketch, figure 3. A, A, are the exhaust toes ; B B, 
 steam toes ; C C lifting toes ; D D, the valves ; E E', 
 
 FIG. 8. 
 
 palls fitted to the end of the toes B, B' ; F, rock-shaft 
 arm, which is operated from the eccentric in the usual 
 
24 SLIDE CUT-OFFS. 
 
 way ; G G, a cross arm secured to the end of the rock- 
 shaft arm ; a a, rollers on the end of the cross-arm G, 
 G' ; H H, two arms fitted loosely on the rock-shaft. 
 These arms receive their motion from any part of the 
 engine having motion nearly coincident with that of 
 the piston ; b b', rollers on these arms. This cut-off 
 operates thus : The rock-shaft is put in motion by the 
 eccentric. The pall E resting upon the roller a, is 
 raised, and with it the toe B, and lifter toe C ; but 
 after the pall E is raised up so as to clear the roller 5, 
 the pall E slides in on top of #, which, having a down- 
 ward motion, lowers the valve, while the rock-shaft 
 arm continues to rise. The rollers b ', being attached 
 to the arms H H, which having motion nearly coinci- 
 dent with that of the piston, start to go down at nearly 
 the same time the rock-shaft arm starts to rise. Now 
 then by turning around the right and left-hand screw 
 c c, the rollers b b', will be set further apart, or closer 
 together, and will therefore alter the time they will 
 clear the end of the pall E, and hence the point of cut- 
 ting off. To follow farther separate the rollers b b', 
 to cut off shorter, screw them closer together. In 
 altering the point of cutting off we have nothing to do 
 but to turn around the screw c c. 
 
 This cut-off is like " Sickel's," momentarily adjust- 
 able, but it cannot, however, be made to cut off quite 
 so short as " Sickel's." 
 
 SLIDE CUT-OFFS. 
 
 In the use of the ordinary three-ported slide-valve, 
 or other slide-valves combining both the steam and 
 exhaust, the expansive principle can be carried only 
 to a very small extent, owing to the derangement of 
 
SLIDE CUT-OFFS. 25 
 
 the exhaust passages. Suppose, for instance, that suffi- 
 cient lap be given to the steam side of the valve to 
 cause the steam to be shut off at half-stroke, and sup- 
 pose the same amount of lap be given also to the ex- 
 haust side, it is manifest, that when the steam is shut 
 off, the exhaust will be shut off also, and the pent up 
 steam, therefore, having no escape, and increasing in 
 pressure as the piston approaches the end of the stroke, 
 will act as a serious retarding force. This arrange- 
 ment, therefore, cannot operate. 
 
 Now, then, suppose that we put lap on the steam 
 side, as before, but none on the exhaust, in which 
 event another difficulty equally great presents itself. 
 It is this : 
 
 Supposing the valve, Fig. 4, to have neither lap 
 nor lead, when the end a arrives at #', steam will just 
 begin to be admitted into the cylinder, but the point 
 
 Fio. 4, 
 
 J, at the same time, will have arrived at the point b r , 
 and steam just begin also to exhaust ; now, then, let 
 half an inch be added to each end of the valve at a 
 and Z>J when the valve begins to open to steam in this 
 case, #, instead of being at a', will be half an inch past 
 it ; and, as there has been no lap added to the exhaust 
 side, b will be half an inch past &', so that the exhaust 
 
26 SLIDE CUT-OFFS. 
 
 must have opened considerably before the piston ar- 
 rived at the end of the stroke ; hence, in this case, we 
 exhaust too soon. 
 
 All we can do, therefore, in practice, is to strike a 
 mean between these evils ; that is to say, when we add 
 lap to the steam side, add lap also to the exhaust side, 
 but not so much so that we open the exhaust before 
 the piston arrives at the end, and close it again before 
 it reaches the other end. The shortest this kind of 
 valve can be made to cut-off to advantage in practice, 
 is considered about -- from commencement of stroke ; 
 but even this we consider most too short for beneficial 
 working of large engines. 
 
 Owing to these confined limits, the beneficial re- 
 sults obtainable from the expansive principle by this 
 arrangement is very small, which has led to the adop- 
 tion of an independent slide cut-off valve, situated on a 
 separate face, back of the steam valve, as shown in 
 
 FIG. 5. 
 
 Fig. 5, in which a' is the steam, and b b the cut-off 
 valve. The valve a having only sufficient lap to cover 
 the ports a' a' fairly, when it is in the middle of 
 the stroke, operates as in other cases, but the lap 
 on b b can be made to any required extent, so that 
 
SLIDE CUT-OFFS. 27 
 
 during a large part of the stroke the ports b' V 
 are closed, preventing further access of steam to the 
 cylinder, notwithstanding the steam valve itself is 
 open. The valve b b is operated by an independent 
 eccentric, through the valve stem E. In the position 
 shown in the figure the steam is cut off about half 
 stroke: d' shows another opening covered with the 
 valve d, having a stem c sliding loosely through the 
 valve b b ; the other end of the stem passing through 
 the chest, has a handle attached to it for the purpose 
 of moving the valve d, in order to open the port d', 
 when the engine is stopped. This is necessary, for the 
 reason that the engine may stop when the valve b b is 
 in such a position as to prevent the steam from enter- 
 ing to the steam valve a, and the engine could not, 
 therefore, be started. In the figure, the cut-off valve 
 has but two ports for the admission of steam, but any 
 number of ports can be made the more numerous, 
 the less stroke will be required to get the necessary 
 opening. This is what is termed the gridiron valve, 
 from the resemblance it bears to that very useful in- 
 strument. 
 
 After this valve is once made, the point of cutting 
 off usually remains fixed, but it can, however, be varied 
 
 within narrow limits by altering the stroke of the 
 valve. Thus, in Fig. 6, supposing the end of the valve 
 stem to be raised from a to b, the valve, instead of 
 
28 SLIDE CUT-OFFS. 
 
 being closed, as shown, will be open the distance b c, 
 and will therefore have that much additional to travel 
 before the steam is cut off; hence, by increasing the 
 travel of the valve we increase the point of cutting off, 
 and conversely, supposing the pin a had been lowered 
 in the rock-shaft arm the distance a e, equal to a b, 
 the ports, instead of being closed, as shown, would 
 be closed the distance b c; the steam, therefore, would 
 be cut off sooner. But by altering the point of cutting 
 off we also alter the lead of the valve ; for, taking the 
 case in which we increased the travel of the valve, we 
 see that when it would have been closed with the 
 original lead, it lacked the distance b c. If its travel 
 had been reduced, it would have lacked that much of 
 being open. To obviate this, whenever the travel of 
 the valve is altered, the eccentric should also be altered^ 
 so as to retain the original lead. 
 
 If the travel of the valve be made too great, the 
 valve d will pass entirely over the port <?, and gradu- 
 ally close e\ unless they be set some distance apart. 
 If the travel be made too small, the steam will be shut 
 off, and the motion of the eccentric being reversed 
 long before the piston arrives at the end of the stroke, 
 steam will be admitted to it again before the steam 
 valve closes. 
 
 From the above facts, and the figure before us, we 
 draw the following general conclusions in reference to 
 this kind of slide cut-off valves : 
 
 That, with a given amount of lap, the cutting off 
 point can be varied from the longest point of cutting 
 off allowable by said lap, to a certain point within the 
 stroke, by reducing the stroke of the valve and alter- 
 ing the eccentric so as to retain the original lead. If 
 the stroke be reduced beyond this, steam will be shut 
 
SLIDE CUT-OFFS. 
 
 29 
 
 off and given to the piston again before it arrives at 
 the end of the stroke. In practice, this variation will 
 not amount to more than from about | to f of the 
 stroke. 
 
 In altering the stroke of the valve, the slot through 
 which the pin a moves should be an arc of a circle, 
 struck with a radius equal to the length of the link d a, 
 and with d as a centre. 
 
 With equal leads, the cutting off point cannot be 
 effected equally on both ends of the cylinder with a 
 slide valve, owing to the connecting rod acting out of 
 parallelism, or, in other words, owing to the crank not 
 being at 90 when the piston is half way. The shorter 
 the connecting rod, the greater the discrepancy. 
 
 FIG. 6f 
 
 CONNECTS CONDENSER 
 
 LLJJ 
 
 Pig. 6^, is an arrangement of cut-off valve as con- 
 structed by Messrs. Merrick & Son, of Philadelphia, 
 in 1855, for the U. S, Steam Frigate " Wabash." 
 
 In consequence of the satisfactory manner in whicL 
 it worked on board that vessel ; its simplicity, and 
 easy adjustment for cutting off at any portion of the 
 
30 OTHER KIKD OF VALVES. 
 
 Btroke likely to be required, it lias been applied to 
 nearly all the U. S. Screw ships recently constructed, 
 as also to a number of other engines. C is the steam 
 valve ; D D are the cut-off valves, attached to the valve 
 stem E by right and left hand screws working in nuts 
 let into the valves ; F F, rings in the steam chest cover, 
 fitting close down on the back of the main steam valve, 
 enclosing the space G, which is connected to the con- 
 denser by the pipe H, for the purpose of balancing 
 the valve. 
 
 This cut-off can be worked by a separate eccentric, 
 or from any part of the engine having a motion coin- 
 cident with that of the piston. 
 
 To alter the point of cutting-off, a wheel is on the 
 end of the valve stem E, which, if turned in one direc- 
 tion, will draw the valves closer together, and the 
 openings will not be closed so soon, consequently the 
 steam will follow the piston farther, i. e. cut off longer. 
 To cut off shorter, the operation is reversed. 
 
 OTHER KIND OF VALVES. 
 
 Having explained the principles of the leading cut- 
 offs, we will now take a glance at some of the most 
 prominent steam and exhaust valves now in use; but, 
 inasmuch as the student is supposed to understand the 
 leading features of most of these, we will not devote 
 much time to this part of our study. 
 
 Figure Y is a diagram of a double poppet valve, 
 in which the rectangular space, a b c d is the open- 
 ing to the cylinder ; A B, the steam valves, and C D, 
 the exhaust valves. The object of this arrangement is 
 to make the valve a balance valve. Thus the steam 
 acting on the top of A and bottom of B, if they were 
 
OTHER KIND OF VALVES. 
 
 of equal size, an equilibrium would be established, but 
 the valve B is made just small enough to slip through 
 
 Fie. 7. 
 
 FIG. 8. 
 
 the upper seat, so that the difference in area serves to 
 keep the valves fairly in their seats.* On the exhaust 
 side the reverse is the case. The steam acts under C, 
 and on top of D, the lower valve D is usually made 
 the larger. In order to get D into its place, the upper 
 seat is either made removable by being secured in its 
 place by tap-bolts, or a hand-hole is cut in the side of 
 the steam-chest, or, in some cases, it is passed in through 
 the cylinder nozzle. 
 
 Figure 8 is a diagram of the single poppet valve, 
 in which A is the steam valve, and B, the exhaust. 
 With these kinds of 
 valves we see that we 
 require considerable 
 power to operate 
 them by hand, as we 
 have the full pressure 
 of steam on the back 
 of A, and also the 
 exhaust on B; but 
 when the engine is hooked on the pressure is in part 
 balanced. On the steam valve this is occasioned at 
 the time the valve is opened, by the exhaust valve 
 
 *In some cases, the areas of the valves are equal, and they are seated by their own weight. 
 
 8 
 
32 
 
 OTHER KIND OF VALVES. 
 
 being closed before the piston arrives at the end of the 
 stroke, producing the pressure called cushion. And 
 on the exhaust valve the pressure is reduced (at the 
 time the valve is opened) by expansion. In some 
 cases this pressure is but little above that in the con- 
 denser. It is therefore obvious that these valves can 
 be made to work with but little power from the engine. 
 They also have the advantage of being easily made 
 tight and occupying but little room. 
 
 The disadvantage of working by hand, however, 
 led to the adoption of the double poppet valve, the 
 single poppet being the earlier invention. The double 
 poppet valve is the one now almost universally used in 
 American low-pressure river, or marine paddle-wheel 
 engines,, 
 
 Figure 9 is a representation of what is termed 
 " Horn blower's " valve, in which a a b b are the valve 
 
 seats ; A A, the valve ; B, one of a number of cross- 
 bars secured to the top of the valve, to which the 
 
OTIIEK KIND OF VALVES. 
 
 valve stem is attached. From the figure it will be 
 seen that the only surface the steam has to act upon 
 to keep the valve in its seat, is the upper edge, c c, of 
 the valve ; it is therefore an equilibrium valve. 
 
 t Figure 10 is what is termed a box valve; a a 
 are the parts communicating with the cylinder; 5, 
 
 FIG. 10. 
 
 steam-pipe ; <?, the exhaust ; A A, the valve having an 
 opening through its center communicating with the 
 exhaust, c ; d d, packing. An inspection of the figure 
 will show the operation of the valve. The object of 
 this kind of valve is also to establish an equilibrium. 
 Figure 11 is a longitudinal section, and figure 12 
 
 FIG. 11 
 
 a top view of what is termed the equilibrium slide. 
 
OTHER KIND OF VALVES. 
 
 FIG. 12- 
 
 This valve has a ring, A A, on the back of it, which 
 being made steam tight, the 
 pressure is taken off the space 
 enclosed by the ring. The pres- 
 sure is taken off the back of 
 nearly all the valves of large en- 
 gines now-a-days, fitted with the 
 short slide, either in this way or 
 by having the ring secured to 
 the top of the chest, and the valve sliding under it. 
 
 Figure 13 shows a slide valve A A A, having 
 openings b b through it for the admission of steam ; 
 
 FIG. 13. 
 
 a a a is another valve sliding on the back of the 
 valve A A A; a a a is the cut-off, which operates 
 thus : The valve A A A being put in motion, and 
 the cut-off valve lying loosely on its back, is carried 
 with it until the end of the valve #, a, &, strikes the 
 steam chest, when its motion is arrested, while the 
 steam valve continues to move, the result is the clos- 
 ing the opening 5, and the cutting off the steam. The 
 sooner, therefore, the slide a a a strikes the chest, the 
 sooner the steam is cut off. The point of cutting-off 
 can be varied by having a screw running through the 
 
OTHER KIND OF VALVES. 
 
 chest, which can be moved further 
 against which the valve a a a strikes. 
 With this arrangement it will be seen 
 that the cut-off must close at further- 
 est a little before the piston arrives at 
 half stroke, or not close at all. This 
 cut-off is applicable to horizontal sta- 
 tionary engines. 
 
 Fig. 14 is a piston valve, in which 
 a a' are the openings into the cylin- 
 der ; C, exhaust opening ; A B D E 
 the valve packed at b c d e with 
 rings or other packing. In the position 
 shown in the figure, steam is being 
 exhausted through the openings a' 
 and C into the condenser, while steam 
 is being admitted into the opposite 
 end of the cylinder through the open- 
 ing a. When the valve has its full 
 throw in the opposite direction, steam 
 will be admitted through the opening 
 a' while it is being exhausted through 
 #, and the opening F F through the 
 valve and through C into the con- 
 denser. 
 
 in or out 
 
 Fig.14. 
 
 and 
 
36 OTHER KIND OF VALVES. 
 
 Figure 15 shows the long D slide, with the full 
 
 FIG. 15. 
 
 opening for steam under the piston; Fig. 16, same 
 
 FIG. 16. 
 
 valve showing full opening for steam on top of the 
 piston ; Fig. 17, longitudinal section of the valve alone. 
 
 FIG. 18. 
 
 FIG. 17. 
 
 and Fig. 18, cross section of the same. A is the steam 
 pipe, B, the exhaust, C, packing to keep the steam and 
 exhaust separate, steam being admitted into the chest 
 or valve casing at A, fills the vacant space under and 
 around the valve, but cannot escape past the ends 
 
OTHER KIND OF VALVES. 
 
 Fio. 19 
 
 
 owing to the packing C C ; and, when the valve is 
 placed in the position shown in Fig. 15, steam is ad- 
 mitted under the piston in the direction shown by the 
 arrows, at the same time that it is exhausted through 
 the upper opening, and the valve being hollow 
 through it and pipe B into the condenser. When the 
 valve is moved in the opposite direction, steam is ad- 
 mitted above the piston in the direction shown by the 
 arrows in Fig. 16, and exhausted 
 through the lower opening directly 
 through the pipe B to the condenser. 
 
 This style of valve is in extensive 
 use on English marine, and other 
 engines. The objection to it is the 
 friction, requiring several men to 
 work the starting bar when the en- 
 gine is operated by hand. 
 
 Fig. 19 is a longitudinal section 
 of the short D slide, and Fig. 20, an 
 end view of the same. A A' are the 
 openings into the cylinder ; B B, the 
 communications to the condenser ; C, 
 steam pipe. In the position shown 
 in the figure, steam is being admitted 
 through A into the cylinder, and ex- 
 hausted through A' into the con- 
 denser, c c is packing on the back of 
 the valve. 
 
 
 coj 
 
 FIG. 20. 
 
 LlQ 
 
 'fib \| 
 
38 
 
 OTHER KIND OF VALVES. 
 
 FIG. 21. 
 
 1S3EI 
 
 FIG. 22. 
 
 VALVE 
 
 FACE 
 
 Figure 21 is a view of the Worthington pump 
 
 steam valve; figure 
 22, the valve face, 
 and figure 23, the 
 valve seat. The fig- 
 ures explain them- 
 selves. In the or- 
 dinary slide valve, 
 when it is moved 
 in one direction, 
 steam is given to 
 the piston in the 
 same direction, but 
 the object of this 
 valve, as invented 
 by H. E Worth- 
 ington, of N. York, 
 is to cause it, when 
 moved in one direc- 
 tion, to give steam 
 to the piston in tl^ 
 opposite direction. 
 The valve being operated by an arm projecting from 
 the piston rod, which strikes collars on the valve stem, 
 renders it necessary that when the valve is moved in 
 one direction, steam should be given to the piston in 
 the opposite direction, in order to reverse its motion ; 
 by this arrangement the intervention of levers is un- 
 necessary, as the end is accomplished direct. 
 
 FIG. 23. 
 
 VALVE 
 
 SEAT 
 
THE PITTSBUPwG CAM. 
 
 39 
 
 FIG. 24. 
 
 FIG. 25. 
 
 The Pittsbwg Cam. Figures 24, 25, and 26, show 
 
 different forms of this 
 cam. Like letters refer 
 to like parts. A B C D 
 is a yoke fitting over the 
 cam a l> c ; E is a rod 
 attached to the valve 
 stem. F, main shaft of 
 the engine to which the 
 cam is secured. It will 
 be seen that by the revo- 
 lution of the cam a b c, 
 within the yoke ABC 
 D, the rod E will be 
 caused to move back and 
 forth, and thereby open 
 and shut the valve. 
 
 Fig. 24 is a cam made 
 to cut off at half stroke ; 
 figure 26, J stroke, and 
 figure 25 follows full 
 stroke. The manner in 
 which these cams are 
 laid off is this. From 
 the centre F, with a ra- 
 dius dependent upon the 
 stroke of the valve, de- 
 scribe a circle, as shown 
 partly in dots and partly 
 in full lines in the fig- 
 ures ; divide this circle 
 into any convenient even 
 number of equal parts, 
 say sixteen ; then, supposing we wish to cut off at half 
 
40 OTHER KIND OF VALVES. 
 
 stroke, taking figure 24, place one foot of the dividers 
 having a radius equal to the diameter of the circle at 
 j$, and describe the arc terminating at , then move 
 the foot of the dividers from c to a, and describe 
 another arc terminating also at b ; then, with the same 
 radius, and b as a centre, describe the arc a c; the 
 figure thus enclosed will be the required cam. It will 
 be observed that, while the cam is traveling the dis- 
 tance a 1 that being an arc of a true circle no mo- 
 tion can be given to the valve, but while it travels 
 from 1 to 2 the valve is opened and shut. Now, then, 
 inasmuch as the piston moves from one end of the cyl- 
 inder to the other for each semi-revolution of the cam, 
 and inasmuch as the distance from a to 1 is the same 
 as from 1 to 2, the valve remains necessarily closed 
 during one-half of the stroke. 
 
 In figure 25, as no part of the outline of the cam is 
 concentric to the shaft F, the valve must be in motion, 
 all the time the cam is in motion. In figure 26, as 
 three-quarters of the semi-periphery of the cam is con- 
 centric to the shaft F, the valve will remain closed 
 during three-quarters of the stroke. Instead of making 
 the points b sharp, as shown in the figures, they can be 
 turned off, and, to retain the same dimensions on the 
 cam, an equal amount added to the arc a c. Thus, 
 taking figure 25, suppose we cut off the point of the 
 cam to x y, and increase the lower extremity to H I, 
 this will not alter the point of cutting off, but it re- 
 duces the travel of the valve, and has the effect of 
 keeping the valve stationary when wide open, while 
 the earn travels through the arc x y. 
 
CHAPTER II. 
 
 THE INDICATOR AND INDICATOR DIAGRAMS. 
 
 THE steam engine indicator is an instrument used 
 for the purpose of exhibiting the performance of the 
 steam engine. By its application to the steam cylinder 
 we can ascertain the following particulars: Whether 
 the valves are properly constructed and set ; steam and 
 exhaust passages of the right size ; whether the piston 
 or valves leak ; the amount of vacuum or back pres- 
 sure, and pressure of steam upon the piston ; the power 
 of the engine; power required to overcome its friction, 
 and also to work any machinery attached to the same, 
 &c. In truth, it is the stethoscope of the physician, 
 revealing the internal working of the engine. 
 
 The following description of the instrument and cut, 
 Fig. 27, we take from Paul Stillman's Treatise on the 
 Indicator. The cut shows the style manufactured at 
 the Novelty Iron Works, New York city : 
 
 A is a brass case enclosing a cylinder, into which a 
 piston is nicely fitted. To the piston-rod a spiral 
 spring is attached to resist the steam and vacuum 
 when acting against it. B is a pencil attached to the 
 piston rod. C is an arm attached to the case, and sup- 
 porting a cylinder D, which may be caused to rotate 
 back and forth a part of a revolution in one direc- 
 tion, by means of a line or cord 0, attached to a suit- 
 able part of the engine and in the other by means of 
 
42 
 
 THE INDICATOR AND INDICATOR DIAGRAMS 
 
 FlGi 
 
 a strong watch spring within the cylinder D. Outside 
 
 this cylinder is to be wound a 
 
 paper, upon which a diagram 
 
 will be made, by the combined 
 
 action of the piston and paper 
 
 cylinder, representing, by its 
 
 area, the power exerted on one 
 
 side of the piston during the 
 
 whole revolution of the engine. 
 
 ^/' are springs to secure the paper 
 
 to the cylinder ; g is a scale 
 
 divided into parts corresponding 
 
 to the pounds of pressure on the 
 
 square inch. These divisions, 
 
 for convenience of measuring the 
 
 diagrams with a common rule, 
 
 are generally made in some re- 
 
 gular parts of an inch, as 8ths, 
 
 lOths, 12ths, 20ths, 30ths; h is 
 
 a cock by means of and through 
 
 which it is connected with the 
 
 engine cylinder. 
 
 HoW r TO ATTACH THE INDICATOR. 
 
 Into whatever part of the 
 engine it may be desired to ap- 
 ply the indicator, there must 
 first be inserted a small stop-cock, with a socket to 
 receive the one connected with the indicator. The 
 instrument is to be set into this in such a position that 
 the line attached to the paper cylinder shall lead 
 through or over the guide pulley toward the place 
 whence it is to receive its motion. An extension of 
 this line should be connected with some part of the 
 
THE INDICATOR AND INDICATOR DIAGRAMS. 43 
 
 engine, the motion of which is coincident with that of 
 the piston, and which would give the paper cylinder a 
 motion of about three-fourths of a revolution. If the 
 engine is of the construction denominated beam or 
 lever engine, and is provided with a " parallel motion " 
 the parallel bar, or a pulley on the radius shaft, fur- 
 nishes the proper motion; if otherwise, the beam 
 centre may be resorted to. In the kind denominated 
 square engines, the centre of the air pump gives it. In 
 horizontal and vertical direct acting engines, it will 
 frequently be found necessary to erect a temporary 
 rock-shaft, or lever, connected with the cross-head. 
 Particular care should be taken, when the power of the 
 engine is to be estimated, that the motion communi- 
 cated be perfectly coincident with that of the piston. 
 
 In nearly all forms of the steam engine, the proper 
 motion may be obtained by attaching a line to the 
 cross-head, and passing it over a delicately constructed 
 pulley, to the axis of which should be attached a 
 smaller one, from which a line shall connect with the 
 indicator. The proportional sizes of the two pulleys, 
 of course, should be as the distance traveled by the 
 piston to the length of motion given to the paper 
 cylinder of the indicator. It will be necessary to at- 
 tach a strong spring to the axis of these pulleys, to 
 produce the reverse motion promptly. In an oscillat- 
 ing engine, it will be necessary that the indicator, with 
 its fixtures, should be attached to the cylinder. 
 
 As the paper cylinder cannot make more than 
 about three-fourths of a revolution without disturbing 
 the point of the pencil, it will be seen that the line 
 communicating the motion must be of a definite length. 
 It also require* to be readily connected and discon- 
 nected. 
 
44 THE INDICATOR AND INDICATOR DIAGRAMS. 
 
 The indicator having been attached to the steam 
 cylinder, the paper secured smoothly on the cylinder 
 D, figure 27, and the length of the line e being ad- 
 justed so that by the vibration of D it does not strike 
 the stops, we will proceed to take a diagram, first 
 taking care to see that the paper cylinder D is so fixed 
 that the springs// do not come in contact with the 
 pencil B. The pencil B being adjusted so that it 
 touches lightly on the paper, throw it back and attach 
 the hook on the line E to the line receiving motion 
 from the engine ; then open the cock A, and allow the 
 piston to work up and down several times, in order to 
 heat and expand all the parts of the instrument. This 
 being accomplished, turn the pencil on and take the 
 diagram. Shut off the cock A, and apply the pencil 
 again to the paper, and it will describe the atmospheric 
 line. 
 
 Figure 28 is a diagram taken from the U. S. S. 
 
 FIG. 28 
 
 10) 204.5 
 
 20.45 Ibs. mean unbalanced pressure; 
 
THE INDICATOR AND INDICATOR DIAGRAMS. 45 
 
 Frigate " Powhatan," fitted with the double-poppet 
 balanced valves, and Sickels' cut-off, on the 15th of 
 January, 1854, while on the passage from Hong Kong, 
 China, to the Loo-Choo Islands. At #, the piston of 
 the indicator being at the bottom of its stroke, steam 
 is admitted, forcing it up to b / at b the cylinder upon 
 which the paper is wound having motion coincident 
 with that of the steam piston starts to turn, describ- 
 ing the line b c; at c the expansion valve closes, and 
 the pressure therefore gradually falls to d, where the 
 exhaust valve opens and the pressure falls suddenly to 
 e f the steam piston now starts on the return stroke, 
 and the spring within the cylinder D, fig. 2Y, forces it 
 back to the beginning a of the diagram. The line 
 from a to b is called the receiving line ; from b to c the 
 steam line ; from c to d, the expansibn line ; d to 0, the 
 exhaust; e to #, the vacuum line. The numbers in 
 the vertical column on the right-hand side of the figure, 
 are the pounds pressure ; 14.Y is the true vacuum line, 
 0, the atmospheric line, and 14, the initial pressure of 
 steam above the atmosphere. The figures along the 
 top line are the feet in length of the cylinder. It will 
 be seen that the cut-off valve closed when the piston 
 had traveled a very little beyond half stroke. The 
 rounding at d and a is the lead and cushion on the 
 exhaust. That is to say, the exhaust valve opened at 
 d, before the piston arrived at the end of the stroke, 
 and it also closed again at &, before the piston reached 
 the other end of the stroke. Had there been no lead 
 both of these corners would have been well defined. 
 
 LTorder to calculate the power of the engine, the 
 mean pressure on the piston must be known, and from 
 no source but the indicator can it be accurately ascer- 
 tained. The manner of arriving at this is simply by 
 
46 INDICATOR DIAGRAMS. 
 
 taking the total pressure at different points and adding 
 them up and taking the mean, as shown in fig. 28. 
 
 Figure 28 is what would be termed among en- 
 gineers a good diagram ; so is also figure 29, which we 
 will take for a further elucidation of the subject. 
 
 FIG. 29. 
 
 Steam, 10 " Powhatan " stb. cylinder, bottom 
 
 Vacuum, 27 Nov. 7, 1855, 10 A. M. 
 
 Hot well, 106 Fahr. One engine and one wheel in 
 
 Revolutions,.... 9.5 operation. 
 
 Throttle, 8. Smooth sea. 
 
 ATMOSPHERIC LINE 
 
 Tc// \ 
 
 i 
 
 \l 
 
 It appears from this diagram, however, that the 
 piston of the indicator worked rather tightly, which 
 occasioned it to stick a little in some places, as is evi- 
 denced by the steps in the expansion line, and also at 
 a 1> in the vacuum line. If the piston of the indicator 
 become much scratched, similar effects will be produced. 
 Great care should, therefore, be taken in its use, to see 
 that neither the piston works too tightly nor too loose- 
 ly ; for on the one hand it will stick, and thereby pro- 
 duce an imperfect outline, and on the other hand will 
 produce the same effect by exhibiting false vacuum and 
 expansion lines. 
 
INDICATOR DIAGRAMS. 47 
 
 Should figure 29, instead of being as shown in full 
 lines, have the lower right hand corner cut off as shown 
 in dots at c d, the defect would have been that the ex- 
 haust valve closed too soon at c instead of e occa- 
 sioning excessive cushioning. With some engines, 
 however, a large amount of cushioning is necessary to 
 prevent them from thumping on the centres. 
 
 Had the upper right-hand corner been rounding, as 
 shown by the dotted line f g, the defect would have 
 been that the steam valve opened too late. Had the 
 exhaust corner been cut off, as shown by the dotted 
 lines Ji i, the exhaust valve would have opened too 
 soon ; but had it been in the form shown by the dot- 
 ted line Jc ?, it would have opened too late, and after it 
 did commence to open, would move with too slow a 
 velocity, preventing the free escape of steam, or the 
 exhaust passages would have been too small, which 
 would produce a similar effect to the valve opening too 
 slowly. Had the steam line, instead of being parallel 
 to the atmospheric line, fallen down in the direction 
 m n, it would have shown that the throttle was par- 
 tially closed, or the steam passages too small, prevent- 
 ing the full flow of steam into the cylinder. 
 
 Should there be excessive lead given to the steam 
 valve, the line d m, instead of being at right angles to 
 the atmospheric line, will have the top inclined to the 
 right as from L to M. 
 
 In taking a diagram for the purpose of estimating 
 the power of the engine only, the atmospheric line is 
 not necessary ; but in order to ascertain the vacuum 
 it cannot be dispensed with, unless the indicator piston 
 be forced down to the perfect vacuum and held there 
 until that line be described. 
 
 In a diagram taken 'from a non-condensing engine, 
 
45 INDICATOR DIAGRAMS. 
 
 the atmospheric line will of course be entirely below 
 it, owing to the back pressure occasioned from the 
 passage of the exhaust steam through the openings 
 and pipes. Had figure 29 been taken from a non-con- 
 densing engine, A B would have been the atmospheric 
 line. 
 
 Figure 30 we have copied from Main and Brown's 
 Treatise on the Indicator and Dynamometer. It was 
 
 Fio. 30. 
 
 taken from an engine fitted with the long D slide. 
 There are two defects exhibited in this diagram ; the 
 steam communication is opened too late and the ex- 
 haust too soon. At C the exhaust closes, causing the 
 steam to be compressed to O, when the piston having 
 arrived at the end of the stroke starts on its return, 
 and the pressure falls to O' ; at O' steam is admitted, 
 causing the line O' A to be traced ; at B the exhaust 
 opens long before the piston arrives at the end of the 
 stroke, allowing the steam to escape too soon. The 
 hook, as shown at O, would only be made in very 
 aggravated cases, where the steam is very much be- 
 hind time. 
 
INDICATOR DIAGRAMS. 
 
 49 
 
 Fig. 31 is obtained from the same source as figure 
 30. In this case the engine was working y as a non- 
 
 FIQ. 81. 
 
 condensing engine with a very low pressure of steam. 
 The exhaust closes at A, causing the pent-up steam to 
 be compressed to B, where the steam valve opens, 
 and the pressure in the cylinder being greater than 
 that in the boiler, immediately falls to C. The hook 
 at C is occasioned by the momentum of the indicator 
 piston. At D the cut-off closes, causing the steam to be 
 expanded to E, below the atmosphere. At E the 
 exhaust valve opens and the pressure rises up equal to 
 the back pressure, causing the loop on that corner of 
 the diagram. 
 
 Figure 32 is a diagram drawn from memory, from 
 one of a non-condensing 
 engine that was once 
 shown the author, with 
 the request that he 
 point out the defect in 
 the engine from which 
 such a diagram was 
 taken. At first we did 
 not see any reason why 
 the pressure should rise from b to <?, for supposing the 
 exhaust to open at $, there could be no reason why 
 the pressure should rise beyond J, the amount of back 
 pressure on the opposite side of the piston. After 
 looking at it a little closer, however, it occurred to us 
 
 FIG. 32. 
 
50 
 
 INDICATOR DIAGRAMS. 
 
 that such a diagram could be formed from a slide valve 
 engine, and in this manner : Steam being admitted in 
 the usual way until the piston arrived at #, the inde- 
 pendent slide cut off the steam, whence it was expanded 
 to the point b j at b the steam valve having neither 
 lap nor lead, and consequently still open the cut-off 
 again opened the communication with the cylinder, 
 admitting fresh steam, which caused the line b c to be 
 traced, partaking of the motion of the steam and piston. 
 At c the steam is shut off by the steam valve itself, 
 and the exhaust opened, the pressure therefore falls 
 from that point to d, and the exhaust line is traced. 
 In a non-condensing engine diagram, where of course 
 there can be no vacuum line, the line from c to e in- 
 clusive is termed the exhaust. 
 
 A perfect Diagram. According to the law laid 
 down by Marriotte, which we have previously studied 
 under the head of expansion of steam, the expansion 
 curve of an indicator diagram should be a true hyper- 
 
 FIG. 83. 
 
 bolic curve, were there no extraneous circumstances to 
 cause it to be otherwise ; but unfortunately in practice 
 this perfection is not attainable were Marriotte's law 
 
INDICATOR DIAGRAMS. 51 
 
 literally true, owing to the time required for steam to 
 enter and leave the cylinder^ clearance of piston, space 
 in nozzles between the valves, leakage of valves, piston 
 condensation in the cylinder, <fec. Fig. 33 is intended 
 to show a perfect diagram, having all the corners well 
 defined and the expansion line a true hyperbolic curve. 
 From this figure we purpose explaining the manner of 
 laying out a true hyberbolic curve. Let A E be the 
 true vacuum line, and B C the steam line. Divide 
 A E into any number of equal parts, and erect the 
 perpendiculars A B, 1 1', 2 2', <fec. 'Now we see that 
 the steam follows the distance A, 2, or two divisions 
 before it is cut off; the length of the ordinate 3 3', 
 being three divisions from the commencement should 
 be | of 2, 0- the length of 4 4', | of 2, C; of 5 5',f ; 
 of 6 6' 5 1 ; of 7 7', \ ; of E D, f. With the lengths 
 of all these ordinates marked on the diagram, draw 
 through the points 3', 4', 5', 6', 7', &c., the line C D, 
 and you have the required curve. 
 
 An experienced engineer can tell at a glance 
 whether an engine is in good working order from its 
 diagram ; but nevertheless, in most cases it would be 
 well to draw the true curve, in order to ascertain how 
 much the actual one differs from it, for by this means 
 we can ascertain, while under way, whether the valves 
 or piston leak; but in drawing the true curve, the 
 clearance of the piston and space in the nozzles, &c., 
 must be ascertained, and that much added to the length 
 of the diagram, in order to obtain the curve accurately. 
 Thus, supposing this space to be equal in capacity to 
 six inches in length of the cylinder, make the diagram 
 six inches longer than it actually is, and proceed in the 
 manner we have shown. 
 
 Should the steam valves leak while every thing 
 
52 INDICATOR DIAGRAMS. 
 
 else remains tight, the termination of the expansion 
 line will be too high, and if the exhaust valves or pis- 
 ton leak, it will be too low, allowance being made 
 for condensation in the cylinder. 
 
 FIG. 34. 
 
 Steam 10 Ibs. " Powhatan " stb. cylinder-top. 
 
 R ev 9 February 13th, 1854. 
 
 Vac 26 
 
 Hot well 100 
 
 Throttle wide. 
 
 Figures 34 and 35 are two diagrams taken from 
 the U. S. Steamer Powhatan, on the 13th of February, 
 1854 ; 34 was taken about ten minutes after 35. In 
 both of these figures we have the true hyperbolic- 
 curves drawn in, with and without taking the clear- 
 ance, &c., into account. The upper curve in small 
 dots is the true curve, when the clearance, Ac., is 
 taken into consideration, and the lower one in large 
 dots is the true curve without reference to the clear 
 ance, <fec. In figure 35, where the steam was cut off 
 at a very early part of the stroke, the importance of 
 taking the clearance, &c., into consideration, is very 
 conspicuous. The dotted lines on the right of these 
 
INDICATOR DIAGRAMS. 53 
 
 diagrams show the amount they are lengthened by 
 adding the clearance, space in nozzles, cfec., to them. 
 
 FIG. 36. 
 
 Steam 8 Ibs. " Powhatan " stb. cylinder-top. 
 
 Rev 6 February 13th, 1854. 
 
 Vac 26 
 
 Hot well 82 
 
 Throttle wide. 
 
 From a casual inspection of these diagrams, they 
 seem to present an anomaly that at first is difficult to 
 solve. Thus, in figure 34, the termination of the true 
 expansion curve, considering clearance, &c., is about 
 one pound above the actual curve, whereas in figure 
 35 it is two pounds below it. The first would indicate 
 that the exhaust valves or piston leaked, and the 
 second that the steam valves leaked, while the exhaust 
 valves and piston were tight. Now, then, since one 
 was taken only about ten minutes after the other, it is 
 not at all probable that this sudden change was 
 brought about in that short space of time ; hence we 
 must look for some defect in the engine that would 
 occasion it. We account for it in this way : In the 
 
54 INDICATOR DIAGRAMS. 
 
 first case the steam valve leaked, and also the steam 
 piston, but the piston leaked to a greater extent than 
 the valve, that is to say, more steam passed through 
 the piston and into the condenser from the leakage of 
 the piston than entered the cylinder from the leakage 
 of the valve ; therefore, the actual curve must fall be- 
 low the true curve. In the second case, the steam 
 valve also leaked, but the pressure on the piston fell 
 so rapidly, from expansion, that it became too low to 
 force a passage through the piston, the elasticity of the 
 packing being sufficient, in this case though not in 
 the other, where it had a greater pressure to sustain 
 to keep it tight ; hence, the true curve in this case 
 must be below the actual curve, agreeing precisely 
 with the conditions of the figures. 
 
 There is, however, another thing which would pro- 
 duce diagrams similar to those before us, and which 
 most probably caused the formation of these, viz., leak- 
 age about the cylinder heads. Thus, supposing the 
 stuffing box, for instance, to leak. So long as the 
 pressure in the cylinder remained above the atmo- 
 sphere, steam would blow out, occasioning the curve 
 to fall ; on the other hand, when cutting off short, the 
 pressure in the cylinder would soon fall below the 
 atmosphere, and air would enter, causing the curve to 
 rise, exactly as shown in the figures. 
 
INDICATOR DIAGRAMS. 
 
 55 
 
 Fig. 36 is a diagram taken from the U. S. Steamer 
 San Jacinto," fitted with Allen & Wells' cut-off. 
 
 Fio. 36. 
 
 Steam in boilers ll|lbs. November 7th, 1855, 11$ A. M. 
 
 Revolutions 18 After Engine, inboard end. 
 
 Vacuum 25 Coal 18 tons in 24 hours. 
 
 Hot well 104" 
 
 Throttle 4 holes open. Scale = Vio. 
 
 From inspection of the expansion curve of this dia- 
 gram, it appears that this cut-off does not close so 
 quickly as Sickel's, occasioning the corner a to be 
 more rounding. 
 
 Fio. 37. 
 
 Steam in boilers 9 Ibs. "Powhatan," Feb. 13th, 1854. 
 
 Revolutions 5 stb. cylinder bottom, working by hand. 
 
 Hot well 100 
 
 Throttle 4 
 
 Figure 37 is a diagram showing the operation of 
 
AIR-PUMP DIAGBAMS. 
 
 the valves while working by hand. This valve ex- 
 hibits large cushioning and steam lead, the exhaust 
 valve closing at a, and the steam valve opening at 5, 
 so that the engine actually passed the centre against a 
 pressure of 6^ Ibs. above the atmosphere. 
 
 Steam 16.5 Ibs. 
 
 Revolutions 9.25 
 
 Hot well 106 
 
 Vacuum gauge out of order. 
 
 " Powhatan " stb. air-pump, 10.50 A. M., 
 January 18th, 1854. 
 
 Calculated for Vs full of water. 
 
 Number 1 is a diagram taken from the " Powhat- 
 an's " starboard air-pump. The Powhatan's air-pumps 
 are of the lifting kind, and the piston fitted with one 
 large brass conical valve. We will explain the dia- 
 gram. At #, the piston being at the bottom of the 
 stroke, starts to rise, compressing the air and vapor 
 above it, until it arrives at b, at which place a sudden 
 discharge of air and vapor seems to have taken place, 
 and the pressure fell to <?, from which point the pres- 
 sure again gradually rose until it arrived at ^7, where 
 the water began to be delivered and continued to the 
 end of the stroke. 
 
AIR-PUMP DIAGRAMS. 57 
 
 Attached to the top of the air-pumps is a pipe, run- 
 ning down into the bilge, for the purpose of pumping 
 off the bilge water. Where this pipe is attached to 
 the pump is fitted a valve, operating like an ordinary 
 check valve, a handle being made to screw down on 
 the top of it to keep it firmly in its seat, when there is 
 no water in the bilge. 
 
 Steam 15lbs. "Powhatan" stb. air-pump, 10.55 A. M. 
 
 Revolutions 10 January 18th, 1854. 
 
 Hot well, 106 
 
 Vacuum gauge out of order. 
 
 Resistance of vapor and water in Air-pump 
 
 = (6.6+312 x .0969=) .6697 Ib. per square inch of steam piston. 
 Calculated for 1 5 full of water. 
 
 There being no water in the bilge at the time No. 1 
 "was taken, No. 2 was taken five minutes after, for the 
 purpose of ascertaining what effect the opening of this 
 valve and admitting air would produce. It shows 
 that no extra power, from the admission of this air, 
 was required to work the pump, the average pressure 
 being about the same as in No. 1, and that the vacuum 
 in the pumps at no time was more than 4 Ibs. There 
 was no alteration in the vacuum, as shown by the 
 gauge, however attached to the condenser, and the 
 engines continued to work in the same manner as be- 
 
58 AIll-PUMP DIAGIIA.MS. 
 
 fore the bilge valve attached to the air-pump was 
 opened. 
 
 Steam 15lbs. " Powhatan " port air-pump, 11.6 A. M. 
 
 Revolutions 10 - January 18th, 1854. 
 
 Hot well 108 
 
 Vacuum gauge out of order. 
 
 Resistance of vapor and water in Air-pump 
 
 (6.46 -f. 223 x .0969 =) .6476 Ib. per square inch of steam piston 
 Calculated for y, full of water. 
 
 Nos. 3 and 4 were taken in the same manner from 
 the port air-pump a few minutes after 1 and 2 were 
 taken from the starboard pump. 
 
 In these diagrams the pressure at the termination 
 of the up stroke, it will be seen, is about 2| Ibs. per 
 square inch above the atmosphere, which is due to the 
 height of the level of the water surrounding the ship 
 above the top of the air-pump. The pressure increased 
 to between T and 8 Ibs. per square inch, as shown in 
 other parts of the diagram, is occasioned by the fric- 
 tion of the water and vapor through the delivery pipes 
 and valves. The slanting off in the diagram, No. 1, 
 from x to ?/, we think partly owing to two causes : 
 First, the decreased velocity of the piston as it ap- 
 
AIR-PUMP DIAGRAMS. 59 
 
 preaches the end of its stroke does not expel the water 
 with such force, and hence there is not so much fric- 
 
 Steam 15lbs. " Powhatan " port air-pump, 11.15A.M. 
 
 Revolutions 10 January 8th, 1854. 
 
 Hot well 108 
 
 Vacuum gauge out of order. 
 
 Resistance of vapor and water in air-pump 
 
 = (8.16-1-223 x .0969 ==) .8123 Ibs. per square inch of steam piston. 
 Calculated for V, full of water. 
 
 tion ; but this would not occasion the slanting off from 
 h to z on the return stroke ; and secondly, there- 
 fore, we are inclined to think that the string slipped or 
 stretched a little from x to y, and recoiled again to its 
 original place from Ji to z. 
 
 We will now proceed to ascertain the 
 
 Power required to work the Air-pump. 
 
 Ascertain the capacities of the steam cylinder and 
 air-pump, by multiplying the areas of their cross-sections 
 by the lengths of their strokes, and divide the latter 
 by the former, which will give the ratio of the cylinder 
 capacity to that of the air-pump. But the air-pump 
 makes but one delivery stroke to every two strokes of 
 the steam piston, consequently divide this ratio by 
 two, which will give the coefficient for our present 
 
60 POWER REQUIRED TO WORK THE AIR-PUMP. 
 
 calculation, and this coefficient multiplied by the mean 
 pressure per square incli of air-pump piston which 
 can be ascertained from an indicator diagram will 
 give the mean pressure per square inch required to 
 expel the air and vapor. 
 
 This of course must be augmented by the weight 
 of the water raised. 
 
 The indicator diagram will show very nearly at 
 what part of the stroke the pump begins to deliver 
 the water, and therefore what fraction of the pump is 
 filled, from which can be easily ascertained the number 
 of cubic feet of water lifted ; and this number multi- 
 plied by 64.3 or 62.5, as the vessel may be running in 
 salt or fresh water, will give the number of pounds. 
 And the number of pounds of water lifted, divided by 
 the area of the air-pump piston, and multiplied by the 
 coefficient before obtained, will give the pressure per 
 square inch of steam piston required to expel the water 
 from the pump. 
 
 The sum of these results will give the pressure per 
 square inch of steam piston required to work the air- 
 pump independent of friction, an amount that is usually 
 estimated. 
 
 Example : The capacity of the " Powhatan's " cyl- 
 inder, i. e., the space displaced by the steam piston per 
 stroke, is 267.25 cubic feet: ditto in air-pump, 51.8 
 cubic feet ; proportion of steam piston displacement to 
 that of half of air-pump piston displacement, 1.000 to 
 .0969; area of air-pump piston, 2134 square inches. 
 The pump was filled -J- full of water, as shown by dia- 
 gram No. 1, and the mean pressure throughout the 
 stroke was 6.5 Ibs. per square inch ; hence, 6.5 X .0969 
 ~ .6298 Ib. per square inch of steam piston resistance 
 from vapor in air-pump, and .312 x .0969 = .0302 Ib. 
 
POWER REQUIRED TO WORK THE AIR-PUMP. 61 
 
 per square inch of steam piston resistance from the 
 weight of water lifted ; total = (.6298 + .0302 =) .66 
 pounds per square inch of steam piston, required to 
 work the air-pump, independent of friction. 
 
 Now, supposing the mean unbalanced pressure on 
 the steam piston per square inch to have been 20 Ibs., 
 we have 20 : .66 : : 100 : 3.3 per cent, of the total 
 power of the engine required to work the air-pump. 
 
CHAPTER III. 
 
 THE HYDROMETER. 
 
 FIG. 42. 
 
 THE Hydrometer is an instrument used for the 
 purpose of determining the specific gravi- 
 ties of liquids. When applied to the 
 water of marine boilers, it indicates the 
 amount of saline matter the water con- 
 tains. Figure 42 shows the kind of hy- 
 drometer usually used on board Ameri- 
 can steamers. The lower globe is filled 
 with shot, or other weighty substance, 
 for the purpose of keeping the instru- 
 ment upright. When the hydrometer is 
 placed in fresh water, the point O stands 
 even with the surface of the water ; when 
 placed in water containing one pound of 
 saline matter in thirty-two pounds of 
 water, it stands at % 2 ; when the water 
 contains two pounds of saline matter in 
 thirty two pounds of water it stands at 
 % 2 , and so on. So that by placing this 
 instrument in a small quantity of water, 
 drawn from the boilers at intervals, it 
 will show the exact density, by which 
 we know how to regulate the bio wing-off. 
 
 In the boilers of sea-going vessels the 
 water is usually carried from 1 % to 2 per 
 hydrometer, i. e., from the point a to , 
 figure 42. In the Gulf of Mexico, how- 
 ever, in the vicinity of the Florida reefs, where the 
 
 '32 
 
THE HYDROMETER. 63 
 
 water is impregnated with an unusual amount of lime, 
 it is found not to be prudent to carry it beyond 1 y a . 
 
 The hydrometer, when made for a certain temper- 
 ature, is not adapted to any other, but the water 
 should be allowed to cool down to the temperature 
 marked on the hydrometer before observing the indi- 
 cation, and for this purpose it becomes necessary also 
 to use a thermometer. The hydrometers used in this 
 country are usually graduated for a temperature of 
 200 Fahr. We can allow, however, for a few degrees 
 either above or below this figure, without appreciable 
 error a difference of 10 in temperature making a 
 difference of about an eighth of % 2 in the scale. Thus, 
 supposing the water to be at a temperature of 210, 
 and the hydrometer graduated for 200 to stand at #, 
 or 1%, the actual density of the water will not be 1%, 
 but ! 7 / 8 , or halfway between a and b. On the other 
 hand, if the temperature be 190, and the hydrometer 
 stand at 1%, the true density will be 1%. Neverthe- 
 less, in practice, it is always best to allow the water to 
 cool to the temperature for which the hydrometer is 
 graduated, whenever it can be done without the waste 
 of too much time. 
 
 It will be observed that the divisions on the scale 
 are not of equal lengths. Thus : the distance from O 
 to % 2 is greater than from % 2 to % 2 , and from % 2 to 
 % 2 , greater than from % 2 to % 2 , and so on. The reason 
 of this can be explained in this manner : When the 
 instrument stands at O, the two bulbs, and all the 
 tube below O, of course, are immersed, having the 
 weight due to the length of the tube only above O to 
 support. When it rises to % 2 it has more weight to 
 support, from the fact of there being more tube out 
 
 of water, and it also has less bulk immersed ; at % 2 it 
 5 
 
64 LOSS BY BLOWING OFF. 
 
 has still more weight to support, while there is still 
 less of the instrument immersed, and so on down to 
 the bottom of the scale, occasioning the lengths of the 
 divisions to become less and less. 
 
 The proportional quantity of saline matter con- 
 tained in sea water, at different localities, varies very 
 considerably, as will be seen in the following 
 
 TABLE : 
 
 Baltic Sea, 
 Black Sea, 
 Arctic Sea, 
 
 Mediterranean, . 
 Atlantic at Equator. 
 South Atlantic, 
 
 124 
 , . . . -i, North Atlantic, . . 2*3 
 
 British Channel, . . ft \ Dead Sea, -|j 
 
 LOSS BY BLOWING OFF. 
 
 When water contains 3 per cent, by weight of sa- 
 line matter, no deposit takes place at the boiling 
 point ; under atmospheric pressure or 212 Fahr. 
 When it contains 10 per cent, it makes a deposit of 
 lime, principally sulphate, and at 29, 5 per cent, com- 
 mon salt. 
 
 The precise saturation, however, at which deposit 
 commences to take place is not well established, but 
 there is one thing which is well known, and that is, 
 the higher the temperature of the water, the greater 
 will be the deposit, and from this we conclude that 
 common sea water would deposit a portion of its saline 
 matter if heated to a sufficiently high temperature. 
 The reason of the increase in deposit, as the tempera- 
 ture is increased, is probably owing to the expansion 
 of the water, or the separation, as it were, of the par- 
 ticles. 
 
 Water carried at a density that would cause no 
 
LOSS BY BLOWING OFF. 65 
 
 deposit at a temperature of 220, would make consid- 
 erable deposit at a temperature of 260 or 270; and 
 this is the reason why we are limited to comparatively 
 low steam in boilers using sea water. Independent of 
 the saving of the loss by blowing off, repairs to boilers, 
 labor of cleaning them, &c., this is a powerful reason why 
 inventive genius should endeavor to bring forth a relia- 
 ble fresh water condenser, and why steamship owners 
 and others, having it within their power, should encour- 
 age all such attempts, from the fact of the great advan- 
 tage to be derived from carrying high pressure steam, 
 and using the expansive principle to its fullest extent. 
 
 To the minds of those who cannot clearly see that 
 an increase of temperature occasions an increase in de- 
 posit, a practical demonstration can be obtained by 
 examining the crown sheets, and other parts of marine 
 boilers, subject to the highest temperature, where it 
 will be found the largest deposit takes place. 
 
 The deposit of lime, or " scale," as it is technically 
 termed, on the heating surface of boilers, being nearly a 
 non-conductor of caloric, prevents a large portion of the 
 heat from entering the water, allowing it to escape up 
 the chimney, and is therefore lost ; and, if the deposit 
 of scale be large, the metal of the boiler, being no 
 longer protected by the water, becomes over-heated 
 and " burnt." To prevent these results, a portion of 
 the water is extracted periodically, or continuously, 
 by the brine pump, or is discharged by the blow-off, 
 in order to keep the density of the water below 'the 
 point at which any serious deposit may take place. 
 But as all the water discharged from the boiler has 
 first to be heated, and as it is replaced by water of a 
 lower temperature, a loss of heat (which is virtually a 
 loss of fuel) is occasioned thereby. This is technically 
 
66 LOSS BY BLOWING OFF. 
 
 termed " loss by blowing off," and we shall proceed to 
 illustrate the manner of calculating it. Take an ex- 
 ample. 
 
 Supposing the density of the water entering the 
 boiler to be -J^ an d that of the boiler to be maintained 
 at -/$, there will be one part converted into steam, and 
 one part blown out. Supposing also the temperature 
 of the water entering the boiler to be 100 Fahr., and 
 the temperature of the water in the boiler to be 248 
 Fahr., we have all the data required. 
 
 Referring to Regnault's experiments, (page 9), we 
 see that the total heat in steam having 248 for the 
 sensible heat, is 1189.58, now then 
 
 1189.58 = total heat; 
 100.00 = temperature of the water entering the 
 
 boiler ; 
 1089.58 = heat required from the fuel for the 
 
 water to be evaporated ; 
 
 248 = temperature of the water in the boiler ; 
 100= " " " entering " 
 
 148 = heat lost by blowing off. 
 
 Therefore, since one part (requiring 1089.58) is 
 converted into steam, and the other part (requiring 
 148) is blown off, the total heat required of the fuel is 
 (1089.58 + 148=:) 1237.58; and as 148 of this is 
 blown off, we have 1237.58 : 148 : : 100 : 11.95 + per 
 cent, loss by blowing at the above density and tem- 
 perature. 
 
 If the water had been carried at a density of If 
 per hydrometer, one part would have been blown off 
 as before, but only three-quarters part would have 
 
^ 
 
 _ W <^ r ^/ 
 
 LOSS BY BLOWING OFF. 67 
 
 been converted into steam, hence we would have pro- 
 ceeded thus 
 
 1189.58 
 100.00 
 
 1089.58 
 .75 
 
 817.1 850 = heat required from the fuel for the 
 water to be evaporated. 
 
 248 
 100 
 
 148 = heat lost by blowing off. 
 
 Therefore (817.185 + 148 =) 965.185 : 148 : : 100 : 
 15.33 + per cent. 
 
 And had the water been carried at a density of 
 3, i. e. -3^, two parts would have been used for steam 
 and one part blown off, hence the following : 
 
 1189.58 * 
 100.00 
 
 1089.58 
 2 
 
 2179.16 = heat required from the fuel for the 
 water to be evaporated. 
 
 248 
 100 
 
 148 = heat lost by blowing off. 
 
 Therefore (2179.16 + 148) = 2327.16 : 148 : : 100 : 
 6.35 per cent., and so on for any density. These per 
 
68 GAIN BY THE USE OF HEATERS. 
 
 cents, are the losses in fuel, combustible, minus that 
 lost from radiation and heated gases passing up the 
 chimney. 
 
 The above calculations apply only to cases where 
 the water enters the boiler at a density of ^ ; should 
 it enter at a lower density, the loss will be less, or a 
 greater density more, because to retain the water in 
 the boiler at the density assumed in the above ex- 
 amples, there would either have to be a less or greater 
 quantity blown off than we have considered to be the 
 case. 
 
 In order not to lose entirely all the heat in the 
 water blown off, some boilers are fitted with heaters, 
 or as they are sometimes termed incorrectly, " refrige- 
 rators." These are a series of pipes surrounded by the 
 feed water, and through which the water leaving the 
 boilers has to pass ; by this means the temperature of 
 the feed water is considerably increased before it 
 enters the boiler. The following will illustrate 
 
 THE GAIN BY PUMPING WATEE INTO THE BOILER AT AN 
 INCREASED TEMPERATURE. 
 
 For this purpose two examples will be sufficient, 
 and we will .commence with the first one given above 
 in the calculation on the loss by blowing off; viz. 
 steam, 248 ; feed water, 100 ; and density, -fa. Now 
 suppose by the application of the heater, the feed- 
 water, instead of entering the boiler at 100, is made 
 to enter at 150, what will be the saving in fuel by its 
 application ? 
 
GAIN BY THE USE OF HEATERS. 69 
 
 Solution. 
 
 1189.58 = total heat in the steam ; 
 100.00 = temperature of the feed water ; 
 
 1089.58 = heat required from the fuel to evapo- 
 rate one part of water ; 
 248 = temperature of the water blown off; 
 100 = " " feed water ; 
 
 148 = heat lost by blowing off; 
 
 and 1089.58 + 148 = 1237.58 = total heat required 
 from the fuel where the water is pumped into the 
 boiler at 100. Let us now see what the total heat 
 will be when the water is pumped in at 150, and the 
 difference between these results will be, of course, the 
 
 saving 
 
 1189.58 = total heat in the steam ; 
 150.00 = temperature of the feed water ; 
 
 1039.58 = heat required from the fuel to evapo- 
 rate one part of water ; 
 248 = temperature of the water blown off ; 
 150 = " " feed water ; 
 
 98 == heat lost by blowing off ; 
 
 and 1039.58 + 98 = 1137.58 total heat required 
 from the fuel when the water is pumped into the boiler 
 at 150. Therefore 
 
 1237.58 
 1137.58 
 
 100= saving in degrees; 
 
 whence 1237.58 : 100 : : 100 : 8.08 per cent. That is 
 to say, if without the heater the boilers consumed 100 
 
70 GAIN BY THE USE OF HEATERS. 
 
 tons of coal per day, with it they would produce the 
 same quantity of steam with 91.92 tons. 
 
 EXAMPLE 2o. 
 
 Suppose that the density of the water in Example 1 
 was If, and all the other conditions to remain unalter- 
 ed, what would be the saving in that case ? 
 
 Solution. 
 
 1189.58 = total heat in the steam ; 
 100.00 = temperature of the feed water ; 
 
 1089.58 = heat required from the fuel to evapo- 
 rate one part of water ; 
 .75 = part of water evaporated ; 
 
 817.185 = heat required from the fuel for the 
 
 water that is evaporated ; 
 248 = temperature of the water blown off ; 
 100= " " feed water; 
 
 148 = heat lost by blowing off; 
 817.185+ 148 = 965.185 total heat required from 
 the fuel when the water is pumped into the boiler at 
 100. 
 
 1189.58 = total heat in the steam -, 
 150.00 = temperature of the feed water; 
 
 1039.58 = heat required from the fuel to evapo- 
 rate one part of water ; 
 .75 = part of water evaporated; 
 
 779.685 = heat required from the fuel for the 
 water that is evaporated ; 
 
INJECTION WATER. 71 
 
 248 = temperature of the water blown off; 
 150= " " feed water; 
 
 98 heat lost by blowing off; 
 
 779.685 + 98 = 877.685 = total heat required from 
 the fuel when the water is pumped into the boiler at 
 150. Therefore 
 
 965.185 
 
 877.685 
 
 87.5= saving in degrees. 
 
 Whence 965.185 : 87.5 : : 100 : 9.06 per cent. And 
 in this manner the calculation can be made for any 
 density and temperature. 
 
 In making calculations on the theoretical saving 
 from the use of the heater, we have seen some engineers 
 who calculate the loss by blowing off without it, and 
 again with it, and take the difference between these 
 two results for the saving ; but it will require but 
 little reflection for any one at all conversant with such 
 subjects, to perceive the error of this mode of calcu- 
 lation, as it takes no cognizance whatever of the extra 
 heat given to that portion of the water which is evap- 
 orated. The mode of calculation given above is the 
 only correct one, as it takes into consideration all the 
 elements. 
 
 INJECTION WATEK. 
 
 After the steam has performed its duty in the 
 cylinder, and been exhausted into the condenser, a cer- 
 tain amount of cold water is admitted into that vessel 
 for the purpose of condensing it, and this quantity 
 depends upon the temperatures of the water and the 
 steam. We will take an example. 
 
72 EVAPORATION. 
 
 Suppose the temperature of the injection water to 
 be 60; steam as it enters the condenser, 212; and 
 water in the condenser, 110. Required the proportion 
 of injection water to the water evaporated in the 
 boiler : 
 
 Solution. 
 
 1178.6 = total heat in the steam at the sensible 
 
 temperature of 212 ; 
 
 110.0 = temperature of the water after conden- 
 sation ; 
 1068.6 heat to be destroyed ; 
 
 110 = temperature of the water after conden- 
 sation ; 
 60 = temperature of the injection water, 
 
 50 difference. 
 
 Now then we see that we have 1068.6 of heat to 
 be destroyed, and only 50 to do it with, therefore we 
 must make up this difference in quantity ; hence 1068.6 
 -r-50 rr 21.372 times the evaporated water to be ad- 
 mitted into the condenser to condense the steam and 
 retain the condenser at the temperature of 110. 
 
 EVAPORATION. 
 
 Among the important elements to be ascertained 
 in the performance of the steam engine, is the quantity 
 of water evaporated in the boilers per unit of coal, or 
 other fuel. In sea boilers using salt water, one pound 
 of coal evaporates from 4 to 9 pounds of water, de- 
 pendent upon the quality of the coal, the construction 
 and cleanliness of the boilers. Those boilers are of 
 course the best which evaporate the largest quantity, 
 and hence the importance of knowing the exact per- 
 formance of each boiler, as well as of the different kinds 
 
EVAPORATION. 3 
 
 of fuels used in the same. To secure this desirable end 
 we proceed thus : 
 
 Ascertain from indicator diagrams the fraction of 
 the cylinder filled at each stroke, from which, know- 
 ing the diameter of the cylinder, we ascertain the 
 number of cubic feet of steam required to fill that 
 space, and to this we add the space in nozzles, clear- 
 ances, &c., which gives the number of cubic feet of 
 steam used per stroke ; and the number of cubic feet of 
 steam used per stroke, multiplied into the number of 
 strokes per hour, and divided by the relative volumes 
 of steam and water, at the pressure the steam is admit- 
 ted into the cylinder, gives the number of cubic feet 
 of water evaporated per hour, and the number of cubic 
 feet of water evaporated per hour, multiplied by 64.3, 
 (the weight in pounds avoirdupois of one cubic foot of 
 sea water,) and divided by the number of pounds of 
 coal used per hour, gives the number of pounds of water 
 evaporated per -pound of coal, provided there is no 
 blowing off done ; but wherever there is blowing off, 
 this last result has to be increased to the extent of the 
 loss by blowing. 
 
 Suppose for instance, proceeding in the manner 
 given above, we find 6 Ibs. of water to be evaporated 
 per pound of coal ; and the loss by blowing off to keep 
 the water at the proper density to be 15 per cent., 
 the remaining 85 per cent, is that which evaporates 
 the 6 Ibs. ; hence 85:6:: 100 : 7.06 Ibs. of water evap- 
 orated per pound of coal. 
 
 EXAMPLE. Suppose you have a cylinder TO inches 
 diameter by 10 feet stroke ; the initial pressure of 
 steam in the cylinder 24.5 Ibs. per square inch, in- 
 clusive of the atmosphere, cut off at \ from commence- 
 ment of stroke; clearance, &c., 10 cubic feet; revolu- 
 
74 EVAPORATION. 
 
 tions, 15 per minute; coal consumed per hour, 1,500 
 Ibs.; water carried at 1J per hydrometer; temperature 
 of feed water, 107 Fahr. ; required the number of 
 pounds of water evaporated per pound of coal : 
 
 Solution. 
 70 2 X .7854 10 1Q = Y6 8125 cubic feet Qt 
 
 144 4 
 
 steam used per stroke ; and 76.8125 x 15 X 2 X 60 = 
 138262.5 cubic feet of steam used per hour. 
 
 The relative volumes of steam and water at the 
 pressure of 24.5 Ibs. are 1064 to 1 ; hence 
 
 i QQ9A9 5 
 
 7 -r^- X 64.3 ~ 1500 = 5.57 Ibs. of water per pound 
 1064 
 
 of coal, neglecting the loss by blowing off; but, ac- 
 cording to the conditions of the example, the loss by 
 bio wing off is found to be 14.1 per cent., the remain- 
 ing 85.9 per cent, is that therefore which evaporated 
 the 5. 5 7 Ibs. of water; hence the true evaporation is 
 found to be 85.9 : 5.57 : : 100 : 6.48 Ibs. of water per 
 pound of coal. 
 
 The above calculation takes no cognizance of the 
 leakage of the valves, loss by radiation, or condensa- 
 tion in the cylinder, pipes, &c. ; hence the results show 
 too small, but it is the only standard of comparison. 
 
 Some parties calculate the evaporative power of 
 boilers by measuring the quantity of water pumped 
 into them during any given time, and also the quantity 
 of coal consumed in the furnaces during the same time, 
 and dividing the weight of the former by the latter, 
 which they conceive gives the weight of water evapo- 
 rated per unit of coal. Upon first sight this mode of 
 operating appears very simple and correct ; but unfor- 
 tunately, notwithstanding its simplicity, the results are 
 
STEAM AND VACUUM GAUGES. 75 
 
 never accurate, the evaporation being always shown 
 too large, for the very simple reason, that all the water 
 pumped into a steam boiler is never evaporated. All 
 boilers, and pipes, and cocks attached thereto, leak 
 more or less, and sometimes boilers foam, occasioning 
 water to be worked into the cylinders, and as, accord- 
 ing to this mode of calculation, all water escaping by 
 this means is supposed to be evaporated, the result 
 manifestly cannot be correct. 
 
 Steam and vacuum Gauges. 
 
 As applied to the marine steam engine, the mer- 
 curial steam and vacuum gauges are the most common, 
 though of late years there have come into use a variety 
 of metallic gauges, many of which, from the little 
 attention they require, appear to be very well adapted 
 to the purpose for which they were intended. 
 
 The most prominent of these are " Schaffer's," 
 "Hearson's," "Schmidt's," " Ashcroft's," "Eastman's," 
 " Stubblefield's," and "Allen's." In the first three, 
 the spring is a thin corrugated plate, upon which the 
 steam acts, communicating motion to a hand or pointer 
 which moves around a circular disc marked in pounds: 
 the spring in Ashcrofb's gauge is a bent tube, which 
 the elasticity of the steam tends to straighten. East- 
 man's gauge is a combination of springs and levers. 
 As these gauges are all constructed on the same prin- 
 ciple, viz., the elasticity of metal, we shall not stop 
 here to describe them, as it is more directly our object 
 to deal with principles, rather than mechanical ar- 
 rangements, which are the chief peculiarities of these 
 gauges. We will pass on to the mercurial closed top 
 vacuum gauge. 
 
STEAM AND VACUUM GAUGES. 
 
 Fig. 43. 
 
 abed, figure 43, is a basin filled 
 with mercury up to the point A ; the 
 tube B is also filled with mercury. 
 The pipe e communicates with the 
 condenser, and when that vessel is 
 filled with air of the atmospheric 
 pressure, the surface of the mercury 
 in the basin is pressed with a pres- 
 sure of about 15 Ibs. per square inch, 
 causing the tube B to remain filled ; 
 but when a partial vacuum is created 
 in the condenser, the mercury having 
 no longer the atmospheric pressure 
 to sustain, falls in the tube B, and 
 the figures marked on the scale will 
 exhibit the extent of the vacuum. 
 With this arrangement, therefore, there is no necessity 
 of making the tube 30 inches in length, as all engines 
 are supposed to maintain at least 17 or 18 inches of 
 vacuum, and a tube long enough to show this is all 
 that is required. Could the surface of the mercury 
 remain constantly at A, the divisions on the scale 
 would be of equal lengths, and one inch apart, but as 
 the mercury rises a little in the reservoir as it falls in the 
 tube, the lengths of these divisions vary a little, depend- 
 ent upon the relative volumes of the tube and reservoir. 
 The aperture in the lower end of the tube is made 
 very small, to prevent the oscillation of the mercury. 
 At A is a small hole fitted with a screw. This is left 
 open, while filling the gauge, as an overflow to the 
 surplus mercury, it being so situated that the contents 
 of the tube B is just sufficient to fill the reservoir to 
 the point 30, or the true vacuum line. 
 
 The pressure of the atmosphere, as it varies from 
 time to time, does not alter the indications of this 
 
STEAM AND VACUUM GAUGES. 
 
 77 
 
 FIG. 44. 
 
 gauge, inasmuch as it always exhibits the difference 
 between the vacuum in the condenser and a perfect 
 vacuum. 
 
 Had the top of the tube B communicated with the 
 condenser, and the basin abed been open to the 
 atmosphere, the gauge would then have been what is 
 termed an open-top vacuum gauge, and would require 
 to have been 30 inches in length the scale being 
 reversed, the lowest figure commencing at the bottom. 
 With such a gauge, all variation in the pressure of the 
 atmosphere affects its indications. 
 
 Figure 44 is a siphon steam gauge, 
 filled with mercury to the level a a. 
 The short leg connects to the boiler, 
 and the long leg is open to the atmo- 
 sphere. The steam pressing upon the 
 mercury at &, forces up the stick resting 
 oa the mercury in the other leg at #', 
 showing the pressure in pounds per 
 square inch, marked on the scale at the 
 top of the gauge. These divisions are 
 one inch apart, and indicate pounds 
 pressure, for the reason that the descent 
 of one inch in the short leg causes a rise 
 of one inch in the long leg, making a 
 difference in the level of the mercury 
 of two inches, which corresponds to one 
 pound pressure ; that is to say, a column 
 of mercury two inches high, and having 
 a base equal in area to one square inch, 
 will weigh in round numbers one pound. 
 In making a gauge, it matters not 
 what may be the diameter of the tube, 
 but whatever it may be, it should be uniform through- 
 out, in order that the indications may be correct. 
 
 a. 
 
78 STEAM AND VACUUM GAUGES. 
 
 The stick that is put in the long leg, when there is 
 no steam on, has one end resting on the mercury, while 
 the other stands at 0. This stick should be made of 
 some very light wood soft white pine answers the 
 purpose very well, with the lower end a little the 
 largest, in order to have a good bearing on the mer- 
 cury. 
 
 To convert this gauge into a vacuum gauge, it 
 would be necessary only to connect the long leg to 
 the condenser, and attach a scale to the short leg with 
 the lowest number commencing at the top. 
 
 
CHAPTER IV. 
 
 CASUALTIES, ETC. 
 
 How to act if the Eccentric be broken in an irreparable 
 
 manner. 
 
 IF there be two paddle engines connected at an angle 
 of 90, connect the starting bar of the deranged engine, 
 by means of a line and guide pulleys, to the cross-tail, 
 air-pump beam, air-pump cross-head, or other part 
 having motion coincident with the piston of the other 
 engine, to give the bar motion in one direction, and 
 attach a heavy weight to it, with a line running over 
 a pulley, to give it motion in the opposite direction. 
 
 If there be but one engine, connect by similar 
 means, to the connecting rod of the deranged engine, 
 which will give the proper motion. 
 
 Sow to act when a Steamer springs aleak and com- 
 mences to fill rapidly. 
 
 9 
 
 Put on immediately all bilge injections and bilge 
 pumps, and shut off all other injections. If they do 
 not keep the water down, break the joints on the bot- 
 tom or side injections, and allow them to draw water 
 from the bilge, taking care to station a man at each 
 one to prevent any thing from passing in that would 
 choke the valves. 
 
 Vessels are sometimes saved from foundering by 
 6 
 
80 CASUALTIES, ETC. 
 
 covering the leak with a sail-cloth passed over the 
 bows and under the bottom. 
 
 If the leak be a large one, such as one occasioned 
 by a collision, it may be possible to force a mattress, or 
 something of that nature, into it from the outside. 
 
 How to proceed when all the feed is on and the water 
 does not rise in the boilers. 
 
 It sometimes happens that when all the feed is on, 
 and the feed pumps are apparently performing their 
 usual duty, the water does not rise in the boilers, but 
 either retains its level at the time the feed was put on, 
 or gradually falls. In this event, one of two things 
 must be manifest either that the water does not enter 
 the boiler, or if it does enter, is escaping through some 
 other orifice. The first thing, therefore, to do, is to 
 examine the check valve to see if it is in operation. 
 This can be done by applying the ear to the chamber, 
 to ascertain if the valve rises and falls, at each stroke 
 of the pump, and also by applying the hand to the 
 pipe, immediately below the check valve, in order to 
 ascertain if it be cool. If these are found to be all 
 right, examine the blow-off cocks, and all other water 
 connections with the boilers, to ascertain if they be 
 closed ; some of which, in all probability, will be par- 
 tially open, but if they should all be found closed, the 
 pump must be pumping air into the boilers instead of 
 water. The next step would therefore be, to examine 
 the pump and induction pipe, in order to ascertain and 
 stop the air leak. 
 
 Upon examining the check valve, should it not be 
 found in operation, the next step would be to examine 
 the pump, to see if it was hot ; also relief and pump 
 
CASUALTIES, ETC. 81 
 
 valves, to see if they were gagged ; and lastly, the 
 eduction pipe, to see if it were burst either of which 
 causes would prevent the pump from delivering water. 
 A feed pump may get hot from four causes : 
 
 First. There may be so small a quantity of injec- 
 tion water used as to cause it, when delivered to the 
 hot well, to be of sufficiently high temperature to heat 
 the pump. 
 
 Second. Friction, occasioned from muddy water, or 
 tight packing. 
 
 Third. The check and delivery valves may be 
 caught up or very leaky, allowing the hot water from 
 the boiler to run back to the pump. 
 
 Fourth. External application of heat, the pump 
 being situated near the boiler or other hot body. 
 
 A feed-pump cannot deliver water when hot, for 
 the reason that the vapor constantly generated within 
 it, by its elasticity prevents the induction valve from 
 opening and admitting water. 
 
 Should the feed pipe burst, it can be repaired tem- 
 porarily by wrapping it with canvas coated with white 
 lead ; this being secured by strong twine or marline, 
 wound closely around the pipe the full length of the 
 canvas. 
 
 Should the pipe be split open for a considerable 
 distance, it might first be closed with* wood or iron 
 clamps, as came most convenient, before applying the 
 canvas and twine. 
 
 Foaming. 
 
 Foaming, or priming, as it is sometimes termed, is 
 violent ebullition or agitation of the water, occasioned 
 by an undue relation of temperature between the 
 steam and water. Thus, supposing a large quantity 
 
82 
 
 of steam to be suddenly taken from the boiler, the 
 pressure of steam is immediately reduced below what 
 is due to the temperature of the water, and the result 
 is a sudden rising up of the water from all parts of the 
 boiler. Foam can, therefore, be defined to be a mix- 
 ture of steam and water. Boilers are known to be 
 foaming when the water does not come out of the 
 gauge cocks solid, or when there is a considerable agi- 
 tation of the water in the glass gauges. 
 
 To suppress foaming, put on a strong 'feed and 
 blow off, cut off shorter or partially close the throttle. 
 Oil or melted tallow, injected into the boilers through 
 the feed pumps, will also prevent foaming, but these 
 are somewhat expensive expedients. 
 
 Boilers constructed with insufficient steam room, 
 are most likely to foam, because at each stroke of the 
 piston a large proportion of the steam is taken from 
 the boiler, and the pressure therefore becomes mate- 
 rially reduced. Boilers also constructed in such a 
 manner as to prevent the easy escape of steam from 
 the surfaces on which it is generated, are likely to 
 foam. Thus, supposing there be a large amount of 
 heating surface on the crowns and other parts towards 
 the bottom of the boiler, and that the steam generated 
 on these surfaces in consequence of coming in contact 
 with the flues, tubes, braces, &c., can find but a com- 
 paratively small exit to the surface of the water, 
 the result will be, that where it does escape, it will 
 force a large body of water up, mixing it with the 
 steam. 
 
 To carry too much water in boilers will cause them 
 to foam by reducing the steam room. Running from 
 salt to fresh water, or vice versa, will also cause foam- 
 ing; in the former case, because fresh water boils at a 
 
CASUALTIES, ETC. 83 
 
 lower temperature, but a satisfactory explanation of 
 the latter case appears to be difficult to arrive at. The 
 boilers of sea steamers, when running in muddy rivers, 
 usually foam considerably. 
 
 It sometimes occurs, while the boilers are foaming 
 badly, that the engines have to be stopped in order to 
 take soundings, or from other causes. Now, the first 
 thing after stopping the engines, in any case, is always 
 to try the water; for it will mostly always be found 
 to be lower when the engines are standing still than 
 when under way, but when the boilers are foaming, it 
 is of the highest importance to try immediately the 
 height of the water, for as the foaming ceases after the 
 engines are stopped, it may happen that the water has 
 fallen entirely out of the gauges and left the flues, in 
 which event, if the engines were going to be started 
 again in three or four minutes, the better plan would 
 be to open the safety valve to keep the water foaming, 
 so as to keep the flues covered, and when the engines 
 are started again to put all the feed on. But if the 
 engines were going to stand still for a considerable 
 time, blow off a portion of the steam, if it be too high, 
 dampen the fires a little, and put on the auxiliary feed. 
 
 The Condenser heats. 
 
 When engines are standing still, it sometimes 
 occurs that the condenser gets so hot, that when it 
 becomes necessary to start again, the pressure has be- 
 come so great in it, that the injection water will not 
 enter. Leaky steam and exhaust valves will alone 
 cause this, but in no case should it ever be allowed to 
 occur. When an engine begins to get hot, the crack- 
 ing noise in the condenser, and about the foot valves, 
 
84 CASUALTIES, ETC. 
 
 will always indicate what is going on, time enough to 
 check it, which can be done by giving a little injec- 
 tion, and causing the engines to make two or three 
 revolutions back and forth. If, however, the engine 
 should become too hot to take the injection water, the 
 only plan will be to blow through, or pump water into 
 the condenser if there be such an arrangement, or to 
 cool the condenser by external application of cold 
 water. 
 
 If when under way it is indicated by the gauge 
 that the engine is gradually losing its vacuum, apply 
 the hand to the condenser, in order to ascertain if it 
 be getting hot, and if such be found to be the case 
 give a little more injection; but if that does not help 
 the cause, give more still. If the vacuum continues to- 
 grow less, the probability is that the injection pipe 
 has become choked ; in which event shut off that in- 
 jection and put on another. Should both the bottom 
 and side become choked, inject from the bilge. Should 
 the bilge injection also be out of order, the engine will 
 have to be stopped, and the sjnftmg. valve secured 
 down (if there be one) while the injections are blown 
 through to clear them. Sea weed, and things of that 
 nature, sometimes get over the strainers of injection 
 pipes, preventing the entrance of water. 
 
 Most if not all marine engines of modern construc- 
 tion are fitted with a thermometer to the hot well, to 
 ascertain the temperature of the water, which is usually 
 carried from 100 to 115 Fahr. This instrument is 
 very important, in order to maintain an even temper- 
 ature (the sense of touch of the engineer's hand not 
 being delicate enough for that purpose), for it may 
 often occur that there may start small leaks about the 
 condenser and exhaust pipe joints, which would cause 
 
CASUALTIES, ETC. 85 
 
 a decrease in the vacuum, and, as without the ther- 
 mometer, the first impulse would be to give more 
 injection, with it we would turn our attention to find- 
 ing and stopping the leak. This can be done by hold- 
 ing a lighted candle around the joints, and wherever 
 there is a leak the flame will be drawn in. To stop it, 
 mix a little putty, of white and red lead, and apply it 
 to the crevice ; the presence of the atmosphere will 
 force it in. 
 
 Getting under way. 
 
 When lying in port, where the steam will not be 
 required for at least four or five days, it is proper that 
 the water should be blown or pumped out of the 
 boilers, and a portion of the man and hand-hole plates 
 removed, to allow a circulation of air. When, there- 
 fore, the order is given to get up steam, the first thing 
 is to see that all these plates are put on, and the joints 
 properly made, and this duty should receive the direct 
 superintendence of the engineer having charge of the 
 same ; for should any one of them leak badly after the 
 steam is raised, the departure of the ship might be de- 
 layed some hours in consequence. After this duty has 
 been properly attended to, open the blow-off cocks and 
 run the water up in the boilers to the proper level, or, 
 if the boilers are so situated that the water will not run 
 up high enough, finish the supply with the hand 
 pumps, wood the furnaces while the water is entering 
 the boiler, and when the proper height of water is 
 attained start the fires. If it be important to raise 
 steam quickly, start the fires as soon as water is dis- 
 covered in the gauges, continuing the supply while the 
 fires are burning. As a small quantity of finely split 
 wood, with a little shavings or oily waste placed in 
 
86 CASUALTIES, ETC. 
 
 the mouth of the furnaces, is all that is necessary to 
 start the fires, the back part of the furnaces, particu- 
 larly in boilers with inferior draft, should be covered 
 with a layer of coal to keep out the cold air. 
 
 In raising steam it has been the custom to recom- 
 mend that the valves of the engine be blocked open, 
 so as to allow the heated air from the boilers to pass 
 in and warm up the engine before steam begins to be 
 generated ; but as in many cases this is attended with 
 considerable trouble, and as the advantages to be de- 
 rived from it are very small, it hardly appears to the 
 author's mind to " pay." The safety or vacuum valve 
 should, however, be kept open until steam begins to 
 form, in order to let the heated air escape. The strain 
 upon boilers being from the inside, they are con- 
 structed and braced with the special view of with- 
 standing this strain, many of the braces being entirely 
 useless in sustaining a pressure from without ; marine 
 boilers are therefore fitted with a small valve opening 
 inwards, and weighted so as to open and admit air 
 whenever the pressure from within falls to about five 
 pounds per square inch below the atmosphere. These 
 valves are called differently by different parties, as 
 follows : vacuum valve, air valve, reverse valve, <fec. 
 
 After steam has been raised to 3 or 4 Ibs., the 
 engine should then be blown through and warmed up, 
 and after sufficient steam is raised to move the piston, 
 the engine should be turned over two or three times, 
 to see that every thing is right, before reporting 
 ready. 
 
 On Coming into Port. 
 
 After the engines are no longer needed, before 
 hauling the fires, after a long run, it would be well 
 
CASUALTIES, EIC. 87 
 
 to try the pistons and valves, in order to ascertain 
 if they be leaky. To try the piston, open the water 
 valve on one end of the cylinder and the steam 
 valve on the opposite end; if the piston leaks, the 
 steam will escape through the water valve. To asce^- 
 tain if the steam valves leak, open the water valves on 
 both ends of the cylinder. To ascertain if the exhaust 
 valves leak, open the steam valves and any cock 
 in the exhaust side of the steam chest or exhaust 
 pipes. 
 
 While under way it may be discovered that there 
 is a slight thump in the engine when passing one or 
 or the other or both centres, and the indicator hav- 
 ing been applied shows the usual lead, the inference 
 is that some part of the working engine is loose ; it is 
 important, therefore, to find out what it is on coming 
 into port. To do this place the engine on the centre, 
 and give the piston steam suddenly by raising and 
 lowering the starting bar ; observe closely the cross- 
 head, crank-pin, main-shaft, and other main connections, 
 to see where the jar is. Should it not be discovered 
 after this, jam the cross-head fast, so as to prevent the 
 slightest motion, and then give steam as before, in 
 which event, if the thump be still felt, the piston will 
 doubtless be found to have worked a little loose. 
 
 If it be the intention to remain in port several 
 days, before hauling the fires, sufficient steam should ** 
 be raised, if the boilers be capable of bearing the 
 pressure, to blow all the water out of the boilers. After 
 the boilers become cool, the hand-hole plates, over the 
 furnaces particularly, should be taken off, to examine 
 the crowns, where the greater amount of scale will be 
 found deposited, and from which we can judge if the 
 boilers require scaling. Mere dampness in boilers is 
 
88 
 
 found to be injurious, by occasioning a rapid oxida- 
 tion, and in order to prevent this, one or two hand- 
 hold plates should be taken off the bottom of the 
 boilers, in order to let the water drain out dry. It 
 would be well also to remove a man-hole plate from 
 the top of the boilers to allow a circulation of air. 
 If these things cannot be done it will be better to keep 
 the boilers filled with water, rather than a small 
 quantity in the bottoms. In damp climates, such as 
 the Isthmus of Panama, light fires should be made in 
 the ash-pits occasionally. 
 
 Scaling Boilers. 
 
 Notwithstanding the water in the boilers is not 
 allowed to exceed in density If to 2 per saline hydrom- 
 eter, it will be found after a time that a quantity of 
 scale, composed principally of lime, has accumulated 
 on the crown sheets, tubes or flues, and other parts of 
 the boiler. If this be allowed to remain the metal 
 will become overheated and burned ; it becomes ne- 
 cessary, therefore, to remove it, which can be alone 
 done by mechanical means. Sharp-faced " scaling 
 hammers " can be used to knock the scale off those 
 places that are within the arm's reach, and long bars 
 flattened at both ends, and sharpened, called " scaling 
 bars," will knock it off the more remote parts. In the 
 Martin tubular boiler, which is accessible in every 
 part, it is only necessary to condense the steam in the 
 boilers for a day or so after the ship comes to anchor ; 
 this will soften the scale so that a gang of men may be 
 put into them as soon as the man-hole plates are re- 
 moved, and scrape off all of it in a few hours. The 
 scale, however, must never be allowed to exceed the 
 thickness of writing paper. 
 
COMING TO ANCHOR. 89 
 
 It has been proposed in some quarters to heat the 
 tubes or flues by burning shavings, or some other such 
 substance in them, and then to cool them off suddenly 
 by pumping cold water upon them, the sudden con- 
 traction causing the scale to crack off. This plan, how- 
 ever, to our mind, does not deserve much favor, and 
 never should be resorted to, if the scale can be reached 
 in any other manner, for the production of leaks will 
 mostij? always be the result. 
 
 It is, however, hoped that engineers will soon be 
 relieved from this duty, and steamer owners benefited 
 by the introduction of fresh water condensers into all 
 sea steamers. 
 
 Preparatory to coming to Anchor, or securing to the 
 
 Wharf. 
 
 Fifteen or twenty minutes before coming to anchor, 
 or making fast to the wharf, the chief engineer should 
 be informed of the fact by the officer of the deck, or 
 some other person informed on the matter, so that the 
 fires can be allowed to burn down, and the pressure of 
 steam permitted to fall to such an extent that the 
 necessity for blowing off is avoided. By this means 
 the great nuisance of blowing off steam is not only 
 obviated, but there is a considerable saving in fuel, 
 the fires being permitted to burn down sufficiently low 
 to supply only the amount of steam required while 
 working the engines by hand, rendering it much easier 
 also on the firemen (whose duties on any occasion are 
 arduous enough) by having a very light, instead of a 
 very heavy fire to haul. 
 
 In coming to anchor it is usually well to pump a 
 little extra water into the boiler, so as to insure a 
 proper supply while operating the engines by hand. 
 
90 THE FIEES WHILE UNDER WAY. 
 
 When it is desired to raise steam, the order from 
 the captain should always be what time it is intended 
 to get underway, leaving to the discretion of the chief 
 engineer to start the fires at such time as he may con- 
 sider proper, in order to secure steam and every thing 
 ready at the proper time. 
 
 Regarding the Fires while under Way. 
 
 Small as this may appear in the eyes of one not 
 practically conversant with the management of the 
 steam engine, it is one of the most important things 
 that the engineer is called upon to regulate : on the 
 one hand, that a proper and uniform supply of steam 
 is maintained, and on the other, that more fuel is not 
 consumed than is actually necessary to produce the re- 
 sult. Different fuels and differently constructed boil- 
 ers require the fires to be regulated in a different 
 manner, and notwithstanding the repeated efforts, the 
 adoption of specific rules, which shall apply alike to 
 all, is positively absurd. A few general hints, how- 
 ever, touching the leading features, may be useful to 
 those who have not had much experience in this mat- 
 ter, but they must bear in mind, nevertheless, that 
 actual service and observation for themselves, will 
 alone make them proficient, no matter how well they 
 may understand the chemistry of coal, or the natural 
 laws governing the combustion of matter. 
 
 The proper supply of atmospheric air, and the 
 proper time for the combustion, are the important ele- 
 ments in the consumption of coal. A slow rate of 
 combustion, and a moderate draft, always producing a 
 better evaporative result, than when the fires are urged, 
 occasioning them to be more rapid; and hence, on 
 
THE FIKES WHILE UNDER WAY. 9l 
 
 no occasion, should " blowers " be resorted to, if the 
 proper supply of steam can be maintained without 
 them. 
 
 The fire should be spread uniformly all over the 
 grate bars, and in the use of bituminous coal, should 
 be from 6 to 8 inches in thickness, but with anthracite 
 coal, 4 or 5 inches will be thick enough. So long as 
 the ash pit remains bright, there is no necessity for 
 slicing or stirring up the fire, but whenever the spaces 
 between the bars become choked with clinker, or 
 ashes, it will be indicated by the darkness in the ash 
 pit, and, if burning bituminous coal, a slice bar should 
 be run in through the stoke holes or furnace doors to 
 break up the fire and clear out the air spaces. A pick 
 applied from below is also very useful in this respect. 
 In the use of anthracite coal the pick alone should be 
 used ; the breaking up of the surface of such fire, as 
 it does not amalgamate or run together, forming a 
 crust like the bituminous, prevents the regular uni- 
 form combustion by allowing too much air to enter 
 among the disturbed parts of the coal, it requiring 
 considerable time for them again to unite in regular 
 ignition after being once disturbed. It is very impor- 
 tant that no part of the grate bars be left bare, as the 
 admission of cold air, through such space, deadens the 
 fire, and cools the flues. It has been ascertained of 
 late, that better results are obtained by admitting air 
 through a number of small holes in the furnace doors, 
 on the plan of W. Wye Williams, Esq., of England. 
 
 No two furnaces should be fired at the same time ; 
 the fresh coal of the one should be fairly ignited before 
 a new supply is added to another, in order to keep a 
 regular supply of steam. Anthracite coal requires less 
 frequent firing than bituminous, but with either, the 
 
92 THE FIRES WHILE UNDER WAY. 
 
 coal should not be thrown upon any particular part 
 of the furnace, but uniformly all over it. Before 
 firing with bituminous coal, it is well to break up the 
 upper crust of the fire, which sometimes amalgamates 
 so closely as to exclude the proper supply of air. The 
 trouble with most firemen is, that they are disposed to 
 heap their fires too much, particularly in front, some- 
 times half way to the crowns ; this they do for three 
 reasons : first, because they suppose the larger the fire 
 the greater the supply of steam; second, the more 
 coal there is piled in at one time, the less frequent 
 they will have to fire ; and third, it requires much less 
 labor to shovel the coal into the mouth of the furnace, 
 than to supply it uniformly, all over the grates. No 
 coal larger than one's fist should be allowed to enter 
 the furnace, nor in cleaning the fires, should more than 
 one be cleaned at the same time, which should be done 
 at stated intervals, unless it so happens, that they all 
 or many of them, have got so dirty that a further sup- 
 ply of coal is useless, when the engine can be throttled 
 off a little while the cleaning is going on. In cleaning 
 anthracite fires, care should be taken not to reduce 
 them too low, otherwise they will take a long time to 
 recover. 
 
 In cleaning fires, as well as when supplying them, 
 the furnace doors should not be kept open longer than 
 necessary, admitting an undue supply of cold air ; and 
 the party, therefore, who, performing his duty as well, 
 does it the quickest, is the best fireman. 
 
 The slower a steamer runs the greater distance she 
 will perform with the same amount of fuel, provided 
 she has not an adverse tide or head winds to contend 
 with ; with men-of-war, therefore, it often occurs that 
 the saving of fuel is a more important consideration 
 
PATCHING BOILERS. 93 
 
 than high speed, and for this reason the consumption 
 of coal is reduced far below what would be required 
 to keep the vessel up to her maximum speed. This 
 can be done in two ways : either by shutting off a por- 
 tion of the furnaces entirely, by shutting the ash pit 
 doors and closing up the cracks around them with wet 
 ashes, or else reducing the quantity of coal consumed 
 in each, by covering the back part of the grates with 
 a thick layer of ashes. When the diminution in the 
 quantity of coal is not very large, this latter plan is 
 the better, by retaining the original heating surface at 
 the same time that the combustion of coal is allowed 
 to go on very slowly, an end very desirable to secure. 
 When, however, the reduction in coal is very consid- 
 erable, some of the furnaces can be shut off, while the 
 back ends of the grates of the remainder can be kept 
 covered with ashes. Men-of-war sometimes proceed at 
 half or less speed, and as a large extent of boiler sur- 
 face occasions considerable loss from radiation, in such 
 cases it will be more economical to shut off some of the 
 boilers and continue with a moderate supply of fuel in 
 the remainder. The furnaces and ash pits of the boil- 
 ers shut off should be closed tightly, to prevent cold 
 air from passing in to cool the surfaces of the other 
 boilers, or to injure the draft. 
 
 After a boiler is shut off, the steam should not be 
 Allowed to escape, but to remain in it and condense, to 
 freshen the water. 
 
 Patching Boilers. 
 
 Inasmuch as all things constructed by human hands 
 are liable to decay, steam boilers are not exempt from 
 this infallible law ; they therefore frequently require 
 to be patched, new stay bolts and braces to be put in, 
 
94 PATCHING- BOILERS. 
 
 old rivets cut out and replaced with new ones, <fec. In 
 patching boilers, wherever the defective part can be 
 reached so as to work at it well, it is best to cut it out 
 and rivet a patch on, calking the seams ; but as this 
 cannot always be done, the most common practice is 
 to put a patch over the defective part, securing it with 
 bolts and nuts, or tap bolts, and making the joint with 
 stiff putty, composed of white and red lead, and a 
 small quantity of fine iron borings. A piece of sheet 
 lead fitted over the place to be patched, will answer 
 for the pattern to make the patch by, which, however, 
 before the joint is made, should be fitted snugly to its 
 place while hot. 
 
 Owing to imperfection in the iron, small cracks are 
 sometimes discovered in the flues or other parts of the 
 boiler, subject to a high temperature. Should these 
 not be more than two or three inches in length, they 
 can be stopped by drilling holes and putting in three 
 or four small rivets, hammering the heads well down 
 so as to cover the crack. 
 
 A leaky stay-bolt, or rivet, has, like the toothache, 
 but one sure remedy, and that one is to cut it out and 
 put in a new one. 
 
 In cutting out a stay-bolt fitted with a socket, the 
 latter can usually be saved and retained in its place, 
 ready to receive another bolt ; but sometimes a screw 
 bolt is cut out which has to be replaced with a socket 
 bolt, and as this may be in such part of the boiler 
 which cannot be reached by the arm, or tongs, a very 
 good plan to get the socket in its place, is to pass a 
 string through both holes and secure the ends, drop- 
 ping the centre down and hauling it out through a 
 hand hole ; cut the string in two, pass the ends through 
 the socket, join them together again, and haul the 
 
FLUES AND ASH PITS. 95 
 
 socket to its place. In the fitting of sockets, it is very 
 important that they should be the exact distance be- 
 tween the sheets, with the ends filed square, otherwise 
 the sheets will be drawn out of shape. 
 
 Sweeping Flues. 
 
 One of the most disagreeable parts of the duties is 
 that of cleaning flues, from the fact of its dirtying 
 every thing round about or in the vicinity of the boil- 
 ers, the slightest draft being sufficient to waft the light 
 dry ashes in every direction. A little water sprinkled 
 on them before they are hauled out of the connections 
 or smoke-boxes will prevent this in a measure, the 
 damper and ash-pit and furnace doors being closed, to 
 prevent the men from being suffocated who go inside. 
 The lower flues, particularly, are apt to leak a little, 
 and the salt water, mixing with the ashes, forms a solid 
 mass, which can only be removed by being cut out, 
 the flue brush being of no avail. The hammer and 
 chisel, and long, sharp-pointed bars, and sledge, are 
 best adapted to the purpose. In the use of these 
 instruments, care should be taken that they be not 
 driven through the metal or under the seams. 
 
 Ash Pits. 
 
 The ash pits should be cleaned out every watch, 
 and the ashes thrown overboard, picking out first any 
 lumps of coal that may have fallen among the ashes. 
 When not running at full speed, a portion of the cin- 
 ders may be thrown upon the fires again, after damp- 
 ing them with a little water. So also should fine 
 bituminous coal be dampened before being supplied 
 to the furnaces, the arguments to the contrary not- 
 
96 STAYS AND GKATE BARS. 
 
 withstanding ; for though it does take a little heat from 
 the fire to evaporate the water mixed with the coal, a 
 saving is effected, by preventing the coal from being 
 drawn particularly in boilers with strong draft- 
 through the flues and lodged in the connections, or out 
 of the smoke-pipe. No more water, however, should 
 be put on the coal than just sufficient to dampen it. 
 
 Smoke-pipe Stays 
 
 Require to be looked to occasionally, when made 
 of rope, as they grow a little slack from time to time. 
 These should always be adjusted while the pipe is hot ; 
 otherwise, if they be set up while the pipe is cool, the 
 expansion after it becomes heated will, in all proba- 
 bility, " carry " either the stays themselves away, or 
 the band securing them to the pipe. In a gale of 
 wind, when the ship is rolling heavily, these stays 
 should be looked to, in order to tighten any of them 
 that may have become slack, so as to throw the strain 
 alike on all. Hemp rope is a very inferior article for 
 such purpose as stays for smoke pipes, and we can see 
 no good reason, unless it be prejudice, (which is always 
 a good reason to those under such influence,) why it 
 has been so long retained. Good wire rope looks bet- 
 ter, is cheaper, and will last a great deal longer, and 
 requires much less attention. 
 
 Grate JBar$, &c. 
 
 When fitted new, are usually allowed plenty of 
 play, both fore and aft and sideways, to allow for ex- 
 pansion after they become heated. The spaces at the 
 end of the bars, however, become choked up with 
 ashes, which become, by and by, so hard as to form 
 
BROKEN" AIR-PUMP. 97 
 
 almost a solid mass, defeating the objects for which 
 they were left. These spaces, therefore, in port, 
 should be cleaned out occasionally. 
 
 Ash pits, in port, should also be well cleaned and 
 painted, to prevent oxidation. At sea, no water should 
 be thrown into them upon the ashes, but they should 
 be kept as dry as possible. With these precautions, 
 they will last as long as other parts of the boiler. 
 Boilers unused for any considerable time should be 
 kept dry of water, and have fires made occasionally in 
 the ash pits, to evaporate all interior deposit of damp- 
 ness the neglect of this precaution is the sole cause 
 of the oxidation and deterioration of all boilers when 
 not in use. 
 
 Broken Air-Pump. 
 
 Should the air-pump become broken in an irrepar- 
 able manner, and the engine be a single one, there is 
 but one thing that can be done, and that is to work 
 non-condensing. If there be two engines, we have 
 three resorts: to work the broken engine non-conden- 
 sing, to disconnect from the crank pin and proceed 
 with one engine, or, if there be facilities on board, to 
 join the exhaust of both engines with a pipe, and use 
 one air-pump and one condenser for both engines. 
 This latter plan was tried very successfully for a short 
 run on board the U. S. Steam Frigate " Powhatan," 
 on the China station, in the summer of 1855. Peculiar 
 facilities were, however, offered in this case, as the ex- 
 haust side pipe of each engine had a man-hole in it, to 
 which the connecting pipe was joined. 
 
 In running under such circumstances, care should 
 be taken not to overload the air-pump. 
 
98 CYLINDER HEAD AND SELECTION OF COAL. 
 
 Broken Cylinder Head. 
 
 Water may be worked over into the cylinder sud- 
 denly, from boilers foaming badly, or otherwise, faster 
 than it can escape through the water valves, and being 
 nearly non-compressible, something must give way, the 
 cylinder head, or bottom, being the most likely thing to 
 go. In. such an event, if there be a spare one on board, 
 put it on ; if not, while the old one is being repaired, if it 
 be reparable, the following plan can be resorted to ; 
 Disconnect the steam and exhaust valves from the 
 damaged end of the cylinder, if the engine be fitted 
 with poppet valves, and let the atmospheric pressure 
 force the piston in one direction, the steam being used 
 for the opposite direction. Should the engine be fitted 
 with a slide valve, close up the opening into the dam- 
 aged end of the cylinder, by fitting in, steam-tight and 
 in a substantial manner, a block of soft wood. This 
 should not, however, be resorted to, except in cases of 
 great emergency. Cylinder heads should have man- 
 hole plates of less strength than the heads ; this would 
 prevent the destruction of heads in all cases. 
 
 The selection of Goal. 
 
 The kinds and qualities of coals are so varied that 
 no general rules can be given for their selection, but 
 there is one point, however, which we think will not 
 be disputed, and that one is, whenever there is a 
 choice, the only sure plan is to select the best ; for, 
 though its first cost may be a little more, it will prove 
 to be the cheapest in the end. What economy is there 
 in purchasing one coal because it can be obtained 10 
 
SAFETY VALVE. 99 
 
 or 15 per cent, cheaper than another, when there will 
 be burned, to produce the same effect, from 20 to 25 
 per cent, more than would be burned by the better 
 kind ? Yet this is a thing of daily occurrence. But, 
 regardless of the money view, there are other disad- 
 vantages attending the use of the inferior coal. From 
 the fact of there being more burned, the firemen have 
 more to supply to the furnaces, and it requires, on 
 their part, greater care and attention to keep the fires 
 in good order ; thus imposing extra duty on a portion 
 of the ship's crew whose energies are usually overtaxed. 
 Besides, to convey the vessel a given distance, an extra 
 quantity has to be taken on board, which, in the case 
 of merchant ships, diminishes their freight capacity, or, 
 in war ships, lumbers the deck with a useless number 
 of bags. 
 
 Some boilers are best adapted to bituminous coals, 
 others to anthracite, and the one or the other of these 
 coals which should be selected, depends upon the cir- 
 cumstances, therefore, for which they are intended. 
 
 In the selection of coals, it is an object to obtain 
 those free as possible from earthy impurities. Slate, 
 and such like matter, is to be avoided. Sulphur in 
 bituminous coals makes them the more liable to spon- 
 taneous combustion. So also receiving them on board 
 wet will endanger spontaneous ignition. Coals which 
 have been exposed a long while to the rays of the sun, 
 particularly in tropical climates, undergo a gradual 
 decay, reducing their evaporative qualities. 
 
 Safety Valve. 
 
 Steam, when once commencing to blow off, will 
 not cease when the pressure has fallen to the pressure 
 
100 SAFETY VALVE. 
 
 due to that for which the safety valve is loaded, but 
 will continue to blow-off until the pressure has fallen 
 some pounds below this. This is owing to the increased 
 area which the steam has to act upon when the valve 
 is open over what it has when the valve is closed, oc- 
 casioned by the bevel of the valve face. In a heavy 
 sea, the safety valve may be forced open for a short 
 time, even when the pressure is below that for which 
 the valve is loaded, by the oscillation of the ship. 
 
CHAPTER V. 
 
 MISCELLANEOUS. 
 
 The Theory of the Paddle Wheel; the Radial compared 
 with the Feathering Wheel. 
 
 To all those whose minds have a tendency to probe 
 beyond the superficial crust of any thing that may be 
 presented to their consideration, the theory of the ac- 
 tion of the paddle wheel on the water must be one of 
 interest, and any thing, therefore, tending to make 
 this subject the more clear, cannot fail to receive the 
 proper attention and a careful perusal. 
 
 In regard to the paddle wheel, many theories have 
 been advanced, some of them so positively absurd that 
 it is difficult for us to conceive how they ever found 
 their way into print. Even in reference to the subject 
 of centre of pressure of the paddles, such rules as the 
 following have been put forth from quarters to which 
 we should have looked for more correct information : 
 
 " The circle described by the point whose velocity 
 equals the velocity of the ship, is called the rolling cir- 
 cle, and the resistance due to the difference of velocity 
 of the rolling circle and the centre of pressure is that 
 which operates in the propulsion of the vessel." * * * 
 
 Rule : " From the radius of the wheel subtract the 
 radius of the rolling circle, to the remainder add the 
 depth of the paddle board, and divide the fourth 
 
102 THEORY OF THE PADDLE WHEEL. 
 
 power of the sum by four times the depth ; from the 
 cube root of the quotient subtract the difference be- 
 ^tweeiv'tte- radii of the wheel and the rolling circle, and 
 , the remainder -will be the distance of the centre of 
 pressure -from ' the upper edge of the paddle. The 
 diameter of the rolling circle is very easily found, for 
 we have only to divide 5280 times the number of miles 
 per hour by 60 times the number of strokes per min- 
 ute, to get an expression for the circumference of the 
 rolling circle, or the following rule may be adopted : 
 Divide 88 times the speed of the vessel in statute miles 
 per hour, by 3.1416 times the number of strokes per 
 minute ; the quotient will be the diameter in feet of 
 the rolling circle." 
 
 Now, then, I suppose no one who has given the sub- 
 ject the slightest attention would imagine, for one mo- 
 ment, that so long as the immersion remained constant, a 
 difference in the slip of a common radial wheel would 
 make a difference in the centre of pressure of the pad- 
 dles ; yet if any one will take the trouble to work out 
 the centre of pressure of any wheel by the above rule 
 with different slips, he will find the centre of pressure 
 continually changing. To suppose such a thing to be true 
 would be as absurd as to suppose the centre of pres- 
 sure of a plank immersed vertically in a stream moving 
 at the rate of 10 miles per hour, to be in a different 
 place from what it would be should the stream move 
 at the rate of 5 miles per hour. 
 
 We have thought it advisable, therefore, to go into 
 this subject the more fully, and give the following as 
 an illustration of our views : 
 
 It is generally admitted that the total loss of effect, 
 or power, in the common radial wheel, is the sum of 
 the losses of the oblique action on the water and the 
 
THEORY OF THE PADDLE WHEEL. 
 
 103 
 
 slip. The former is calculated by taking the mean of 
 the squares of the sines of the angle of incidence at 
 which the paddles strike the water, or which is the 
 same thing, the means of the squares of the cosines of 
 the angles of the arm and water ; for one angle is the 
 complement of the other. This will appear plain from 
 an inspection of figure 1. A C is the arm, making 
 
 FIG, L 
 
 an angle at C, with the vertical line C A' ; A B, the 
 breadth of the paddles, and E F, the surface of the 
 water. Now, it is manifest, that, inasmuch as the ves- 
 sel is moving in a horizontal direction, the line B D at 
 right angles to that direction, represents the only por- 
 tion of the paddle A B that is efficient in propelling 
 the vessel, and the line A D represents that portion 
 of the paddle that tends to lift the vessel out of the 
 water, which, consequently, as it produces no propul- 
 sive effect, must be entirely lost. But the line A B, 
 being the breadth of the paddle, we will suppose rep- 
 resents the pressure it exerts on the water, which, 
 
104 THEORY OF THE PADDLE WHEEL. 
 
 * 
 
 according to the resolution of forces, is divided into 
 two other pressures. A D, tending to lift the vessel, 
 is the useless pressure, and B D, at right angles to the 
 vessel's path, is the efficient pressure, or the portion 
 that is utilized in propelling the vessel. Power, how- 
 ever, is not composed of pressure alone, but is com- 
 pounded of pressure and velocity, and as the velocities 
 of the columns of water, having A D B D for the base 
 depend upon the lengths of those lines respectively ; 
 that is to say, if we double the length of either one 
 of them, say B D, for instance, diminishing the angle 
 at C, we not only double the quantity of water dis- 
 placed in any given time, but it is also displaced with 
 double the velocity ; the power, therefore, developed 
 is the product of these two, or as the square. Hence, 
 it follows that, since A D represents the useless pres- 
 sure, the square of that line must represent the useless 
 or lost power ; or, more correctly, the loss of useful 
 effect, and the square of B D, the power that is applied 
 to propelling the vessel. Now, then, considering A B 
 to be unity, the square of B D will be the square of the 
 natural sine of the angle BAD, and the square of 
 A D the square of the natural sine of the angle A B D ; 
 but the triangles A B D, A C D', being similar, the 
 angles at B and C are equal, and the loss of effect is, 
 therefore, simply represented by the square of the sine 
 of the angle that the oblique arm makes with the per- 
 pendicular ; but as the angle is continually changing, 
 as the arm moves through the water, we have to take 
 the mean, and the more numerous, therefore, the divi- 
 sions are made, the nearer correct will be the result. 
 
 Thus, supposing, as per figure 2, a wheel 26 feet 
 diameter, from outside to outside of paddles, 6 feet 
 immersion of lower edge of paddles, and 20 inches 
 
THEORY OF THE PADDLE WHEEL. 
 
 10; 
 
 breadth of paddles, the loss from oblique action is 
 calculated as follows, the arc being divided into divi- 
 
 Fio. 2. 
 
 Bions of 5 each, which are considered sufficiently nu- 
 merous for practical purposes : 
 
106 
 
 THEOEY OF THE PADDLE WHEEL. 
 
 
 Aiiyleb 
 of 
 Incidence. 
 
 Sines of the 
 Angles of 
 Incidence. 
 
 
 * 
 
 55 
 
 .81915 
 
 .33550 = half of the square of sine 
 
 1 
 
 50 
 
 .76604 
 
 .58681 = square of sine. 
 
 1 
 
 45 
 
 .70711 
 
 .50000 " 
 
 1 
 
 40 
 
 .64279 
 
 .41317 ^ " 
 
 1 
 
 35 
 
 .57358 
 
 .32899 = " 
 
 1 
 
 30 
 
 .60000 
 
 .25000 = " 
 
 
 25 
 
 .42262 
 
 .17860 = " 
 
 
 20 
 
 .34202 
 
 .11697 = " 
 
 
 15 
 
 .25882 
 
 .06698 = " 
 
 
 10 
 
 .17365 
 
 .03015 = " 
 
 
 5 
 
 .08716 
 
 .00759 = " 
 
 
 
 
 .00000 
 
 .00000 = " 
 
 
 5 
 
 .08716 
 
 .00759 = " 
 
 
 10 
 
 .17365 
 
 .03015 = " 
 
 
 15 
 
 .25882 
 
 .06698 = " 
 
 
 20 
 
 .34202 
 
 .11697 = " 
 
 
 25 
 
 .42262 
 
 .17860 = " 
 
 
 30 
 
 .50000 
 
 .25000 = " 
 
 
 35 
 
 .57358 
 
 .32899 = " 
 
 
 40 
 
 .62279 
 
 .41317 = " 
 
 
 45 
 
 .70711 
 
 .50000 = " 
 
 
 60 
 
 .76604 
 
 .58681 = 
 
 * 
 
 55 
 
 .81915 
 
 .33550 = half of the square of sine. 
 
 22 
 
 
 
 5.62952 
 
 As 22 : 5.62952 : : 100 : 25.588 per cent, of the 
 power applied to the wheels. 
 
 Half of the square of the sine at the angle of 55 is 
 taken, because the paddle in that position is only half 
 immersed, consequently only half the power can be 
 expended on it as if entirely immersed ; and the angles 
 are put down twice, because the loss is the same after 
 the paddle leaves the vertical position as before it 
 reaches it. The power in the latter case being ex- 
 pended in forcing the water downwards, and in the 
 former case in lifting the water, neither of which as- 
 sists in propelling the vessel, the only tendency being 
 to lift the bow, and depress the stern. 
 
 Slip. 
 
 The loss of effect from slip is usually considered 
 the difference between the velocity of the centre of 
 pressure of the paddles and the velocity of the vessel. 
 
^^T" 
 
 

THBOEY OF THE PADDLE WHEEL. 107 
 
 Thus, if the velocity of the centre of pressure of 
 the paddles exceeds the velocity of the vessel by 18 
 per cent, of the speed of the paddles, 18 per cent, is 
 considered the loss of effect from slip. This we con- 
 ceive to be an error. The 18 per cent, is the difference 
 between the velocity of the paddles and the velocity 
 of the vessel, nothing more; and, therefore, simply 
 represents the slip in per cent, of the paddles, but not 
 the loss of effect from slip. For it has been shown 
 that the loss resulting from the oblique action of the 
 paddles on the water, is as the squares of the sines of 
 the angles of incidence, and if we suppose the wheel 
 to be immersed to its axis, the loss from this cause on 
 the paddle, when in the horizontal position the angle 
 being 90 is 100 per cent., and if the loss from slip 
 of 18 per cent, be added to that, we have a total loss 
 of 118 per cent., or more than the power applied. A 
 positive absurdity. Or, again, supposing the vessel to 
 be made fast to the wharf, the difference between the 
 velocity of the paddles and the velocity of the vessel 
 will be 100 per cent., and as the loss from oblique ac- 
 tion cannot, from this circumstance, be any less than 
 if the vessel was moving ahead, there will be a total 
 loss of the power applied to the wheels of 125.588 per 
 cent. A result equally absurd. 
 
 At the angle of 45 it has been seen that only 
 .70711 part of the area of the paddle is effective in 
 propelling the vessel, and that at this angle the ve- 
 locity of the column of water driven aft is only .70711 
 of what it is when the whole area of the paddle is 
 effective, hence the power expended in slip = .70711 
 X .70711 = 5, the slip in the vertical position being 
 considered 1. 
 
 Now, then, if 18 per cent, is the loss from slip 
 
108 THEORY OF THE PADDLE WHEEL. 
 
 when the paddle is in the vertical position which 
 must be the case if its velocity exceeds that of the 
 vessel by 18 per cent, of its own speed from what 
 has just been shown, at the angle of 45, the loss can- 
 not be more than half of 18, or 9 per cent. The same 
 reasoning will demonstrate, that at the angle of 30 
 the loss from slip cannot exceed J of 18, or 13.5 per 
 cent. Thus we see the loss from slip goes on decreas- 
 ing from the vertical to the horizontal position, at 
 which place it becomes nothing. We can, therefore, 
 approximate very nearly to the true loss in the present 
 radial wheel, by taking the mean of these losses at the 
 angles as laid down in figure 2. They are as follows: 
 
 At = 
 
 18 
 
 
 
 .0000 
 
 = 18 per 
 
 cent, 
 
 a 
 
 5 = 
 
 18 
 
 
 
 .1366 
 
 = 17 
 
 .8634 
 
 u 
 
 u 
 
 u 
 
 10 = 
 
 18 
 
 
 
 .5427 
 
 = 17 
 
 .4573 
 
 tt 
 
 u 
 
 u 
 
 15 = 
 
 18 
 
 - 1 
 
 .2056 
 
 = 16 
 
 .7944 
 
 a 
 
 a 
 
 it 
 
 20 = 
 
 18 
 
 - 2 
 
 .1055 
 
 = 15 
 
 .8945 
 
 tt 
 
 u 
 
 u 
 
 25 = 
 
 18 
 
 - 3 
 
 .2148 
 
 = 14 
 
 .7852 
 
 a 
 
 tt 
 
 a 
 
 30 = 
 
 18 
 
 - 4 
 
 .5000 
 
 = 13 
 
 .5000 
 
 u 
 
 a 
 
 u 
 
 35 = 
 
 18 
 
 - 5 
 
 .9218 
 
 = 12 
 
 .0782 
 
 a 
 
 u 
 
 u 
 
 40 = 
 
 18 
 
 - 7 
 
 .4371 
 
 = 10 
 
 .5629 
 
 a 
 
 1C 
 
 u 
 
 45 = 
 
 18 
 
 9 
 
 .0000 
 
 = 9 
 
 .0000 
 
 u 
 
 a 
 
 u 
 
 50 = 
 
 18 
 
 -10 
 
 .5626 
 
 = 7.4374 
 
 it 
 
 u 
 
 a 
 
 55 = 
 
 18 
 
 - 12.078 
 
 = 5 
 
 .9220 
 
 a 
 
 a 
 
 
 
 
 2 
 
 
 138 
 
 .3343 
 
 
 
 
 
 
 
 
 
 2 
 
 
 
 bled for both sides of the verti 
 position 
 
 ical ) 
 
 - 276 
 
 .6686 
 
 
 
 
 
 
 
 
 18 
 
 .0000 
 
 
 
 
 
 
 
 
 294 
 
 .6686 
 
 
 
 294.6686 
 2<>- = 13.394 per cent, of the power applied to 
 
 the wheels. 
 
THEORY OF THE PADDLE WHEEL. 109 
 
 The same result is obtained as follows : 
 
 100.000 (power applied) 25.588 (oblique action) 
 
 X 18 per cent, (slip of the vertical paddle) = 13.394 
 
 per cent. 
 
 We have, therefore, for a total loss in this radial 
 
 wheel, 25.588 + 13.394 38.982 per cent, of the power 
 
 applied to it. 
 
 Feathering Wheel. 
 
 Let us take a feathering wheel, of the same di- 
 ameter of centre of pressure, i. e., 26 feet 4 inches in 
 diameter from outside to outside of paddles same 
 immersion, breadth, and number of paddles, and see 
 how it compares with this. 
 
 It is conceived by some that the only losses in this 
 kind of wheel are the friction of the eccentrics, &c., 
 and the slip, but there is another loss with deep im- 
 mersions, or light slips, occasioned by the drag of the 
 paddles as they enter and leave the water. 
 
 In figure 3, the paddles are supposed to be verti- 
 cal from the time they enter until they leave the 
 water, and the positions of the arms will be seen at 
 the degrees there laid down. The perpendicular lines 
 drawn across the arcs are intended to represent the 
 breadth of the paddles. It is plain that while the axis 
 of the paddle moves from A to B, it moves horizon- 
 tally the distance A C, and vertically the distance 
 C B, and, supposing the vessel to be moving with the 
 same velocity as the paddles, it will travel the distance 
 A B, while the paddle travels horizontally the distance 
 A C. Now, the distance A C being less than A B> 
 the paddle in this position cannot be giving out any 
 power, but must be keeping the vessel back, by carry- 
 
110 
 
 THEORY OF THE PADDLE WHEEL. 
 
 ing a column of water before it, the base of which is 
 equal to the area of the paddles, and the length equal 
 to the difference in the lengths of the two lines. 
 
 If A B be represented by unity, A C will be rep- 
 resented by the natural sine of the angle ABC, and 
 if the arc be supposed to be divided into an infinite 
 
THEORY OF THE PADDLE WHEEL. Ill 
 
 number of parts, or composed of an infinite number of 
 straight lines, A B will be at right angles to A D, and, by 
 consequence, the angle ABC will be equal to the angle 
 DAE; and as the sine of B represents the distance 
 traveled horizontally by the paddle, the sine of D A E 
 must manifestly represent the same thing, but the sine 
 of D A E is the cosine of D, which therefore repre- 
 sents the horizontal velocity of the paddle at the angle 
 of 50, its circular velocity being 1. The difference 
 between these two lines is, therefore, the loss from 
 dra<7, supposing there to be no slip, but as all paddle 
 wheels must have some slip, when they are propelling 
 a vessel, the line A B, diminished by the amount of 
 slip, will represent the distance traveled by the vessel, 
 and the loss from drag will therefore, instead of being 
 the difference between A B and A C, be the difference 
 between a fraction of A B and the whole of A C, de- 
 pendent upon the amount of slip. If this fraction of 
 A B be just equal to A C, the loss from drag in this 
 position becomes ; for, though the paddle be giving 
 out no power to the vessel, it occasions no resistance 
 to the vessel's progress through the water, because it 
 is moving horizontally precisely as fast as the vessel 
 itself; and if the fraction be less than A C, the resist- 
 ance will, of course, be on the after instead of the for- 
 ward side of the paddle, and it must, in consequence, 
 necessarily be assisting in propelling the vessel. 
 
 Now, then, from the above, it must be evident to 
 any one, that so long as the paddle, after it enters the 
 water, is moving horizontally at a less rate than the 
 vessel, it cannot be giving out any power, but must be 
 an actual resistance to the vessel's progress through 
 the water. Taking figure 3, and giving the wheel the 
 same mean loss from slip as the radial wheel, viz., 
 
112 THEORY OF THE PADDLE WHEEL. 
 
 13.394 per cent., we will ascertain the loss from slip 
 at the different angles there laid down, and attend to 
 the drag afterwards, which is merely slip in the oppo- 
 site direction, or what might be termed negative slip. 
 
 To give this wheel the same mean loss from slip as 
 the radial wheel, it has to have on the arm when in 
 the vertical position, or 
 
 At Cosines . 26.225 per cent. 
 
 5 = .99619 - .73775 = 25.844 " " 
 " 10 = .98481 - .73775 = 24.706 " " 
 " 15 = .96593 - .73775 = 22.818 " " 
 " 20 = .93969 .73775 = 20.194 
 " 25 = .90631 - .73775 = 16.856 
 " 30 = .86603 - .73775 = 12.828 " " 
 " 35 = .81915 - .73775 = 8.140 " 
 " 40 = .76604 ,73775 = 2.829 
 " 45=: 0.000 " " 
 
 50= 0.000 " " 
 
 55= 0.000 " " 
 
 134.215 
 _ 2 
 
 Doubled for both sides of the vertical \ c) o A Q A 
 
 position, \ JOO.40U 
 
 26.225 
 294655 
 
 294 655 
 
 - = 13.394 per cent, of the power applied to 
 
 22 
 
 the wheel lost by slip. 
 
 At the angle of 55 the paddle is .445 part im- 
 mersed, but, being so near, we have taken it at a half 
 for simplicity, and for like reason have considered the 
 paddle at 50 entirely immersed. 
 
 It will be seen from the above, that the paddle, 
 from the time it enters the water until after it passes 
 
 " " 
 " " 
 
 " 
 " " 
 
THEOEY OF THE PADDLE WHEEL. 
 
 45, is traveling horizontally at a less rate than the 
 vessel, and the same effect ensues as it rises out of the 
 water ; there must, therefore, be a loss from drag or 
 negative slip. Let us see what this amounts to. 
 
 Cosines. 
 
 .73775 - .57358 
 At 55 = - -g- = 8.208 per cent. 
 
 " 50 = .73775 - .64279 = 9.496 " " 
 " 45 = .73775 - .70711 = 3.064 " " 
 
 20.768 
 
 _2 
 
 Doubled for entering and leaving, 41.536 
 
 41.536 
 
 29 = 1.933 per cent. 
 
 We have, then, for a total loss in this wheel, slip 
 (13.394 per cent.) + drag (1.933 per cent.) = 15.327 
 per cent, of the power applied to it. 
 
 The total loss in the radial wheel having been 
 shown to be 38.982 per cent, (and in the feathering 
 wheel 15.327 per cent.), we have 23.655 per cent, 
 in favor of the feathering wheel. But of the whole 
 power applied to the engines, about 20 per cent, is ex- 
 pended in overcoming friction of ditto, friction of load 
 on working journals, working air and feed pumps with 
 their loads, &c. Consequently, only 80 per cent, 
 reaches the wheels, and 23.655 per cent, of 80 per 
 cent, equals 18.924 percent, of the total power applied 
 to the engines in favor of the feathering wheel. 
 
 To stand off against this, we have the friction of 
 the eccentrics, &c. (an amount that, perhaps, can only 
 be estimated) extra weight and wear and tear of the 
 wheels. 
 
 It will be seen also from the above, that the differ- 
 ence between the velocity of the feathering wheel and 
 
114 CENTKE OF 
 
 the vessel being 26.235 per cent, of the speed of the 
 wheel, and the difference between the velocity of the 
 radial wheel and the vessel being 18 per cent, of its 
 speed, it follows that, making the same number of 
 revolutions, the speeds of the vessels will be as Y 3.7 7 5 
 to 82, or as 1.00 to 1.11 ; consequently, the speed of 
 the feathering wheel will have to exceed the speed 
 of the radial wheel 11 per cent, to give the vessel the 
 same velocity, but this speed of the wheel is as shown 
 consequent upon there being less resistance to the pad- 
 dles attained by an expenditure of 18.924 per cent, 
 less power. 
 
 Centre of Pressure. 
 
 The centre of pressure of a rectangular plane im- 
 mersed in a fluid, the upper extremity of which is even 
 with the surface of the fluid, is -J- from the bottom ; 
 but, inasmuch as the pressure is as the depth, when its 
 upper extremity is below the surface of the fluid, this 
 law no longer holds good. To ascertain the centre of 
 pressure in such case, " Jamieson on Fluids " gives the 
 following practical rule deduced from elaborate math- 
 ematical calculations : 
 
 " Divide the difference of the cubes of the extremi- 
 ties of the given plane below the surface of the fluid, 
 by the difference of their squares, and two-thirds of 
 the quotient will give the distance of the centre of 
 pressure below the surface, from which subtract the 
 depth of the upper extremity, and the remainder will 
 show the point in the centre line of the plane in which 
 the centre of pressure is situated." 
 
 This rule can be applied directly to the feathering 
 wheel, by taking the mean immersion of the paddles 
 
CENTRE OF PRESSURE. 115 
 
 as they move through the water, and assuming figure 3 
 to be of the same diameter from outside to outside of 
 paddles, as figure 2, viz : 26 feet, we find the mean 
 immersion of the lower edges of the paddles, after their 
 upper extremity gets below the surface, to be 
 
 (29.23 + 37.84 -f 46.69 -f- 62.44 -f 58.32 -f 63.09 + 67.02 -fr 69.78 -f * 1.44) 
 
 19 
 
 2 + 72 = 55.87 inches, and upper edge 35.87 inches. 
 The mean centre of pressure of the paddles in these 
 
 (C 0>73 _ OC 073 \ 
 55 ; 872 _ 35 ; 87 -i)|- = 46.59 - 35.87 = 10.72 
 
 inches from top, or 9.28 inches from bottom, and the 
 mean centre of pressure from the time the paddle 
 enters until it leaves the water, 
 
 In the radial wheel, however, as the outer ex- 
 tremity of the paddle moves more rapidly than the 
 inner extremity, and as the resistance is as the square 
 of the velocity, the centre of pressure must be consid- 
 erably nearer the outer extremity on this account. 
 One-third from the bottom, in this case, is, therefore, 
 probably, not much out of the truth ; but as a portion 
 of the paddle only part of the time is immersed, we 
 take the mean of the third of that portion and a third 
 of the whole breadth of the paddle during the time it 
 is entirely immersed. 
 
 (20 3)x21 + (10-f-3)2 
 
 Thus : v - 6.37 inches from 
 
 23 
 
 the bottom, showing the centre of pressure under these 
 circumstances to be (8.52 6.37 = ) 2.15 inches nearer 
 the lower edge of the paddle in the radial than it is in 
 the feathering wheel. 
 
116 THE SCREW PROPELLER. 
 
 Practical Remarks on the Foregoing. 
 
 From what has been shown, it would appear that 
 the use of the feathering wheel over the radial wheel, 
 from the great saving it effects, would lead to its uni- 
 versal adoption ; but, unfortunately, the practical diffi- 
 culties are such that its use is confined within very 
 narrow limits. The increased weight of the wheel, 
 occasioned by the eccentrics, levers, arms, &c., required 
 to work the paddles, amounting, in some cases, to 
 several tons, causing the pillow-block brasses to wear 
 away very rapidly, is a sad objection, to say nothing 
 of the excessive friction they produce. Besides, the 
 pins operating as the axis about which the paddles 
 vibrate are found to wear away very rapidly, requiring 
 not only to be replaced frequently, but the noise and 
 jar occasioned from the wear becomes very objec- 
 tionable. The latter objection, however, can be re- 
 moved by the use of lignumvitse pin bearings. 
 
 i 
 
 The Screw Propeller. 
 
 The great advantages derivable from the successful 
 adaptation of the screw propeller, particularly to ves- 
 sels of war, became well understood in its early his- 
 tory, and inventive genius set to work thenceforth to 
 perfect this important invention ; all kinds of propel- 
 ]ers sprang into use, many of them possessing neither 
 the merit of novelty nor usefulness. One, two, three, 
 four, five, six-bladed, true screws, expanding pitch and 
 no screw at all, are among the number that have been 
 tried experimentally and practically since the intro- 
 duction of the screw propeller, and, strange as it may 
 appear, notwithstanding the large share of attention it 
 has received, the theory of the screw propeller is yet not 
 
THE SCREW PROPELLER. 
 
 generally understood ; but, to our mind, this is owing 
 to one great cause ; and that is, to the very important 
 fact, that those who have undertaken to explain and 
 illustrate it, have apparently thought it more impor- 
 tant to give the history and accounts of the experi- 
 ments though both very useful in themselves than 
 to explain the leading features and the laws governing 
 its action. Besides, a practical engineer does not wish, 
 or if he did, has not the time to spare, to examine 
 large volumes to find what might be condensed into a 
 few pages. We have, therefore, determined to make 
 our remarks on this subject brief, and to confine them 
 to those points which we think are the more impor- 
 tant, allowing the student to build upon them for him- 
 self. 
 
 The surface of a screw blade may be supposed to 
 be generated by a line revolving around a cylinder, at 
 right angles to the axis, at the same time that it moves 
 along it, and should the revolving motion be a constant 
 ratio to the motion lengthwise, it will be a true screw. 
 Should such a screw as this, Fig. 4, be developed upon 
 a plane it will form a no. 4. 
 
 right-angled triangle, in B 
 which A B is the pitch, 
 A C the circumference 
 described by the extrem- 
 ity of the blade, and B C 
 the line described by any 
 point in the periphery 
 of the blade by one con- 
 volution of the thread. To make this the more clear, 
 suppose the triangle A B C to be wound round a cyl- 
 inder, having a circumference equal to A C, and sup- 
 pose at C we start to trace a line around the cylinder. 
 
118 THE SCREW PROPELLER. 
 
 moving along it at the same time in a constant ratio r 
 and that when we have gone all the way around, ar- 
 riving over the starting point C, (C and A will be one 
 and the same point in the case supposed) we have 
 reached the point B, C B will be the line described, 
 which is technically termed the directrix, and A B, 
 being the distance moved in the direction of the axis, 
 will be the pitch. Should the line A B be a curve, 
 instead of a straight line, the screw would have an in- 
 creasing or expanding pitch, instead of an uniform 
 pitch. Figure 5 will illustrate this: Let the curve 
 FIG. 5. B C be the curve of the blade, 
 
 and the dotted lines B , C c 
 be tangents drawn to this 
 curve, it will be seen that, at 
 different points in the curve 
 B C, the velocity of rotation 
 remaining constant, the ve- 
 locity lengthwise of the axis 
 A B varies, growing greater 
 as we approach B. This is what is termed an expand- 
 ing pitch ; that is to say, the pitch at the anterior por- 
 tion of the blade, is less than the pitch at the posterior 
 portion. The object of such a pitch is this: the ante- 
 rior portion of the blade striking upon water at rest, 
 encounters the resistance due to a solid body moving 
 through water at rest, but this portion of the blade 
 puts the water in motion, it being a yielding medium, 
 so that when the posterior portion of the blade follows 
 it has to act on water in motion, instead of water at 
 rest, and in order, therefore, to make the resistance 
 due to all parts of the blade alike, the pitch of the pos- 
 terior portion of the blade is increased to the extent 
 of the motion given to the water by the anterior por- 
 tion. 
 
THE SCEEW PROPELLER. 119 
 
 To measure the pitch of a screw blade, did it ex- 
 tend all the way round the shaft to a full convolution 
 of the thread, all we would have to do, would be to 
 measure along the line of the shaft from any point in 
 the blade to any point directly over it, and the dis- 
 tance would be the pitch, or the distance traveled in 
 the direction of the axis by one convolution of the 
 thread; but since in practice, in order to secure the 
 proper resisting area, a full convolution of the thread 
 is not required a very small fraction of it being 
 used it becomes necessary, therefore, to find the pitch 
 from this fraction. Taking figure 4, for instance, let 
 B b be the length of the blade, measured on the peri- 
 phery, and A C the circumference described by the 
 extremity of the blade, B b will be the fraction of the 
 blade used, and B a the fraction of the pitch. We 
 know, therefore, that, starting from B, and traveling 
 along the line B Z>, when we arrive at the point J, we 
 have traveled along the axis the distance B &, and from 
 this we can ascertain what distance will be moved 
 along the axis by continuing all the way round until 
 we arrive at C, which will be the pitch. Practically, 
 we can measure this in two ways : measure the length 
 B b of the blade, and also B a, the length in line with 
 the axis, we have then two legs of a right-angled tri- 
 angle, from which we ascertain the third, a b. Now, 
 then, knowing the circumference described by the ex- 
 tremity of the blade, we derive the following simple 
 proportion : 
 
 As a b : the whole circumference : : B a : the whole 
 pitch. 
 
 Or we proceed thus: Lay a straight-edge across 
 the face of the propeller, at right angles to the axis, 
 and a bevel on the periphery of the blade, and look 
 
120 THE SCREW PROPELLER. 
 
 them out of wTnd, the angle enclosed by the two legs 
 of the bevel will be the angle B b a, which is termed 
 the " angle of the propeller ; " and hence, if B b be 
 supposed unity, the fraction of the pitch of the one 
 blade will be (B a) the natural sine of the angle B b a, 
 therefore, knowing the angle B b a, and the length of 
 the blade B #, we ascertain the pitch thus : 
 
 As cosine b : whole circumference of propeller : : 
 sine b : to whole pitch. 
 
 The pitch can also be determined by construction, 
 without any calculation whatever. Thus, supposing 
 the line a b represents the whole circumference of the 
 propeller, we draw the line B b at the angle to a b as- 
 certained from measurement, and erect the perpendic- 
 ular a B, which will give the pitch required. 
 
 In a true screw, it matters not whether we take 
 the angle at the periphery or any other part of the 
 blade ; for, though the angle will be different, increas- 
 ing as we approach the centre, the pitch will be the 
 same, it only being necessary to know the circumfer- 
 ence at the point where we measure the angle. 
 
 Should the blade not be a true screw, but an ex- 
 panding pitch, we have to take the angle at two or 
 more points, by drawing tangents to the curve, and 
 take the mean, for the mean angle of the blade. Thus, 
 in figure 5, the mean of the angles B b A and c C A 
 will give the mean angle of the blade. 
 
 Some propellers are made to expand from hub to 
 periphery, instead of from anterior to posterior portion 
 of the blade. 
 
 To ascertain the pitch of such a propeller, take the 
 mean of the angles at several points in the blade, and 
 proceed as above. In order to ascertain the pitch of 
 any propeller, it is always proper to take the angles at 
 
THE SCREW PROPELLER. 
 
 two or more points in the blade, from which we learn 
 whether it expands from hub to periphery, whether it 
 be true screw, or no screw at all. 
 
 The fraction of the pitch, as we have explained it 
 above, is the fraction of the pitch of one blade, but as 
 screw propellers usually have two, three, four, six, &c., 
 blades, constituting fractions of a, double-threaded, 
 treble-threaded, four-threaded, six-threaded, &c., screw, 
 the sum of these constitute the fraction of what is 
 usually termed the fraction of the pitch of the screw ; 
 that is to say, if the screw have three blades, and the 
 fraction of the pitch of one of those blades be y 1 ^, the 
 real fraction of the pitch will be 3 times T V, or J ; 
 for it evidently matters not, as far as this is concerned, 
 whether the screw be in one, or divided into a dozen 
 parts. 
 
 How to lay down a Propeller. 
 
 Knowing the diameter, number of blades, and frac- 
 tion of pitch, we intend to use, we proceed thus : 
 
 Taking figure 6, for in- FIG. & 
 
 stance, draw the line A C, 
 equal the circumference of 
 the extremities of the blades, 
 and from A erect the per- 
 pendicular A B, equal the 
 pitch ; join B C. Now, then, 
 supposing we desire the pro- A 
 peller to have four blades, and the fraction of the pitch 
 to be -J-, lay off B a, equal to ^ B A, and draw a c, 
 parallel to AC. a c will be the circumference of the 
 extremity of one blade viewed as a disc. Then, taking 
 figure *7, we describe the circle a b c, equal A C, figure 
 
122 THE SCREW PROPELLER. 
 
 6, and also the smaller circle, equal the circumference 
 of the hub of the propeller ; divide the 
 larger circle into four equal parts, and, 
 from the centres thus obtained lay off 
 a d, Ti i, bf, e c, each equal to a c, fig- 
 ure 6, and draw lines from each of these 
 points to the centre, terminating in the 
 hub ; such will be the projection of a four-bladed, true 
 screw propeller, viewed from the stern, from which 
 the longitudinal elevation can be drawn. The dimen- 
 sions of the sections of the blade depend upon the 
 diameter of the propeller, the material of which it is 
 constructed, and the pressure it has to sustain. 
 
 Centre of Pressure. 
 
 All solid bodies moving through a fluid have a cer- 
 tain point called the centre of pressure, which is the 
 point where the outer and inner pressures just exactly 
 balance. In a screw propeller, the radius of the cir- 
 cle, which is equal to half the area of the whole circle, 
 described by the periphery of the blades, is the centre 
 of pressure from centre of motion. Thus, if a propeller 
 be 16 feet diameter, the area of the circle described by 
 the extremity of the blades =201.06 square feet, and 
 the radius of the circle, having an area equal to half 
 this, is 5 feet 7-f- inches, consequently the centre of 
 pressure in this propeller is 5 feet Y-f- inches from the 
 centre of shaft. 
 
 The centre of pressure can also be ascertained in 
 the following manner : 
 
 1 + 4 + 9 +16+25+36+49+64 o 04 
 
 I 1 1 1- 1 - -I i = = 5 feet 8- 
 
 1 +2+3+4+5+6+7+8 
 inches, nearly as before. 
 
THE SCREW PROPELLER. 123 
 
 The line per sketch represents the radius of the 
 propeller, and i$ divided into divisions of 1 foot each ; 
 the more numerous, of course, the divisions are made, 
 the nearer correct will be the result. 
 
 In these calculations, the area of the hub is 
 neglected. 
 
 The above rule holds good so long as there is no 
 variation in the pitch from hub to periphery ; but 
 should the pitch vary in this direction, the velocity of 
 the column of water driven aft from different parts of 
 the blade will also vary, effecting the centre of pres- 
 sure correspondingly. 
 
 Slip. The slip of a screw propeller is the differ- 
 ence between the velocity of the propeller and the 
 velocity of the ship. 
 
 EXAMPLE. A propeller having 20 feet pitch makes 
 70 revolutions per minute, which propels the vessel at 
 the rate of 12 knots an hour, required the slip, the sea 
 knot containing 6082-J feet? 
 
 ANSWER. 
 
 20 X 70 X 6084000 speed of propeller in ft. per hour. 
 6082| X 12=72992= " vessel " " 
 11008= slip in feet. 
 
 84000 : 11008 : : 100 : 13.1 = slip in per cent, of 
 the speed of the propeller. 
 
 Thrust. A propeller being put in revolution throws 
 a column of water off from the blades in line with the 
 axis of the propeller, which, as explained above, is the 
 slip ; the resistance of this water acting upon the pro- 
 peller blades, tends to force the shaft inboard, which 
 
124 THE SCREW PROPELLER. 
 
 resistance has to be sustained by heavy bearings called 
 thrust bearings, and the amount of this resisting pres- 
 sure is called the thrust. In order, in practice, to as- 
 certain the extent of the thrust, an instrument called 
 the dynamometer is attached to some part of the shaft. 
 This instrument consists of a combination of levers or 
 weighing beams, to the final end of which is attached 
 a spring balance, or scale, which indicates the pressure 
 in pounds ; and this pressure being augmented by the 
 number of times the levers are multiplied, gives the 
 total pressure, or thrust on the shaft. And the total 
 thrust being multiplied into the distance moved over 
 in a unit of time by the vessel, shows the actual power 
 absorbed in propelling the vessel. 
 
 In the application of the dynamometer, care must 
 be taken that it receives the entire thrust of the shaft 
 before the indication of the scale is noted. 
 
 Did the propeller and steam piston travel through 
 the same distance in any given time, and were all the 
 power applied to the piston transmitted to the water 
 through the propeller, the total pressure upon the 
 steam piston and the thrust of the propeller would be 
 identical, but since such is never the case, we ascertain 
 the theoretical thrust, thus : 
 
 Total effective pressure on piston in Ibs. x 2 length of stroke in ft. x No. of revols. per min. 
 Pitch of propeller in feet x number of revolutions per minute. 
 
 = Theoretical thrust in Ibs. The difference between 
 this and the actual thrust, shows the amount lost in 
 friction of engines, propeller, and load, overcoming 
 resistance to edge of propeller blades, working pumps, 
 etc. The loss from slip is independent of this. 
 
THE SCKEW PROPELLER. 
 
 125 
 
 Strain u/pon a Screw Propeller-blade. 
 
 We can best illustrate this by an example. 
 
 Given, circumference of centre of pressure of a 3 
 bladed propeller, 30.9 feet ; distance from hub to cen- 
 tre pressure 41 inches ; pitch 22.5 feet ; thrust 12700 
 pounds : required, the strain upon each blade at the hub. 
 
 SOLUTION. 
 
 Let F G H be the 
 development of the he- 
 lix on a plane, draw B D 
 at right angles to F H, 
 and A E at right angles 
 to G H. Trigonometri 
 cally, we ascertain the c 
 angles at A and D to be 
 each 37 9', and at C and B to be each = 52 5', and 
 the lengths of the lines A E, B D, to be relatively as 
 1.000 to 1.23Y. 
 
 Now, inasmuch as the whole thrust can be supposed 
 to be concentrated in the centre of pressure of the blade, 
 and as the 12YOO Ibs. is in a line with the axis, it follows 
 that, if the line A E represents the direction and amount 
 of this thrust, the line B D, at right angles to the pro- 
 peller blade at the centre of pressure, according to the 
 resolution of forces, will represent the resultant of the 
 pressures on the blade, or the total pressure tending 
 to break it. But inasmuch as there are three blades, 
 the pressure will be divided equally among them all ; 
 therefore, each has to sustain but a third of this pres- 
 sure; hence 
 12700 X 1.237 (proportion B D bears to A E) __ 
 
 3 
 Ibs. pressure on each blade at the centre of pressure. 
 
126 THE SCREW PKOPELLEK. 
 
 The pressure at the hub on each blade equals 
 5236 Ibs. X 41 ins. 214676 Ibs. acting with the 
 leverage of one inch. 
 
 EXAMPLE 2D. Suppose, in example 1, the breadth 
 of the blades at the hub to be 32 inches, and the pro- 
 peller to be made of composition, capable of sustaining 
 a pressure per square inch of cross-section of 520 Ibs., 
 acting through the leverage of 1 inch ; required, the 
 mean thickness of the blade at the hub ? 
 
 SOLUTION. The strength of beams is directly as 
 their breadths and the squares of their depths, and in- 
 versely as their lengths. In the example before us, 
 the propeller resolves itself into a simple beam ; we 
 
 214676 x 1 -,, 
 
 nave, then, =12.9 inches = square of the 
 
 o2i X o^O 
 
 thickness, and v/12.9 = 3.59 inches in thickness. 
 
 Helicoidal Area. As has already been shown, the 
 development of the helix on a plane is the hypothe- 
 nuse of a right-angled triangle, having the pitch of the 
 screw for the height; and the circumference, corre- 
 sponding to the radii of the helix, for the base. Now, 
 as the propeller can be supposed to have an infinite 
 number of helices, each one becoming longer and longer 
 as we approach the periphery, which alter the lengths 
 at the same time, of the hypothenuse and base of the 
 triangle, we will suppose the propeller to be divided 
 into a number of concentric rings, taking the centre 
 line of each, for the helix or hypothenuse of the trian- 
 gle ; the circumference corresponding to radii of said 
 helix for the base, and the pitch for the height, from 
 which we have all the elements required for the cal- 
 culation. 
 
THE SCREW PROPELLER. 
 
 127 
 
 To make this the more clear, take the triangle 
 BAG; the lines B 1, B 2, B 3, B C, represent the 
 
 helices having the corresponding circumferences of 
 A 1, A 2, A3, and A C. Now, then, if these helices 
 be the lengths of the rings, or elements for one entire 
 convolution of the thread, all we have to do is to mul- 
 tiply it by the breadth of the element, which will give 
 the area for one convolution ; but as only a fraction 
 of a convolution is used in practice, we multiply by 
 this fraction, whatever it may be, and the product 
 gives the area for the part used. This mode of calcu- 
 lation is, of course, only an approximation ; but when- 
 ever the blade is divided into a considerable number 
 of elements, say 6 inches in breadth each, the result 
 obtains sufficiently near the truth for all practical pur- 
 poses. 
 
 The following is a calculation on the screw of the 
 U. S. Steam Frigate "Wabash," and which agrees, 
 within a very small fraction, of the area as projected 
 upon a plane : 
 
128 
 
 THE SCREW PROPELLER. 
 
 Diameter of screw, IT feet 4 inches ; diameter of 
 hub, 2 feet 4 inches. 
 
 
 1 
 
 If* 
 
 A 
 
 | 
 
 4 
 
 i 
 
 i 
 
 
 
 fjTJ .2 
 
 o>2 2 *> 
 
 "S OB 
 
 *o S 
 
 *O OD 
 
 to 
 
 Pitch. 
 
 * 
 
 ^ S o c 
 
 111! 
 
 fl 
 
 ill 
 
 II 
 
 i s 
 
 II 
 
 
 i 
 
 eP 
 
 |t 
 
 
 
 *l 
 
 1 
 
 A 
 
 o 
 
 A 
 
 B 
 
 c 
 
 D 
 
 E 
 
 F 
 
 G 
 
 H 
 
 
 
 2.B x 3.1416 
 
 VAM-C 3 
 
 
 DxE 
 
 
 FxG 
 
 ft. 
 
 ft. 
 
 ft. 
 
 ft. 
 
 
 ft. 
 
 ft. 
 
 sqr. feet. 
 
 23 
 
 1.5 
 
 9.42 
 
 24.89 
 
 h 
 
 7.11 
 
 .5 
 
 3.555 
 
 it 
 
 2. 
 
 12.56 
 
 26.20 
 
 
 7.48 
 
 u 
 
 3.74 
 
 " 
 
 2.5 
 
 15.70 
 
 27.85 
 
 ji 
 
 7.96 
 
 u 
 
 3.98 
 
 " 
 
 3. 
 
 18.84 
 
 29.73 
 
 
 
 8.49 
 
 C( 
 
 4.245 
 
 
 3.5 
 
 21.99 
 
 31.82 
 
 1 
 
 9.09 
 
 u 
 
 4.545 
 
 
 4. 
 
 25.13 
 
 34.07 
 
 1 
 
 9.73 
 
 (( 
 
 4.865 
 
 
 4.5 
 
 28.27 
 
 36.44 
 
 I 
 
 10.41 
 
 II 
 
 5.205 
 
 
 5. 
 
 31.41 
 
 38.93 
 
 1 
 
 11.12 
 
 ( 
 
 5.56 
 
 
 5.5 
 
 34.55 
 
 41.50 
 
 1 
 
 11.86 
 
 u 
 
 5.93 
 
 
 6. 
 
 37.69 
 
 44.15 
 
 /61 
 
 12.12 
 
 II 
 
 6.06 
 
 
 6.5 
 
 40.84 
 
 46.87 
 
 ' 
 
 12.86 
 
 II 
 
 6.43 
 
 
 7. 
 
 43.98 
 
 49.63 
 
 
 13.54 
 
 u 
 
 6.77 
 
 
 7.5 
 
 47.12 
 
 52.43 
 
 v 11 
 
 13.78 
 
 
 
 6.89 
 
 
 8. 
 
 50.27 
 
 55.27 
 
 V 4 6 
 
 13.82 
 
 u 
 
 6.91 
 
 
 8.5 
 
 53.40 
 
 58.14 
 
 V. 
 
 11.63 
 
 
 5.815 
 
 * Helicoidal area of one side of both blades 80.5 square feet. 
 
 Practical Remarks on the Screw Propeller. 
 
 In the application of power to the propulsion of 
 the hulls of vessels through water, a portion of the 
 effect is lost by the instrument through which it is 
 transmitted. In the common radial wheel this loss of 
 effect is compounded of two losses, slip, plus oblique 
 action ; in the feathering wheel, slip, plus drag, and in 
 the screw propeller, slip, plus friction of the propeller 
 blades on the water. That instrument, therefore, which, 
 possessing no more practical disadvantages than other 
 
 * For the calculations of the friction of a screw surface on the water, see 
 Isherwood's calculation on the " San Jacinto," (Journal of the Franklin Insti- 
 tute, Third Series, Vol. XXL, p. 349,) or on the " Arrogant," (Appleton's Me- 
 chanics 1 Magazine, Vol. I., p. 156,) from which the form for the above table is 
 
 taken. 
 
THE SCREW PROPELLER. 129 
 
 instruments, and which has the sum of its losses the 
 least, must be the most economical propelling instru- 
 ment. The feathering wheel, from what we have 
 seen, would present itself very conspicuously to our 
 eye as being the best instrument within our knowledge ; 
 but, unfortunately, the practical difficulties are such as 
 to preclude its universal adoption. The loss from ob- 
 lique action in the common radial wheel, particularly 
 where the diameter is comparatively small and the dip 
 of the paddles considerable, amounts to an important 
 percentage of the total power of the engines; and 
 since this loss in the screw propeller does not exist, but 
 is replaced by one of much smaller magnitude, viz., 
 friction of the blades, it follows, that were the slip of 
 the two instruments alike, the screw propeller would 
 be the more economical. In practice, however, with 
 the screw propeller, when contending against head 
 winds, or other increased resistance, the slip is increased 
 to a very serious extent. In fact, in some cases it has 
 occurred, when the engines were going ahead at nearly 
 full speed, the vessel stood nearly still. On the other 
 hand, however, when the sails are set to a fair wind, 
 the slip of the propeller is materially reduced, while 
 the thrust remains unaltered. The increased slip 
 when contending with head winds is also experienced 
 with paddle wheels, but they are not affected to the 
 same extent as the propeller, the increasing or decreas- 
 ing the resistance with the latter instrument, not 
 making a vast difference in the revolutions of the en- 
 gines (as is the case with the paddle wheel) so long as 
 the pressure on the piston remains unaltered. 
 
 In the application of the sere w propeller, it is well 
 to sink it as low as possible in the water, in order that 
 the hydrostatic pressure above may be sufficient to 
 
130 THE SCREW PROPELLER. 
 
 cause the water to flow in solid, even to the centre of 
 the propeller, which, therefore, having the proper 
 resisting medium, is less liable to excessive slip. This 
 will also prevent the centrifugal action the throwing 
 of the water off radially from the centre which exists 
 to a small extent in some very aggravated cases. 
 
 Increasing the helicoidal surface of the screw be- 
 yond what is barely sufficient to transmit the power 
 given to it, has no other effect than to occasion an 
 increased loss by friction, by the increased surface in- 
 terposed. The friction of solids on fluids, unlike solids 
 on solids, depending upon the extent of rubbing sur- 
 face as one of the elements. The object, therefore, to 
 be sought after in practice, is to make the sum of the 
 loss by slip, plus friction, as little as possible, and this 
 sum, manifestly, must depend, to a considerable extent, 
 on the amount of helicoidal surface ; but, nevertheless, 
 there appears to be no general rules yet devised, from 
 theory or practice, which can be used as a reliable 
 guide ; different engineers making considerable differ- 
 ence in the areas of propellers applied to the propulsion 
 of the same sized and modeled steamers. 
 
 Negative Slip. It would certainly appear a very 
 strange anomaly, were one on board a vessel, which he 
 should discover from the indications of the log was mov- 
 ing actually faster through the water than the screw, 
 there being no other propelling instrument ; yet such 
 has been apparently the case, and there are, perhaps, to 
 this day, persons though we hope they are very 
 few who think that a screw propeller may drive a 
 vessel faster than it is moving itself. There have been 
 cases, it is true, where the log has shown that the ves- 
 sel was apparently moving faster than the screw, which 
 
THE SCREW PEOPELLER. 131 
 
 alone was the propelling instrument, but that such a 
 thing could be true is absolutely absurd, and hence 
 attention was turned to discovering the anomaly. It 
 is accounted for in two ways. 
 
 When a body having a blunt stern is drawn through 
 water at a high velocity, the water, not being able to 
 flow in from the sides of the body sufficiently rapid to 
 fill the vacuity occasioned by its passage, flows in from 
 all other directions, and a column of water, therefore, 
 necessarily, follows in the wake of such a body. This 
 is the case with screw propeller vessels having blunt 
 runs, and, by consequence, the propeller, instead of 
 acting upon water at rest, acts upon water in motion, 
 having the same direction as the vessel. Now, then, 
 supposing a propeller, acting upon water at rest, to 
 have a slip of 10 per cent., if a column of water follow 
 the ship with the velocity of 11 per cent, of the speed 
 of the propeller, which still retains its ten per cent, 
 slip, the log, as it takes no cognizance of the velocity 
 of this water, would show a negative slip of 1 per cent., 
 i. e., it would show the vessel to be actually moving 1 
 per cent, faster than the propeller, when in reality the 
 latter would be moving 10 per cent, the faster. 
 
 To produce such a result as this, of course, possesses 
 no mechanical or other advantage ; for power must 
 have been originally taken from the engines to pro- 
 duce the current, which cannot be returned to its full 
 extent. It is, therefore, a Very important element in 
 the design of a screw vessel to make the run very 
 sharp the lines fine in order that the water may 
 flow in solid at once, to fill the vacuity occasioned by 
 the vessel's progress, or the propeller's revolutions. 
 
 The other theory in regard to negative slip is this : 
 All known bodies yield to pressure, it being only 
 
132 ALTERING THE PITCH. 
 
 necessary in order to cause the amount of yield to be 
 measurable to make the pressure sufficiently great. 
 It is hence conceived, that when a screw propeller is 
 in motion, the pressure of the water on the blades causes 
 them to spring, thereby increasing the pitch; conse- 
 quently, in calculating its speed through the water, if 
 we use the true pitch, instead of the pitch assumed, 
 while it is in niotioD, the velocity given to it will be 
 too small, and may be less than the velocity of the 
 vessel. 
 
 We would, however, remark, that negative slip in 
 a screw propeller, unassisted by sails, is more imaginary 
 than real, and could only exist under very aggravated 
 circumstances, for a screw propeller usually has about 
 20 per cent, slip, at least, and to reduce this to nothing, 
 even under the conditions set forth above, would be 
 rather a perversion of circumstances. 
 
 Altering the Pitch. 
 
 Propellers are sometimes constructed in such a 
 manner that the pitch can be altered, from time to 
 time, by altering the angle of the blades, which are 
 made adjustable in a large spherical hub. Thus, if it 
 be desired to increase the pitch, increase the angles by 
 turning round the blades ; or if it be desired to de- 
 crease the pitch, reverse the operation. Such an ar- 
 rangement, however, in practice, must be confined 
 within very narrow limits, for, inasmuch as the surface 
 of a screw propeller blade, being that of a helicoid, 
 every point in the blade must have a different angle, 
 which increases as the hub is approached, and if the 
 propeller be constructed so that all the angles be 
 adapted to one particular pitch, it is not very likely 
 
PARALLEL MOTION. 133 
 
 that they will, after being distorted, be adapted to any 
 other pitch ; that is to say, if the propeller be a true 
 screw, for instance, and have a certain angle at the 
 periphery, if we move the blade so as to increase the 
 angle at that point 10, the angle at, every other point 
 in the blade will also be increased 10, which should 
 not be the case, but should be correspondingly less as 
 the hub is approached; thus, by this arrangement, we 
 give a greater pitch at the hub than there is at the 
 periphery ; and if the operation be reversed, and we 
 decrease the angle at the periphery, the angle at the 
 hub, and every other point in the blade, is decreased 
 to precisely the same extent, thus giving less pitch at 
 the hub than there is at the periphery, or any other 
 point in the blade. We therefore arrive at this con- 
 clusion : 
 
 That having three conditions presented to us, viz., 
 true screw, expanding screw, from periphery to hub, 
 and expanding from hub to periphery the latter two 
 not in regular ratio it is more than probable that 
 one or the other of these must be found practically to 
 be the superior, and whichever it may be, and that 
 one adopted, the advantage to be derived from alter- 
 ing it, after it is once adopted, does not appear very 
 plain, the arguments to the contrary notwithstanding. 
 
 Parallel Motion. 
 
 Parallel motion is a combination of bars and rods, 
 having for its object the guiding of the piston-rod of a 
 steam-engine in a constant straight line, or as near a 
 straight line as can be practically attained. It is ap- 
 plicable, in different forms, to any type of engine, but 
 
134 
 
 PARALLEL MOTION. 
 
 its adaptation to the side-lever engine is the more 
 general. 
 
 We have constructed figure 10 with the view of 
 
 FIG. 10. 
 
 illustrating its application to this type of engine, and 
 to clear it, if possible, of the mystery that usually 
 hangs over it in the shape of formulas. A B is half 
 the length of the side lever, vibrating on the centre B ; 
 A C, the side rod attached to the cross-head at C ; 
 G F, the parallel motion side rod ; D F, the parallel 
 bar, and E F, the radius bar vibrating on the centre E. 
 The object to be attained is to make the point C 
 travel vertically in a straight line, or as near so as pos- 
 sible ; and from the construction of the figure, it will 
 be seen that, when the point G moves to the right the 
 point F moves to the left, and vice versa ; hence it is 
 manifest, that there must be some point H, in the rod 
 F G, which will describe very nearly a straight line, 
 and if the lengths G B and E F were equal, that point 
 would be in the centre of F G ; but, since they are of 
 unequal lengths, H must be in such a position that 
 EFxFHrrBGxGH. 
 
PARALLEL MOTION. 135 
 
 Now, then, having secured the point H, draw the 
 line B C through H, which will determine C, the cen- 
 tre of the cross-head ; and the triangles B H G, B C A, 
 being similar, and joined together in such manner that, 
 no matter how much the angles of the one may alter, 
 the angles of the other must alter to precisely the 
 same extent ; and hence, these triangles always remain- 
 ing similar, it follows that if the apex (H) of the one 
 moves in a straight line, the apex (C) of the other 
 must move in a straight line also. 
 
 It matters not where the points D F G may be 
 situated, so long as D does not coincide with C, and 
 the figure A D F G is a parallelogram ; nor does it 
 matter about the respective lengths of the sides of the 
 parallelogram, so long asEFxFH=:BGxGH. 
 
 In practice, it happens sometimes that the parallel 
 motion gets out of adjustment, the piston rod perhaps 
 rubbing hard on one side of the stuffing-box at the top 
 of the stroke, and hard on the opposite side on the 
 bottom of the stroke ; or it may rub hard on the stuff- 
 ing-box at one end of the stroke, and be quite free at 
 the other. Such a result can be brought about in 
 three ways only : either the sides of the parallelogram 
 A D F G have got out of parallelism, the radius bar 
 E F, of incorrect length from the wear of the brasses, 
 <fec., or the centre E has by some means been moved 
 from its true position. 
 
 These can be all remedied by interposing liners 
 at the proper places ; of course, taking care about 
 the centre A, in order not to endanger striking 
 the cylinder-head, by interposing too much at that 
 point. 
 
136 STRENGTH OF MATERIALS. 
 
 Strength of Materials. 
 
 This is a subject which does not properly come 
 within the province of the present Notes; but we 
 have, however, thought it well to devote a short space 
 to it at this place, confining ourselves to a few practi- 
 cal examples. 
 
 Seams. The strength of beams are to each other 
 directly as their breadths and square of their depths, 
 and inversely as their lengths. 
 
 EXAMPLE. The depth of the beam of an engine 
 75 ins. diameter of cylinder, and 7 ft. stroke, at centre 
 is 42 ins., and using this as a standard, required the 
 depth of one for an engine of 80 ins. diameter of cyl- 
 inder, and 8 ft. stroke, the breadth, and also the maxi- 
 mum pressure on the steam piston to remain the same ? 
 
 ANSWER. 75 2 X 7 : 80 2 X 8 : : 42 2 : 2293.76 ins. ^ 
 square of the depth ; the square root of which, 47.9 
 ins., is the depth required. 
 
 These figures, of course, do not apply to the truss, 
 but to the solid parabolic beam. 
 
 Shafts. The strength of shafts to resist a trans- 
 v^rse, or torsional strain, are to each other as the 
 s-sq^Wea^pf their diameters ; for the reason that, if the 
 diameter of a shaft be doubled, the quantity of metal is 
 increased fourfold, which would occasion the strength 
 to increase as the square, but at the same time there 
 being double the leverage interposed in consequence 
 of the double diameter, which, being multiplied . by 
 the square (or 4), will give the cube (or 8). 
 
STRENGTH OF MATERIALS. 137 
 
 EXAMPLE. The shaft of a steamer is 17 inches 
 diameter; cylinder, 75 inches diameter; by 7 feet 
 stroke ; required the diameter of a shaft for a steamer, 
 having an engine of 80 inches diameter of cylinder, by 
 8 ft. stroke, taking the shaft here given as the standard, 
 the maximum pressure on both steam pistons to be 
 alike. 
 
 ANSWER. 75 2 x 7 : 80 2 X 8 : : 17 3 : 6388.459, the 
 cube of the diameter, the cube root of which, 18.55 
 inches, is the required diameter of the shaft. 
 
 This is about the diameter of the shafts used in 
 practice for two engines of 80 inches diameter of cyl- 
 inder, and 8 feet stroke each. The proportion in prac- 
 tice for a shaft for a single engine of this size, is about 
 15.5 ins. diameter, which is a little more than half the 
 strength of the above shaft, owing to the weight of the 
 wheels, &c., (which have also to be sustained by the 
 shaft) being more than half. 
 
 Screw Propeller Shaft. The strain on the shaft of 
 a screw propeller is of two kinds one in line with the 
 axis tending to compress, the other at right angles to 
 the axis tending to twist it. And, inasmuch as the 
 strength of a shaft to resist compression, is much 
 greater than that to resist torsion, we need only take 
 the latter strain into consideration. 
 
 Hence, to ascertain the diameter of a screw shaft, 
 the dimensions of the propeller and thrust being given, 
 let A B, figure 11, be the pitch, B C, the circumference 
 at centre of pressure, and A C, the helix for one con- 
 volution at centre of pressure. Draw B D at right 
 angles to A C, and D E at right angles to B C ; the 
 lines D E and B E will be proportionally the com- 
 pressional and torsional strains on the shaft : hence, if 
 
138 STRENGTH OF MATERIALS. 
 
 B E be multiplied by the thrust in pounds, and divid- 
 ed by D E, the quotient will be the pressure in Ibs., 
 FIG. IL acting at the centre of pressure 
 
 of the blade to twist the shaft. 
 This pressure being multiplied in- 
 to the leverage of the centre 
 of pressure, and divided by the 
 standard of the metal used, will 
 give the cube of the shaft's diame- 
 ter, the cube root of which will 
 be the diameter. But since the triangles A C B, 
 B D E, are similar, from the construction of the figure, 
 the angles being respectively equal, the sides must be 
 proportional, viz. : A C to B D, A B to B E, and B C 
 to D E. Therefore, having the lengths of the two 
 sides A B, B C, of the triangle ABC, we have 
 
 ~B c x b 
 - 
 
 diameter of shaft in inches, 
 
 in which A B = pitch in feet, 
 
 B C = circumference at centre of pressure in 
 
 feet, 
 
 t = thrust in pounds, 
 b = distance from centre of shaft to centre 
 
 of pressure in feet, 
 
 c = practical coefficient of the metal used 
 for the shaft, per sq. inch of section 
 for a leverage of one foot. 
 
 Paddle Shafts. EXAMPLE 1. Area of the piston 
 3848.4 sq. ins. ; maximum pressure per sq. inch 40 Ibs. ; 
 stroke 10 feet; one engine; required the diameter of 
 the paddle shaft, the practical value of the metal being 
 200 Ibs. per sq. inch of cross-section, with a leverage 
 of 1 foot. 
 
STRENGTH OF MATERIALS. 139 
 
 */ 3848.4 X 40 X 5 ... 
 
 ANSWER. 4- ~ - = 15| ins. diameter. 
 
 EXAMPLE 2. Same as Example 1, excepting there 
 are two engines instead of one, connected at right 
 angles ? 
 
 ANSWER. With two engines connected at 90, the 
 position in which the greatest pressure on the shaft 
 will be interposed will be when both engines are in 
 such a position that a perpendicular, let fall from the 
 centre of the crank upon the centre line passing 
 through the centre of the shaft, will enclose an angle 
 of 45, which, with a 5 feet crank, will give a leverage 
 of 5 x .70711 (nat. sin. of 45) = 3.535 feet; hence, 
 supposing the pressure at this position of the engines 
 to be 40 Ibs. per square inch, we have 
 
 3848.4 X 40 X 3.535 _ . ,. 
 
 X 2 = 17.6 ins. diameter. 
 
 200 
 
 Piston Hods. The piston rod of a reciprocating 
 steam-engine is subject alternately to a tensile and 
 compressing strain ; and there is nothing more absurd 
 than the rules given in books on the steam-engine, de- 
 fining its diameter to be a certain fraction of the diam- 
 eter of the cylinder, independent of all other elements. 
 For instance, suppose a rod of a certain diameter and 
 length to be just able to sustain a certain weight 
 placed upon the top of it, without deflexion; it is ab- 
 surd to suppose that it would sustain the same weight 
 if the rod was made double the length, retaining the 
 same diameter ; yet the rules given for the diameters 
 of piston rods are regardless, not only of their lengths, 
 but also of the pressure of steam. We have, therefore, 
 
140 STRENGTH OF MATERIALS. 
 
 thought it well to copy the following remarks and ta- 
 ble from Johnson's translations of the book of Indus- 
 trial design, by M. Armengaud, the elder, and M. M. 
 Armengaud, the younger: 
 
 " Compression is a force which strives. to crush, or 
 render more dense, the fibres or molecules, of any sub- 
 stance which is submitted to its action. 
 
 " According to Rondelet's experiments, a prism of 
 oak, of such dimensions that its length or height is not 
 greater than seven times the least dimensions of its 
 transverse section, will be crushed by a weight of from 
 385 to 462 kilogrammes to the square centimetre of 
 transverse section, or a weight of from 5470 to 6547 
 per square inch of transverse section. 
 
 " In general, with oak or cast iron, flexure begins 
 to take place in a piece submitted to a crushing force, 
 as soon as the length or height reaches ten times the 
 least dimension of the transverse section. Up to this 
 point the resistance to compression is pretty regular. 
 
 " Wrought iron begins to be compressed under a 
 weight of 4900 kilog. per square centimetre, or of 
 nearly 70000 Ibs. per square inch, and bends pre- 
 viously to crushing, as soon as the length or height of 
 the piece exceeds three times the least dimension of 
 the transverse section."" 
 
 We show, in the following table, to what extent 
 per square inch we may safely load bodies of various 
 substances : 
 
SURFACE CONDENSERS. 
 
 141 
 
 Table of the Weights which Solids such as Columns, Pilas- 
 ters, Supports will Maintain without being Crushed. 
 
 WOODS AND METALS. 
 
 Description of Material, 
 
 Proportion of Length to Least Dimensions. 
 
 Up to 12. 
 
 Above 12. 
 
 Above 24. 
 
 Above 48. 
 
 Above 60. 
 
 Sound Oak 
 
 U. 
 
 426.750 
 '270.275 
 533.437 
 137.982 
 14225.000 
 28450.000 
 11707.175 
 
 Ibs. 
 355.625 
 119.490 
 440.975 
 116.645 
 11877.875 
 23755.750 
 
 Ibs. 
 213.375 
 71.125 
 266.007 
 69.709 
 7112.500 
 14225.000 
 
 Ibs. 
 71.125 
 
 106.687 
 
 2375.575 
 4741.666 
 
 Ibs. 
 35.562 
 
 1994.900 
 2375.575 
 
 
 Pitch Pine 
 
 Common Pine 
 
 Wrought Iron 
 
 Cast Iron 
 
 Rolled Conner.... 
 
 EXAMPLE. What is the least diameter of a piston 
 rod for a cylinder having a cross-section of 3848.4 
 square inches, to sustain with safety a pressure per 
 square inch of piston of 40 Ibs., the proportion of 
 length to be about 24 to 1 ? 
 
 ANSWER. Taking one half the number in the 
 above table for the practical value, we have 
 
 H-i -10 r . = 43.28604 sq. ins. cross section of the rod, 
 
 and/ 48 ' 28604 
 
 .7854 
 
 =7.4 ins. diameter of the rod. 
 
 Surface Condensers. 
 
 A surface condenser is an instrument for condens- 
 ing steam by contact with cold metallic surfaces, in- 
 stead of bringing it directly into contact with a shower 
 of cold water. The object of using such a condenser in 
 lieu of the common jet, is to furnish boilers of marine 
 steamers with distilled instead of sea water, conse- 
 
142 SURFACE CONDENSERS. 
 
 quently to provide against the loss of fuel otherwise 
 occasioned by blowing off a portion of the water, to 
 keep the concentration at a desired point, as shown at 
 pages 66 and 67. Also to prevent the loss due to the 
 little conducting power of the envelope of scale which 
 attaches to all heating surfaces of boilers using sea 
 water. 
 
 By the use of such an instrument there is also 
 gained the saving in labor of scaling and cleaning the 
 boilers, which belongs to all sea steamers using the 
 common jet, and this is of no small importance to 
 those having the care of steam machinery. 
 
 Again, by its use the expense of repairs to the 
 boilers is considerably reduced, their durability greatly 
 increased, the pressure of steam which can be ju- 
 diciously carried is unlimited, and the expansion of the 
 steam can be carried to a greater extent. 
 
 With these many marked advantages, it seems ex- 
 traordinary that the introduction of surface condensers 
 should have met with so little encouragement ; the 
 slow progress made has not been owing to any want 
 of engineering ability, but solely for the want of pat- 
 ronage ; for engineers of talent both here and in 
 Europe have devoted their time to the subject for 
 many years, and have produced many forms, some of 
 which have been so successful as to render, in our 
 opinion, the use of jet condensers absurd. Of the 
 number invented and introduced into practice, the one 
 known as Pirsson's has thus far met with the most 
 favor. It is termed a double vacuum condenser, i. e., 
 it has a vacuum within and without the condensing 
 tubes. The injection water is received upon a scatter- 
 ing plate, and showered down on the tubes, which 
 condenses the steam within them; this injection water 
 
SURFACE CONDENSERS. 143 
 
 with the air and uncondensed vapor is extracted by 
 an air-pump, in the same manner as when the jet con- 
 denser is used, and the water of condensation is drawn 
 away by a separate pump, called the fresh water pump, 
 and discharged into a reservoir, whence it is delivered 
 by the feed-pumps into the boilers. 
 
 Another variety of condenser, known as Sewell's, 
 has recently attracted considerable notice. It has been 
 highly reported upon by a Board of naval engineers 
 appointed by the Hon. Secretary of the Navy, and has 
 been introduced into some of the most successful 
 steamers. It is of the close surface type, that is, it has 
 a vacuum upon only one side of the condensing tubes, 
 the condensation being effected by currents of cold 
 water driven through the tubes by a pump. The joints 
 of the tubes are made with india-rubber sleeves, so that 
 they give perfect tightness, and allow each tube to ex- 
 pand or contract by itself, independent of the others, 
 and each or all of them can be taken out for cleaning 
 or repairs. The vacuum produced by this condenser 
 is unequalled, and as there is but one air-pump, it is 
 obtained with less power than by the other method. 
 
 Close tube surface condensers had been made with 
 the tubes secured at both ends without any provision 
 for expansion or contraction, except the buckling of 
 the tubes when hot, and stretching when cold. They 
 have also been made with one end of the tubes only 
 secured, the other ends being fitted to an expansion 
 plate. The advantages of Mr. Sewell's over the latter 
 named plans are manifest. 
 
 The following figure* will give the student a clearer 
 idea of the construction and operation of Pirsson's 
 condenser. A A, is the condenser, in which there is a 
 
 * Taken from "Steam for the Million''' by Commander WARD, F. S. N. 
 10 
 
144 
 
 SURFACE CONDENSERS. 
 
 series of small tubes : p, the air-pump ; /, fresh water- 
 pump ; b, the exhaust pipe ; I, the injection pipe. The 
 
 operation is as follows : The engine being put in mo- 
 tion, the exhaust steam flows through the exhaust pipe 
 b, into the chambers c c, thence in direction of the ar- 
 rows through the tubes to the lower chamber d, injec- 
 tion water being admitted at the same time from the 
 sea through the injection pipe ?, is showered by the 
 scattering plate m over the tubes, and by its gravity 
 takes the direction of the arrows to the channel way n, 
 from which it is removed by the air-pump />, and de- 
 livered into the hot well q to the delivery pipe r and 
 overboard. 
 
 The water resulting from condensation is drawn 
 by the fresh water pump/ from the chamber d, through 
 the pipe e e, and delivered into the fresh water reser- 
 voir g ; from this reservoir it passes to the feed pump 
 i, through the pipe A, and is delivered into the boilers 
 through the pipe &. The pipe s is for the purpose of 
 supplying salt water when deficiencies occur. 
 
 In this condenser, as drawn, all the tubes are firmly 
 secured to both tube heads, but one end of the tube 
 box is free, so that all the tubes can expand and con- 
 
CYLINDRICAL BOILERS. 145 
 
 tract together ; those recently constructed have each 
 tube secured to the tube head at one head only, the 
 other ends being fitted so that they just pass through 
 the holes, thus allowing each tube to expand or con- 
 tract regardless of the others. There is also a com- 
 munication from the exterior to the interior side of the 
 tubes, so that the vacuum within created by the fresh 
 water pump is equal to that without, created by the 
 large air-pump. In close tube surface condensers, the 
 position of the steam and water, as shown in the figure, 
 is reversed. The exhaust steam is received on the ex- 
 terior of the tubes as at Z, and is condensed by water 
 entering at c' c, and driven through thetubes by a cir- 
 culating pump, attached at b ; it is then discharged 
 through a pipe from d. The pump p is converted into 
 a fresfi water air-pump, receiving the fresh water 
 through the channel-way n and foot- valve <9, and dis- 
 charging it into the reservoir q, whence it is received 
 by the |eed-pump and pumped into the boilers. 
 
 Cylindrical Boilers. 
 
 The force tending to rupture a cylinder 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 diameter x 
 pressure per unit of surface X 
 length of boiler, neglecting any 
 support derivable from the heads,, 
 which, in practice, depends on 
 the length. The shorter the 
 tube, the greater its powers of resistance. This is in 
 
146 CYLINDRICAL BOILERS. 
 
 consequence of the ends being rigid and unyielding.-^ 
 See latest experiments on this subject by William Fair 
 bairn, Esq., C. E., F. R. S. 
 
 The force tending to rupture a boiler is termed, by 
 Professor Johnson, the divellant force, and the tenacity 
 or strength of the metal which resists the divellant 
 force is termed the quiescent force. When rupture is 
 about to take place, these two forces must be exactly 
 equal. 
 
 EXAMPLE. What pressure will a cylinder boiler, 
 12 ins. diameter, and i in thickness of metal, sustain 
 per square inch, the iron to be of the best English 
 iron? 
 
 The experiments of the Franklin Institute give for 
 the strength of single riveted seams, 56 per cent, of 
 the sheet, and assuming the tensile strength of the best 
 English iron to be 60,000 Ibs. per square inch of sec- 
 tion, we have 
 
 12 (diameter) x 4 (length of band to make 1 eq. in. area of cross section) =70 lb8 ' per 8q< in> 
 
 But as the opposite side of the boiler will support an 
 equal amount, the true pressure will be double this, or 
 1400 Ibs. per square inch, one-fourth of which only 
 (350 Ibs.) would be safe to subject it to in practice. 
 
 From this we see that the bursting pressure of a 
 boiler of the dimensions above given, in a transverse 
 direction, is 1400 Ibs. per square inch. We will now 
 see what force this 1400 Ibs. exerts to tear the boiler 
 asunder in a longitudinal direction. To do this, we 
 have only to multiply the area of the head by the 
 pressure per square inch, and divide by J the circum- 
 ference, (since the iron is J inch thick,) which will 
 give the strain upon each square inch of sectional area. 
 
CYLINDRICAL BOILERS. 14:7 
 
 113.09 X 1400 . , 
 
 Thus ^- - = 1 6800 IDS. per square men 
 
 oT.uy r~ 4 
 
 of sectional area, in a longitudinal direction, and 
 
 1400 X 12 X 4 
 
 = 33600 Ibs. per square inch of sec- 
 tional area in a transverse direction. 
 
 The 4 in the latter case is the length of the band 
 to give one inch square of sectional area, and we divide 
 by 2 because there are two sides of the boiler to sup- 
 port the pressure. 
 
 From these figures, it is observed that the strain 
 upon a cylindrical boiler, or other cylindrical vessels, 
 subject to internal pressure, transversely, is exactly 
 double what it is longitudinally. In cast iron, or other 
 cast metal cylindrical vessels, this is made amends for, 
 in a certain degree, by casting ribs, or bands, around 
 the external surface ; but with boilers there appears to 
 have been no attempt to increase the strength by riv- 
 eting bands at intervals on the outer surface, though 
 we see no good reason why such a thing could not be 
 done very advantageously. 
 
 We remark, from what has appeared, that the 
 strain upon cylindrical boilers increases transversely 
 directly as the diameters, and longitudinally as the 
 squares of the diameters because the areas of the 
 heads increase in that ratio but the circumferences 
 increase also as the diameters ; and hence, though we 
 obtain four times the pressure longitudinally by doub- 
 ling the diameter, we have double the metal in the 
 circumference of the boiler to sustain it, and, therefore, 
 the strain upon a unit of metal, in this direction, in- 
 creases also as the diameter. Hence, no matter what 
 may be the diameter of a boiler, the transverse pres- 
 sure tending to tear it asunder, will always be double 
 the longitudinal pressure. 
 
BOILER EXPLOSIONS. 
 
 Boiler Explosions. 
 
 There is only one grand direct cause of boiler ex- 
 plosions, and that is the incapacity of the metal, at the 
 time, to sustain the pressure to which it is subjected. 
 This can be brought about in several ways ; defective 
 material of which the boiler is constructed, defective 
 construction, all parts of the boiler being incapable of 
 sustaining the same pressure, gradual accumulated pres- 
 sure without the means of escape, sudden accumulated 
 pressure occasioned by pumping water on red-hot sheets, 
 collapse occasioned by a vacuum in the boiler, the re- 
 verse valve being inoperative ; collapse of flue occa- 
 sioned by internal pressure in the boiler and a partial 
 vacuum in the flue ; overheating the plates, brought 
 about by the accumulation of large quantities of scale 
 upon them, thereby reducing their tenacity. 
 
 Boilers having been previously tested by hydros- 
 tatic pressure considerably beyond the limit to which 
 it is intended ever to allow the steam to reach, and 
 each and every boiler being fitted with steam and wa- 
 ter-gauges, proper sized safety-valves and such like in- 
 struments, there is never any good excuse, under any 
 circumstances, for the cause of boiler explosions. In- 
 competency or recklessness must be somewhere mani- 
 fest, for the engineer, knowing the pressure which his 
 boiler will with safety bear, should under no circum- 
 stances allow it to exceed that pressure. We would T 
 however, observe here, that we have noticed in many 
 cases, both ashore and afloat where there are a number 
 of boilers connected together, instead of having a 
 steam gauge attached to each one separately, there was 
 but one gauge to the whole number ; and hence, if one 
 or more boilers be shut off from the others, there would 
 
BOILER EXPLOSIONS. 149 
 
 be no means of ascertaining the pressure within them ; 
 and it is a very common thing with land boilers and 
 boilers of small river boats to have no steam-gauge 
 whatever. In such cases as these the owners take 
 upon themselves the responsibility, which would other- 
 wise be attached to the engineer, of any disastrous 
 result. 
 
 The legislation in regard to the inspection of steam- 
 boilers is hardly adequate to the cause ; for though the 
 testing the strengths of boilers, from time to time, is 
 very good as far as it goes, it falls short of what the 
 seriousness of the case demands. The same amount of 
 strict, unbiased inspection on the parties who have 
 charge of the very powerful, yet governable element 
 of steam, would be followed by far more beneficial 
 results. Place only those in charge or the steam- 
 engine, boilers, and dependencies, who are competent 
 to the task ; prevent owners from employing any one 
 simply because his services can be secured for a small 
 compensation, and then you touch the subject in a vital 
 point. It is too prevalent an opinion, that any one 
 who can stop and start an engine, have the fires started 
 and hauled, is an engineer, regardless of his knowledge 
 of the element of which he has charge. 
 
 It is true, however, that the system of rivalry and 
 competition, carried on by steamboat owners and others 
 using steam power, is such as to prevent any one inde- 
 pendently from paying a very high rate of compensa- 
 tion; but if all were compelled to employ equally 
 competent services, no difficulty could be experienced 
 on this head. 
 
150 HOUSE POWER. 
 
 Hoi*se Power. 
 
 The standard for a horse power in England and the 
 United States is pretty generally established at 33000 
 Ibs. raised one foot high in a minute ; but in France a 
 horse power is estimated at 75 kilogrammetres, which is 
 75 kilogranimiBBs raised one metre high per second, 
 equal to 32554.7 Ibs. avoirdupois, raised one foot high 
 per minute. To ascertain the horse power of a steam 
 engine, multiply the mean unbalanced pressure per 
 square inch on the piston, by the a/i*ea of the piston in 
 square inches, by the length of the stroke in feet, and 
 by the number of strokes in a minute; and divide by 
 33,000, the quotient will be the Iwrse power. 
 
 From this figure, in order to ascertain the actual 
 power utilized in propelling the vessel, a deduction has 
 to be made for working the air and feed pumps with 
 their load, friction of working journals, friction of load 
 on working journals, amounting in all to about 20 per 
 cent, of the total power, leaving 80 per cent, to be ap- 
 plied to the propelling instrument, which 80 per cent, 
 has to be reduced by the amount of loss which obtains 
 in the propelling instrument. 
 
 EXAMPLE. Required the horse power of a con- 
 densing steam-engine, having a cylinder 70 inches 
 diameter, by 10 feet stroke, making 15 revolutions per 
 minute ; mean pressure of steam throughout the stroke 
 23 Ibs. ; back pressure 3 Ibs. ; and also the actual 
 power utilized in propelling the hull of the vessel, the 
 sum of losses in the propelling instrument being 40 
 per cent, of the power applied to it ? 
 
 ANSWER IST. 
 
 70 2 X. 7854 x(23-3)x 10x15x2 
 
 -33000 --699.7 horse power. 
 
HORSE POWER. 151 
 
 ANSWEK 2D. Considering 20 per cent, of the total 
 power to be expended in working pumps', in friction, 
 <fec., we have 80 per cent/ applied to the propelling 
 instrument, and 40 per cent, of 80 per cent. = 32 per 
 cent, of the total power expended in transmission 
 through the propelling instrument ; wherefore, 80 
 32 = 48 per cent, of the total power applied to pro- 
 pelling the hull of the vessel = 335.856 horses. 
 
 Nominal Horse Power, is a term which expresses 
 neither the actual power, the size of the engine, nor 
 any thing else which is useful ; and though it has be- 
 come almost obsolete among well-informed engineers 
 in this country, our trans-atlantic friends seem yet to 
 cling to it with some tenacity. 
 
 The usual rule for determining it is this : Multiply 
 the square of the diameter of the cylinder in inches, by 
 the cube root of the length of the stroke in feet, and 
 divide by 47 ; the quotient is- the Jiorse power. 
 
 Now, the chief object for establishing a rule for 
 nominal horse power was to create a commercial unit, 
 by which the power of one engine could be compared 
 with that of another engine ; and this rule might meet 
 the wants of the case, did the lengths and breadths of 
 all cylinders bear the same ratio, and did the pressure 
 of steam remain an invariable quantity : but as these 
 elements are constantly varying, it is of no use what- 
 ever ; and further, if they did not vary, the simple 
 square of the diameter would express an unit equally 
 incorrect. In order to show further the utter useless- 
 ness of the term horse power, as expressed above, we 
 will take two engines, each having 70 inches diameter 
 of cylinder, one 10 feet stroke, the other 5 feet stroke, 
 and ascertain the nominal horse power of each. 
 
152 
 
 VIBRATION OF BEAMS. 
 
 J = 224.7 horse, 
 
 70 2 x V 5 
 
 _ =178.2 horses. 
 
 Now, then, if the pressure of steam was the same 
 in these two cylinders, and the pistons moved with 
 the same velocity, it is manifest that the powers must 
 be the same ; yet, according to the rule for nominal 
 horse power, they are made widely different ; and if 
 so much difference is made while the pressure of steam 
 is supposed to remain constant, what must we expect 
 when that element also varies ? 
 
 Vibration of Seams. 
 
 Given, the length, O c, from centre of beam, to a b, 
 line passing through centre of cylinder = 10 feet ; and 
 
 length of stroke =10 feet ; required, the length O A, 
 or O C, of half the beam ? 
 
MARINE ECONOMY. 153 
 
 The line a b bisects the versed sine of the arc, and, 
 supposing one half (c (7) of the versed sine to be = a?, 
 we have (10 + a?) a = (10 - xf + 5 2 
 
 100 + 20# + x* 100 20x + x* + 25 
 20^=25 
 
 Hence, half the length of the beam = (10 + .625) 
 = 10.625 feet. 
 
 Marine Economy. 
 
 A body moving through water with a certain 
 velocity displaces a certain quantity of water in a given 
 time, with a certain velocity ; if the velocity be doubled, 
 the quantity of water displaced will also be doubled, 
 because the body moves double the distance, and each 
 particle of water will, therefore, be displaced with 
 double the velocity ; hence, the resistance to the body 
 will be as 2 x 2, or as the square of the velocity. Thus 
 it appears that, if a ship consumes 500 tons of coal to 
 perform a certain distance, at the rate of 5 miles the 
 hour, to perform the same distance at the rate of 10 
 miles the hour, would require 5 2 : 10 2 : : 500 : 2000 
 tons, or 4 times 500 ; but the quantity of coal required 
 for any one day, at the rate of 10 miles, will not be 4 
 times the quantity required at that rate for 5 miles, 
 but will be 8 times ; for, supposing the speed be in- 
 creased to 10 miles the hour, the same distance will be 
 performed in 5 days ; hence, we have, in the first case, 
 500 tons consumed in 10 days = 50 tons per day, and 
 in the latter case, 2000 tons in 5 days = 400 tons per 
 day, or 8 times 50 tons. Now, then, taking the coal 
 .as the exponent of the power, we see that the power 
 
* - " 
 
 154 MARINE ECONOMY. 
 
 has to increase as 2x2x2, or as the cube of the 
 velocity. Hence the importance, wherever speed is 
 not an object, of running the engines as slow as possi- 
 ble, in order to economize the fuel. 
 
 But whenever there is an adverse current to con- 
 tend with, the most economical speed is half as fast 
 again as the current. That is to say, if the velocity 
 of the current be 4 miles the hour, the velocity of the 
 vessel should be 6 miles. We will endeavor to demon- 
 strate this without the use of mathematical formula. 
 
 Let 1 represent the power required for a speed of 
 one mile per hour, then, inasmuch as the power in- 
 creases as the cube of the velocity, the power required 
 for the speed of 6 miles = 6 3 216, and the ground 
 moved over 4 2 = 2. 
 
 Suppose, now, the velocity of the ship be reduced 
 to 5 miles per hour, the power will be = 5 3 = 125, and 
 the ground moved over =5 4 = 1. 
 
 Suppose, again, the speed to be increased to Y miles 
 per hour, the power will be = Y 3 = 343, and the ground 
 moved over = 7 4 = 3. 
 
 Summing up these figures, we have for a speed of 
 Y miles per hour a power expended of 343, to make 
 good a distance of 3 miles = 114^- per mile; for a 
 speed of 5 miles, a power of 125 to make good 1 mile 
 = 125 per mile; and for a speed of 6 miles, 216, to 
 make good 2 miles =108 per mile. Consequently, 
 the least power is required at the speed of 6 miles, 
 which is half as fast again as the current. 
 
 Had the calculation been made for any fraction of 
 a mile, either above or below 6, the same result would 
 have been obtained. 
 
 These calculations apply alike to head winds, &c., 
 at sea, as well as to a tide-way in a river ; whence it 
 
LOUT TO EXPANSION. 155 
 
 follows that a vessel can be run even too slow for 
 economy, but nevertheless, when having a heavy head 
 sea to contend with, there are other elements besides 
 economy of fuel to be taken into consideration ; the 
 strain upon the vessel and machinery, the plunging 
 and staving in of the light work about the bows and 
 other places, shipping of seas, &c., are matters which 
 also require the judgment of the commanding officer. 
 
 Limit to Expansion. 
 
 Theoretically, supposing a perfect vacuum to ob- 
 tain in the cylinder, there is no limit to expansion ; 
 but, practically, there is. The unbalanced pressure at 
 the end of the stroke should never be less than suffi- 
 cient to overcome the friction of the engine, and ought 
 always to be a little more. 
 
 EXAMPLE. Length of stroke = 8 ft, ; initial pres- 
 sure of steam 30 Ibs. per square inch, inclusive of the 
 atmosphere ; back pressure 4 Ibs. per sq. inch ; friction 
 of engines, &c., = 2 Ibs. per square inch ; required the 
 point where the steam should be cut off to yield all its 
 useful effect ? 
 
 x = the point, 
 4 + 2 = 6 = the pressure at the end, 
 
 x X 30 = 6 X 8 
 30^=48 
 
 x = 1.6 ft. from commencement. 
 
 The Proper Lift for a Valve 
 
 Is equal to the area of the valve divided by the 
 circumference. 
 
156 TEMPERATURE OF CONDENSER. 
 
 And the metal of which they are made is either 
 brass or cast iron ; the latter has the advantage of ex- 
 panding nearer equal with the steam chest. 
 
 Temperature of Condenser. 
 
 EXAMPLE. Water in the boilers, carried at a den- 
 sity of If per saline hydrometer; temperature of the 
 condenser, and water entering the boilers, 105 Fahr. ; 
 vacuum in condenser, 27.82 inches. Compare the eco- 
 nomic performance of the engine, under these circum- 
 stances, with the same engine, carrying the water in 
 the boilers at the same density, but the water in the 
 condenser at 120 Fahr. ; the mean pressure of steam 
 in both cases on the piston being 20 pounds per square 
 inch? 
 
 SOLUTION. Neglecting the difference of power in 
 the two cases required to work the air-pump, taking 
 the boiler pressure at 20 Ibs., and 2 inches of mercury 
 to be equal to 1 Ib. pressure, we proceed thus : 
 
 1184-105)x.75+228.5-105 : 228.5-105 : : 100 : 
 13.23 per cent, loss by blowing off, in the first case. 
 
 1184-120X.75+228.5-120 : 228.5-120 : : 100 : 
 11.96 per cent, loss by blowing off, in the second case. 
 
 20x2 : 2.18 (back pressure) : : 100 : 5.45 per cent, 
 of the effect of the engine lost by back pressure, in the 
 first case. 
 
 20 X 2 : 3.33 (back pressure) : : 100 : 8.325 per cent, 
 of the effect of the engine lost by back pressure, in the 
 second case. 
 
TEMPERATURE OF CONDENSER. 157 
 
 Now, then, letting the fuel represent the power, 
 we observe, in the first case, that only (100 13.23=) 
 86.7? per cent, reaches the engine, of which 5.45 per 
 cent, is lost in back pressure, and 5.45 per cent, of 
 86.77 per cent.=4.73 per cent, of the total effect lost 
 by back pressure, leaving (86.774.73=) 82.04 per 
 cent, to be applied to operating the engine. 
 
 In the second case, (10011.96=) 88.04 per cent. 
 of the power reaches the engine, of which 8.325 per 
 cent, is lost in back pressure, and 8.325 per cent, of 
 88.04 per cent.=7.33 per cent, of the total effect lost 
 by back pressure; leaving (88.04 7.33=) 80.71 per 
 cent, to be applied to operating the engine. 
 
 Therefore, under the conditions of the example, 
 the engine, in the first case, performs the same amount 
 of work with (82.04 80.71=) 1.33 per cent, less fuel. 
 
 This calculation can be made accurate by taking dia- 
 grams from the cylinder and air-pump, under the con- 
 ditions of the example, and estimating the power in 
 each case ; then, the power to work the air-pump is 
 considered. 
 
CHAPTER VI. 
 
 WESTERN RIVER BOAT ENGINE. 
 
 FIG. 1 is a side elevation, and Fig. 2 an end view of 
 the celebrated high-pressure engine, so extensively 
 employed on all the Western rivers, also in many iron- 
 rolling mills, and other manufacturing establishments 
 of the West. 
 
 The first steamboat that ever navigated the great 
 rivers Ohio and Mississippi was called the New Or- 
 leans, built at Pittsburgh, Pa., by Mr. Rosevelt, for 
 Messrs. Fulton &> Livingston, of New York ; launched 
 March, 1811, and made a passage to New Orleans the 
 latter part of the same year. We have no reliable 
 information in regard to the kind of machinery used 
 on board that boat. The type at present employed, 
 however, came into use early in the history of Western 
 river steam navigation. It subsequently underwent 
 several modifications, but for a quarter of a century it 
 has been made essentially as represented by the fol- 
 lowing cuts. In fact, so alike have they been made, 
 for many years, that those engaged in constructing 
 them^make no drawings, but continue from year to 
 year to cast from the same patterns, and make and 
 erect without variation. 
 
 In all the side- wheel boats, the engines are discon- 
 nected, separate, and distinct, so that by revolving the 
 wheels in opposite directions, the boats can be turned 
 on a pivot. 
 
WESTERN RIVER BOAT ENGINE. 
 
 159 
 
 11 
 
 Section through X F. 
 
160 WESTERN RIVER BOAT ENGINE. 
 
 S 
 
 FIG. 9. 
 
 Section through W Z. 
 
 EXPLANATIONS OF DIAGRAMS. 
 
 The piston is represented to be proceeding in the 
 direction indicated by the arrows, both steam valves 
 closed and one exhaust valve open ; the steam is there- 
 fore cut off, and acting expansively. 
 
 Like letters refer to like parts in both views : 
 -4, steam cylinder ; B, steam piston, with metallic 
 packing set out with springs, as recently introduced ; 
 c c, piston follower ; Z>, piston rod ; EE, steam side 
 pipe, to which the steam pipe from boilers is attached ; 
 F F, steam valves ; G, exhaust valve ; H H, valve 
 
WESTERN RIVER BOAT ENGINE. 161 
 
 stems ; II, valve levers ; K K, steam valve lifters ; 
 L L', arms connecting steam rock shaft with exhaust 
 lifters, on opposite side of engine, shown in Fig. 2 ; 
 N N, points of application of weight or pressure to 
 levers ; P P, fulcrums of levers ; R^ steam rock shaft 
 arm, to which cut off cam rod is connected ; T T, pins 
 of rock shaft arms, to which full stroke cam rod is 
 hooked ; S, starting bar. 
 
 The lifters for working the exhaust valves, with 
 arm L cast on, are loose, and vibrate on the steam 
 rock shaft. They are on the opposite side of engine, 
 as shown in Fig. 2. The arms L L are of the same 
 length, being used only to connect the exhaust rock 
 shaft to the exhaust lifters. 
 
 The valves are worked by cams ; the exhaust cam 
 being made for full stroke, and the steam cam to cut 
 off the steam at defined points of the stroke. 
 
 There is a short shifting link to connect the ex- 
 haust rock shaft arm at Twith the steam rock shaft 
 arm J?, so that when it is desired to work the steam 
 full stroke, instead of expansively, it is only necessary 
 to unhook the steam cam rod from the pin on the arm 
 H, and hook on the short link ; thus connecting all 
 the valve levers, and working all the valves by the 
 full stroke cam. To back the engine, the engineer has 
 only to shift the full stroke cam rod from the lower 
 pin T to the upper pin T. The laborious working of 
 the engines by hand is therefore entirely avoided ; and 
 as there is much backing to be done at the different 
 landings, this is of importance. 
 
 The pitman (connecting rod) is of wood strapped 
 with iron, and from 3 to 4 times the length of stroke. 
 
 The valves are of cast iron, sometimes double and 
 
162 WESTERN RIVER BOAT ENGINE. 
 
 balanced, but most frequently single and unbalanced, as 
 represented in the diagrams. In the latter case, con- 
 siderable power is expended in working them against so 
 high a pressure, unless the valve gear be constructed. 
 to reduce the power to a minimum at the point of its 
 application. This, however, is not often done, though 
 it can be so arranged. And, as a matter of exercise 
 for the student's mind, we will give some explanation 
 of it, and of the operation of the valves. 
 
 The gear may be considered a compound lever, or 
 two connected levers, transmitting the power from the 
 cam rod pins through each other to the point of resist- 
 ance, weight, or pressure. The explanation, then, is 
 as follows: Call lever I No. 1, and lifters K K lever 
 No. 2 ; say the length of the long arms of the levers 
 are 64 and 9 inches, and the short arms 16 and 3 
 inches. That is, the distance from fulcrum P of lever 
 No. 1 to the end or point where the lifter first touches 
 it and begins to raise the valve is 64 inches, and the 
 distance from centre of steam rock shaft, which is the 
 fulcrum of lever No. 2, to cam rod pin centre is 9 
 inches ; also that from P to jVJ of lever No. 1, is 16 
 inches, and from centre of steam rock shaft of lever 
 No. 2 to point on lifter where it commences to raise 
 the valve lever is 3 inches. Now, suppose there to be 
 a pressure of 140 Ibs. per square inch in the pipe HIE, 
 consequently on the valves, and that the diameter of 
 the valve is 6 inches, there is hence a pressure on each 
 valve of 6 X 6 X .7854 = 28.274 x 140 = 3958.36 Ibs., 
 which, added to weight of valve and lever, weighed at 
 N, say 40 Ibs. more, 3998.36. This will be reduced 
 at /, end of lever No. 1, to 3998.36 4 = 999.59 Ibs., 
 and at the pin of steam rock shaft arm to 999.59 -f- 3 
 
WESTERN RIVER BOAT ENGINE. 163 
 
 = 333.196 Ibs. required to operate the valves, friction 
 not included. Or the work may be shortened by mul- 
 tiplying all the long arms together, all the short arms 
 together, dividing one by the other, and the weight 
 by this result, thus : 
 
 fvi v Q 
 
 j^| = 12, and 3958.36 + 40. + 12 = 333.196. Ibs. 
 
 To work the engine by hand, this weight can be 
 reduced by the length of starting bar to say 54.97 Ibs. 
 And it can be further reduced by closing the exhaust 
 valves sooner, so as to partially balance the steam 
 valves : for instance, suppose they be closed when the 
 piston is in the position to leave 6 inches between it 
 and the cylinder head ; that there is a clearance of f 
 of an inch, and that the back pressure against the pis- 
 ton is 5 Ibs. per square inch when the valve is closed ; 
 now, according to the law of expansion and compres- 
 sion of gases, when the piston has travelled 3 inches 
 further, or half the distance from point of closing the 
 valve to cylinder head, there will be a pressure against 
 it of 10 Ibs. per square inch, and when it has travelled 
 1 inches further, there will be a pressure of 20 Ibs. 
 per square inch, and when f of an inch further, or at 
 end of stroke, there would be a pressure of 40 Ibs. per 
 square inch for the piston to cushion against, but the 
 valve is not relieved to this extent if it has any lead ; 
 say it is opened 1 \ inches before the piston arrives at 
 the end of its stroke, we then have only 20 Ibs. per 
 square inch pressure under the valve to be deducted 
 from the 140 Ibs. per square inch above it, or a total 
 steam pressure on the valve of 3390.08, instead of 
 3958.36. 
 
 We have been considering the power necessary to 
 
164 WESTERN RIVER BOAT ENGINE. 
 
 work each steam valve separately : we will now con* 
 sider that requisite to operate each exhaust valve. 
 The proportion of levers and gear remaining the same, 
 the steam cut off at half stroke, and the diameter of 
 valve ^ inches this being the ratio considered neces- 
 sary for the free and quick escape of the steam there 
 will consequently be by the reduction of pressure com* 
 mon to expansion, at the time the valve is to be opened, 
 70 Ibs. per square inch on it, or in round numbers 
 1979.18 Ibs. less than on the steam valve. To cut off 
 shorter, this pressure is still further reduced ; to follow 
 longer, it is increased the reduction of pressure and 
 temperature by leakage and condensation in the cylin- 
 der not being considered. 
 
 This type of engine is peculiarly adapted to the 
 boats on which it has been exclusively employed 
 for more than quarter of a century ; and when well 
 constructed, correctly proportioned, and properly man- 
 aged, it performs the work satisfactorily, can be han- 
 dled with facility, is durable, and could be made eco- 
 nomical. But all these elements are seldom found in 
 any of them. The valve gear is generally arranged so 
 that the valves cannot be worked by hand against the 
 full pressure on them ; the steam valves are set with 
 little or no lead, and the exhaust valves do not close 
 until the piston arrives at the end of the stroke, so 
 that there is only a very small cushion against the pis- 
 tons at the end of the cylinders, and the cranks pass 
 the centres against an unbalanced pressure of from 50 
 to 60 Ibs. pressure per square inch. The cams for 
 working the steam valves are usually made to cut off 
 the steam at half, five-eighths, or three-quarters from 
 commencement of stroke ; and the cylinders, steam 
 
WESTERN RIVER BOAT ENGINE. 165 
 
 pipes and drums, upper portions of boilers, etc., are 
 always uncovered (not jacketed) by non-conducting 
 substances, and exposed to the cold winds sweeping 
 between the decks. It will therefore be seen that a 
 large margin is left for improvement in proportions, 
 and more so for saving fuel. The temperature of the 
 steam in boilers, pipes, etc., may be averaged at 360 
 Fahrenheit, and the temperature of the atmosphere 
 during the year at 60 ; hence there is a difference be- 
 tween the temperature of steam within the vessels and 
 the atmosphere outside of BOO ; and considering the 
 unusual large radiating surface exposed to the winds 
 and cold air, the loss from the condensation of steam 
 in cylinders, pipes, etc., cannot be less than 15 per 
 cent, of the fuel consumed. And the saving which 
 could be realized in fuel from a high degree of expan- 
 sion, where the pressure is about 140 Ibs. per square 
 inch, may be estimated by the student from calcula- 
 tions under that head commencing at page 12 of this 
 work. 
 
 The lifter represented in the diagrams was intro- 
 duced not very long ago, and patented by Mr. A. Har- 
 tuper, of Pittsburg, Pa. It is a great improvement 
 over the lifter formerly employed and still used to a 
 great extent. 
 
 The improvement consists in commencing to lift 
 the valve lever close up to the rock shaft, and starting 
 with an easy curve from the horizontal centre line of 
 the rock shaft downward. Its advantage is to be found 
 in a smooth-working valve gear, and reduced power 
 to work the valves consequent on the reduced distance 
 between the fulcrum of lever No. 2 and application of 
 power on lever No. 1 ; that is, between the centre of 
 
166 WESTERN KIVER BOAT ENGINE. 
 
 rock shaft and point where the lifter first touches the 
 lever and begins to raise the valve. The valve once 
 started from its seat, steam rushes under it, and assists 
 its ascent; hence, as the bearing point of the lifter 
 approaches its end, the valve becomes balanced from 
 the steam under it. Furthermore, the shape of the 
 lifter is such as to raise the valve quickly. 
 
 The ordinary lifter begins to raise the valve lever 
 from and near its end, and several inches from the end 
 of lever I, instead of near the fulcrum of lever No. 2 r 
 and at the end of lever No. 1. It will therefore be 
 readily seen that, if this lifter should be substituted 
 for the one represented in the drawing, the power to- 
 work the valves would be greatly increased. As an 
 illustration, suppose the arms TTJTto commence lift- 
 ing 12 inches from centre of rock shaft, and 9 inches 
 from end of lever No. 1 , then there would be a power 
 of 1160.9 Ibs. required at I, and 1546.78 Ibs. at the 
 end of arm JR. 
 
 In addition to this increased power to work the 
 valves, the sudden striking of the valve levers by the 
 old-fashioned lifters is objectionable, and involves the 
 necessity of putting a leather shoe on the lever to ease 
 the disagreeable noise. 
 
 In explanation of the reduction of power conse- 
 quent upon the combination of levers, the student 
 must bear in mind that what is gained in power is 
 lost in time, the lifters being but a short space of time 
 raising the valves, during the stroke of the engine. 
 
 The kind of lifter represented in the diagram, Fig. 
 1, but with much greater curve downward, is some- 
 times used on land engines, and operated by the eccen- 
 tric to cut off the steam at defined points of the stroke, 
 
WESTERN RIVER BOAT ENGINE. 16? 
 
 in the same manner as tho Stevens cut off; namely, by 
 lost motion, or, in other words, by causing the toes to 
 travel a considerable distance before commencing to 
 raise the valves. 
 
 In order to get a clear understanding of this, the 
 student can refer to the diagram of the Stevens cut off, 
 page 22, and consider the steam-lifting toes B B, in 
 that diagram, in the same light as the valve levers // 
 of Fig. 1 in the above. The principle on which the 
 two kinds of cut offs are operated is precisely alike, 
 the only difference being that one is made adjustable 
 and the other is not. 
 
 Some of the boats plying on the upper rivers have 
 stern wheels, i. e., one paddle wheel applied at and 
 projecting over the stern the whole width of the boat. 
 Many of such of 300 tons burthen draw only from 16 
 to 20 inches of water : lightness of machinery, compat- 
 ible with strength, is therefore of the first importance 
 in such vessels. The boilers of all of them are, as a 
 rule, placed near and fronting the bow ; and as the 
 stern wheel variety involves the necessity of placing 
 the engines near the stern, the steam pipes are as a 
 consequence exceedingly long, not unfrequently from 
 90 to 100 feet or more, thus causing still further loss 
 from condensation of the steam. It is proper, however, 
 to remark, that when coal can be furnished, as it is on 
 the upper rivers, at less than one dollar per ton, econ- 
 omy of fuel is a secondary consideration. It is also 
 proper to state that the owners and operators of the 
 boats are slow to make improvements in their steam 
 machinery, even when the advantages of such can be 
 practically demonstrated. As an instance of this, we 
 may mention that spring cylinder piston packing, so 
 
168 WESTERN RIVER BOAT ENUIXE. 
 
 long successfully applied to the pistons of all types of 
 engines, is now, the year 1862, introduced in the river 
 engines for the first time. 
 
 It is to be regretted that the Indicator, engine reg- 
 isters, and correct guages have not come into use, and 
 records kept on board of some of the boats, so that 
 correct data for calculating their efficiencies and com- 
 parative economy could be had. If we are not misin- 
 formed, Mr. S. H. Gilman is the only engineer who ever 
 applied the Indicator and made experimental tests for 
 the purpose of getting correct results from the Missis- 
 sippi steamers. Among the few records kept by him, 
 we select for the benefit of those interested that of the 
 " Magnolia," one of the finest and largest steamers ply- 
 ing on the lower Mississippi when the record was taken, 
 namely, in the year 1853, and published immediately 
 afterward in the " Franklin Institute Journal." 
 
 The diagrams taken from the cylinders of that ves- 
 sel showed the valves to have been set without lead, 
 and that the engines passed the centres with the un- 
 balanced pressure of 60 Ibs. per square inch'; the 
 stroke being 10 feet, and the steam following the pis- 
 tons 6 feet before being cut off that is to say, both 
 the steam and exhaust valves opened and shut pre- 
 cisely at the end of the stroke, and that the steam was 
 expanded down to 60 Ibs. pressure above the atmos- 
 phere when the pistons reached the ends of the cylin 
 ders. 
 
WESTERN RIVER BOAT ENGINE. 169 
 
 DIMENSIONS AND PROPORTIONS OP THE MAGNOLIA. 
 
 Length from stem to stern 295 feet. 
 
 Breadth of beam 35 " 
 
 Breadth of floor 28 " 
 
 Depth of hold < . . 9 " 
 
 Draft of water when light 4 " 
 
 Tonnage,' carpenters' measurement . . . .914 tons. 
 
 Diameter of water wheels 40 feet. 
 
 Length of bucket 12 feet 6 in. 
 
 Width of do 2 feet. 
 
 Revolutions per minute up stream . . . , 13.5. 
 
 Diameter of cylinders 30 inches. 
 
 Length of stroke 10 feet. 
 
 Length of connecting rod . . . . . . 35 " 
 
 Point of cutting off steam from commencement . . 6 " 
 
 Number of boilers . 6 
 
 Length of each boiler 30 feet. 
 
 Diameter of each boiler 42 inches. 
 
 Diameter of each flue 16 " 
 
 Grate area 98.4 sq. ft. 
 
 Diameter of each chimney 5 feet. 
 
 Height of chimneys above grates . . . . . 80 " 
 
 Area over each bridge wall 42.7 sq. ft. 
 
 Area of cross section of all flues 16.7 " 
 
 Area of cross section of two chimneys . . . 39.3 u 
 
 Heating surface of all the boilers .... 2617.8 * 
 Proportion of grate to heating surface . . . 1 to 26.4 
 
 Proportion of grate to area bridge wall . . . 1 to 0.47 
 Horse power developed by engines .... 1229 
 
 The fuel consumed was wood : no correct results 
 .as regards evaporation, or coal per horse power per 
 hour, therefore given. 
 
 In conclusion, we would earnestly direct the atten- 
 tion of western engineers to a study of the subjects 
 here presented, especially the Indicator and its use. 
 We have witnessed some very faulty working engines 
 on the Ohio, occasioned principally by the manner of 
 working the steam ; i. &, the valves not being opened 
 and shut at the proper points of the stroke. On this, 
 
170 WESTERN BIVER BOAT KM; INK. 
 
 everything else being in order, depends the regularity 
 of motion and smooth working of the engine. It is true 
 that much may be gained by practical tests ; that is, 
 by giving more or less lead to the steam valves, and 
 by closing the exhaust valves sooner or later to give 
 more or less cushion for the pistons to bring up against, 
 until the engines are found to perform best ; but nothing 
 accurate can be arrived at without the application of 
 the Indicator to every cylinder. It is therefore highly 
 important that every engineer having charge should 
 understand that instrument and its use. The diagrams 
 will at first sight doubtless appear intricate and diffi- 
 cult to comprehend, by many of those considering;, 
 themselves entirely practical; but a little study of 
 chapter 2 of this work, together with a few applica- 
 tions of the instrument, and some perseverance, will 
 soon overcome all difficulties, and result in a clear un- 
 derstanding of the subject, and a high appreciation of 
 its importance. 
 
CHAPTEE VIL 
 
 BOILERS, ETC. 
 
 BOILERS being the source from which the power to 
 actuate steam engines is derived, it becomes of the first 
 importance that not only the best and most improved 
 types be used, but also that the proportions be such as 
 to secure the highest results. 
 
 Since the introduction of steam to sea and river 
 navigation, many varieties of boilers have been de- 
 signed, tried, and abandoned, and many others having 
 but little merit are still in use. As it is not, however, 
 the purpose of these notes to give the history of in- 
 ventions, but to assist in directing the mind of the stu- 
 dent into a channel of reasoning for himself, we will 
 for the present be content with mentioning only a few 
 of those now most generally used ; namely, the Martin 
 water tube, the horizontal fire tube, and the western 
 river boilers. 
 
 In designing a boiler for a steam vessel, there are 
 many elements to be considered ; such as cost, proper 
 materials, strength to bear the intended pressure, quan- 
 tity of steam to be furnished in a given time, space occu- 
 pied, weight, circulation of water, durability, facilities 
 for cleaning and repairing, requisite water and steam 
 room, heating and grate surface, area through flues, 
 and area and height of smoke pipe. 
 
172 
 
 BOILERS, ETC. 
 
 All things being equal^ that boiler producing the 
 largest weight of steam per given weight of combusti- 
 ble is the best boiler ; that is, evaporating the greatest 
 number of pounds of water per pound of fuel. By 
 combustible is meant that portion of the fuel put into 
 the furnaces, minus the ashes, clinker, and refuse re- 
 moved. 
 
 The above drawing represents a side elevation of 
 the water-tube boiler, with the tubes arranged verti- 
 cally above the furnaces, as patented by D. B. Martin, 
 Esq., late Engineer-in-Chief of the U. S. Navy. 
 
 These boilers are almost exclusively employed in 
 the steamers of our navy. 
 
BOILERS, ETC. 173 
 
 EXPLANATION OF THE DRAWING. 
 
 The line r s represents side and bottom of the 
 ship ; o o -s, boiler keelsons, or timbers on which the 
 boiler rests ; a, ash pit ; 0, furnace door ; , grates ; d, 
 furnace ; ra, back connection ; e e, the vertical tubes 
 containing the water within them, and surrounded by 
 the products of combustion tf, arch over furnace ; A, 
 line of water level ; k, steam room ; Z, steam chimney ; 
 g, passage of gases to smoke pipe ; i, water bottom ; n, 
 fire-room. 
 
 These boilers are generally situated in the vessel 
 face to face, and separated by a fire room of 8 or 9 
 feet, in the fore and aft direction. 
 
 The Horizontal Fire Tube, or common marine 
 tubular boiler, has the tubes arranged horizontally 
 above the furnaces, containing the products of combus- 
 tion within, and surrounded with water. In all other 
 respects the two types of boilers can be constructed 
 alike. If, therefore, we imagine all the tubes to be 
 removed from the boiler represented by the drawing> 
 and a set of tubes arranged in it horizontally with the 
 smoke and gases passing through them, we have the 
 common marine tubular boiler so extensively employed 
 in the steamers of all European nations. 
 
 To an inexperienced eye this simple difference of 
 arrangement of tubes would doubtless appear of little 
 or no consequence ; but as simple as it may seem, it 
 nevertheless makes an important difference in the re- 
 sults utilized ; also in many other respects, as will be 
 seen from the extracts given below, from a report of a 
 Board of four Chief Engineers of the Navy, who, by 
 
174 BOILEKS, ETC. 
 
 the directions of the Navy Department, tested the 
 efficiency of the two types of boilers, one of each kind 
 having been constructed and placed on board the U. S. 
 Steamer " San Jacinto " for the purpose, of precisely 
 the same shell, both as regards form and dimensions. 
 The only difference between them was in the arrange- 
 ment of the tubes, one being the English or horizontal 
 fire tube ; the other of the water tube type. This ex- 
 periment may be considered the most important, and 
 certainly the most extensive and accurate ever made 
 with marine boilers. 
 
 EXTRACTS FEOM REPORT. 
 
 The experiments were made to determine the rela- 
 tive evaporative efficiencies of the two boilers, under 
 the conditions of actual practice on board marine 
 steamers. For this purpose, a short experiment would 
 be valueless from the impossibility of knowing whether 
 the condition of the fires were exactly the same at the 
 commencement and at the end, from the inequality in 
 firing ; from the different proportions of refuse found 
 in different weights of coal ; from fluctuations in draft ; 
 from losses by cleaning the fires ; and from the differ- 
 ent quantity of air in proportion to fuel admitted at 
 different times. It was therefore considered necessary 
 that the experiments with each boiler should continue 
 uninterruptedly four days, or 96 hours. 
 
 The weight of water evaporated was ascertained 
 from the steam pressure in the cylinders at the end of 
 the stroke of piston, as given by the indicator. The 
 cost of this evaporation was the weight of combustible 
 
BOILERS, ETC. 175 
 
 consumed. ****** Every pound of coal put 
 into the furnace, and every pound of ashes, clinker, and 
 refuse removed was weighed each hour. The experi- 
 ments were conducted in precisely the same manner 
 with both boilers, and as follows ; namely : At the 
 commencement, no account was taken of the coal re- 
 quired to raise steam, or of the temperature of the 
 water in the boilers ; but after the steam was raised 
 to 22 Ibs. per square inch pressure above the atmos- 
 phere, the level of the water in the boiler was noted, 
 the condition of the fires estimated as nearly as pos- 
 sible by the eye, and the engines started. At the end 
 of each experiment, the water in the boiler and the 
 condition of the fires were left as at the commence- 
 ment. The experiments with both boilers were begun 
 and ended at midday, and continued uninterruptedly 
 96 hours. During that time, the boiler steam pres- 
 sure and the vacuum in the condenser, by barometer 
 gauges, were noted every 5 minutes ; and at the close 
 of each hour there was recorded for that hour the 
 mean steam pressure and vacuum ; the temperature of 
 the engine room, of the fire room, of the salt and fresh 
 water hot wells, and of the injection water ; also the 
 weight of coal thrown into the furnaces, and the 
 weight of dry refuse in ashes, clinkers, and fine coal 
 withdrawn. Every hour an indicator double diagram 
 was taken from both cylinders, and from the mean of 
 the final pressures as given by these diagrams the 
 evaporation was calculated. ****** At the 
 commencement of each experiment, the boiler was filled 
 with sea water ; and at the expiration of every hour 
 the saturation was recorded ; also the number of inches 
 
 12 
 
176 
 
 BOILERS, ETC. 
 
 in depth of water blown off to maintain it at 1 times 
 the natural concentration. 
 
 The number of double strokes made by the pistons 
 were taken by a self-registering counter. 
 
 The same firemen fired both boilers, and the same 
 engineers directed them. The experiments were first 
 made on the Horizontal Fire-Tube Boilers ; they were 
 begun at noon on the 10th of June, 1859 ; and after 
 being completed, the steam was shut off from it and 
 let on from the Vertical Water-Tube Boiler, without 
 stopping the engines. The coal was Pennsylvania an- 
 thracite. 
 
 > 
 
 RESULTS OF THE EXPERIMENTS. 
 
 
 English Horizon- 
 
 Martin's Vertical 
 
 
 tal Fire-Tube 
 
 Water-Tube 
 
 
 Boiler. 
 
 Boiler. 
 
 Total number c* Ib,, 01 coal consumed . 
 
 100436.00 
 
 92512.00 
 
 of refuse ashes, etc. . 
 
 24908.00 
 
 24178.00 
 
 " of combustible consumed 
 
 75528.00 
 
 68334.00 
 
 Per centum of coal in refuse .... 
 
 24.80 
 
 26.14 
 
 Mean gross horses power developed by the engines 
 
 187.25 
 
 201.07 
 
 Mean number of Ibs. of coal consumed per hour 
 
 1046.21 
 
 963.67 
 
 Mean No. of Ibs. of coal consumed per sq.ft. of grate 
 
 9.7 
 
 9.00 
 
 Total No. of Ibs. of water evaporated from feed 
 
 
 
 water of 100 Fah 
 
 .671813455 
 
 .720 6914 
 
 Pounds of water evaporated from feed water tem- 
 perature of 100 Fah. by 1 Ib. of coal . 
 
 6.7 
 
 7.8 
 
 Pounds of water evaporated from feed water of 
 
 
 
 100 Fah. by 1 Ib. of combustible 
 
 8.9 
 
 10.6 
 
 COMPARATIVE ADVANTAGES AND DISADVANTAGES. 
 We are directed by your order to report to the De- 
 partment the relative advantages and disadvantages 
 of the two kinds of boiler as regards space occupied, 
 weight, cost, accessibility for cleaning and repairs, du- 
 rability, evaporative efficiency, and the relative quan- 
 tities of steam that can be furnished in equal times. 
 
 1st : As regards -space. In the particular specimens 
 
BOILERS, ETC. 
 
 experimented on, the space occupied by both types of 
 boiler was equal, but not so the area of contained 
 heating surface. If the proper measure of that surface 
 be, as we think it is, the extent exposed to the recep- 
 tion of heat from the products of combustion, then the 
 heating surface in the vertical water-tube boiler ex- 
 ceeded that in the horizontal fire-tube boiler by nearly 
 23f per centum of the latter. If, however, it be meas- 
 ured by the extent from which water is evaporated, 
 then the superiority will still remain with the vertical 
 water-tube boiler, but reduced to Ty per centum. 
 
 2d : As regards the weight of the tivo Boilers. By 
 referring to the table of their dimensions and weights, 
 it will be seen that in this respect the experimental 
 boilers were nearly equal, the horizontal fire tube hav- 
 ing a slight advantage in lightness ; but if the aggre- 
 gate weight of boiler and contained water at the 
 steaming level be compared, then the vertical water 
 tube has a superiority of nearly 5J per centum over its 
 competitor. 
 
 3d: Cost. In this particular the horizontal fire- 
 tube boiler is slightly the cheapest, but the difference 
 is unimportant. 
 
 4th : Accessibility for cleaning and repairs. For 
 the removal of scale or any insoluble sediment on the 
 water surfaces of the tubes, the vertical water-tube 
 boiler has a decisive superiority from the complete 
 and easy manner in which the entire of those surfaces 
 can be reached by a scaling tool and cleaned mechani- 
 cally. With the horizontal fire-tube boiler this ope- 
 ration is very tedious and difficult, and at the best is 
 only partial. It may indeed be said that the whole 
 of the horizontal tubes cannot be scaled without the 
 
178 BOILERS, ETC. 
 
 removal of a portion of them ; and from the fact of 
 their becoming more and more coated with scale as 
 their age increases, their evaporative efficiency will be 
 continuously impaired to the extent of the loss of heat 
 thus intercepted. On the other hand, the horizontal 
 fire tubes are much more easily and completely swept 
 of soot and deposit from the furnaces ; they are also 
 more easily plugged when leaking. Furthermore, they 
 are only about one fourth the number of the vertical 
 water tubes, and the liability to leakage is correspond- 
 ingly lessened, but this liability is so trifling as to be 
 of no value in a practical estimate. The remaining 
 portions of both boilers are equally accessible for clean- 
 ing and repairs. 
 
 5th : Durability. We have no data on which to 
 base an opinion in this respect, but we believe both 
 boilers to be about equal. 
 
 6th : Evaporative Efficiency. The relative evapo- 
 rative efficiency, as given by the experiments, applies 
 rigorously only to the particular specimens of the types 
 of boiler employed, with their peculiarities of propor- 
 tion and under the conditions of the trials ; under other 
 conditions and with other proportions, the relative 
 evaporative efficiency would doubtless be different, 
 and in direction as determined by better or worse pro- 
 portions, and by conditions more or less favorable for 
 one kind of boiler over the other. The proportions 
 given to both boilers in the present case, however, are 
 such as are now generally approved in practice. With 
 these proportions and under the actual conditions of 
 the trials, the evaporative efficiency of the vertical 
 water-tube boiler exceeds that of the horizontal fire 
 tube by 18 per centum of the evaporation of the lat- 
 
WESTERN RIVER BOILERS. 
 
 t 
 
 ter, making the comparison by weight of combustible 
 consumed ; and by 16| per centum if the comparison 
 be made by weight of coal consumed ; the former is, 
 of course, the proper result. 
 
 Yth : Relative Quantities of Steam that can be fur- 
 nished in equal times by tlie two Boilers. In this 
 respect the superiority remains with the horizontal 
 fire-tube boiler, in which the combustion of the fuel 
 can be forced to a considerably greater extent than in 
 the vertical water-tube boiler. The additional steam, 
 however, thus obtained will be at a greater pro-rata 
 cost of coal, but we have no data to determine either 
 the increased quantity or its increased cost. 
 
 Finally, in view of the much greater evaporative 
 efficiency of the vertical water-tube boiler, and of the 
 facility and completeness with which it may be scaled, 
 the two qualities of paramount importance with 
 marine boilers, we would express our decided opinion 
 that its superiority over the horizontal fire-tube boiler 
 is so strongly marked as to unquestionably entitle it 
 to the preference. 
 
 WESTERN RIVER BOILERS. 
 
 The first steamboat constructed for the western 
 rivers had cylindrical boilers. Since that date, many 
 types of boilers have been made, and tried on board 
 some of the many steamboats navigating those immense 
 inland waters ; but none of them, except those repre- 
 sented by the following drawings, have ever gained 
 general favor. In consideration of this fact, of the 
 great number constructed every year at different 
 places on the rivers, and of the high pressure of steam 
 used, they deserve more than a passing notice. 
 
180 
 
 WESTERN RIVER BOILERS. 
 
 Transverse Section through 
 Fire Bed. 
 
 Front Elevation. 
 
 Longitudinal Section through A B of Front View. 
 
WESTERN RIVER BOILERS. 181 
 
 DESCRIPTION OF DRAWINGS. 
 
 <z, ash pit ; &, furnace doors ; <?, grate bars ; <$, flues ; 
 jEj smoke pipe ; 6r, steam room ; F, steam drum ; H, 
 mud blow pipe ; I, feed ; K, brick work. 
 
 The safety valve is put on the top of the boiler 
 shell. These boilers are placed side by side on the 
 deck of the vessel, near ,.id fronting the bow, ar- 
 ranged in numbers from one to eight, according to the 
 size of the boat. ^ 
 
 The fronts are of cast iron, resting on the deck ; 
 the back ends are also supported by cast brackets 
 under the feed. Brickwork surrounds the outside, and 
 also forms the bottom of the lower smoke flues. 
 
 The only variations from the drawing ever made 
 in these boilers, consists in the diameter and length of 
 shells, and diameter and number of flues. 
 
 The majority are two-flued ; but they are made 
 with four, five, and six flues, varying in diameter from 
 5 to 18 inches each. The shells are made of 44, 42, 
 38, 36, and 34 inches diameter, with lengths varying 
 from 32 to 22 feet. The iron used in the shells of the 
 two largest diameters is -/^ of an inch thick, but for 
 those of 40 inches diameter and under it is never more 
 than \ inch thick; for the smallest sizes it is even 
 occasionally -f T thick. In the largest flues it is some- 
 times T * T of an inch thick, but for all medium sizes it 
 is \ inch. The headfc are all wrought iron, generally 
 \ of an inch thick, with the flanges turned on the 
 front one. 
 
 All the seams are single riveted, with % rivets, 
 many of which are driven cold in all seams accessible 
 for the purpose. 
 
182 WESTERN KIVER BOILEKS. 
 
 The maximum pressure of steam carried on these 
 boilers is about 150 Ibs. per square inch ; but, prior 
 to the law limiting the pressure, from 200 to 220 Ibs. 
 per square inch was not an unusual daily working 
 pressure on a boiler of 40 inches diameter of shell, and 
 i inch thickness of iron, such as the above drawing 
 represents; and although many explosions occurred 
 and flues were collapsed during the early days of west- 
 ern river steam navigation, yet all of them have been 
 attributed either to defective materials, imperfect work- 
 manship, incompetent and reckless engineers, or to the 
 omission of steam pumps (Doctors, as they are called 
 by western engineers) to supply the boilers with 
 water during the time that the boats were landing 
 passengers and freight at the different stopping points. 
 
 All the iron from which they have been constructed 
 within the past few years has been made from cold- 
 blast charcoal pigs, worked into blooms in charcoal 
 furnaces. The rivets are also made from the best char- 
 coal blooms. In fact, their success as regards safety 
 may in a great degree be attributed to the superior 
 quality of the materials used in their construction. 
 
 The lifetime of the boats in which they are em- 
 ployed is averaged at five years, and when they ceaso 
 to be fit for use, the engines are transferred to a new 
 boat sometimes to a third, and occasionally to a 
 fourth boat : the boilers are never used on the second 
 boat, but always removed to the shore, and worked at 
 reduced pressures the objections to their further use 
 on board vessels being their reduced strength corfse. 
 quent upon a chemical change in the iron, occasioned 
 by the high temperatures. Hence extreme and varied 
 expansions and contractions ; this causes crystallization^ 
 
WESTERN EIVEK BOILEKS. 183 
 
 and the sheets to crack through the line of the rivet 
 holes where the laps come directly in contact with the 
 greatest heat. To double rivet the seams, or increase 
 the thickness of iron, increases the evil ; to cut out 
 the defective piece and replace it with a new piece of 
 iron starts fresh leaks, because there is a difference 
 between the expansion of the old and new metal. The 
 only remedy is to remove one circle of sheets. 
 
 The products of combustion are discharged into 
 the smoke pipes at such a high temperature that it 
 involves the necessity of making the pipes in area of 
 cross section about twice that of the flues. The dis- 
 tance between the grates and bottoms of boilers does 
 not often exceed 16 inches. The coals are frequently 
 piled up in the furnaces to the boilers, and consequent 
 upon the extreme height (sometimes 80 feet) of the 
 pipes, assisted by a blast of steam discharged into the 
 back end of the flues, or the exhaust steam admitted 
 into the chimneys on the locomotive fashion, the draft 
 is very strong, the combustion rapid, and the heat 
 applied to the boiler iron intense. There are no com- 
 bustion chambers or provision for admitting air through 
 holes into the furnace doors or back of the grates. The 
 coal is highly bituminous, used extravagantly, and as a 
 consequence produces large volumns of dense black 
 smoke. The cheap rate at which this coal is furnished 
 is the only excuse for making no efforts to economize 
 it and prevent the smoke nuisance. 
 
 We feel convinced that time must effect an entire 
 change in the mode of generating steam on the western 
 waters, for it is evident that tubular boilers can be 
 constructed suitable to the purpose, that will not only 
 be lighter and more durable, but that can be operated 
 
 m 
 
184 BOILER FLUES. 
 
 with 50 per cent, less fuel than those now in such high 
 favor. 
 
 BOILER FLUES. 
 
 The well established law that the strength of cyl- 
 inders is inversely as their diameters, and the hitherto 
 undisputed axiom among practical engineers that cyl- 
 indrical tubes or boiler flues when subjected to uniform 
 external pressure were equally strong in every part 
 regardless of length, led to erroneous opinions regard- 
 ing the strength of boiler flues. For flues to collapse 
 under the ordinary working pressure of steam, in what 
 was supposed to be properly proportioned and well 
 made boilers, was formerly not an unusual occurrence; 
 and although many theories were advanced on the 
 subject, it was not until the celebrated English engi- 
 neer, William Fairbairn, LL.D., F. E. S., made an ex- 
 tensive set of experiments on the strengths of tubes of 
 various forms, sizes, and lengths, that the hidden weak 
 ness was revealed. These experiments were made by 
 hydrostatic pressure, applied both externally and inter- 
 nally, to test the strength under ordinary conditions 
 of practice, and they proved conclusively that the 
 strength of flues exposed to external pressure, as ordi- 
 narily used, is inversely as the length; that is, a flue 
 30 feet long will collapse with just half the pressure 
 of a flue 15 feet long, everything else being equal; in 
 other words, a flue 30 feet long, which would bear a 
 pressure of 100 Ibs. per square inch, if shortened to 15 
 feet, or, what is the same thing in effect, if it be hooped 
 in the middle of its length by angle or T iron, it will 
 then bear a pressure of 200 Ibs. per square inch. 
 
BOILER FLUES. 185 
 
 If this important law had been familiar to the en- 
 gineer who designed the boilers of the " Great East- 
 ern," the disastrous accident which attended the first 
 trial of that vessel would have been entirely avoided. 
 It will be remembered that the smoke pipe of that ship 
 was surrounded by a water jacket for the purpose of 
 increasing the temperature of the feed water previous 
 to entering the boilers. This jacket contained a column 
 of water nearly forty feet in height, and the pipe was 
 six feet in diameter ; there was consequently a pressure 
 of steam in the jacket which, united to the heavy col- 
 umn of water at the base, was sufficient to collapse the 
 pipe, and cause the fearful accident. 
 
 Another source of weakness in lap joint riveted 
 flues must also be noticed ; namely, the deviation from 
 a true circle common to the lap. 
 
 Although it had long been established, that a circle 
 is the strongest possible form that can be made, and 
 that no deviation from it can be made without reduc- 
 tion of strength, yet it was not previously known that 
 a 9 -inch diameter of tube was reduced in strength 
 more than one-third by deviating from a circle only 
 sufficient to make a lap joint, the ratio being as 7 to 
 10 so proved by the tests. 
 
 These facts are conclusive, in showing the necessity 
 of adhering to the true circle for boiler flues using 
 high pressure steam. 
 
 In consideration of this, and the reduction in 
 strength consequent upon the rivet holes, it will be 
 readily seen that the lap-welded flues, which are both 
 seamless and round, have superior advantages over 
 those now in use on the western waters. 
 
186 RIVETING. 
 
 EIVETING. 
 
 The weakest point is the measure of strength ; 
 therefore, in the construction of steam boilers, the riv- 
 eted joints require close attention, and should receive 
 the best workmanship. They are either single or 
 double riveted, and the holes should not only be 
 punched the proportionate distances apart, but should 
 exactly correspond with each other, so that no ream- 
 ing need be required. 
 
 In the United States there are three mechanical 
 modes of uniting the sheets together ; namely, ma- 
 chine riveting, and hot and cold hand riveting. On 
 the seaboard, all kinds of boilers are riveted by the 
 two first-named methods, in both of which the rivets 
 are put in hot. West of the Alleghanies, all riveting 
 is done by hand, and at Pittsburgh, Louisville, and 
 other places, the rivets are driven cold in all places 
 accessible for the purpose. 
 
 For the cold process, a superiority is claimed con- 
 sequent upon the holes being well filled with the body 
 of the rivets ; that is, there can be no contraction 
 hence reduction in the strength and in the rivets' 
 diameters after the workmen cease hammering on the 
 heads. The reverse must be the case when driven 
 hot ; for, in cooling, the diameters are reduced by con- 
 traction. Moreover, none but the best quality of iron 
 can be used in rivets driven cold ; because, if the iron 
 be inferior, it is sure to crack or split through the 
 head, each one being tested by the heading. 
 
 For hot riveting, it is claimed that, in cooling, the 
 rivets contract in length, drawing the sheets more 
 
187 
 
 closely together, thereby creating adhesion sufficient 
 to add to the strength of the joint. Mr. Clarke, Resi- 
 dent Engineer of the Britannia Bridge, made some 
 experiments to determine the value of this. Three 
 plates were riveted together by a machine, maintain- 
 ing a temperature of 900 degrees in the rivets ; each 
 outside plate had a circular hole in which the rivets 
 fitted exactly; but in the centre one the hole was 
 oval, or 2^ inches long for a f rivet, and the rivet was 
 not allowed to touch either end of this hole. A strain 
 was then put on the centre plate till it began to slide, 
 which it did abruptly. Several trials were made, and 
 the least result was an adhesion equal to 4 tons with 
 | rivets. Mr. Clarke infers from this experiment that, 
 by judicious riveting, the adhesion may in many cases 
 be nearly sufficient to counterbalance the weakening 
 of the plates from punching the holes. In this par- 
 ticular we regard his opinion as in error ; for if he had 
 continued the strain on the plate until it parted, or the 
 rivets broke, he would doubtless have found that the 
 total pressure, or breaking strain, would have been 56 
 per cent, if single riveted, and 75 per cent, if double 
 riveted, of the sheet, as fully tested by other experi- 
 ments. Theoretically, there is a gain from adhesion 
 in hot-riveted joints, but practically this seems to be 
 lost by the contraction of the rivets'' diameter, thus 
 making the total or breaking pressure the same. 
 
 In our western river boilers, where the pressure of 
 steam used is higher than in any part of the world, no 
 difficulty has ever been experienced from the cold- 
 riveted joints not being closely united and perfectly 
 tight ; and as regards strength compared with the hot 
 
188 RIVETING. 
 
 riveted, superiority is claimed by those having cold- 
 riveted boilers in charge. 
 
 In either mode of hand riveting the rivets can be 
 seriously injured by too much hammering, and in any 
 case by overheating. Due regard should be had to 
 the temperature, and the blows of the hammer should 
 be hard and quick, and not continued longer than 
 necessary to form the head. Machine riveting has the 
 advantage of forming the head at a single blow, and 
 the rapidity with which the work can be performed 
 must always give it preference over all other methods 
 where it can be employed. 
 
 It is to be regretted that no extended set of ex- 
 periments have ever been made in this country to 
 determine the relative strengths of the different modes 
 of riveting and uniting the sheets of steam boilers and 
 other iron structures ; also to test the relative value 
 of the materials used in this country at the present 
 day, for it must be evident that although the results of 
 European experimenters on iron and steel are of value 
 to us, yet they cannot be regarded as entirely applica- 
 ble to our constructions, because our iron ores, the 
 temperature of blast of smelting furnaces, and manner 
 of working the metal through the different processes, 
 and the fuel used, all differ in a large degree from 
 those abroad. 
 
 In the year 1861 we constructed an excellent hy- 
 drostatic machine at the Navy Yard, Brooklyn, N. Y., 
 for this very purpose, and were about to commence an 
 extended and complete set of such experiments, when 
 the war broke out, and we were relieved from that 
 station for other duties. 
 
 The only published account of experiments on this 
 
STJPEKHEATED STEAM. 
 
 189 
 
 subject of any value, known to us, are those made in 
 England by Mr. Fairbairn, and at Glasgow, Scotland, 
 by David Kirkaldy, Esq. 
 
 The following is given by the former author, as ex- 
 hibiting the strongest form and best proportions of 
 such joints, as deduced from his experiments and ac- 
 tual practice. 
 
 Thickness of 
 
 Diameter of 
 
 Length of rivet 
 
 Distance from 
 
 Quantity of Lap in 
 
 plates. 
 
 rivet. 
 
 from head. 
 
 centre to centre. 
 
 single riveted. 
 
 double riveted. 
 
 in. 16th. 
 
 in. Eatio. 
 
 in. 
 
 Katio. 
 
 in. 
 
 Eatio. 
 
 in 
 
 Eatio. 
 
 in. 
 
 Eatio. 
 
 0.19= 3 
 
 0.38= 2 
 
 0.88 
 
 4.5 
 
 1.25 
 
 6 
 
 1.25 
 
 6 
 
 2.10 
 
 10 
 
 0.25= 4 
 
 0.50= 2 
 
 1.13 
 
 4.5 
 
 1.50 
 
 6 
 
 1.50 
 
 6 
 
 2.50 
 
 10 
 
 0.31= 5 
 
 0.63= 2 
 
 1.38 
 
 4.5 
 
 1.63 
 
 5 
 
 1.88 
 
 6 
 
 3.15 
 
 10 
 
 0.38= 6 
 
 0.75= 2 
 
 1.63 
 
 4.5 
 
 1.75 
 
 5 
 
 2.00 
 
 5.5 
 
 3.33 
 
 9.2 
 
 0.50= 8 
 
 0.81=1.5 
 
 2.25 
 
 4.5 
 
 2.0C 
 
 4 
 
 2.25 4.5 
 
 3.75 
 
 7.5 
 
 0.63 = 10 
 
 0.94 =1.5 
 
 2.75 
 
 4. 
 
 2.50 
 
 4 
 
 2.75 4 5 
 
 4.58 
 
 7.5 
 
 0.75 = 12 
 
 1.18 =1.5 
 
 8.25 
 
 4. 
 
 3.00 
 
 4 
 
 3.25 
 
 4.5 
 
 5.42 
 
 7.5 
 
 
 
 
 
 
 
 i 
 
 
 
 STJPEKHEATED STEAM 
 
 Is steam, the temperature of whicli is increased after 
 it leaves the boilers. This is generally accomplished 
 by passing it through a series of pipes exposed to the 
 heat of the discharged gases in the chimney. (See 
 drawing of such an apparatus in Nystrom's Pocket 
 Book, page 259.) The advantage to be derived from 
 the process depends on the condition in which the 
 steam leaves the boilers. The theory is steam gen- 
 erated in boilers, and being supplied to engines in 
 operation, carries with it to the cylinders water in the 
 vesicular state ; that is, in minute globules or innumer- 
 able particles; and that if it be passed through a 
 superheating apparatus, these small globules are ex- 
 panded into steam, thus utilizing its full effect. This 
 vesicular state in which steam is found in boilers when 
 in active operation differs more or less according to 
 
190 SUPERHEATED STEAM. 
 
 the construction of the boilers. In those properly 
 proportioned, with elevated steam chimneys, exposing 
 much heating surface to the action of the steam, the 
 quantity of water carried to the cylinders in this state 
 is inconsiderable ; hence, in boilers so constructed, the 
 application of a superheating apparatus would not pay 
 the extra cost and complication. When, therefore, we 
 are informed of large gains in the consumption of fuel 
 resulting from the application of such an apparatus to 
 a set of boilers, it becomes necessary to examine the 
 construction of the boilers before giving credit of the 
 results to superheating the steam. 
 
 In some steamers (and this applies especially to 
 many of those belonging to the English), where the 
 boilers are very low, and but little height to the steam 
 chimneys, gains in the consumption of fuel of from 20 
 to 40 per cent, have been effected by the application 
 of the superheater ; whereas the same kind of an 
 apparatus, if applied to some of our Hudson Eiver 
 steamers, would not probably make an average gain of 
 5 per cent. 
 
 In the summer of 1854, by the invitation of E. K. 
 Collins, Esq., we witnessed some extensive experiments 
 on superheating steam, on board the splendid, but ill- 
 fated U. S. Mail Steamship " Arctic." In this case, 
 the superheating steam pipes were carried down the 
 back connexions and through the furnaces close to the 
 arches, connecting in the engine room to one common 
 chamber, to which a branch pipe from the usual main 
 steam pipe was also attached. Thus the arrangements 
 were perfected to work the steam : 1st, in the usual 
 way, and at the ordinary pressure and temperature ; 
 2d, in a highly heated condition, from the pipes passing 
 
DRAFT. 
 
 through the furnaces ; 3d, at a medium temperature, 
 that is, the highly heated steam mixed in the chamber 
 with the ordinary working steam. So that a fair op- 
 portunity was offered, on a large scale, to test the ben- 
 efit to be derived from superheating the steam to 
 various temperatures ; and the results of the trial 
 proved conclusively that the saving of fuel would not 
 pay the expense of the apparatus on board that vessel, 
 to say nothing of the labor of keeping it in order. 
 
 This vesicular state in which steam is found in 
 boilers must not be confounded with foaming or 
 priming, explained at page 81. 
 
 DRAFT. 
 
 Draft is produced by the difference of temperature 
 between a column of heated, consequently rarefied air, 
 in a chimney, and the surrounding atmosphere ; and 
 this draft will be strong and effective just in propor- 
 tion to the difference of temperatures and the height 
 of the column. The cold and heavy column outside 
 the chimney presses down, and forces up the warm 
 and light column within. The greater the difference 
 between the weight of these two columns the greater 
 will be the draft. A column of two feet high rises, or 
 is pressed up, with twice as much force as a column of 
 one foot, and so in proportion for all heights to a cer- 
 tain extent, just as two or more corks strung together 
 and immersed in water tend upward with proportionally 
 more force than a single cork. In a chirnney where a 
 column of hot air one foot in height is one ounce 
 lighter than the same bulk of external atmosphere, if 
 13 
 
192 DRAFT. 
 
 the chimney be fifty feet high, the air and smoke in it 
 is propelled upward with a power of fifty ounces. 
 
 In a correctly proportioned chimney, the area of 
 cross section of the flues smoke passage should grad- 
 ually contract from bottom to top, being the widest at 
 the bottom and smallest at the top ; because at the 
 base the hot column of expanded air and gases fills the 
 entire passage, but in ascending they gradually cool 
 and contract, occupying less space. 
 
 There is a limit to the useful height of a chimney, 
 consequent upon the friction of the heated air and 
 products of combustion, and this limit is dependent on 
 the temperature of the discharged gases compared to 
 the area of cross section of the chimney. 
 
APPENDIX. 
 
 MATERIALS. 
 
 THERE is no subject connected with the Engineer- 
 ing profession more important to be understood than 
 materials. Yet young engineers rarely give it study, 
 and but few of those in the higher grades have a 
 thorough knowledge of the materials used in the con- 
 struction of steam machinery; indeed, many cannot 
 distinguish the best from the inferior quality of pig 
 metal, composition of copper and tin from copper and 
 zinc, or charcoal flange boiler plate from ordinary 
 puddle plate. 
 
 It is in a large degree owing to this fact that we 
 have had so many break downs in our sea-going steam- 
 ers, and that the weights of those parts made of 
 wrought and cast iron are so much in excess of what 
 is necessary for the best materials. We have, there- 
 fore, concluded to devote a short space to this branch 
 of the profession, solely with the view of directing the 
 mind of the young engineer to this channel as one of 
 his studies. 
 
 Some of the following has been extracted from the 
 Army Ordnance Manual, and all of it accords with 
 our experience of many months among the various 
 
194 CAST IRON. 
 
 iron rolling mills, furnaces, and steel works of Penn- 
 sylvania. 
 
 IKON. 
 
 Of all the useful metals none plays so important 
 and extensive a part in the steam engine as iron. It 
 is obtained from ores, in which it generally exists in 
 the state of an oxide combined with earthy or stony 
 matters, and frequently with carbon, phosphorus, sul- 
 phur, arsenic, magnesia, manganese, &c. Iron ores are 
 classed and named according to their combinations, as 
 magnetic, specular, clay iron-stone, red hematite, and 
 brown hematites the last named is the ore from 
 which the Salisbury and Juniatta irons are extracted, 
 the first from which the Swedish iron is obtained, 
 and the clay iron-stone that from which the greater 
 portion of English iron is made. For producing some 
 varieties of pig, different kinds of ores are mixed. The 
 foreign substances which iron is found to contain mod- 
 ify, in a marked degree, its essential properties. Car- 
 bon adds to its hardness, but destroys some of its 
 characteristic qualities, and produces cast iron or steel, 
 according to the proportion of carbon it contains ; sul- 
 phur renders it fusible, difficult to weld, and brittle 
 when heated hot short. Phosphorus renders it cold 
 short, but may be present in very small proportion 
 without effecting injuriously its tenacity. 
 
 CAST IKON. 
 
 The process of making cast iron depends much on 
 the kind of fuel used charcoal, coke, bituminous and 
 anthracite coals are all used, and the quality of pig 
 metal is influenced to a great extent by the kind of 
 
CAST IRON. 195 
 
 fuel, as well as by the temperature of the blast with 
 which the ore is reduced. When anthracite coal is 
 employed, the ore is placed at once into the blast fur- 
 nace. When charcoal is used, the ore is first roasted, 
 by distributing it in alternate layers with waste coal, 
 wood, or, sometimes, with charcoal, and the pile thus 
 formed is ignited and burned in the open air. For 
 the more refractory ores a kiln similar to that used for 
 burning lime is required. The ore is rendered, by 
 this operation, more porous and easily broken into 
 small pieces, by which it is more readily acted upon 
 in the smelting furnace. The small pieces would be 
 disadvantageous in an anthracite furnace. 
 
 Smelting is the process by which the iron is sepa- 
 rated from the refractory substances with which it is 
 combined in the ore. It consists in raising the ore to 
 a high heat in contact with carbon and a suitable flux 
 in the blast or smelting furnace. The flux unites with 
 the earthy matter of the ore, forming a glassy sub- 
 stance called slag or cinder, and the carbon unites with 
 the oxygen of the ore, setting the iron free, which in 
 turn unites with a portion of the carbon and forms a 
 fusible compound, carburet of iron, or cast iron. 
 
 The melted iron and slag descend to the bottom 
 of the furnace, the slag forming a covering to the pool 
 of iron and protecting it from the action of the blast. 
 As they accumulate, the slag runs off over the dam, 
 and is a good indication, to an experienced eye, of the 
 quality of metal the furnace is making. 
 
 The furnace is generally tapped once every twelve 
 hours, and the metal is run out into channels formed 
 in the sand, and is known as pigs. 
 
 Limestone is the flux used for most ores ; clay is 
 
196 CAST 
 
 sometimes required to mix with ores containing much 
 limestone. 
 
 A larger yield from the same furnace, and a great 
 economy in fuel, are effected by the use of a hot blast* 
 The greater heat thus produced causes the iron to com- 
 bine with a larger percentage of foreign substances, 
 and the strength of the cast iron is thus injured. 
 
 Cast iron, for all purposes requiring great strength, 
 should be smelted with the cold blast. 
 
 Pig iron, according to the proportion of carbon 
 which it contains, is divided into foundry iron and 
 forge iron, the latter being adapted only to conversion 
 into malleable iron : while the former, containing the 
 largest proportion of carbon, can be used either for 
 casting or for making bar iron. 
 
 There are many varieties of cast iron, differing from 
 each other by almost insensible shades ; the two prin- 
 cipal divisions are gray and white, so called from the 
 color of the fracture when recent. Their properties 
 are very different. 
 
 Grray iron is softer and less brittle than white iron ; 
 it is in a slight degree malleable and flexible, and is 
 not sonorous ; it can be easily drilled and turned in 
 the lathe, and does not resist the file. It has a bril- 
 liant fracture, of a gray, or sometimes a bluish-gray 
 color ; the color is lighter as the grain becomes closer, 
 and its hardness increases at the same time. 
 
 White iron is very brittle and sonorous ; it resists 
 the file and the chisel ; the fracture presents a silvery 
 appearance, generally fine grained and compact. 
 
 Mottled iron is a mixture of white and gray ; it 
 has a spotted appearance. 
 
 The pig metal is generally known in our market as- 
 
CAST IRON. 197 
 
 charcoal cold blast, charcoal hot blast, anthracite, and 
 coke iron, and the quality is decided on by breaking 
 the pigs and examining the fractures. A medium- 
 sized grain, bright gray color, lively aspect, fracture 
 sharp to the touch, and a close compact texture, indi- 
 cate a good quality of iron. A grain either very large 
 or very small, a dull, earthy aspect, loose texture, dis- 
 similar crystals mixed together, indicate an inferior 
 quality. 
 
 Besides these general divisions, the manufacturers 
 distinguish more particularly the different varieties of 
 pig metal by numbers, according to their relative 
 hardness. 
 
 No. 1 is the softest iron, possessing in the highest 
 degree the qualities described as belonging to gray 
 iron ; it has not much strength, but on account of its 
 fluidity when melted, and of its mixing advantageously 
 with other kinds of irons, it is of great use to the 
 founder, and commands the highest price. 
 
 No. 2 is harder, closer grained, and stronger than 
 No. 1 ; it has a gray color and considerable lustre. 
 
 No. 3 is still harder its color is gray, but inclining 
 to white ; it has considerable strength, but is princi- 
 pally used for mixing with other kinds of iron. 
 
 No. 4 is bright iron, No. 5 mottled, No. 6 white 
 which is unfit for general use by itself. 
 
 East of the Alleghany mountains, the anthracite 
 hot-blast iron is used for all ordinary purposes, and 
 west of the Alleghanies coke hot-blast iron is in gen- 
 eral use. 
 
 Pig metal is improved by being remelted in an air 
 furnace. All cast iron expands forcibly at the moment 
 of becoming solid, and again contracts in cooling; 
 
198 MALLEABLE IRON. 
 
 gray iron expands more and contracts less than other 
 iron. 
 
 The color and texture of cast iron depend greatly 
 on the size of the casting and the rapidity of cooling ;. 
 a small casting, which cools quickly, is almost always- 
 white, and the surface of large castings partakes more 
 of the qualities of white metal than the interior. Care 
 should always be taken to cool them as equally as pos- 
 sible, and not too rapidly 
 
 West of the Alleghanies, where bituminous coal is 
 so plentiful and cheap, air furnaces are in general use 
 in foundries, and the castings made from them are 
 superior to those from the cupola furnace, as was 
 proved at Pittsburg, Pa., by many experiments. 
 
 MALLEABLE IKON. 
 
 The manner of converting iron ore into malleable 
 iron has undergone many changes since the seventh 
 descendant from Adam. Tubal Cain was an " in- 
 structor of every artificer in brass and iron." It is 
 made from the pig, in the bloomery fire, or in the 
 puddling furnace generally the latter. The process 
 consists in melting the pig metal in a reverberatory 
 furnace, where the flame is made to act directly on 
 the metal, keeping it exposed to a great heat, and con- 
 stantly stirring the mass, bringing every part of it 
 evenly under the action of the flame, until it loses its 
 remaining carbon. It then loses its fluidity, and is 
 formed into a puddler's ball, weighing from 80 to 100 
 pounds. This is the point or connecting link between 
 cast and malleable iron. 
 
 The operation of puddling is a most important one, 
 
MALLEAI5LE IRON. 199 
 
 as the quality of the iron depends so much upon the 
 skill with which it is conducted. After the puddler's 
 ball has been formed, it is passed to a heavy strong 
 squeezer, or steam hammer, most frequently the former. 
 Its object is to press out, as perfectly as possible, the 
 liquid cinder which the ball still contains; it also 
 forms the ball into shape. It is now called a bloom, 
 and is ready to be rolled or hammered while yet hot 
 it is generally passed between the rolls several times, 
 and drawn into a bar about five inches wide and three 
 quarters of an inch thick; this is called muck bar. 
 The next thing is to refine it. To prepare bars for 
 this operation, they are cut by a strong pair of shears 
 into such lengths as are best adapted to the size of bar 
 or sheet required. The sheared bars are then piled 
 one on the other, according to the quantity of metal 
 necessary to make the finished piece. They are then 
 brought to a welding heat, in the heating furnace, and 
 passed between the finishing rolls successively until 
 drawn to the proper dimensions. For heavy plates, 
 and many other forms, pieces called tops and bottoms 
 are first rolled some three by two feet and about an 
 inch thick, and the before named bars piled breaking 
 joints between them. Sometimes these tops and 
 bottoms are of good stock and the pile very inferior ; 
 the result is a poor quality. For better material, the 
 iron is double refined ; i. e., the rough, or muck bar, as 
 it is called, being cut to proper lengths, is piled, heated 
 as before, rolled into bars, and again piled, heated, and 
 rolled to the required dimensions. Another, and we 
 consider the better process, is to hammer the heated 
 pile into a slab of say 18 by 12 inches and 6 inches 
 thick, heat this slab, rehammer it, then roll it to de- 
 
200 MALLEABLE IRON. 
 
 sired dimensions. By reheating, hammering or rolling, 
 other things being equal, the iron is improved up to 
 some five or six workings, after which, further heating 
 causes deterioration. 
 
 The quality depends on the kind of pig used, 
 the skill of the puddler, and the absence of deleteri- 
 ous substances in the furnace. For the best sheets, 
 bars, and for converting into steel, charcoal iron is 
 used exclusively, and it can be relied upon for 
 strength and toughness with greater confidence tha 
 any other. 
 
 Bloomery. This resembles a large forge fire, and 
 in it are made the charcoal blooms from which the 
 best qualities of all iron and steel are manufactured. 
 The pig metal, after being broken into pieces of the 
 proper size, is placed before a strong blast directly in 
 contact with charcoal ; as the metal fuses it falls into 
 a cavity left for the purpose below the blast, when the 
 bloomer works it into the shape of a ball, which he 
 places again before the blast surrounded with fresh 
 charcoal; after repeating this, the ball is ready for 
 and put under the hammer and hammered into a 
 bloom. The bloom is then removed to the reverbera- 
 tory furnace, and heated with bituminous coal, to a 
 welding heat, then again hammered into a slab, or 
 rolled into rough bar. If the former, it is again heated 
 . and rolled as required. If the latter, it is cut, piled, 
 and re-rolled into bar then treated as before explained. 
 Flange boiler plate is made according to both opera- 
 tions, and there is a difference of opinion among iron 
 masters regarding which process produces the best 
 quality. 
 
 Cold Short is the term given to iron that will not 
 
MALLEABLE IRON. 201 
 
 stand working cold, bending, twisting, or punching 
 very near edges, &c. 
 
 Hot Short is iron that will not work advantageously 
 hot, but is strong when cold. Both kinds are suitable 
 for special purposes, but for machinery neutral iron is 
 the kind to be relied upon. By neutral is meant iron 
 that can be worked either cold or hot at all ordinary 
 temperatures. 
 
 Forging. Good iron is often injured by being un- 
 skilfully worked. Care should be taken that the iron 
 while heating is not exposed to the air. Iron heated 
 for any purpose, especially for welding, should be 
 heated as rapidly as possible, in order to expose it the 
 least possible time to the action of the air and coal; 
 for this purpose, the strongest fuel with an abundant 
 steady blast is necessary. 
 
 Bessemer 1 s Patent Process for making Malleable 
 Iron. We have seen that the principal impurities in 
 cast iron consist of carbon, sulphur, phosphorus, silicon, 
 &c. These substances, Mr. Bessemer asserts, combine 
 with the oxygen of the atmosphere at high tempera- 
 tures ; he therefore runs the metal from the smelting 
 furnace into a close vessel ; when this vessel is about 
 half full, numerous small jets of atmospheric air are 
 forced in among the fluid metal, and in sufficient quan- 
 tities to produce a vivid combustion among the par- 
 ticles of the fluid metal. By this process an intense 
 heat is generated without the application of any fuel, 
 and the labor and expense of puddling are saved. The 
 process has been progressing in England for several 
 years, and at this date 1862 a number of iron mas- 
 ters are experimenting with it in this country. If suc- 
 cessful, a cheaper and wider field will be open to the 
 
202 CAST STEEL. 
 
 manufacturers of iron. One of the difficulties Mr. Bes- 
 semer has to contend with, is to obtain any kind of 
 material that will stand the intense heat. 
 
 PUDDLED STEEL. 
 
 If, in the operation of puddling, the process be 
 stopped at a particular time, determined by indications 
 given by the metal to an experienced eye, an iron is 
 obtained of greater hardness and strength than ordi- 
 nary iron, to which the name of semi-steel, or puddled 
 steel, has been applied. Chemicals are also used in 
 some such furnaces. 
 
 STEEL. 
 
 Steel is a compound of iron and carbon, in which 
 the proportion of the latter is from five to one per 
 cent., and even less in some kinds. Steel may be dis- 
 tinguished from iron by its fine grain, and its suscepti- 
 bility of hardening by immersing it, when hot, in cold 
 water. 
 
 There are many varieties of steel, the principal of 
 which are blistered steel, shear steel, and cast steel. 
 
 Blistered Steel is prepared by the direct combination 
 of iron and carbon. The process is to take the best 
 bars and plates of wrought iron and expose them in a 
 converting furnace, for seven or eight days, to a me- 
 dium temperature, in contact with powdered charcoal, 
 so as to totally exclude the air. The bars, on being 
 taken out, exhibit in the fracture a uniform crystalline 
 appearance. The degree of carbonization is varied 
 according to the purpose for which the steel is in- 
 tended. 
 
CAST STEEL. 203 
 
 Shear Steel is generally made from blistered steel 
 refined by piling into fagots, which are brought to a 
 welding heat in a reverberatory furnace, hammered 
 and rolled again into bars ; this operation is repeated 
 several times to produce the finest kind of shear steel. 
 The name is derived from the fact that this variety of 
 steel was used in England for shears. 
 
 Cast Steel. For this important invention we are 
 indebted to Benjamin Huntsman, of the village of 
 Handsworth, near Sheffield, England, who, about the 
 year 1740, perfected his invention, from which the 
 civilized world has derived such vast and varied ad- 
 vantages. It is made by breaking blistered steel or 
 cutting bar iron into small pieces, and melting it in 
 combination with a small quantity of charcoal (when 
 it is made from iron, manganese is mixed with it) in 
 close air-tight crucibles, from which it is poured into 
 iron moulds ; the ingot is then reduced to a bar by 
 hammering or rolling, as described under the head of 
 malleable iron. 
 
 Cast steel is the finest kind of steel. It is known 
 by a very fine, even, and close grain, and a silvery and 
 homogeneous fracture ; it is very brittle, and acquires 
 extreme hardness, but is difficult to weld without the 
 use of a flux. The other kinds of steel have a similar 
 appearance to cast steel, but the grain is coarser and 
 less homogeneous; they are softer, less brittle, and 
 weld more readily. 
 
 Properties of Steel. The best steel possesses the fol- 
 lowing characteristics : Heated to redness and plunged 
 into cold water, it becomes hard enough to scratch 
 glass and to resist the best files ; the hardness is uni- 
 form throughout the piece ; after being tempered it is 
 
204 CAST STEEL. 
 
 not easily broken ; it welds readily ; it does not crack 
 or split ; it bears a very high heat, and preserves the 
 capability of hardening after repeated working ; the 
 grain \sfine, even, and homogeneous, and it receives a 
 brilliant polish. 
 
 Hardening and Tempering. On these operations 
 the quality of manufactured steel in a great measure 
 depends. 
 
 Hardening is effected by heating the steel to 
 cherry red and plunging it into a liquid, generally cold 
 water; the degree of hardness depends on the heat 
 and rapidity of cooling. 
 
 Tempering. Steel in its hardest state being too 
 brittle for most purposes, the requisite strength and 
 elasticity are obtained by tempering, which is per- 
 formed by heating the hardened steel to a certain 
 degree and cooling it quickly. The requisite heat is 
 usually ascertained by the color which the surface of 
 the steel assumes a straw color is common for cold 
 chisels and machinists' tools. 
 
 Case Hardening. This operation consists in con- 
 verting the surface of wrought iron into steel, by heat- 
 ing the iron to a cherry red, in a close vessel, in contact 
 with carbonaceous materials, and then plungiog it into 
 cold water. Bones, leather, hoofs, and horns of animals 
 are used for this purpose, after having been burnt or 
 roasted, and pulverized. Soot is also frequently used. 
 
 To Test the Quality of Boiler Iron. Bend it cold 
 at sharp angles, and double the pieces together ; heat 
 it cherry red, and perform the same operation, and 
 punch holes very near the edges of the sheets. If it 
 stands these tests without cracking, it is neutral iron, 
 and of the best quality. 
 
CAST STEEL. 205 
 
 To Test the Quality of Ba/r Iron. Cut a notch on 
 one side with a cold chisel, then bend the bar over 
 the edge of an anvil at sharp angles. If the fracture 
 exhibits long silky fibres, of a leaden gray color, co- 
 hering together, and twisting or pulling apart before 
 breaking, it denotes tough, soft iron, easy to work and 
 hard to break. In general, a short, blackish fibre in- 
 dicates iron badly refined. A very fine close grain 
 denotes a hard steely iron, which is apt to be cold 
 short, but working easily when heated, and making a 
 good weld. Numerous cracks on the edges of the bar 
 generally indicate a hot short iron, which cracks or 
 breaks when punched or worked at a red heat, and 
 will not weld. Blisters, flaws, and cinder holes are 
 caused by imperfect welding at a low heat, or by iron 
 not being properly worked, and do not always indicate 
 inferior quality. 
 
 To Test Iron when Hot. Draw a piece out, bend 
 and twist it, split it and turn back the two parts, to 
 see if the split extends up ; finally, weld it, and observe 
 if cracks or flaws weld easily. Good iron is frequently 
 injured by being unskilfully worked: defects caused 
 by this may be in part remedied. If, for example, it 
 has been injured by cold hammering, moderate anneal- 
 ing heat will restore it. 
 
 Steel. To test steel, break a few bars, taken at 
 random, make tools of them, and try them in the 
 severest manner. 
 
 For further information on the subject of materials, 
 we refer the reader to an excellent work called "Use- 
 ful Metals and their Alloys," by Messrs. Clay, Aitken, 
 Vospicket, and Fairbairn. 
 
206 
 
 TENACITY OF MATERIALS. 
 
 Tenacity of Materials. 
 
 Cast Steel 134,000 Ibs. 
 
 Swedish 72,000 "| Experiments by Frank- 
 Salisbury, Conn 66,000 I lin Institute, on bars 
 
 Bar-iron Bellefonte, Pa 58,500 f whose cross section 
 
 English 56,000 I was about one-fifth 
 
 Pittsfield, Mass 57,000 j of a square inch. 
 
 Pig metal 15,000 
 
 . Good common castings 20,000 Experiments of Maj. W. 
 
 Cast Steel 128,000 on pieces whose cross 
 
 Bronze-gun metal { ^ j ,~ 1 ' l 
 
 Copper, cast, (Lake Superior) 24,138 
 
 Brass 18,000 
 
 Conner J Wrou S ht 34 > 000 
 
 J Cast 19,000 
 
 Tin, cast 4,800 
 
 Zinc 3,500 
 
 Platinum 56,000 
 
 Silver 40,000 
 
 Gold 30,000 
 
 Lead 1,800 
 
 WOODS. 
 
 Ash 15,800 
 
 Mahogany 11,500 
 
 Oak 11,600 
 
 White Pine 11,800 
 
 Walnut 7,700 
 
 In general, the tenacity of metals is increased by 
 hammering and wiredrawing. The strength of Pitts- 
 field bar iron, given in the above table, is the mean of 
 four trials, with cylinders 1 inch long and 0.9 inch di- 
 ameter. They were extended in length, before frac- 
 ture, to 1.4 in., and they were reduced in diameter to 
 0.6 in. in the middle. 
 
 A bar of wrought iron is extended about one-hun- 
 dredth part of its length for every ton of strain on a 
 square inch. 
 
 Trcmsverse Strength. 
 
 S the weight in pounds required to break a beam 
 1 in. square and 1 in. long, fixed at one end and loaded 
 at the other ; b the breadth, d the depth, and I the 
 
RESISTANCE TO TORSION. 207 
 
 length, in inches, of any other beam of the same mate- 
 rial, and W the weight Vhich will cause it to break, 
 neglecting the weight of the beam itself. 
 
 1. If the beam is supported at one end, and loaded at the other : 
 
 2. If the beam is supported at one end, and the load distributed over ita 
 whole length : 
 
 3. If the beam is supported at both ends, and loaded in the middle : 
 
 bd* 
 W = 4S -y- 
 
 4. If the beam is supported at both ends, and loaded uniformly over ita 
 whole length : 
 
 6. If the beam is supported at both ends, and loaded at the distance in from 
 one end : 
 
 \\( n^ o 77 \" 
 
 m (lm) 
 
 Resistance to Torsion. 
 
 S = the weight in pounds required to break, by 
 twisting, a solid cylinder, 1 inch diameter ; the weight 
 acting at the distance of 1 inch from the axis of the 
 cylinder ; c?, the diameter in inches of any other cylin- 
 der of the same material ; r, the distance from its axis 
 to the point where the breaking weight W is applied ; 
 then : 
 
 Results of Repeated Heating Bar Iron. 
 
 In a series of experiments, with regard to the im- 
 provements and deterioration which result from oft- 
 repeated heating and laminating of bar iron, made by 
 William Clay, Esq., of the Mersey steel and iron works, 
 Liverpool, he says that, taking a quantity of ordinary 
 
 14 
 
208 EESULTS OF EEPEATED HEATING BAR IKON. 
 
 fibrous puddled iron, and reserving samples marked 
 No. 1, we piled a portion five high, heated and rolled 
 the remainder into bars marked No. 2, again reserving 
 two samples from the centres of these bars, the remain- 
 der were piled as before, and so continued until a por- 
 tion of the iron had undergone twelve workings. 
 
 " The following table shows the tensile strain which 
 each number bore : 
 
 No. 
 1. Pud 
 2. Re-1 
 3. 
 4. 
 5. 
 6. 
 7. 
 8. 
 9. 
 10. 
 11. 
 12. 
 
 Pounds, 
 died bar 43,904 
 
 leated 52 864 
 
 59 585 
 
 59 585 
 
 .-. 57,344 
 
 61 824 
 
 59585 
 
 57 344 
 
 57 344 
 
 54,104 
 
 51 968 
 
 .. 43.904 
 
 " It will thus be seen that the quality of the iron 
 increased up to No. 6, (the slight difference of No. 5 
 may, perhaps, be attributed to the sample being slightly 
 defective) ; and that from No. 6 the descent was in a 
 similar ratio to the previous increase." 
 
 TENSILE STRENGTH OF IRON AND STEEL BARS PER SQUARE INCH. 
 
 Description of Iron and Steel. 
 
 Tensile Strength. 
 
 Authority. 
 
 
 62 644 
 
 
 
 56 532 
 
 American Board of 
 
 
 56,103 
 
 Ordnance. 
 
 American Hammered 
 
 53 913 
 
 
 
 
 
 Krupp's Cast Steel, average of 3 samples... 
 Cast Steel highest 
 
 111,707 
 142 222 
 
 Min. of War, Berlin. 
 Mallett. 
 
 
 88,657 
 
 do. 
 
 it <( 
 
 134,256 
 
 
 *' tempered 
 
 150,000 
 
 
 
 124,400 
 
 
 Blister " 
 
 133,152 
 
 
 Mersey Steel and Iron Co. Puddled steel, 
 highest 
 
 173 817 
 
 
 
 160 832 
 
 
 Average of three samples tested at the Liv- 
 erpool Corporation testing machine 
 
 1 1 2,000 
 
 
STEENGTH OF JOINTS OF BOILEK PLATES. l!09 
 
 On the strength of the joints of single and double riveted 
 boiler plates , by William Faii-ljairn, Esq., F.R. S. 
 
 On comparing the strength of plates with their 
 riveted joints, it will be necessary to examine the sec- 
 tional areas taken in a line through the rivet-holes with 
 the section of the plates themselves. It is perfectly 
 obvious, that in perforating a line of holes along the 
 edge of a plate, we must reduce its strength : it is also 
 clear that the plate so perforated will be to the plate 
 itself, nearly as the areas of their respective sections, 
 with a small deduction for the irregularities of the 
 pressure of the rivets upon the plate ; or, in other 
 words, the joint will be reduced in strength somewhat 
 more than in the ratio of its section through that line 
 to the solid section of the plate. It is evident that the 
 rivets cannot add to the strength of the plates, their ob- 
 ject being to keep the two surfaces of the lap in contact. 
 
 When this great deterioration of strength at the 
 joint is taken into account, it cannot but be of the 
 greatest importance that in structures subjected to such 
 violent strains as boilers and ships, the strongest 
 method of riveting should be adopted. To ascertain 
 this, a long series of experiments jy- ^ 
 were undertaken by Mr. Fairbairn, 
 some of the results of which will 
 be of interest here. The joint or- 
 dinarily employed in ship building 
 is the lap joint, shown in Figs. 1 
 and 2. The plates to be united 
 are made to overlap, and the rivets 
 are passed through them, no cov- 
 ering-plates being required, except 
 at the ends of the plate, where they butt against each 
 
210 STRENGTH OF JOINTS OF BOILER PLATES. 
 
 other. It is also a common practice to countersink the 
 rivet-heads on the exterior of the vessel, that the hull 
 may present a smooth surface for her passage through 
 the water. This system of riveting is only used when 
 smooth surfaces are required; under other circum- 
 stances, their introduction would not be desirable, as 
 they do not add to the strength of the joint, but, to a 
 certain extent, reduce it. There are two kinds of lap- 
 joints, those said to be single-riveted (Fig. 1), and those 
 which are double-riveted (Fig. 2). At first, the former 
 were almost universally employed, but the greater 
 strength of the latter has since led to their general 
 adoption in the larger descriptions of vessels. The rea- 
 son of the superiority is evident. A riveted joint gives 
 way either by shearing off the rivets in the middle of 
 their length, or by tearing through one of the plates 
 in the line of the rivets. In a perfect joint, the rivets 
 should be on the point of shearing just as the plates 
 were about to tear ; but in practice, the rivets are 
 usually made slightly too strong. Hence, it is an estab- 
 lished rule, to employ a certain number of rivets per 
 lineal foot. If these are placed in a single row, the 
 rivet-holes so nearly approach each other, that the 
 strength of the plates is much reduced ; but if they 
 are arranged in two lines, a greater number may be 
 used, and yet more space left between the holes, and 
 greater strength and stiffness imparted to the plates at 
 the joint. 
 
 The experiments of Mr. Fairbairn and others have 
 established the following relative strengths as the 
 value of plates with their riveted joints : 
 
 Taking the strength of the plate at 100 
 
 The strength of the double-riveted joint would then be 70 
 
 And the strength of the single-riveted joint 56 
 
MOTION. 211 
 
 THE ELEMENTS OF MACHINERY. 
 
 IN consequence of having found many young en- 
 gineers unacquainted with the principles of mechani- 
 cal powers, we have thought best to devote a short 
 space to the subject, prefacing it with the description 
 of motion, and application of power, by David A. 
 Wells, A. M. 
 
 Motion. 
 
 Motion is the act of changing place. It is absolute 
 or relative. Absolute motion is a change of position 
 in space, considered without reference to any omer 
 body. Relative motion is motion considered in rela- 
 tion to some other body, which is either in motion or 
 at rest. 
 
 When a body commences to move from a state 
 of rest, there must be some force to cause its motion, 
 and this force is generally termed " Power." On the 
 contrary, a force acting to retard a moving body, de- 
 stroy its motion, or drive it in a contrary direction, 
 is termed " Resistance." The chief causes which tend 
 to retard or destroy the motion of a body are gravi- 
 tation, friction, and resistance of the air. 
 
 The speed, or rate, at which a body moves, is 
 termed velocity. The momentum of a body is its 
 quantity of motion, and this expresses the force with 
 which one body in motion would strike against 
 another. This momentum, or force, which a moving 
 body exerts, is estimated by multiplying its weight 
 by its velocity. Thus a body weighing 20 Ibs., and 
 moving with a velocity of 200 feet per second, will 
 have a momentum of 20 X 200 = 4000. 
 
212 APPLICATION OF POWER. 
 
 Action and Reaction. 
 
 When a body communicates motion to another 
 body, it loses as much of its own momentum, or force, 
 as it gives to the other body. The term Action is 
 applied to designate the power which a body in mo- 
 tion has to impart motion, or force, to another body ; 
 and the term Reaction to express the power which 
 the body acted upon has of depriving the acting body 
 of its force or motion. There is no motion, or action 
 without a corresponding and opposite action of equal 
 amount ; or, in other words, action and reaction are 
 always equal and opposed to each other. 
 
 Application of Power. 
 
 The principal agents from whence we obtain 
 power for practical purposes, are men and animals, 
 water, wind, steam, and gunpowder. 
 
 When work is performed by any agent, there is 
 always a certain weight moved over a certain space, 
 or resistance overcome ; the amount of work per- 
 formed, therefore, will depend on the weight, or re- 
 sistance that is moved, and the space over which it is 
 moved. For comparing different quantities of work 
 done by any force, it is necessary to have some stand- 
 ard ; and this standard is the power, or labor, ex- 
 pended in raising a pound weight one foot high, in 
 opposition to gravity. 
 
 A machine is an instrument, or apparatus, adapted 
 to receive, distribute, and apply motion derived from 
 some external force in such a way as to produce a 
 desired result ; but it cannot, under any conditions, 
 create power, or increase the quantity of power or 
 force applied to it. Perpetual motion, or the con- 
 struction of machines which shall produce power 
 sufficient to keep themselves in motion continually, is r 
 
APPLICATION OF POWER. 213 
 
 therefore, an impossibility, since no combination of ma- 
 chinery can create, or increase, the quantity of power 
 applied, or even preserve it without diminution. 
 
 The great general advantage that we obtain from 
 machinery is, that it enables us to exchange time and 
 space for power. Thus, if a man could raise to a cer- 
 tain height 200 pounds in one minute, with the 
 utmost exertion of his strength, no arrangement of 
 machinery could enable him unaided to raise 2000 
 pounds in the same time. If he desired to elevate 
 this weight, he would be obliged to divide it into ten 
 equal parts, and raise each part separately, consuming 
 ten times the time required for lifting 200 pounds. 
 The application of machinery would enable him to 
 raise the whole mass at once, but would not decrease 
 the time occupied in doing it, which would still be 
 ten minutes* 
 
 The power will overcome the resistance of the 
 weight, and motion will take place in a machine, 
 when the product arising from the power multiplied 
 by the space through which it moves in a vertical 
 direction, is greater than the product arising from 
 the weight multiplied by the space through which it 
 moves in a vertical direction. Thus if a small power 
 acts against a great resistance, the motion of the lat- 
 ter will be just as much slower than that of the 
 power, as the resistance or weight is greater than the 
 power, or if one pound be required to overcome the 
 resistance of two pounds, the one pound must move 
 over two feet in the same time that the resistance, 
 two pounds, requires to move over one. 
 
 All machines, no matter how complex and intri- 
 cate their construction, may be reduced to one or 
 more of six simple machines, or elements, which we 
 call the 
 
214 THE LEVEK. 
 
 Mechanical Powers. 
 
 The simple machines, six in number, are usually 
 denominated the lever, inclined plane, wheel and 
 axle, pulley, screw, and wedge. 
 
 The wheel and axle is, however, a revolving lever, 
 the screw a revolving inclined plane, and the wedge 
 a double inclined plane, thus reducing them to three 
 in number, viz. : lever, inclined plane, and pulley. 
 
 All these machines act on the same fundamental 
 principle of virtual velocities ; accordingly, the weight 
 multiplied into the space it moves through is equal to 
 the power multiplied into the space it moves through. 
 This is the general law which determines the equi- 
 librium of all machines ; and keeping this principle 
 in mind, there will be no difficulty in solving any of 
 the propositions appertaining to the simple machines.. 
 
 In all machines, a portion of the effect is lost in 
 overcoming the friction of the working parts; but, 
 in making calculations upon them, it is made first as 
 though no friction existed, a deduction being after- 
 wards made. And so also we have to assume a per- 
 fection in the machine itself which does not exist ; 
 that is to say, the inclined plane, screw, wedge, &c., 
 to be a perfectly smooth hard inflexible substance, 
 and the rope of the pulley, and wheel and axle, to be 
 perfectly flexible and non-elastic, conditions, for which 
 allowance has to be made after the calculation is 
 completed. 
 
 Lever. Of the lever there are three orders, as 
 shown respectively by the figures 1, 2, 3. 
 
THE LEVEK. 
 
 215 
 
 JL 
 
 A 
 
 JT 
 
 Tig-. 2 
 
 3 
 
 Fig. 3 
 
 
 
 W = weight, P = power, F = fulcrum. 
 
 EXAMPLE 1. Given the Weight W = 1000 Ibs., 
 required the power P, the lengths of the arms re- 
 spectively as marked in the figures ? 
 
 ANS. 1. P x 3 = 1000 X 1 
 3P = 1000 
 P = 333^ Ibs. 
 
 ANS. 2. P x 4 = 1000 X 1 
 4P = 1000 
 P = 250 Ibs. 
 
 ANS. 3. P X 1 = 1000 X 4 
 P = 4000 Ibs. 
 
 EXAMPLE 2. Given a compound lever with lengths 
 
 < J: X JL6 : 
 
 < 2 ) 
 
 1^^ 
 
 / 1000 Ibs. \ 
 and weight as marked in fig. 4, required the power P. 
 
216 THE LEVEE. 
 
 p X 16 = 1000 x 4 
 16p = 4000 
 
 p = 250 Ibs. = weight required at 
 p, supposing there to be but one lever therefore 
 
 P X 10 = 250 x 2 
 10P = 500 
 
 P = 50 Ibs. 
 Or, 
 
 1000 x4x2 = PxlOxl6 
 8000 = 160P 
 P= 50 
 
 EXAMPLE 3. Given, as per figure 5, a safety valve 
 
 . 5. 
 
 20 > 
 
 100 sqr. ins. area 
 
 20 Ibs. per sq. in. pressure 
 2000 Ibs. total pressure. 
 
 100 sq. ins. area, subject to a pressure per square inch 
 above the atmosphere of 20 Ibs., lengths of the long 
 and short arms of the lever as shown in the figure, 
 required the weight W to balance the pressure on the 
 valve ? 
 
 W x 25 = 100 X 20 X 5 
 25W = 10000 
 W = 400 Ibs. 
 
 EXAMPLE 4. Suppose, in example 3, the valve and 
 stem should weigh 20 Ibs., and the lever, which is 
 uniform throughout its length, weigh 2 5 Ibs., what 
 would be the weight W, in that case, to balance the 
 same pressure of steam ? 
 
 The valve and stem being 5 inches from the ful- 
 crum, act with a leverage of 5 inches, but the lever 
 being uniform, its action is the same as though the 
 
INCLINED PLANE. 
 
 217 
 
 whole weight was concentrated at x (the centre of 
 gravity) half way of its length. Wherefore 
 
 W X 25 + 20 X 5 + 25 X 12.5 = 100 X 20 X 5 
 25W + 100 + 312.5 = 10000 
 
 25 W = 10000 -412.5 
 
 W = 383.5 Ibs. the re- 
 quired weight. 
 
 Practically, the pressure a safety valve lever ex- 
 erts on the valve can be ascertained by fixing it in its 
 place, and attaching a spring balance to the pin hole 
 immediately over the valve. If the valve and weight 
 be also attached, the balance will indicate the total 
 pressure which tends to keep the valve in its seat, 
 which pressure being divided by the number of square 
 inches in the valve, will give the pressure per square 
 inch at which steam will commence to blow off. 
 
 Inclined Plane. 
 Ex. 1. Weight W 500 Ibs., 
 length, and height of the plane, 
 as per figure 6, 20 and 9 ins. $/' ^ O z> 
 
 respectively, required the pow- ^ 
 erP? 
 
 Considering the weight W to be started at the 
 base of the plane and rolled up to the top, it will 
 travel vertically the height of the plane, (9 inches), 
 while the power, P, will descend a distance equal to 
 the length of the plane (20 ins.), therefore, according 
 to the principle of virtual velocities, 
 
 P X 20 = 500 X 9 
 20P = 4500 
 P = 225 Ibs. 
 
 Ex. 2. Length and 
 height of the plane as 
 per fig. 7, weight 500 
 pounds, required the 
 
 
218 
 
 INCLINED PLANE. 
 
 power P applied in a line with the base of the 
 plane ? 
 
 In this case, when the weight will have risen from 
 the base to the top of the plane, 9 ins., the distance 
 descended by P will manifestly not be equal to the 
 length but to the base. Wherefore 
 
 Px 
 
 v' 20* -9*= 500 X 9 
 17.86P = 4500 
 
 P = 251.96 - Ibs. 
 
 In order to establish Equilibrium between the 
 weight and power, this calculation is also applicable 
 
 when the power is 
 applied in the di- 
 rection of the base 
 as shown in dots, 
 figure 7. 
 
 If the power be 
 applied at an angle 
 with the plane, as 
 C A, figure 8, in 
 order to ascertain the proportion of weight to the 
 power, to establish equilibrium, we proceed thus : 
 Draw CD, the vertical of the centre of gravity of the 
 weight, of any convenient length ; CE, at right angles 
 to BF, and DE parallel to AC. CD can represent 
 the length of the plane, and DE the height. Where- 
 fore 
 
 Weight x DE = Power x CD 
 Power = Weight x DE 
 
 "CD" 
 
 Geometrically, the angles B$C and CDE, from 
 the construction of the figure, can be demonstrated 
 to be equal, and also ECD, and BFG ; from which T 
 knowing the lengths of two legs of the triangle BFG, 
 
WHEEL AND AXLE. 
 
 219 
 
 and the angle G, to be a right angle, the lengths of 
 the lines CD ED can be determined. 
 
 Wheel and Axle. In the wheel and axle, when 
 the power is applied tangentially to the wheel, 
 
 W X radius of axle = P x radius of wheel 
 W X diameter of axle = P x diameter of wheel 
 W X circumference of axle = P x circum. of wheel. 
 
 When the power is not applied 
 tangentially to the wheel, but in the 
 direction shown in fig. 9, the length 
 of the line ab at right angles to the 
 power will give the leverage of the 
 power, hence 
 
 W x radius of axle = P x ah* 
 
 rig. 9 
 
 Pulley. If a cord be pulled at one end the ten- 
 sion throughout its whole length must be alike. 
 Taking figure 10, and supposing the power to be 1, 
 the tension throughout the entire 2 ? 
 
 length of the cord will be 1, but " 6 
 as there are two parts of the cord 
 supporting the lower block, the 
 weight must be 2. The pressure 
 on the fulcrum or support must 
 be always equal to the weight, 
 plus the power. If there be 
 more than one support, the sum 
 of the pressures on them will be 
 equal to the sum of the weight 
 and power. Or, in figure 10, 
 according to the principle of virtual velocities, the 
 weight is double the power, because the power must 
 descend 2 feet for every foot ascent of the weight. 
 
 . 1O 
 
220 
 
 THE PULLEY. 
 
 * 
 
 A 
 
 The numbers above the top blocks in all the ex- 
 amples of pulleys here shown represent the pressure 
 on the supports. 
 
 In fig. 11, the power and weight are as 1 to 8, because 
 the power supports 4 weights, each one double its size. 
 
 In fig. 12 the tension 
 on the 1st cord is 1 ; on 
 the 2d 2 ; 3d 4 ; 4th 8 ; 
 5th 16 ; and as there are 
 2 parts of the cord hav. 
 CJ)^ ing a tension of 16, the 
 weight to establish equi- 
 librium, must be 32. 
 
 In fig. 13 the weight 
 to the power is as 3 to 
 1, there being 3 parts 
 of the cord having a 
 tension of 1 supporting 
 the weight. 
 
 V c V V 
 
 oooo 
 
 Jlg-,13 
 
THE PULLEY 
 
 221 
 
 In fig. 14 the power 
 to the weight is as 1 
 to 12, the power being 
 multiplied four times 
 by the application of 
 the second set of pul- 
 leys, or luff-tackles, 
 as they are technically 
 termed. 
 
 In fig. 15 the power 
 is to the weight as 
 1 to 12, the tension 
 throughout the first 
 cord being 1 ; the sec- 
 ond cord 2 ; third 5, 
 and as there are two 
 parts of the cord hav- 
 ing a, tension of 5, and 
 one part of the cord 
 having a tension of 2, 
 supporting the weight, 
 if all the cords be 
 supposed parallel, the 
 weight must be the 
 sum of these, or 12. 
 
 In fig. 16 the power 
 to the weight is as 1 
 to 4. 
 
 In figure 17, where 
 the power is applied 
 at an angle, we ascer- 
 tain the proportion of 
 the weight and power 
 thus: Draw AD, of 
 any convenient length^ 
 and from the point A 
 draw AB parallel to 
 
 rig. 
 
222 
 
 THE PULLEY. 
 
 Cc and AC parallel to B5. The 
 power and weight will be re- 
 spectively as the lengths of the 
 lines DC or DB and AD. 
 
 Tig. 16 
 
 From which it will be seen that the greater the 
 angle CDB the longer will be the 'line DC or DB, and 
 hence the greater the power. So that the weight of the 
 line itself will be sufficient to prevent any power 
 whatever from drawing it mathematically straight 
 
 IT- 
 
 QUESTION. In figure 18, two blocks of granite, 
 joined together as shown, are laid upon a horizontal 
 plane ; required their relative sizes in order that they 
 may commence at the same time to move, and con- 
 tinue to move with equal velocity ? 
 
 ANS. 2 to 1, because the larger block is supported 
 by two parts of the cord, and has in consequence, 
 double the force exerted upon it of the smaller block. 
 
THE SCREW. 
 
 223 
 
 Screw. In the screw, 
 "p like all other simple ma- 
 chines the power X space 
 moved through = weight 
 X space moved through. 
 Ex. Length of lever 
 20 ins., pitch of screw i 
 inch, weight 500 Ibs., re. 
 quired the power P at 
 the end of the lever ? 
 ANS. PX20X 2x3.1416 
 
 = 500 X T 
 125.664P = 250 
 
 P = 1.989 Ibs. 
 
 The screw is simply a 
 revolving inclined plane, 
 the power being applied 
 parallel to the base of 
 the plane, which is repre- 
 sented by the circumfer- 
 ence described by P, and 
 the height of the plane 
 by the pitch of the screw. 
 
 Fig. 20 is a compound 
 screw. The upper screw 
 AA is fitted to the thread 
 in the nut B which re- 
 mains fixed. The cylin- 
 der AA being hollow has 
 another screw C, of a finer 
 thread, fitting into it. 
 The nut D is fixed, al- 
 lowing C to slide up and 
 down within it, without 
 
224 
 
 THE WEDGE. 
 
 turning. By this arrangement it will be seen, that 
 when the screw AA is turned once round, the distance 
 ascended by the weight will not be equal to the pitch 
 of AA, but the difference between the pitch of AA 
 andC. 
 
 EXAMPLE. Pitch of A A \ inch, of C T 7 T inch, 
 weight 16000 Ibs., required the power P, applied 20 
 inches from the centre ? 
 
 Am P x 20 X 2 x 3.1416 = 16000 X T 8 T - T V 
 125.664P = 1000 
 
 P = T.957 Ibs. 
 
 In order to multiply the power the same number 
 of times with a single screw, the pitch would have to 
 be -fa inch, which would render the thread too weak 
 to withstand a heavy pressure. 
 
 Wedge. LetWW, 
 fig. 21, be two weights 
 of 1000 Ibs. each, rest- 
 ing upon a horizontal 
 plane, required the 
 power to be applied 
 at P, to the wedge, 
 having the dimensions 
 shown in the figure to 
 to separate them ? 
 
 P X 20 = 1000 X 2 
 20P = 2000 
 P = 100 Ibs. 
 
 Because, when the power P has descended to the 
 point A, the weights have been separated 2 inches 
 while the power has travelled 20 inches, the length 
 of the wedge. 
 
 -p. 
 
GRAVITY. 
 
 225 
 
 Centre of Gravity. 
 
 The centre of gravity of a cone from the vertex 
 equals |- the axis. 
 
 In a paraboloid, the distance from vertex equals -J 
 the axis. 
 
 In a parabolic space, equals -f- the axis from the 
 vertex. 
 
 In a triangle, equals f the axis from the vertex. 
 
 Centre of Pressure. 
 
 The centre of pressure of a parallelogram, when 
 the upper surface is level with the water, = \ from the 
 bottom ; of a right-angled triangle with 
 the base down = \ from the bottom, 
 measured on the perpendicular line 
 B C ; with the base up = B C. See 
 Hanris Mechanics. 
 
 Semi-parabolic plane. 
 
 FORMULA : 
 m =. centre of pressure, 
 
 I m = -f- of a c, 
 m n = T 5 T of a d. 
 
 Gravity. 
 
 The spaces described by a body acted upon freely 
 by gravity are as the squares of the times ; i. e., a body 
 falling 2 seconds, will describe 4 times the distance of 
 
226 GRAVITY. 
 
 a body falling one second. Hence, in order to ascer- 
 tain the distance fallen by a body, it is only necessary 
 to multiply the square of the number of seconds by 
 the distance fallen in the first second ; the product will 
 be the total distance fallen. 
 
 All bodies fall with the same velocity in vacuo, 
 namely, 16.08 feet in the first second, having a velocity 
 of 32.166 feet at the end of the second. Where the 
 atmosphere is interposed, the velocity will be some- 
 what less, say for heavy bodies, such as the metals, 16 
 feet for the first second. 
 
 EXAMPLE. Which will strike with the greater 
 effect, a weight of 200 Ibs., falling through 144 ft., or 
 100 Ibs. falling through 256 feet ? 
 
 The velocity of a body at the end of a fall is equal 
 to the number of seconds it is falling, multiplied into 
 (32 feet) the velocity at the end of the first second, 
 and the momentum of a body is equal to the weight 
 multiplied into the velocity. We have, then, first to 
 find the velocity, and afterwards the momentum. 
 
 v/16 : 1 : : N/144 : 3 seconds time of falling of 200 Ib. 
 vT6 : 1 : : v/2^6 : 4 " " 100 Ib. 
 
 32 x 3 = 96 ft. per second velocity at end of fall 
 
 of 200 Ib. weight. 
 32x4 = 128 ft. per second velocity at end of fall 
 
 of 100 Ib. weight. 
 
 96x200=19200= momentum of the 200 Ib. weight. 
 128x100=12800= momentum of the 100 Ib. weight. 
 "6400= difference, which is 33^- per cent 
 of the larger number. 
 
DISPLACEMENT OF FLUIDS. 227 
 
 Centre of Gravity of Several Bodies taken together. 
 
 Suppose there be several weights placed as follows 
 in the same plane, required the centre of gravity of 
 them all taken together ? 
 
 Cylinder. Air-pump. Shaft. Boilers. 
 
 Tons. Tons. Tons. Tons. 
 
 5 2 10 30 
 
 <: 8ft. x 10ft x 20ft. > a 
 
 Assume a point ($), at any distance (say 2 feet) 
 from either of the extreme weights, and multiply each 
 weight separately by its distance from this point ; the 
 sum of these products, divided by the sum of the 
 weights, will be the distance of the centre of gravity 
 from the assumed point. Thus : 
 
 30 X 2 = 60 
 10 X 22 = 220 
 
 2 x 32 = 64 
 
 5 X 40 = 200 
 
 47 ) M4 (11. 5T ft, = centre of 
 
 gravity from the point a, or 9.57 feet from the boilers 
 towards the shaft. 
 
 Displacement of Fluids. 
 
 Solid bodies immersed in fluids will displace an 
 amount of the fluid equal to their own weight. If the 
 specific gravity of the body be greater than that of 
 the fluid, it will sink ; otherwise it will float. 
 
 EXAMPLE. Required the distance a cube of cherry, 
 one foot high, will sink in fresh water ? 
 
 The specific gravities of fresh water and cherry are 
 relatively as 1.00 to .606 ; the cherry will therefore 
 sink .606 feet. 
 
228 FORCE, TEMPERATURE, AND VOLUME OF STEAM. 
 
 Table of the Elastic Force, Temperature, and Volume of Steam, from a 
 Temperature of8Qto 387.3, and from a Pressure of one to 410 Inches 
 of Mercury. 
 
 Elastic force in 
 
 Tempera- 
 ture. 
 
 Volume. 
 
 Elastic force in 
 
 Tempera- 
 ture. 
 
 Volume. 
 
 inches of 
 mercury. 
 
 pounds per 
 sq. inch. 
 
 nches of 
 mercury. 
 
 >ounds per 
 sq. inch. 
 
 1 
 
 .49 
 
 80 
 
 41031 
 
 53.04 
 
 26 
 
 243.3 
 
 1007 
 
 1.17 
 
 .573 
 
 85 
 
 35393 
 
 55.08 
 
 27 
 
 245.5 
 
 973 
 
 1.36 
 
 .666 
 
 90 
 
 30425 
 
 57.12 
 
 28 
 
 247.6 
 
 941 
 
 1.58 
 
 .774 
 
 95 
 
 26686 
 
 59.16 
 
 29 
 
 249.6 
 
 911 
 
 1.86 
 
 .911 
 
 100 
 
 22873 
 
 61.2 
 
 30 
 
 251.6 
 
 883 
 
 2.04 
 
 1 
 
 103 
 
 20958 
 
 63.24 
 
 31 
 
 253.6 
 
 857 
 
 2.18 
 
 1.068 
 
 105 
 
 19693 
 
 65.28 
 
 32 
 
 255.5 
 
 833 
 
 2.53 
 
 1.24 
 
 110 
 
 16667 
 
 67.32 
 
 33 
 
 257.3 
 
 810 
 
 2.92 
 
 1.431 
 
 115 
 
 14942 
 
 69.36 
 
 34 
 
 259.1 
 
 788 
 
 3.33 
 
 1.632 
 
 120 
 
 13215 
 
 71.4 
 
 35 
 
 260.9 
 
 767 
 
 3.79 
 
 1.857 - 
 
 125 
 
 11723 
 
 73.44 
 
 36 
 
 262.6 
 
 748 
 
 4.34 
 
 2.129 
 
 130 
 
 10328 
 
 75.48 
 
 37 
 
 264.3 
 
 729 
 
 5 
 
 2.45 
 
 135 
 
 9036 
 
 77.52 
 
 38 
 
 265.9 
 
 712 
 
 5.74 
 
 2.813 
 
 140 
 
 7938 
 
 79.56 
 
 39 
 
 267.5 
 
 695 
 
 6.53 
 
 3.1 
 
 145 
 
 7040 
 
 81.6 
 
 40 
 
 269.1 
 
 679 
 
 7.42 
 
 3.636 
 
 150 
 
 6243 
 
 83.64 
 
 41 
 
 270.6 
 
 664 
 
 8.4 
 
 4.116 
 
 155 
 
 5559 
 
 85.68 
 
 42 
 
 272.1 
 
 649 
 
 9.46 
 
 4.635 
 
 160 
 
 4976 
 
 87.72 
 
 43 
 
 273.6 
 
 635 
 
 10.68 
 
 5.23 
 
 165 
 
 4443 
 
 89.76 
 
 44 
 
 275 
 
 622 
 
 12.13 
 
 5.94 
 
 170 
 
 3943 
 
 91.8 
 
 45 
 
 276.4 
 
 610 
 
 13.62 
 
 6.67 
 
 175 
 
 3838 
 
 93.84 
 
 46 
 
 277.8 
 
 598 
 
 15.15 
 
 7.42 
 
 180 
 
 3208 
 
 95.88 
 
 47 
 
 279.2 
 
 586 
 
 17 
 
 8.33 
 
 185 
 
 2879 
 
 97.92 
 
 48 
 
 280.5 
 
 573 
 
 19 
 
 9.31 
 
 190 
 
 2595 
 
 99.96 
 
 49 
 
 281.9 
 
 564 
 
 21.22 
 
 10.4 
 
 195 
 
 2342 
 
 102 
 
 50 
 
 283.2 
 
 554 
 
 23.64 
 
 11.58 
 
 200 
 
 2118 
 
 104.04 
 
 51 
 
 284.4 
 
 544 
 
 26.13 
 
 12.7 
 
 205 
 
 1932 
 
 106.08 
 
 52 
 
 285.7 
 
 634 
 
 28.84 
 
 14.13 
 
 210 
 
 1763 
 
 108.12 
 
 53 
 
 286.9 
 
 525 
 
 29.41 
 
 14.41 
 
 211 
 
 1730 
 
 110.16 
 
 54 
 
 288.1 
 
 516 
 
 30 
 
 14.7 
 
 212 
 
 1700 
 
 112.02 
 
 55 
 
 289.3 
 
 508 
 
 30.6 
 
 15 
 
 212.8 
 
 1669 
 
 114.24 
 
 56 
 
 290.5 
 
 500 
 
 31.62 
 
 15.5 
 
 214.5 
 
 1618 
 
 116.28 
 
 57 
 
 291.7 
 
 492 
 
 32.64 
 
 16 
 
 216.3 
 
 1573 
 
 118.32 
 
 58 
 
 292.9 
 
 484 
 
 38.66 
 
 16.5 
 
 218 
 
 1530 
 
 120.36 
 
 59 
 
 294.2 
 
 477 
 
 34.68 
 
 17 
 
 219.6 
 
 1488 
 
 122.4 
 
 60 
 
 295.6 
 
 470 
 
 35.7 
 
 17.5 
 
 221.2 
 
 1440 
 
 124.44 
 
 61 
 
 296.9 
 
 463 
 
 36.72 
 
 18 
 
 222.7 
 
 1411 
 
 126.48 
 
 62 
 
 298.1 
 
 456 
 
 37.74 
 
 18.5 
 
 224.2 
 
 1377 
 
 128.52 
 
 63 
 
 299.2 
 
 449 
 
 38.76 
 
 19 
 
 225.6 
 
 1343 
 
 130.56 
 
 64 
 
 300.3 
 
 443 
 
 39.78 
 
 19.5 
 
 227.1 
 
 1312 
 
 132.62 
 
 65 
 
 301.3 
 
 437 
 
 40.80 
 
 20' 
 
 228.5 
 
 1281 
 
 134.64 
 
 66 
 
 302.4 
 
 431 
 
 41.82 
 
 20.5 
 
 229.9 
 
 1253 
 
 136.68 
 
 67 
 
 303.4 
 
 425 
 
 42.84 
 
 21 
 
 231.2 
 
 1225 
 
 138.72 
 
 68 
 
 304.4 
 
 419 
 
 43.86 
 
 21.5 
 
 232.5 
 
 1199 
 
 140.76 
 
 69 
 
 305.4 
 
 414 
 
 44.88 
 
 22 
 
 233.8 
 
 1174 
 
 142.8 
 
 70 
 
 306.4 
 
 408 
 
 45.90 
 
 22.5 
 
 235.1 
 
 1150 
 
 144.84 
 
 71 
 
 307.4 
 
 403 
 
 46.92 
 
 23 
 
 236.3 
 
 1127 
 
 146.88 
 
 72 
 
 308.4 
 
 398 
 
 46.94 
 
 23.5 
 
 237.5 
 
 1105 
 
 148.92 
 
 73 
 
 309.3 
 
 393 
 
 48.96 
 
 24 
 
 238.7 
 
 1084 
 
 150.96 
 
 74 
 
 310.3 
 
 388 
 
 4<>.98 
 
 24.5 
 
 239.9 
 
 1064 
 
 153.02 
 
 75 
 
 311.2 
 
 383 
 
 51. 
 
 25 
 
 241 
 
 1044 
 
 155.06 
 
 76 
 
 312.2 
 
 379 
 
FORCE, TEMPERATURE, AKD VOLUME OF STEAM. 
 
 Elastic force in 
 
 Tempera- 
 
 
 Elastic force in 
 
 Tempera- 
 
 
 inches of 
 mercury. 
 
 pounds per 
 sq. inch. 
 
 ture. 
 
 V 01UID6. 
 
 inches of 
 mercury. 
 
 pounds per 
 sq. in. 
 
 ture. 
 
 Volume. 
 
 157.1 
 
 77 
 
 313.1 
 
 374 
 
 254.99 
 
 125 
 
 349.1 
 
 240 
 
 159.14 
 
 78 
 
 314 
 
 370 
 
 265.19 
 
 130 
 
 352.1 
 
 233 
 
 161.18 
 
 79 
 
 314.9 
 
 366 
 
 275.39 
 
 135 
 
 355 
 
 224 
 
 163.22 
 
 80 
 
 315.8 
 
 362 
 
 285.59 
 
 140 
 
 357.9 
 
 218 
 
 165.26 
 
 81 
 
 316.7 
 
 358 
 
 295.79 
 
 145 
 
 360.6 
 
 210 
 
 167.3 
 
 82 
 
 317.6 
 
 354 
 
 306 
 
 150 
 
 363.4 
 
 205 
 
 169.34 
 
 83 
 
 318.4 
 
 350 
 
 316.19 
 
 155 
 
 366 
 
 198 
 
 171.38 
 
 84 
 
 319.3 
 
 346 
 
 326.39 
 
 160 
 
 368.7 
 
 193 
 
 173.42 
 
 85 
 
 320.1 
 
 342 
 
 336.59 
 
 165 
 
 371.1 
 
 187 
 
 183.62 
 
 90 
 
 324.3 
 
 325 
 
 346.79 
 
 170 
 
 373.6 
 
 183 
 
 193.82 
 
 95 
 
 328.2 
 
 310 
 
 357 
 
 175 
 
 376 
 
 178 
 
 203.99 
 
 100 
 
 332 
 
 295 
 
 367.2 
 
 180 
 
 378.4 
 
 174 
 
 214.19 
 
 105 
 
 335.8 
 
 282 
 
 377.1 
 
 185 
 
 380.6 
 
 169 
 
 224.39 
 
 110 
 
 339.2 
 
 271 
 
 387.6 
 
 190 
 
 382.9 
 
 166 
 
 234.59 
 
 115 
 
 342.7 
 
 259 
 
 397.8 
 
 195 
 
 384.1 
 
 161 
 
 244.79 
 
 120 
 
 345.8 
 
 251 
 
 408 
 
 200 
 
 387.3 
 
 158 
 
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22 SCIENTIFIC BOOKS PUBLISHED BT 
 
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D. VAN NOSTRAXD. 
 
 RECENT WORKS. 
 
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 1012 pages. 8vo. Cloth, $7.50. Half morocco. $10.00. 
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