72 
PROFESSOR R. THRELFALL AND MR. J. H. D. BREARLEY 
rather below 120° C.. and will be dealt with when the films forming the subject of 
experiment are considered. The detail of some other physical properties will be dealt 
with as occasion arises. 
Section III. 
Methods of Determining the Electrical Constants of Pure Sulphur. 
The chief constants determined by us are the Specific Resistance and Specific 
Inductive Capacity. Observations have also been made on the residual charge of 
sulphur regarded as a dielectric. No observations on the conduction of electricity 
through liquid sulphur have as yet been made, this having been provisionally accom¬ 
plished by previous workers. On the other hand, the phenomena attending conduc¬ 
tion through solid sulphur have been made out by us, at least, in their more important 
features. 
It will be convenient here to give a sketch of the information obtained by previous 
observers. 
Resistance of Sulphur. 
Wiedemann, ! Lehrbucb,’ vol. 1, p. 498. Sulphur is mentioned as a non-conductor. 
Boltzmann, ‘Wien. Sitzb./ vol. 70, p. 342. In this paper, which deals more 
particularly with dielectric constants, it is stated incidentally that sulphur is a 
perfect insulator, and is free from “ dielectrische Nachwirkung.” 
G. Foussereau, ‘ C.R.,’ vol. 95, 1882. This paper contains an account of a method 
of determining high specific resistances, together with results as to the resistance of 
glass, which do not concern us. The method employed is that of placing the 
substance to be examined between two cylindrical electrodes. These electrodes are 
in series with a battery and condenser, the latter having its armatures connected to 
the poles of a Lippmann electrometer. The observation consisted in noting the time 
required for the electrometer to register a known difference of potential. From this, 
and the voltage acting on the resistance cell, and the capacity of the condenser, the 
specific resistance can be calculated. In ‘C.R.,’ vol. 97, p. 996, 1883, this method is 
applied to liquid sulphur, the electrodes being concentric zinc cylinders. We did not 
believe in the freedom of zinc from action on sulphur, but after a good many 
experiments on bright plates, in no case observing any effect even up to the boiling- 
point, we must admit that zinc is probably a safe material to use. No details are 
given by Foussereau as to the methods (if any) used to purify the sulphur. The 
method adopted for examining the conductivity is free from error so far as the action 
of the containing vessel goes, but not with respect to the surface conductivity. The 
sulphur experimented upon is stated as having existed in various states which are 
named, but the paper is not sufficiently detailed to admit of any judgment being 
formed as to whether these states were actually attained. The results are in brief:—* 
