258 M. Viard on the Electro-chemical Deportment of Oxygen. 



It may be perceived, that in the above tables batteries formed 

 by zinc and sulphuric acid are not mentioned. In reality, in 

 these batteries, as far as could be recognized in a number of ex- 

 periments in other respects very regular, the influence of oxygen 

 apparently disappears. Nevertheless, the fact cannot be regarded 

 as contrary to the theory above exposed; for these batteries 

 possess a considerable electromotor force, and disengage hydrogen 

 in abundance, so that almost all the oxygen, which could act by 

 its presence upon the negative plate, is destroyed or dispelled 

 before the needle of the galvanometer has ceased to oscillate. 



Such an inconvenience may be evidently remedied by intro- 

 ducing contrary electromotor forces into the circuit, so as to 

 diminish the circuit's total electromotor force. A convenient 

 voltameter introduced into the circuit effects this. 



From experiments made by Grove, it results that an element 

 of zinc, sulphuric acid, and platinized platinum, which alone 

 cannot decompose the acidulated water between two platinum 

 plates, decomposes it when the platinum plate of the element is 

 in contact with oxygen gas. 



Analogous results would probably be obtained, by this method, 

 with all kinds of batteries, in which a too great electromotor 

 force has a tendency to hide the action of oxygen. 



In conclusion, I may add, that all that has hitherto been said 

 of the elements of a battery, may with equal justice be repeated 

 of any decomposing apparatus placed in the circuit of a battery ; 

 that is to say, that the presence of oxygen upon all the negative 

 plates in the circuit has always the effect of increasing the cur- 

 rent by augmenting the electromotor force, unless the current 

 be already very energetic in the absence of oxygen. 



The following fact is also demonstrated by an experiment of 

 Grove's. 



It was before said, that a pile of zinc, sulphuric acid, and pla- 

 tinized platinum, which alone could not decompose the water 

 between two platinum plates, decomposed the same when a 

 part of the negative pole of the element was covered with oxygen. 

 Grove has shown that decomposition also takes place when oxygen 

 is passed .up the side of the negative plate of the voltameter : 

 this fact ought evidently to receive a similar explanation. 



In a future memoir I propose to examine the chemical phse- 

 nomena, which, according to theory, should accompany the cur- 

 rents whose existence has been verified in this memoir. 



