Negative Ions by Glowing Metallic Oxides. 



81 



The platinum wire was heated by an alternating current 

 from a small transformer having a well-insulated secondary, 

 and could be raised to any desired potential by connecting it 

 to one pole of a high-voltage battery, whose other pole was 

 earthed. The cylinder was connected to earth through a 

 galvanometer. 



In the case of a pure platinum wire, as well as in that of 

 one covered with oxide, no well-marked saturation currents 

 are reached at atmospheric pressure. Hence the current was 

 in every instance measured at the same constant potential 

 difference of 1000 volts. 



The oxides of the following metals were investigated: — 



(1) Barium, strontium, calcium, magnesium, zinc, cadmium, 

 yttrium, lanthanum, zirconium, thorium. 



(2) Beryllium, aluminium, thallium, titanium, cerium, iron, 

 nickel, cobalt, chromium, uranium, tin, lead, bismuth, silver, 

 copper. 



Oxides belonging to group (2) showed an emission of cor- 

 puscles which was either not at all or else only very slightly 

 higher than that of pure platinum, while oxides of the first 

 group showed a considerably stronger discharge of negative 

 electricity. The oxides of calcium, barium, and strontium 

 exhibited an abnormally powerful discharge, and this led 

 me to select these oxides for a more detailed quantitative 

 examination. 



Table I. contains the currents which flowed through the 



Table I. 



Relation connecting current (i, in 10~ 8 amp.) with 



temperature (T), at atmospheric pressure. 



1 



Pure Platinum Wire. 



Wire coated with BaO. 



T. 



1 







+«. 



— i. 



+«'• 



— i. 



880 



0-95 



095 







970 







0-95 



3-8 



1050 



i-14 



0-95 



1-14 



237 



1070 









507 



1090 









87-5 



1105 









200 



1120 









400 



1140 









780 



1220 



1-9 



0-95 



1-52 





1300 



475 



0-95 



2-85 





1380 



101 



2-28 



8-56 





1460 



26-6 



27-6 



43-7 





[+* and — i indicate, respectively, positive and negative potential of the 

 glowing wire.] 



Phil Mag. S. 6. Yol. 10. No. 55. July 1905. G 



