12 Reynolds, Dryness of Saturated Steam. 



in Rankine's formula, the constant C x is found to be 

 not 1092, as given by Rankine, but between 1076*4 and 

 1053*7, with a mean of about 1055. Taking this value, 

 the heat necessary to raise water from 32 0 to 248°F. 

 at constant pressure of I4*7lbs. per square inch is 



1055+0*48 (2i6) = ii58*68 



To raise water from 32 0 to saturated steam at 21 2° requires 

 by Regnault's formula for total heat of saturated steam 



i09i*7-{-'305 (180) = 1146*6 



Hence, to raise saturated steam from 212 0 to 248 0 at con- 

 stant pressure would require 12*08 T.U., which, divided 

 by the difference of temperature, gives for the mean 

 specific heat of steam from saturation at 212° to 248°F. 

 at constant pressure 



12*08 



which shows that the specific heat, at constant pressure, 

 of steam rises with the temperature. And this, although 

 in accordance with the results obtained by Regnault for 

 other vapours, presents great thermo-dynamical diffi- 

 culties ; since many experiments have shown that the 

 steam, on being heated from saturation to 36°F. above, 

 expands three or four times as much as it would if it 

 were gas. It is to be noticed that an error of 3% in 

 estimating the total quantity of steam, which in these 

 experiments would only mean an error of 



0*0004 



in the actual weighings, would account for the differences 

 in the values of Ci as determined by Rankine and as esti- 

 mated from Regnault's experiment on specific heat, while 

 such an error on the determination of the specific heat 

 would fall within the limits of experimental accuracy. 

 It thus seems probable that Rankine's determinations of 

 the constants in his formula are approximately right. 



