Sulphuric acid of 1.0274 density and at a temperature of + 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.
Ilydrosulphuric acid (density 1.00628) sepa rated from water by an animal membrane, always shows endosmosis towards the water ; 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 + 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 + 25° centes. (I have made no experiments on endosmosis at higher tem(eratures.) W'hen 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 bad 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 endosinosis 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. Ilydrosulphuric 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 flict I ascertained under a variety of temperatures from + 4° to + 2.5^ 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 duetion 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 front 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 endosmotie 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 greater ease and more rapidity than pure water.