CHEMISTRY. 
•quantity of tannin, of gallic acid, and a coloured ex¬ 
tra# of a fine maroon red, which gives a red tinge to 
wool, cotton, and thread. 
Of the JUICES of VEGETABLES. 
The fucculent vegetables give out their juice by fim- 
ple exprelfion ; fuch as have it vifcous, or in fmall quan¬ 
tity, require water to increafe and dilute it. Juices differ 
in taffe, fmell, colour, and confidence. In general, the 
juice of young plants is very watery, with little taffe, 
and hardly any fmell. Evaporated to drynefs, it yields 
but little extra#, and very little faline matter. As the 
plant advances in age, the fap has a fenfible fmell and 
taffe ; the colour is alfo more evident; and the quantity 
of-its produ#s is in every refpe# more confiderable. 
To extra# the juices of plants: Firft clean and wadi 
the plant well; then beat it in a (lone or marble mortar, 
and afterwards put the pulp in a hair-cloth, and fqueefe 
it in a prefs as much as may be neceflary. This fluid is 
found to contain a green colouring matter, and a portion 
of the folids of the vegetables beaten fmall by the peftle, 
and confequently requires depuration ; which may be ef- 
fe#ed either, iff, By fubfidence, or filtration, when they 
are very fluid, as is the cafe with the juice of purflain, 
boufeleek, See. ad. By white of egg, which colle#s the 
fecula, by coagulation, as is requilite with the juice of 
borage, nettle, &c. 3d, By Ample heat, which coagu¬ 
lates and precipitates the parenchyma, as Baume advifes 
with refpe# to juices that contain volatile principles, fuch 
as thofe of cochlearia, creffes, &c. The phial which 
contains the juice, being covered w ith a perforated pa¬ 
per, muff be plunged in boiling water, and taken out as 
loon as the juice is clarified. Immerfion in cold water 
brings it to a proper temperature for filtration. 4th, By 
l'pirit of wine, which coagulates the fecula. 5th, By ve¬ 
getable acids, as the London Pharmacopoeia preferibes 
for the juices of cruciform plants. 6. By filtration cold, 
which is the method preferred by La Grange on every 
account; the procefs, he fays, is indeed long, but this 
inconvenience is more than counterbalanced by the ad¬ 
vantage of preferving the juices in .their natural ftate, 
and confequently without altering any of their proper¬ 
ties, Yet there are fome juices fo thick and vifcous, that 
it would be impoffible to depurate them by cold filtra¬ 
tion ; fuch, e. g. as thofe of dogs tooth, nettles, borage, 
buglofs, &c. but this may be remedied, fays the fame 
author, by mixing them with other more aqueous juices, 
or adding fome fluid, which, by leflening the vifeofity, 
enables them to pafs through the filtre, without the ne- 
ceflity of recurring to heat, or the whites of eggs. 
Some kind of juices require a different treatment. 
Thele are called acid juices. We fhall fpeak only of the 
acid juices of the gool’eberry and the lemon, as-the fame 
procefs will ferve tor all others of the fame kind. Moll 
of the juices are furnilhed by the fruit. To extra# the 
juice of lemon, firft take off the outer fkin, then the 
white (kin very carefully, fo as to leave the fruit entirely 
bare, and take out the feeds; afterwards cut the lemon 
into thin flices, and fqueefe them with the hand. Leave 
the fruit in this ftate for fome days in a temperature of 
15 or 16°. A flight fermentation takes place, fufficient 
to leparate the mucous and parenchymetous matters, 
which made the juice vifcous. By degrees it floats on the 
furface, and fometimes is fo clear as not to require filtra¬ 
tion. This firft juice being drawn off, the remaining 
matter.is put into the prefs, by which means more juice 
is obtained, not fo clear indeed as the firft, but which 
eafily depurates itfelf, if it be immediately put into bot¬ 
tles, and left to ferment a few days. Laftiy, draw it oft', 
either by decantation, or with a iyphon, or by filtration; 
and it will loon receive all the tranlparency of which it 
is fufceptible. 
Goofeberries, ftrawberries, &c. will not afford a tranf- 
parent juice but by fermentation; yet it is to be obferv- 
ed, that thefe fruits have a principle not found in the 
Vol. IV, No. 199. 
321 
lemon, namely, the mucous faccharine principle ; fo 
that their juice undergoes the fpirituous fermentation, 
and might be converted into wine, not very ftrong in¬ 
deed, but from which alcohol might be extra#ed by dil- 
tillation. The period at which the acid fermentation 
fucceeds to the vinous, is the time wherein the depura¬ 
tion of the juice is performed quickeft ; then it may be 
feparated with much facility, and obtained very clear, 
by means of filtration. 
Of EXTRACTS. 
That which is obtained from the juices of plants by 
thickening, or rather by feparation from the aqueous 
vehicle, is called an extra#. All clarified juices are ei¬ 
ther red or yellow, never green. We may diftinguilh 
two kinds of extra#, the foft, and the dry. The extra# 
never has a pleafant tafte, but a tafte more or lefs dis¬ 
agreeable, which may be called njedicamentous. In ge¬ 
neral, it has three kinds of tafte : agreeable, or nutritive, 
difagreeable.or medicamentous; and bitter, orpoifonous. 
A n extra# is a matter of a reddifh-brown colour, which 
flightiy attra#s the humidity of the air, gives out am¬ 
moniac by diftillation, and is fometimes tranfparent. All 
extra#s, when expofed to the air, precipitate an infoluble. 
matter, which is only matter already diffolved, and which 
has imbibed a quantity of oxygen which renders it infolu- 
ble: this evidently proves the continual change which vege¬ 
tables undergo. Vauquelin, by evaporating the juice 
of the elm in a copper veffe), covered with verdigris, 
oblerved, that in.the midft of the ebullition, the juice 
was of a beautiful red colour, which changed to brown, 
like the brown oxyd of copper, as foon as the liquor had 
acquired the confidence of an extra# ; which proves the 
great affinity of the extra# for oxygen, fince it takes it 
even from copper. 
Extra#s are prepared, either from the juice of the 
plant, in which cafe it is clarified with white of egg, and 
brought to the required confidence with a gentle heat; 
or from dry and ligneous plants, in which cafe mace¬ 
ration, infufion, or deco#ion, are employed, according 
to the nature and ftate of the matter to be wrought upon : 
maceration is often fufficient. Odoriferous plants lhould 
be only infufed; decodion exhaufts them too much, by 
feparating the refinous parts; it forms a very thick over¬ 
charged fluid, which grows turbid in cooling. By means 
of water, extra#s of different natures are produced, as, 
of juniper, bark, fenna, rhubarb, &c. 
We fhall borrow from Vauquelin, fome general obler- 
vations on the extra#ive principles of vegetables ; and 
here we may remark, that all extra#s have an acid tafte. 
If into thelolution of an extra#, prepared from the juice 
of plants, fome drops of ammoniac be poured, a brown 
precipitate is formed, confiding of lime and a portion 
of the extra# now become infoluble. If fulphuric acid, 
even a little concentrated, be poured over any extra#, 
a very penetrating acid vapour is prefently diiengaged: 
this is acetous acid. If quicklime be mixed with an ex¬ 
tra#, ammoniac will be diiengaged. If into a folution 
of any extra#, be poured a lolution of fulphat of alu- 
mine, faturated with an excels of acid, by boiling, there 
will be formed a precipitate in flocks, compofed of alu- 
mine and vegetable matter, not foluble in water. Moll 
metallic folutions, mixed with folutions of extra#s, pro¬ 
duce the lame effe# : thus, with muriat of tin, we have 
a brown precipitate perfe#ly infoluble, compofed of a 
portion of oxyd of tin, and fome vegetable matter. By 
pouring oxygenated muriatic acid into a lolution of an 
extra#, there is immediately a plentiful yellow precipi¬ 
tate ; and the liquor retains oftentimes only a faint le¬ 
mon-colour commonly holding muriatic acid in folution. 
If wool, cotton, or thread, firft fteeped in alum-water, 
be boiled in an extra#ive folution, theie lubftances will 
imbibe a great quantity of the extra#ive matter; they 
are dyed of a fawn-colour, and the folution lofes much 
of its colour. Nearly the fame effe# will be produced, 
4 N If 
