274 Mr. William Sutherland on the 



k/{v — k), we get for the reciprocal of the virial constant of 

 the mixture 



s-H-k-i-WK^H 



V + k 



... X=fo/(w + A), 



and therefore the virial term is l/(v + k). 



This would be no demonstration of the pairing of molecules 

 in compounds, if we did not already have it proved in the 

 case of the elements that the virial term varies inversely as 

 the volume at all volumes. Remembering this we can accept 

 our form l/(v+k) as indicating the existence of a mixture of 

 paired and single molecules, the number of pairs at volume v 

 being to the number of single molecules as k to v— k. 



The form of the energy term, 



RT 



K-&) 



must also be partly determined by this existence of pairs, but 

 it would be foreign to our immediate subject to attempt to 

 investigate it. 



14. Brief Discussion of the Constitution of the Alcohols as 

 Liquids. — To learn a little more on the subject of pairing, it 

 will be of some profit to consider briefly here the alcohols and 

 water, which so far have been left aside, after having been 

 proved in Table XII. to follow in the supracritical region a 

 different law from the usual one. But also in the liquid state 

 the alcohols and water, while conforming to the general liquid 

 laws in many respects, are still exceptional in others. Thus 

 Eotvos (Wied. Ann. xxvii.) has shown that the alcohols will 

 conform to his generalization if at the lower range of tempe- 

 rature, from 20° 0. to 170° C, the molecules be considered 

 complex (double relatively to ordinary liquids) and water 

 also conforms if from 100° upwards its molecules be con- 

 sidered double ; the molecular lowering of the freezing-point 

 of water produced by the solution of bodies in it as measured 

 by Raoult and compared with the molecular lowering for 

 other liquids proves that relatively to these the molecule of 

 water is double. Taking all the facts into consideration, it 

 seems to me that the alcohols and water may be assumed, in 

 the liquid state, to have the pairs of molecules again paired, 

 the second pairing, however, not being of so intimate a nature 



