Fig. 69.
75. Voltameters measure the strength of a current by chemical means, the quantity of metal deposited or gas generated being proportional to the time that the current flows and to its strength. In the water voltameter, Fig. 71, the hydrogen and oxygen produced in a given time are measured. (See "Study," Chapter XXI.)
Fig. 70.
The copper voltameter measures the amount of copper deposited in a given time by the current. Fig. 72 shows one form. The copper cathode is weighed before and after the current flows. The weight of copper deposited and the time taken are used to calculate the current strength.
Fig. 71.
76. Unit of Quantity; The Coulomb is the quantity of electricity given, in one second, by a current having a strength of one ampere. Time is an important element in considering the work a current can do.
Fig. 72.