nts as will prevent the formation of oxides.

The parts to be united may be of the same, or of different materials,
and it is in this particular that the workman must be able to make a
choice of the solder most available, and whether hard or soft.

SOFT SOLDER.--A soft solder is usually employed where lead, tin, or
alloys of lead, tin and bismuth are to be soldered. These solders are
all fusible at a low temperature, and they do not, as a result, have
great strength.

Bismuth is a metal which lowers the fusing point of any alloy of which
it forms a part, while lead makes the solder less fusible.

HARD SOLDER.--These are so distinguished because they require a
temperature above the low red to fuse them. The metals which are alloyed
for this purpose are copper, silver, brass, zinc and tin. Various alloys
are thus made which require a high temperature to flux properly, and
these are the ones to use in joining steel to steel, the parts to be
united requiring an intense furnace heat.

SPELTER.--The alloy used for this purpose is termed "spelter," and
brass, zinc and tin are its usual components. The hard solders are used
for uniting brass, bronze, copper, and iron.

Whether soft or hard solder is used, it is obvious that it must melt at
a lower temperature than the parts which are to be joined together.

There is one peculiarity with respect to alloys: They melt at a lower
temperature than either of the metals forming the alloys.

SOLDERING ACID.--Before beginning the work of soldering, the parts must
be cleaned by filing or sandpapering, and coated with an acid which
neutralizes the oxygen of the air.

This is usually muriatic acid, of which use, say, one quart and into
this drop small pieces of zinc. This will effervesce during the time the
acid is dissolving the zinc. When the boiling motion ceases, the liquid
may be strained, or the dark pieces removed.

The next step is to dissolve two ounces of sal ammoniac in a third of a
pint of water, and in another vessel dissolve an ounce of chloride of
tin.

Then mix the three solutions, and this can be placed in a bottle, or
earthen jar or vessel, and it will keep indefinitely.

THE SOLDERING IRON.--A large iron is always better than a small one,
particularly for the reason that it will retain its heat better. This
should always be kept tinned, which can be done by heating and plunging
it into the soldering solution, and the solder will then adhere to the
iron and