Richardson's handbook of projection (1930)

MANAGERS AND PROJECTIONISTS 1089 now have available more plate surface, hence greater opportunity for chemical action. We therefore have a battery with greater capacity. Of course it is necessary to insulate the positive plates from the negative plates when they are put together, as shown in Figs. 402 and 403, in the battery itself, or else we would have a short circuit and it would discharge internally. We do this by putting thin pieces of wood, called separators, between each positive and negative plate. Sometimes a perforated sheet of rubber is used in addition to the wood separator for additional insulation. The positive and negative plate groups are assembled with the wood separators between the plates, the whole assembly put in a rubber jar, a rubber cover put on and the jar filled with a mixture of sulphuric acid and water, which is the electrolyte. The storage battery cell is then connected to a charging source and charged until the plates are converted chemically to lead peroxide for the positive and pure spongy lead for the negative. The storage battery cell is then ready for service. Now, a word about specific gravity readings as taken with hydrometer syringe. There are very good reasons for taking these readings, because from them we can tell exactly what state of charge or discharge the battery is in. Here is the explanation : Chemically pure sulphuric acid has a specific gravity of 1.835, water being taken as the standard, with a specific gravity of 1.000. Pure sulphuric acid therefore is almost twice as heavy as water. Electrolyte in a battery of the type you use is about 1.285 to 1.300 specific gravity. This specific gravity is obtained by mixing a pure acid of 1.835 specific gravity with water of 1.000 specific gravity in proportions set forth further