contents of the crucible are poured into any suitable mould.

The quickest and most convenient way of preparing the alloy for use is
to convert it into filings with the assistance of a coarse file, or by
milling it, if a milling machine is available.

Equal volumes of filings and powdered glass borax are made into a thin
paste with water, and applied in an exactly similar manner to that
described under the head of "brazing." In fact all the processes
there described may be applied equally to the case under discussion,
the substitution of silver for spelter being the only variation.

The silver solder is more manageable than spelter, and does not tend
to run wild over the work: a property which makes it much more
convenient both for delicate joints and in cases where it is desired
to restrict the solder to a single point or line. Small objects are
almost invariably soldered with silver solder, and are held by forceps
or on charcoal in the pointed flame of an ordinary blow-pipe.

Sec. 101. On the Construction of Electrical Apparatus: Insulators.

It is not intended to deal in any way with the design of special
examples of electrical apparatus, but merely to describe a rather
miscellaneous set of materials and processes constantly required in
its construction.

It is not known whether there is such a thing as a perfect insulator,
even if we presuppose ideal circumstances. Materials as they exist
must be regarded merely as of high specific resistance, that is if we
allow ourselves to use such a term in connection with substances,
conduction through which is neither independent of electromotive force
per unit length, nor of previous history.

Even the best of these substances generally get coated with a layer of
moisture when exposed to the air, and this as a rule conducts fairly
well. Very pure crystalline sulphur and fused quartz suffer from this
defect less than any other substances with which the writer is
acquainted, but even with them the surface conductivity soon grows to
such an extent as totally to mask the internal conduction.

It is proposed to give a brief account of the properties of some
insulating substances and their application in electrical
construction, and at the same time to indicate the appliances and
methods requisite for working them.

With regard to the specific resistances which will be quoted, the
numbers must not be taken to mean too much, partly for the reason
already given. It i