42 PHYSICAL PROPERTIES AND COMPOSITION 



methyl and ethyl alcohols, is prevented by solution in 

 water, consequently the abnormal density so caused in the 

 bodies mentioned vanishes in aqueous solution. In the 

 second place, according to modern views, electrolytes, on 

 sufficient dilution, decompose into identical parts the 

 ions so that sharply additive relations of volume should 

 show themselves. 



A difficulty arises, however, in the fact that the molecular 

 volume in solution cannot be calculated in a manner quite 

 free from objection from the formula 



7Yi + n n 



m " = ~~^ 7 ; 



di o 



where m represents the molecular weight of the dissolved 

 substance in grams, n the weight of solvent containing it, 

 d the density of the solution, 8 that of the solvent. The 

 difficulty lies in the density of the solvent, which is not 

 necessarily the same in the solution as in the pure state. 

 We will, first, however, in making calculations on the 

 subject, leave this objection out of account, as we are 

 doubtless justified in doing, for the case of ideal dilution. 



Let us consider, first, the effect of doubling of molecules, 

 or of so-called association, on the volume of liquids. Ac- 

 cording to p. 26, it appears that this is probably not 

 large. With this agrees the result that the molecular 

 volume determined as such (M v ), and the volume in dilute 

 solution, do not differ much, whether for associated or 

 non- associated liquids : 



