Properties of Gases and Vapours, &c. 



281 



values of the total heat and latent heat, and of the rate of variation of 

 the saturation pressure and the total heat with temperature, namely 

 dp /dO (sat.), and dH/dO. It will be observed that the rate of increase 

 of the total heat diminishes rapidly at high temperatures, while the 

 rate of diminution of the latent heat increases. This must necessarily 

 be the case, as the latent heat should vanish near the critical tem- 

 perature, which occurs about 365 C., according to the observations of 

 Cailletet and Colardeau, whereas the linear formula of Regnault would 

 make the latent heat vanish at about 870 C. This is an additional 

 indication of the impossibility of Eegnault's formula. It may be 

 observed, however, that the average rate of increase of the total heat, 

 according to Table III between 100 and 200 C., over the range of 

 Regnault's experiments from which the linear formula (1) was calcu- 

 lated, is only 0'330 calorie per degree, which differs so little from the 

 coefficient O305 given by Regnault as to be well within the limit of 

 accuracy of his experiments, considering the acknowledged leakage of 

 the distributing tap, and that the whole difference is only one-half 

 of 1 per cent, on the quantity of heat measured. 



The values of dp/dO, given in column 6 of the table, are calculated 

 from those of L by means of the thermodynamic relation (3) already 

 quoted, assuming the values of the specific volume from Table I. 



Table III. Total Heat and Latent Heat of Steam in terms of the 

 Thermal Capacity of Water at 20 C. 



