immersed in pure water and in oxygenated water. 353 



t»esults were in the same order, giving the highest action at 

 the time the water is parting with dissolved air, and lowest 

 when the water is thoroughly boiled. Where zinc is the 

 positive element the action falls considerably, as the boiled 

 water cools before it has time to re-absorb air. With a little 

 common salt added to the water of a zinc and platinum couple, 

 ebullition serves greatly to exalt the action, for the arrange- 

 ment is no longer dependent on oxygen from the atmosphere. 



These experiments, in extension of those I formerly sub- 

 mitted to the public through the Edinburgh Philosophical 

 Journal, do not militate against the general conclusion then 

 drawn, that the water battery supported its action by absorb- 

 ing oxygen from the atmosphere ; they only show that there 

 is in addition a minute degree of action when two metallic 

 elements are excited by pure water. 



Perhaps the experiments of the most importance for deter- 

 mining the theory of the action of gas absorbing galvanic 

 couples, are those where one metal only is excited by oxy- 

 genated water ; to illustrate this action I made the following 

 experiments : — 



Two slips of zinc cut side by side from the same sheet were 

 placed in a running brook, the one opposed to a rapid part of 

 the current, the other in a still place at the edge. Connecting 

 these in the usual manner with the galvanometer, there was 

 a permanent deflection of 25° ; and on changing the respective 

 places of the plates in the stream without disturbing their 

 attachments to the galvanometer, the needles immediately 

 passed to the opposite side of the card ; in both cases the 

 piece of zinc in the current acted as a negative or platinode 

 plate. With both plates in still water and a tube filled with 

 oxygen inverted over one, the effect was the same. It is the 

 greater supply of oxygen to the plate in the current which con- 

 verts it into a negative or platinode. A cell containing two 

 small silver wires and the cyanide of silver solution used for 

 electro-plating was attached in place of the galvanometer, 

 when, after a lapse of two hours, metallic silver was seen pre- 

 cipitated in a minute quantity on the silver wire connected 

 with the piece of zinc in still water. 



Two plates of iron were placed in the stream, under like 

 conditions to the zinc ; after two hours metallic silver was 

 distinctly seen precipitated on the silver wire connected with 

 the iron plate in still water. 



The fact here shown, of two similar pieces of iron giving 

 rise to a galvanic current capable of precipitating metallic 

 silver, appears to me to be important, for it proves that the 

 electricity in passing through the water intervening between 



Phil, Mas. S. 3. Vol. 31 . No. 209. 'Nov. 184.7. 2 A 



