1887.] 



Voltaic Electricity by Atmospheric Oxidation. 



215 



In order to examine separately the fluids collecting round the two 

 plates after action had gone on for some time, we employed cells of 

 U -shape ; and to obtain as large an aeration surface as possible, we 

 adapted to one leg of the \J a funnel (as indicated in the figure) 

 with the stem cut off, and united to the U-fot-be a piece of india- 

 rubber tubing, a, slipped tightly over the junction. The other end of 

 the (J-^be was closed with an india-rubber cork, b, through which 

 passed a piece of glass tubing with a platinum wire, c, sealed into it 

 at the lower end and filled with mercury, thus forming a mercury 

 cup, and serving to make contact with the copper plate, d, which was 

 soldered to the end of the platinum wire, the soldering and platinum 

 being coated with gutta-percha, so that only the copper plate was in 

 contact with the fluid with which the (J -tube was subsequently filled. 

 A similar glass tube and platinum wire mercury cup, /, served to 

 make contact with the aeration plate, which was conveniently sup- 

 ported horizontally at the surface of the fluid in the funnel by means 

 of a disk of porous earthenware, e ; by fixing a rim of gutta-percha 

 round this disk so as to convert it into a sort of tray like the lid of a 

 pill-box, and filling this tray with platinum sponge, an aeration plate 

 of spongy metal was readily obtained. By interposing suitable re- 

 sistances, galvanometer, silver voltameter, &c, in the external circuit 



