Abstracts of Technical Articles from Bell System Sources (01 April 1930)

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. W h e n current is d r a w n 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 surface 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. Metallicbarium 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 technique is also employed to determine the factors which control the evaporation of oxygen from a coated filament.