THE NEW THEORY OF SOLUTIONS. 387 



In all except the most dilute solutions, the curves ob- 

 tained on plotting the above values show that the molecu- 

 lar weights determined at the boiling-point are slightly 

 the larger. Here no definite temperature effect is notice- 

 able. No observations at the boiling-point have been made 

 on solutions of the great majority of the other hydroxy-com- 

 pounds, as they are too volatile to give satisfactory results 

 using the ordinary experimental method. 



Nature of the solvent. — Besides the nature of the dis- 

 solved substance the second main factor instrumental in 

 producing an associated solution is the nature of the solvent. 

 In general the properties of indifferent solutions give little or 

 no indication of a specific action of the solvent on the 

 molecular condition of the dissolved substance ; the solvent 

 apparently merely supplies a medium in which the mole- 

 cules of the dissolved substance mav distribute themselves. 

 The properties of associated solutions clearly prove, however, 

 that in certain cases the solvent cannot be regarded as pas- 

 sive. They show that whereas certain solvents, like water, 

 acetic acid, etc., can resolve the complex molecules of hydroxy- 

 compounds into simple molecules, other solvents cannot effect 

 this decomposition. According to the work of Raoult, 

 Beckmann, Eykmann, Paterno and Montemartini (1894), 

 and Beckmann, Fuchs, and Gernhardt (1895), the follow- 

 ing solvents may give associated solutions : benzene, nitro- 

 benzene, paraxylene, naphthalene, diphenyl, diphenyl-me- 

 thane, methyl-propyl ketone, alkyl bromides and iodides, 

 ethylidene dichloride, ethylene dichloride and dibromide, 

 chloroform, and carbon bisulphide ; a less marked tendency 

 to form such solutions is also shown by azobenzene, anethol, 

 and benzophenone. These solvents are mainly hydrocarbons 

 or their simple substitution products which are not of the 

 water-type ; other solvents, including, it has to be noticed, 

 hydroxy-compounds themselves, like water, acids, alcohols, 

 phenol, etc., give normal values for all indifferent substances 

 if the solutions be dilute, although in concentrated solutions, 

 even in water, indication of molecular aggregation can be 

 detected (Abegg, 1895). 



Little has up till now been done in explaining the dif- 



