22 THE ROYAL SOCIETY OF CANADA 



surface carrying this dissociated hydrogen. However, Lewis does 

 not consider the very important part which oxygen plays in this 

 catalyst of hydrogénation. As we have seen, a nickel catalyst 

 carrying only dissociated hydrogen and no oxygen has a very low 

 activity, and that the normal nickel catalyser always carries a relatively 

 large amount of oxygen. Also, Langmuir (13) has shown that a 

 highly heated tungsten wire will dissociate hydrogen at low pressure 

 and this hydrogen can be made to condense on a glass surface cooled 

 by liquid air. When the wire is allowed to cool and the glass is 

 allowed to warm to room temperature hydrogen is set free. On 

 again cooling the glass without heating the wire the hydrogen does 

 not condense. Also, Langmuir found that, on repeating the experi- 

 ment and pumping out the free hydrogen, hydrogen still being on the 

 glass, and now admitting oxygen, that the hydrogen on the glass 

 combined with the oxygen, thus indicating a very active hydrogen. 

 These effects, which Langmuir ascribes to dissociation, are more 

 marked with platinum and palladium than with tungsten. Also, 

 Klemenc (14) has calculated the equilibrium constant for the reaction 

 H"^4-H~ ^ * Ho, and has calculated the energy difference between a 

 hydrogen atom and hydrogen carrying a negative charge. Still more 

 recently, Hughes (15) has secured evidence which shows that dis- 

 sociation can occur by a single impact of an electron with a hydro- 

 gen molecule. 



This conception of negative hydrogen is directly connected with 

 the electronic conception of valence, and the interpretation of chemical 

 reactions in general by means of the electron theory. 



In the mechanism of catalysis which is here advanced this 

 electronic conception is applied to the experimental data. 



It follows from the experimental data that the absorptive capacity 

 of nickel for hydrogen depends on the method of preparation. If 

 prepared from oxide by reduction with hydrogen at temperatures 

 below 275° it would probably require many months to completely 

 remove all the oxygen. And as we have seen the capacity of a nickel 

 catalyst to hold hydrogen depends largely on its oxygen content. 

 By continuous reduction at 275° for only ten hours a condition is 

 reached where the water evolved in half an hour is relatively very 

 small. Should this be taken as an indication of the attainment of 

 complete reduction an utterly erroneous result would be obtained for 

 the hydrogen adsorption capacity of nickel, for the catalyst would 

 still contain a large percentage of oxygen. This probably explains 

 the widely varying statements in the literature regarding the amount 

 of hydrogen which nickel can adsorb, varying from 0.2 vols, of 



