478 A. P. Mathews 



Using the critical data of T c = 32.3 and P 13 atmospheres 

 as found by Olszewski; and d c as 0.033 as determined by 

 Dewar, the critical coefficient S, where S = RT C /P C V is 

 equal to 2.860. This value of S is, however, much lower than 

 that of any other substance. Thus for O 2 , S is 3.5; for N 2 , 

 3.6; for N 2 O, 3.4 and even for helium it is 3.13 according to 

 Onnes. It is probable then that 2.86 is too low. The critical 

 temperature and pressure have recently been determined by 

 Buller 1 who finds T c = 31.95; P c = n. With these values 

 and d c = 0.033 S computes 3.903, which is higher even than 

 such complex substances as octane and is clearly too high. 

 If S is calculated by my formula which gives a result within 

 1-2 percent in most cases, namely, S 2 = R(Wi - - d^T^ 3 /- 

 (T c T) 1/3 MP using Buller's values for P c and T c and 

 taking d\ as that of hydrogen at the melting point [ 258.9 

 (Travers)] as 0.086 (Dewar) and disregarding the value of d v 

 at that temperature then S is computed as 3.517. If P c were 

 11.5 atmospheres, and the uncertainty is at least half an 

 atmosphere, S would be 3.365. I believe S of hydrogen may 

 be taken as approximately that of oxygen or as 3.4. If S 

 is assumed to be 3.4 then with P c n and d c 0.033, 

 a = (S 2 S + 2)/(S 2) P C V 2 C = 0.301 X io 12 . Dividing 

 this by N 2 where N = 6.062 X io 23 , M 2 K for hydrogen would 

 be 8.191 X io~ 37 from which C is found to be 3-23 X io~ 37 . 

 If, however, S = 3.4 and P c 13, then "a" would be 0.317 X io 12 , 

 M 2 K, 8.626 X io- 37 and C would be 3-45 X io~ 37 . Since 

 from Buller's results it is probable that P c should be lower than 

 13 atmospheres, the value for M 2 K is probably not far from 

 correct so that C should be very nearly 3.23 X io~ 37 . 



Another simple substance from which a calculation of 

 C might be made is methane, since the amount of its residual 

 valence is certainly small and the total number of valences 

 per molecule is very nearly 8. Unfortunately the critical 

 density of methane is unknown and T c and P c have not been 

 recently determined. However, if T c is 191.2 and P c is 54.9 



1 Buller: Phys. Zeit., 14, 860-2 (1913). 



