ASSOCIATION AND DISSOCIATION. 181 



(3) The solvent may be monomolecular and the dis- 



solved compound may be associating. 



(4) The solvent may be associating and the dissolved 



compound may be monomolecular. 



In the first and second cases experience shows that the 

 osmotic pressure of the resulting solution is usually normal, 

 and agrees with that calculated by the Van't HofT rule. 

 The third case has been already considered, and it has been 

 shown that a lower osmotic pressure than the theoretical 

 should be, and actually is, observed. For the fourth case 

 it is impossible at present to bring forward recognised 

 instances, but it is highly probable that electrolytes belong 

 to this class of solutions. 



In the first place evidence is gradually accumulating that 

 electrolytes are only formed when the solvent is associating. 

 Solvents which, with dissolved metallic salts, yield solutions 

 having a high electrical conductivity, usually contain the 

 hydroxyl group, and are associating. And other associating 

 solvents which do not contain the hydroxyl group, as, 

 for example, acetone, propionitrile and nitroethane, have 

 been lately shown by Miss Aston and P. Dutoit to yield 

 with metallic salts solutions of high conductivity. On 

 the other hand, Kablukoff found that when a monomo- 

 lecular solvent is taken, the resulting solution has 

 practically no conductivity. That the dissolved salt is 

 either monomolecular or approaches to this condition can- 

 not be shown directly, as no satisfactory examination of 

 metallic salts in the liquid state can be carried out. But 

 ethereal salts as a class are monomolecular compounds, and 

 analogy would therefore point to this being true of the 

 metallic salts. It will also be noticed that those com- 

 pounds which dissolve in water and other associating 

 solvents without formation of electrolytes belong to the 

 class of associating compounds ; as, for example, alcohol, 

 glycerol, and cane sugar. 



Now it has been pointed out that when, as in the 

 instances last quoted, the solvent and the dissolved sub- 

 stance are both associating (Case II.) normal osmotic 

 pressures are obtained, although when the solvent is mono- 



