being supported on a brick, and the solder is
allowed to "sweat" into the joint. Enough solder must be present to
penetrate right through the joint. Nothing is gained by rubbing
violently with the iron. If the copper is clean it will tin, and if
it is dirty it won't, and there the matter ends.

Beginners generally use too small or too cold a bit, and produce a
ragged, dirty joint in consequence. If the saving of time be an
object, the joint may be twisted together on ordinarily dirty oxidised
wires and heated to, say, 200 deg. C. It is then painted with chloride of
zinc and soldered with the bit.

There is a difference of opinion as to the relative merits of chloride
of zinc and of resin as a flux in soldering copper. Thus the standing
German practice is, or was, to employ the former flux in every case
for soldering electric light wires, while in England the custom used
to be to specify that soldering should be done by resin, and this
custom may still prevail; it lingers in Australia at all events.

However, it is agreed on all hands that when chloride of zinc is used
it must be carefully washed off. I have known of an electrical
engineer insisting on his workmen "licking" joints with their tongues
to ensure the total removal of chloride of zinc; it has a horrible
taste; and I have occasionally pursued the same plan myself when the
soldering of fine wires was in question.

In any case, it is very certain that chloride of zinc left in a joint
will ruin it sooner or later by loosening the contact between copper
and solder.

Very often it is requisite to solder together two extensive flat
surfaces--for instance, in "chucking" certain kinds of brass work.
The surfaces to be soldered must be carefully tinned, most
conveniently by the help of the blow-pipe and chloride of zinc. After
tinning, the surfaces are laid together and heated so as to "sweat"
them together; the phrase, though inelegant, is expressive.

96. Soldering Tin Plate.

If the plate be new and clean, a little resin or its solution in
alcohol is all that is necessary as a flux. If the tin plate is rusty
the rust must be removed and the clean iron, or rather mild steel,
surface exposed. The use of chloride of zinc is practically essential
in this case. Tin plate is often spotted with rust long before it
becomes rusty as a whole, when, of course, it may be regarded as worn
out, and such rust spots are most conveniently removed by means of t