esistance falls to from 10^25 to 10^26 at
ordinary temperatures; and the specific inductive capacity increases
up to 3.75, according to the amount of insoluble sulphur present.

The residual charge under circumstances similar to those described
above, but with an intensity of about 4000 volts per centimetre is,
say, 2 per cent of the initial charge. So far as the writer is aware
sulphur is the only solid non-conductor which can be easily obtained
in a condition of approximate purity and in samples sufficiently
exactly comparable with one another; it is the only one, therefore,
that repays any detail of description.

Very pure sulphur can be bought by the ton if necessary from the
United Alkali Company of Newcastle-on-Tyne. It is recovered from
sulphur waste by the Chance process, which consists in converting the
sulphur into hydrogen sulphide, and burning the latter with
insufficient air for complete combustion. The sulphur is thrown out
of combination, and forms a crystalline mass on the walls and floor of
the chamber.

The sulphur which comes into the market consists of this mass broken
up into convenient fragments. In order to purify it sufficiently for
use as an insulator, the sulphur may be melted at a temperature of
120 deg. to 140 deg. C, and filtered through a plug of glass wool in a zinc
funnel; as thus prepared it is an excellent insulator. To obtain the
results mentioned in the table it is, however, necessary to conduct a
further purification (chiefly from water) by distillation in a glass
retort.

The sulphur thus obtained may be cast of any desired form in zinc
moulds, the castings and moulds being immediately removed to an
annealing oven at a temperature of from 100 deg. to 110 deg. C, where they
are left for several hours. If the sulphur is kept melted for some
time at 125 deg. C. the annealing is not so important.

The castings may be removed from the mould by slightly heating the
latter, but many breakages result. Insulators made on this plan are
much less affected by the condensation of moisture from the air than
anything except fused quartz. They are, however, very weak
mechanically, and apt to crack by exposure to such changes of
temperature as go on from day to day. It is clear, however, that in
spite of this their magnificent electrical properties fit them for
many important uses.

If the sulphur be cooled rapidly from 170 deg. C. or over, a mixture of
the crystalline and amorp