298 COLLOIDS 



energy* which no doubt, in part, explains the remarkable 

 catalytic activity exhibited by colloidal solutions of the 

 metals. 



Bredigf and his collaborators have shown that a colloidal 

 solution of platinum containing 194 grams of metal (i.e. 

 I gram atom) in 70,000,000 litres of water, or a colloidal 

 solution of gold containing 197 grams of metal in 1,000,000 

 parts of water, are still able to produce a distinct accelerating 

 influence on the decomposition of hydrogen peroxide into 

 water and oxygen. 



It has long since been known that metallic platinum, more 

 especially the variety known as spongy platinum, when left 

 in contact with hydrogen peroxide induces the decomposition 

 of this substance into water and oxygen, and Berzelius,| as 

 long ago as 1836, pointed out an analogy between this cata- 

 lytic action of platinum and the action of an insoluble ferment, 

 such as yeast on sugar. 



This suggestion has since been borne out by a number of 

 examples of chemical changes which could be effected equally 

 well either by means of finely divided platinum or by a 

 ferment, e.g. the oxidation of alcohol to acetic acid by Myco- 

 derma aceti, the bleaching of indigo solution by hydrogen 

 peroxide in presence of red, blood corpuscles, the blueing of 

 tincture of guaiacum by hydrogen peroxide in presence of red 

 blood corpuscles, etc., all of which can also be effected by 

 spongy platinum. 



Bredig carried our knowledge of the subject a step farther ; 

 by preparing colloidal solutions of the metals and comparing 

 their action with that of various enzymes, he traced out such 

 a remarkable analogy between the two that he has called the 

 colloidal metal solutions " Inorganic Ferments ". 



The chief points of similarity between enzymes and 

 colloidal platinum may be summarized as • follows : — 



1. Both platinum hydrosol and enzymes are colloids and 

 as such are detrimentally affected by electrolytes. 



2. Both platinum hydrosol and enzymes gradually decom- 

 pose spontaneously or decompose more rapidly by heating. 



*Ostwald: "Z. physik. Chem.," 1897, 23, 172. 



t Bredig: " Anorganische Fermei.te," Leipsig, iQOi, p. 96. 



JBerzelius: " Jahresber.," 1836, 13, 237. 



