146 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



air, for the reaction to begin. The wire continues to glow so 

 long as the gases pass over it. 



The oxidation of alcohol vapour by means of platinum 

 black can be shown by the following simple experiment. 



A wide shallow porcelain dish is 

 placed upon a water-bath and a little 

 alcohol poured in, about a gram of 

 platinum black is placed in a watch 

 glass resting on a small tripod, the whole 

 is covered by a large inverted funnel, 

 through the neck of which a piece of 

 blue litmus paper is suspended (Fig. 23). 

 On gently warming the alcohol it 

 vapourises and oxidation takes place 

 at the surface of the platinum black ; 

 aldehyde, and finally acetic acid, being ob- 

 tained, the presence of which is rendered 

 evident by the reddening of the litmus 

 paper. Care must be taken to vapourise 

 the alcohol very slowly, or oxidation 

 may take place with explosive violence. 

 The oxidation of alcohols by means of 

 platinum black has been dwelt on at 

 some length because it offers the nearest 

 analogy to bacteriological or enzyme re- 

 actions. There are good reasons for think- 

 ing that the progressive oxidation of an 

 alcohol to an acid takes place by addition of oxygen, through 

 the formation of additional hydroxyl groups, and subsequent 

 elimination of water. Thus the addition of oxygen to the 

 group CH 2 OH may be considered to result first in the forma- 



H 



tion of the group C OH ; such a combination is 



\H 



FIG. 23. THE OXI- 

 DATION or AL- 

 COHOL VAPOUR. 



