No. X.] APPENDIX. 191 



11. In what way are the metals reduced if they are not transferred 

 from pole to pole ? A careful investigation of a solution depositing its 

 metal will at once explain the phenomenon, for from the negative surface 

 a colourless lighter fluid is seen to rise, which in some cases will destroy 

 the electro -metallurgist's hopes, by causing grooves on the reduced metal, 

 sometimes even to the extent of an inch or more in depth, and the same 

 fluid at other times will cause a sandy or spongy deposit. From these 

 facts it is evident that water is formed at the negative surface, and that 

 hydrogen probably reduces the metallic salt. 



12. We have now as arguments in favour of the reduction of the 

 metals by hydrogen gas liberated by decomposition of the water, first, the 

 results obtained by the cinder experiment ; secondly, the non-transference 

 of the metal ; thirdly, the imperfect transference of the acid ; fourthly, the 

 rise of a light aqueous fluid from the negative pole of a metallic solution. 

 We have, fifthly, besides these cases, the analogy of the reduction of nitrous 

 acid, in Grove's battery by hydrogen, for the removal of the gas by the acid 

 gives to it its intensity ; and in this case no other mode can even be sup- 

 posed by which the decomposition of the acid is effected, save and except 

 its decomposition by hydrogen. The further alteration of the persalts of 

 metals into protosalts favours strongly, by analogy, the same opinion. 

 Such evidence is amply sufficient, but I have now to detail some direct 

 experiments in which hydrogen alone reduces metals from various salts. 



13. The mode in which this satisfactory result is obtained is very 

 simple. The metallic solution to be examined is placed in a glass, a test 

 tube filled with the same solution is then procured, into which a slip of 

 platinum, platinized as for the construction of my battery, is then placed. 

 The whole is then placed within a glass of metallic solution, and a current 

 of hydrogen introduced sufficient to extend half-way up the platinized 

 platinum. It will be seen that the arrangement is similar to that of one 

 gf the tubes of Professor Grove's elegant gas battery, and the various 

 results obtained by this mode of examination it will be my duty im- 

 mediately to explain. 



14. If the solution employed be chloride of platinum, the hydrogen 

 disappears gradually, and the black powder of platinum is coated here and 

 there by a beautiful bright layer of reguline metal. 



15. With a solution of chloride of gold the same result is seen, the 

 platinum being gilt with a beautiful deposit of metal. With this salt the 

 action is immediate. 



16. With nitrate of palladium the hydrogen is rapidly absorbed and 

 bright palladium deposited. 



17. With nitric acid and platinized platinum the hydrogen is gradually 

 absorbed and the acid decomposed. 



18. A solution of sulphate of copper under similar examination yields 

 a plentiful crop of small crystals of copper in a short period. 



19. A solution of persulphate of iron yields rapidly its oxygen and 

 becomes converted into the protosulphate. 



crude notions, for the practical man must, to be successful, not only adopt, but 

 act upon the true rationale of the phenomena. Societies may determine that 

 the metals are directly electrolysed, but the practical man will find that their 

 edicts will have but very little effect upon his processes. A. S. 



