HAYES. — ELECTRICAL CONDUCTIVITY OF ARGENTIC SULPHIDE. G19 



current had passed for a short time a good connection was estabhshed 

 at the terminal in the vise and the third condition of the action was 

 established. 



What actually takes place at the negative electrode I have not 

 determined. Both Faraday and Hittorf were inclined to the belief 

 that conduction through the sulphide of silver is electrolytic, and 

 Hittorf states that silver was found by him at the j unction with the 

 negative electrode. Hittorf also found that, in similar tests made with 

 the oxide of copper, antennae of copper were thrown out from the 

 specimen at the negative pole. 



Consideration of Condition II. The second condition exists when a 

 more or less ^perfect connection has been established at the negative 

 electrode and the contact at the positive terminal is still faulty. All 

 tests of specimens in this condition show the characteristics of meas- 

 urements of currents and potentials at imperfect contacts in an electrical 

 circuit. The really remarkable peculiarity of the silver sulphide is that 

 contact cannot be established even when the electrodes and the speci- 

 men are pressed together under a weight of many tons. 



Attention might be called to the fact that there is present a condi- 

 tion of " unilateral " conduction such as has been extensively studied 

 by Professor Pierce,^ the magnitude of the action being dependent upon 

 the degree to which perfect contact has been obtained at the negative 

 terminal of the specimen. This differential action is shown in Table 

 H., and Table HI. given below as a fairly characteristic set of measure- 

 ments made upon specimens in the second condition. It should be 

 noted that the repeated reversals of current gradually establish perfect 

 connections at the two terminals of the specimen, and thus rapidly 

 obliterate the unilateral conduction and tend to establish the third 

 condition. 



« Pierce, Physical Review, 25 (1907); 28 (1909). 



