[boswell] catalysis OF HYDROGENATION BY NICKEL 23 



hydrogen per volume of nickel to a capacity for hydrogen as great as 

 that possessed by cocoanut charcoal. 



No meaning attaches to the measurement of hydrogen adsorption 

 by nickel unless the whole history of the nickel is also described in 

 detail. The term, it seems, should be restricted to the amount of 

 hydrogen taken up by a known weight of nickel spread over a definite 

 surface, the nickel having been prepared by the reduction of nickel 

 oxide by hydrogen at a definite temperature until all the oxygen has 

 been removed. 



As nickel oxide has an indefinite composition, being always a 

 mixture of oxides, the completion of reduction by hydrogen cannot be 

 determined by continuing the reduction until the water equivalent of 

 the oxygen in the oxide has been evolved. There appears to be two 

 ways of determining whether reduction has been complete or not : (1) to 

 continue the reduction in hydrogen until no water is evolved even 

 after allowing the nickel to stand in the cold in an atmosphere of 

 hydrogen for several hours and subsequently heating in a current of 

 hydrogen, and (2) completely reduce at 400°C. and then oxidize 

 with a known volume of oxygen at 400° and reduce at the desired 

 temperature until the water equivalent of the oxygen adsorbed has 

 been evolved. 



From the standpoint of catalysis of hydrogénation, however, the 

 measurement of hydrogen adsorption is, as we have just seen, of little 

 importance, as the normal nickel catalyst is never in the condition 

 of holding hydrogen alone. 



Willstatter (9) has also pointed out that a nickel catalyst freed 

 from oxygen by reduction at 400°C. has a very low action for catalysing 

 hydrogénation. He produced his oxygen free nickel by the reduction 

 by nickel oxide at 400° for six hours. Now our experiments have 

 shown that a nickel oxide distributed in an extremely' fine layer over 

 asbestos still holds considerable oxygen after six hours' reduction at 

 400°. The nickel of Willstatter, we believe, still contained oxygen. 

 However, it was probably buried in the interior of the particles, so 

 that the action of the adsorbed surface hydrogen on this oxygen was 

 extremely slow and as a consequence, as far as the surface was con- 

 cerned, the catalyst acted as though it had lost all of its oxygen and 

 held only hydrogen adsorbed. 



Notwithstanding the relatively large amount of hydrogen ad- 

 sorbed on a nickel catalyst prepared by partial reduction at 275 ethylene 

 alone, in the absence of free hydrogen, does not react at 150°C. For 

 hj^drogenation free hydrogen must also be present. This is also true 

 for nickel prepared by complete reduction at 40.0°. That is, the 



