chapter Eight 

 FLAMES OF ATOMIC HYDROGEN 



PART ONE 



When a tungsten wire is heated to incandescence in a vacuum by an 

 electric current (as in a vacuum type tungsten lamp) the heat is dissipated 

 almost wholly Ijy radiation, the energy radiated increasing quite accurately 

 in proportion to the 4.7th power of the absolute temperature T. If an inert 

 gas such as nitrogen, argon or mercury vapor is introduced into the bulb 

 at atmospheric pressure a relatively large amount of heat is carried away 

 from the wire by conduction and convection. This energy loss may be 

 determined by subtracting from the total power input the power (in watts) 

 corresponding to the radiation which has previously been measured in the 

 vacuum at the same filament temperature. In this way it was found ^ that 

 the heat loss by conduction and convection increases in proportion to about 

 the 1.9th power of the temperature even up to temperatures as high as the 

 melting point of tungsten (3660 deg. K.).- This result was found to be in 

 excellent agreement with a theory of heat convection which was based 

 on the assumption that in the immediate neighborhood of the filament the 

 heat is carried by conduction. 



In the case of a tungsten wire in hydrogen ^ the heat loss by conduction 

 and convection increased with about the 1.9th power of the temperature up 

 to only about 1700 deg. K. and then increased much more rapidly. For 

 example, between 2600 deg. and 3400 deg. the heat carried away by 

 hydrogen at atmospheric pressure increased with the 5.0th power of the 

 temperature and with hydrogen at a pressure of 50 mm. of mercury the 

 exponent was even 6.0. 



This abnormal behavior of hydrogen suggested that at high tem- 

 peratures the hydrogen molecules are dissociated into atoms according to 

 the reaction 



Ho = 2H (I) 



' Langmuir, Phys. Rev., 34, 401 (1912). 



^ These temperatures are on the absolute (Kelvin) scale and can be converted to 

 centigrade by subtracting 273 deg. 



'^ Langmuir, Trans. Amer. Electrochcm. Soc, 20, 225 (1911), and Jour. Amer. 

 Chcm. Soc, 34, 860 (1912). 



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