Skey. — Fallacy of the Electro-capillary Theory. 365 



Solutions of potassium sulphide and cupric sulphate are 

 connected by two siphons filled with a solution of sodic 

 chloride, as shown in the accoinpanying diagram : — - 



A. Potassium sulphide. B. Sodic chloride. C. Cupric sulphate. 



In the solution of potassium sulphide a plate of sulphurised 

 platinum, galena, or covelline is placed, and this is connected 

 with a platinum electrode placed in the cupric sulphate. In 

 a short time it will be found that the platinum which has con- 

 tact with the cupric salt is covered with metallic copper, and 

 it may be observed that this effect is produced before any film 

 or precipitate of cupric sulphide or any other compound has 

 formed. Clearly, then, in this instance no portion of the effect 

 is due to capillary or osmotic force. 



In Becquerel's so-called electro-capillary apparatus what 

 really takes place is this : The first action is the formation of 

 sulphide of copper in that part of the fissure joining the two 

 solutions which is contiguous to the potassium sulphide. This 

 blocks the fissure at that point, cuts it off from the sulphide, 

 and produces a measure of electric force — in fact, a current — 

 which, being conducted by the sulphide, finds its way to the 

 copper solution by another part of the fissure, and, manifest- 

 ing itself on the opposite side of the cupric sulphide, thereon 

 deposits copper, which under the circumstances, being pro- 

 tected by a crust of cupric sulphide and the walls of the fis- 

 sure, does not sulphurise, but remains as copper and forms a 

 nucleus for succeeding metallic deposits. 



Through the wider parts of the fissure the liquids slowly 

 mix, and the cupric sulphide which forms there continues the 

 electric currents, and so carries on the electro-deposition of 

 copper in the fissure or along the walls of the vessel contain- 

 ing the metallic salt. If the wider part of the fissure is under 

 a certain width the cupric sulphide forming may completely 

 dissolve in the sulphide solution, and so keep the space open 

 for the electric current. 



The narrow fissure is no doubt necessary for these results, 

 which, however, can certainly be produced by electric action 

 without being in any way aided or supplemented by capillary 

 force. 



