PROFESSOR GRAHAM ON OSMOTIC FORCE. 
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portion, if not the whole, of the small osmose of chloride of sodium, sulphate of mag- 
nesia, alcohol, sugar, and many other organic substances may be due to the relatively 
low diffusibility of such liquefied bodies compared with the diffusibility of water. But 
many substances, it will immediately appear, are replaced in experiments of endos- 
mose, not by four or six, but by several hundred times their volume of water, and 
manifestly some other force besides diffusion is at work in the osmometer. 
An explanation of osmose has been looked for in capillarity by Poisson, Magnus, 
and by Dutrochet himself. Combining diffusion with this idea, we might imagine 
that the pure water which first occupies the pores of the septum, suffers a sudden and 
great loss of its capillarity-force when the salt of the osmometer enters the pores by 
diffusion and mixes with the water they contain. Experiments published by Dutro- 
chet give a capillary ascension to pure water of 12 millimeters, and to a solution of 
common salt, of density IT 2, 6’ 14 millimeters, or only one-half of the former ascen- 
sion. If a porous septum, occupied by such a saline solution, had the same solution 
in contact with one surface and pure water in contact with the other surface (the 
actual condition of the septum in an osmotic experiment), the pure water should 
enter the pores from its high capillary attraction, and, like a solid piston, force out 
the saline solution from them : the saline solution so displaced would go to swell the 
liquid within the osmometer. When the pure water, now again occupying the pores, 
came in time to acquire salt by diffusion, the displacement would be repeated, and a 
continuous osmose or flow of water inwards be in fact established. 
This explanation is attended with certain physical difficulties, but it is unnecessary 
to discuss these, as the experimental basis of the hypothesis is unsound. The great 
inequality of capillarity assumed among aqueous fluids does not exist. Many saline 
solutions which give rise to the highest osmose are, I find, undistinguishable in capil- 
larity from pure water itself. To obtain constant results with saline solutions, the 
capillary tube must be retained for some minutes in the saline solution at a boiling 
temperature, and afterwards be cooled without removal from the liquid, otherwise 
the indications are singularly irregular and most fallacious. 
The near equality in capillarity of solutions of the most different composition is 
very apparent in my observations, which are placed together in the following series 
of capillary ascensions : — 
Capillary ascension of several liquids in the same glass tube. 
Millimeters. 
Water, at 58° Fahr 1 7*75 
Water, at 66° 17*55 
Carbonate of potash, 0*25 per cent., in water, at 63° .... 17*2 
Carbonate of potash, 10 per cent., in water, at 66° 17*55 
Carbonate of soda, 1 per cent., at 61° 17*55 
Carbonate of soda, 10 per cent., at 55° 16*85 
Sulphate of potash, 1 per cent., at 58° 17*15 
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