374 



Prof. C. Sheard on the 



were in general negligible in comparison with those obtained 

 after the introduction of the salts. 



The samples of salt investigated were inserted in the same 

 half of the double-tube arrangement. In the presentation of 

 results, the tube carrying the salt will be referred to as A 

 and the " unsalted " one as B. 



The connexions and method of operation are outlined in 

 fig, 2. The outer electrodes, and D, were connected to 



Fie- 2. 



a source of high potential. The inner electrodes, A and B, 

 were connected in turn to one pair of quadrants of the 

 electrometer, or earthed, by means of suitable keys re- 

 presented as E, F, G, and H. For currents less than 

 10~ 8 ampere, the time rate of deflexion method was used, 

 a one-microfarad subdivided condenser M being- connected in 

 parallel with the insulated quadrants. For larger currents 

 the electrometer was shunted with a resistance of a megohm 

 N, or any fraction thereof, and the steady deflexions 

 observed. 



Experiments slioiving that the Ionization is partly an 

 Ionization of the Vapour. 



Current-E.M.F. curves were obtained for both the posi- 

 tive and negative ionization from samples of cadmium iodide 

 under different conditions of pressure and temperature. 

 Table I. contains a representative set of data given under a 

 pressure of 9 cm. and at a temperature of 450-5° 0. 

 Approximate saturation of currents in both tubes was 

 btained at a potential of ±160 to ±200 volts. The currents 

 emained fairly constant under potentials ranging from 160 



