2 THE ROYAL SOCIETY OF CANADA 



supposed to exist in the nickel in some specially active condition, so 

 that from this standpoint the nickel acts as a hydrogen carrier. 



Sabatier (2) postulates the existence of definite hydrides of nickel, 

 Ni-H 



NiH2 and " , which, giving up their hydrogen to unsaturated 



Ni-H 



compounds, are changed into elementary nickel, which once more 

 combines with free hydrogen to reform the hydrides. Here also, as 

 in the former view, the nickel acts as hydrogen carrier. However, 

 Sabatier replaces the conception of hydrogen activated by solution or 

 absorption in the nickel, by the idea of hydrogen temporarily fixed in 

 the form of definite hydrides of nickel holding hydrogen in a very 

 labile or active condition. It is of interest to observe, in view of 

 what will be pointed out later in this paper, that Sabatier expressed 

 his belief in the formation of tVv^o hydrides, differing in the ease with 

 which they give up their hydrogen, because of the experimental fact 

 that nickel, prepared by the reduction of the oxide at a low tempera- 

 ture, varies in its activity, the more active form, which Sabatier be- 

 lieved to be NiH", is able to hydrogenate benzene while the less active 



Ni-H 



form to which Sabatier ascribed the formula li is unable to hydro- 



Ni-H 



genate benzene but has the capacity of hydrogenating hydrocarbons 

 of the ethylene series and other more easily hydrogenated com- 

 pounds. 



Wieland like Sabatier, believes in the intermediate formation 

 of a hydride but goes a step farther in the picture of mechanism by 

 indicating the existence of a loose addition compound between the 

 hydride and the unsaturated compound, which unstable complex 

 then breaks up with the formation of the hydrogenated compound and 

 the regeneration of elementary nickel, which latter then reforms the 

 hydride, and so the cycle of reactions continues. 



Titofï and also Firth from measurements of the adsorption 

 of hydrogen by various charcoals, were led to the conclusion that 

 hydrogen is contained in charcoal in two states, one as a surface 

 condensation of the gas which he designates adsorption, and the other 

 as absorbed or dissolved hydrogen. It is the former adsorbed hydro- 

 gen which is believed to be active in effecting hydrogénations. 



Fokin (3) found that in electrolytic reductions at the cathode that 

 only those metals used as cathodes were effective in reductions 

 electrolytically, which were found active in hydrogénation with 

 ordinary hydrogen by the Sabatier method. Fokin believes that 

 the special capacity of these metals to effect cathodic reduction is 



