106 MOTIVE POWER OF HEAT. 



We will examine another case in which vapor of 

 alcohol is acted upon by heat. The reasoning is 

 precisely the same as for the vapor of water. The 

 data alone are changed. Pure alcohol boils under 

 ordinary pressure at 78.7 Centigrade. One kilo- 

 gram absorbs, according to MM. Delaroche and 

 Berard, 207 units of heat in undergoing transfor- 

 mation into vapor at this same temperature, 78.7. 



The tension of the vapor of alcohol at one de- 

 gree below the boiling-point is found to be dimin- 

 ished -gig-. It is 2^ less than the atmospheric 

 pressure ; at least, this is the result of the experi- 

 ment of M. Betancour reported in the second part 

 of V Architecture hydraulique of M. Prony, pp. 

 180, 195.* 



If we use these data, we find that, in acting upon 

 one kilogram of alcohol at the temperatures of 

 78. 7 and 77. 7, the motive power developed will 

 be 0.251 units. 



This results from the employment of 207 units 

 of heat. For 1000 units the proportion must be 



207 1000 



0.254 



whence x = 1.230. 



estimate leads us to attribute a great advantage to atmos- 

 pheric air, but it is derived by a method of considering the 

 action of heat which is quite imperfect. 

 * Note F, Appendix B. 



