FLAMES OF ATOMIC HYDROGEN 113 



with the absorption of a large amount of energy. The enormous heat con- 

 ductivity of hydrogen at liigh temperatures (at 3400 deg., about 23 times 

 that of nitrogen) would thus be due to the absorption of energy from the 

 hot wire by the dissociating hydrogen molecules and the liberation of this 

 energy in the cooler gas at a distance from the wire ])y the recombination 

 of the atoms which diffuse away from the wire. 



Confirmation of the view that this efifect is due to the formation of 

 hydrogen atoms rather than to the formation of an endothermic poly- 

 morphic form of hydrogen, such as H3 (corresponding to ozone, O3) was 

 obtained by observation of the fact that the heat loss from filaments at high 

 temperatures is actually greater with low pressures of hydrogen (50 mm.) 

 than with hydrogen at atmospheric pressure. According to the law of mass 

 action, the degree of dissociation of a gas into atoms must be greater at low 

 pressures than at high, whereas the opposite would be true if molecules con- 

 taining more than two atoms were formed. 



Experimental evidence was soon obtained ^ showing that hydrogen at 

 low pressures, when brought into contact with tungsten or platinum wires 

 at 1300 deg. K. or more, acquired entirely new chemical properties which 

 were quite in accord with those to be expected of an atomic form of the 

 element. 



It was found that metallic oxides ^ '^ such as WO3, CuO, FcoOs, ZnO, 

 or Pt02 in a bulb containing hydrogen at low pressure are rapidly reduced 

 to the metallic state if a tungsten filament in the bulb (or in another bulb 

 connected to it by glass tubing) is heated to a temperature above about 

 1500 deg. K. Simultaneously the hydrogen in the bulb gradually disappears. 

 Thus the atomic hydrogen produced by the filament can react with certain 

 metallic oxides at room temperature, although molecular hydrogen cannot 

 do so. The atomic hydrogen can also react at ordinary temperature with 

 oxygen or with phosphorus (to form PH3). This dissociation of the 

 hydrogen by the hot tungsten wire is prevented,'^ however, by even a minute 

 trace of oxygen (or water vapor) if this comes in contact with the wire. 



The atomic hydrogen also shows the property of dissolving in platinum ^ 

 at room temperature and causing a marked increase in the electrical re- 

 sistance of the platinum. Allowing oxygen to come into contact with the 

 platinum brings the resistance back to the normal value. 



By a quantitative study of the heat losses from tungsten wires at various 



temperatures in hydrogen, especially at low pressures, it has been possible 



** Langmuir, Jour. Anier. Chciii. Soc, ^4, 1310 (1913). 

 ^ Langmuir, Trans. Amer. Electrochein. Soc, 2g, 294-5 (1916). 

 " Langmuir, General Electric Review, 16, 962 (1913). 



'Langmuir, Joiirn. Amer. Chcm. Soc, 38, 2271 (1916) ; Trans. Aiiicr. Elcctro- 

 chem. Soc, 2g, 261 (1916) ; General Electric Rcznezv, 25, 445 (1922). 

 ^ Freeman, Jour. Amer. Chem. Soc, 35, 927 (1913). 



