500 



Substances wiiicli are most suitable tor this purpose are metals 

 wliicli form carbides as well as hydrides. Tiieir catalytic action will 

 be the most powerful^) in the region where these combinations 

 exist in a condition of dissociation, where, consecpientlj the "activa- 

 tion" is greatest without the catalyst being paralyzed by too great 

 a chemical action. 



To these metals appear to belong in the first place nickel and 

 cobalt (Mayer and Altmayeh I.e.); to their action must be attributed 

 the fact that during the hydrogenations according to .Sabatier and 

 SENDEREi^is ^) considerable quantities of methane are often formed. 



The activating power of a catalyst will, however, have to be 

 unequal, under the same conditions, for each of the bonds, because 

 the dissociation regions of the carbides and the hydi'ides will not as 

 a rule coincide, and experience has taught that nickel is eminently 

 suited for the hydrogenation. of hydrocarbons without methane being 

 evolved, if only we keep below ± 240°. 



Hence, the C-C-activation of nickel at tlie ordinary pressure only 

 appears to, become appreciable above that temperature, which we 

 may call the catalytic limit for that bond. Little is know^n of 

 the limit of the hydrogen activation of nickel, which seems to be 

 greatly dependent on the condition of the metal, anyhow the tempe- 

 ratures at which this activation becomes important and the hydro- 

 carbon activation limit do not diverge greatly. 



In the case of other metals these limits may differ more seriously. 

 This is shown in a vei'y convincing manner from the research of 

 Zelinsky '). He demonstrated that palladium black, which at 0° is an 

 excellent hydrogen "activator" did, at 300°, resolve cyclo-hexane 

 into benzene and hydrogen only ; the catalytic limit of palladium 

 black for the 0-C-bond of cyclo-hexane is therefore situated above 300°. 



Hence, if we wish to study the resolving or combining reactions 

 of a hydrocarbon and hydrogen, palladium black is the catalyst 

 per excellence. '). 



1) Compare Ann. Gh. et Ph. [8] 4, 3o6 (1905J. 



2) B 44, 3122 a911) ; 45, 3678 (1912). 



3) In reality, at least two bonds are activated simultaneously, for instance the 

 GH and the HH bond or the G-G and the other bonds; in order not to become 

 too prolix we will distinguish provisionally the carbon and hydrogen activation 

 only. Under carbon activation I, therefore, understand here the influence which 

 is not limited to causing a dislocation but leads to a dissociation of the saturated 

 carbon-carbon bond. Before this point is attained some activation still takes 

 place but this can lead at most to linking and splitting off of hydrogen ; hence 

 to simplify matters 1 am speaking in thai case only of hydrogen activation. 



