58 RELATION OF ENDOSMOSIS TO CAPILLARY ATTRACTION. 



181. It is necessary, before entering into a critical examination of these points, to 

 explain briefly the leading experiments which have been reported in connexion with 

 the subject. Often received upon doubtful evidence, and sometimes implying the exist- 

 ence of laws which, if established, would compel us to modify our opinions of chemical 

 agency in general, it is time that the whole of them should pass under a connected 

 review, their bearings upon each other be properly designated, and the true value which 

 ought to be attached to them ascertained. If thus examined, it will be found that they 

 are very far from establishing the points supposed ; and in compliance with the usages 

 of science, their application must be rejected. 



182. We shall have to consider, 1st, those experiments which refer to changes of 

 hydrostatic level of liquids, and the production of mechanical results ; 2dly, those which 

 are reputed to be examples of chemical depositions brought about by tissue action. 



83. The original experiments of Porrett, Fischer, and Dutrochet, are instances of 

 the first class ; from them the terms endosmose and ex osmose are derived. They are 

 essentially illustrations of the fact, that if two fluids be separated from one another by 

 a porous barrier, they will mutually traverse it, but very often not with equal velocities, 

 for the volume of the one passing in a given time may exceed the volume of the other, 

 and hence a disturbance oCitheir hydrostatic level results. If, for example, we take a 

 tube, and close one of its ends with a piece of bladder, securely tied on, and fill it to a 

 certain mark with alcohol, and then place it in a vessel of water, taking care that the 

 hydrostatic level inside the tube, and that on the outside, shall coincide, in the course 

 of a few hours it will be found that this equilibrium has been entirely disturbed, and the 

 level of the alcohol risen. On reversing the arrangement, and placing the water in 

 the tube and alcohol on the outside, there will be, at the completion of the experiment, 

 a similar disturbance, but now the level will be found to have fallen. 



" (a.) In this way it was found that there was endosmose from water to gum-water, 

 to acetic acid, to nitric acid, and especially to hydrochloric acid ; but that there was 

 not endosmose from a liquid to itself. 



" (6.) And that different animal and vegetable membranes enjoyed the same proper- 

 ties as bladder, in different degrees, and that plates of burned earth, or calcined slate, or 

 clay, and, in general, all aluminous substances, possessed analogous powers, though to 

 a much less extent. 



" (c.) To explain these phenomena, it is necessary to resort to some force different 

 from ordinary capillary attraction, or, at least, to some new modification of it ; for the 

 forces of capillarity, such as they are now understood, are totally insufficient to produce 

 these results." (Pouillet^) 



184. The second class of experiments, though often affording well-marked illustra- 

 tions of change of hydrostatic level, is chiefly important from the instances of apparent 

 decomposition exhibited. From these it has been inferred, not only that membranes 

 possessed certain definite chemical powers, but that at times they gave proof of a predi- 

 lection for the passage of certain bodies in determinate directions through them. 



185. If litmus water be placed on one side of a piece of bladder, and alcohol on the 

 other, the water will forsake the colouring matter to pass through the bladder and unite 

 with the alcohol. 



