Skey. — On the Oxidation of Mercury. 585 



1. Iron in metallic connection with copper in an aqueous 

 solution of ammonia prevents this metal from going into solu- 

 tion and so communicating a blue colour to the liquid, as it 

 would do if placed therein alone. 



This clearly indicates that the affinities of iron for the 

 oxygen present in that solution are greater than those of 

 copper for this substance, and it as clearly indicates that the 

 iron is being oxidized. 



2. Iron in a strong solution of potassic cyanide or caustic 

 potash is positive to iron in weak solutions of these salts 

 respectively. 



3. Iron paired with gold or platinum in any alkaline solu- 

 tion is positive thereto, and slowly becomes tarnished, while, 

 if the negative metal has a much smaller surface than the 

 other has, hydrogen gas is evolved therefrom for about half an 

 hour. 



These results make it very certain that when iron is elec- 

 trically connected in a caustic solution with a metal negative 

 to it, it becomes coated with a film of oxide of iron of a thick- 

 ness suflicient to render it visible. It may be urged here, in 

 defence of the old-estabhshed theory which I am combating, 

 that these negative metals initiate the oxidation of the iron 

 — ^that, in fact, there is as yet no proof given that iron when 

 alone in alkaline liquids will oxidize, which is the question 

 under consideration. To this I would answer that, to my 

 way of thinking, chemical action {e.g., oxidation) must in such 

 cases as this always precede electrical action — that is, polarisa- 

 tion — as being its cause, and the only effect that should be 

 ascribed to the negative metals (gold and platinum) is that of 

 accelerating the chemical action that has been already initiated 

 by the iron and the oxygen of the water and of the air present. 

 And it is effected, as I conceive, in this way : The hydrogen 

 that is set free from the water by the abstraction of its oxygen 

 by the iron is not allowed to remain upon the surface of this 

 metal to clog it, and so retard oxidation, but is set free at a 

 distance away — e.g., at the surface of the other metal — thus 

 leaving the iron all bared to the exciting solution. But, what- 

 ever force there may be in this argument, the following results 

 of experiments especially designed to settle this point appear 

 to be decisive, and, besides, show the great intensity of 

 the currents that are produced by iron in these kinds of 

 solutions. 



4. Iron in a solution of caustic potash is positive to iron in 

 sulphuric or hydrochloric, also in nitric, acid. In the case 

 where the last acid is used the positive element is rapidly en- 

 filmed with ferric oxide. 



6. Iron in solution of potash paired with platina or iron in 

 nitric acid is able to deposit copper from its sulphate. 



