Mr GRAHAM on the Crystallization of Saline Solutions. 



aqueous solutions. The soluble gases I suppose to possess a si- 

 milar property. 



These facts appear to warrant the conclusion, that air deter- 

 the crystallization of supersaturated saline solutions, by 

 dissolving in the water, and thereby giving a shock to the feeble 

 power by which the excess of salt is held in solution. 



Before concluding, I may be allowed to make a remark, on 

 ;he usual description of the sudden congelation of the solution 

 of sulphate of soda upon the admission of air. It is said that the 

 solution expands in solidifying, in the same way as water does 

 in becoming ice. But the expansion which takes place is mere- 

 ly temporary, and not due to such a cause, but entirely to a mo- 

 mentary dilatation of the whole contents of the phial, both liquid 

 and solid, by the evolution of heat, which occurs on the instant 

 of crystallizing, and which always amounts to 20 or 30. That 

 the salt does not permanently expand on crystallizing is easily 

 proved, by the sinking of a crystal in the densest solution of the 

 salt which can be formed. 



