366 Transactions. — Chemistry. 



A wide fissure allows the diffusion of the liquids to such an 

 extent that each atom of copper as it is reduced is immediately 

 sulphurised, and so there is no metallic decomposition mani- 

 fested. The narrower fissure allows of an electrical current 

 being set up in one direction, thus favouring metallic deposi- 

 tions, and this solely by limiting the chemical action to a 

 certain line or point. On the other hand, while wide fissures 

 do not prevent the production of electrical currents, they 

 hinder any ocular demonstration of their presence. The 

 liquids mix in a confused, irregular manner, whereby innume- 

 rable currents are set up, which, having no determinate direc- 

 tion, either neutralise each other or form only minute metallic 

 deposits, which almost simultaneously with tlfeir formation are 

 sulphurised to the cupric sulphide, and thus become oblite- 

 rated. 



I shall now pass on to a criticism of those minor state- 

 ments of Becquerel's communications upon this subject which 

 also appear to me to be erroneous. 



His suggestion that the walls of these capillary fissures 

 conduct a current of electricity before copper is deposited 

 thereon seems to be wrong for two reasons. First, there can 

 be no electric current produced until copper sulphide has 

 formed in the narrow part of the fissure ; and this compound, 

 being, as I have already shown, an excellent conductor, will 

 certainly conduct the current. Second, as glass — the material 

 Becquerel used for his cell— is a dielectric, and the solutions 

 electrolytes, it is manifest that the current was conducted by 

 the saline solutions filling the fissure itself, and not by means 

 of its walls. 



His assumjation that the copper which is deposited in his 

 cell or any part of it is due to the decomposition of the cupric 

 sulphide is very difficult of belief. It is well known that this 

 sulphide is a very fixed compound, the affinities of its elements 

 for each other being very strong. Neither potassium sulphide 

 nor cupric sulphate separately have any reducing effect upon 

 it, and it is very improbable that any product arising from 

 their interaction would be able to effect what they separately 

 could not do. 



In his controversy with Loew regarding the deposition of 

 copper in capillary spaces Becquerel is undoubtedly correct in 

 affirming the existence of electric currents ; also in assuming 

 that these are used in the deposition of the copper. His error 

 consists in the assumption that capillarity is necessary to sup- 

 plement and complete the action. 



In regard to Loew's own results with cupric-sulphate 

 crystals placed in a solution of potassium sulphide, they show 

 that even here electric force has had a large share in producing 

 them — that his experiments, in fact, are merely a modifica- 



