DEPOSITES PRODUCED BY ENDOSMOTIC CURRENTS. 



67 



Some physicians have made important, but unwarrantable deductions from them. Sacs 

 formed of animal tissues have been supposed to be competent to expel saMine matters 

 from them by exosmose, while they were introducing water by endosmose. No general 

 rule of this kind will apply, nor will the hypothesis that a current passes in one direction 

 only, bear the test of a close examination. It has been stated that, when oxalic acid 

 and lime-water are separated from each other by a membrane, a precipitate of oxalate 

 of lime takes place on the side of the lime-water, and, therefore, the current sets from 

 the acid to the lime-water, but none in the opposite direction. The same occurs in the 

 case of Prussian blue, which is always found on one side of the membrane. The ac- 

 tion is correctly reported, but the inference is erroneous. 



2 IS. I took a number of tubes, open at both ends, and tied a piece of bladder on 

 each. They served to contain a fluid which might communicate with one of a differ- 

 ent kind, capable of giving a precipitate, contained in a glass receiver. 



a Contained sulphocyanate of potassa in the tube, and solution of persulphate ot 

 iron iu the reservoir. 



b Contained solution of iodide of potassium in the tube, and solution of bichloride of 

 mercury in the reservoir. 



c Contained solution of oxalic acid in the tube, and lime-water in the reservoir. 



d Contained solution of chloride of barium in the tube, and dilute sulphuric acid in 

 die reservoir. 



e Contained prussiate of potassa in the tube, and persulphate of iron in the reservoir. 



/ Contained prussiate of potassa in the tube, and protosulphate of iron in the reservoir. 



g Contained bichromate of potassa in the tube, and acetate of lead in the reservoir. 



h Contained dilute muriatic acid in the tube, and solution of nitrate of silver in the 

 reservoir. 



i Contained solution of prussiate of potassa in the tube, and sulphate of copper in 

 the reservoir. 



219. In the course of a few days it was found that, in the arrangement marked a, c, 

 d,f, the level within the tube had risen, and the deposite of sulphocyanate of iron, oxa- 

 late of lime, sulphate of baryta, and Prussian blue, had taken place within the tube ; in 

 the arrangements b and g, the precipitates of biniodide of mercury and chroinate of 

 lead were entirely interstitial, the pores and cellular tissue of the membrane being 

 choked with them, but none had escaped into the fluids on either side of the barrier ; 

 the membranes, when thus injected, formed very pretty microscopical objects; the level 

 in the tube b had risen, but that in g had fallen. In the arrangements e and h, the level 

 in the tube had risen, but the deposite was found on the outside. In i, after several 

 days, no action of any kind could be perceived, due, perhaps, to the unusual thickness 

 of the membrane. 



220. From the aggregate of these experiments we gather, that in nearly all cases 

 where two fluids, which, being mixed, give rise to an insoluble precipitate, are separa- 

 ted from each other by a membrane, the precipitate will be found on one or other 

 of the sides of that membrane, but hardly ever on both ; sometimes the action appears 

 to be checked by the choking of the pores and interstices, and then little or no depos- 

 ite is found on either side of the tissue. 



