[ 469 ] 



LY. On Measurements of the Resistance of Imperfectly 

 Purified Sulphur. By Prof. Richard Threlfall, and 

 Arthur Pollock, Esq.* 



T 



HE galvanometer having been brought to a state of 

 sensitiveness of 5 scale-divisions for 10 -11 amperes, the 

 measurement of the resistance of the sample of sulphur in 

 question became a tolerably easy matter. The sulphur had 

 been supplied by Messrs. Hopkin and Williams as " precipi- 

 tated, washed." It looked clean when melted ; but on 

 examination turned out to have the following substances 

 existing as impurities : — 



Calcium sulphate. 

 Ferric oxide. 

 Organic matter. 



Dr. Helms, Demonstrator of Chemistry in the University of 

 Sydney, was kind enough to investigate a sample of this 

 sulphur with a view to discovering whether it contained 

 selenium or tellurium. The result of his examination of about 

 two hundred grammes of the substance was, that neither of 

 these substances was present in quantity large enough to be 

 detected. The examination was carried out by means of the 

 oxidation and sulphurous acid method ; and also by the 

 cyanide method. We desire to express our thanks to Dr. 

 Helms. The importance of this result, so far as our work is 

 concerned, lies in the fact that it shows that pure sulphur 

 can probably be obtained from the sample at hand by means 

 of distillation. The following measurements refer to the 

 unpurified sample ; the only substance existing in any con- 

 siderable quantity was calcium sulphate. The sample was 

 probably rather more pure than ordinary " roll " or flour 

 sulphur. The general arrangement of the apparatus will be 

 clear from the following diagram (p. 470). 



By means of the key K x a current can be sent in either 

 direction through the resistance R and the galvanometer G. 

 The source of this current is a suitable number of small 

 Clark cells SC. The E.M.F.'s of these cells and of the large 

 one LC were watched during the experiments with the aid of 

 an auxiliary galvanometer and balance arrangement not 

 shown in the diagram. The key K 2 allowed the upper metal 



* Communicated by the Physical Society : read March 23, 1889. 



