56 



THE TRUE VALUE OF a OF VAN DER WAALS' 



erature and pressure, with the values computed from the molecular 

 weight and valences. I have accordingly taken the values of « given 

 by Guye and Mallet (Comptes rendus, 133, 1901, p. 1288) for 

 a few of these compounds and computed them in dynes, in place 

 of atmospheres, and compared them with the values computed from 

 the valences and weight. The result was as follows : 



Substance 



Naphthalene, C 10 Z/ 8 . . . 

 Durene, (\ J/ l4 



Diphcnyl, 6 r ]2 #, 



Diphenyl methane, C' 13 H l 



a, Guye and 



Mallet, in 



dynes. 



40.31 X 10 12 

 45.90 X LO 12 

 53.51 X 10 12 

 59.03 X 1U 12 



a computed 

 from valence 

 and weight. 



39.40 X10 12 



44.03 X 10 ' 2 

 50.64 X 10 1 " 

 57.33 X1U 1 ' 2 



Mol. Wt. 

 XVa- 

 lences. 



128 X 48 

 142 X 54 

 154 X 58 

 168 X 64 



The agreement is on the whole very good, but it will be noticed 

 that the computation of a by the formula a = 27 7' c 2 /64 X 273 2 P c 

 gives in these complex substances a value of a somewhat higher 

 than that computed from the valences and weight, while with the 

 simple substances it gives a value somewhat Lower. 



III. DISCUSSION OF RESULTS. 



The foregoing calculations are all brought together for easv com- 

 parison in Table 2. 



