Jan., 1916] Electrical Behavior of Porcelain and Glass 83 



times as similar to metallic conduction, at other times as 

 electrolytic in character. It is possible that these ceramic 

 bodies fvmction in both manners. 



The author undertook these experiments without expecta- 

 tion of answering this question, but to obtain some experimental 

 data on the magnitude of the currents obtained by Plenderson 

 and Weimar in their experiments, also to find if possible whether 

 one could give a true ohmic value to the resistance offered by 

 the porcelain bodies at temperatures where they became very 

 appreciable conductors. Henderson and Weimar had used 

 periodic e. m. f's. from a 60 cycle source. The general plan 

 here adopted was to employ the high potential storage battery 

 in our laboratory for maintaining constant and fairly high 

 potentials (up to 1,000 volts) and apply the potentials directly 

 to the specimen at the same time measuring the current. 

 Then from Ohm's Law we could infer the resistance 



Vi-V2 = RI. 



Vi — Vo = potential difference in volts. 

 I = current in amperes. 

 R — resistance in ohms. 



Figure 1 shows the very simple arrangement of the circuits. 

 The battery has one terminal earthed. The other terminal was 

 connected to the specimen (S) through a high resistance (R). 

 A Weston volt meter (V) with a multiplier (M) measured the 

 potential difference between the upper face of the specimen and 

 the earth. The regulating resistance (R) made it possible to 

 maintain a constant potential if desired. The regulating 

 resistance was a liquid contained in a tube 80 cm. long, 2 cm. in 

 diameter. 



The liquid is a solution 25% saturated of Cadmium Iodide 

 in Amyl alcohol. The terminals are Cadmium. This gives 

 a high resistance quite free from polarization and capable of 

 carrying currents of 50 milliamperes. 



The ammeter (A) introduced between the specimen and 

 earth measured the current passing through the specimen only. 

 This consisted of a resistance with a D'Arsonval galvanometer 

 in shunt. Knowing the resistance of shunt and galvanometer 

 one can calculate the fall in potential through the specimen 

 for any values given by the voltmeter. Through the courtesy 

 of the Ceramics Department, samples of porcelain were secured 



