C H E M I S T R Y. 
323 
very (Imple and fuccefsful mode of purifying it. Mix 
lip the impure acid with white fand 5 put the whole into 
a cucurbit with a head adapted to it, and place it on a 
fand-bath ; by the help of a gyntle heat, the fuccinic acid 
volatilizes and (licks to the fides of the veifel; in this (late 
the acid is very pure and very white. To obtain it in 
cryllals, it mud be diffolved in water ; evaporate about 
two-thirds of the liquor in a gentle heat, and by cooling, 
it produces cryllals. Guyton diddled this acid with ni¬ 
tric acid; and thus obtained very pure and beautiful 
cryllals. The fuccinic acid is bitter; it reddens tin£lure_ 
of turnfole ; is foluble in twenty-four parts of cold, and 
two of boiling, water. It crydallizes in triangular prifms 
with truncated angles. Its combinations with different 
bafes form Juccinats. 
CITRIC ACID. 
Scheele fil'd fucceeded in obtaining this pure acid cry- 
ftallized, and’feparated from the mucilage which accom¬ 
panies it in.the juice of lemons. According to this che- 
miit, the lemons are to be fqueezed, and the juice is to 
be left at red for four-and- twenty hours, to promote the 
reparation of the mucilage; filter the juice through pa¬ 
per, then faturate it with carbonat of iirne. The calca¬ 
reous citrat which arifes from this combination, being 
infoluble, falls to the bottom of the liquor; when this 
has well fettled, draw off the fupernatant water; wa(h 
the precipitate till it becomes tadelefs and very white; 
decompofe this fait with half its weight of fulphuric 
acid, in fix parts of water, with a gentle heat; the ful¬ 
phuric acid feparates _the lime from the citric acid, the 
i'ulphat of lime which is formed is for the mod part pre¬ 
cipitated, and the citric acid remains free in the water. 
By buffering it to evaporate to the confidence of a fyrup, 
by cooling, the acid is obtained in a crydalline form. 
Dize, who made leveral experiments upon this fubjeCl, 
found that an excefs of fulphuric acid was neceffary to 
dedroy the portion of mucilage, which the acid obfti- 
nately retains in its combination with lime, and which 
prevents the citric acid from cryllallizing, or at lead re¬ 
tards it. He obferved alfo, that, to obtain the citric 
acid quite pure, the diffolution and crydaliization (hould 
be feveral times repeated. The cryllals he obtained 
were rhomboidal prilms, with inclined planes of 60 or 
120 0 , and terminating with four-faced fummits, inter¬ 
cepting the folid angles. One part of diddled water, at 
the temperature of ic°, will diffolve, according to this 
author, rjj of crydallized citric acid, producing 13 0 
degrees of cold during the folution. Water, at its boil¬ 
ing point, diffolves double of its weight of this acid, 100 
parts of citric acid, diffolved in a fuflicient quantity of 
boiling water, diffolves 50 parts of calcareous citrat. 
The citric acid thus prepared is very pure and con¬ 
centrated ; its tade is ftrongly acid, and it reddens all 
the blue vegetable.,colours which are capable of that 
change. Fire decompoles and converts it into an acidu¬ 
lous phlegm, gafeous carbonic acid, and carbonated hy¬ 
drogenous gas ; a fmall portion of charcoal remains in 
the retort: its cryllals efflorefce in the air; it is very fo¬ 
luble in water, and its folution is decompofed by a true 
putrefaction, which is very flow. 
The ufes of the citric acid are fufficiently numerous. 
With water and fugar it forms a very agreeable drink, 
knownyunder the name of lemonade. It is employed in 
medicine as refrelhing, cooling, antifeptic, antifcorbutic, 
diuretic; more particularly it correfts acrid bile, 'it is 
fometimes ufed as a flight efcharotic in fcorbutic ulcers, 
dartrous eruptions, and fpots on the (kin. 
Of Citrats. —Vauquelin has lately examined the 
combinations of this acid. The following is his account 
of the falts hereby formed : 1. Alkaline citrats are de¬ 
compofed by a folution of barytes, and the pi ecipitate 
is foluble in a large quantity of water. 2. They decom¬ 
pofe the calcareous falts, forming a precipitate which is 
foluble in 500 parts of water. 3. They are decompofed 
by mineral acids ; but make no precipitates as in the 
tartrits and oxalats, becauie they do not make acidulous 
citrats like thefe falts. 4.. They are decompofed by the 
oxalic and tartarous acids, which form cryltallized or 
pulverulent precipitates infoluble in water. 5. Thefe fa'lts, 
efpecially the metallic citrats, give marks of acetous acid 
by dillillation. 6. Thrown upon burning coals, the ci¬ 
trats melt, boil up, exhale an empyreumatic fmell of 
acetous acid, and leave behind a fmall portion of char¬ 
coal. The affinities of the citric acid for alkaline and 
earthy- bafes, according to different authors, are as 
follows. 
Bergman. 
Lime, 
Bury tes, 
Magnefia, 
Potalh, 
Soda, 
Ammoniac. 
Brejfey, 
Barytes, 
Lime, 
Magnefia, 
Potalh, 
Soda, 
Ammoniac. 
La Grange. 
Barytes, 
Lime, 
Potalh, 
Soda, 
Magnefia, 
Ammoniac, 
Aiumine. 
GALLIC ACID. 
We give the name of gallic acid to that extraQed from 
the nut-gall, which grows on the oak by the pundlure of 
ail infedt. This acid exills in general in greater or lefs 
quantities, in all aullere vegetable, or allringent fub- 
llances: fuch are the woods of the oak, the afh, the wil¬ 
low, the barks of the fame trees, the quinquina, fima- 
rouba, pomegranate, fumach, tormentilla; the nuts of 
cyprels ; the hulks of nuts ; the Hem and leaves of the 
marlh iris, the llrawberry plant, the nenuphar, &c. Che- 
inills were formerly acquainted in this fubltance, which 
they diftinguilhed by the name of ajlringentprinciple, with 
no other property than that of precipitating the lolutions 
of iron in acids of a black colour,'or of forming ink, 
which, indeed, is an exclufive and very charadleriilic pro¬ 
perty. Macquer, Monnet, Lewis, Cartheufer, and Gio- 
anetti, made experimental inquiries into the mode of ac¬ 
tion of this principle upon iron. Monnet had more par¬ 
ticularly remarked, that the nut-gall, and allringent ve¬ 
getable juices, adled immediately on iron, and gave.it 
a black colour. Gioanetti had obferved, that the preci¬ 
pitate, or ntramenfary fecula, was not attracted by the 
magnet, and that the iron was not in the metallic Hate, 
as had been fuppofed before his time. Thefe obferva- 
tions ought to have led to the notion that the allringent 
principle of the nut-gall was an acid ; or at lead that it 
adled as an acid in chemical operations. Sequin firlt dif- 
covered, in the infufio'ns and decoftions of aftringent 
barks, the new principle, which, from the elfefts it pro¬ 
duces on animal matters, is called tannin. 
Scheele has not only (hewn, that all aullere and allrin¬ 
gent plants exhibit ligns of acidity, but he has likewife 
difeovered and delcribed a procefs to obtain this vegeta¬ 
ble, pure and cryllallized. Six pounds of diltdled water 
are poured upon one pound of nut-galls in powder; 
this is left to macerate during fifteen days, at the tem¬ 
perature of between 16 and 20 degrees of Reaumur; it 
is then filtrated, and the fluid is left in a tureen of Hone 
ware, or a large glafs capfule. It is fuffered to evaporate 
flowly by expofure to the air. A mouldinefs and thick 
pellicle is formed, which appears as if glutinous ; very 
abundant’ mucilaginous flocks fall down ; the folution 
then no longer poffelfes a very aftringent tafte, but is 
ftrongly acid-; and after two or three months expofure to 
the air, a brown cruft is obferved adhering to the fides 
of the veffels, and covered with granulated, brilliant, 
yellowiffi, grey cryllals; the fame cryllals likewife exilt 
in large quantities beneath the thick pellicle which co¬ 
vers the liquor: the fluid is then decanted, and alcohol 
is poured on the depofit of pellicle and of cryftalline 
cruft, and heated. This lolvent takes up the whole of 
the crydallized fait, but dees not touch the mucilage. 
