190 
PROFESSOR GRAHAM ON OSMOTIC FORCE. 
when two membranes are used together. Some observations made on the compara- 
tive loss of weight of the outer and inner membrane have not, however, shown any 
remarkable difference. But this again may arise from the great proportion of the 
loss in both membranes being due to the ordinary solvent action of water alone, and 
the operative solvent action of the osmotic salt being comparatively minute in 
amount ; or it may depend, and I am most inclined at present to take this view, upon 
the chemical actions being of a different kind on the two sides of the membrane, and 
not upon the inequality simply of one kind of action. Such a supposition was 
suggested by the fact, which will immediately appear, that osmotic activity and easy 
decomposition are properties often found together in binary compounds. The basic 
and acid agents then developed are both capable of acting upon albuminous septa. 
We may imagine, for instance, in the osmotic action of a neutral salt, the formation 
within the thickness of the septum of a polar circle, one segment of which (composed 
of the binary molecules of the salt) presents a basic molecule to the albumen at the 
inner surface of the septum, and an acid molecule to the albumen at the outer surface, 
the circle being completed through the substance of the septum which forms the 
second segment. Both surfaces of the septum would be acted upon, but at one side 
we should have combination of the albumen with an alkali, on the other side with an 
acid. This however must be taken as a purely ideal representation of the condition 
of the septum in osmose. I have not discovered such a polar condition of the septum, 
and I doubt whether the galvanometer could be properly applied to exhibit it, as the 
placing of the poles of that instrument in the dissimilar fluids existing on opposite 
sides of the septum would alone be sufficient to give rise to voltaic polarization. At 
present I must confine myself to the enunciation of certain general empirical con- 
clusions respecting the operation of chemical affinity in osmotic experiments. 
With animal septa, frequent examples of the outward flow of liquid from the 
osmometer present themselves, causing the liquid column to fall instead of rise in 
the tube. This phenomenon (exosmose) I have spoken of as negative osmose. The 
observation of Dutrochet, that oxalic acid in the osmometer, and also tartaric acid 
at a certain point of concentration, give rise to negative osmose, I have been able to 
generalise in so far as acids have universally either a negative osmose, or lie at the 
very bottom of the positive class. 
Oxalic acid gave in membrane, for 1 per cent, acid,— 148 ms. and — 141 ms. ; and for 
0’1 per cent., — 10 and — 27 ms. In another membrane, 1 per cent, of the same acid 
alone gave — 136 ms. ; with the addition of 0T per cent, hydrochloric acid, — 181 and 
— 168 ms. By the addition of O’] per cent, of chloride of sodium, a salt which in 
small proportions is nearly neutral to osmose, the negative osmose of 1 per cent, oxalic- 
acid fell in the same membrane to —45 ms., and with the addition of 0'25 per cent, 
of chloride of sodium the osmose was +6 ms., or became slightly positive. The 
negative osmose of 1 per cent, of oxalic acid, in a membrane where it amounted to 
— 56 and —57 ms. in two experiments, became, with the addition of CM per cent. 
