M. De la Rive on Chemico- capillary Actions. 443 



the interval between the plates is only a few hundredths of a 

 millimetre, most of the metals are reduced ; while when it is 

 only a few thousandths of a millimetre, silver and gold are easily 

 reduced, but the others only slowly and with difficulty. 



Using as a capillary space the interval between two plane 

 glass plates kept pressed against each other by a ligature, so that 

 there is only a very small capillary interval, the effects obtained 

 are much more regular than with slit tubes, which have not 

 everywhere the same width. The liquid, which is a solution of 

 a metal, is introduced between the plates by means of a small 

 reservoir at the top, and the supply is so arranged that the 

 exit of the liquid by the edges is inappreciable, which is easily 

 effected. The system of two plates between which is the liquid 

 is then immersed in an outer vessel containing the other solu- 

 tion, that of the monosulphide for instance. 



It sometimes happens that the metallic deposits formed be- 

 tween glass plates merely separated by an interval of a few hun- 

 dredths of a millimetre, between which is a band of filtering- 

 paper, and kept firmly bound, exert such an expansive force that 

 even when the bands are not broken one of the plates is. From 

 this it is readily seen how rocks through which various solutions 

 infiltrate, and in which are produced capillary effects resembling 

 those we have described, may crack or even burst. 



We shall not follow M. Becquerel in the applications which 

 he makes of his new researches to explain various natural phe- 

 nomena, either in inorganic or in organic nature. It is, in fact, 

 readily understood that, as soon as we are concerned with cases 

 in which capillarity plays an important part, this application is 

 a natural consequence. In inorganic nature the infiltrations 

 which take place in the slits of rocks ought to produce effects 

 resembling those of which we have spoken, and, especially under 

 favourable circumstances, produce a reduction of metals. In 

 organic nature it is easy to understand the important part which 

 the porous tissues and narrow vessels of vegetables and animals 

 necessarily play. M. Becquerel has endeavoured to establish 

 relations between endosmose, exosmose, and dialysis and elec- 

 tro-capillarity, of which, in his opinion, the former phenomena 

 are only particular cases. 



In conclusion M. De la Rive sums up the results of these re- 

 searches as follows : — 



The fundamental point is the influence exerted on the pheno- 

 mena which occur in the contact of the two liquids by the fact 

 that this contact takes place through a very narrow space, in other 

 words, a capillary one. Is this influence merely negative ? that is, 

 does it simply arise from the fact that the two liquids being sepa- 

 rated by a narrow space cannot mix, being all the while in contact? 



