[ 109 ] 



XV. Theory of Voltaic Action. By J. Bkown*. 



SINCE the publication of a former paper on this subject f 

 the apparatus employed in the bimetallic-ring experi 

 ment has been much improved by using a finer suspension-wir 

 ('001 inch diameter) for the needle, and electrifying it by 

 means of a Daniell's battery of 100 cells. Each cell is made 

 of a 4-in. x |-in. test-tube, with the copper at the bottom 

 surrounded by copper-sulphate crystals, and connected by 

 gutta-percha-covered wire with the zinc of the next cell. The 

 space between the coppers and zincs is filled with sand satu- 

 rated with weak solution of zinc sulphate ; and zinc filings are 

 mixed with the upper layers of sand to reduce any copper 

 sulphate that might diffuse upwards. The cells are mounted 

 in an ebonite stand. With this arrangement and the copper- 

 iron ring described before f , it is quite easy to get decided de- 

 flections of about 3 centims. in air, copper negative to iron. 

 After admission of the hydrogen sulphide the deflections are 

 considerably greater, copper being now the positive metal. 



As copper is negative to nickel in water and positive to it 

 in hydrochloric acid, a ring was made of these metals similar 

 in size to the copper-iron one. Here the deflection obtained 

 was about 4 centims. in air, copper negative. Hydrochloric 

 acid gas was caused to flow into the case ; and after a few 

 oscillations the negatively electrified needle crossed zero and 

 turned towards copper, the deflection gradually increasing to 

 1*5 centim. The flow of gas was then stopped ; and the deflec- 

 tion slowly decreased. In four hours after, it had fallen to 1 

 millim. It then began to increase ; but the admission of fresh 

 hydrochloric acid gas caused it to diminish, a phenomenon the 

 explanation of which is not clear. The reversal of the poten- 

 tial of these metals, on the admission of the gas, however, was 

 quite decided. The experiment was not repeated, as the cor- 

 roding action of the acid was destructive to the apparatus. 

 The ratio of differences of potential given by these deflections 

 is, of course, rough, as the apparatus is not adapted for exact 

 measurements. 



In a simple voltaic cell, consisting of a copper and a zinc 

 plate in connexion and immersed in an oxidizing electrolyte, 

 the current due to the chemical action in the cell flows in the 

 electrolyte from zinc to copper. If, then, we divide the elec- 

 trolyte by a non-conducting plate, positive electricity ought to 

 accumulate on the side of the plate towards the zinc, and 



* Communicated by the Author, 

 t Phil. Mag. August 1878. 



Phil Mag. S. 5. Vol. 7. No. 41. Feb. 1879. K 



