ENDOSMOSIS. 



109 



gradually in the tube of the endosmometer, so 

 that the endosmosis was from the water towards 

 the acid, the reverse of that which takes place 

 when the endosmometer is furnished with an 

 animal membrane. The tartaric and citric 

 acids of densities below 1.05, and at a tempe- 

 rature of + 25 cent, exhibit endosmosis to- 

 wards the water with an animal membrane ; 

 but with a vegetable membrane the case is 

 altered ; the endosmosis being then directed 

 from the water towards the acid. I have tried 

 solutions of tartaric acid, decreasing gradually 

 in density from 1.05 (11 tartaric acid to 100 

 solution) to a density so low as 1.0004, (1 tar- 

 taric acid, 1000 solution,) and always seen the 

 endosmosis towards the acid. A gradual fall 

 in the temperature from -j- 25 to near zero did 

 not affect the result. 



Sulphuric acid of 1.0274 density and at a 

 temperature of + 4 centes* when separated 

 from water by a vegetable membrane, exhibited 

 endosmosis towards the acid ; separated by an 

 animal membrane, however, the endosmosis 

 was towards the water. 



Hydrosulphuric acid (density 1.00628) sepa- 

 rated from water by an animal membrane, 

 always shows endosmosis towards the water j 

 but separated by a vegetable membrane, the 

 current is as uniformly towards the acid. The 

 experiment from which I deduce this result 

 was only performed at a temperature of -f- 5. 



Sulphurous acid (density 1.02) separated 

 from water by an animal membrane, exhibits 

 an active endosmosis towards the water, at 

 every temperature from zero up to -f- 25 centes. 

 (I have made no experiments on endosmosis at 

 higher temperatures.) When sulphurous acid, 

 of the density of 1.02, is separated from water 

 by a layer of vegetable membrane, it presents 

 neither endosmosis towards the acid nor endos- 

 mosis towards the water ; it then appears to be 

 under the influence of the simple laws presiding 

 over the flow of fluids by filtration : there is 

 abolition of endosmosis. I was anxious to see 

 what endosmotic effects it would produce with 

 an endosmometer closed with a layer of .baked 

 clay, and it was not without surprise that I saw 

 the current flowing vigorously towards the 

 water. I had put the acid into the reservoir of 

 the endosmometer ; and the included fluid rose 

 to a considerable height in the tube of the in- 

 strument, which I had taken care to immerse 

 in water to the place where the acid rose in the 

 tube. The acid continued to sink in the tube 

 of the endosmometer for four hours, and had 

 then fallen to about 12 centimetres below the 

 level of the external water ; it subsequently be- 

 gan to rise slowly in the tube, and finally 

 gained the level of the external water, where it 

 remained. It was obvious that the sulphurous 

 acid had sunk in the tube below the level of the 

 water, in consequence of endosmosis towards the 

 water, and that its subsequent rise to the level 

 of the water was due to simple filtration through 

 the membrane. Endosmosis had then ceased. 

 Sulphuric acid, diluted with water to the den- 

 sity of 1.0549, exhibits the same phenomena as 

 sulphurous acid when separated from water by 

 a lamina of baked clay : it first occasions en- 



dosmosis towards the water, but after some 

 minutes this endosmosis ceases, and is not re- 

 placed by endosmosis of an opposite nature ; 

 simple filtration from the effect of gravity is all 

 that then takes place; endosmosis of each kind 

 is put a stop to. Hydrosulphuric acid, sepa- 

 rated from water by a lamina of baked clay, 

 gives the same results precisely as the sulphu- 

 ric acid. This phenomenon is rendered still 

 more strange by the fact of its not being general. 

 Thus the oxalic acid exhibits endosmosis to- 

 wards the acid when this is separated from 

 water by a lamina of baked clay. This fact I 

 ascerlained under a variety of temperatures 

 from + 4 to -h 25 centes. and with solutions 

 of the acid of" as great density as could be ob- 

 tained at each temperature, as well as with so- 

 lutions of very low density. The tartaric acid 

 also presents endosmosis towards the acid when 

 separated from water by a lamina of baked 

 clay. I had formerly found * that a little sul- 

 phuric or hydrosulphuric acid added to gum- 

 water, causes the current of endosmosis to cease 

 flowing from the water towards the gum-water, 

 so that the latter fluid, instead of rising in the 

 tube of the endosmometer, begins gradually to 

 falL I then attributed this phenomenon to the 

 abolition of endosmosis ; but it is evident that 

 in certain cases it is owing to the current of en- 

 dosmosis changing its direction and flowing 

 from the acid towards the water. Thus, with 

 reference to the acidulated gum-water, of which 

 I have just spoken, when placed above water, 

 from which it was separated by an animal 

 membrane, it fell in the stem of the endosmo- 

 meter and flowed towards the water, either from 

 the abolition of endosmosis, and in virtue of its 

 gravity, or in consequence of the establishment 

 of an endosmotic current towards the external 

 water. Experiment can alone determine which 

 of these two causes is the efficient one of the 

 descent of the acidulated fluid in the stem of 

 the endosmometer. The whole of the acids 

 used of such density as comports with the pro- 

 duction of endosmosis towards water, and in 

 sufficient quantity, are adequate to overcome 

 the disposition which any fluid may possess to 

 produce endosmosis in the opposite direction. 

 Here is a case in illustration of this point. The 

 power of sugar-water in causing endosmosis is 

 very great, as I have shown already. Water 

 holding no more than one-sixteenth of its 

 weight of sugar in solution causes rapid endos- 

 mosis from the water towards the solution. But 

 I have found that, by adding to this sweet 

 liquid a quantity of oxalic acid equal in weight 

 to that of the sugar which it holds in solution, 

 the direction of the endosmotic current is im- 

 mediately changed ; the flow is no longer from 

 the water towards the solution, but from the 

 sweet-sour solution towards the water, so that 

 the oxalic acid may be said to compel the sac- 

 charine solution to which it is added to take 

 the direction of the endosmotic current which 

 is proper to it. Here it is the viscid and dense 

 fluid, with little power of capillary ascent, 

 which traverses the animal membrane with 



* Nouv. Rech. sur 1'Endosmose, p. 8. 



