506 TRANSACTIONS OP THE AMERICAN INSTITUTE, 



and cranks at each one-eighth of a revolution, showing the manner 

 in which the air was received, expanded and discharged ; and 

 showed by means of another diagram the theoretical pressure at 

 each of these positions. 



Mr. Dibben wished to know if that diagram exhibited the prac- 

 tical working pressure ? 



Mr. Babcock. — These figures are reduced in practice by the 

 lost space and other elements, perhaps from 25 to 30 per cent ; 

 that the pressure is slightly above the atmosphere when exhausted 

 is shown by a puff which may be distinctly noticed. The pres- 

 sure therefore must have been within 30 per cent of these figures 

 to have produced this result. 



Mr. Garvey. — Do you take in one volume of air and expand it 

 to two ? 



Mr. Babcock. — Yes. It requires about 600" to double the vol- 

 ume of air at ordinary temperatures. In practice this is usually 

 attained. 



The Chairman. — What name did the economizer go by first? 



Mr. Babcock. — Stirling called it a "regenerator," but Mr. Wil- 

 cox calls it an economizer, as more properly indicating its office. 



The Chairman asked why air was a more economical power 

 than steam, when its expansion was so much less ? 



Mr. Babcock. — The specific heat "of air being about one quarter 

 that of steam or water the same amount of heat produces a 

 greater expansion. 



The Chairman asked if this engine was more economical as 

 regards fuel than steam ? 



Mr. Babcock said that it was more economical than steam en- 

 gines of the same power. It was perfectly safe. 



The Chairman thought that great economy might yet be real- 

 ized in the working of locomotive engines. He thought that en- 

 gineers would yet be paid in proportion to the amount of work 

 performed, and the saving of fuel. The Wilcox engine is capable 

 of running light at 200 revolutions per minute. It performs to 

 the best advantage from 100 to 140 revolutions per minute. 



Mr. Seeley said that the same heat which would heat water to 

 100° would heat the same weight of air to 4,000". One pound of 

 water is 2*7 cubic inches, expand it to steam, and it occupies 27 

 cubic feet. One pound of air occupies 13 cubic feet. The same 

 heat which would expand one pound of water to 27 cubic feet 

 would expand one pound of air to 104 cubic feet. He then went 



