LOSS OF COLOUR IN WINE. 313 



wines, according to M. PREYSS (I.), are found to have a special 

 tendency to loss of colour. In order to understand why southern 

 wines are so prone to this malady, it is necessary to recall the fact 

 already mentioned in previous chapters, and first quantitatively 

 investigated by N. SIEBER (I.) that putrefaction does not ensue 

 in strongly acid liquids, whereas these wines are poor in acid. 

 FONSECA and CHIAROMONTE (I.) recommended the addition of citric 

 acid to increase their power of resisting the complaint. The de- 

 struction of the acids of wine must therefore precede its final 

 putrefactive fermentation ; hence the primary object of research 

 must be the discovery of the changes produced in these acids. 

 Here, again, everything still remains to be done, since all the 

 information at present available is derived almost exclusively from 

 experiments in which pure cultures were not employed. 



According to the discoveries of PASTEUR (IX.) and A. FITZ 

 (IV.), tartaric acid (in the form of its calcium salt) can be de- 

 composed by bacterial agency in three ways : viz., either into 

 propionic acid (along with a little acetic acid) ; to butyric acid ; 

 or, finally, to acetic acid, small quantities of ethyl alcohol, succinic 

 acid, and butyric acid being also produced. Malic acid also may 

 yield very different fermentation products, among which BECHAMP 

 (IV.) mentions acetic acid, propionic acid, butyric acid, carbon 

 dioxide, and hydrogen. According to the researches of A. FITZ 

 (IV.), malic acid (combined with lime) may be split up by different 

 species of ferments in three different ways. In the first case, 

 succinic acid, acetic acid, and carbon dioxide are formed, the 

 relative proportions being approximately represented by the 

 equation 



3COOH CH 2 CH.OH COOH = 2COOH CH 2 CH 2 COOH + 

 CH 3 COOH + 2C0 2 + H 2 O. 



In a second case, propionic acid, acetic acid, and carbon dioxide 

 may be found ; or, thirdly, butyric acid may be the chief product, 

 along with a small quantity of carbon dioxide. With regard to 

 succinic acid, BECHAMP (V.) asserts that this also may be split up 

 (by a bacterial mixture not more precisely specified) into propionic 

 acid and carbon dioxide, the following equation 



COOH CH 2 CH 2 COOH = CH 3 CHa COOH + C0 2 , 



approximately expressing the reaction. The succeeding homologue 

 of this acid, viz., pyrotartaric acid, breaks up, under similar 

 conditions, into carbon dioxide and methane, according to the 

 equation 



2COOH-CH 2 -CH.CH 3 COOH + 2 H 2 = 5CH 4 + 5C0 2 . 



According to the researches of Fitz, citric acid is converted, 

 by an unspecified bacterial mixture, into acetic acid and small 

 quantities of ethyl alcohol and succinic acid. A series of experi- 



