GALLIC ACID. 
curing the acid in a ftate of purity. It will be fufficient to 
mention briefly thefe _ appear moilt adequate to - 
purpofe. Mr. Davy’s met Boil eatboust of ba 
in an infufion of galls ; geadval ly add dilute fulphuric Le 
to the bluish-green ia which is thus produced, till all the 
barytes is fepat ‘ated : the licnid, onthe application of the com- 
mon tefts, appears to be perfeQly f free from tannin and extrac- 
tive matter ; evaporate it to drynefs, and the gallic acid will be 
obtained. This method is far ‘preferable to the one recpm- 
mended by Mz. Fiedler, which confilts in oe alumine with 
a folution of galls, decanting the clear iquor, and feparating 
the cryttals of gallic acid, (mote probably of fapor calla 
alumine. ) which are produce by flow evaporation. 
thod: Take any quantity of ‘gall a ined 
to a fine get digett them in cold water ; agitate the 
mixture; pafs the liquid tsroug sh a cloth ; add more water 
to the ae ulp 5 and fe ‘para e the water by means of a 
prefs: join the liquors, ar di fox vi [ pile ate them ; a brittle 
dark coloured fubftance re r this fubthance, re- 
duced to a fine powder, with ike ane a folution of a pale 
ftraw-colour is formed ; a fecond infufion of alcohol acquires 
but very little colour. Diftil the two extraéts together in 
a {mall glafs retort to one-eighth ; add water to the refidue, 
and expofe it to a gentle heat ; evaporate the folution thus 
formed, and very {mall white prifmatic ery! ‘feals of gailic acid 
will appear. By this procefs, half an 2 of cryitals may 
be procured from a pound of gall-nuts. M. Bouillon La 
Grange, who has employed it, tays, he was never able to 
shee acid of the pu el deferibed by Mr. Richter. The 
als he procured were always of a light ftraw-colour ; 
he found that repea’ on diltillations with alcohol did not 
render them white, the gallic acid itfelf being partially de- 
age eae by this treatment. One objection to this method 
, that unlefs the alcohol is highly reétified it diffolves a 
n of tannin 
The properties of gallic acid appear, in fome meafure, to 
depend on the method employed for its produ€tion. The dif- 
ferent eee Fae confidered, are of two kinds, the 
dry and the n \ccor ingly, there appear two varieties 
of gallic acid, ae procured by diftillation differing con- 
tiderably from that formed by cryftallization, if < any credit 
is to be-attached to the obfervations of M. Bouillon La 
ounce 
Grange. 
Gallic acid, procured in the moift way, is of a li ht ftraw- 
colour ; it has a fharp acid tafte, but poflefles lefs altringency 
than nut-galls ; it changes vegetable blues to red. Fo its 
mee 1t requires 12 ae of cold w si or 12 of boiling ; 
een cold, vee ith oe its aeee of this acid; but ata 
ili rly its own weight. i 
xpofed to heat, it readily fites4 ; it forms jut 
before it begins to fublime a brown vifcid fluid ; full of air- 
bubbles ; and emits vapours which an odorous {mell, 
‘The a f a ftrong heat partially decompofes it ; but t 
accomplith this completely, it requires, count of its 
produ o vary ing t 
aie applied. Schecle es by ai ae it in a glafs 
ort, Hrft, an acid liquor, free from oil ; f the 
acid itfelf, which, condenfed in the liquid, forms and fhootsinto 
eryftals, as it gradually cools, and a ‘large refidue of char- 
oal. Deyeux has found that it is capable of being 
eonver.ed by heat into oxygen and charcoal. From whence 
he concluded that it differs only from carbonic acid in con- 
taining lefs oxygen ; but his reafoning is fallacious, from his 
not having taken into confideration’ the acid fluid that is alfo 
roduced. On the contrary, M. Bouillon La Grange ob- 
eer by its difilaion, an acidulous liquid, charcoal, and 
much carbonic — gas, with which was mixed a ittle car- 
buretted h as. he latter 
the former, ae it di 
carbonic acid gas was feparated by mcans of lime-water. 
Gallic acid is decompofed and iol by ftrone ful- 
phuric acid; the fame aff t, moit probably, is produced by 
licuid fiuori ie acid ; 
malic and oxalic ee oxymuriatic acid, according to 
i Grange, has so action on it; it is foluble 
in the other acids without decompofition. 
: combines, forming falts, 
denominated gallats, of which very liitle is known, Th 
alkaline gallats poffels a etia wee! of folubility ; 
ve a = 
o 
4 
oO 
of this acid, an exces of acid rendering the falts ver foluble, 
which before poffeffed little Beene Gallic acid precipitates 
glycine, yttria, and zircon from their acid folutions, and 
decompofes all the ca horas 
he gallats are decompofed by a ftrong heat. Some of 
them have been fi foun d to yield acctic acid when diftilled with 
cid. 
gallic acid on metallic falts appears to be 
proportiona le to the ftrength of the affinity which the 
The folution of this acid 
ders a folution of filver wis and cccaions wie the affift- 
ance of a gentle heat, the depofition of a owder, which 
is finely divided filver. The precipitate 4 it gives with 
a Pa of mercury is orange yellow; with a solution of 
brown; witha folution of acetat oflead, whit 
wae bifmuth, lemon coloured. It imparts to molybdic 
acid a dark yellow, without occafioning any precipitate. It 
appears to ee no effet on the falts of platma, zine, tin, 
cobalt, and manganefe. boiled on red oxyd of mer- 
id 
cury, the acid itfelf is decompofed, and running mercury is 
roduce fers the Jame whe fimilacly 
eated wi e black oxvd of are or oxyd o ; 
but thefe metals, inftead of being reduced, are brought only 
into lower ftates of oxydation. 
perty this acid pofleffes, is that of giving dark-blue coloured 
aa ne with the oxygenated faits of i iron. A.ccording 
M. Berthallet’s views of the fubject, it is not apapoed 
per ae that the iron fhould be at the maximn oxy- 
dation for this effe€t to be produced, for he cbterves that 
the falts which contain the ox yd at the minimum, though 
not changed at firlt by ¢ 
when the folution con ned from air is much 
pacar te and M. Richter is of the fame o 
very thing which ues the a inity of the 
t xyd promotes the = ination of 
the gallic.acid with the metal in v eee of oxydation 
it may be: indeed the eee pea cv ne afolution of 
green fu ulphat of iron is n y gallic ae unlefs 
annin be oer ae cone ordi ne i ake attracts the ful- 
phuric acid, and then the allie acid unites with the 0 oxyd of 
iron feparated. Mr. Prouit, from his obfervations, has been 
led toa different conclufion. He thinks that i iron is incapa-« 
ct 
green 
fulphat of iron and gallic acid acquires by expofure to the 
air ; the blackening of ink after being poured out of clofe 
4E2 veffel 
