256 Prof. Graham on the Diffusion of Liquids. 



carbonic acid water, containing also 200 grs. of chloride of 

 sodium dissolved. Distilled water was then carefully poured 

 over the saline solution, so as to fill up the jar, a float being 

 used and the liquid disturbed as little as possible in the ope- 

 ration. The mouth of the jar was lastly closed by a ground 

 glass plate, and it was left undisturbed upon the mantel-piece 

 of a room without a fire, from March 20 to September 24 of 

 the present year, or for six months and four days. Afterwards, 

 on removing the cover, the fluid was observed not to have 

 evaporated sensibly, and it exhibited no visible deposit. This 

 I was not surprised at, as no deposit appeared in a similar 

 experiment with the jar uncovered, after the lapse of six weeks. 

 The liquid in the former jar was now carefully drawn off by 

 a small siphon with the extremity of both its limbs recurved 

 so as to open upwards, in four equal portions, which may be 

 numbered from above downwards. Equal quantities of the 

 four strata of liquids gave the following proportions of chlo- 

 ride of sodium and carbonate of lime: — 





Chloride of sodium. ( 



Carbonate of lime. 



No. 1. 



21-91 



o-io 



No. 2. 



23-41 



0-22 



No. 3. 



23-55 



0*38 



No. 4, 



23-99 



0'42 



The diffusion of the chloride of sodium has therefore not 

 yet reached complete uniformity, although approaching it, 

 the proportion of that salt obtained from the top and bottom 

 strata being as 11 to 12. But the diffusion of the carbonate 

 of lime appears much less advanced, the proportion of that 

 substance being as 1 to 4 at the top and bottom of the liquid 

 column. The slight difference in density of the strata, it may 

 be further remarked, must have been sufficient to preserve 

 such a column of liquid entirely quiescent, as shown by the 

 distribution of the carbonate of lime, during the considerable 

 changes of temperature of the season. 



Chemical analysis, which gives with accuracy the propor- 

 tions of acids and bases in a solution, furnishes no means of 

 deciding how these acids and bases are combined, or what 

 salts exist in solution. But it is possible that light may be 

 thrown on the constitution of mixed salts, at least when they 

 are of unequal diffusibility, by means of a diffusion experi- 

 ment. With reference to sea-water, for instance, it has been 

 a question in what form the magnesia exists, as chloride or as 

 sulphate; or how much exists in the one form and how much 

 in the other. Knowing however the different rates of diffu- 

 sibility of these two salts, which is nearly chloride 2 and sul- 



