of zinc.
For brazed joints, spelter or powdered brass is employed, and the flux
is usually borax. The borax will not cover the joint until it has been
deprived of its water of crystallization, and this is effected by
raising it to a full red heat, when it swells in bulk, "boils," and
afterwards sinks quietly and spreads over, or into the joint. There are
differences in details of working. The borax is generally powdered and
mixed with the spelter, and both with water. But sometimes they are
applied separately, the borax first and over this the particles of
spelter. Another flux used for copper is sal ammoniac, either alone or
mixed with powdered resin.

As brazed joints often have to be very strong, other precautions are
frequently taken beyond that of the mere overlapping of the joint edges.
In pipes subjected to high steam pressures, and articles subjected to
severe stresses, the joints are "cramped" before the solder is applied.
That is, the edges are notched in a manner having somewhat the
appearance of the dovetails of the carpenter; the notched portions
overlap the opposite edges, and on alternate sides. Such joints when
brazed are stronger than plain overlapping joints would be. Steam dome
coverings are jointed thus longitudinally as cylinders, and the crown is
jointed thereto, also by cramping. Another common method of union is
that of flanges to copper pipes. In these the pipe passes freely within
a hole bored right through the flange, and the solder is run between.
The pipe is suspended vertically, flange downwards, and the spelter run
in from the back of the flange. The fused borax works its way in by
capillary action, and the spelter follows.

The "copper bit" is used in soft soldering. Its end is a prismatic
pyramid of copper, riveted to an iron shank in a wooden handle. It is
made hot, and the contained heat is sufficient to melt the solder. It
has to be "tinned," by being heated to a dull red, filed, rubbed with
sal ammoniac, and then rubbed upon the solder. It is wiped with tow
before use. For small brazed work the blow-pipe is commonly employed;
large works are done on the brazier's hearth, or in any clear coke fire.
If coal is used it must be kept away from the joint.

In "sweating on," a variation in soldering, the surfaces to be united
are cleaned, and solder melted and spread over them. They are then
brought together, and the temperature raised sufficiently to melt the
solder.

A detail of firs