o melt the shellac.
The best way is to heat the glass surfaces and rub on the shellac from
a bit of flake; the glass should not be so hot as to discolour the
shellac appreciably, or its valuable properties will be partly
destroyed. Both glass surfaces being thus prepared, and the shellac
being quite fluid on both, they may be brought together and clamped
tightly together till cool. Shellac that has been overheated, or
dissolved in alcohol, or bleached, is of little use as compared with
the pale orange flaky product. Dark flakes have probably been
overheated during the preliminary refining.

For many purposes a cement is required capable of resisting carbon
bisulphide. This is easily made by adding a little treacle (say 20
per cent) to ordinary glue. Since the mixture of glue and treacle
does not keep, i.e. it cannot be satisfactorily melted up again after
once it has set, no more should be made up than will be wanted at the
time. If the glue be thick, glass boxes for carbon disulphide may be
easily put together, even though the edges of the glass strips are not
quite smooth, for, unlike most cements, this mixture remains tough,
and is fairly strong in itself.

I have found by experiment that most fixed and, to a less degree,
essential oils have little or no solvent action on shellac, and I
suspect that the same remark applies to the treacle-glue mixture, but
I have not tried. Turpenes act on shellac slightly, but mineral oils
apparently not at all. The tests on which these statements are based
were continued for about two years, during which time kerosene and
mineral oils had no observable effect on shellac--fastened
galvanometer mirrors.

Sec. 49. Fusing Electrodes into Glass.

This art has greatly improved since the introduction of the
incandescent lamp; however, up to the present, platinum seems to
remain the only substance capable of giving a certainly air-tight
result. I have not tried the aluminium-alumina method.

Many years ago it was the fashion to surround the platinum wire with a
drop of white enamel glass in order to cause better adhesion between
it and the ordinary glass. [Footnote: Hittorf and Geissler (Pogg.
Ann. 1864, Sec. 35; English translation, Phys. Soc. London, p. 138)
found that it was impossible to make air-tight joints between platinum
and hard potash glass, but that soft lead glass could be used with
success as a cement.] However, in the case of flint glass, if one may