3 24- C H £ M I 
By evaporation of this fpiritous folution, the pure gallic 
acid is obtained in fmall granulated cryltals, of a bril¬ 
liant appearance, and (lightly yellowilh grey colour. 
Deyeux has pointed out, in the Journal de Phifique 
for June 1793, the two following modes of procuring 
this acid. 1. Diftil extraCt of nut-galls in a glafs : it 
liquefies with the firft degree of heat, then tumefies ; by 
increafing the fire, a great quantity of carbonic acid is 
difengaged ; at the fame time a fait is fublimed, which 
flicks to the neck of the retort, fometimes in the form of 
very fmall thin needles, fometimes in fmall fcales. If 
the fire be continued, the (alt is foon difi'olved by a 
fluid which condenfes and falls down in the receiver 
The fluid contained in the receiver is extremely 
acid, as is the fait which is fublimed in the neck 
of the retort. 2. Putthe nut-galls into aretort to which 
a receiver is adapted ; for obtaining the gafeous fluid, 
the pneumatic apparatus muft.be ufed. Place the. retort 
on a fand-bath, or on a naked fire, and increale the heat 
by little and little, till the temperature exceeds boiling 
water. A tranfparent liquor comes over, colourlefs, 
acid, and affording by fpontaneous evaporation needled 
cryftals eroding each other in every direction. This is 
pure gallic acid. For a fecond product, there is a con¬ 
crete lalt fublimed in the neck of the retort in the form 
of fmall needles, extremely white; and towards the end 
of the operation, a pretty large quantity of oil. 
The acid obtained by this procels is always coloured, 
and Clogged with oil, efpecially that which is formed 
near the conclufion of the experiment. Deyeux employ¬ 
ed fublimation to purify it. For this purpofe, two cap- 
fules of glafs are inverted one over the other, in fuch a 
manner, that only the lower capfule containing the matter 
to be purified can receive the heat. When the apparatus 
is well luted, heat the lower capfule ; and by degrees the 
upper one will .be filled with the fublimed acid cryltallized 
in white filvery needles. When the operation is finiflted, 
there will -be found at the bottom of the lower capfule a 
black magma, as it were carbonated. If the heat em¬ 
ployed (hould be too great, the fublimate, after it is 
• formed, will liquefy, andaffumea brown colour in cooling. 
This acid reddens the blue vegetable tin&ures. Placed 
on burning.charcoal, it inflames and emits an aromatic 
■jfmell. Placed on a hot metallic plate, it melts, boils, 
becomes black, and is converted into charcoal. Diltilled 
.in a retort, it gives out a yellow acid liquor. Come of 
the fait fublimes into the neck of the retort, and a car¬ 
bonaceous matter is left behind. During the diftillation, 
an aeriform fluid efcapes, which appears to be purer than 
atmofpheric air. The gallic fait is completely decompof- 
ed by repeated diftillations, but this may be effected 
more eaiily by diltilling the folution of this fait in water. 
Heated with the contaft of air, it fwells up, and takes 
fire, emitting a. fomewhat agreeable fmell, and leaves a 
charcoal of difficult incineration. When diltilled by a 
gentle heat, part riles, diffolved in the water of cryltal- 
iization ; another part rifes in fmall fil’ky cryftals, with¬ 
out decompofition ; a ftrong fire feparates fome drops of 
oil, carbonic acid gas, and carbonated hydrogen. The 
nut-gall, diltilled in fubftance, affords a fmall quantity. _ 
of concrete fait, analogous to the fublimed gallic acid. 
The gallic acid requires twenty-four parts of cold water, 
but no more than three of boiling water, to diflolve it: 
repeated folutions and cryftallizations do not render it 
lepfibly whiter. Alcohol diffolves it much more efteft- 
ually ; four parts of this liquid are fufficient when cold, 
but when boiling it is foluble in an equal weight of that 
fluid. This acid difongages the carbonic acid from 
earthy and alkaline bales, when its a&ion is aflifted by 
heat. With barytes, magnelia, and lime, it forms falts, 
foluble in water, more efpecially by the afliftance of an 
excels of thefe bafes. Potafh, foda, and ammoniac, 
unite very readily with it, and form gallats, whofe pro¬ 
perties are not yet-known. The nitric acid converts the 
gallic acid into the oxalic acid. 
S T R Y. 
The gallic acid precipitates gold its folvent in the form 
of a brown powder, and part of the metal appears at the 
furface in a brilliant and metallic pellicle. Silver is pre- 
cipitated.of a brown colour, and a film of this metal re¬ 
duced, Toon covers the furface of the liquor. Mercury 
is precipitated of an orange yellow ; copper of a brown 
colour ; iron of a beautiful bright black; and bifmuth 
of a yellow lemon colour. The folutions of platina, 
zink, tin, cobalt and manganefe, are not altered by this 
acid. 
The folution of fulphat of iron is the only one upon 
which this acid a6ls in an uniform manner. The preci¬ 
pitate is conftantly of a fine (hining black ; and, accord¬ 
ing to Deyeux, is a combination of carbonated oxyd of 
iron and gallat of iron. If a very weak acid, efpecially 
the fulphuric acid, be poured into a folution of fulphat of 
iron precipitated by the gallic acid, the liquor prefently 
becomes tranfparent; but, by faturating the excefs of 
acid, and then adding gallic acid, the precipitate appear* 
again. 
The gallic acid effervefees with earthy and alkaline 
matters, efpecially with the afliftance of heat. This is 
the method ufed in preparing of gallats, falts as yet but 
little known. It is only known, that thofe with potafli 
and foda are irregular cryftals, brown, and of a difagree- 
able tafte; and that they are decompofed in a temperature 
fomewhat beyond boiling water, in which cafe the alkali 
remains in the retort. The ufes of the nut-gall for dying 
black are fufficiently known. We (hall only add, that, 
by employing the purified gallic acid for the preparation 
of ink, this fluid is very beautiful, very black, and may 
be kept a long time without alteration. 
Of TANNIN. 
The fubftance now' called tannin, was long confound¬ 
ed with the gallic acid or aftringent fubftances. Seguin 
gave much attention to this fubjedl, and made fome im¬ 
portant difeoveries in the application of this matter, in 
Amplifying and improving the art of tanning. The me¬ 
moirs of Pelletier, Darcet, Chauflier, Vauquelin, and 
La Grange, on this fubftance, are alfo worthy of atten¬ 
tion. Tannin exifts not only in the oak, nut-gall, and 
fliumach, but alfo in the role-bu(h, larch-tree, feveral 
kinds of pines, of acacias, and lote-trees ; and in 
fome fpecies of onion, the roots of biftort, rhubarb, pa¬ 
tience, &c. 
Water poured upon tar, after feveral hours infufion, 
only at the temperature of the atmofphere, becomes co¬ 
loured, four, and takes up the mod foluble parts of the 
tan ; by pouring on frefli water feveral times, and by re¬ 
peated infuiions, all the foluble parts of the tan are ta¬ 
ken up, the water is void of colour; and there remains 
nothing but a fibrous mafs, acid and fpongy infoluble 
In water, and entirely improper for the purpofes of 
tanning. 
This liquor contains two fubftances very different in 
their properties: the one gives a black precipitate of 
iron ; this is the acid or gallic principle. The other, 
which precipitates the animal gelatin, or glue, is defig- 
nated by the name of tannin, becaufeofits aCtion in the 
tanning of hides. To preferve in laboratories a folution 
of this glue, a twentieth part of alcohol (hould be added : 
this prevents the putrefaction to which animal fubftances 
are fo much inclined. 
It will appear by experiment, that the liquor of the 
laft lixiviations makes no precipitate with the glue; which 
feems to indicate, that the gallic acid contained in tan 
is not fo foluble as tannin. ; that the liquor of the firft 
lixiviatinm, after having been faturated with glue, or 
animal gelatin, and having made a plentiful precipi¬ 
tate wdth it, is entirely deprived of tannin ; that, as 
tannin has ahvays a great affinity with animal gelatin, as 
it forms an infoluble precipitate therewith, this mode 
will furnifti a very convenient re-agent to deteCl imme¬ 
diately the pretence, and to determine the quantity, of 
gelatin 
