GAS BATTERY. 261 



hydrogen at/', q f and the air in solution around the part cf y /; 

 this would add nothing to the general current, but would also 

 tend to diminish the hydrogen. As this last is totally inde- 

 pendent of the general action, it could be abstracted by 

 merely placing a cell charged similarly to the battery out of 

 the circuit with the terminals unconnected, as in fig. i. In a 

 cell so placed the hydrogen was found to be absorbed in the 

 ratio of rather less than O'l cubic inch in twenty-four hours. 



On some occasions I found the rise of liquid in the 

 hydrogen cell to be unequal in different tubes of the battery, 

 and this I found more particularly the case in the battery 

 fig. 4. It was some time before I discovered the cause of this. 

 I will not enumerate my different conjectures, but state that 

 which proved to be the correct one. As, in using the two 

 forms of batteries (figs, i and 4), the chief difference consisted 

 in the introduction of the finger, it occurred to me that my 

 assistant's hands, which were employed in various manipula- 

 tions, might, in placing the tubes in the cells of fig. 4, intro- 

 duce into the electrolyte small portions of foreign matter, 

 particularly metals, and that thus a local action might be 

 occasioned ; this view was strengthened by my frequently 

 observing copper deposited upon some of the immersed por- 

 tions of the platinum, and where this happened an excess of 

 hydrogen was generally found to have been absorbed. To 

 examine the accuracy of this view, in 



Experiment 2, 1 caused four cells to be charged with a solu- 

 tion of sulphate of copper, and connected in closed circuit ; 

 after twenty-four hours' work, the liquid in the oxygen and 

 hydrogen tubes had risen equally in three of the pairs, but in 

 the fourth the liquid in the hydrogen tube had risen rather more 

 than twice as high as in any of the others, and the whole of 

 the platinum in this tube, from the water-mark downwards, 

 was covered with metallic copper ; it was thus evident that a 

 slight precipitation having commenced on this platinum from 

 some local circumstance, which offered less resistance in this 

 cell than in the others, a separate local current had been 

 established ; the hydrogen and the copper acting as a voltaic 

 circuit, fresh copper had been constantly deoxidated at the 

 expense of the hydrogen. The phenomenon is analogous 



