[Electric engineering.] . attery, one must alwaysbe sure to get the positivepole of the battery con-nected to the positive poleof the dynamo, so that thecharging current will flowin at the positive the charging currentis discontinued and the cellallowed to supply currentto a circuit, the discharg-ing current will flow outfrom the positive pole of thecell. The positive platesare, or should be, marked,so that there will be no danger of incorrectly connectingthe cells. When a pole indicator is not at hand, the polar-ity may always be found by connecting a wire to each poleand dipping th
[Electric engineering.] . attery, one must alwaysbe sure to get the positivepole of the battery con-nected to the positive poleof the dynamo, so that thecharging current will flowin at the positive the charging currentis discontinued and the cellallowed to supply currentto a circuit, the discharg-ing current will flow outfrom the positive pole of thecell. The positive platesare, or should be, marked,so that there will be no danger of incorrectly connectingthe cells. When a pole indicator is not at hand, the polar-ity may always be found by connecting a wire to each poleand dipping the ends into a dilute solution of sulphuricacid. The wire from which the greater number of bub-bles is given is connected to the negative pole. Whenconnecting cells in series, care should be taken to see thatthe positive pole of one cell is connected to the negativepole of the next. Any person that has worked aroundstorage cells for any length of time can tell the positiveplates from the negative by their dark-brown Fig. 47. 15 ELECTRIC TRANSMISSION. 47 56. The complete chemical reactions that take place ina storage battery are complicated and many of them arenot as yet well understood. When the cell is charged, theprincipal action is the formation of lead peroxide on thepositive plate and spongy lead at the negative. Lead per-oxide is a chemical compound consisting of 1 atom of leadand 2 atoms of oxygen; its chemical formula is PbO^. Thislead peroxide gives the positive plates the dark-brown colorthat they have when the cells are fully charged. When thecell is discharged, the lead peroxide gradually changes tolead sulphate and the metallic lead on the negative plate isalso changed to lead sulphate. Lead sulphate PbSO^ isformed by the action of the sulphuric acid in the electrolyteof the cell on the spongy lead. These chemical changes arerepeated over and over as the cell is charged and discharged. 57. In Fig. 47, the plugs c, c seen in the negative plateare the portions
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