471 



the outer steam-bath, and, in consequence, the column in the globe 

 stem rose, and that in the outer tube fell, the difference of level 

 forming a measure of the expansion of the steam. Observations of 

 the levels of the columns were made by means of a cathetometer at 

 different temperatures, up to 10 or 20 above the saturation point ; 

 and the maximum temperature of saturation was, for reasons deve- 

 loped by the experiments, deduced from a point at which the steam 

 was decidedly superheated. 



The results of the experiments, which in the paper are given in 

 detail, show that the density of saturated steam at all temperatures, 

 above as well as below 212, is invariably greater than that derived 

 from the gaseous laws. 



.The apparatus for the experiments at pressures below that of the 

 atmosphere was considerably modified ; and the condition of the steam 

 was determined by comparing the column which it supported with 

 that of a barometer. The results of these experiments, reduced in 

 the same way, are extremely consistent. 



As the authors propose to extend their experiments to steam of a 

 very high pressure, and to institute a distinct series on the law of 

 expansion of superheated steam, they have not at present given any 

 elaborate generalizations of their results. The following formulae, 

 however, represent the relations of specific volume and pressure of 

 saturated steam, as determined in their experiments, with much 

 exactness. 



Let V be the specific volume of saturated steam, at the pressure P, 

 measured by a column of mercury in inches ; then 



. . . . (2.) 



49513 





V-25-62 



In regard to the rate of expansion of superheated steam, the ex- 

 periments distinctly show that, for temperatures within about ten 

 degres of the saturation point, the rate of expansion greatly exceeds 

 that of air, whereas at higher temperatures the rate of expansion 

 approaches very near that of air. Thus in experiment 6, in which 

 the maximum temperature of saturation is 174'92, the coefficient of 

 expansion between 174- 92 and 180 is yj^, or three times that of 

 air ; whereas between 180 and 200 the coefficient is very nearly the 



