24 THE ROYAL SOCIETY OF CANADA 



hydrogens on the nickel catalyst in either of the two states, (1) positive 

 hydrogens and negative hydroxyls and (2) positive hydrogens and 

 negative hydrogens, do not react with ethylene at 150° in the absence 

 of free hydrogen. 



According to the mechanism of hydrogénation by nickel just 

 described most of the conflicting views of investigators are, we believe, 

 explained. The conception of definite hydrides as intermediate 

 products in hydrogenating actions is not valid as the normal catalyst 

 always contains oxygen and functions, as catalyst for hydrogénations, 

 chiefly through the hydroxyl groups on the surface. Even where the 

 catalyst carries only hydrogen this can not be said to exist in the form 

 of definite compounds called hydrides of definite proportion of hydro- 

 gen to nickel, but rather as complexes in which nickel carries the 

 hydrogen adsorbed on the surface as positive and negative hydrogens. 



Likewise the oxygen present in the normal catalyst is not there 

 as a definite hydroxide of nickel, but as a complex carrying hydroxyl 

 groups negatively charged along with hydrogens positively charged. 

 However, although these combinations are "complexes" rather than 

 compounds yet the hydrogens and hydroxyls react, it would appear, 

 in stoichiometric proportions. 



A great deal of additional support for the mechanism here pre- 

 sented comes from the satisfactory interpretation which its expansions 

 seem to furnish for the facts known regarding phenomena at the 

 electrodes in electrolytic cells, of over voltage, of matter in the col- 

 loidal state, of the phenomena of precipitation of colloids and adsorp- 

 tion of electrolytes on precipitated colloids. The state of platinum, 

 for instance, when in solution as a sol in water is, probably, very 

 closely connected with its state when active as a catalyser. That 

 is, a similar relationship of hydrogen and hydroxyl to platinum exists 

 in the two states. This theory has been further extended to express 

 the relationship of solvent to solute in the case of true solution. In 

 other words a similar relationship is believed to exist between solute 

 and solvent in true solution, between dispersed substance and dis- 

 persion medium in colloidal solution and between macroscopic par- 

 ticles acting as catalysts and the surface water film. 



These expansions of the theory will be considered in later papers. 



Summary 



A quantitative study of the reduction of nickel oxide by hydrogen, 

 as well as of the catalysis of the hydrogénation of ethylene by partially 

 reduced nickel oxide, indicates that the oxygen necessarily present 

 in a normal nickel catalyser is present in two conditions (1) as un- 



