FER 
diminish again ; after which they proceed 
very slowly, but are long before they en- 
tirely cease. The fermented liquor has 
then no longer the sweet taste it had be- 
fore, but becomes brisk and lively, with a 
punguent spirituous flavour. Its specific 
gravity is also considerably less than be- 
fore; and when exposed to distillation it 
affords a light inflammable spirit. The 
quantity of this spirit or alcohol, any fer- 
mented liquor will produce, is thought to 
follow some proportion of the change its 
specific gravity undergoes in fermentation; 
but the truth of this has not been clearly 
ascertained. Wine, cyder, and beer, are 
well known liquors of this kind. 
It is usual to put fermented liquors into 
casks before the vinous fermentation is 
completely ended; and in these closed 
vessels, the change goes on for many 
months. But if the fermentative process 
be suffered to proceed in open vessels, 
more especially if the temperature be 
raised to ninety degrees, the acetous fer- 
mentation comes on. In this a still greater 
portion of oxygen from the air is gradually 
absorbed ; and this more especially as the 
surfaces of the liquor are oftener changed 
by lading it from one vessel to another. The 
usual method of doing this consists in ex- 
posing the fermented liquor to the air, in 
casks placed so that the sun may shine on 
them ; which seems to be of advantage by 
raising the temperature of the liquor. By 
this absorption of oxygen the inflammable 
substance becomes converted into an 
acid. If the liquor be then exposed to 
distillation, vinegar comes over instead of 
alcohol or spirit. 
When the spontaneous decomposition is 
suffered to proceed beyond the acetous 
process, the vinegar gradually becomes 
viscid and foul ; a gas is emitted with an 
offensive smell; ammonia flies off - , an 
earthy sediment is deposited, and the re- 
maining liquid, if any, is mere water. This 
is the putrefactive process. 
Though fermentation is much better un- 
derstood at present, in consequence of 
modem researches into the nature of the. 
gases, than it formerly was ; it still remains 
an interesting object of research. It is 
not clearly ascertained what the yeast or 
fermented matter performs in this opera- 
tion. It seems probable that the fermen- 
tative process in considerable masses would 
be carried on in succession from the sur- 
face downwards ; and would perhaps be 
eompleted in one part of the fluid before 
FER 
it was perfectly begun in another part, 
if the yeast, which is already in a state of 
fermentation, did not occasion the process 
to begin in every part of the fluid at once. 
Experiments yet remain to be made to- 
wards ascertaining the arrangements and 
quantity of the component parts of alcohol. 
It appears that hydrogen in combination 
with carbon and water, in certain propor- 
tions, form this compound ; that a greater 
proportion of oxygen converts it into vine- 
gar; and that in the putrefactive process 
the hydrogen, carbon, and oxygen, are se- 
parated from each other, and fly off in the 
elastic state. 
In the fermentation of wine, the tartar, 
which probably existed for the most part 
already formed in the juice of the grape, 
is separated and exhibits the properties 
which are described in treating of that sub- 
stance. 
The fermentation of bread, by leaven, is 
thought to be of a different nature from the 
vinous fermentation. In this, the mucilage of 
the corn is not previously brought into the 
saccharine state. It quickly becomes 
sour, if the process be not stopped by 
baking ; in which particular the fermenta- 
tion seems to be of the acetous kind. The 
developement of carbonic acid, divides the 
dough into thin parts, which are more effect- 
ually and better baked than they could 
have been in the solid consistent mass. 
When bread is fermented by means of 
yeast, the process seems to be of a saccha- 
rine or vinous nature. A very minute pro- 
portion of alum, renders bread whiter, and 
its pores more small and numerous, but 
how it acts has not been ascertained. It 
does not seem either from its quantity or 
quality to be unwholesome. 
FERN. See Filices. Fern is very 
common in dry and barren places. It is 
one of the worst of weeds for lands, and 
very hard to destroy where it has any thing 
of a deep soil to root in. In some grounds 
the roots of it are found to the depth of 
eight feet. One of the most effectual ways 
to destroy it is often mowing the grass, and 
if the field be ploughed up, plentiful dung- 
ing thereof is very good : but a most certain 
remedy for it is urine. However, fern, cut 
while the sap is in it, and left to rot upon 
the ground, is a very great improver of land ; 
for if burnt, when so cut, its ashes will yield 
double the quantity of alkali that any 
other vegetable can do. 
In several places, in the north, the inhabi- 
tants mow it green, and burning it to ashes, 
