ELECTRICAL AND OTHER FACTORS 243 



sharply drawn. If, in fact, the two processes are 

 indistinguishable, the case becomes essentially one of 

 alteration of equilibrium following the introduction of an 

 additional reagent into a reaction-mixture. Bancroft 

 cites instances where the same compound undergoes 

 different reactions under otherwise similar conditions 

 according to the nature of the contact-agent present;^ 

 thus with colloidal nickel as catalyzer, alcohol forms 

 acetaldehyde and hydrogen, while with colloidal silica 

 or alumina it forms ethylene and water; and he refers 

 this difference in the catalytic action to the differences 

 in the selective adsorptive action of the two substances, 

 nickel adsorbing hydrogen and alumina water. The rate 

 and character of the reaction undergone by a given 

 reaction-mixture may thus vary with the character of 

 the catalyzer, according to the latter's special adsorbent 

 properties. 



It has been mentioned that simple adsorption is 

 insufficient to account for the great activity of certain 

 contact catalyzers. Taylor^ points out that charcoal 

 adsorbs carbon monoxide and oxygen but does not 

 catalyze the reaction; but in the case of ethylene and 

 oxygen it both adsorbs and catalyzes; hence as catalyzer, 

 it differentiates between carbon monoxide and ethylene, 

 although adsorbing both. Metallic oxides, on the 

 contrary, catalyze the oxidation of carbon monoxide. 

 It would appear, therefore, that specific, presumably 

 chemical, relationships enter even in such simple cases. 



^Bancroft, Journal of Physical Chemistry, XXI (191 7), 573; 

 Applied Colloid Chemistry, pp. 40 £f. 



* Hugh S. Taylor, Trans. Amer. Electrochem. Soc, XXXVI (19 19), 

 150. 



