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



I believe we should form a false notion of the phenomena 

 which now occupy our attention, if, considering entirely the 

 deportment of the oxygen adhering to the aerated plate, in rela- 

 tion to the other plate, we neglected to examine the deportment 

 of this oxygen in relation to the plate to which it adheres. 



AVe must take well into consideration that the oxygen does 

 not form a continuous stratum upon the aerated plate ; conse- 

 quently, every point of the surface of this plate, covered with 

 oxygen, tends to form a current, not only with the second plate, 

 but also with all points of the first plate where the copper is 

 exposed. At one and the same time, therefore, there are cur- 

 rents traversing the liquid itself (these are indicated by the 

 galvanometer), as well as currents traversing the liquid strata in 

 contact with the aerated plate. Both kinds of currents have the 

 same electromotor force, but the latter have incontestably the 

 advantage of a much feebler resistance to overcome in the circuit 

 which they traverse ; their intensity should therefore exceed that 

 of the former. The oxidation of the non-aerated plate is not the 

 sole effect produced, which, by absorption of oxygen, produces 

 a current ; it is accompanied by a still more powerful oxidation 

 of the aerated plate by means of its adhering oxygen and a series 

 of superficial currents. It is not here asserted that all the oxi- 

 dation is thus produced, for such an assertion would be in ad- 

 vance of facts ; but it will scarcely be disputed, that at least a 

 part of the oxidation is produced by means of the electric current. 



It might be thought, according to the ideas of Faraday him- 

 self, that the action of oxygen in all the cases just cited is but 

 a secondary one ; that the oxygen acts upon the metal, forming 

 oxide, and that a current is thus produced between the molecules 

 of the metal and those of the oxide at the other extremity of the 

 current, accompanied with reduction of this oxide. 



This appears to me less probable; for on the one hand, 

 with metals less oxidable than hydrogen (such as copper and 

 silver), I do not understand how the united actions of metal and 

 oxide could determine the decomposition of water ; and on the 

 other hand, with metals such as iron and zinc, more oxidable 

 than hydrogen, I do not see how the oxide could be reduced. It 

 may be further remarked, that if the presence of a molecule of 

 metal and a molecule of oxide in water, united by a metallic 

 circuit, had the property of producing a current accompanied 

 with reduction of the oxide, then the molecule of metal would 

 be transformed into oxide, and the molecule of oxide into 

 metal, so that a series of alternating currents should be the 

 result. 



According to the present hypothesis, it is only in the case 

 where the oxide formed in presence of the oxygen is superior 



