ABSTRACTS OF TECHNICAL ARTICLES 249 



that an enhanced emission of electrons could be obtained by smearing 

 sealing-wax on a platinum ribbon and burning it off in air. The first 

 authentic study is recorded by Wehnelt, who investigated the voltage- 

 drop in a gas discharge tube with cathodes coated with various metallic 

 oxides. Its further evolution and development to the status of a 

 cathode in Western Electric vacuum tubes has been described by H. D. 

 Arnold. A comprehensive treatment of its history, the various 

 modifications in current use, and divergent theories of its preparation 

 and behavior has been given by Saul Dushman in a treatise on "Ther- 

 mionic Emission." A later review is given by J. H. deBoer. 



The present work is devoted to a quantitative determination of the 

 relation between thermionic emission and the content of free alkaline 

 earth metal. To this end we have employed a filament which is a 

 platinum rhodium core coated with barium, strontium, and nickel 

 carbonates. On heating in a reducing atmosphere this coating becomes 

 a grossly homogeneous colloidal mixture of barium oxide, strontium 

 oxide, and free nickel. After a thorough preliminary clean-up of the 

 experimental tube, the requisite amounts of free alkaline-earth metal 

 are generated by reaction with methane. The electrical measure- 

 ments are summarized by the use of the Richardson equation for 

 thermionic emission. Free alkaline earth metal has been determined 

 by oxidation with carbon dioxide and analysis of the gaseous reaction 

 products. 



Using a filament coated with a colloidal mixture of barium oxide, 

 strontium oxide, finely divided nickel, and free alkaline earth metal, 

 we have investigated the quantitative relation between thermionic 

 emission and the content of active metal. A high level of activity 

 was found from 15 ;ug./sq.cm. to 60 /xg./sq.cm. of equivalent Ba, with 

 a slight apparent maximum at 30 /ig./sq.cm. where the thermionic 

 current at 1050° K. is 600 m. a./sq.cm. The electron work function 

 is 1.37 V. 



The radiant emissive power at 0.66 m is approximately 64%, in- 

 dependent of the content of active metal. 



The free alkaline earth metal was determined by oxidation with 

 carbon dioxide and analysis of the gaseous reaction products. 



A Single- Sideband Receiver for Short-Wave Telephone Serviced 

 A. A. RoETKEN. A new radio telephone receiver has been developed 

 for the reception of reduced-carrier single-sideband signals in the 

 frequency range from 4 to 22 megacycles. This receiver employs 

 triple detection in which the first beating oscillator is continuously 



^Proc. I. R. E., December 1938. 



