No. X.] APPENDIX. 193 



37. In a solution of sulpliate of copper, after many days, no action 

 apparently occurred ■with paper and hydrogen. 



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

 paper occurred.* 



39. The persulphate of iron was not changed into the protosalt by the 

 action of that gas in contact with paper. 



40. As a summary of results obtained on the direct reduction 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, spoi^y 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 platinum, 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 phenomena. To the electro- 

 metallurgist they assume a much higher importance, for they point out to 

 him, that in the decomposition of the metallic fluid the uniform strength 

 will not be preserved by the changes taking place by virtue of the voltaic 

 current. He must therefore remember in aU 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. Prom 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 of the decomposition of nitric acid and 

 persalts of iron, and finally the direct experiments of the reduction of 

 gold, silver, platinum, palladium, nickel, copper, tin, and the decomposi- 

 tion of the persalts of iron and nitric acid enclosed within a tube, appear 

 to set the question to rest, and to point out in the clearest manner that 



* After some time the paper exhibited a black deposition of silver ; the 

 surface of the glass tube became encrusted with a brilliant layer of metallic 

 silver. The importance of this experiment is manifest, for it shows that 

 hydri^en 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 he proved by fiiture 

 investigations. The decomposition of organic matter will always yield hydrogen, 

 and hydrogen, under certain circumstances, will always reduce metals from the 

 solutions of their salts. 



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