FLAMES OF ATOMIC HYDROGEN 



127 



Nernst ^ in 1904 had developed the theory of heat conduction in a dis- 

 sociating gas and had shown that dissociation results in a great increase in 

 the heat conductivity. The dissociation products diffuse from the hot 

 portions of the gas into the £oId portions and there, by recombining, give 

 up the large energy of the chemical reaction. This suggested that the 

 abnormal heat conductivity of hydrogen at high temperatures is due to 

 dissociation of the hydrogen into atoms according to the reaction 



H2 = 2H (i) 



An abnormal heat conductivity might, however, be due to the formation of 

 an endothermic polymorphic form of hydrogen such as H3, corresponding, 

 for example, to ozone. 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 containing more than 

 two atoms were formed. 



At temperatures below 1700° K. the heat carried away by convection 

 and conduction was greater at higher pressures of hydrogen than at lower 

 pressures. For example, a wire of 0.0706 mm. diameter at 1500° K. dis- 

 sipated over twice as much energy in hydrogen at 760 mm. as in hydrogen 

 at 50 mm. pressure. At temperatures above 2700° K., however, more 



tooo 



ieoo 



Z'tOO X600 



oee. K 



taoo 



sooo 



Fig. I. — Heat Loss from a Tungsten Filament Due to Dissociation of Hydrogen 

 by Filament in Hydrogen at Various Pressures. 



energy was dissipated at 50 mm. than at 760 mm. There are evidently two 

 factors acting in opposite directions. Since the heat loss by convection and 

 normal conduction increased with temperature according to a law which 

 had been determined, it was possible to extrapolate to the higher tem- 

 ^ Boltzmann Festschrift, p. 904 (1904). 



