136 



Dr. J. Monckman. The Specific 



" The Specific Resistance and other Properties of Sulphur." 

 By James Monckman, D.Sc. Communicated by Professor 

 J. J. Thomson, F.R.S. Received November 10, — Read 

 December 6, 1888. 



Resistance. 



It is well known that sulphur in a solid state insulates electricity of 

 very high potential, and conducts heat badly ; also that it undergoes 

 a curious series of changes when heated — melting at about 120° C, 

 becoming thicker at 200° to 250°, more liquid at 250° to 300°, and 

 boiling under atmospheric pressure at 440°. During the past three 

 terms I have been engaged in the Cavendish Laboratory in trying to 

 determine whether these changes are accompanied by corresponding 

 ones in the electrical resistance and other properties of the element. 



I expected that the changes would be within the limits of an insu- 

 lating body, hence my first experiment was designed to test the 

 insulating power for frictional electricity. 



Two platinum wires were placed in a beaker of melted sulphur at 

 a distance of about 1 cm. apart, one being connected to an electro- 

 scope, the other going to earth. When the sulphur became solid the 

 leaves of the electroscope remained open on charging for a con- 

 siderable time, but fell at once if any portion of the sulphur 

 between the wires was liquid. To avoid all discharging by the flame 

 used in melting the sulphur, the platinum wires were fixed to an 

 ebonite rod at the proper distance apart. After melting the sulphur 

 the flame was removed to a distance and the wires placed in the liquid. 

 The discharge was complete and, apparently, as sudden as when con- 

 tact was made with a wire. 



The same experiment was tried with paraflm, and the discharge 

 found to be very slow. 



Seeing then that the resistance was removed by melting the sulphur 

 into the region of conductors, it became necessary to find some method 

 that could be used for conductors of very high resistance. 



At Mr. Grlazebrook's suggestion I tried placing the wires in melted 

 sulphur in circuit with a high resistance reflecting galvanometer and 

 a set of accumulators giving a total electromotive force of 60 volts. 

 With platinum wires in the sulphur no reliable results could be 

 obtained as the current quickly fell away. 



While thus engaged my attention was directed to a paper by 

 M. Duter (' Comptes Rendus,' vol. 106, 1888, p. 836), in which he 

 describes some experiments on boiling sulphur. Platinum he found 

 to be attacked by the sulphur, but gold gave good results; no 

 measurements were, however, given. Following Duter's plan I used 



