106 



ENDOSMOSIS. 



membrane of the endosmometei: must have 

 been kept plunged in the watery solution about 

 to be experimented on for at least a quarter of 

 an hour, in order that it may become tho- 

 roughly impregnated with the solution, and to 

 secure that this should take the place of the 

 water which the membrane had formerly con- 

 tained in its pores. Without this measure of 

 precaution, the results of the second experi- 

 ment would be faulty. It is also indispensa- 

 ble that the circumstances under which the 

 two experiments are performed are in all re- 

 spects exactly alike. It was in this way that I 

 proceeded to ascertain comparatively the capa- 

 city of nitration of water to that of a watery 

 solution of oxalic acid through a piece of blad- 

 der. I found that the nitrating power of rain- 

 water, at the temperature of -4- 21 cent, being 

 denoted by 24, the nitrating power of a watery 

 solution of oxalic acid of no greater density 

 than 1.005, (1.2ofacidto lOOof solution,) was 

 denoted by 12. A solution of the same acid, of 

 thedensityof 1.01, beingtried, its filtrating power 

 was found to be represented by 9. By these ex- 

 periments it is therefore proved that water tra- 

 verses an animal membrane more readily than 

 a solution of oxalic acid. Why then does the 

 latter solution traverse an animal membrane 

 more readily and in greater quantity than water, 

 when it is water which is in contact with the 

 surface of the membrane opposite to that which 

 is in contact with the acid ? This is a question 

 which I find it impossible to answer in the 

 present state of our knowledge. 



The discovery of this singular property of 

 the oxalic acid to cause the endosmotic current 

 to flow towards the water when separated from 

 the latter fluid by a lamina of animal mem- 

 brane, led me to imagine that all the acids 

 would be found to possess a similar property. 

 And this I ascertained, in the first instance, to 

 be the case in regard to the tartaric and citric 

 acids. Both of these acids are much more so- 

 luble in water than oxalic acid. The saturated 

 solution of oxalic acid at + 25 cent, has no 

 higher a density than 1.045 (11.6 acid to 100 

 of the solution.) But the solubility of the tar- 

 taric and citric acids is such that their watery 

 solutions may have a density of far greater 

 amount. I tried the endosmotic effects of the 

 tartaric and citric acids in watery solution of 

 various density, and I discovered, not without 

 surprise, that very dense solutions of them and 

 solutions of inferior density exhibited endos- 

 motic phenomena in inverse ratios. Thus, 

 when a solution of tartaric acid was of a den- 

 sity above 1.05, (11 crystallized acid in 100 of 

 solution,) and it was divided from water by an 

 animal membrane, the temperature being + 25 

 cent, the endosmotic current is directed from 

 the water towards the acid ; but when, under 

 the same circumstances, the density of the acid 

 solution is below 1.05, the current of endos- 

 mosis is directed from the acid towards the 

 water, just as we have found it to be with refe- 

 rence to the oxalic acid. Consequently, ac- 

 cording to its greater or less density, tartaric 

 acid presents the phenomenon of endosmosis in 

 two opposite directions. At the mean density 



of 1.05, at a temperature of + 25 cent, it 

 exhibits no obvious endosmotic phenomena 

 whatever ; not that there is not reciprocal pe- 

 netration between the acid and the water, which 

 are divided by the animal membrane ; but this 

 reciprocal penetration takes place so equally on 

 either side, that there is no increase of bulk of 

 the one fluid at the cost of the other there is 

 no endosmosis. The citric acid exhibits pre- 

 cisely the same phenomena; the point of mean 

 density, which divides its two opposed endos- 

 motic capacities, is also very nearly the same, 

 namely, 1 .05 at a temperature of -\- 25 cent. 

 These facts induced me to imagine that if the 

 oxalic acid alone presented the endosmotic cur- 

 rent directed from the acid towards the water, 

 this arose from the fact of its solution at + 25 

 cent, falling short of the density necessary to 

 permit the acid solution to cause the endosmo- 

 tic current to flow from the water towards the 

 acid. 



The preceding observations were made during 

 the heats of summer. The centigrade thermo- 

 meter was standing at + 25 when I determined 

 the mean term of density of the solution of tar- 

 taric acid, above and short of which the endos- 

 mosis happening between this solution and 

 water is directed towards the acid. It was of 

 importance to know whether a depression of 

 temperature would cause any modification in 

 these phenomena. I therefore repeated the 

 same experiments when the temperature was 

 + 15 cent, and I was astonished to find that 

 the mean term of density, of which we have 

 spoken above, was considerably altered, being 

 made to move in the direction of the increase 

 of density of the acid solution. Thus the mean 

 term of density being 1.05, (11 crystallized 

 acid to 100 solution,) at a temperature of + 25 

 cent, it came to be 1.1, (21 acid to 100 solu- 

 tion,) at a temperature of +15 of the same 

 scale ; that is to say, the solution of tartaric 

 acid, which now occupies the mean term, con- 

 tains nearly twice as much acid as the solution 

 which stood at the previous mean term, when 

 the temperature was ten degrees of the centi- 

 grade scale higher. This first essay was enough 

 to lead to the inference that the mean term of 

 density, which we are now discussing, would 

 undergo further alterations in the same sense 

 with further depressions of temperature; and 

 this was actually found to be the case. At a 

 temperature of 8 cent, the solution of tarta- 

 ric acid, of the density 1.1, was no longer the 

 solution of mean density dividing the two op- 

 posed endosmotic currents, as it was when the 

 temperature was + 15 cent. This solution 

 then caused the endosmotic current to flow 

 freely towards the water. I had to increase its 

 density to 1.15 (30 acid to 100 solution) to 

 come to the new mean term, beyond which the 

 current of endosmosis was directed towards the 

 acid, and within which it was directed towards 

 the water. With the temperature depressed to 

 a quarter of a degree cent, above zero, the 

 solution of tartaric acid, of the density of 1.15, 

 no longer presented the mean term; this solution 

 now occasioned endosmosis towards the water, 

 which indicated that the mean term was to be 



