In every kind of battery it is essential that the connections be bright, and that the metal surfaces which are to be united should be brought together under considerable pressure. Those batteries which depend for contact upon light springs, and the mere placing of wires in holes, lose a great deal of available power. The surfaces ought invariably to be filed bright and pressed together by means of screws. We have frequently seen the action of the batteries used for medical purposes entirely stopped by a thin film of oxide.
The zincs also should always be thoroughly amalgamated to prevent waste. When the zincs are new and uncorroded, amalgamation is an easy process. Dip the zincs in dilute sulphuric acid (8 parts water and 1 of acid), and rub them with mercury. The mercury will adhere quite readily and render the entire surface brilliant and silvery. But when the zincs are old and corroded it will be found that the mercury does not adhere to some parts. In such cases wash the surface of the zinc with a solution of nitrate of mercury and it will become coated with amalgam. Once the surface is touched, it is easy to add as much mercury as may be desired by simply rubbing on the liquid metal.
The coating of mercury adds greatly to the durability of the zincs, as when so prepared the acid will not act on them except when the current is passing, and from the excellent condition of the entire surface the power of the battery is greatly increased.