toward* a Dynamical Theory of Solutions, 49 



offered above in connexion with alcohol and water to account 

 for the fact that the reduction of viscosity which ought to 

 accompany the change of trihydrol into dihydrol does not 

 appear, that it is masked by a greater increase of viscosity 

 of mutual origin. With formic acid this increase of mutual 

 origin is almost equal to the decrease, and so as regards 

 viscosity, formic acid and water behave almost as if no 

 molecular changes were going on at all. On the other hand, 

 the other acids, like alcohol, show the increase of viscosity 

 preponderating over the decrease and producing the con- 

 spicuous maximum. The two equations for the fluidity of 

 each acid are further evidence for the two processes when 

 these acids are mixed with water, first a change of trihydrol 

 into dihydrol along with production of hydrol, and second 

 a process which is chiefly production of hydrol. In "The 

 Mol. Const, of Solutions ,J it is shown that most electrolytic 

 solutes change trihydrol into dihydrol and therefore >roduce 

 contraction on solution. But they generally produce icrease 

 of viscosity. Probably with them also there is an increase in 

 the mutual part of the viscosity which is greater than the 

 decrease due to change of trihydrol into dihydrol. Probably 

 the chief reason for the difference of the action of formic acid 

 from that of the other acids is the closer approach of its 

 dielectric capacity to that of water. 



Specific Heat ; Heat evolved on mixing, 



Dupre and Page (Phil. Trans, clix. p. 591, 1869) found 

 that a mixture of alcohol and water containing 20 per cent, 

 of alcohol has a specific heat 1044, although that of 

 alcohol is 0*604, a result which led them to investigate the 

 specific heat and other physical properties of such mixtures 

 systematically. They discovered that the heat evolved on 

 mixing alcohol and water is proportional to the change ot: 

 specific heat which occurs on mixing. This remarkably 

 simple relation between heat evolved and change of a 

 physical property was not verified by Winkelmaun (Pogg. 

 Ann. cl. p. 592, 1873), who obtained values for the heat, 

 evolved agreeing well with those of Dupre and Page, but 

 values for the change of specific heat diverging from those 

 of Dupre and Page with increasing percentage of alcohol. 

 At first then we shall use quite recent data for the specific 

 heat of mixtures of alcohol and water, namely those of 

 Bakowski (Ann. d. Ph/s. Beibl. xxxiii. p. 858, 1909) between 

 22° and 99° C. He summarises his results in the following 



Phil. Mu<,. S. 6. Vol. 22. *No.. 127. Jul,, 1911, K 



