810 Transactions of the American Institute. 



the Boston engine. The first cylinder cuts off at half stroke. 

 jNow, I will agree to take the power thrown away at that first 

 cylinder, and, by carrying the expansion up to its limit, obtain 

 all the power that is obtained from the bi-sulphide of carbon, and 

 at a less expense. The same principle will apply in every step, begin- 

 ning with mercury, if you please. Here is the mercury diagram, 

 expanding right down to the line. That fills a cylinder of a certain 

 size. Exhaust that into another cylinder, and it will require so much 

 the more area. You can go on indefinitely ; but you are merely sav- 

 ing the power you have thrown away. I admit that increasing the 

 pressure, the same difference of temperature produces a greater differ- 

 ence of pressure ; but we must take into consideration that if we 

 increase the pressure six times we have only one-sixth the volume, and 

 it requires six times as many units of heat to change the temperature ; 

 so that when we come to calculate the power of the engine, the effect 

 is the same in both cases. If you expand steam, under a pressure of 

 sixty pounds, the effect will be the same as expanding it in a cylinder 

 of four times the area under a pressure of fifteen pounds. It seems 

 to me that the whole thing is explained by the principle stated by 

 Dr. Tan der "Weyde at the outset of his remarks, that whatever the 

 liquid, it takes the same number of units of heat to make the same 

 volume. Consequently there cannot possibly be any economy in 

 using different fluids. 



Dr. Van der Weyde — The gentleman mixed up latent heat and 

 temperature. The latent heats are alike, but not the temperatures. 



Mr. John B. Root — You leave out of view the fact that you can- 

 not increase the volume ; that you cannot make any more volume 

 with the same amount of heat, from bi-sulphide of carbon than from 

 steam ; and unless you can make a great volume, you cannot make a- 

 greater pressure. 



The President — The chair understood Dr. Van der Weyde to take 

 the same ground, with regard to volume, at first. 



Dr. Yan der Weyde — The latent heat required to change a liquid 

 into vapor is entirely independent of the temperature at which it 

 boils. Steam at 212° coming in contact with bi-sulphide of carbon, 

 which boils at 110°, the bi-sulphide of carbon will flash into vapor. 

 This will condense the steam into water; and 9GG units of latent 

 heat will be given out, of which 190 units will be absorbed by every 

 pound of the bi-sulphide of carbon, and produce some four atmos- 

 pheres pressure in exchange for the waste steam without pressure. 

 The advantage is in favor of the bi-sulphide of carbon, at every step. 



