With a paddle or ladle, drop in a cleaning compound of equal parts of powdered rosin, borax, and flower of sulphur. Use a teaspoonful of this compound for each ten pounds of metal, and be sure that the compound is absolutely dry. Stir the metal a little, and if it is at the proper temperature, there will be a flare, flash, or a little burning. A sort of tinfoil popcorn effect will be noticed oil top of the lead. Stir until this melts down.
Have the ladle with which you dip up the melted lead quite dry. When dipping up some of the lead, skim back the dark skin which forms oil top of the lead and dip up the clean bright lead for pouring.
In throwing additional lead into a pot which is partly filled with melted lead, be sure that the lead which is thrown in the pot is dry, or else hot lead may be spattered in your face.
Have the moulds clean and dry. The parts with which the lead comes into contact should be dusted with a mould compound which fills in the rough spots in the metal so that the flow of lead will not be obstructed, and the lead will fill the mould quickly. Dip tip enough lead to fill the part of the mould you use. When you once start pouring do not, under any circumstance, stop pouring until the lead has completely filled the mould. Lead cools very quickly after it is poured into the mould, and if you stop pouring even for all instant, you will have a worthless casting.
In a shop having an ordinary room temperature, it is generally unnecessary to heat the moulds before making up a number of castings. If it is found, however, that the first castings are defective due to the cold mould chilling the lead, the mould should be heated with a soft flame. After a few castings have been made, the mould will become hot enough so that there will be no danger of the castings becoming chilled.
When the castings have cooled sufficiently to be removed, strike the mould a few blows with a wooden mallet or a rawhide hammer to loosen, the castings before opening the mould. The castings may then be removed with a screwdriver.
Cracked castings indicate that the mould was opened before the castings had cooled sufficiently, or that there is too much antimony in the castings. The remedy is to let the castings cool for a longer time, or to add pure lead to the melting pot.
HANDLING AND MIXING ACID
The electrolyte used in the battery is made by mixing chemically pure concentrated Sulphuric Acid with chemically pure water. The concentrated acid, or "full strength" acid cannot be used, not only because it would destroy the plates, but also because water is needed for the chemical actions which take place as a cell charges and discharges. The water therefore serves, not only to dilute the acid, but also to make possible the chemical reactions of charge and discharge.
The full strength acid has a specific gravity of 1.835, and is mixed with the water to obtain the lower specific gravity which is necessary in the battery. The simplest scheme is to use only 1.400 specific gravity acid. This acid is used in adjusting the specific gravity of a battery on charge in case the specific gravity fails to rise to a high enough value. It is also used in filling batteries that have been repaired.