130 



PHENOMENA, ATOMS, AND MOLECULES 



Q = 97,000 -h 1.5 T - 0.00045 72 



(7) 



}Jote — This result for the heat of dissociation which was published in March, 

 1926,* is in excellent agreement with the value 98,570, subsequently found by Witmer * 

 from studies of a hydrogen band spectrum found by Lyman. In a later paper ° from a 

 more careful analysis of similar data Witmer concludes that Qo is 100,000 ± 5000 

 calories. 



CHEMICAL PROPERTIES OF ATOMIC HYDROGEN 



While the measurements of the heat losses from filaments in hydrogen 

 were being made, other experiments ^^ showed that hydrogen which had 

 been in contact with heated filaments acquired entirely new chemical 

 properties, and they were quite in accord with those to be expected of an 

 atomic form of the element. 



If a tungsten or platinum filament is heated to 1300° K. or more in dry 

 hydrogen at low pressures, preferably less than i mm., a limited amount 

 of the hydrogen gradually disappears or cleans up. When the limiting clean- 

 up has taken place no additional clean-up occurs if a second filament is 

 lighted, so we know that the gas is not absorbed by the filament. It was 

 found that part of the hydrogen can be recovered by heating the bulb. The 

 amount of hydrogen that can be cleaned up increases considerably, but not 

 indefinitely, when the bulb is kept cooled by liquid air. If the liquid air is 

 removed after the filament has been allowed to cool, the excess of absorbed 

 hydrogen is evolved but does not recondense when the liquid air is re- 

 placed unless the filament is again lighted. The hydrogen on the bulb is thus 



*Proc. Natl. Acad. Set., 12, 238 (1926). 



^ Phys. Rev., 28, 1233 (1926). 



"Langmuir, Jour. Atner. Chem. Soc, 34, 1310 (1912). 



