THE ELECTROLYSIS OF WATER. 89 
arranged into a coil. When used, it is immersed 
in water, in order, by keeping it cool, to prevent 
the increase of its resistance. 
The Battery I used is on Prof. Daniell’s plan. 
Each of its cells is twenty-five inches high, and 
five and a half inches in diameter. ‘They were 
charged in the usual way, with acidulated sulphate 
of copper in contact with the copper; and dilute 
sulphuric acid, mingled with a variable* quantity 
of sulphate of zinc, in contact with the amalga- 
mated zinc. Szv of these cells in series formed 
the battery used in all the subsequent experi- 
ments: but at the same time I may observe that 
trials were also made with only ¢hree in series, 
in order to satisfy myself that the results are 
independent of the. extent of the battery. 
The Electrolytic Apparatus consisted of a 
glass jar, containing a pound of liquid, and fur- 
nished with electrodes each of which exposed an 
active surface of about six square inches. 
* As I do not throw away my old solution, but content 
myself with mixing it occasionally with new, the liquid must 
have contained considerably more free acid at one time than 
at another. This cannot, however, interfere with my results, 
because it did not interfere with the intensity of the battery. 
