ON THE ELECTRICAL PROPERTIES OF PURE SULPHUR. 115 
Limit of certain discrimination, owing to thermal effects, was about '25 tooth only, 
but it is put at '5 tooth for certainty. 
Specific resistance is greater than 5 X 10 26 C.G.S. (The capacity was taken again 
just after the test, and found to be the same as before.) 
In order to check this, it was made the subject of experiment by the electrometer 
method. At first we intended to experiment with different voltages in order to test 
the sulphur with respect to its law of conduction, and made a number of experiments 
on the lines of the experiments of Thomson and New all ( £ Proc. F.S.,’ vol. 42, p. 410, 
1887). For reasons formerly given, however, we ended by observing the leak during a 
given time, and then assuming Ohm’s law, we will not enlarge on our troubles in this 
work, for they must have been such as would come to anyone trying to get at a very 
high resistance by this method. We will, however, ask the reader to believe that all 
such sources of error as are introduced by incorrect knowledge of capacities and 
electrometer law—imperfect insulation, &c., were attended to by us with great care, 
and the results we offer are, we believe, free from objection. Mr. Pollock was kind 
enough to check the algebraical and arithmetical work for us, and as he used no 
approximations, we give his results rather than ours—with which they agreed within 
the limit of approximation adopted by us. 
From the results, the specific resistance of the sulphur is as follows, neglecting 
fractions :—- 
1. Oct. 6, 1892 . Specific Resistance , 6 X 10 28 C.G.S. 
2. Oct. 7, 1892 . Specific Resistance, 1 X 1 0 28 C.G.S. 
3. Oct. 7, 1892 . Specific Resistance, 8 X 10 27 C.G.S. 
These results were obtained with a voltage of about six Clark cells. 
All these observations were taken on sulphur after it had been in its silvered brass 
box with phosphorus pentoxide for at least twelve hours. 
The effect of exposing the sulphur to air was tried on one occasion, wdien the 
resistance fell at once (i.e., in ten minutes) about one thousand-fold, and seemed to 
stay there. After replacing the lid of the box and leaving for about twenty minutes, 
the resistance had again increased to six times its value when exposed freely to air. 
This explains partly how it was that we got only a small or negligible effect by 
exposing to moist air when we used the galvanometer. At the time the plates were 
exposed to air for ten minutes, as just recorded, the thermometer wet bulb was at 
61 0, 6 F., and the dry bulb at 71°‘6 F.—a rather damp day. Nearly all the reduction 
in resistance took place during the first few minutes of exposure, but the method 
does not admit of this matter being treated satisfactorily, for it takes too long to get 
a good measurement. The influence of moisture seems to be to reduce the resistance 
of the sulphur condenser, but not to such a point as would enable the conductivity to 
be detected in any measurements hitherto described by means of the galvanometer. 
It is possible that the small conductivity observed by the electrometer may be wholly 
A 9 
