PROFESSOR GRAHAM ON OSMOTIC FORCE. 
20 ! 
In 2 per cent, solution, 1 sulphate of magnesia is replaced by 5T6 water. 
In 5 per cent, solution, 1 sulphate of magnesia is replaced by 574 water. 
In 10 per cent, solution, 1 sulphate of magnesia is replaced by 6’01 water. 
In 20 per cent, solution, 1 sulphate of magnesia is replaced by 6 - 57 water. 
According to the average of the whole proportions, sulphate of magnesia is replaced 
by 5 - 87 times its weight of water. 
While in the later observations of the same Table — 
In 2 per cent, solution, 1 sulphate of magnesia is replaced by 533 water. 
In 5 per cent, solution, 1 sulphate of magnesia is replaced by 5 - 9 water. 
In 10 per cent, solution, l sulphate of magnesia is replaced by 6 - 32 water. 
According to the average of the whole proportions of salt in these later obser- 
vations, sulphate of magnesia is replaced by 5‘85 times its weight of water. 
The want of uniformity exhibited above in the relation between the quantities of 
water and salt goes some way to prove that the osmose of sulphate of magnesia in 
membrane is not pure diffusion, for the ratio between the exchanging water and salt 
(the diffusion-volumes) should then remain constant. 
On the other hand, the approximation to uniformity favours the idea of the exist- 
ence of a numerical relation between the osmose and diffusate. So also may the cir- 
cumstance be considered, that sugar and sulphate of magnesia, which approximate as 
seen above in their osmose, were found before to have a similar degree of diffusibility *. 
The facts appear to afford a strong presumption, but no demonstrative proof, of the 
intervention of diffusion in governing the results of osmose in such neutral sub- 
stances. The influence of diffusion becomes more difficult to trace in the osmose of 
three other neutral salts, which I shall now introduce. What has been represented 
as the chemical agency now begins to interfere more sensibly, although not to govern 
the results entirely as it appears to do in less strictly neutral salts. 
Chloride of Sodium . — The osmose of chloride of sodium possesses a certain interest 
independently of such theoretical considerations. 
* Philosophical Transactions, 1850, p. 10. 
2 D 
MDCCCLIV. 
