Resistance and other Properties of Sulphur, 137 



gold electrodes, but failed to get a steady current to pass ; neitlier did 

 ordinary carbon plates answer any better. 



Having some graphite rods which had been procured from Hogarth 

 and Hayes, Keswick, for some experiments on carbon, I tried two of 

 them, and obtained a perfectly constant flow of electricity even at the 

 boiling point. The change in the resistance between melting point 

 and boiling point was so great that it was difficult to arrange a 

 method that would give reliable readings. In the Cavendish Labora- 

 tory, where this work was done, we have a set of 26 accumulator 

 cells which when charged give a potential of about 60 volts. This 

 is conducted to all the rooms, and is so arranged that we can use any 

 number of cells, so that we can vary the potential from 60 volts to 

 about 2^- volts. 



When the sulphur was melted (125° C.) 60 volts gave a deflection 

 with a reflecting galvanometer of 11,770 ohms resistance of only half 

 a millimetre on the scale, while at 440° C. one cell gave a deflection 

 of 60 mm. 



By changing the number of cells, and measuring the potential by a 

 Thomson's graded voltmeter at each change, the results given in the 

 following tables were obtained. 



The graphite rods were carefully insulated from each other by hard 

 glass tubes, over which shorter pieces of tube of unequal length 

 were placed, and fixed with plaster of Paris, the object being to give 

 as much insulating surface as possible. A cell of mica was placed 

 around the projecting part of the graphite rods to render the path of 

 the current fairly parallel; the ends were left open to allow free 

 access of sulphur and to prevent vapour taking the place of the 

 liquid when ebullition commenced. 



The form of the mica cell was preserved by an outer cell of thin 

 glass. 



In the figure, A, A are the graphite rods, B, B glass tubes, C, C 



