1 882. Ill Trans. N. Y.Ac. Set. 



lo. The theories proposed by Berthelot, Daddow, Byasson, and 

 Mendelejeff, for the genesis of petroleum, are the results of specula- 

 tion in the study or irrelevant experiments in the laboratory, and have 

 no confirmation or illustration in the facts of nature. 



February 13, 1S82. 



Section of Physics. 



The President, Dr. Newberry, in the Chair. 



Forty persons present. 



Prof. Robert H. Thurston read a paper,' entitled 



ON THE BEHAVIOR OF STEAM IN THE STEAM-ENGINE CYLINDER, 

 AND ON CURVES OF EFFICIENCY. 

 (Abstract.) 

 In an earlier paper^ the writer had shown what are the conditions 

 determining the ratio of expansion in steam engines working at maxi- 

 mum efticiency, and how those conditions vary in different types of 

 engine, and also how essentially different is the actual working engine, 

 in all that effects that ratio, from the hypothetical case usually taken, 

 in which the steam is assumed to expand adiabatically in a non-con- 

 ducting steam-cylinder. It was finally shown what were the best val- 

 ues of this ratio for several standard types and representative cases, as 

 determined by the writer by direct observation and by the study of 

 experimentally obtained results, the precise figures given being obtained 

 by rules of simple form so deduced. 



It was shown that first friction and then — often to a vastly greater 

 extent — cylinder condensation, due to expansion of a heated fluid in a 

 working cylinder made of a material of high conducting power, modify 

 the methods of expansion and of expenditure of heat so greatly that 

 the ratio of expansion for maximum efficiency, in unjacketed en- 

 gines, rarely exceeds X\/ A where P is the gauge pressure in pounds 

 per square inch, although its value would otherwise be, often, several 

 times greater. It was also shown that these modifying conditions very 

 differently affect different kinds of steam engine, and different engines, 

 and also individual engines, at various pressures and piston speeds. 



In this paper it was proposed to show more fully what is the behav- 

 ior of steam in the steam-engine cylinder and to exhibit the form taken 

 by the expansion-line ; to give values of mean pressures obtained under 



1 Published in full in the Journal of the FraDklin Institute, February, 1882. 



"^ On the Ratio of Expansion at Maximum Efficiency in Steam Engines ; Trans. Am. See. 

 Mech. Engrs., i83i ; Jour. Franklin Institute, May, 1881. 



