neral
sufficient. One is the ordinary tinman's solder composed of lead and
tin. The second is "spelter," or soft fusible brass, and the third is
an alloy of silver and brass called silver solder.

Tinman's solder is used for most purposes where high temperatures are
not required, or where the apparatus is intended to be temporary. The
"spelter," which is really only finely granulated fusible brass, is
used for brazing iron joints. The silver solder is convenient for
most purposes where permanency is required, and is especially suited
to the joining of small objects.

Sec. 93. Soft tinman's solder is made by melting together two parts of
grain tin and one of soft lead--the exact proportions are not of
consequence--but, on the other hand, the purer the constituents the
better the solder. Within certain limits, the greater the proportion
of tin the cleaner and more fusible is the solder. It is usually
worth while to prepare the solder in the laboratory, for in this way a
uniform and dependable product is assured. Good soft lead is melted
in an iron ladle and skimmed; the temperature is allowed to rise very
little above the melting-point. The tin is then added little by
little, the alloy stirred vigorously and skimmed, and sticks of solder
conveniently cast by sweeping the ladle over a clean iron plate, so as
to pour out a thin stream of solder. If the solder be properly made
it will have a mat and bright mottled surface, and will "crackle" when
held up to the ear and bent.

Perhaps the chief precaution necessary in making solder is to exclude
zinc. The presence of a very small percentage of this metal entirely
spoils the solder for tinman's work by preventing its "running" or
flowing smoothly under the soldering bit.

Fig. 75.

Fig. 76.

Fig. 77.

Sec. 94. Preparing a Soldering Bit.

The wedge-shaped edge of one of the forms of bit shown in the sketch
is filed to shape and the bit heated in a fire or on a gas heater. A
bit of rough sandstone, or even a clean soft brick, or a bit of tin
plate having some sand sprinkled over it, is placed in a convenient
position and sprinkled with resin.

As soon as the bit is hot enough to melt solder it is withdrawn and a
few drops of solder melted on to the brick or its equivalent. The
iron or bit is then rubbed to and fro over the solder and resin till
the former adheres to and tins the copper head. It will be found
advisable to tin every side of the poi