VII. On the Influence of the Air in determining the Crystallization 

 of Saline Solutions. By THOMAS GRAHAM, Esq. A.M. 



(Read December 17. 1827. J 



THE phenomenon referred to has long been known, and popu- 

 larly exhibited in the case of Glauber's salt, without any ade- 

 quate explanation. A phial or flask is filled with a boiling satu- 

 rated solution of sulphate of soda or Glauber's salt, and its mouth 

 immediately stopped by a cork, or a piece of bladder is tied tightly 

 over it, while still hot. The solution, thus protected from the 

 atmosphere, generally cools without crystallizing, although it con- 

 tains a great excess of salt, and continues entirely liquid for hours 

 and even days. But upon withdrawing the stopper, or punc- 

 turing the bladder, and admitting air to the solution, it is im- 

 mediately resolved into a spongy crystalline mass, with the evo- 

 lution of much heat. The crystallization was attributed to the 

 pressure of the atmosphere suddenly admitted, till it was shewn 

 that the same phenomenon occurred, when air was admitted to 

 a solution already subject to the atmospheric pressure. Re- 

 course was likewise had to the supposed agency of solid particles 

 floating in the air, and brought by means of it into contact with 

 the solution ; or it was supposed that the contact of gaseous mo- 

 lecules themselves might determine crystallization, as well as so- 

 lid particles. But although the phenomenon has been the sub- 

 ject of much speculation among chemists, it is generally allowed 

 that no satisfactory explanation of it has yet been proposed. 



In experimenting upon this subject, it was found, that hot 

 concentrated solutions, in phials or other receivers, might be in- 



