44 
PROFESSOR GRAHAM ON THE DIFFUSION OF LIQUIDS. 
A similar solution of sulphate of potash diffused for 9*9 days, or half the preceding 
period, at a mean temperature of 55°'4, or 0°’7 higher, gave a mean product, for two 
cells, of 679 grs., as before stated, or for one cell, of 3’40 grs. The diffusion of sul- 
phate of potash being 100, that of sulphate of magnesia is therefore 1037? a fair ap- 
proximation to equality. 
(2.) In a second series of experiments upon 1 per cent, solutions of the same two 
salts, diffused in the vault for fourteen and seven days respectively, with a mean tem- 
perature of 53°‘8 for the sulphate of magnesia, and 54°’3 for the sulphate of potash, 
the temperature was remarkably uniform, gradually falling from 55° 2 to 53° during 
the longer period, but without any injurious oscillation. 
From eight cells, evaporated two together, the sulphate of magnesia obtained was 
6T2, 6T2, 6'04 and 6‘03 grs. ; mean 6'08 grs., or 3*04 grs. for one cell. 
The sulphate of potash gave from eight cells, in experiments already detailed, a 
mean result of 5'84 grs. of salt for two cells, or 2’92 grs. for one cell. The diffusion 
is in the proportion of 100 sulphate of potash to 104*11 sulphate of magnesia, the 
times being as 1 to 2 for the two salts respectively. 
From these two series of experiments, it appears that, at 54°, sulphate of magnesia 
has nearly, if not exactly, half the diffusibility of sulphate of potash, and consequently 
one-fourth of that of hydrate of potash. Or, the times of equal diffusion for these 
three salts appear to be ], 2 and 4. The squares of these times and the solution den- 
sities are 1, 4 and 16. Hydrate of potash may possibly therefore have the same rela- 
tion to sulphate of magnesia in solution density and diffusibility that hydrogen gas 
has to oxygen gas. 
(3.) A two per cent, solution of sulphate of magnesia, diffused for fourteen days, 
gave at 53°*9, for two pairs of cells, 9*57 and 10*00 grs. of salt, of which the mean is 
9*79 grs., or 4*85 grs. for one cell. 
A similar solution of sulphate of potash diffused for seven days gave a mean result 
of 4*97 grs. of salt for one cell, at 54°*2, as already stated. The result is a diffusion 
of 100 sulphate of potash to 97*59 sulphate of magnesia. 
(4.) A four per cent, solution of sulphate of magnesia, diffused for fourteen days, 
gave at 53°*7, in two pairs of cells, 18*00 and 18*20 grs. of salt; mean 18*10 grs. for 
two cells, or 9*05 grs. for a single cell. 
A similar solution of sulphate of potash, diffused for seven days at 54°*2, gave a 
mean result of 9*30 grs. of salt for a single cell, as already stated. This is a diffusion 
of 100 sulphate of potash to 97*4 sulphate of magnesia. 
The diffusion of the 2 and 4 per cent, solutions of sulphate of magnesia is so nearly 
equal to the diffusion of the same proportions of sulphate of potash in half the time, 
that they may be considered as supplying additional support to the assumed relation 
between the diffusibilities of these salts. 
I may add, that a 4 per cent, solution of anhydrous sulphate of zinc was diffused 
for fourteen days, simultaneously with the similar solution of sulphate of magnesia. 
