16 
PROFESSOR GRAHAM ON THE DIFFUSION OF LIQUIDS. 
The relatively diminished diffusibility of sulphate of magnesia, when associated 
with sulphate of water, is probably connected with a similar circumstance; sulphate 
of magnesia being less soluble in dilute sulphuric acid than in pure water. 
(5.) The salt which diffused from a strong solution of sulphates of zinc and mag- 
nesia, consisting of 1 part of each of these salts in the anhydrous state and 6 parts of 
water, did not consist of the two salts in exactly equal proportions. The mixture of 
salts, diffused for eight days, as in the late experiments, gave the following results : — 
Exp. I. 
II. 
III. 
Sulphate of zinc .... 
. . 8-12 
7-49 
8-12 
Sulphate of magnesia . . 
. . 8-68 
8-60 
8-75 
16-80 
16-09 
16-87 
There is therefore always a slight but decided preponderance of sulphate of mag- 
nesia, the more soluble salt, in the diffusion product. These last e.xperiments were 
made at an early period with another object in view, namely, to ascertain whether in 
closely related salts, such as the present sulphates of magnesia and zinc, the two salts 
might be elastic to each other, like the particles of one and the same salt, so that one 
salt might possibly suppress the diffusion of the other, and diffuse alone for both. 
The experiments lend no support to such an idea. 
It appears from all the preceding experiments, that the inequality of diffusion 
which existed, is not diminished but exaggerated in mixtures, a curious circumstance, 
which has also been observed of mixed gases. 
5. Separation of Salts of different Bases by Diffusion. 
It was now evident that inequality of diffusion supplies a method for the separa- 
tion, to a certain extent, of some salts from each other, analogous in principle to the 
separation of unequally volatile substances by the process of distillation. The potash 
salts appearing to be always more diffusive than the corresponding soda salts, it 
follows, that if a mixed solution of two such salts be placed in the solution phial, 
the potash salt should escape into the water atmosphere in largest proportion, and 
the soda salt be relatively concentrated in the phial. This anticipation was fully 
verified. 
(1.) A solution was prepared of equal parts of the anhydrous carbonates of potash 
and soda in 5 times the weight of the mixture of water. Diffused from a small thou- 
sand-grain phial of T1 inch aperture, into 6 ounces of water, for nineteen days, at a 
temperature above 60°, it gave a liquid of density T0350, containing a considerable 
quantity of the salts. Of these mixed salts, converted into chlorides by the addition 
of hydrochloric acid, 9'39 grs., being treated with bichloride of platinum in the usual 
manner, gave 19’39 grs. of the double chloride of platinum and potassium, equivalent 
to 5’91 grs. of chloride of potassium; and left in solution 3*44 grs. of chloride of 
sodium : loss 0’04 gr. These chlorides represent 5'46 grs. of carbonate of potash and 
