Abstracts of Technical Articles from Bell System Sources 



Phenomena in Oxide Coated Filaments.^ Joseph A. Becker. A 

 theory of the changes in activity in oxide coated filaments is proposed. 

 From a comparison of the behavior of these filaments and filaments 

 with composite surfaces such as thorium on tungsten, caesium on 

 tungsten, and casium on oxygen on tungsten it appears probable 

 that oxide coated filaments owe their high activity to adsorbed metallic 

 barium. The changes in emission from a coated filament produced 

 by changes in plate potential and by currents sent into or drawn from 

 it, are ascribed to electrolysis of the oxide. When electrons are sent 

 into a coated filament barium is deposited on the surface and the 

 activity increases until an optimum is reached beyond which the 

 activity decreases. When current is drawn from the oxide, oxygen is 

 deposited on the surface. If the oxygen is beneath the adsorbed 

 barium, it increases the activity; if it is above the barium, it decreases 

 the activity. Both barium and oxygen diffuse readily from the sur- 

 face into the oxide and vice versa. This theory is tested, confirmed, 

 and extended by numerous experiments. 



An experimental technique is employed by which relative rates of 

 evaporation of small amounts of electropositive and electronegative 

 materials can be determined with considerable precision. The same 

 technique might be useful in a number of similar investigations. 

 Metallic barium or oxygen which evaporate from a coated filament 

 are allowed to deposit on one side of a flat tungsten ribbon whose 

 thermionic activity is followed. When the plausible assumption is 

 made that an optimum activity is obtained when the tungsten is 

 covered with a single layer of electropositive material, the relative 

 rates of evaporation can be converted to absolute rates. This tech- 

 nique is also employed to determine the factors which control the 

 evaporation of oxygen from a coated filament. 



Estimation of the Volatile Wood Acids Corrosive to Lead Cable Sheath.^ 

 R. M. Burns and B. L. Clarke. The detection of volatile acids in 

 the air drawn from creosoted wood conduit corrosive to lead cable 

 sheath made desirable the development of a suitable method for the 

 extraction and estimation of volatile wood acids. Such a method 

 consists in the condensation of the volatile constituents of wood 

 sawdust removed under reduced pressure and titration of the conden- 



1 ThePhys. Rev. Nov. 1929. 



' Jndust. and Eng. Chem., Jan. 1930. 



398 



