216 PHENOMENA, ATOMS, AND MOLECULES 



high temperatures 68% of the molecules which strike the filament reach 

 chemical equilibrium. The explanation of this apparent paradox, according 

 to the new theory, is that the surface of the tungsten is largely covered by 

 adsorbed hydrogen at the lower temperatures, whereas at the higher 

 temperatures it is practically bare. The 19% thus corresponds to the frac- 

 tion of molecules which condenses when they strike a surface already 

 covered with hydrogen, while the 68% represents the fraction condensing 

 on a bare surface. 



Another fact which proves nearly conclusively that the surface of a 

 highly heated tungsten wire is not covered to an appreciable extent by 

 hydrogen is that the electron emission from tungsten is not perceptibly 

 influenced by the presence of pure hydrogen. ^^ A large amount of unpub- 

 lished work in this laboratory has demonstrated that the electron emission 

 affords an extraordinarily sensitive method of detecting the presence of a 

 film of adsorbed material, so thin that it only partly covers the surface with 

 a layer one atom deep. Some of this evidence will soon be published. 



In subsequent papers, the theory of heterogeneous reactions here out- 

 lined, will be applied to a large number of reactions. It will be shown 

 that the equations derived by Fink, in his work on the contact sulfuric 

 acid process, may also be derived by the new theory, and that definite proof 

 that the mechanism postulated by Bodenstein and Fink cannot apply in 

 this work may be adduced from the experiments themselves. 



The work of Bodenstein and Ohlmer on the reaction between carbon 

 monoxide and oxygen is also in quantitative agreement with the new 

 theory. Other cases, including several studied experimentally in this 

 laboratory, will also be discussed. 



SUMMARY 



1. The velocity of the reaction by which hydrogen is dissociated in 

 contact with a heated tungsten wire is so enormous that it definitely 

 proves that the reaction cannot depend upon a diffusion of hydrogen into 

 the metal even if the depth of penetration should be only that of a single 

 atom. 



2. A general theory of heterogeneous chemical reactions is outlined 

 in which the reaction is assumed to take place in the actual surface layer 

 of atoms. 



3. This theory is worked through in detail for the case of the dissocia- 

 tion of hydrogen. It leads to equations which become identical with that 

 previously derived by other methods, when it is assumed the hydrogen 



11 



Langmmr, Phys. Z., 15, 523 (1914)- 



