Phenomena of some Substances and Mixtures. 195 



36. Now the three combinations investigated offer a good 

 opportunity for calculating a 12 and b l2 . We saw that the 

 same formulae hold for the critical point of the max. mixture 

 as for a single substance. From the T and p in the maximum 

 point B we can therefore calculate a x and b x and deduce from 

 these the o 12 and b 12 . The values of a l2 will give some idea 

 of the relative attraction of the two kinds of molecules, 

 probably quite as accurate an idea as the ordinary a gives of 

 the mutual attraction of the same molecules. The b 12 obtained 

 may be compared with the theoretical value. 



37. The results of my calculations are the following : — 



Table XVI. 





t e - 



Pc- 



a. 



b. 



N,0 



309 

 308-25 

 304-1 

 305 



302-8 



292-96 



2918 



305-55 



719 

 61-02 

 73-26 

 48-8 



65-3 



54-7 

 61-3 



66-5 



„ 000753 

 ^000881 

 0-00714 

 01078 



a vl . 



000859 

 0-00789 

 0-008076 



000792 



0-00197 

 000231 

 0-00190 

 0-00286 



K- 

 000239 

 0002295 

 0-002357 



000210 



C,H, 



cb 2 " 



C,H 6 



N,0-C 2 H 6 (^=0-18) ... 

 C.;H.-0,H 6 (^=0-51) ... 

 00 2 -C 2 H 6 0=0-30) ... 



C0 2 -C 2 "H 2 O=0 50) ... 



I have added to the table calculated values of a 12 and b i2 

 for the combination C0 2 -C 2 H 2 . The mixture of these two 

 gases was proved to have a very narrow border-curve, and 

 consequently the critical point observed cannot have been 

 very much above the hypothetical critical point. The calcu- 

 lation of a 12 and b i2 from the critical constants, though not 

 legitimate, must have given values for a l2 and b 12 not very 

 far wrong. 



The values of b 12 calculated from the formula in § 35 coin- 

 cide with the values in Table XVI. in the case of N 2 0-0 o H 6 

 and of C0 2 -C 2 H 6 : for C 2 H 2 -C 2 H 6 b 12 is even smaller than b 

 for C 2 H 2 . a 12 is in all cases smaller than the mean of the 

 a's, and for C 2 H 2 -C 2 H 6 even smaller than a for C 2 H 2 . It 

 is chiefly on this smallness of a 12 that the existence of a 

 minimum critical temperature depends. 



38. Knowing a 12 and b 12 , we may calculate the critical 

 constants for the other mixtures, if supposed to remain 

 undivided. It is with the temperature that we are chiefly 

 concerned. 



