( 174 ) 



Chemistry. — - ''(Ju tJu' hiUnitlieat of ntidng for a.ssorittting solvents.'''' 

 By J. J. VAN Laak. (Communicated by Prof. H. W. Bakhuis 

 Roozeboom). 



(Communicaled in the mceliiig of June 25, l'J04). 



1. When 8ome siibstiince is solved in an assoc'uit'uhj liquid, as 

 e.g. ivater, and we try to find an expression for the latent heat of 

 mixing of these two substances, we shall in (he lirst [dace have 

 to take into account, besides the change of the polejitial energy, 

 the heat of ionlsdüon of the solved substance, if this substance is 

 an electrolyte. The fact, however, that the state of association is 

 changed by the solving, is nearly always overlooked. We are inclined 

 to reason, that in much diluted solutions tiie influence of the addition 

 of a few molecules of the solved suf)stance must necessarily be 

 exceedingly slight, with regard to tiie degree of association of tlie 

 solvent; but in doing so it is overlooked that the //////^Acy of molecules 

 of the solvent which each undergo a very sHght chauge in their 

 state of association, is reri/ yreat. For infinitely (bluted solutions 

 therefore, a value is obtained approaching to X ^» ^"^^ 1 shall 

 demonstrate in what follows, thai the absorbed Iwat in consequence 

 of the change in the state of association, approaches to a definite 

 value, which is finite and even conqiarativeiy Ingh. 



2. In (lilutcd sobitions — which we solely have in view in tlio 

 following pages — the state of e([uilib!-ium of the associating mole- 

 cules of the solvent may be expressed as follows: 



'(l-..)/i^ 



N . 



7,(1-^) (1-/?) 

 i.e. : 



W-^ = V,^ (1) 



For, given 1 — ,/; mol. H^O, iioruially reckoned, ,/; mol. salt 

 (calling the solved substance salt for convenience' sake), then there 

 are Vs (1—'') inol. H^O, if all are double. Therefore if the degree 

 of dissociation of these double-molecules is ji, then tiiere are: 



V, (1— .f) (1 — ,i) double mol. ; \ , (1—.') 2,i = (1 — ./) (i single mol. 



The total number of particles is X. If the degree of dissociation 

 of the saltmolecules is a, then there are (in hinanj electrolytes): 



