PROFESSOR GRAHAM ON OSMOTIC FORCE. 
199 
incapable of passing* into the condition of a stable supersulphate or subsulphate by 
combining* with an excess of either acid or base, and is not decomposed in diffusion. 
Such properties secure to a salt a remarkable indifference, or absence of chemical 
activity, and recommend sulphate of magnesia for our present purpose. 
In a fresh double membrane, 1 per cent, of sulphate of magnesia (anhydrous) gave 
the small osmose of 13 and 14 ms., at 63°, in two experiments. 
A full series of observations was made by means of the osmometer F, used above 
with sugar, but with the osmotic septum of course changed. 
Table VI. — Sulphate of Magnesia in Osmometer F of double membrane 
for five hours. 
I. 
II. 
ill. 
IV. 
V. 
VI. 
VII. 
Sulphate 
of magnesia 
(anhydrous). 
Rise in 
millimeter 
degrees . 
Same in 
grammes of 
water. 
Diffusate of 
salt in 
grammes. 
Previous 
maceration. 
Hydrostatic 
resistance. 
Temperature, 
Fahr. 
per cent. 
• 2 
30 
1-254 
days. 
2 
min. 
10 
72 
2 
33 
1-368 
0-265 
1 
10 
70 
5 
73 
3-078 
0-540 
1 
10 
67 
5 
76 
3-192 
0-553 
1 
10 
67 
10 
152 
6-384 
1-020 
1 
10 
67 
10 
134 
5-529 
0-962 
1 
10 
67 
20 
238 
9*918 
1-623 
10 
15 
64 
20 
283 
11-836 
1-687 
1 
3-5 
64 
1 
23 
0-969 
0-119 
1 
5 
68 
1 
20 
0-855 
0-120 
1 
5 
65 
2 
30 
1-254 
0-227 
1 
5 
65 
2 
29 
1*197 
0-233 
1 
5 
64 
5 
69 
2-907 
0-490 
2 
6 
66 
5 
68 
2-850 
0-485 
1 
6 
67 
10 
132 
5-529 
0-959 
2 
6 
67 
10 
140 
5-871 
0-845 
1 
6 
69 
20 
277 
11-628 
1 
6 
70 
20 
291 
12-198 
2-012 
2 
6 
70 
The diffusate increases in a somewhat less ratio than the proportion of salt in 
the osmometer in both of the two series of observations contained in the preceding 
Table. But a similar falling off in the amount of diffusate from the higher pro- 
portions of salt takes place in the diffusion of the same salt, from open phials, as 
appeared in former experiments on the diffusion of sulphate of magnesia*. 
The different solutions then operated upon, and the ratio between the diffusates they 
gave, were as follows : — 
Solutions of sulphate of magnesia diffused .2 4 8 16 24 per cent. 
Ratio of diffusate of these solutions ... 2 3*671 6*701 11*785 15*678 
* Philosophical Transactions, 1850, p. 822. 
