384 



Prof. C. Sheard on tlie 



the whole system had been heated for over an hour at 460° C. 

 The glass vessel, the lower 15-20 cm. of which were inserted 

 in the furnace, served as the outer heated non-metallic 

 electrode. Auxiliary experiments showed that the glass was 

 a good conductor of electricity in the vicinity of 300° C, 

 the currents varying linearly with the applied voltages. 

 Aluminium foil wrapped tightly about the outside of the 

 tube and baked to the glass furnished a convenient method 

 of connecting with the source of potential. 



The modus operandi, connexions of the tube with the 

 remainder of the testing system, &c, were essentially the 

 same as those described in connexion with fi>. 2. The 

 empty tube, properly cleaned, when heated to 500 C. at 

 low pressure gave currents of the order of 1 X 10~ 12 to 

 1 X 10 _11 ampere. 



Table V. contains a set of data for positive and negative 

 current-E.M.F. relations obtained at 460° C. and 1 cm. 

 pressure. These values were obtained in the steady current 

 regions reached after an hour's heating under potential. 



Table V. 



1 div. = 10" n ampere. 



Potential. 



+ Currents. 



— Currents. 







o-i 



2-1 



33 



60 



9-2 



10-4 



104 



10-8 



005 



0-13 

 0-22 

 032 

 0-43 

 0-45 

 0-46 



10 



20 



40 



80 



120 



160 



200 



Two grams of cadmium iodide were heated at a temperature 

 of 465-475° C. and at a pressure of 1*8-2 cm. under potentials 

 of + 200 volts. The current-time relations obtained are 

 exhibited in fig. 6. Curve 1 (o) shows the positive and 

 curve 2 (•) the negative current readings. The most 

 noticeable feature is the quantitative relation existing between 

 the maximum values of the negative and positive ionizations, 

 for the former is over three hundred times as great as the 

 latter. The negative current decayed from a value of 

 1638 x 10~ 10 ampere to 118 x 10" 10 ampere during the first 

 ten minutes. This was followed by the slow decay with 

 time period for the succeeding forty minutes, after which 



