448 Pi'of. Schonbein on the Connexion of 



which the ferment plays in it '\%, I fear^ at the present time a 

 complete secret. 



Berzclius considered the decomposition of sugar into alcohol 

 and carbonic acid as a catalytic action of yeast, and compared it 

 witli the decomposition of peroxide of hydrogen into water and 

 oxygen which is effected by gold, platinum, &c. ]\Iitscherlich 

 also considers the vinous fermentation to be a phsenomenon of 

 contact produced by the yeast ; that is, he assumes that the fer- 

 ment remains unchanged, while it causes the decomposition of 

 the sugar into alcohol and carbonic acid. Liebig seeks the im- 

 mediate cause of this phsenomenon in the state of decomposition 

 of the yeast. He assumes that a substance in decomposing, or 

 in entering into combination, can decompose other substances 

 in contact with it; or to express it in a general manner, that the 

 chemical activity of a substance can be transferred to other sub- 

 stances. 



There can be no doubt that there is a large class of facts Avhich 

 speak in favour of the assumption of the great German chemist, 

 that is, show that the chemical activity of a substance very often 

 excites that of another, and in this respect there can be no more 

 striking example adduced than that of phosphorus ; for during 

 its oxidation in atmospheric air, many other substances placed 

 in contact with it experience also an oxidation, which would not 

 take place in its absence. And many substances left in contact 

 with oil of turpentine oxidize in the air, which if alone would 

 under the same circumstances remain perfectly unchanged. 

 Many other examples of a similar kind might be adduced. 



But I have endeavoured to show, both here and elsewhere, 

 that the ultimate cause of these oxidations effected by means of 

 phosphorus or of oil of turpentine, is to be sought, not in the act 

 of oxidation of these substances as such, but in an ozonization 

 effected by them in atmospheric air. 



Liebi*g also, like Berzelius and Mitscherlich, has compared the 

 decomposition of sugar by yeast to the breaking up of peroxide 

 of hydrogen under the influence of certain substances, but, if I 

 may so say, in a reverse manner. In his view the oxides of the 

 noble metals act the part of the sugar, the peroxide of hydrogen 

 that of the yeast. Because oxidized water, says Liebig, is in a 

 state of decomposition even at ordinary temperatures, it sets oxide 

 of gold, &c. placed in contact with it in the same condition, and 

 hence it decomposes into metal and oxygen, as sugar decom- 

 poses into alcohol and carbonic acid under the influence of yeast 

 in a state of decomposition. 



Peroxide of hydrogen decomposes, as is well known, only slowly 

 at ordinary temperatures; but if oxide of gold, &c. be added to it, the 

 decomposition of both compounds proceeds with extreme violence. 



