rant characteristic smell.

If the coating is too heavy, or if the heating is commenced before the
shellac is sufficiently dry, the latter will draw up into "tears,"
which are unsightly and difficult to dry properly. On no account must
the shellac be allowed to get overheated. If the varnish is not quite
hard when cold it may be assumed to be doing more harm than good.

In varnishing glass tubes for insulating purposes it must be
remembered that the inside of the tube is seldom closed perfectly as
against the external air, and consequently it also requires to be
varnished. This is best done by pouring in a little varnish
considerably more dilute than that described, and allowing it to drain
away as far as possible, after seeing that it has flooded every part
of the tube.

During this part of the process the upper end of the tube must be
closed, or evaporation will go on so fast that moisture will be
deposited from the air upon the varnished surface. Afterwards the
tube may be gently warmed and a current of air allowed to pass, so as
to prevent alcohol distilling from one part of the tube to another.
The tube is finally heated to the softening point of shellac, and if
possible closed as far as is practicable at once.

Sec. 105. Ebonite or Hard Rubber.

This exceedingly useful substance can be bought of a perfectly useless
quality. Much of the ebonite formerly used to cover induction coils
for instance, deteriorates so rapidly when exposed to the air that it
requires to have its surface renewed every few weeks.

The very best quality of ebonite obtainable should be solely employed
in constructing electric works. It is possible to purchase good
ebonite from the Silvertown Rubber Company (and probably from other
firms), but the price is necessarily high, about four shillings per
pound or over.

At ordinary temperatures ebonite is hard and brittle and breaks with a
well-marked conchoidal fracture. At the temperature of boiling water
the ebonite becomes somewhat softened, so that it is readily bent into
any desired shape; on cooling it resumes its original hardness.

This property of softening at the temperature of boiling water is a
very valuable one. The ebonite to be bent or flattened is merely
boiled for half an hour or so in water, taken out, brought to the
required shape as quickly as possible, and left to cool clamped in
position.

The sheet ebonite as it comes from the makers is generally far from