278 ILLINOIS STATE ACADEMY OF SCIENCE 



in these same circuits and gave louder and clearer speech 

 amplification with six volts on the plate than did the 

 vacuum amplifier tubes with 30 or 40 volts. 



The potassium-sodium alloy is used for the sensitive 

 coating in the photo-electric cell, and it seems certain 

 that the resulting plate current with zero applied plate 

 voltage is dne to the photo electric effect of the light 

 from the incandescent filament. The plate current, and 

 also the detector action at zero plate voltage, were main- 

 tained when the return plate circuit was connected to 

 either the negative or positive terminal of the filament, 

 indicating that the result was not due to potential drop 

 along the filament. 



CONCLUSION 



Investigation of the action of the various gases men- 

 tioned in detector tubes shows that if inert gases are 

 used the pressure should not exceed .005 mm. of mercury 

 for best results as regards sensitiveness and non-critical 

 adjustments. If certain metallic vapors are used, low 

 ''operating plate voltages" may be used if the ionizing 

 potential of the vapor is low, and the tubes will be still 

 more sensitive and much less critical in adjustment than 

 low vacunm tubes containing an inert gas. The sensi- 

 tiveness increases with the atomic weight of the gas in 

 the tube, or more probably with the number of free elec- 

 trons in the gas atom. It is hoped that further investi 

 gation will show some other gas or metallic vapor to be 

 still better than the ones discussed in this paper. The 

 potassium-sodium alloy and rubidium were kindly fur- 

 nished by Dr. Jakob Kunz. Dr. Knnz recommended 

 these substances in response to an inquiry as to what 

 gases had very low ionizing potentials. Acknowledg- 

 ment is also due Mr. W. E. Davis, a senior student, for 

 his faithful assistance in the work. 

 Laboratory of Physics 



University of Illinois 

 April 21, 1922 



