The varieties of sulphate of lime which may be employed in endosmometrical experiments are not sufficiently numerous or of sufficient variety of permeability for it to be possible to appreciate the properties of this substance in relation to endosmosis. I found that the sul phate of lime used in the manufacture of plaster in the environs of l'aris, employed in thin plates to close an endosmometer, did not produce endosmosis. But this mineral is per haps too easily permeable. In fact it is found impossible to obtain endosmosis when the in terior fluid of the endosmometer flows easily by filtration, in virtue of its weight, through porous plates. I should say as much of plates of freestone (grey) which I have employed without success in these experiments, but that I recollect to have obtained the phenomenon in a very slight degree with a plate of freestone very close-grained and very little permeable to fluids.
I have tried a variety of experiments slim ing that an increase of temperature increases endosmosis. This result has been confirmed by repeated experiments.
The quantity of the same fluid introduced by endosmosis, and with the same sort of per meable partition, is generally in proportion to the extent of surface of this partition. The following experiment demonstrated this fact. I took two endosmometers, the membranes of which, taken from the same bladder, were of diameters in the relation of one to two; I filled the reservoirs of these two endosmometers with syrup of equal density, and then plunged them into pure water. I had taken care to weigh them previously with great exactness. After continuing the experiment for two hours, I weighed the instruments afresh, and found in the large endosmometer four times as great an increase of weight as in the small one, which proved that the first had introduced, by endos mosis, four times as much water as the second. This relation was exactly that of the extent of surface of their respective membranes, the diameters of which were as one is to two, and their surfaces consequently as one is to four.
I have thus enumerated the effects; let us now endeavour to ascertain their causes.
The first idea which presented itself to my mind to explain the phenomenon of endosmosis was that it was owing to electricity. We know that effects exactly similar to those of endos mosis are produced by means of the electricity of the voltaic pile in the experiment of 1\I. I'orret, inserted in the Annales de Chimie, vol. xi. p. 137. This naturalist having divided a vessel into two compartments by a septum of bladder, filled one of the compartments with water, and put only a small quantity in the other. Having placed the positive pole of the
pile in communication with the compartment full of water, and the negative pole with the compartment containing little water, the fluid was forced through the bladder from the full compartment into the almost empty one, and there rose to a higher level than that to which it was reduced in the original full compart ment.
I varied this experiment by applying it to my own apparatus. I put pure water into an endosmometer, the membrane of which was plunged into water. I made the interior water of the endosmonicter communicate with the negative pole of the pile, and the exterior water with tho positive pole. I soon saw the water rise in the tube of the instrument : en dosmosis had taken place. The similarity of effects led me to admit that some particular and unknown mode or funn of electricity was the cause of the endosmosis produced by the heterogeneous nature of fluids. It was in vain, however, that I tried to discover signs of this electricity with the most delicate electro meters.
In reflecting afterwards upon what might be the common cause of the phenomenonpre sented in Porret's experiment and that or dinary eodusmosis, I was inclined to think that electricity might not be the immediate cause of the effects exhibited, and that it only acted in the case cited by producing heteroge neousness of quality in the two fluids subjected to the positive and negative poles. Experience seems to have confirmed may doubts on this point. I took a small endosmometer of glass, closed by a piece of bladder, and filled its re servoir with water coloured blue with the co louring matter of violets; I plunged the reser voir of this endosmometer into the same co loured water contained in a small glass vessel; I put this latter fluid in communication with the positive pole of the voltaic pile, and the interior fluid of the endosinometer in commu nication with the negative pole. The exterior blue fluid soon became red, and consequently acid, and the interior blue fluid became green, and consequently alkaline. These two fluids having thus become heterogeneous, to this may be ascribed the endosmosis which manifested itself, and which increased the volume of the interior fluid at the expense of the volume of the exterior fluid. Thus electricity would not be in this case the immediate cause of endos mosis, but the remote one ; it would only act in producing the heterogeneous quality in the two fluids, and it would be this quality which would produce the passage of fluids as in the experiments mu endosmosis, the discovery of which belongs to me.