chapter Nine 



THE DISSOCIATION OF HYDROGEN 



INTO ATOMS* 



PART ONE 



Some early measurements ^ of the heat loss by convection from heated 

 tungsten wires in hydrogen showed that the loss increased at an abnormally 

 high rate when extremely high temperatures were reached. 



A little later ^ a series of measurements on the heat convection from 

 various kinds of wires in different gases led to a general theory of convec- 

 tion from hot bodies, which makes possible the approximate calculation of 

 heat losses from a wire at any temperature in any gas which behaves 

 normally. 



With hydrogen, the theory led to results in close agreement with the 

 experiments, up to temperatures of about 2300° K. Above this, however, 

 the observed heat loss increased rapidly until at 3300° K., it was over four 

 times the calculated value. 



This fact suggested that the hydrogen was partly dissociated into 

 atoms at these high temperatures. 



In a subsequent paper,^ the theory of heat conduction in a dissociating 

 gas was developed to apply to this case.^ It was shown that the power re- 



* In collaboration with G. M. J. Mackay. 



* Langmuir, Trans. Am. Electrochem. Soc, 20, 225 (1911). 

 ^Langmuir, Phy. Rev., 34, 401 (1912). 



^Langmuir, Jour. Amer. Chem. Soc, 34, 860 (1912). 



* At the time of publication of the above mentioned paper, I was unaware that 

 Nernst had previously (Boltzmann, Festschrift, 1904, p. 904) developed a quantitative 

 theory of the heat conduction in a dissociating gas, and had shown that the heat con- 

 ductivity of nitrogen peroxide, deLermined by Magnanini, agreed well with that cal- 

 culated by his equations from the known degree of dissociation of this substance. 

 Nernst showed that the effect of the dissociation is to increase the heat conductivity of 

 a gas by an amount equal to 



He does not, however, show that this leads to the very simple and useful form of 

 equation developed by the writer, namely, 



Wd = SDg (C-C). 

 Nernst points out that the heat conductivity of gases may be used not only to detect 

 dissociation qualitatively, as R. Goldschmidt (Thesis, Brussels, 1901) had shown, but 

 in some cases to determine the degree of dissociation quantitatively. (I. Langmuir.) 



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