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and protocatechuic acids which are formed in the reaction, and
is then freed from any unaltered dimethylprotocatechuic acid by
conversion into the acetyl compound, which is then recrystallized
and saponified by dilute caustic potash. 10



Tiemann and Reimer, Ber. Dcutsch. Chcm. Gcs. viii. 515.
Tiemann and Nagai, ibid. viii. 1142.
Tiemann, ibid. ix. 409.
Tiemann and Mendelsohn, ibid. x.'57.
Tiemann and Nagai, ibid.x. 201.
Kraaz and Tiemann, ibid. xv. 2068.
Ibid. viii. 513.

Journ. Chcm. Soc. 1876, i. 302.
Proc. Roy. Soc. xii. 502.
10 Ber. Dcutsch. Chtm. Gcs. xi. 125.
VOL. III. PART IV. -A A



354 AROMATIC COMPOUNDS.

Isovanillic acid crystallizes in lustrous, transparent prisms,
melting at 250, which dissolve in 1,700 parts of water at 14,
and in 160 parts at 100. It is readily soluble in alcohol and
ether ; it gives no colour reaction with ferric chloride.

Acdylisovanillic acid, C 6 H 3 (OCO.CH 3 )(OCH 3 )CO 2 H, crystal-
lizes from dilute alcohol in scales, melting at 206 207.

2195 Veratric acid or Dimcthylprotocatechuic acid, C 6 H 3 (OCH 3 ) 2
CO 2 H. In the year 1839, E. Merck discovered veratric acid,
CgHjoC^, 1 in the seeds of Veratrum Sabadilla, and W. Merck
then observed that it decomposes into carbon dioxide and
veratrol, C 8 H 10 2 , on heating with caustic baryta. 2 By the
oxidation of methyleugenol, Grabe and Borgmann obtained
bimethoxybenzoic acid, 3 which was shown by Tiemann 4 and by
Erlenmeyer and Wassermann 5 to be identical with the di-
methylprotocatechuic acid which Kolle had prepared by
heating protocatechuic acid with caustic potash, methyl iodide
and wood-spirit ; 6 Korner then showed that this compound is
also identical with veratric acid, veratrol being dimethylcate-
chol. 7 Veratric acid is also formed when veratrin and pseudo-
aconitine are heated with alcoholic potash. 8 In order to prepare
it, 1 part of methyleugenol, C 6 H 3 (OCH 3 ) 2 C 3 H 5 , is shaken up
with 10 15 parts of water, and a solution of 3 '5 parts of potas-
sium permanganate in 20 30 parts of water heated to 80 90
gradually added. The filtrate is concentrated by evaporation
and precipitated with hydrochloric acid. 9 Veratric acid dissolves
in 2,100 parts of water at 14, and in 160 parts at 100, and
crystallizes from a concentrated solution at a temperature above
50 in anhydrous needles, while crystals containing a molecule of
water are obtained from very dilute solutions at any temperature
below this. It melts at 174 175 and can be sublimed. It
dissolves readily in alcohol and ether ; ferric chloride produces
no colouration.

Methyl veratrate, C 6 H 3 (OCH 3 ). 2 CO 2 .CH 3 , is formed, together
with methyl protocatechuate and methyl isovanillate, when
protocatechuic acid is heated with caustic potash, methyl iodide
and wood spirit, 10 no methyl vanillate being formed. 11

Ann. Chem Pharm. xxix. 188. 2 Ibid, cviii. 60.

Ibid, clviii. 282. 4 Ber. Deutsch. Chcm. Gcs. viii. 514.

Ann. Chcm. Pharm. clxxix. 366. 6 Ibid. clix. 240.

Ber. Deutsch. Chem. Gcs. ix. 582.

Wright and Luff, Jwirn. Chem. Soc. 1878, i. 160 and 352.
Tiemann and Matsmoto, Ber. Dcutuch. Chem. Ges. ix. 937.
Matsmoto, ibid. xi. 122.
11 Tiemann, Ber. Deutsch. Chcm Gcs. viii. 513.



PIPERONIO ACID. 355



The ether is obtained pure when a solution of the acid in
anhydrous methyl alcohol is saturated with hydrochloric acid,
or when vanillic acid is heated with caustic potash and methyl
iodide. It crystallizes in odourless needles, melts at 59 60
and boils at about 300 (Matsmoto).

Melting- Boiling-
point, point.
Ethyl veratrate, 1

C 6 H 3 (OCH 3 ) 2 C0 2 .C 2 H 5 43 44 295 296

Ethylvanillic acid, 2

C H 3 (OC 2 H 5 )(OCH 3 )C0 2 H . . . 193 194
Diethylprotocatechuic acid, 3

C 6 H 3 (OC 2 H 5 ) 2 C0 2 H, 149

Piperonic acid, C 6 H 3 (0 2 CH 2 )CO 2 H, was prepared by Fittig
and JVIielk by the oxidation of piperic acid or piperonal with
potassium permanganate, 4 while Fittig and Remsen obtained it
by heating protocatechuic acid with caustic potash and methy-
lene iodide : 5

/OK X ON >CH 2

C 6 H 3 f OK + CH 2 I, = C H 3 - / + 2KI.

\C0 2 K \C0 2 K

It occurs in small quantity in Paracoto bark, which is collected
on the river Mapiri in Bolivia, and has been detected in true
Goto bark, which is also found in Bolivia. 6

Piperonic acid is scarcely soluble in cold water, slightly in
boiling water, from which it separates in small needles, or, on
very gradual cooling, in characteristic crystals, which resemble
in appearance small twisted threads of sewing cotton. It is also
slightly soluble in ether and cold alcohol, separating from a
hot alcoholic solution in larger crystals. It is obtained in the
purest state by sublimation, which yields large, compact, glitter-
ing prisms with acute terminal planes ; it melts at 227'5
228 '5, but sublimes at a lower temperature.

When it is heated with phosphorus pentachloride, a liquid
chloride is formed which yields a chlorinated acid on decom-
position with cold water ; this substance is probably a dichloro-
pipcronic acid and is resolved on heating \\ith water into

' Tiemann and Matsmoto, Ber. Dcutsch. Chcm. Gc*. ix. 942.

2 Tiemami, ibid. viii. 1130; Wassermann, Ann. Chem. Pluirm. clxxix. 379.

3 Kiille, ibid. clix. 245. 4 Kolle, ibid. clii. 40.

5 Ibid, clxviii. 93. 6 Hesse and Jobst, ibid, oxcix. 63.

A A 2



350 AROMATIC COMPOUNDS.

hydrochloric acid, carbon dioxide and protocatechuic acid.
Piperonic acid is decomposed by dilute hydrochloric acid at
170, or by water at 210, into carbon dioxide and protocatechuic
acid, so that it behaves in an analogous manner to its aldehyde l
(p. 347).

Potassium piperonate, C 8 H 5 O 4 K + H 2 O, crystallizes in long
needles, which are readily soluble in water.

Calcium piperonate, (C 8 H 5 4 ) 2 Ca + 3H 2 O, is slightly soluble
in cold, readily in hot water, and crystallizes in fascicular groups
of needles or plates.

Silver piperonate, C 8 H 5 O 4 Ag, is a granular precipitate, which
crystallizes from hot water in large, narrow plates.

Ethyl piperonate, C 8 H 5 O 4 .C 2 H 5 , is a mobile, strongly refractive
liquid, which has a pleasant fruity odour (Jobst and Hesse).

Ethyleneprotocatccliuic acid, C 6 H 3 (O 2 C 2 H 4 )C0 2 H, is formed by
heating protocatechuic acid with caustic potash and ethyl ene
bromide. 2 It is slightly soluble in cold water and crystallizes
from a boiling solution in splendid, broad, lustrous needles. It
dissolves in almost every proportion in alcohol, from which it
separates on dilution in druses composed of short, lustrous
prisms, which melt at 133'5, and sublime in lustrous prisms
when carefully heated.

The calcium salt, (C 9 H 7 O 4 ) 2 Ca + 2H 2 0, crystallizes from hot
water in well-developed, compact, monoclinic prisms.

Bromf.protocatechuic acid, C 6 H 2 Br(OH) 2 CO 2 H, is prepared by
triturating piotocatechuic acid with bromine ; it crystallizes
from hot water in fine, rhombic needles, and is converted into
gallic acid by fusion with potash. 8

2196 Madurin, C 13 H 10 O 6 + H 2 O, occurs in fustic (Morus,s. Ma-
dura tinctoria), and was described by Wagner as morintannic
acid* Its correct formula has been determined by Hlasiwetz
and Pfaundler. 5 According to Wagner, the dirty yellow, crys-
talline masses found in the centre of the logs consist almost
entirely of impure maclurin, which can readily be purified
by repeated crystallization from slightly acidified water. Bene-
dikt employs as his raw material the muddy deposit which
is obtained as a by-product in the manufacture of fustic
extract, and which consists of maclurin and its calcium

Fittig and Rcmsen, Ann. Chcm. Pharm. clix. 129.

Fittig and Macalpine, ibid, elxviii. 99.

Barth, ibid, cxlii. 246 ; Bcr. Dcutech. C/icm. Gcs. viii. 1484.

Journ. Prakt. Chcm. li. 82 ; Hi. 449.

Ann. Chem. Pharm. cxxvii. 352.



MACLURIN AND LUTEOLIN. 357



salt. It is ground up with dilute hydrochloric acid pressed, aud
repeatedly crystallized from hot water. In order to remove any
adhering colouring matter, it is dissolved in water and treated
with lead acetate. A current of sulphuretted hydrogen is then
passed through the hot liquid, which is subsequently filtered and
allowed to cool ; the pure maclurin is thus obtained as a light
yellow, crystalline powder. It becomes anhydrous at 130, and
melts at 200. On boiling with water and barium carbonate
one molecule of carbon dioxide is evolved for every two
molecules of maclurin present (Benedikt), while the salt
C 13 H 8 PbO 6 -|- H 2 O is deposited in yellow plates when lead
acetate is added to the boiling solution (Hlasivvetz and
Pfaundler).

When maclurin is boiled with concentrated caustic potash solu-
tion or heated to 120 with dilute sulphuric acid, it decomposes
smoothly into protocatechuic acid and phloroglucinol.

Benedikt therefore proposes the following formula for maclurin
and its lead salt: 1

/OH /OH

CTT ^_OTT (i TT ' (\\3

6 rl 3 Ul ^6*13 Uii

C 6 H 3 OH C 6 H 3 - O Pb v

\CO.OH \ >

CO.CK

Luteolin, C 20 H U O 8 , was discovered by Chevreul in weld
(Reseda lutea), 2 and analyzed by Moldenhauer, 3 who obtained
numbers which led to the formula given above, while Paraf
and Schlitzenberger calculated the composition 2C l2 H 8 O 5 -!-3H 2 O
from the results of their investigation and somewhat unsatis-
factory analyses. 4 It is obtained by extracting the dried plant
with water containing 5 6 per cent, of alcohol, concentrating
the filtrate by evaporation and purifying the crude luteolin thus
obtained by recrystallization from alcohol or a mixture of water
and glycerol.

It crystallizes in small, yellow needles, which dissolve in
14,000 parts of cold water, in 5,000 parts at 100 and in 37
parts of alcohol. It readily forms a deep yellow solution in
alkalis, and dissolves in cold sulphuric acid forming a reddish
yellow solution from which it is precipitated by water. A small

1 Ann. Cham. Pharm. clxxx. 114. ' Berzelius, Jahresb. xi. 280.

3 Ann. Clicm. Pharm. c. 180. 4 Compt. Rend. lii. 92.



358 AROMATIC COMPOUNDS.

quantity of ferric chloride produces a green colouration, which
passes into brownish red on the addition of more of the reagent.
Its hot aqueous solution dyes wool, mordanted with alum, a
beautiful daffodil-yellow (Chevreul). On fusion with potash it
is decomposed with evolution of hydrogen into phloroglucinol
and protocatechuic acid : 1

CH M 8 + 8H 2 = 2C 7 H 6 4 + C 6 H 6 O 3 + H 2 .

Rochleder states, however, that the amount of phloroglucinol
formed is much greater than corresponds to this equation. The
formula of luteolin is by no means accurately determined and
its constitution is quite unknown.






SYMMETRIC METADIHYDROXYBENZOIC ACID
OR a-RESORCYLIC ACID (1:3: 5).

2197 This substance is obtained by fusing /3-disulphobenzoic
acid, 2 metabromosulphobenzuic acid and parabromosulphobenzoic
acid 3 with caustic potash. It crystallizes with one and a half
molecules of water in needles or prisms, which melt at 232
233, are tolerably soluble in cold, readily in hot \\ater,
alcohol and ether, and give no colouration with ferric chloride.
On fusion with caustic soda it decomposes above 300 into
resorcinol and carbon dioxide. 4 A very characteristic reaction
is that when heated with 4 parts of sulphuric acid to 1 40, a
deep red solution is formed from which water precipitates green
flocks of anthrachrysone, C U H 4 (OH) 4 O 2 , which is a derivative of
anthracene, and is also formed by the dry distillation of the
acid. Lead acetate does not produce a precipitate when added
to an aqueous solution of the acid.

Ethyl a-resorcylatc, C 6 H 3 (OH) 2 CO 2 .C 2 H 5 , crystallizes from
water in long prisms which melt below 100.

Dimethyl-a-resorcylic acid, C 6 H 3 (OCH 3 ) 2 CO 2 H, is formed when
a-resorcylic acid is heated with caustic potash, methyl iodide and
^vood-spirit, and when dimethylorcinol is oxidized with potassium

1 Rochloler, Journ. Prakt. Chrm. xcix. 433.

- Karth and Senhofer, Ann. Chcm. Phann. clix. 217.

3 Rbttingi-r, Brr. Dcutsch. Chcm. Gr,t. viii. 374.

4 Earth and Schroder, ibid. xii. 1258.



RESORCYLIC ACIDS. 359

permanganate. 1 It crystallizes from hot water in fine needles,
which melt at 175 176.

Diethyl-a-resorcylie acid, C 6 H 3 (OC 2 H 5 ) 2 CO 2 H, was prepared
by Earth and Senhofer from the acid by the action of ethyl
iodide.' 2 It forms elongated prisms, which melt at 87 88, and
are decomposed by distillation with lime into carbon dioxide and
diethylresorcinol. 3

a-Bromorcsorcylic acid, C 6 H 2 Br(OH) 2 CO 2 H, is formed by the
action of bromine water on an aqueous solution of a-resorcylic
acid, and crystallizes from hot water in long needles, which melt at
253, and give a yellowish brown colouration with ferric chloride.
It gives the same reaction with sulphuric acid as a-resorcylic
acid, and is converted into gallic acid by fusion with caustic
potash (Barth and Senhofer).



ASYMMETRIC METADIHYDROXYBENZOIC
ACID OR /2-RESORCYLIC ACID, (1:2:4).

2198 This acid is formed when paracresolsulphonic acid, 4 and
a-disulphobenzoic acid 5 are fused with caustic potash, and may
also be obtained, together with a large amount of resorcinol,
when its aldehyde is fused for a short time with caustic potash.
It may also be prepared, together with y-resorcylic acid and
dihydroxyphthalic acid, C f) H 2 (OH) 2 (CO 2 H) 2 , by heating 1 part
of resorcinol with 4 parts of ammonium carbonate and 5 parts
of water to 120 ISO , 7 and still more readily by heating
resorcinol in an open flask with a concentrated solution of
potassium bicarbonate. It is very slightly soluble in cold water,
and crystallizes from a hot solution in needles containing one
and a half molecules of water, one of which is lost on exposure
to the air (Fahlberg). It melts at 204 206, and simultane-
ously decomposes into carbon dioxide and resorcinol. Its

J Tiemann and Strong, Bcr. Dcutsch. Chcm. Oes. xiv. 2002.
" Ann. Chcm. Pliarm. clxiv. 121.

3 Barth, Bcr. Dcutsch. Chcm. Ges. xi. 1569.

4 Aschcr, Ann. Chcm. Pharm. clxiv. 11.

5 Blomstraiul, Bcr. Dcutsch. Chcm. Gcs. v. 1088 ; Fahlberg, Amcr. Chcm. Journ.
ii. 196.

11 Ticmann and Reitner, Bcr. Dcutsch. Chcm. Ges. xii. 997 ; Tiemann and
Parrisius, ibid. xiii. 2358.
7 Brunnur and Senhofer, ibid. xiii. 2356 ; Bcr. Wicn. Akad. 1879, ii. 504.



360 AROMATIC COMPOUNDS.



solution is coloured dark red by ferric chloride, and does not
give a precipitate with lead acetate.

Orth<yrnethyl-p-resorcylic acid, C 6 H 3 (OH)(OCH 3 )CO 2 H(OCH 3 :
OH = 2:4), is formed when the acetyl-derivative of its aldehyde
is oxidized with potassium permanganate and the product
decomposed by caustic potash. It is tolerably soluble in water,
does not crystallize well, and gives no colouration with ferric
chloride. 1

Paramethyl-p-resorcylic add, (OH : OCH 3 = 2 : 4). The methyl
ether is prepared by adding sodium to a solution of ^-resorcylic
acid in wood-spirit and then heating with methyl iodide, the
acid being obtained from this by boiling with caustic potash
(Tiemann and Parrisius) ; it is also formed when sodium methyl-
resorcinol is heated to 215 in a current of carbon dioxide : 2

C 6 H 4 (OCH 3 )ONa+ C0 2 = C 6 H 3 (OCH 3 )(OH)C0 2 Na.

It crystallizes from hot water in lustrous needles, which melt
at 151'5, and decompose into methylresorcinol and carbon
dioxide when rapidly heated. Its aqueous solution is coloured
an intense reddish violet by ferric chloride.

Dimethyl-fi-resorcylic acid, C 6 H 3 (OCH 3 ) 2 CO 2 H, is not readily
formed by the further methylation of the preceding compound,
but may be obtained by the oxidation of its aldehyde with
potassium permanganate ; it crystallizes from hot water in fine
needles, melting at 108 (Tiemann and Parrisius).

Dicthyl-(3-resorcylic acid, C ( .H 3 (()C 2 H 5 ). 2 CO 2 H, was prepared in
a similar manner ; it forms needles which melt at 99. 3



ADJACENT METADIHYDROXYBENZOIC ACID
OR 7-RESORCYLIC ACID (1:2:6).

2199 The formation of this acid has already been mentioned ;
it is very soluble in water, and crystallizes in fine, fascicular
needles, which contain one molecule of water and commence to
fuse at 140, a partial decomposition into resorcinol and carbon
dioxide occurring, which becomes complete at a higher tempera-

1 Tiemann and Parrisius, Bcr. Dcutech. Cham. Ges. xiii. 2375.

2 Korner and Bertoni, ibid. xiv. 847.

3 Tiemann and Lewy, ibid. x. 2215.






HYDROXYSALICYLIC ACID. 361

ture. Its aqueous solution is coloured a deep bluish violet by
ferric chloride.

y-Eromoresorcylic acid, C 6 H 2 Br(OH) 2 CO 2 H + H 2 O, is formed
by the action of bromine on an ethereal solution of the acid. It
is slightly soluble in cold water, readily in alcohol, and crystallizes
in fine prisms, which lose their water at 100 and melt at
184 with decomposition. It is coloured violet by ferric
chloride.

Dimcthyl-y-resorcylic acid, C 6 H 3 (OCH 3 ) 2 C0 2 H. When meta-
diriitrobenzene is treated with methyl alcohol and potassium
cyanide, methoxynitro&enzonitril,C 6 TL 3 ('NO 2 )(OCH^)C~N,is formed;
it crystallizes from chloroform in pliant needles, which melt at
171, and are converted on heating with methyl alcohol and
caustic potash into dimeihoxybenzonitril, C 6 H 3 (OCH 3 ) 2 CN, which
crystallizes from alcohol in needles or rectangular tablets,
melting at 118. It boils at about 310, and when heated with
baryta water yields dimethyl-^-resorcylic acid, which forms
crystals melting at 179, and is converted into 7-resorcylic acid
by heating with caustic potash.

If methoxynitrobenzonitril is heated with caustic potash nnd
ethyl alcohol, ethoxymethoxylenzonitril, C 6 H 3 (OCH 3 )(OC 2 H 5 )
ON, is formed, and crystallizes from alcohol in prisms or tablets,
melting at 66. This compound is also formed when meta-
dinitrobenzene is treated with ethyl alcohol and potassium
cyanide, and the cthoxynitrobenzmiitril, C (J H 3 (NO ) )(OC 2 H 5 )CN,
thus formed, which melts at 137, is heated with methyl alcohol
and caustic potash. A new and simple proof is thus afforded
of the identity of the positions 1 and 6 in the benzene nucleus. 1



HYDROXYSALICYLIC ACID OR PARADIHY-
DROXYBENZOIC ACID (1:2: 5).

2200 This isomeride has been prepared by fusing iodosalicylic
acid with caustic potash ; 2 it is more readily obtained, however,
by fusing bromosalicylic acid with caustic soda, 3 and is also

1 Lobry de Bruyn, Bcr. Dcutxch. Chcm. Oes. xviii. Ref. 148 ; Chcm. Ccnlralbl.
1884, 119; 1885, 357.

2 Lautumann, Ann. Chcm. Pharm cxx. 311 ; Licchti, ibid. Buppl. vii. 144
Demole, Bcr. Dcutsch. Chcm. Gcs. vii. 1438 ; Goldberg, Journ. Prakt,. Chtm. ['!]
xix. 371.

3 Luppcrt and Rakowski, Bcr. DeiOsch. Chcm. Gcs. viii. 788.



S62 AROMATIC COMPOUNDS.

formed by the action of nitrous acid on a-amidosalicylic acid, 1
and when quinol is heated with potassium bicarbonate, water
and a little potassium sulphite. 2 Hlasiwetz and Habermann, by
fusing gentisin, Ci4H l0 O 5 , from Gentiana lutca, with caustic
potash, obtained a dihydroxybenzoic acid, which they named
gentisic acid, since they believed that it was different from
those previously known ; 3 they subsequently found, however,
that it is identical with hydroxysalicylic acid. 4 It is readily
soluble in water, alcohol and ether, crystallizes in needles or
prisms, which melt at 196 197, and gives a deep blue coloura-
tion with ferric chloride. It reduces Fehling's solution and
ammoniacal silver solution on heating. On dry distillation it
is resolved into carbon dioxide and quinol.

Ethyl hydrozysalitylate, C 6 H,(OH) 2 C0 2 .C 2 H 6 , crystallizes from
hot water in needles, which have a pleasant fruity odour and
melt at 75 (Goldberg).

Methylhydroxysalicylic acid, C 6 H 3 (OCH 3 )(OH)CO 2 H.(CO 2 H
: OH : OCH 3 ~1 : 3 : 5), was prepared by Korner and Bertoni
by the action of carbon dioxide on sodium methylquinol
at 220 225 , 5 and named a-methylhydroquinoncformic acid.
Tiemanri and Miiller then obtained it by oxidizing the acetyl-
derivative of the corresponding aldehyde with potassium per-
manganate and saponifying the product with caustic soda. 6 It
crystallizes from hot water in long needles, melting at 142, and
gives a light blue colouration with feme chloride.

Dimcthylhydroxy salicylic ac : d, C 6 H 3 (OCH 3 ) 9 CO 2 H, is formed
by the oxidation of its aldehyde ; it crystallizes from hot water
in silky needles, melting at 76. 7

When the reactions of the bodies just described are compared,
it is found that protocatechuic acid, its aldehyde, and also
catechol, which contain the hydroxyls in the ortho-position,
give a green colouration with ferric chloride. Those com-
pounds, on the other hand, in which a hydroxyl is situated in
the ortho-position with regard to a carboxyl, and which can
therefore be considered as derivatives of salicylic acid, give a
blue to dark red colouration, while those in which the hydroxyls
are in the meta-position, give as little colouration as meta-
hydroxybenzoic acid.

1 Gol.lberg, loc. cit.

2 Scnhofer and Sarlay, Monatsh. Chem. ii. 448.

3 Ann. Chem. Pharm. olxxv. 06.

4 Ibid, clxxx. 343. 5 Bcr. Dcutsch. Chcm. Gcs. xiv. 848.
e Ibid. xiv. 1997. - 7 Ibid, 11-93.



GALLIC ACID.



According to theory, six dihydroxybenzoic acids can exist.
In addition to the five just mentioned, two others have been
shortly described. One of these was obtained by Leeds by
allowing toluene saturated with nitrogen peroxide to stand in a
loosely covered vessel for a whole summer. It crystallizes from
alcohol in small plates, which sublime at 170 without fusing
and give no colouration with ferric chloride. 1

Ac'-cioxalic acid, C 7 H C O 4 , is the name given by Rochleder to a
compound which he obtained, together with formic acid, oxalic
acid and frequently protocatechuic acid, by boiling aesculetin,
C 9 H 6 O 4 , with concentrated caustic potash or baryta water. It
forms an extremely fine crystalline mass and gives a reddish
brown colouration with ferric chloride, which is changed by
sodium carbonate to purple-violet, while ferrous sulphate and a
little carbonate of soda produce an intense blue colouration. 2



TRIHYDROXYBENZOIC ACIDS, C 6 H 2 (OH) 3 CO 2 H.
GALLIC ACID.

2201 The history of this substance goes hand in hand with
that of tannic acid. In the introduction to organic chemistry it
has already been mentioned how Pliny states that paper dipped
in an extract of nut-galls was used to ascertain whether
verdigris was adulterated with green vitriol. He also informs
us that the juice of nut-galls was used to recognize a kind of
alumen, employed for dyeing wool black, which was either
natural green vitriol or a mineral containing this salt.

It was also known in very early times that certain parts of
plants, which have an astringent taste, give a black colouration
with bodies containing iron. In addition to nut-galls, Paracelsus
enumerates the sap of oaks, alders, &c., which colour solutions of
iron and copper black, and Libavius used this reaction in the
analysis of mineral waters, which were coloured black in the
presence of iron, but only darkened when containing copper ; he
thus discovered the presence of copper vitriol in the " Wein-
brunnen " at Schwalbach.

Tachenius states in Hippocrates chymicus, 1766, that tinc-
ture of nut-galls produces various coloured precipitates with

1 Bcr. Dcutsch. Chcm. Ges. xiv. 482. 2 Jnhrcsb. Chcm. 1S(>7 : 75:2.



364 AROMATIC COMPOUNDS.

solutions of iron, copper, lead and mercury, and separates
metallic gold from solutions of its salts. Other astringent
plants have a similar action, which he compares with that
of the volatile alkalis, since these remove acids from vitriols
in a similar manner. Leniery takes the same view in his
paper on the kinds of vitriol and the formation of ink, which
is published in the Memoirs of the Paris Academy for 1707 ;
nut-galls, according to him, are of an absorbent or alkaline
nature, and therefore act like salt of tartar, lime-water, ammonia,
&c. That the latter do not produce a black precipitate with
iron is accounted for by the fact that the sulphurous particles
present in nut-galls are absent in the alkalis. As a proof of
this he mentions that when these absorbent substances are made
to combine with sulphur, they do give a black precipitate with
solutions containing iron.

Bergman, on the other hand, suggested in 1775, that a
vegetable acid is contained in astringent substances, and in
his JZlemcns de Chymie 1777, published by Morveau, Maret, and
Durande, it is stated that on the dry distillation of nut-galls a
substance sublimes which blackens solutions of iron and behaves
as a true acid. In order to obtain it in a p \irer condition,



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