374 Scientific Intelligence.-, — Chemistry. 



mosphere, for the phenomenon is retarded as well by covering the 

 solution with spirits of turpentine, which preserves it from contact 

 with the air, as by keeping it in a vacuum ; and he has proved also, 

 that the solvent powers of water are quite independent of pressure on 

 its surface. Likewise when crystallization fails, as is sometimes the 

 case when the atmosphere is admitted, no advantage is gained by 

 adding to its pressure. This distinguished chemist was inclined to 

 the opinion, that the crystallization might be owing to the diminution 

 of solvent power, occasioned by the absorption of air. This opinion 

 is strengthened by the experiments of Mr. Graham. By placing the 

 hot solution of sulphate of soda in a tube, and inverting it in the mer- 

 curial bath, having previously heated the mercury, to prevent crystal- 

 lization from a rapid cooling of the solution, he ascertained, by 

 throwing up bubbles of air of different kinds, that their influence in 

 determining crystallization, is precisely proportional to their degree of 

 solubility in water, and in saline solutions : Thus a bubble of car- 

 bonic acid is more powerful than common air, and a bubble of am- 

 moniacal gas or sulphurous acid, has more effect than carbonic acid. 

 With ammoniacal gas, the crystallization follows the ascent of the 

 bubble so rapidly, that the latter sometimes becomes imprisoned 

 among the crystals before it reaches the top of the tube. Hydro- 

 gen, on the other hand, and other gases less soluble in water than 

 common air, have decidedly less effect. A very small quantity of a 

 liquid, soluble in water, causes the solution immediately to crystal- 

 lize, as may be evinced by using alcohol : now, it is well known that 

 alcohol precipitates sulphate of soda dissolved in water, and the solu- 

 ble gases appear to possess a similar property. 



The enlargement of volume, which ensues upon the sudden crys- 

 tallization of sulphate of soda, the author ascribes altogether to the 

 expansive effect of the heat thus developed. 



The various influence of the different gases is an important fact, 

 not before remarked ; but is it sufficient to demonstrate completely 

 the explanation advanced by Mr. Graham ? We think not, and we 

 are of opinion that the phenomenon which sulphate of soda presents, 

 belongs to that class of facts, which, though still small, is constantly 

 increasing, and which, isolated thus far in the partial explanation 

 which each one of them has received, constitute, in their totality, that 

 molecular philosophy, still so very imperfectly understood, and so 

 difficult to investigate. — A. D. L. R. Bib. Univ. Juin, 1829. 



