Voltaic BatterieSi 8fc, 65 



readily refilled with liquid by immersion in the trough itself. 

 Another trough and meter of larger dimensions were also pro- 

 vided for such experiments as required the use of larger plates 

 than such as could be introduced into the smaller trough. 



37. The zinc used throughout the experiments was always 

 of the same kind and always amalgamated. Its equivalent 

 number was 34*5, requiring in consequence of impurities con- 

 tained in it 34*5 grains, instead of 32, to yield 1 grain of hy- 

 drogen. The connecting wires both of the zinc and copper 

 plates were partly covered, but to the same extent in each, 

 with bee's wax, so as to protect them from the action of the 

 acid, so far as they were at any time immersed in it, and to 

 confine the voltaic action entirely to the surfaces of the plates 

 which were the subject of experiment. The circumstance 

 that the surfaces of the wires, protected by the wax, were of 

 uniform extent in every case, will need afterwards to be re- 

 membered. 



38. These precautions against error, by preserving uniform- 

 ity in the kind of metal used, in the kind and lengths of the 

 connecting wires, and in the extent of surfaces to be acted 

 upon, are independent of other precautions requiring equally 

 to be observed. A variety of modifying causes are incessantly 

 operating in experiments of this nature, and producing effects 

 of a most perplexing kind, each of which needs to be fully 

 appreciated and guarded against, or as fully as possible cor- 

 rected, in order to ensure any satisfactory degree of accuracy 

 in the results of experiment. 



39. I. It has been shown by yourself*, that immediately 

 afteV the first immersion of a zinc plate under voltaic arrange- 

 ment, its amount of action is greatly impeded by an accumu- 

 lation upon its surface of minute air-bubbles, which adhering 

 to it interpose a surface of air between the plate and the ex- 

 isting acid ; thus preventing the full voltaic action so long as 

 they continue to be attached to the plate. By my own ex- 

 periments I found that a zinc plate, after such accumulation 

 had taken place, yielded a certain measure of gas in 240 se- 

 conds, but by repeatedly clearing its surface from these bub- 

 bles, by agitating it or otherwise, the same measure of gas was 

 produced in two-thirds the time, or in 160 seconds. When, 

 however, the copper plate is at its maximum size in any ar- 

 rangement little or no such accumulation occurs. 



40. II. The gas arising from the copper plate will do so 

 more rapidly if the water be agitated than if it remain tran- 

 quil during the action : an arrangement yielded voltaic action 



* Phil. Trans. 1836. 

 ^ Phil. Mag, S. 3. Vol. 13. No. 79. July 1838. F 



