The "U. S." Storage Cell.
This cell is of the lead-zinc type, being the practical form of the Reynier cell. It is to be recommended for working Ruhmkorff coils, its output weight for weight being far in excess of the lead-lead types. This cell is readily portable and easy of operation, the zinc electrode being the only one needing renewal, and that at very infrequent intervals.
The lead electrode consists of plates of peroxide clamped together, and presents quite a large surface. The zinc in most types is of the circular sheet form, and encloses the lead block, being kept amalgamated by mercury lying in the bottom of the cell. The E. M. F. on open circuit is about 2.5 volts, which is higher than any lead-lead combination. On closed-circuit work this drops to from 2.35 volts downwards. During action, when a large amount of current is being drawn from the cell, a white sulphate appears, but this disappears upon the cell being recharged or even left to rest. Bubbles of gas, which sometimes form under the peroxide block, should be removed by gently tilting the cell or hitting the table or shelf upon which it stands a smart blow. The large type No. 3 is suitable for X-ray work, and a still larger cell is made, which is preferable for heavy or continuous discharges of current.