1862.] 53 



April 3, 1862. 

 Major-General SABINE, President, in the Chair. 



The following communications were read : 



I. "On the Law of Expansion of Superheated Steam/' By 

 WILLIAM FAIRBAIRN^ Esq., LL.D., F.R.S., and THOMAS 

 TATE, Esq. Received March 20, 1862. 



(Abstract.) 



In a former paper selected for the Bakerian Lecture, entitled 

 "Experimental Researches to determine the Density of Steam at 

 different Temperatures, and to ascertain the Law of Expansion of 

 Superheated Steam " (Phil. Trans. I860, p. 185), it was shown that 

 although Dumas, Gay-Lussac, and other distinguished physicists 

 had determined the density of steam at 212, it was, however, left for 

 these researches to ascertain the law of density, volume, &c. at all 

 temperatures, and also the law of expansion of superheated steam. 

 These experiments have therefore been continued, and have elicited 

 remarkable results as regards the rate of expansion at various tempe- 

 ratures. 



The earliest experiments on this subject were made by Mr. Frost 

 in America, but without sufficient accuracy to be of scientific value. 

 Mr. Siemens has also experimented on steam isolated from water ; 

 his results give a much higher rate of expansion for steam than for 

 ordinary gases ; but, owing to some obvious defects of Mr. Siemens's 

 method of conducting the experiments, we consider his results are 

 not reliable. 



For gases, the rate of expansion is expressed by the formula for 

 constant volume, 



where E is a constant determined by experiment, and decided by 

 Regnault as 459 in the case of air. In the paper alluded to, it was 

 shown that, with a certain proviso, the rate of expansion of super- 

 heated steam nearly coincided with that of air. Within a short 



