Prof. Graham on the Diffusion of Liquids. 261 



solution of the double salt, exhibited notwithstanding a sen- 

 sibly different result of diffusion, giving 7*28, 7'37 and 7'26 

 grs. in three cells; mean,7'30 grs. The diffusion of the double 

 salt was greater, namely, 7 95 grs. Hence a strong presump- 

 tion that the mixed salts last diffused were not combined, and 

 that the double sulphate of magnesia and potash is not neces- 

 sarily formed immediately upon dissolving together its consti- 

 tuent salts. 



In early experiments of a similar nature made upon the 

 double salt, sulphate of copper and potash, and upon a mix- 

 of the two sulphates newly dissolved together, a similar result 

 was obtained. While the diffusion of the mixed salts was 

 25*6 grs., that of the same weight of the combined salts (the 

 double sulphate) was 30 grs. The double salt appears more 

 diffusible, in both cases, than its mixed constituents. 



These double salts appear to dissolve in water without de- 

 composition, although the single salts may meet in solution 

 without combining. Hence in a mixture of salts we may have 

 more than one state of equilibrium possible. And when a 

 salt, like alum, happens to be dissolved in such a way as to 

 decompose it, the constituents are not necessarily reunited by 

 subsequent mixing. Many practices in the chemical arts, 

 which seem empirical, have their foundation possibly in facts 

 of this kind. 



8. Diffusion of one Salt into the Solution of another- Salt. 



It was curious and peculiarly important, in reference to the 

 relation of liquid to gaseous diffusion, to find whether one salt 

 A would diffuse into water already charged with an equal or 

 greater quantity of another salt B, as a gas a freely diffuses 

 into the space already occupied by another gas b; the gas b 

 in return diffusing at the same time into the space occupied 

 by a. Or whether, on the contrary, the diffusion of the salt 

 A is resisted by B. The latter result would indicate a neu- 

 tralization of the water's attraction, and a kind of equivalency 

 or equality of power and exchangeability of different salts, in 

 respect of that effect, which would divide entirely the pheno- 

 mena of liquid from those of gaseous diffusion. 



(1.) A solution of 4 parts of carbonate of soda to 100 water, 

 of density T0406, was placed in the six-ounce diffusion phial 

 of 1*175 inch aperture, and allowed to communicate with 24 

 ounces of water. 



Two similar diffusion phials, equally charged, were im- 

 mersed in 24 ounces of a solution of 4 parts of chloride of 

 sodium to 100 water, having the density J -0282. The diffu- 

 sion proceeded for eight days, in all cases, at 64°. The pro- 

 portion of carbonate of soda found without in the water-jar 



