HAYES. — ELECTRICAL CONDUCTIVITY OF ARGENTIC SULPHIDE. G21 



The characteristics of the second condition, it will be seen, have 

 entirely disappeared, and the resistance with increasing current or 

 temperature instead of falling appears to have increased. As stated 

 by Faraday, the removal of the positive electrode from the specimen, 

 and the scraping of the surface so as to present a new layer of the 

 sulphide restores in every case the specimen to the properties previ- 

 ously possessed by it under the second condition. 



The conclusions which may be drawn from the above are : 



(a) That electrical connection cannot be made between compressed 

 silver sulphide and electrodes of platinum, steel, silver or copper simply 

 by pressure. 



(b) That conduction through compressed silver sulphide cannot be 

 obtained until sufficient ionization has occurred at the contacts to allow 

 the passage of an arc. 



(c) That connection, when a current has passed, is most readily and 

 completely obtained at the negative terminal of the specimen. 



(d) That it is probable that, when perfect connections have been 

 established between the sulphide of silver and its electrodes, the sul- 

 phide has a positive rather than a negative coefficient of resistance for 

 increasing temperatures. 



Boston, January 25, 1910. 



