S-t PHENOMENA, ATOMS, AND MOLECULES 



where /x is the rate of arrival of the gas molecules expressed in molecules 

 cm~^ sec~^, and m is the mass of the molecule. By inserting numerical 

 values this equation becomes 



/( = 2.65 X io"p (MT)-V2 ^ (5) 



where M is the molecular weight of the gas (oxygen = 16) and p is ex- 

 pressed in baryes. By using filaments of small size and bulbs of large size, 

 it was possible to measure experimentally such high rates of disappearance 

 of gas (clean-up) that every molecule that struck the filament disappeared. 

 Under usual conditions, however, the rates of clean-up were far less than 

 this theoretical maximum. The fraction, e, of all the impinging molecules 

 which reacted on striking the filament could thus be determined. 



Working in this way, a systematic study was undertaken of the efifects 

 of such gases as oxygen, hydrogen, nitrogen, carbon monoxide, and their 

 mixtures, etc., on filaments of tungsten, carbon, molybdenum and platinum, 

 I shall refer only to those cases where the experiments have thrown light 

 upon the phenomenon of adsorption. 



Clean-up of Hydrogen. (3) 



When a tungsten filament is heated to temperatures of i,5oo°K in 

 hydrogen at about 20 baryes pressure, the hydrogen slowly disappears, the 

 pressure decreasing with time as indicated in curve I of Fig, i. The pressure 

 falls to a very low value in 10 to 20 minutes. If more hydrogen is intro- 

 duced, the rate of clean-up is somewhat slower, the pressure decreasing 

 according to curve II. Although analysis shows the residual gas to be pure 

 hydrogen, the clean-up gradually comes to a standstill. 



With a bulb containing 2 filaments, it is found that the lighting of the 

 second filament does not cause a recovery in the rate of clean-up. This 

 proves that the gas which disappears is not taken up by the filament itself. 

 By keeping the bulb in liquid air, a greater total amount of clean-up is 

 obtained. Such investigations show that the hydrogen which disappears 

 becomes adsorbed on the surface of the bulb, but that the bulb is capable 

 of adsorbing only a limited amount of hydrogen. This hydrogen adsorbed 

 on the glass is capable of reacting with oxygen at room temperature after 

 the filament has been allowed to cool. The adsorbed hydrogen is therefore 

 in a chemically very active state. It was finally proved that the heated 

 tungsten filament dissociates (4, 5, 6, 7, 8) a small fraction of the incident 

 hydrogen molecules into atoms, and that these atoms, because of their un- 

 saturated chemical nature, exhibit a strong tendency to be adsorbed on 

 glass. These hydrogen atoms, however, are capable of reacting with one 

 another and forming molecules. From this point of view, it should be im- 

 possible to hold on the glass more hydrogen than could form a layer one 

 atom deep. 



