248 Messrs. Gladstone and Tribe on an Air-battery. [Apr. 3, 



in fact, we convert it into a small silver tray full of crystals of the same 

 metal which rise in projections to the very surface. The copper plate 

 lies horizontally under it, separated, if need be, by a piece of muslin, and 

 connexion is made by a wire as usual. The vertical part of the copper 

 plate, from a little above the liquid to the bend, should be varnished ; 

 otherwise solution principally takes place there, which causes the 

 horizontal part of the plate to drop off. Holes are made in the silver 

 tray with the view of shortening the communication between the air- 

 surface and the copper plate and of facilitating the movements of the 

 salt in solution. The solution itself may be contained in a shallow 

 trough or saucer, and the whole arrangement will be somewhat as in the 

 sectional view here given : — 



That dissolved oxygen is absolutely necessary for this chemical change 

 has been already shown ; but it was interesting to measure by a galva- 

 nometer the difference of the currents obtained by means of an ordinary, 

 that is aerated, solution of copper nitrate, and one from which the air had 

 been separated to the greatest possible extent. A Thomson's galvano- 

 meter was employed, which had a resistance of 2631*5 units at 18°*3 0. 

 Two cells were prepared with vertical plates and alike in all respects, 

 except that the one contained an ordinary 6 per cent, solution of copper 

 nitrate, and the other a similar solution which had been deoxygenized by 

 the means described in our former paper. Another experiment was 

 made with a different pair of cells and an 11 per cent, solution. It 

 was necessary to use the 1-99 shunt ; and the following were the 

 amounts of deflection : — 



