ON THE ELECTRICAL PROPERTIES OF PURE SULPHUR, 
103 
experiment was then made in order to reduce the surface conductivity (if it existed) 
to zero. A number of thick rods of fused quartz were prepared, carefully cleaned 
and heated to redness; when they were sufficiently cool, i.e., when they would just 
melt the sulphur, they were arranged to lie in the surface of the sulphur between the 
upper plate and the gold dish, and were caused to lie half embedded in the sulphur. 
Now, if any surface conductivity exists in the sulphur, it will be checked where the 
surface of the sulphur is interrupted by the quartz—in other words, the current would 
have to climb over the exposed part of the quartz rods. Now, the surface conductivity 
of the quartz is certainly very small—indefinitely less than anything we could detect 
by means of the old galvanometer. The quartz rods were intended to form a com¬ 
plete fence round the upper plate, and practically formed a fence which was very 
nearly perfect, being only interrupted by gaps a few millimetres wide at the corners. 
The result was a slight apparent increase of resistance, but the irregularities were so 
great that no certain conclusion could be drawn except the following :—The con¬ 
ductivity observed was almost entirely, if not entirely, in the sulphur itself, and not 
on the surface. This was further proved by removing the drying substance (phos¬ 
phorus pentoxide) and blowing in a current of warm air saturated with water vapour, 
when it was again noticed that no appreciable change of resistance took place. We 
shall see later on that the explanation of this result lies in the fact that sulphur 
does not appear to condense moisture so as to reduce its apparent resistance, as glass 
does. With the arrangement described the conductivity of the condensed layer was 
small compared with that of the sulphur itself. This result was true whether the 
quartz rods were in or out. The facts as to the conductivity of the surface of annealed 
sulphur were confirmed and completed at a later time. 
With respect to the tests of specific inductive capacity and residual charge, we 
will only state that by a comparison of this film with a bit of specially-prepared 
mica, we observed, for the first time, that striking absence of residual effect which 
will be described when we deal with a film free from the objections we have raised 
to this one. 
It now became clear that we must reduce the electric stress on the sulphur if we 
desired to be free from the risks of breaking the film. Consequently a number 
of films were prepared during February, 1891, some soluble, some a mixture of 
soluble and insoluble sulphur, and these were tested with lower voltages. In one 
case the film wms cooled by carbon dioxide snow. All these films went wrong. In a 
very thin one the plates were found to touch at one corner. One insoluble film was 
dirty from having caught fire. The film cooled by carbon dioxide snow was- got so 
cold that it became wet round the edges with condensed moisture, and some of the 
snow had been in contact with the sulphur, and traces of grease were suspected 
in the snow. One good soluble film gave no conductivity at all, but our galvano¬ 
meter was not sensitive enough with the reduced voltage-to make the negative 
result worth anything. A mixed film showed no conductivity till it was heated 
