1871.] 



Action of Metals and Liquids. 



325 



platinum was electro-negative to cold platinum in liquids of acid reaction, 

 and positive to it in alkaline ones, provided in all cases chemical action was 

 completely or sufficiently excluded. In the present experiments I have 

 endeavoured to ascertain what electrical changes are produced in cases 

 where chemical action more freely occurs, and I have therefore employed 

 not platinum plates, but plates composed of a metal (copper) which is more 

 easily corroded. 



To effect the object I had in view, I used the apparatus shown in sec- 

 tion in fig. 1, and in perspective, with its wooden support, in fig. 2. 



Fig. 1. 



A and B, fig. 1, are two open thin glass dishes, 6^ inches diameter, 

 and H inch deep, with open necks. The dishes are joined together, water- 

 tight, by a bent glass tube, C, about I inch in diameter ; and the whole 

 arrangement is securely fixed upon a wooden frame or stand, so that it 

 may be at once placed in an exactly horizontal position, or inverted to pour 

 out its contents. D and E are two dishes of sheet copper of moderate 

 thickness, made from contiguous portions of a sheet of metal to ensure 

 electrical homogeneity in the experiments. Wires of similar metals are 

 attached to the dishes for the purpose of connexion with a galvanometer. 

 A galvanometer, containing about 180 turns of moderately fine copper 

 wire, is sufficiently sensitive for the experiments. The outside of the metal 

 dishes must be made perfectly clean and bright immediately before each 

 experiment. 



In using the apparatus it is first set exactly horizontal, and a known and 

 measured volume of the clear liquid to be examined, at the temperature of 

 the atmosphere and sufficient to fill it to the line F F, is poured in ; the 

 metal dishes are then steadily placed in the glass vessels and connected with 

 the galvanometer, taking care that no air-bubbles remain beneath them. 



