CHEMICAL SCIENCE. 199 



Content, for a time, in merely observing the new phenomena, and 

 in applying them to the explanation of the processes of absorption 

 and nutrition, we find, in the first few years following the discovery, 

 but little controversy as to the actual reason why the occurrences 

 observed took place. At first, we believe, it was vaguely suspected 

 that the phenomena were determined by the specific gravities of the 

 two fluids ; that, in short, the fluid of highest specific gravity at- 

 tracted that of lower specific gravity, and thus the main current was 

 set up. This view, although in no way sufficient to account for the 

 facts observed, nor, indeed, based on any logical argument, has, as it 

 were by mere force of verbiage, made its way. 



Another hypothesis, invented to explain the occurrence of osmotic 

 currents, referred them to capillary attraction, or to that form of at- 

 traction resident in porous bodies by which oil is raised through the 

 wick of lamps, or water through the fibres of cotton immersed in it. 

 Dutrochet himself explained osmosis on this theory, and gave a series 

 of calculations, in which he argued that the capillary ascension of 

 water was twice greater than a solution of salt of a density of 1.12. 

 Thus, if a porous septum, holding a saline solution having a density 

 of 1.12, were brought in contact, on its opposite surface, with pure 

 water, the pure water would enter the pores of the septum, displace 

 the saline matter contained in those pores, ascend into the solution 

 above, increase its bulk, and determine the osmotic current in a di- 

 rection from the solution of lowest to that of the highest specific 

 gravity. 



This theory, largely accepted, was destroyed by Prof. Graham, in 

 his paper on osmotic force, published in 1854. He there showed that 

 the experimental basis of the hypothesis was unsound ; that the great 

 inequality of capillary attraction assumed to exist between different 

 solutions had no existence ; and that many saline solutions which 

 gave rise to the highest osmose were undistinguishable in capillarity 

 from pure water itself. 



In this remarkable paper, the author showed that whenever osmotic 

 action was going on, the intervening septum, whether it consisted of 

 earthenware or of animal membrane, was constantly undergoing de- 

 composition. When membrane was employed, soluble organic mat- 

 ter was always found both in the fluid of the osmometer and in the 

 water of the outer jar after every experiment ; the action of the mem- 

 brane appeared also to be exhaustible, although in a slow and grad- 

 ual manner. Those salts and other substances, of which a small pro- 

 portion was sufficient to determine a large osmose, were also shown to 

 be all of the class of chemically active substances, while the great mass 

 of neutral or organic substances, and perfectly neutral monobasic 

 salts of the metals, such as the alkaline chlorides, possess only a low 

 degree of action. 



It is impossible to follow the arguments of Prof. Graham through 

 the whole of his earlier paper, which we have just mentioned. Suf- 

 fice it to say that he announced the following statements: 1. That 

 an obvious and essential condition of osmose consists in a difference 

 of composition of two fluids in contact with the opposite sides of the 

 septum. 2. That with the same solution, or with pure water, in 

 contact with both surfaces of a membrane, there will be no chemical 



