442 M. De la Rive on Ckemico-capillary Actions. 



decomposed, and not the metallic solution, so long at least as 

 the two solutions are not mixed. 



If, now, two cracked vessels be taken containing acidulated 

 water and immersed in a solution of nitrate of copper, the sides 

 of the fissures act in that case like intermediate conductors; the 

 outside of the positive vessel becomes covered with metallic 

 copper, while the acid is given off on the negative electrode. 

 The part of the narrow fissures is here that of preventing the 

 mixture of solutions ; they act then like intermediate conduc- 

 tors; the two plates of platinum are in conducting non-metallic 

 solutions, which do not mix with the metallic one, though they 

 are in contact with it. 



The phenomenon we have described is quite analogous to an 

 experiment of Faraday, in which that illustrious physicist passes 

 an electrical current through a concentrated solution of sulphate 

 of magnesia in contact with a certain quantity of pure water 

 placed above, and arranged so that the two liquids cannot mix. 

 Putting the positive electrode in the sulphate of magnesia and 

 the negative one in water, the magnesia, instead of being depo- 

 sited, on the surface of the negative platinum electrode, stops in 

 the water at the boundary of it and the sulphate. This fact, 

 which is easily explained on Grothiiss's theory, is owing to the 

 fact that the molecule reaching the water no longer finds a mo- 

 lecule of acid with which it can combine, which would not be 

 the case if the water and the sulphate could have become mixed 

 even in small proportion. It is probably a phenomenon of the 

 same kind which occurs in BecquerePs experiment, and that the 

 fact he has observed is due to the circumstance that, the solution 

 of nitrate of copper only being connected with the two acid so- 

 lutions by the intervention of the capillary fissures, there can 

 be no mixture between them. But when there is no mixture 

 in more or less considerable proportion between two adjacent 

 solutions, there can be no ordinary electrolysis. 



In his fourth memoir, M. Becquerel describes a very ingenious 

 method of M. E. Becquerel of measuring capillary spaces, and 

 especially the magnitude of fissures, and even the dimensions of 

 the pores of vegetable or animal membranes. The method in 

 question consists in comparing the conducting- power of a liquid 

 enclosed in the capillary space to be measured with the conduct- 

 ing-power of the same liquid placed in a capillary tube, the dia- 

 meter and length of which are exactly known. This method is 

 extremely delicate, and by its means intervals of a few thou- 

 sandths of a millimetre may be measured ; yet it requires in its 

 application some precautions and certain preliminary deter- 

 minations. 



Measurements made by this method have shown that when 



