from their Solutions hy the Galvanic Current. 437 



which was ascertained by the circuit being completed some 

 time before gas was evolved from its surface. Pieces of coke 

 thus charged with hydrogen were dipped into various metallic 

 solutions, when the metal was instantly deposited as a brilliant 

 coating on the coke. The deposit of copper affords the most 

 beautiful example, though the deposit of other metals, as of 

 silver and gold, is also striking. Coke charged with hydro- 

 gen retains the property of reducing metals many days after 

 its first saturation. 



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 promul- 

 gated 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 re- 

 sult. I prepared an uniform solution of sulphate of copper, 

 and placed at the bottom of a tall vessel containing it a po- 

 sitive 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 va-. 

 riety of ways and with various metallic salts, with the details of ' 

 which there is no need to trouble the Society, because the ex- 

 periment 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 por- 

 tion of the metallic solution at the other. In a neutral solu- 

 tion 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 posi- 

 tive pole is frequently coated with oxide of copper of consi- 

 derable 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 



