38 Prof. Threlfall and Messrs. Brearley and Allen. [May 24,. 



A very large quantity of exact numerical data referring to these 

 points is contained in the paper. 



Part II of the paper is interposed as the facts disclosed bear on 

 the general argument. This part of the paper bears on several corre- 

 lated questions. 



Section 1 deals with the contact force in air between purely soluble 

 sulphur and mixtures of insoluble and soluble sulphur containing 

 about 10 per cent, of the former. 



The result of some rather interesting work on this point by the 

 electrometer needle method, shows that when soluble and mixed 

 sulphur is in contact (produced by melting the parts together), there 

 is a contact force of the order of from one to two volts between them. 

 The positive charge is on the insoluble sulphur. These experiments 

 were made by using a double sulphur needle over metallic semicircles, 

 and also by using the ordinary metallic electrometer needle over 

 sulphur quadrants. The latter gives the best results. The phe- 

 nomena are very complicated, and require to be carefully sifted ; for 

 an account of the very considerable difficulties the paper must be 

 consulted. 



Section 2 deals with the question as to whether light has any 

 effect on the conductivity of sulphur. Monckman (' Boy. Soc. Proc.,' 

 vol. 46, 1890) considers that he has discovered such an. effect. A 

 very large number of experiments, however, on mixed and crystal- 

 line sulphur cells, failed to indicate to us any such peculiarity, and 

 we consider that Monckman must have been mistaken in this 

 matter. 



Section 3 deals with the qualitative phenomena of conduction in 

 sulphur cells containing from 5 per cent, to 20 per cent, of insoluble 

 sulphur. The general results agree with those already described, 

 although the methods of preparing and quenching the viscous 

 sulphur were different. The electrodes were also of platinum, wire 

 instead of aluminium plates. The temperature resistance changes 

 are treated rather fully in this section, and bring into prominence 

 the enormous influence of the annealing process. 



Section 4 deals with a determination of the specific inductive 

 capacity of sulphur by the method of weighing, and contains an 

 account of the different sources of error to which we discovered the 

 method was subject. Several ways of obtaining the required 

 potential difference were investigated, with the result that the most 

 satisfactory is by the use of an alternator giving a frequency of about 

 sixty, and an induction coil used as a transformer. This avoids the 

 difficulty which occurs when the sulphur plates get charged in virtue 

 of their conductivity, and is noticed whenever (1) a continuously 

 directed P.D., or (2) an unequal alternating one (as by a coil with 

 hammer or mercury break) is used. 



