way, that is in the opposite direction to that in which the current flows when the accumulator is being discharged. It is this feature of the accumulator which renders it a practical appliance. When it has given out an electric current for a certain time, it is merely necessary to connect it to the terminals of a suitable source of current at the required pressure to recharge it. It is generally advisable to charge an accumulator at about the same rate that is to say, at about the same number of amperes that it normally discharges at, but this is not absolutely essential, as the charging rate may exceed that very considerably, and with a good type of cell it is practically only limited by the heating produced. The pressure or voltage required to charge a battery is somewhat higher than that which it gives out, and is generally about 2·5 to 2·6 volts per cell.
There are two types of accumulator batteries, those in which both positive and negative plates are 'pasted,' and those in which the positive plates are originally composed entirely of metallic lead, cast so as to expose a large surface to the action of the dilute sulphuric acid, a coating of peroxide of lead being formed upon it by the action of the electric current. In both types at the present day the negative plate is 'pasted.' Electromobiles have also been built by the Electric Motive Power Co. and successfully propelled with Plante positives and negatives, in which zinc in a pure form is deposited on a special conducting support unacted upon by dilute sulphuric acid. This gives the advantages of the Plante; positive durability and great length of life without increased weight. Batteries of this type have been two years in constant use. In general it may be assumed, however, that the type of automobile battery chiefly employed has both negatives and positives formed by 'pasting.' The process of manufacture of an accumulator cell will be best comprehended by reference to a special example. Fig. 8 shows the type of plate employed in the construction of the batteries built by the Accumulator Industries, Ltd. for the vehicles of the British Electromobile Co., Ltd., of which the 'Powerful' is a good example.
