must be filed clean and then brushed with chloride of zinc
solution. Some people add a little sat ammoniac to the chloride of
zinc, but the improvement thus made is practically inappreciable. If
the iron is clean it tins quite easily, and the process of soldering
it is perfectly easy and requires no special comment.

Brass.

The same method as described for iron succeeds perfectly. The brass,
if not exceedingly dirty, may be cleaned by heating to the temperature
at which solder melts (below 200 deg. C.), and painting it over with
chloride of zinc, or dipping it in the liquor. If now the brass be
heated again in the blow-pipe flame, it will be found to tin perfectly
well when rubbed over with solder.

German Silver, Platinoid, Silver, and Platinum are treated like iron.
With regard to silver and platinum the same precautions as recommended
in the case of zinc must be observed, for both these metals form
fusible alloys with solder.

Gold when pure requires no flux. Standard gold, which contains copper,
solders better with a little chloride of zinc.

Lead must be pared absolutely clean and then soldered quickly with a
hot iron, using tallow as a flux. Since solder if over hot will
adhere to lead almost anywhere, plumbers are in the habit of specially
soiling those parts to which it is not intended that solder shall
adhere. The "soiling" paint consists of very thin glue, called size,
mixed with lampblack; on an emergency a raw potato may be cut in half,
and the work to be soiled may be rubbed over with the cut surface of
the potato.

Hard Carbon or gas coke may be soldered after coating with copper by
an electrolytic process, as will be described.

Sec. 99. Brazing.

Soldering at a red heat by means of spelter is called brazing.
Spelter is soft brass, and is generally made from zinc one part,
copper one part; an alloy easily granulated at a red heat; it is
purchased in the granular form.

The art of brazing is applied to metals which will withstand a red
heat, and the joints so soldered have the strength of brass.

The pieces to be jointed by this method must be carefully cleaned and
held in their proper relative positions by means of iron wire. It is
generally necessary to soften iron wire as purchased by heating it red
hot and allowing it to cool in the air; if this is not done the wire
is usually too hard to be employed satisfactorily for binding.

Very thin wire--i.e. above No. 20 on the Birming