and the Critical Volumes of Liquids. 

 Sarrau's Calculated Yalues. 



215 





T, 

 Critical 



temperature. 



P, 



Critical 

 pressure. 



T 

 P' 



Hydrogen. 



o 

 -174 



-105-4 



-124 



989 



48-7 

 42-1 



10 

 3-4 

 3-5 



Oxygen 



Nitrogen 





It will be observed that the calculated critical temperatures 

 of oxygen and nitrogen are remarkably near the truth, being 

 respectively 8° and 22° too high. On the other hand, the 

 values of the ratios of the calculated critical temperatures and 

 pressures are almost identical with those obtained by direct 

 experiment. The only peculiarity to be noted is in the case 

 of hydrogen, which has such a high critical pressure, and 

 therefore leads to a remarkably small molecular volume at 

 the critical point. If the values of the T-s-P ratio be taken 

 as proportional to the molecular volumes, then it is easy to 

 infer the densities of the fluids at their respective critical tem- 

 peratures, provided the density of one standard substance is 

 known by experiment. The simple formula thus stated is 



S MV r V" 

 where S and S' are the specific gravities of two bodies, W 

 and W their molecular weights, and V and V / their molecular 

 volumes* It will be convenient to take the density of car- 

 bonic acid at the critical point as the standard density to 

 which the others can be referred. The density of carbonic 

 acid under such conditions maybe taken as 0'65. Calculating 

 with the above formula, the density of acetylene would be 

 032, whereas the experimental number of Ansdell is 0*36. 

 In the same way the density of hydrochloric acid is found to 

 be 0*6, the true value being 061. The density of oxygen 

 would be 0*63, and that of nitrogen 0*45. The calculated 

 density of hydrogen at its critical point would be 0*12, if we 

 assume the correctness of Sarrau's values for the critical tem- 

 perature and pressure. We may compare these values with 

 the numbers obtained by Cailletet and Hautefeuille for the 

 densities of oxygen, nitrogen, and hydrogen from their expe- 

 riments on the density of liquid carbonic acid obtained 

 from mixtures of this body with these gases. At the tempera- 

 ture of 0° C. the experiments found for oxygen, nitrogen, and 

 hydrogen the respective values of 0'65, 037, and 0'025. It 



