12 THE ROYAL SOCIETY OF CANADA 



(NiO),.Ni 



H + 

 OH- 

 H + 

 OH- 



Taylor and Burns (8) express the general opinion that adsorp- 

 tion in the case of metal catalysts is a surface phenomenon, somewhat 

 chemical in character, possibly involving re-arrangements of elec- 

 trons in both the adsorbent and gas. The mechanism brought 

 forward in this paper is a picture of such a surface phenomenon. 

 However, Taylor and Burns also express the opinion that because 

 the disappearance of catalytic activity is accompanied by suppression 

 of adsorptive power, therefore the varying adsorptive capacity of the 

 material accounts for the variable catalytic behaviour, thus con- 

 necting the catalytic capacity directly with adsorption of hydrogen 

 alone. That this is not a complete picture of the mechanism seems 

 clear from the experimental facts cited above and the argument 

 based upon them. It may further be pointed out, that in the reduc- 

 tion of nickel oxide, and also in the hydrogénation of ethylene by a 

 partially reduced nickel oxide, a condition is reached after long action, 

 where the negative hydroxyls on the nickel, being slowly used up 

 by reaction with hydrogen, are replaced with increasing slowness 

 from the underlying nickel oxide. The surfaces approach more and 

 more the condition of nickel carrying positive and negative hydrogens 

 alone. Now if the catalysis of the hydrogénation of ethylene depends 

 primarily on the presence of negative hydroxyls on the nickel surfaces, 

 evidently a diminution of these would produce a falling off in the 

 velocity of hydrogénation. Thus, although adsorption of hydrogen 

 does occur as represented in reactions (2) and (4) under experiment 

 7, and although a falling off in adsorption of hydrogen accompanies 

 diminution of catalytic activity, yet the adsorbed hydrogen is not 

 primarily the active agent in hydrogénation with a normal nickel 

 catalyser, but the negative hydroxyls, acting according to the mechan- 

 ism represented under experiment 7. 



The gas in the apparatus was replaced by nitrogen and ethylene 

 passed back and forth between the burettes aa at 150°C. No ethane 

 was formed. 



Experiment 6. 



10 litres of a mixture of hydrogen and ethylene was now passed 

 at 150°C. over the catalyst from the last experiment. A careful 



