250 Messrs. Gladstone and Tribe on an Air-battery. [Apr. 3^ 



Time after immersion. 



In air. 



InC0 2 . 



1 minute. 



165 



76 



5 minutes. 



135 



82 



10 „ 



135 



58 



As the cell in an atmosphere of carbonic-acid gas showed considerable 

 action, in fact nearly half as much as that in the air, each cell was short 

 circuited for 23 hours, with the expectation that any oxygen in the 

 closed vessel would be used up ; and, indeed, the most prominent crystals 

 of silver in the cell in carbonic-acid gas became reddened, while a cuprous 

 deposit extended over the whole of the crystals in the other cell. When, 

 however, the short vires were removed and the galvanometer interposed, 

 the cell in the air gave a deflection of 136, practically the same as 

 before, but that in carbonic-acid gas, instead of showing a great decrease, 

 rose to 80. It was then found that the vessel containing the latter 

 slowly admitted air ; so the contents were swept out by a fresh stream 

 of carbonic-acid gas, and it was made properly air-tight. After connexion 

 by a short wire for 3 days the galvanometer indicated a deflection of 20, 

 that of the cell in the air being 110, temperature 10° 0. As this showed 

 a very great reduction of the chemical action, carbonic-acid gas was 

 again passed through the vessel for an hour or two ; and after a 

 connexion of two more days the indication of the galvanometer was 

 only 3, while the other cell gave 115, the temperature being now 10 o, 5 C. 

 The action, therefore, was at last reduced almost to nothing ; and the 

 original fault in the experiment brought out, perhaps more clearly than 

 would otherwise be seen, how eagerly the solution will absorb even 

 minute quantities of oxygen from the surrounding gas. 



An important point to determine was the best strength of the copper 

 nitrate solution. Six per cent, was generally preferred, for two reasons : — 

 first, it gives about the maximum of effect — a solution four times as 

 strong gives less than half the deflection, and a solution only a quarter 

 as strong gives only two thirds ; secondly, a stronger solution than this 

 6 per cent, is apt to produce a deposit, not of pure cuprous oxide, but of 

 a subnitrate, which was supposed to clog up the silver crystals to a 

 greater extent. 



Another point investigated was the best proportion between the areas 

 of the metallic surfaces. Experiments were made with vertical plates, 

 in which the silver was kept at a uniform size and the copper was 

 diminished by covering it more and more with varnish ; and another set 

 was made in which the copper remained the same, while the silver plate 

 was reduced. 



