An old piece of soft cotton cloth, such as a stocking, on which is sprinkled a little powdered sal-ammoniac is an excellent thing to keep handy when soldering or tinning. The tin coating of the point of the copper should be rubbed on this cloth where the sal-ammoniac is sprinkled, when the copper is hot. This will be found to keep the copper in excellent condition. The sal-ammoniac removes the oxide from the tinning and brightens it up generally about the point.
The tinning will last much longer on the copper if it is dipped occasionally into the soldering paste or acid while hot. This is particularly true if the copper has been a bit overheated.
When the tinning shows signs of wearing off and the copper does not pick up solder readily, it must be retinned, filed, fluxed, heated, and rubbed on the solder which has been put on the tin first used for this purpose. This piece of tin should be kept about the bench, as the copper will have to be retinned frequently. Always remember that the copper will not carry solder to the work unless it is well tinned.
If an electrical soldering copper is used it is usually furnished already tinned at the point, so that it is ready for use as soon as it is connected to a suitable electric socket and the current turned on. The heating coil inside the copper will soon heat it up to the melting point of the solder. After heating, it may be treated as a common copper, wiped occasionally on the cotton cloth and retinned when the tinning is worn away. An electrical copper should never be placed in a vise for filing, but should be held against the bench and filed carefully. A vise is apt to crush the hollow copper and injure the heating coil inside. These coppers should never be placed in a fire or heated in any way except by the electric current.
Electrical coppers do not need as much attention as an ordinary copper for the even heat supplied by the current keeps the copper heated to the flowing point of the solder and is incapable of heating beyond this temperature.
How to Make Soldering Fluid or “Killed Acid”
Soldering fluid may be very simply made as follows: Pure zinc is dissolved in muriatic acid until the acid will not dissolve any more of the zinc. The solution thus obtained is then allowed to stand for a time and is then strained through a cloth and poured into a bottle which is kept tightly corked when not in use.
First purchase about six ounces of muriatic acid from a druggist. Take care not to spill any of this acid on the hands or clothes. Next get some pure sheet zinc. The sheet zinc employed for stove mats as it is sold in the plumbers’ shops is not suitable for making soldering fluid, as this form of zinc is alloyed with other metals. Pure zinc may be very easily obtained from old dry batteries which may be found anywhere.
Remove the paper covering from the battery and crack it open with a hammer—remove the carbon from the center of the battery and dump out all the powdered material. Soak the zinc covering of the battery in warm water to remove any paper or material adhering to the zinc and then cut the zinc into pieces about ¼ inch square.
Find an old tea cup or earthen-ware marmalade jar and pour into it about half a teacupful of the muriatic acid. Set the vessel containing the acid out of doors or near an open window and away from all steel tools, so that the fumes of the acid may escape and not be breathed into the lungs or rust any tools.