146 



Dr. J. Monckman. The Specific 



of the importance and beauty of the law which classified them 

 together. 



During the course of this work I have often consulted Professor 

 J. J. Thomson, F.R.S., and received many valuable suggestions and 

 some corrections, for which I desire to acknowledge my obligation. 



Addendum. May 22, 1889. 



It having been suggested that the passage of the current at high 

 temperatures through roll and precipitated sulphur was caused by the 

 presence of impurities, and not by any change in the properties of the 

 sulphur itself, that some of the impurities distil over with the element, 

 especially sulphuric acid, compounds of mercury and selenium, whose 

 presence would be quite sufficient to account for the effects given by 

 *he specimens used in the previous experiments, it was necessary to 

 btain the purest possible specimens of sulphur, and with this object 

 no pains have been spared. 



As there also arose the question whether a liquid, being neither a 

 metal nor an electrolyte, could conduct an electric current, it appeared 

 to be preferable to try various methods of purification, and to compare 

 the results obtained. 



To make this comparison more valuable, the methods should not 

 be simply variations of the one system, but proceed upon distinct 

 lines, so that any impurities, left after all possible care had been used, 

 should be different in the different specimens, and in the measure- 

 ments there would appear the effects due ta distinct bodies, and if so, 

 give some indication of the presence, in one or other of the portions 

 used, of some foreign body changing the electric properties of the 

 melted sulphur differently from the cases in which that particular 

 body could not possibly occur. Three methods of purification were 

 employed: — 1st, solution, crystallisation, and distillation; 2nd, distil- 

 lation, without solution, in an atmosphere intended to remove hydrogen 

 compounds ; 3rd (pure soluble bodies only were used, easily tested 

 chemically), precipitation, washing with water, and distillation. 



In numbers 1 and 2, foreign bodies acting upon sulphur were added 

 and afterwards removed ; they were different bodies, and if not per- 

 fectly removed might be expected to change the conductivity accord- 

 ing to their own individual properties. In number 3 no such body 

 was introduced. Consequently, if 1, 2, and 3 were alike in their 

 resistances at various temperatures, it must arise from changes in the 

 one body common to all three, namely, sulphur. 



Before giving further particulars of these three methods, I wish to 

 describe experiments undertaken to prevent the electrodes and the 

 containing vessels from spoiling the liquid after it had been purified. 



