ON THE ELECTRICAL PROPERTIES OP PURE SULPHUR. 
79 
that an admixture of less than I per cent, of insoluble sulphur with monoclinic 
sulphur reduces the specific resistance of the latter (in one case) to at least the 
millionth part. There is still room, however, for a careful study of the specific 
inductive capacity of sulphur in its several allotropic states, and with varying 
duration of charge, in order to discover whether the great differences between the 
values obtained can be accounted for by what Roller calls the “ Schliessungs 
Strom,” for, from our experiments, residual effect exists only to a very small extent, 
even in tolerably conducting mixtures of soluble and insoluble sulphur. This is one 
of the matters which requires further investigation and is dealt with later. 
The drawings which accompany this paper will show the exact arrangements of the 
experiments, as well as the dimensions of the various parts of the apparatus, for the 
drawings are to scale with the exception of the resistance boxes in the ground plan. 
We will now mention one or two points in which we have found it requisite to 
exercise particular caution ; the first of these is the insulation of the apparatus. We 
have found that if the apparatus is to be left in position for any great length of time 
there appears to be a distinct gain in making use of a combination of different 
insulating substances. Thus the “old galvanometer,” which is very well insulated 
itself, stands on three bits of ebonite placed on a clean sheet of glass. This sheet of 
glass is supported by three combined flint-glass and paraffin insulators, made by 
placing a small cylinder of paraffin on the top of a flint-glass bottle, and inverting 
over it a cylindrical glass dish. The outer dish serves to protect the paraffin against 
dust; the whole stands on a large slab of ebonite 1 inch thick. All the apparatus is 
insulated with extraordinary care, including the galvanometer and set of test-tube 
storage cells. Then, as a precaution against electrostatic effects, one end of the 
galvanometer is put definitely to earth by means of a wire soldered to the water 
supply. The galvanometer is enclosed in an iron case which is kept in connection 
with the earth, and affords a screen against external electrostatic effects. Referring 
to the diagram (see Plates), it will be seen that the effect is to put the lower plate of 
the sulphur condenser and one pole of the battery to earth as well, which insures 
that except for the small P.D. corresponding to the small current flowing, the greater 
part of the circuit and all the coils of the galvanometer are at zero potential. This 
has the effect of throwing the whole stress of insulation on the sulphur film, and on 
one insulating pole which supports the wire coming from the upper plate, and on two 
terminals of the reversing key. 
The effect of accidental leakage, if any, is always observed by making all the connec¬ 
tions except that leading to the top plate of the sulphur condenser, the wire simply 
hanging from the pole. Though this pole is of splendid flint-glass most carefully var¬ 
nished and having a resisting length of about one metre, and is provided with an ebonite 
cross-arm about 20 centims. long, to the ends of which the wire is fastened, the insulation 
is seldom sufficient till the glass has been dried and the long, thin cross-arm of ebonite 
scraped. The connecting and reversing keys (see Plate 3, figs. 3 and 2) are formed of 
