silver or any combination of these metals can be easily soldered,
while iron and aluminum are common metals that cannot be soldered.

It is necessary to possess a soldering copper, a piece of solder,
tinner's acid, sandpaper or steel wool, a small file and a piece
of sal ammoniac. If the soldering copper is an old one, or has
become corroded, it must be ground or filed to a point. Heat it
until hot (not red hot), melt a little solder on the sal ammoniac,
and rub the point of the copper on it, turning the copper over to
thoroughly tin the point on each face. This process is known as
tinning the iron and is very necessary to successful work.

After the copper is tinned you may place it in the fire again,
being careful about the heat, as too hot an iron will burn off the
tinning.

The parts to be soldered must be thoroughly cleaned by
sandpapering or the use of steel wool until the metal shows up
bright. Then apply the acid only to the parts to be soldered with
a small stiff brush or a small piece of cloth fastened to a stick,
or in a bent piece of tin to form a swab.

Tinner's acid is made by putting as much zinc in commercial
muriatic acid as will dissolve. This process is best accomplished
in an open earthenware dish. After the acid has ceased to boil and
becomes cool it may be poured into a wide-mouthed bottle which has
a good top or stopper, and labeled "Poison."

Place the parts to be soldered in their correct position and apply
the hot copper to the solder, then to the joint to be soldered,