M. Viard on the Electro-chemical Deportment of Oxygen. 253 



closed by a stratum of mercury (fig. 7). The plates were termi- 

 nated by tongues of metal, which traversed glass tubes partially 

 filled with gum-lac, or rather with mercury, when the latter did 

 not attack the plates. The electrolytes employed had been 

 deprived of air by ebullition. When the elements were thus 

 arranged, the circuit was closed, and allowed to remain so until, 

 by the action of the plates, the intensity of the current was made 

 very feeble. The glass bells were then replaced by glass tubes 

 of the same diameter, but open at their upper extremities, and 

 the electrolytes were replaced by aerated liquids of the same 

 nature. Plates of zinc, iron, and copper were successively em- 

 ployed, and opposed to platinum in water, sulphate of potash, 

 and marine salt ; in all cases it was found that the presence of 

 oxygen increased the intensity of the current considerably. 



But the difference is still more visible when, according to 

 Adie's method, the electrolytes are hermetically enclosed in glass 

 tubes, bearing at their extremities wires of iron or copper, of 

 silver or of platinum, affixed by means of the blowpipe. The 

 apparatus, figs. 8 and 9, is filled by means of a lateral aperture, 

 which can be subsequently closed before the lamp. By allowing 

 the circuit to remain closed for fifteen d^ys or a month, the in- 

 tensity of the current may be rendered very feeble ; it increases 

 considerably, however, on the admission of oxygen. The latter 

 may be effected by breaking the lateral tube, and allowing the 

 apparatus thus to remain for some hours. Adie thus obtained a 

 deviation of from i to 84 degrees in the needle of his galvano- 

 meter. I have not obtained so great a deviation, and have found 

 it preferable completely to replace the electrolyte by a liquid 

 freshly. aerated, which could be effected by means of two lateral 

 apertures affixed to the tube, for then the whole instrument could 

 be used as a siphon (fig. 9). Experiments have been made with 

 iron and platinum, in presence of water, the sulphates of potash 

 and magnesia, and the chlorides of sodium and barium, as well 

 as with iron and silver, and copper and platinum, in presence of 

 water, sulphate of potash and marine salt ; and in fifteen expe- 

 riments, permanent deviations at least a hundred times greater 

 than those with the primitive electrolytes, were always observed 

 after the introduction of the aerated liquids. 



In place of employing the galvanometer to verify the influence 

 of oxygen, chemical decompositions may be effected by operating 

 upon iodide of potassium and starch, or upon dilute sulphuric 

 acid. The inconvenience most often encountered here is, that 

 a certain number of elements are necessary in most cases. 



Whatever may be the method employed, the effect of oxygen 

 may be always increased by allowing a part of the plates to 

 remain exposed to the air, instead of immersing them entirely in 

 the oxidized liquid. 



