190 APPENDIX. [No. X. 



7. The repetition of these experiments deeply impressed my mind 

 that hydrogen evolved from the decomposition of water is really the 

 cause of the reduction of the metals, and I pursued my experiments to test 

 this idea, the first promulgated on the subject, and the one supported by 

 our eminent galvanist, Dr. Faraday. 



8. The next stage of investigation consisted in inquiring as to whether 

 the transfer of the metal took place uniformly and synchronously with 

 this reduction. It is apparent that such a transfer is absolutely necessary 

 to the theory of the direct electrolysis of the metallic salt, but let us see 

 what is the result. I prepared a uniform solution of sulphate of copper, 

 and placed at the bottom of a tall vessel containing it a positive copper 

 pole, and at the upper part a negative pole of the same metal, forming a 

 circuit by means of one or two cells of my galvanic battery. On the action 

 of the voltaic force bright reguline copper at first appeared at the negative 

 pole ; this was followed by a brittle, this by a sandy, this by a spongy 

 deposit, this by black powder, and finally hydrogen was evolved. 



9. This most important experiment was repeated in a variety of ways 

 and with various metallic salts, with the details of which there is no need 

 to trouble the Society, because the experiment just described as an example 

 points out in the most positive manner that the transfer of metal is not 

 proportionate to the metal reduced. The positive pole indicates the same 

 fact, for it became coated with metallic salt, showing beyond all source of 

 fallacy that the metallic salt was directly formed at one pole and the 

 metal directly reduced from another portion of the metallic solution at 

 the other. In a neutral solution of any metallic salt, as that of copper, 

 the acid is no more equally transferred to the positive pole than the metal 

 is to the negative ; and we find in its decomposition that the positive pole 

 is frequently coated with oxide of copper of considerable thickness, and 

 from the liberation of an equivalent of sulphuric acid from the sulphate 

 the solution speedily becomes acid. 



10. Not only in the above-described experiments have I observed this 

 fact, but in the experiments of the decomposition of above one hundred 

 different salts, including those of twenty distinct metals, which I performed 

 for my work on 'Electro-Metallurgy,' did the results show themselves 

 more or less evidently; and I may state that no electro-metallurgical 

 process can be conducted without the production of these phenomena ; 

 and one of the greatest, if not the very greatest difficulty which the 

 electro-metallurgist has practically to contend with, is the variation 

 in the strength of the metallic salts subjected to decomposition.* 



* Nov. 20, 1844. I happened to call yesterday upon that excellent practical 

 electro-metallurgist, Mr. Home, of Newgate Street, and found that he was 

 making an electro statue of Sir John Crosby, in a mould prepared by the 

 sculptor, Mr. Samuel Nixon, from the original model also executed by him. 

 Mr. Home was engaged about the leg, and he stated that he was much troubled 

 by the non-uniform diffusion of the metallic salt through the solution. The 

 mode in which he overcame the difficulty was very simple : he introduced a 

 glass tube every now and then to the bottom of the leg and blew through it, 

 which caused a proper mixture of the exhausted and saturated solutions. The 

 fact was a pretty practical example of the opinions which I have been endeavour- 

 ing to enforce ; it shows that the theorist may in vain attempt to bolster up 



