HAYES, — ELECTRICAL CONDUCTIVITY OF ARGENTIC SULPHIDE. 617 



inilliammeter and voltmeter, included in circuit with the specimen, and 

 a battery having an electro-motive force of 20 volts. The voltmeter 

 was connected about the terminals of the specimen and the current was 

 controlled by the use of resistance coils placed in the direct circuit with 

 specimen, ammeter and battery. A telephone was also so arranged 

 that it could be connected with the terminals of the specimen under 

 test. 



An extremely large number of measurements was made on many 

 specimens under varying conditions. The characteristics of this mate- 

 rial, as described above, were found throughout the tests and agree 

 with those found and recorded by former experimenters. The use of 

 the telephone in my experiments, however, has, I believe, thrown some 

 new light upon the action Avhich is taking place within the specimen of 

 sulphide of silver during the passage of the electrical current through it. 



Consideration of Condition I. I have frequently found that speci- 

 mens had an initial resistance so high that w'ith 20 volts no measure- 

 ments of current could be made with the instruments at hand. When 

 connected with a 110-volt lighting circuit there was an immediate fall 

 in resistance and thereafter the 20-volt source sufficed for current 

 measurements. Placing a heated soldering iron in the vicinity of the 

 specimen would frequently be equally effective in lowering the initial 

 resistance of a specimen. 



The following table gives characteristic current and voltage readings 

 of specimens when in the first condition. 



This action appeared to be equally conspicuous with platinum, steel, 

 silver or copper electrodes. During the time that the resistance of this 

 specimen was high, violent " sputtering " or " burning " noises were 

 audible in the telephone, and these noises entirely ceased at the time 

 of making the last measurement recorded above. The noises heard in 

 the telephone were characteristic of those frequently present when a 

 C'lrrent is passing through an imperfect contact. The subsidence of 

 these noises was indicative of the formation of more perfect contacts. 



