20 THE ROYAL SOCIETY OF CANADA 



275° with hydrogen for one hour, 60 c.c. hydrogen was taken up 

 in excess of the water formed. After sweeping out with nitrogen 

 a measured amount of oxygen was passed back and forth at tempera- 

 tures from 20° to 300°. No perceptible action occurred until about 

 300°. 



The nickel oxide just obtained was reduced for one hour at 275°, 

 the hydrogen displaced by nitrogen and the catalyst was then treated 

 with oxygen for one hour at 150°C. Only a very small amount of 

 oxygen was taken up. The free oxygen was expelled by nitrogen and 

 a mixture of ethylene and hydrogen now passed at 150°C. During 

 the first fifteen minutes nothing seemed to occur. However, upon 

 letting the mixture stand for one-half hour at 150° in contact with the 

 catalyst and then passing the gases back and forth reaction was found 

 to proceed rapidly. It thus seems that the oxygen formed a very 

 thin protecting layer probably by action with the outer layer of 

 hydrogens. This had to be removed by hydrogen before the activity 

 of the catalyst was restored. That this arrangement of hydrogens 

 and hydroxyls is many layers thick is indicated by at least two 

 considerations: (1) only a very small amount of oxygen is necessary 

 to temporarily inhibit the activity of the normal catalyst, and (2) the 

 amount of hydrogen and hydroxyl held in the surface particles is very 

 considerable as shown by the above measurements. 



Experiment 13. 



It immediately became of interest to observe the nature of the 

 reaction when a mixture of hydrogen and oxygen is passed over the 

 active catalyst, under conditions where, in the reaction, the reduction 

 of unchanged nickel oxide was small, not only because of this tem- 

 porary inactivation of the catalyst by oxygen, but also in view of the 

 possible light it might throw on the correctness of the views 

 regarding the nature of the surface film and the general mechanism 

 of this catalysis, advanced in this paper. 



The catalyst was prepared by reducing nickel oxide for one hour. 

 After displacing the hydrogen in the apparatus by nitrogen a mixture 

 of 165 c.c. hydrogen and 180 c.c. oxygen was passed back and forth. 

 Reaction occurred at 240-260°C. When the reduction in volume 

 amounted to 200 c.c. the experiment was stopped and the residual 

 gas analysed. 



Hydrogen at start *. . 165 c.c. 



Oxygen at start 180 c.c. 



345 c.c. 



