from their Solutions by the Galvanic Current. 441 



38. In a solution of nitrate of silver the same negative re- 

 sult with paper occurred*. 



S9. The persulphate of iron was not changed into the proto- 

 salt by the action of that gas in contact with paper. 



40. As a summary of results obtained on the direct reduc- 

 tion of the metals from their solutions by hydrogen, it may be 

 stated generally, that platinized and palladinized platinum 

 alone were found to be competent to promote that change, 

 negative results being obtained with smooth platinum, smooth 

 silver, black powder of silver, bright copper, spongy copper, 

 cinder or paper. These negative results are by no means to 

 be taken as a proof that under these circumstances hydrogen 

 might not reduce the metals, for it is possible under certain 

 conditions that many other substances, like finely-divided pla- 

 tinum, might possibly take on the power of assisting in this 

 mysterious way the absorption of the gas. 



41. These various direct experiments of the deoxidizing 

 agency of hydrogen gas are valuable to the electrician, as they 

 point out the cause of some of the most interesting galvanic 

 phaenomena. To the electro-metallurgist they assume a much 

 higher importance, for they point out to him, that in the de- 

 composition of the metallic fluid the uniform strength will not 

 be preserved by the changes taking place by virtue of the vol- 

 taic current. He must therefore remember in all cases to 

 bring into play the attraction of gravity, not only to cause the 

 diffusion of the newly-formed salt, from which the metal is to 

 be deposited, but the acid to dissolve the oxide formed at the 

 positive pole. The mode in which the metals are reduced 

 may appear quite immaterial to the practical man, but he will 

 find that the non-uniform diffusion of the metallic salt arising 

 from the particular manner in which the reduction takes place, 

 is the cause nearly of all his troubles. 



42. From all these experiments we have an overwhelming 

 body of evidence, of different kinds, to support the notion of 

 the reduction of metals from their solution by hydrogen. The 

 direct reduction in the cinder experiment, the non-transference 

 of the metal, the imperfect transference of the acid, the rise of a 

 light aqueous fluid from the negative pole, the analogous case 



* November 4, 1844. — After some time the paper exhibited a black depo- 

 sition of silver; the surface of the glass tube became incrusted with a bril- 

 liant layer of metallic silver. The importance of this experiment is mani- 

 fest, for it shows that hydrogen and siliceous matter may at any time reduce 

 metals from their solutions, a power doubtless in frequent operation in 

 the bowels of the earth. How far metallic veins are thus deposited remains 

 to be proved by future investigations. The decomposition of organic 

 matter will always yield hydrogen, and hydrogen, under certain circum- 

 stances, will always reduce metals from the solutions of their salts. 



