76 Mr. J. Kam on Molecular Attraction and 



The accuracy of equation (20), 



2p c . v c = 1, 



is sufficiently demonstrated by the figures of the larger 

 Table * (I.), in which will be found the experimental and 

 'calculated values of 



p ° = i; 



In the smaller Table f (II.) the values of (equation 23 b) 

 273 

 2.p c .v c . 7^- = constant are calculated for gases whose 



-»-c 



critical temperatures are below 273 (0° C.)t- Though the 

 values thus obtained are smaller than 1, they are re- 

 markably constant and equal to about *75, with the exception 

 of air, which shows a value of '69. But the latter is a 

 mixture. 



The constancy is such that the deviation from the value 1 

 must have a general cause. It is conceivable that at the 

 extremely low temperatures of the critical state the co- 

 volume J3 adopts a relatively smaller value. In any case, 

 the fact that the mono-atomic gases with extremely low 

 critical temperatures fall into line with hydrogen, nitrogen, 

 oxygen, CO, CH 4 , and NO deserves attention. 



Deduction of c Q =^v e = b r ct c =^<P c = ot from the corre- 

 sponding equations (Dj) and (E) leads at once to 



P + -,= l (D 2 ) 



and 



^H- ••••••• cm 



It will also be of interest to compare the value of c 

 (eq. 17) and p (eq. 19) with a few experiments. 



* Landolt-Bornstein, ' Physikalische Tabellen,' Berlin, 1905, pp. 181- 

 186. Values marked * are borrowed from U. Winkelmann, ' Handbuch 

 der Physik,' vol. Hi. Leipzig 1 , 1906, pp. 859-868. 



t G. W. C. Kaye & F. H. Laby, ' Physical and Chemical Constants,' 

 1911, p. 34, 



973 3 

 f p . v . -~r- = ~ as found by van der Waals is for such gases evidently 

 -* ° ° ±c 8 



more in correspondence with the experimental values. 



