s also in general doubtful whether sufficient care
has been taken to distinguish the body from the surface conductivity,
and consequently numerical estimates are to be regarded with
suspicion. The question of "sampling" also arises, for it must be
remembered that a change in composition amounting to, say, 1/10000 per
cent may be accompanied by a million-fold change in specific
resistance.

Sec. 102. Sulphur.

This element exists in several allotropic forms, which have very
different electric properties. After melting at about 125 deg. C, and
annealing at 110 deg. for several hours, the soluble crystalline
modification is formed. After keeping for some days--especially if
exposed to light--the crystals lose their optical properties, but
remain of the same melting-point, and are perfectly soluble in carbon
bisulphide. The change is accompanied by a change in colour, or
rather in brightness, as the transparency changes.

The "specific resistance" of sulphur in this condition is above 1028
C.G.S.E.M. units, or 1013 megohms per cubic centimetre for an electric
intensity of say 12,000 volts per centimetre. This is at ordinary
temperatures. At 75 deg. C. the specific resistance falls to about 1025
under similar conditions as to voltage.

In all cases the conductivity appears to increase with the electric
intensity, or at all events with an increase in voltage, the thickness
of the layer of sulphur remaining the same.

The specific inductive capacity is 3.162 at ordinary temperatures, and
increases very slightly with rise of temperature. [Footnote: March
1897.--It is now the opinion of the writer that though the specific
inductive capacity of a given sample of a solid element is perfectly
definite, yet it is very difficult to obtain two samples having
exactly the same value for this constant, even in the case of a
material so well defined as sulphur.]

The total residual charge, after ten minutes' charging with an
intensity of 12,000 volts per centimetre, is not more than 4 parts in
10,000 of the original charge. In making this measurement the
discharge occupied a fraction of a second. The electric strength for
a homogeneous plate of crystalline sulphur is not less than 33,000
volts per centimetre, and probably a good deal more. If the sulphur
is contaminated with up to 3 per cent of the amorphous variety, as is
the case if it is cooled fairly quickly from a temperature of 170 deg. C.
or over, the specific r