1 88 Albert P. Mathews 



Table IV is a summary of the values of C computed for 

 forty-one other substances, of many of which the critical 

 data are not so accurately known as those included in Table 

 III. Since for most of these substances d c and V c were not 

 given in the lyandolt-Bornstein-Meyerhoffer tables, I com- 

 puted V c by the formula V C P C /T C == 21.92 and then M 2 K 

 by the formula M 2 K 3.594 X icT 40 V C T C . The values of 

 V c so computed are of course not so accurate. Wherever 

 the critical volume or density was given it was used. In a 

 few cases, which are specified, M 2 K was obtained by dividing 

 the value of "a," given by Guye and Mallet, by N 2 , i. e., 

 (2.77 X io 19 ) 2 . 



While the values are thus less certain and the deviations 

 somewhat greater, the mean value of all is what it was for the 

 other substances, i. c., C 2.98 X io" 37 . The values are 

 surprisingly uniform. It will be noticed that the more com- 

 plex substances such as diphenyl and diphenyl methane have 

 C a little high. This may possibly be due to slight associa- 

 tion or quasi-association in these substances With this 

 and one or two other exceptions the uniformity of C is marked. 



All substances known to be associating give a value 

 for C higher than 2.98 X io~ 37 when M 2 K is computed by 

 the same formulas as for normal substances, and the weight 

 and valence used in computing C are those of the normal 

 non-associated molecule. This result is to be anticipated, 

 since in these substances the molecular weight and valence 

 do not remain the same throughout the temperature interval. 

 The computation of M 2 K from the critical data is uncertain 

 in the case of associating substances for the reason that there 

 is no certainty that the coefficients of the formulas are the 

 same for these substances as for normal substances. Although 

 the figures for M 2 K are thus uncertain, I have nevertheless 

 calculated M 2 K by the usual formula in order to show that 

 these substances deviate in the direction we should expect 

 from the value of C found in normal substances. The re- 

 sults are given in Table V : 



