102 



ENDOSMOSIS. 



just mentioned;- and filially, that the viscidity 

 of the gum-water, containing two parts of gum 

 to thirty-two of water, (density 1.023,) is twice 

 as viscid as the solution of sugar employed. 



It seems that nothing more is wanting to 

 these proofs of the fact that endosmosis does 

 not depend on the mere viscidity of fluids. 

 Nevertheless I shall cite another proof of this 

 truth. The very singular fact I am about to 

 mention will also prove that the septa employed 

 exert a special influence on the direction in 

 which endosmosis takes place. 



It is well known that, in separating water 

 from alcohol by an organized animal or vege- 

 table membrane, the endosmotic current flows 

 from the water towards the alcohol. I employed 

 oil-silk (taffetas gomme) or silk covered with a 

 layer of caoutchouc, which may be regarded as 

 equivalent to a thin lamina of elastic gum, as 

 the medium of separation between these two 

 fluids. During the first thirty-six hours of the 

 experiment, I observed an extremely slow en- 

 dosmotic current from the alcohol towards the 

 water. After this period the endosmosis, with 

 the same direction, became very rapid. This 

 increase in the rapidity of the endosmosis I 

 considered due to some alteration in the caout- 

 chouc produced by the action of the alcohol, 

 and in consequence of which it became more 

 readily permeable. The endosmotic current, 

 however, let it be observed, is always from the 

 water towards the alcohol in this experiment, 

 instead of being from the alcohol towards the 

 water, as is constantly the case when the septum 

 between the spirit and the water is formed by 

 an organic, whether animal or vegetable, tissue. 

 We have thus a clear demonstration of the 

 great influence possessed by the septum upon 

 the direction of the current of endosmosis. We 

 have, also, in the instance just quoted, a proof 

 that the different degrees of viscidity of two 

 liquids plays no part in the production of this 

 phenomenon. I would remark that the endos- 

 motic current carrying the alcohol towards the 

 water athwart the septum of caoutchouc is ac- 

 companied by a counter-current, which carries 

 the water towards the alcohol through the same 

 septum. I assured myself that the alcohol had 

 received some addition of water; and yet it is 

 well known that caoutchouc is impermeable to 

 water ; which would seem to say that the latter 

 fluid could only have passed through the sep- 

 tum of caoutchouc by becoming mingled with 

 the alcohol occupying the molecular interstices 

 of that substance. Once within these intersti- 

 ces the alcohol attracts the water by the affinity 

 of mixture, (affinite, de mixtion) and enables 

 it to penetrate the substance of the caoutchouc, 

 which denies all access to water when it is 

 pure. It is therefore to the state of commixtion 

 within the capillary tubes of the septum that the 

 two opposed fluids proceed the one towards 

 the other with cross but unequal motions. The 

 means I took to ascertain the fact of water 

 having become mixed with the alcohol was 

 simple enough : I set fire to a quantity of the 

 fluid which had served for the experiment, and 

 found that, after all the spirit had burned out, 



a considerable quantity of water remained, 

 whilst the alcohol, previously to being so em- 

 ployed, burned away entirely, leaving no water 

 behind it. 



The theoretical views of Magnus in regard 

 to endosmosis have been adopted by Berzelius 

 in his Chemistry, and the idea upon which they 

 are based has been reproduced by M. Poisson. 

 To give a clear notion of this theory, let us sup- 

 pose that a measure of salt water is separated 

 from a measure of pure water by a permeable 

 septum, a piece of bladder for example ; the 

 current of endosmosis, in this instance, will be 

 from the pure water towards the salt, and for 

 the following reason : in the salt water there 

 are three attractions, namely, the attraction of 

 the molecules of the water for one another; 

 secondly, the attraction of the molecules of the 

 salt for one another; and thirdly, the reciprocal 

 attraction of the molecules of the water and of 

 the molecules of the salt. The pure water on 

 the opposite side of the septum again has no 

 more than a single form of attraction, to 

 wit, that of its particles for one another. The 

 salt water subjected to three attractions will be 

 moved, it may be imagined, with greater diffi- 

 culty than the pure water, the molecules of 

 which are obedient to but one attraction. Con- 

 sequently, in the reciprocal attraction of these 

 two fluids, the one, the molecules of which are 

 the least subjected to attraction among them- 

 selves, will make its way with greatest rapidity 

 athwart the capillary conduits of the dividing 

 membrane. 



This theory has a seducing aspect, but we 

 shall find immediately that it is inapplicable to 

 certain endosmotic phenomena presented by 

 acids. 



I have shown above that it is not always to- 

 wards the denser fluid that the endosmotic cur- 

 rent is turned. Thus alcohol and ether are 

 very much less dense than water, and yet it is 

 towards these fluids of inferior density that 

 water flows in endosmotic experiments. Alco- 

 hol and ether have this in common with dense 

 fluids generally, that they rise to a less height 

 in capillary tubes than water. From this ob- 

 servation I was led to imagine that the endos- 

 motic current was always from the fluid having 

 the greatest power of capillary ascension, to- 

 wards the fluid having the least of this capa- 

 city. It is true, indeed, as we have already 

 seen, that alcohol proceeds by endosmosis to- 

 wards water when the medium dividing them 

 is caoutchouc. This would seem to say that 

 alcohol would rise higher than water in capil- 

 lary tubes of caoutchouc; and it is certain that 

 caoutchouc has a greater attraction for alcohol 

 than for water, inasmuch as the surface of 

 India-rubber is much more readily wetted by 

 alcohol than by water, which only adheres to 

 it partially and imperfectly. This fact, there- 

 fore, would not be in contradiction to my 

 theory ; although I must confess that it is not 

 reconcilable with certain endosmotic pheno- 

 mena presented by the acids, as we shall imme- 

 diately have occasion to perceive. In spite of 

 this, however, I do not think I ought to pass 



