ENDOSMOS1S. 



107 



sought for in a more dense solution of tartaric 

 acid, and this I actually found in a solution of 

 the density of 1.21 (40 acid to 100 solution). 

 Every solution of this acid of greater density 

 than 1.21, at the temperature of th of a degree 

 above zero cent, caused the endosmotic cur- 

 rent to flow from the water towards the acid, 

 and every solution of the same acid, under the 

 density of 1.21, caused the endosmotic current 

 from the acid towards the water. From all 

 these experiments it follows that a fall of tem- 

 perature favours the endosmosis towards the 

 water, and that a rise of temperature favours 

 the endosmosis towards the acid. In fact, the 

 same solution of tartaric acid occasions at one 

 time endosmosis towards the acid, when the 

 temperature is high ; at another, endosmosis 

 towards the water when the temperature is re- 

 latively low. It would appear from this, that 

 a depression of temperature renders the solu- 

 tion of tartaric acid more apt than water to 

 permeate animal membranes, and that there is 

 a certain concordance between this capacity of 

 permeation and the temperature and the den- 

 sity of the acid solution. This phenonernon, 

 at first sight, appears analogous to that which 

 M. Girard discovered,* in regard to the com- 

 parative flow of a solution of nitre and of pure 

 water through a capillary glass tube. M. Girard 

 found that, at a temperature of -J-10 , a solu- 

 tion of one part of nitrate of potash in three 

 parts of water flows more rapidly than pure 

 water through a capillary glass tube, whilst the 

 same solution flows more slowly than water 

 when the temperature is above -{- 10. To 

 discover whether this apparent analogy was 

 well founded or not, I made an experiment to 

 ascertain the relative duration of the flow 

 through a capillary glass tube of a given mea- 

 sure of pure water, and a like measure of a 

 solution of tartaric acid, the density of which 

 was 1.05 (21.8 parts acid, 100 solution.) The 

 temperature being + 7 cent. I found that 

 fifteen centilitres of water flowed through a ca- 

 pillary glass tube in 157 seconds; but the 

 same quantity of the solution of tartaric acid 

 required 301 seconds to pass through the same 

 capillary tube. There is consequently no ac- 

 tual analogy to be established between the re- 

 sults of the experiments of M. Girard and the 

 fact of the endosmosis towards the water, which 

 takes place when at a temperature of +7 

 cent, a solution of tartaric acid of the den- 

 sity of 1.105, is separated from a volume of 

 pure water by a piece of an animal membrane. 

 It may be as well if I here state that when a 

 solution of one part of nitrate of potash in three 

 parts of water was separated by a piece of 

 bladder from pure water, I have always ob- 

 served the endosmotic current directed towards 

 the solution ; the temperature might be at 

 zero, or -f- 10, or higher, the same phenome- 

 non always occurred. This is sufficient to 

 prove that endosmosis is governed by laws en- 

 tirely different from those that preside over 

 simple capillary filtration. I add, that the 

 solution of tartaric acid, of 1.105 density, hav- 



* Mem. de 1'Acad. des Sciences, 1816. 



ing a viscidity nearly the double of that of 

 water, and passing, nevertheless, by endosmo- 

 sis into the latter fluid, when it is separated 

 from it by an animal membrane, and the tem- 

 perature is + 7 cent, also proves that endos- 

 mosis does not generally depend on the visci- 

 dity of fluids. 



Acid solutions are the only fluids which have 

 yet been found to occasion the endosmotic cur- 

 rent to flow towards water when separated from 

 this fluid by an animal membrane. The whole 

 of the acids, without exception, exhibit this 

 phenomenon, which was long overlooked by 

 me, from its having been confounded with 

 another phenomenon, namely, the abolition of 

 endosmosis. I have in fact shown, in a work 

 already before the public,* that all fluids which 

 act chemically on the membrane of the endos- 

 mometer, put an end, with greater or less cele- 

 rity, to the phenomenon of endosmosis, it 

 goes on for some time, but it never fails to 

 cease at length. Sulphuric acid, above all the 

 other acids, has the property of putting an end 

 to endosmosis. This acid, poured into the en- 

 dosmometer, sinks by virtue of its simple gravity 

 towards the lower water, filtering mechanically 

 through the membrane placed between it and 

 the water. If the position of the two fluids be 

 reversed, the endosmometer being charged with 

 water, and the sulphuric acid placed externally 

 and on the lower level, the water still sinks to- 

 wards the acid, passing in its turn mechani- 

 cally through the membranous septum of the 

 instrument, rendered incapable of effecting en- 

 dosmosis. From these experiments I was led 

 at first to conclude that sulphuric acid was in- 

 active as regards endosmosis ; in other words, 

 was incapable of exhibiting or producing this 

 phenomenon. I have since found, however, 

 that the sulphuric, like all the other acids, has 

 the faculty of exerting endosmosis in the two 

 opposite directions, but always during a very 

 brief space of time only. Thus the tempera- 

 ture being + 10 cent., sulphuric acid, of the 

 density of 1.093, separated from water by a 

 piece of bladder, the endosmotic current is 

 directed from the water towards the acid, but 

 the phenomenon lasts only for a short time ; 

 the current soon ceases, and if the acid be on 

 the higher level, it then begins to sink by sim- 

 ple mechanical filtration towards the water. 

 At the same temperature of + 10 cent., the 

 sulphuric acid attenuated to 1.054 being placed 

 in the endosmometer, and the reservoir and a 

 part of the tube being plunged in water, en- 

 dosmosis is established, but in this case the 

 current is from the acid towards the water, so 

 that the acid liquor sinks in the tube ; and that 

 this sinking is due to endosmosis is demon- 

 strated by the fact of the acid continuing to 

 sink in the tube of the endosmometer a consi- 

 derable way below the level of the external 

 water, and not stopping short when the level is 

 obtained, as it does when the descent is owing 

 to simple mechanical filtration. In this expe- 

 riment, as in the one detailed immediately be- 



* Nouv. Rechcrches sur 1'Kndosmose, &c. p. 25. 

 See also my Memoir in the 49th vol. of the Aunales 

 de Chiinic, p. 415. 



