ASSOCIATION AND DISSOCIATION. 179 



Among those properties of liquids on which association 

 is likely to have a marked influence, and to which a pecu- 

 liar interest attaches, must be ranked their behaviour as 

 solvents. That the solvent properties of a liquid are in- 

 fluenced by its degree of association, is evidenced by the 

 fact, that, as a general rule, associating liquids more readily 

 dissolve associating liquids, and monomolecular liquids more 

 readily dissolve monomolecular liquids, than liquids of the 

 one class dissolve those of the other. Compounds con- 

 taining hydroxyl are, generally speaking, insoluble in the 

 hydrocarbons, in ether or in carbon bisulphide, but soluble 

 in water and alcohol. The higher hydrocarbons, the fats 

 and waxes, are insoluble in water and almost insoluble in 

 alcohol, but dissolve in other hydrocarbons, in ether and 

 in carbon bisulphide. 



Not only is the behaviour of liquids as solvents influenced 

 by their association, but in the properties of the solutions 

 formed the influence of association can still be traced. It 

 has been shown by Linebarger that when monomolecular 

 liquids are mixed one with another, the densities of the 

 mixtures are very nearly equal to those calculated from 

 the densities of their components, no allowance being made 

 for contraction or expansion. Nothing of the kind holds 

 for mixtures of associating and monomolecular liquids, or 

 for mixtures of associating liquids with one another, for 

 here so great a contraction or expansion occurs that the 

 law of mixtures does not apply. 



Reference has been previously made to Van't HofTs 

 application of the gaseous laws to dilute solutions. As 

 is well known, according to Van't Hoff, the osmotic 

 pressure of a dissolved substance is identical with the 

 pressure which the same substance would have in the 

 gaseous state, if the solvent could be completely removed 

 so as to leave the dissolved substance in that state. Solu- 

 tions therefore which contain at the same temperature and 

 in the same volumes equal numbers of dissolved molecules 

 should have the same osmotic pressures. In the majority 

 of cases this is found to be so, but a large number of 

 exceptions have been observed, the osmotic pressure being 



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