THEORETICAL OBSERVATIONS. 



WE have described at considerable length the practical details 

 connected with the art of electro-metallurgy, without pausing to in- 

 quire into the philosophy of the action of the electric currents by 

 which the effects are produced. It will be unnecessary to enter into 

 a long discussion of the numerous theories that have been advanced 

 from time to time to "explain the action that takes place in a battery 

 or decomposing cell, while the current is passing through the solu- 

 tion a brief reference to the more commonly received opinions 

 being sufficient for the present purpose. 



Action of Sulphate of Copper on iron. In order to convey our 

 ideas accurately, let us suppose that the solution undergoing decom- 

 position is sulphate of copper. This salt is composed of sulphuric 

 acid and copper, which may be represented as SO 4 + Cu : these are 

 held together according to the law of chemical affinity ; but if iron 

 is put into the solution, the combination of the acid and copper will 

 be dissolved by the attraction of the acid to the iron, for which it 

 has a stronger affinity than for the copper. Hence iron, put into 

 sulphate of copper, decomposes it thus: 



Cu, SO 4 + Fe = Fe, SO 4 + Cu. 



Were we to put a piece of copper into a solution of sulphate of copper, 

 there would be no action, the forces being equal ; but if by any 

 means we were to communicate to this piece of copper a higher 

 attractive force for the SO 4 than that of the copper which is already 

 in union with it, we should cause the acid to leave the copper it was 

 originally combined with, and to combine with the new piece of 

 copper. Bearing these general principles in view, we shall proceed 

 to state the different opinions of authors on this subject. 



Faraday^ Theory of Electrolysis. Professor Faraday says 

 " Passing to the consideration of electro-chemical decomposition, it 

 appears to me that the effect is produced by an internal corpuscular 

 action, excited according to the direction of the electric current, and 

 that it is due to a force either super added to, or giving direction to. 



