In the case of formed plates, and before the first charging, the positives are of a dark brown color with whitish or reddish gray spots and the negatives are of a yellowish gray. The whitish or reddish gray spots on the positive plates are small particles of lead sulphate which have not been reduced to lead peroxide during the process of forming, and represent imperfect sulphation.
As a general rule the first charging should be carried on until these spots completely disappear. After this, the positive plates should be of a dark red or chocolate color at the end of a discharge and of a wet slate or nearly black color when fully charged. A very small discharge is sufficient, however, to change them from black to the dark red or chocolate color.
If the battery has been discharged to a pressure lower than 1.8 volts, the white sulphate deposits will reappear turning the dark red color to a grayish tint in patches or all over the surface of the plate, or in the form of scales of a venetian red color.
The formation of these scales during charging indicates that the maximum charging current is too large and should be reduced until the scales or white deposits fall off or disappear, after which the current can be increased again.
Ques. Describe the behavior of the electrolyte during discharge.
Ans. There is a definite change in the density of the electrolyte for a given amount of discharge.
The density of the electrolyte is, therefore, one of the best indications of the state of charge, provided, of course, no internal discharge due to local action takes place. If, when the cell is charged, it show a density of 1.200, and when discharged 1.130, the difference .07 represents the total charge. If at any time the density be 1.165, then just one half the amount of capacity has been taken from the cell.
It is necessary to stir the electrolyte well, in order for these observations to be reliable.
If the discharge has taken place at a high rate, the cell must stand for an hour or more before the electrolyte will completely diffuse so that the density readings are correct.
Fig. 1,127.—Electric Storage Battery Co., arc lead burning outfit. In assembling a storage battery element, a negative plate is laid down with a separator on it, then a positive plate, separator, negative plate, etc. The plates are so placed that all the lugs of the positive plates are on one side and all the lugs of the negative plates are on the other side. A strip, consisting of flat strips of lead or lead alloy, having rectangular openings in it of the same dimensions as the cross section of the lug of the plates, these openings being spaced to register with the lugs, is then placed over the plate lugs of the positive plates and a similar strap is placed over the lugs of the negative plates. The lugs are then burned into integral union with the straps.
Ques. Define the term "boiling."
Ans. Boiling means the rapid evolution of gas when a cell is nearly charged.