NOTES ON THE ELECTRICAL CONDUCTIVITY OF 

 ARGENTIC SULPHIDE. 



By Hammond Vinton Hayes. 



Presented February 8, 1911. Received January 18, 1911. 



The peculiar action of the sulphide of silver as a conductor of elec- 

 tricity was described by Faraday^ in 1833. Later Hittorf,^ in 1851, 

 repeated Faraday's experiments and confirmed the results of the earlier 

 work. In 1902 Streintz,^ in a study of the conductivity of compressed 

 powders, investigated the behavior of compressed silver sulphide in an 

 electrical circuit and found all of the phenomena described by Faraday 

 and Hittorf. All of these observers attribute to silver sulphide a neg- 

 ative coefiicient of resistance for heat, Faraday speaking of it as " an 

 extraordinary case . . . which is in direct contrast with the influence 

 of heat upon metallic bodies." 



1 have recently conducted a long series of experiments upon the 

 electrical resistance of compressed silver sulphide and, as a result of 

 my observations, am led to the belief that many, if not all, of the 

 phenomena 'described by earlier experimenters may be explained as due 

 primarily to the condition of the contacts between the specimen of 

 silver sulphide and the electrodes used to connect it into the electrical 

 circuit. 



In order to study the behavior of this material I have found it con- 

 venient to consider the specimen and its electrodes during three dis- 

 tinct stages or phases of their condition. These will be briefly described. 



1st Condition. When the specimen is first placed in circuit it has an 

 extremely high resistance. Upon heating the specimen its conductivity 

 increases with extreme rapidity and, when the source of heat is re- 

 moved, the conductivity frequently falls to nearly that which originally 

 existed. As an illustration of this action the figures given by Streintz 

 of test upon a sample may be quoted. " At a temperature of 100° the 

 specimen showed a resistance from 3,000 to 1,000 ohms ; at 150°, fi:om 

 400 to 150 ohms; at 220° the resistance measured only fi^om .1 to .2 



^ Faraday's Experimental Researches in Electricity, Vol. 1, 432 et seq. 



2 Hittorf, Pogg. Ann., Vol. 84, 1851. 



3 Streintz, Ann. der Physik., Vol. 3, 1900, and Vol. 8, 1902. 



