FERMENTS AND FERMENTATION. 97 



the explanation of this partial decomposition by organic 

 ferments lay in the fact that their action was reversible, 

 that they synthesized from the products of the decompo- 

 sition the substance which was being analyzed. Now it 

 has been shown by NEILSON l that finely divided platinum 

 is able not only to hasten the splitting of ethyl butyrate into 

 ethyl alcohol and butyric acid, but is also able to synthesize 

 ethyl butyrate from ethyl alcohol and butyric acid. Reversi- 

 bility is therefore a characteristic of these inorganic ferments 

 also. 2 The failure of the older observers to discover that the 

 reactions catalyzed by the metallic colloids are incomplete 

 is to be explained by the character of the reactions which 

 they studied. In the catalysis of hydrogen peroxide, for 

 example, by platinumsol, one of the products of the decom- 

 position the oxygen is allowed to escape as soon as liberated, 

 so that even if water could be oxidized to hydrogen peroxide 

 it would not occur under the conditions of the experiment. 

 For, in order that reversion may occur, all the products 

 of the decomposition must be allowed to accumulate. If 

 the products of a chemical reaction catalyzed by any fer- 

 ment are removed 'as fast as formed, that reaction is com- 

 plete and shows no " limit." 



A great analogy exists also between the sensitiveness of 

 the true ferments to certain poisons and the sensitiveness 

 of the colloidal solutions of the noble metals to these same 

 poisons. Acids, bases, and salts affect different organic 

 ferments in different ways. The effect of these same sub- 

 stances upon the inorganic ferments is equally marked. 

 The addition of a mere trace of disodium phosphate to a 

 liter of colloidal platinum solution caused an immediate 

 fall in the " velocity constant' ' of the decomposition of 

 hydrogen peroxide from 0.023 to 0.015. After waiting several 



1 NEILSON: Science, 1902, XV, p. 715. 



2 The spongy platinum used by NEILSON is not a colloid, but the nature 

 of its action is no doubt the same as that of platinumsol. 



