August 20, 1870.] 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
141 
ACETIC FERMENTATION. 
BY BARON VON LIEBIG. 
(Continued from p. 124.) 
The various decompositions of organic substances 
may, as I believe, be grouped in three distinct classes. 
The first class comprises those forms of fermenta¬ 
tion wliicli give rise to alcohol, lactic acid, or butyric 
acid, and the putrefaction of animal materials. These 
processes, once commenced, continue to go on with¬ 
out further aid by atmospheric oxygen. 
The second class comprises acetic fermentation, 
nitrification, also the fermentation of urine. Here 
atmospheric oxygen plays a definitely determining 
part. 
The peculiarity hi the fermentation of urine, or one 
form of it, was first observed by Gay-Lussac. He 
found that fresh urine might be kept for months 
without decomposition hi a clean glass vessel entirely 
filled, but if the vessel was half-filled with air, oxy¬ 
gen was absorbed by the urine, and a corresponding 
quantity of urea was converted into carbonic acid and 
ammonia. This decomposition was limited by the 
quantity of oxygen, and it commenced again when 
fresh oxygen was supplied until eventually all the 
urea was transformed. 
This decomposition of the urea is accompanied by 
an oxidation of the colour constituents of the urine, 
and a small quantity of acetic acid is formed at the 
same time. 
The special peculiarity of this fermentation is that 
two processes take place together, an oxidation and 
a breaking up ; while one or more constituents of the 
urine are being oxidized they act, by virtue of that 
change, like a ferment such as beer-yeast upon cane 
sugar; urea associated with the elements of water 
breaks up as sugar does, without otherwise taking 
part in the oxidation. Fermentation of tills kind 
takes place also in animal materials when access of 
air is not prevented during their putrefaction. 
The fermentation of dextrin in beer-wort presents 
a phenomenon entirely similar. 
In the course of a long series of experiments that 
have been conducted in my laboratory by Dr. Lermer, 
I have had an opportunity of confirming the observa¬ 
tions of Musculus, that by the action of diastase, 
starch is only partially converted into sugar. 
In mashing malted barley the starch is acted upon 
by a large excess of diastase ; but at the utmost the 
sugar produced corresponds only to one-half of the 
starch present. A sample of malt which gave 74 per 
cent, of sugar when heated for twelve hours with dilute 
hydrocliloric acid, yielded only 34 per cent, of sugar 
when mashed until the iodine reaction was no longer 
produced. A solution of dextrin does not undergo 
fermentation when mixed with beer-yeast; but when 
some sugar is added to the mixture, great part of the 
dextrin is converted into alcohol and carbonic acid 
just as the sugar itself is.* 
In this case the influence of the motion communi¬ 
cated to the sugar atoms by the action of yeast ap¬ 
pears very evidently to have been extended to the 
dextrin, upon which yeast has no action. Before the 
* 300 c.c. of a mash containing 8'449 grm. of sugar was 
mixed with 10 per cent, of yeast and left to ferment at 18° C. 
After the lapse of six days all the sugar had disappeared; the 
alcohol then contained in the liquid was ascertained to be 
6 942 grm. According to the amount of sugar, it should have 
been only 4 - 3l7 grm. 
Third Series, No. 8. 
dextrin could break up into alcohol and carbonic 
acid, it must have been converted into sugar.* 
Excepting beer-yeast and the vinegar plant, which 
can easily be collected in quantities and purified, the 
other ferments are scarcely known in regard to their 
chemical relations; but it is to be hoped that by more 
thorough investigation their peculiarities and their 
influence in the production of lactic acid, butyric 
acid, etc., may become explicable in the same way as 
the decomposition of sugar in vinous fermentation, 
or the production of acetic acid by Mycoderma aceti. 
If chemical causes determine the action of yeast- 
cells in vinous fermentation, it might be expected 
that external chemical actions would exercise some 
influence on the progress of the fermentation. There 
are, indeed, many observations as to the influence of 
chemical agents upon the fermentation of sugar, and 
though some of the results I have obtained were al¬ 
ready known, the confirmation of previous statements 
is of some interest. 
A trace of oxide of mercury entirely stops the ac¬ 
tion of yeast upon sugar, f and it acts in the same 
way upon yeast-water. If this is mixed with a little 
of the freshly precipitated oxide, then filtered, and 
mixed with some solution of cane sugar, it will be 
found that no grape sugar is formed. 
Salts of copper exercise the same influence upon 
fermentescible mixtures. The yeast takes up the 
copper salt and becomes green. In that state it has 
no action on sugar. 
Persalts of iron colour yeast dirty yellow; after 
two or three days this colour disappears and then a 
slow regular fermentation sets in. 
In order to avoid repetition, it may be stated that 
in the following experiments the mixtures operated 
upon contained in each instance 5 grm. of sugar with 
the same quantity of washed yeast, and that, with all 
additions included, the total volume was always 100 
c.c. To some of these mixtures were added various 
substances, in order to ascertain their influence on 
the fermentation; one had no admixture, and that 
served as a standard for comparison. 
When the fermentation took place unequally in 
these mixtures within a given time and under the 
same conditions, that could be readily ascertained 
by determining the quantity of sugar remaining at 
the end of the experiments; if, for example, there 
was less sugar in the standard mixture that had re¬ 
ceived no admixture than there was in others, it is 
evident that the fermentation must have been retarded 
in the latter cases. 
The sugar determinations were generally made by 
Fehling’s method, or by a new method which gives 
very accurate results, and in which cyanide of mer¬ 
cury is used. 
The chlorides of sodium and potassium appear to 
promote fermentation somewhat. In mixtures con¬ 
taining these salts there was about 5 5 per cent. 
* After fermenting 385 c.c. of beer-wort containing 22'86 
grm. of sugar, it was found to contain 18 grm. of alcohol, 
but according to the quantity of sugar it contained, only 
1T683 grm. should have been formed. The excess of alcohol 
in this and the preceding experiment can only have originated 
from dextrin. The quantity of dextrin decomposed in fer¬ 
mentation appears also to be very much dependent upon the 
temperature of the wort during fermentation. 500 c.c. of the 
same wort fermented at 8° C. gave 13 - 897 grm. alcohol ; while 
according to the quantity of sugar in the wort, 14'37 grm. 
of alcohol might have been formed, 
f Colin. 
