1894.] On the Electrical Properties of Pure Substances. 37 



The residual charge is larger than when the sulphur is purely 

 soluble, and with about 400 volts per millimeter is about 187 per 

 cent, of the initial charge after 10 minutes' charge ; the condenser 

 being discharged for a fraction of a second and left for 10 minutes. 

 At lower electromotive intensities it is rather greater in comparison 

 with the initial charge, sufficiently so to be distinctly noticeable. 



On heating the sulphur the conduction increases from about 50 C, 

 in fact whenever the process of annealing takes place. When the 

 annealing change (destruction of amorphous sulphur, and formation 

 of soluble sulphur) is taking place rapidly the conduction is consider- 

 able. Many attempts made for the purpose of deciding whether the 

 increase of conductivity depends on the mere proportion of insoluble 

 sulphur present, or whether it depends on the rate at which the 

 conversion process is taking place, yielded no absolutely certain 

 results, but the evidence, such as it is, points to the latter as being 

 probably the most important but we do not consider that it can 

 explain the conductivity at low temperatures. This conductivity is 

 essentially discontinuous, and in this resembles the conduction through 

 moisture films condensed on glass, ebonite, and sulphur itself. 



Several of the above-mentioned peculiarities of sulphur conduction 

 were observed by Quincke in the case of insulating liquids, and were 

 ascribed, in part at all events, to the action of dust motes in the 

 liquids. There is no doubt, however, that in the case of sulphur 

 these effects are inherent to the process of conduction, for they were 

 as strongly marked in what we consider to have been our purest film 

 (as tested by the colour) as in the least pure one. There is some evi- 

 dence that mixtures of insoluble and soluble sulphur show a maxi- 

 mum conductivity when the sulphur contact is between 5 and 3 per 

 cent. All the phenomena of conduction are also noticed the specific 

 resistance being about the same when we examine films containing 

 88 per cent, of insoluble sulphur, produced by applying enormous 

 pressures in a testing machine to the insoluble sulphur formed on 

 suddenly cooling sulphur from a high temperature. The sulphur, 

 which was originally plastic, was exhausted with carbon bisulphide, 

 and the residue treated with sulphur chloride to obtain stability. A 

 pressure equal to the weight of 100,000 pounds on an area of say 

 25 square inches, causes about 12 per cent, of the insoluble sulphur 

 to become soluble, whether it has been treated with sulphur chloride 

 or not. Check experiments on soluble sulphur showed that the very 

 pure benzene used to moisten the sulphur for the purpose of com- 

 pression produces no subsequent change in the conductivity. The 

 pressures were applied for from five to 10 minutes. 



No change in the conductivity of mixed films was produced by 

 stressing in alternate directions with a frequency of, say, five per 

 second, and a voltage of from 100 to 200 volts per quarter millimeter. 



