200 
PROFESSOR GRAHAM ON OSMOTIC FORCE. 
The proportions of sulphate used in the present osmotic experiments were different, 
but ratios may be found for them by interpolation, and are given below. We are 
thus enabled to make the following comparison of the diffusion from different pro- 
portions of sulphate of magnesia: (1) in the absence of membrane; (2) in the first 
series of osmotic experiments given in the preceding Table ; (3) in the second series 
of observations of the same Table : — 
Sulphate of magnesia in solution .... 
. 2 
5 
10 
20 per cent. 
(1) Ratio of diffusates without membrane . 
. 2 
4-43 
8-21 
1373 
(2) Ratio of diffusates with membrane . . 
2 
4-12 
7-48 
12-5 
(3) Ratio of diffusates with membrane . 
2 
4-24 
7-82 
17-34 
If the last number (17'34) given for the 20 per cent, solution of the later osmotic 
series be excluded, and it is manifestly in considerable excess from some accidental 
cause, the three sets of ratios must be allowed to exhibit considerable agreement. 
The membrane appears to have a slight effect in reducing the diffusates of the 
higher proportions of salt ; and this reduction is greater in the early experiments (2) 
than in the late experiments (3), made with the same osmometer. The comparative 
diffusion of different proportions of sulphate of magnesia appears, therefore, not to be 
much deranged by the intervention of membrane. 
The average osmose of sulphate of magnesia likewise exhibits a pretty uniform 
progression. In the first series of experiments of Table VI., we find for the different 
proportions of salt in solution an osmose of 3T5, 74 - 5, 143 and 260-5 ms.; numbers 
which are in the ratio given below: — 
Sulphate of magnesia in solution ..... 2 5 10 20 per cent. 
Ratio of osmose (first series of experiments) . 2 4'73 9‘08 16'54 
In the later experiments of the same Table, the different proportions of salt (omit- 
ting the first and last proportions) give an average osmose of 29"5, 68"5 and 136 ms., 
of which the ratios may be stated as follows : — 
Sulphate of magnesia in solution 2 5 10 per cent. 
Ratio of osmose (second series of experiments) . . 2 4 - 64 9’22 
The osmose appears here to follow more closely in its value the proportion of salt 
in solution than the diffusate can be said to do, either in open vessels or through 
membrane ; so far, therefore, the osmose and diffusate do not preserve a constant 
proportion to each other with this salt. 
No correction need be applied to the observed osmose of sulphate of magnesia, as 
this salt does not sensibly increase the bulk of the water in which it is dissolved. 
The weight of diffusate in Column IV. may, therefore, be immediately compared 
with the weights of water in Column III. It then appears that in the first series of 
the osmotic observations in the Table — 
