EQUATION OF ACETIC FERMENTATION. 395 



viz., oxygen. He stated that "acetic fermentation is nothing more 

 than the souring of wine, effected in the open air by absorption of 

 oxygen." In 1821 Edmund Davy discovered platinum-black, a 

 substance which, when moistened with spirits of wine, becomes 

 white-hot, the formation of acetic acid being evidenced by the odour 

 evolved. This observation was followed up by DOBEREINER (I. ), who 

 found that, in this reaction, the alcohol takes up oxygen water 

 and acetic acid, but no carbon dioxide, being formed. By observing 

 the volume of oxygen consumed by a weighed quantity of alcohol, 

 he arrived at the following equation for this oxidation process : 



C 4 H 6 0. 2 + 40 = C 4 H 4 04 + 2HO, 



which, translated from the symbolical language of equivalent 

 formulae to that of atomic formulae, reads as follows : 



C 2 H 6 + 2 = C 2 H 4 2 + H 2 0. 



Hence, Dobereiner concluded that, for the production of acetic 

 acid, only three substances are required : alcohol, oxygen, and a 

 body capable of absorbing and condensing the latter, and thus 

 bringing it into more intimate contact with the first named, where- 

 upon the reaction ensues. 



The above experiment of Dobereiner's was taken by chemists 

 as a starting-point in attempts at elucidating the phenomenon 

 of acetic fermentation. The intermediary part played by the 

 "mother of vinegar" in the souring of wine was obvious, since 

 it was well known that without this "mother" no conversion 

 occurred. Nevertheless, more than one opinion was rife as to 

 the mode of action of this mucinous skin. 



Berzelius, in 1829, on the basis of his theory of catalytic L 

 action, ascribed the potency of this skin in acetic fermentation 

 to the acetic acid "enclosed within its pores." Ten years later, 

 and two years after the appearance of Kiitzing's work which, 

 being out of harmony with the spirit of the age, was consequently 

 disregarded Liebig published his theory of acetic fermentation, 

 in which the " mother of vinegar " was classed alongside platinum- 

 black, their mode of action being defined as identical and of a 

 purely chemical nature. 



Owing to the endeavours of Pasteur, the theory promulgated 

 by Kiitzing was experimentally shown to be correct, and the true 

 import of the vinegar-mother once more recognised. It would, 

 however, be going too far to also credit the French physiologist 

 with having recognised acetic fermentation as a purely physio- 

 logical process; for remarkable as it may now appear to us 

 Pasteur, with his followers, stopped half-way and defined the 

 vinegar fungus as "acting after the manner of spongy platinum." 

 He characterised the skin-like zoogloea of the fission fungus in 

 question as " vegetations endowed with the remarkable peculiarity 

 of retaining the oxygen of the air and condensing it after the 

 manner of spongy platinum, by inducing the combustion of alcohol 



