20 
PROFESSOR GRAHAM ON THE DIFFUSION OF LIQUIDS. 
In a second experiment, the diffusion product amounted to 6'39 grs., of which 
0-95 gr. was alumina ; and it is represented by 477 alum and 1*52 sulphate of potash. 
In connexion with the low diffusibility of the sulphate of alumina of alum, it was 
found that the addition of caustic potash to the alum solution, so as to convert it into 
an aluminate of potash, increased the diffusibility of the alumina. The diffusion pro- 
duct from the 4 per cent, solution of alum so treated contained T62 gr. of alumina 
in one experiment and T54 in another. 
As alum is a salt of great stability, it presents a severe test of the influence in ques- 
tion. The decomposition of this double salt by diffusion was further confirmed there- 
fore in experiments made by means of the four-ounce diffusion phials of i‘25 inch 
aperture, and the alteration which the salt undergoes in the process more exactly 
ascertained. The experiments were made at a mean temperature of 57°‘9, and lasted 
seven days ; the solution employed being of 4 anhydrous alum to 100 water, as 
before. 
In three experiments, the salt diffused out amounted to 573, 5‘80 and 5*65 grs. ; of 
which the mean is 573 grs. The latter quantity gave 0*82 alumina and 3‘22 sul- 
phuric acid, which correspond to 4T1 anhydrous alum and T62 neutral sulphate of 
potash. Or, we have as the diffusion product of alum, in 100 parts — 
Alum 7173 
Sulphate of potash 28’27 
100-00 
This analysis corresponds closely with the diffusion product of the former ex- 
periments, which gave 71'26 per cent, of alum. The solution of alum which 
remains behind in the solution phials must of course acquire an excess of sulphate of 
alumina. 
The salt, sulphate of alumina, did not appear to be decomposed when diffused 
alone. A four per cent, solution of the hydrated sulphate of alumina, which is manu- 
factured at Newcastle, when diffused in the same circumstances as the preceding 
solutions of alum, gave 3-40 grs. of anhydrous sulphate of alumina, in which the 
acid was to the alumina as 2-95 equivalents of the former to 1 equivalent of the latter, 
or as nearly as possible in the proportion of 3 equivalents of acid to 1 of base. As 
the Newcastle salt contained almost exactly half its weight of water, the 3-40 grs. of 
anhydrous salt diffused out are equivalent to 6-80 grs. of hydrated sulphate of alu- 
mina. The sulphate of alumina appears thus to be more diffusive than the double 
sulphate of alumina and potash, in the proportion of 6-80 to 5-73. 
(3.) It was interesting to observe what really diffuses from the ammoniated sul- 
phate of copper (CuO, SO3, 2NH3-I-HO), and to find if the low diffusibility of that 
salt is attended with decomposition. The diffusion of the ammoniate^d sulphate of 
copper was therefore repeated from a 4 per cent, solution in the six-ounce solution 
phial, for eight days, at 64°-2. In evaporating the water of the jar afterwards, the 
ammoniated sulphate of copper present was necessarily decomposed, by the escape of 
ammonia, and a subsulphate of copper precipitated. The copper found, however, was 
