29 



eight-tenths of an inch in the acid ; platina foil, connected by 

 binding screws with the zincs, was rolled into cylinders two- 

 tenths of an inch in diameter, and then immersed in pipeclay 

 tubes one inch deep. 



Cubic Inches. 



Time, 2 minutes, TO 



After 10 minutes, 1*0 



" Second Experiment. 

 " Platina foil of the same size as the zincs, and zinc rods 

 of the same diameter as the platina cylinders being employed, 

 the effects were precisely the same. 



Cubic Indies. 



Time, 2 minutes, 1*0 



After 10 minutes, I'O 



" Third Experiment. 



" The zinc cylinders being made twice the diameter of the 

 former ; the quantity of gas generated in two minutes was 

 the same as before ; the increased number of lines of elec- 

 trical force compensating the increased resistance offered by 

 the acid solution. 



" Fourth Experiment. 



" With cylinders twice the diameter of these, a very fee- 

 ble current passed, the obstacle being too great to be over- 

 come ; by increasing the diameter of the porous vessels, 

 and thereby of the nitric acid solution, which is a good con- 

 ductor, the impediment is diminished, as shewn in experi- 

 ment fifth. Thus Mr. Binks (Phil. Mag. vol. xi. p. 68) 

 finds, that in dilute sulphuric acid, the size of the copper 

 compared to a given surface of zinc, to produce a maximum 

 effect, should be 16, that of the zinc to a given surface of 

 copper being 7; while in a galvanic arrangement, in which the 

 zinc is immersed in dilute sulphuric acid, inclosed in a mem- 



