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ZttorOt TStiition, laebtecDi anti lEnlargeti 




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As the manuscript of Volume HI. advanced towards 
completion, it became evident that the^ubject-matter 
was too extensive to alio w^; of. i^vjpublication in a 
volume of convenient size. 1 therefore decided to 
issue it in two Parts, each of which should, to a great 
extent, be independent of the other. 

Part L, now published, contains a Chapter on 
Aromatic Acids, with an Appendix descriptive of the 
Tannins; and a Chapter on Dyes and Colouring 
Matters. I have found the latter subject exception- 
ally difficult to treat adequately, and am far from 
satisfied with the result. I look for some indulgence, 
however ; for this part of the work, covering some two 
hundred and seventy pages, is almost entirely new, 
having been represented in the First Edition merely 
by sections on Picric Acid and Basic Aniline Deriva- 

Part II., which will complete the work, will con- 
tain Chapters on Organic Bases, Cyanogen Com- 
pounds, Albuminoids, &c., and will, if space permit, 
close with a General Index to all three Volumes. 
From past experience, I am unwilling to make any 
promise as to its appearance, but it will be published 
at as early a date as circumstances will allow. 


In the Volume uow issued, I have deliberately given 
the references to English translations or abstracts of 
foreign papers, as the German and other foreign 
periodicals, in which the descriptions of new dyes 
and colouring matters usually appear originally, are 
practically, if not absolutely, inaccessible to the 
great majority of English readers. 

It remains for me to thank those chemists who have 
given me the benefit of their special experience in 
certain directions, and by whose assistance some of the 
articles have greatly profited. 


101, Leadknhall Street, 

London, E.C., May 1889. 




General Characters and Constitution of Aromatic Acids, . l 

Phenol-sulphonic Acids, ;} 

Sulphophenates, 7 ; lodo-paraplieuolbulphonic Acids, H ; 
Phenyl-sulphuric Acid, 9. 

Benzoic Acid, 10 

Benzoyl series, 11; Benzoates, 10; Benzoic iUdehyde, 
18 ; Oil of Bitter Almonds, 19 ; Acetophenone, 23 ; 
Hippuric Acid, 23 ; Benzoic Sulphinide (Saccharine), 

CiNNAMic Acid, 30 

Cinnamic Ethers, 33 ; Aromatic Balsams, 34 ; Gum Ben- 
zoin, 35 ; Peru Balsam, Tola Balsam, Storax, 37 ; 
Oil of Cinnamon, 45 ; Coumarin, 46. 

Phthalic Acids, 47 

Orthophthalic Acid, 4b ; Phthalic Anhydride, 49. 

Salicylic Acid, 50 

Hydroxybenzoic Acids, 50 ; SaUcylates, 57 ; Graultheria 
Oil, 58 ; Salol, 59 ; SaHcylic Aldehyde, 00. 

Protqcatechuic Acid, (il 

Vanillin, 02 ; Piperonal, M ; Catechol, 05; Guaiacol, (io. 

Gallic Acid, (}(} 

Pjrrogallol, 70; Pyro^^'allic Ethers, 72; Gallein, 73; 
Ooonilein, 73 ; Cocrolignone, 73 ; Gallocyanin, 74. 



Tannins or Tannic Acids, 74 

Extraction of Tannins, 75; Constitution of Tannins, 77 ; 
Action of Heat on Tannins, 78; Action of Dilute Acids 
on Tannins, 80 ; PlUobaplienes, 82 ; Action of fused 
^Vlkalies on Tannins, Hi\ ; Phloroglucol, 85 ; Varieties of 
Tannic Acid, 8(5 ; Catechins, 07 ; Kinoin, 08; Tannin- 
yielding Materials, 08 ; Assay of Tannin Materials, 
107 ; Tan Liquors, 125 ; Writing Inks. 12() ; Ex- 
amination of Ink-marks, 120. 


Constitution op Colouring Matters, lai 

Relations of Colouring Matters to Fibres, 134 ; Mordants, 
135 ; Classiiication of Colouring Matters, 13(5. 

NiTRo-CoLOURiNo Matter.s, I;i7 

Picric Acid, 130 ; Nitroplienols, 141 ; Nitrophenol- 
sulphonic Acids, 151 ; Flavaurin, 151 ; Nitrocresols, 
152 ; Victoria Yellow, 152 ; Nitronaphthols, 153 ; 
Manchester Yellow, 154; Naphthol Yellows, 150 ; 
Aurantia, 150. 


Resorcin Green, 158 ; Azoressorulin, 158 ; Resorcin Blue, 
150 ; Lacmoid, 150 ; Naplithol Green, 100. 


Rosolic Acid, Kil ; CoriUlin. li}2. 

Phthaleins, 103 

Phenol-plitlialein, 104 ; Fluorescein, 165 ; Chrysolin or 
Uranin, 100 ; Eosins, 100 ; Rhodamine, 173 ; Quino- 
linc Yellow, 174 ; iVzo-eosin, 174. 


Azobenzene, 175; Diazobenzene Compounds, 17(J; Amido- 
azo-Compounds, 178 ; Aniline Yellow, Chrysoidimi, 
Bismarck Brown, &c., 170 ; Hydroxy-azo-Compounds, 
181 ; Sulphonated Azo-Compounds, 182 ; Tropaeolins, 
183; Acid Yellow, Heliantiiin imethyl-orange), Di- 
phenylamine Yellow, AzoUaviue, &c., 187 ; Azo-Reds, 



191 ; Xylidine Red, 195 ; Tetrazo-Dyes, 1»($ ; Crocein 
Scarlet, Biebrich Scarlet, &c., 196 ; Tetrazo-Browns, 
199 ; Azo-;6lack, 200 ; Azo-Dyes from Benzidine, &€., 
201; Chrysamine, Congo-Red, Benzopurpurin, Delta- 
purpurin, Benzoazurin, &c., 206 ; Azurine, 209 ; 
Primulin, 209 : General Reactions of Azo-Dyes, 210. 


Rosaniline, 217 ; Magenta, 220 ; Acid Magenta, 226 ; 
Aniline Blues, 227 ; Aniline Violets, 233 ; Aniline 
Greens, 237; Auramine, 244; Flavaniliiie, 245; Phos- 
pliine, 245 ; Indulines and Nigrosines, 248 ; Aniline 
Black, 250. 

Safranines and their Allies, 252 

Safranine, 25() ; Magdala-Red, 267; Mauveine, 257 ; Eurho- 
dines, 257 ; Indophenols, 258 ; Oxazines, 259 ; Mel- 
dola's Blue, Muscarin, Nile Blue, 260. 

Colouring Matters from Anthracene, 261 

Anthraquinone Derivatives, 263 ; Alizarin, 264 ; Nitro- 
alizsurin, 267 ; Alizarin Blue, 268 ; Purpurin, 270 ; 
Anthrapurpurin and Flavopurpurin, 272 ; Commer- 
cial iVlizarin, 274 ; Antliraflavic Acid, 275 ; Reactions 
of Paste Colours, 27(i ; Detection of Anthracene Dyes 
on the Fibre, 279 ; Chrysophanic Acid, 281. 

Sulphuretted and Unclassified Coal-Tar Dyes, . 284 

Metliylene Blue, 285 ; Canarin, 288; Thionihin, Curcumin, 
Tartrazin, Benzoflavine, 288. 

Colouring Matters of Natural Origin, .... 289 

Indigo, 290 ; Indican, 292 ; Indirubin, 293 ; Indigotin, 
294 ; Isatin, 295 ; Reduced Indigo, 296 ; Indigotin- 
sulphonic Acids, 298 ; Indigo Extract or Indigo- 
Carmine, 299 ; Assay of Commercial Indigo. 302 ; 
Detection of Indigo on the Fibre, 312 ; Chemistry 
.of Lichens, 315 ; Orcinol, 318 ; Arcliil or Orchil, 320 ; 
Cudbear, 324 ; Litmus, 324 ; Indicators of Neutraht^-, 
32() ; Ldgwood or Campeachy, 328 ; Brazil Wood. 
333 ; Sandal Wood, Barwood, 335 ; Alkanet, 33^7 ; 
Safflower, 338 ; Quercitron, 339 ; Old Fustic, 343 ; 



Young Fustic, Uo ; Weld, U1 Yellow Berries, 848 ; 
Safiron, MH ; iViuiatto, .151 ; Butter Colourings, 354 ; 
Carotin, ;i60 ; Turmeric, 357 ; GamlToge, 8fil ; Co- 
chineal, «'US3 ; Carmine. 3H7 ; Kermes, 360; Lac 
Dye, :mi 

Recognition OF CoLouKiNti Matters, .371 

Forms of Combination of Dyes, 372 ; Capillary ^Vnalysis, 
375; Systematic Detection of Coal-Tar Dyes, Wein- 
j:jartners Tables, 377; Absorption-Spectra of Colour- 
ing Matters, 3HI ; Fluorescence of Colouring Matters, 

Examination op Commercial Colourincj ^Iatterb, . 384 

Detection of Adulterants and Impurities of Dyes, 384; 
Common Salt, Sodium Sulphate, Dextrin, Sugar, 
Starch, Arsenic, Foreign Colouring Matters. &c., .381 ; 
Miniature Dye-Tests, 38s. 

Examination of Dyed Fibres, 389 

Fastness of Dyes, 389; Recojoiition of Red Dyes, 390; 
Ilecojj^nition of Dyes of Compound Shades, 392 ; Mar- 
tiiion's Tables for the Detection of Dyes on Silk, 394 ; 
Hummel's and Lepetit's Tablos of Reactions of Dyes 
on Fibres, 39H. 

INDEX, 421 




Among the bodies of acid character derived from phenols, the 
sulphonic acids produced by the action of strong sulphuric 
acid on phenols occupy a prominent place. The nitro-, chloro-, 
and bromo-phenols also exhibit well-marked acid f imctions, 
and might be appropriately considered in the same section. Such, 
however, of the haloid derivatives of phenol as have any practical 
interest have been already described (voL ii. page 540); while 
the nitro-phenols, of which picric acid is the type, will be most 
conveniently considered in the Chapter on " Dyes and Colouring 
Matters." The same remark applies to rosolic acid, the 
phthalei'ns, and some allied bodiea 

The true aromatic acids are a well-defined and important 
group of bodies which bear the same relation to benzene and its 
homologues that fatty acids bear to methane and its homologues 
(paraffins), and the two series of acids present many points of 
resemblance. Just as acetic acid may be regarded as the type 
of a fatty acid, so benzoic acid is representative of the 
aromatic acids ; while a parallel to acrylic acid may be found 
in cinnamic acid, to lactic acid in salicylic acid, 
to succinic acid in phthalic acid, and so on. The 
following tabular arrangement renders these analogies more 
evident : — 

Fatty Series. 

Aromatic Series. 

Formic acid, H.COOH. 

Acetic acid, . CH,.GOOH. 
Propionic acid, . C2H«.C00H. 
Butyric acid, . CsHy.COOH. 

Acrylic acid, . C2H,.C00H. 

^°2dd),'°^^ (Phenyl.fonnic | ^eH, .COOH. 
Tolulc acids, .... C7H7 .COOH. 
XyUc acids, .... C^n, .COOH. 
Camlo acids, .... CsHii.COOH. 

Cinnwnlc acid (Phenyl-acrylic | (c.h^AHj.COOH. 

Propiolic acid, . C,H. COOH. 

Phenyl-pi-»)piollc acid, . . (C«H4)C2.C00H. 






SnccMeuld. C,H.:{^g; 
Glrcolllo acid, CHt(0B>.COOH. 
Luttcieid, C,H.(0H).CO0H. 
OljowllCKU, CHCOH),.CO0H. 

Errtbrto «ctd.^H/OH)..COOH. 

C™»0ll0Kldi.' ■ : '. CH^OH).C00H. 

Many of the aromatic acids occur readj-Iormod, oitlier free or 
combiood, in resins or balsams, and in the animal oiganism. 

Ail, or nearly all, the aromatic acids tabulated above are 
extracted by ether from their aqueous solutions. When heated 
with lime they split up into carbon dioxide and benzene, hydioxy- 
beuzene, or homologues or analogues thereof. Thus : — 

Phthalic acid, . . C8HgO^ = CO^+C;HgO„ Benzoic acid. 

Benzoic acid, . . CTHaOj = GO., + CoHg, " Beniene. 

Toluicacid, . . CsHgOj=CO;+CjH„, Toluene. 

Cinnatnic acid, . . CgHg02 = C0,,-+-C^H^, Cinnamene. 

Salicylic acid, . . 0^11^03 = C(X + CgH^O. Phenol 

Cresotic acid, . . CgHgOs = COJ+C-H/i, CresoL 

Protocatechuic acid. C,Hg6j = CO, + ciiHgOg, Catechol. 

Gallic acid, . . C,HgO5=C03+CflHaOa, PyrogalloL 

The true aromatic acids, together with the phenol-sulphonic acids, 
are considered in detail in the following sections. In connection 
with each of the mors important aromatic acids certain allied or 
derived bodies will be conveniently described. Thus h i p p a r i c 
acid, bittei-almond oil, and saccharine are considered 

' Beddea three iaomeric crcaotic acids of the fonnala given, 
C(Hj(CH,) : 1 QOOH '^^^ other acids of the same compodtion are knomi, 
ol vhich maDdelic 
is the moat interesting. 

Among bomologoas adds are the foUowlDg : — 

C,H^CH,),{°^fj C,H/OH).CH^CHrCOOH. CH^CH^CH { ^"^^ 
Hydnqrmeiltjrleiiic aciiL HjrdniocHuiiirfai add. Pbenjl-UcUo Mid. 

Tni|ilc or FtieDj|.li]rdTaei]rlic ao 



in sections appended to that on benxoic acid, the aromatic 
balaams are deecribed with ctunaiuic acid, and pyrofiallol 
nth gallic acid. The phtbaleina are not considered in coa- 
^eetioD with phlhalic acid, but in a section of the chapter on 
^ DjM and Colouring Matters." The tannins and their 
ivalives will l>e appropriately and conveniently deeeribed in an 
Appendix to the clmptcr on the Aromatic Aeida. 


When phenol is treated with concentrated Bvdphurie a 

id it 

^asolvea readily, with considerable rise of temperature. The 

'e a mixture of two isomeric phenol-sulphonic 

ieide, C(H,(OH).803H. When the phenol and acid are 

[I'dowly mixed, and the liquid prevented from becoming hot, the 

' 'o r t h o-add is chiefly formed, but much phenol remains unattacked. 

"By hmUug the mixture for aome time to 1 00° C, the conversion of 

the phenol into a sulpboitic acid is nearly perfect, even when but 

little more than the tlieoretical proportion of sulphuric acid haa 

heen employed, but the ortho-acid is in great part converted into 

. para-phenolsulphonic acid, though some of the former 

I iody lemnins unchanged however long the heating be continued. 

' M»ta-phenol8tilphonic acid (OH : SOsH=l -. 3) is 

not obtainable by the direct action uf sulphuric acid on phenol, 

bat may be produced by other reactions. The product of the 

action of eulphuric acid on phenol is frequently called a u 1 p h o- 

enio acid or Bul])hoearbolic acid, and many of 

uts salts have received application in medicine, (See page 7.) 

By digesting phenol at 100° C, with a considerable excess of 
dightly fuming sidphuric acid, phenol-diaulphonic acid, 
I^Il,fOH}(S0jH)g, is produced. The solutions of this acid and 
1 salts are coloured deep red by ferric chloride. By heat- 
: phenol under pressure with a mixture of sulphuric acid 
md phosphoric anhydride, a phenol-tiiaulphonic acid, 
I^Hj(0H}(80jH)g, is produced, crystallising in thick prisms and 
a hlood-red colour with ferric chloride. 
Similar scries of bodies, the creaol- and xylenol-sul phonic acida, 
t obtained by the action of strong sulphuric acid on cresols 
hJmo'. Chem. See., liv, 280, 281) and xylenols respectively. 

The phenol-sulphonic acids may be separated from the excess of 
olphuric acid by diluting the mixture with water and digesting 
' g sohition with excess of barium carbonate. From the lii|uid 
^I«red from the insoiuble barium sulphate the free sulphouic 
' I may be prepared by precipitating the barium by an cquiva- 


lent amount of dilute sulphuric acid, or the potassium or sodium 
salt may be obtained by precipitating the solution with a carbonate 
of the alkali-metal. 

The following table shows the characters of the three isomeric 
phenol-monosulphonic acids and some of their salts : — 


Potossimn salt, 

SodiniD salt, 

Barium salt, 

Lead salt, 



p„ rOHO) 

UnknowB in a pore 
state, being partially 
converted into the 
para-aoid on evapora- 
ting the solution at 
lOCr, and completely 
at a higher tempera- 

ing to a vitreous mass. 
Long flat needles con- 
taining 2 aq. Very 

Indistinct crystalline 
masses containing 1^ 

Indistinct crystalline 
masses containing 2 
aq. Very soluble. 

Indistinct tables con- 
taining 1 aq. Very 
slightly soluble. 

Pale blue prisms. 


p „ rOHa) 

Crystallises in fine 
needles containing 
2 aqua. 

Melts at 200* to 210". 
ContuaeA efflores- 
cent microscopic 
needles or scales 
containing 1 aq. 

Flat needles or rhom- 
bic tables contain- 
ing laq. 

Small laminiB of mi- 
croscopic needles 
containing | aq. 
Easily soluble. 

Large rhombic tables 
containing 8 aq. 

Thin bright green 
rhombic prisms 
containing 6 aq. 


Syrupy liquid, or hy- 
drated, highly deli- 
quescent needles. 

Melts at 400°. An- 
hydrous elongated 
hexagonal tables. 
Moderately soluble. 

Long prisms 


Long silky matted 
needles containing 

Long bundles of 
needles containins 
2 aa. Basic salt 
nearly insoluble. 

Deep blue plates, 
resembling cupric 
sulphate. Contains 
10 aq. 

When potassium ortho-phenolsulphonate is heated to 250° with 
caustic potash it yields catechol, or <?rfAo-dihydroxybenzene, 
CeH4(0Hf XOH)^. The saltof the meta-acid when similarly treated 
yields meto-dihydroxybenzene orresorcinol, C6H4(OHy*^(OH)^; 
and the para-acid probably hydroquinol, CeH^(OH)"XOHr- 
The last body, however, is not to be found among the products 
of the reaction ; but q u i n o n e, C3H4O2, is produced in large 
quantity by treating the parasulphonate with sulphuric acid and 
manganese dioxide, while neither the meta- nor ortho-sulphonate 
yields quinone by oxidation. 

The phenol-sulphonic acids are very stable bodies, and are not 
decomposed by boiling with caustic alkalies. , 

By heating the free phenol-sulphonic acids or their salts with 


kydnKhlcric ot dilute sulphuric acid under pressure, thejr are all 
^composed completely with more or less facihty, phenol ' being 
leproduced r— CeH4(OH)S03K + HjO = CflH^.OH + KHSOj. 

Ortho-phenolsulphonic Acid.^ 

This body has been recently introduced as an antiseptic under 
ames of "aaoptol" and "sozolio acid." It ia pre- 
, mixed with more or less of the para-acid, by mixing 
SqaiTalent quantities of phenol and strong sulphuric actd in the 
", and removing unacted-on siilpliuric acid by adding barium 
fearbonate. The free sulpheniu actd is then obtained by treating 
) filtered liquid with an equivalent amount of sulphuric acid, 
isd ngitin filtering. 
Ortho-phenolsulphonic acid is Boluble in water in all proportions, 
' I also soluble in ateohol or glycerin. It has very little 
lorrosive action, and is practically non-poiaonoua. It is alleged to 
6 an antiseptic action three times as powerful as that of phenol, 
tha sodium salt ie still more energetic. In its general reac- 
S it resembles the para-acid, into which it is converted by heat, 
eptol of commerce is a 33 per cent, aqueous solution 
of the phtnol-Hulphonic acid. 

IPara-phenolsulphonic Acid. Sulphophenic Acid. 

This substance, also called sulphocarbolic acid, ia produced com- 

I The homologaos of phenol, the diatomic and triHtnmic phenols, and other 
auala|!0iu bodicii, also form sulphonic acids by treatnient with strong mljihur 
id, the multuut compaundB all being split ap with fonnation of the 
d phaQolniil bodjos whea heatnl with concentrated hydrochlorio add to 
kttmpnmtnre beCweoa 100' and 200°. Tiiii general roactiou is valuable, ai 
■ tba form of wlta of their respective aulphouic acids the various isomera and 
bemuloj^es may usually be separsted with comparative Tacility by fractional 
yalaUidBtioD, and the phenols then regenerated by trratmeut with hydro- 
dune Bcid. 

*H,B. Armatrong and some other autboritios prefer, with good reiiBon, 
I phecol-orthosatphuiiic acid to ortho-phonobulphonii; add. U U 
« fnlpbmuc acid which is the ortho- modification, not the phenol. Bat as 
Q ortho-pbcnolsulpbonic acid U niure gsnerally adopted, it is adhered 
JB b tiM text. 


mercially by the direct action of concentrated sulphuric acid on 
phenol If the acids are diluted beyond a certain point no action 
takes place. Moderate heating and the presence of excess of sulphuric 
acid over the theoretical quantity are conditions facilitating the 
completeness of the reaction. Para-phenolsulphonic acid with 
some admixture of the ortho-acid results, the latter body being 
subsequently more or less eliminated by fractional crystallisation 
of the potassium salts. (See page 4.) 

Phenol is not miscible with sulphuric acid before combination, 
or much more soluble in dilute sidphuric acid than in water, but 
it is miscible in all. proportions with concentrated sulphophenic 
acid, and in less than half its bulk of sulphophenic acid diluted 
with four volumes of water ; addition of more water precipitates 
phenol, which is again dissolved on addition of sulphophenic acid. 
These facts are important, for they show that sulphophenic acid 
cannot be purified from carbolic acid by addition of water. The 
phenol may, however, be removed by repeatedly agitating the 
solution with ether free from alcohol ; or the acid may be neutral- 
ised by soda, and the resultant sulphophenate crystallised from 

Para-phenolsulphonic acid may be concentrated to the condition 
of a syrupy liquid, and has been obtained in colourless, hydrated, 
extremely deliquescent needles. It is soluble in water and in 
alcohol, but insoluble in ether and chloroform. 

Sulphophenic acid is a decided antiseptic, and its solutions 
coagulate albumin, but these properties are not shared by the 
sulphopheuates until after addition of acetic acid. The free acid 
and its salts do not suffer decomposition in aqueous solution even 
when exposed to the air, and their solutions are not decomposed 
by boiling. The commercial sulphocarbolates are salts of para-phenol- 
sulphonic acid. 

Phenol-sulphonic acid and its salts are decomposed into phenol 
and sulphuric acid when heated with concentrated hydrochloric or 
dilute sulphuric acid in sealed tubes to 140° C. 

A characteristic and delicate test for sulphophenic acid is to boil 
the liquid for a minute or two with an equal bulk of strong nitric 
acid, and then to neutralise the solution with potassa. A yellow 
colour, due to formation of potassium picrate, will be produced in 
a liquid containing 1 part of phenol-sulphonic acid in 50,000 of 
water. Carbolic acid gives the same reaction. The reaction of 
sulphophenic acid with nitric acid also results in the formation of 
sulphuric acid. Hence, if any sulphates originally present be 
removed by the addition of excess of barium chloride, and the 
solution be then boiled with nitric acid, white insoluble barium 


tphate will ba thrown down if a. sulpliopheiiate wore preeent,' 
fmm ite freight the amount of sulphoplienic acid Taaj be 
lated. (CoHaS04;BQSO^;:I73:233.) The yoUow liquid 
s picric acid, 

i Another delicate though Dot very characteristic test tor pftra- 
tolsulpbonates is the production of a doep purple colour with 
: chloride, a reaction also produced by ortlio- and raeta- 
iol8Ulphonato§> The colour is discharged by acids. 
/ tho action of excess of bromine on a solution of para- 
lenolsulphonic acid or one of its salts, tribromo-phenol,^ 
Ifj.OH, is produced, and sulphuric acid or a sulphate formed. 
J1-PHEN0L8ULFHONATE3. SuLPHoPHENATBS. Sulphocarbolatea. 
phenol-sulphonates are all soluble in water, and mostly 
table in alcohol, especially when hot, but are insoluble in ether. 
svenil of tbem, notably the sodium and cnlcium salts, have been 
ployed in medicine as a means of internally admiuistering 
"; acid. Only distinctly crystalline specimens should be 
t, and they should have but a very faint odour of phenoL 
' e aulphophenates may be recognised by the tests for eulpho- 
c acid already described. The aulphophenates of the alkali- 
s if ignited alone, or those of other metals if ignited with 
xinate of sodium, leave a residue containing sulphate. This 
m, the formation of sulphate by boding with nitric acid, and 
i-oxtroction by other from acidulated solutions are characters 
' 'h distinguish the sulphophenatea from the salicylates. 

i presence of unconverted J^imtrf in sulphophenates may be 
1 by acidulating the solution with dilute sulphuric acid and 
Ung the liquid with ether or chloroform. The phenol left on 
neous evaporation of the ether may be detected by its odour 
/ the yellow colour developed on waiming with nitric acid 
»ad then neutralising with potassa. A faint yellow colour should 
he negleetetl, as it may be due to a trace of suljiliophenic acid 
dieaolvod by the ether, 

~" 9 barium, calcium, and lead salts of phenol-sul phonic acid are 

or les* soluble. Hence stdphuric acid and nidphaiex moy be 

y detected and estimated by addition of barium chloride to 

J solution. Barium and calcium salts may bo detected 

[ phenolsulphonatea by dilute sulphuric acid and oxalate of 

im respectively. 

n PhfiwUuiphojuile.^a.HO^Ce^i.OK, is prepared by double 

lition fium the barium salt. It forms transparent rhombic 

9 containing 2 aq. The salt is permanent in the air, but 

b retction enables snlphopheoic acid Bud (ulplioiihennteii to be nadily 

~ D proeace of carboliu aciiL 


becomes anhydrous at 100'. At a higher temperature it evolves 
phenol and leaves a residue of sodium sulphate and sulphite 
amounting to 36 per cent of the weight of the crystallised 

Sulphophenate of sodium is readily soluble in water. The 
solution has a cooling, saline, slightly bitter taste. The probable 
impurities have already been indicated (page 7). 

Zinc Phenohndphonate forms transparent efflorescent prisms or 
plates containing 1 aq. It also occurs as a white powder. It 
should leave 14*58 per cent, of zinc oxide on strong ignition. The 
probable impurities are suIphcUes, chlorides, compounds of the ligJii 
metals, and free phenol. If prepared by the B. P. process, a notable 
quantity of sulphate is certain to be present.^ 

Other salts of phenol-sulphonic acid are described on page 4. 


When 1 molecule of iodine (in the form of a mixture of 
potassium iodate and iodide) is added gradually to 1 molecule of 
potassium para-phenolsulphonate dissolved in excess of dilute 
hydrochloric acid, iodine at first separates, but is quickly reabsorbed, 
and after a short time the liquid sets to a dense mass of long thin 
prisms oi potassium diiodo-paraphenolstdphonate, CQH2l2(OH).SOgK 
+ 2H2O. This salt requires about 50 parts of water for solution, 
and when heated decomposes without melting at about 270^ with 
evolution of violet vapours of iodine. It yields with potash an 
extremely soluble basic salt, CqH2I2(OK).S03K. The sodium 
salt (normal) forms a white crystalline powder containing 2 aq., and 
is infusible at 200° G. It is odourless, has a faintly acid taste, is 
soluble in 13 parts of cold water and more readily in hot, and is 
also soluble in alcohoL The barium salt is only slightly soluble 
in cold water, from which it crystallises in white glistening needles. 
The zinc salt forms long colourless needles, and the cojpper salt pale 
green monoclinic prisms. 

Free diiodo-paraphenolsulphonic acid melts at 120°, and 
decomposes with liberation of iodine at 190^ 

**SozoiodoV* is the commercial name given to certain diiodo- 
phenolsulphonates. " Easily soluble sozoiodol " is the sodium salt, 
while the potassium salt forms the ** difficultly soluble " modifica- 
tion (Pharin. Jour., [3], xviii. 538, 621, 1006). 

In preparing sozoiodol, a certain amount of ?no«o-iodo-para- 
phenolsidphonic acid is produced. This acid forms thick, colour- 

^ The British Pharmacopoeia directs the salt to be prepared "by heating a 
mixture of carbolic acid and sulphuric acid, saturating the product with oxide 
of zinc, evaporating and crystallising." The solution of the product is stated 
to be '*only rendered faintly turbid by chloride of barium "I 


, rhombic crystnls, and differs from the di-iodo-derivative iji 
biding readilj-aoluble bariuni and calcium aaita. 

Fhenyl-Sulphnric Acid. Phenyl Hydrogen Sulphate. 

CoHaSO.:={CBH,)HSO,=SoJ q" g 

This acid is metameric with the pheuol-sulphonic 

tkcida, CflH/OH)HSOj. It occurs tt^ether with ita honiologue 

" ■ H ulph uric ocid, (CjHj)HSOj, 118 a potassium Halt in 

of the horse and other heibivora. These salts also occur 

considerable quantity in human urine after taking earholic acid, 

id traces are normally present. During exhibition of pheuol the 

iCgonic sulphates ordinarily present in urine are greatly reduced 

amount or even wholly disappear, being converted into phcnyl- 

ilplmt«a. B a u m a n n has shown that ii the inorganic sulphates 

first precipitated by acidulating the urine with acetic acid and 

' ig the diluted liquid with excess of barium chloride, the 

lt«red liquid will contain any cresyl-eulphates and phenyl- 

Iphatee which may be present. On boiling the Qltrate for one 

with hydrochloric acid these are decomposed, bariutn sulphate 

_ precipitated together with resinous matter, from which impur- 

it mnybe freed by woslungwith hot alcohol. On subsequently 

ig the liquid the distillate contains distinct traces of phenol, 

ly recognisable by the bruraine reaction (voL ii. page 540); 

if the distillate be shaken with ether and tlie ethereal solution 

ipamted and cautiously evaporated, the residue gives a distinct 

lue coloration with ferric chloride (vol. ii. page 539). On the 

ittnry, frnm the original urine no phenol can be extracted by 

itstion with ether, a behaviour evidently due to the fact that the 

lenyl-suli'liates ure not decom]K)sed till the urine is heated with 


B a U m a n n has actually isolated potassium phenyl-sulphate from 

iroea' urine by the following process : — The liquid is evaporated at a 

t^mpcmturc, the residue extracted with alcohol, and the filtered 

> B. Dftviea has deicrlbcd s specimen of urine passed by a person re 
n pnlnoniug by oibatlc Rctd {Pharm. Jour., [3], xiv. 173). It wna nlmast 
'[ in uolour. and on Uiatillation with salphnric acid gave a distillate con- 
Ig both phunol uid creeoL The phenol vm recognised by thu emull, the 
I with ittiiiiioiiU uid sodium hypochlorite, and the fornuition of an 
mdalit prvciliiUle of tribroiaopheDol (of characteriatic cryat&llinv form) and 
D ulditig bromine. Only a trace of phsnol distilled over 
1 th* additiDit of Bolphuiic aoid wu omitted, and no phenol could b* 


liquid concentrated to a syrup and allowed to stand in a very cold 
place. The crystalline plates which form are filtered ofi[^ dried, and 
purified by reciystallisation from strong spirit. The pearly white 
tables obtained consist of potassium phenyl-sulphate 
{Jour, Ckem, Soc, xxix. 726).^ 

Potassium Plvenyl-svlphcde^ (C^^IL^O^^ may also be prepared by 
the action of potassium phenate on potassium pyrosulphate: — 
{C^^,OYi+lL^fi^^lL^&0^+{C^^lL&0^. It crystallises in 
transparent rhombic tablets which feel greasy to the touch. It is 
readily soluble in water and sparingly soluble in cold absolute 
alcohol, but dissolves somewhat more readily in boiling alcohol. 
The aqueous solution exhibits a fine blue fluorescence. 

Potassium phenyl-sulphate decomposes on exposure to moist 
air, sometimes in a few minutes, into phenol and potassium 
hydrogen sulphate. A similar change occurs by boiling the 
aqueous solution for a few hours, or warming it for a few minutes 
with dilute hydrochloric acid, but it is not affected by acetic 
acid. On the other hand, potassium phenyl-sulphate is stable in 
presence of alkalies, and is only gradually attacked by caustic 
potash at ISO"* C. When the solid salt is heated to 150*'-! 60° 
in absence of moisture it is converted into the metameric potas- 
sium para-phenolsulphonate. 

Phenyl-sulphates are readily distinguished from phenol- 
sulphonates by the formation of phenol and a sulphate on heating 
the solution with hydrochloric acid When solid potassium phenyl- 
sulphate is quickly heated to fusion, and then dissolved in water, 
the solution gives a ruby-red colour with ferric chloride. 

Free phenyl-sulphuric acid is so unstable that its aqueous or 
alcoholic solution decomposes almost immediately. 


Phenyl-formio AoicL Benzene-oarbozylio Acid. 

CyHgO, = HCyH^Oj = C7H5O.OH = CeH5.CO.OH. 

Benzoic acid is the central member of a group of highly inter- 
esting bodies, a considerable number of which possess more or less 
practical interest. They all contain the radical benzoyl, 

^ L. Brieger treats fresh nrine with neutral acetate of lead in excessi 
filters, and treats the filtrate with basic lead acetate. The lead is removed 
from the filtered liquid by sulphuretted hydrogen, and the filtrate evaporated 
to a thick syrup and kept some time in a vacuum. The potassium phenyl* 
sulphate forms plates which are recrystallised from hot absolute alcohol 
{Jowr, Chtm, SoCf xlvi 1858). 


C7H^O = C8Hs.C0 = Bk, either intact orsuhstituteil. In the follow- 
Et compounds thi^ benzoyl radical exists intact : — 

acid (Phenyl-formic acid^ CeHj.CO.OH. 
>yl chloride (Benzoic chloride), C,Hj.CO.Cl. 
.yl hydride (Benaoic aldehyde), C9H5.C0.a 
■I niethylido (Acetophenone), CBH5.CO.CHy 
mioyl-glycocine (Hippuric acid), . CaH5.CO.NH.CHj.CO. OH. 

leoyl-ecgonine, CflHs.CO.CgH^NOa. 

^nzoyl-methylecgonine (Cocaine), . CbH5.C0.CbH,3(Ci4)N0s. 
Bonzoyl-aconine (Aconitine), . . CcHj.CO.CjgHjsNO,,. 

la tho foUowing allies of benzoic acid substitution occurs in 
glwOEoyl radical itself : — 

c acid (Benzene-earboxylic acid), . . . CaH5.CO.OH. 
jtanzenwlicftrboxylic acid (Phthalic acid) CaHj(CO .OH).CO.OH. 

ralphobcnzoic acid, CoH.(SOj.OH).CO.OH. 

thoBulphamidobenioic auid, . . . CgH,(S0j.NH5).C0.0H. 

zojl Bulphon 

c-imide (Saccharine), . . C^H, | ^ !■ :NH. 

Sydroxybenzoie acid (Salicylic acid), . . CoH/OH).CO.OH. 

mhydrosybenzoic acid(Pmtocatechuic acid), C„Hj(0H)j.C0.0H. 

Uiydroxybenzoic acid (Gallic acid), . . CflHjCOHVCO.OH. 

! acid occura ready-formed in gnm benzoin, storax, and 
It And Peruvian balsams, and in these and other resins also in 
a form of benzoic ethers. It has also been found in the scent 
known OS ylang-ylan^, in vanilla, and in certain fruits, notably 
phtms and cnuibenies. 

Benzoic acid Is formed in a number of synthetic reactions, and 

is produced by the oxidation of a great number of organic bodies 

including benzoic and cinnamic aldehydes, toluene, cumene, 

ttiri n, gelatin, &c. 

^^■nie following are five of the most important and interesting 

^^^blods of preparing benzoic acid : — 

^^^K Qtim Bemoin. — The benzoic acid may be obtained by sub- 
^^Hartion, or by exhaustion of the powdered gum wilh carbon 
<ti*iilphide. It may also be extracted from the gum by treatment 
with lime in the manner indicated on page 36. Benzoic acid 
pr«pai«d from gum bcnzoiji by sublimation is often more or less 
coloured, and has an aromatic odour. 

K Jlippurie. Arid, contained in the urine of herbivorous animals, 
lUts up into benzoic acid and glycocine on putrefaction 
I urine, or when boiled with hydrochloric acid (page 21). 


Benzoic acid prepared from this source is apt to retain a smell of 
urine which can he got rid of by careful sublimation. 

c. Phthalic Acid when heated with excess of slaked lime yields 
a fixture of calcium carbonate and benzoate (C3hJ.= 
COg +0^11^02), from which benzoic acid may be readily prepared. 

d. Trichlor-methylhenzene (benzenyl chloride), when heated with 
zinc chloride and glacial acetic acid, yields benzoic acid, 
acetyl chloride, and hydrochloric acid : — C7H^Clj+ 
2HC2H802 = C7Hg02+HCl + 2C2H30Cl In order to avoid 
the evolution of hydrochloric acid, which carries oflf acetyl 
chloride with it, half the acetic acid may be advantageously 
replaced by zinc acetate. Or the formation of acetyl chloride may 
be avoided by heating benzenyl chloride with a little acetic acid 
and zinc acetate, and gradually adding the amoimt of water 
necessary for the formation of the benzoic acid. 

e. Benzyl Chloride^ CyH^Cl, (1 part) is boiled with nitric acid (3 
parts of 1*31 sp. gr.) and water (2 parts) in a flask with a reflux con- 
denser, until the odour of bitter-almonds disappears, and the liqiiid 
solidifies on cooling to a crystalline mass, free from oily drops. 

Benzoic acid crystallises in lustrous scales or friable needles, but 
its appearance and other physical characters are greatly modified by 
traces of impurity, so that the impure acid has more than once 
been mistaken for an isomeride. When pure, benzoic acid is 
nearly odourless, but it frequently smells of benzoin, and sometimes 
of urine or almonds. It has a snarp taste and produces a peculiar 
irritation in the throat. Benzoic acid has a density of 1*292, 
melts at 121°, and boils at 249"^; but it volatilises rapidly at a 
temperature much below its boiling point, and forms a beautiful 
feathery sublimate. It is somewhat volatile in a current of steam, 
1 gramme passing over with 2 litres of water, and more or less 
with alcohol, benzene, and other volatile liquids. The vapour of 
benzoic acid has a penetrating aromatic odour, attacks the eyes, 
and provokes coughing. 

In cold water, benzoic acid dissolves very sparingly, requiring 
408 parts at 15°, while at 100° the solubility is about 1 in 17. 
(Bourgoin, -4nn. C^im. PAy«., [5], xv. 168.) Its solubility is 
greatly increased by the presence of certain salts, notably sodium 
phosphate.^ It dissolves very readily in alcohol, ether, chloroform, 

^ Sodium Benzene-sulphinate is a compound obtained by dissolving 
benzoic acid in a concentrated solution of sodium sulphite. It is very soluble 
in water at the ordinary temperature, and the solution has been recommended 
as an antiseptic dressing for wounds. It is said to be more efficient than 
phenol, and to rank with mercuric salts and iodoform, without having the 
poisonooB oharactors of the former or the disagreeable odour of the latter. 



£c alcohol, benzene, petroleum Epirit, carbon ilisulpbide, and 
d and volatOe oils. 

e beuioio acid is soluble in warm concentrated sulphuric acid 
lout coloration, and is precipitated unchanged on dilution. By 
J sulphuric acid, or more readily by Bulpliuric anhydride, it 
mveited into a aulphonic acid. Ordinnry nitric acid, 
I when boilini^, doee not affect it, but it yicMa a nit ro- 
ll with the fuming acid. 
eoic acid is not acted on by chromic acid solution ; but ozone 
aline solution oxidises it to carbonic ticid and water. When 
lowed by mammals, benzoic acid is converted inti) h i p p u r i c 
t (page 31), and appears in this form in the urine; but in 
■ oof birds it yields ornithuric acid, CibHjijNjiO^. 
1 diatillcd with excess of baryta or slaked lime, benzoic 
1 is decomiiosed into benzene and carbon dioxide, and 
. its Ta|)our is passed over faintly ignited zinc-dust it Is 
ito benzoic aldehyde, C,HaO. 

laic acid is employed in medicine and the manufacture of 
iring matters. It possesses decided nntiseptic properties, 
J in this respect, according to some observers, superior to 
kylic acid, and according to others inferior. 
'iHALTnoii. Reactions op Bbnzoio Acid ash Benzdatbs, 

utig solutions of soluble benzoates are precipitated on addition 
ihbric acid, owing to the slight solubility of benzoic acid 
(Succinates give no precipitate with hydrochloric acid ; 
I faippuiates, cinnamates, and salicylates react like benzoates. 
iharic acid should not be substituted for the hydrochloric.) 
i separated benzoic acid dissolves on repeated agitation with 
, chloroform, or benzene. After washing the ethereal solution 
i water the benzoic acid may be determined by diluting with 
'lol and titrating with alkali and phenolphthalein. Sodium 
l,or metallic magnesium or aluminium, gradually reduces a 
^tly acidiliod solution of a bcnzoate, with production of the 
loteristic odour of benzoic aldehyde. 
VJIsutral ferric chloride precipitates neutral benzoates almost 
Iet«Iy OB a light red, bulky, basic ferric benzoate, 
hihle iu acetic acid. Suwinates give with ferric chloride a red- 
rown, cinnamates a yellow, and hippurates a cream-coloured 
tat«, muconatcs a deep red coloration, and salicylates a 
t colomtion. Benzoic ncid ia also distinguished from succinic 
I mtay other acids by not being precipitated by ammoniacal 
■ "ft of barium in presence of alcohol Magnesium benzoate is 
B in alcohol, b\it the succinate is insoluble, 
loic acid may be aejiarated from fixed substances by sub- 


limation, and may be determined in gum benzoin by that 

Benzoic acid may also be approximately estimated, in the 
absence of interfering substances, by converting it into a soluble 
neutral benzoate, and precipitating the cold solution with lead 
acetate, avoiding excess. The precipitate is. filtered off, washed 
once with cold water, then with proof-spirit containing ^ per cent, 
of acetic acid, and finally dried at 100"* and weighed. Its weight, 
multiplied by *5434, gives the amount of benzoic acid present 

Neutral benzoates are precipitated tolerably perfectly by cupric 
acetate or sulphate, and the reaction may be employed for the 
determination of benzoic acid. 

Commercial Benzoic Acid. 

The benzoic acid of commerce is liable to contain various 
impurities, some of which are due to its mode of preparation, 
while others are intentionally added as adulterants. Asbestos, 
boric acid, calcium carbonate and sulphate, sal-ammoniac and sugar 
belong to the latter class. 

Pure benzoic acid does not melt under boiling water, but certain im- 
purities impart this property to it, besides giving it greater solubility, 
and causing it to form smaller crystals of a different form from that 
usually assumed by the pure acid. On treating a sample of benzoic 
acid with ether, nearly all impurities and adulterants are left undis- 
solved, except cinnamic acid, chlorobenzoic acid, and essential oiL 

Fixed impurities in benzoic acid can be detected and estimated 
by subliming the sample, pure benzoic acid being readily and 
entirely volatile. If the residue chars on further heating, sugar 
or kippuric acid may be present. The former gives a smell 
resembling burnt bread, and the latter an odour of burnt feathers, 
and they are readily distinguished in other ways. 

The reduction of permanganate of potassium has beep proposed 
as a test for the origin of benzoic acid, but its indications have 
been proved to be fallacious. Ammonio-nitrate of silver has also 
been recommended, the test being used at a boiling heat Jacobsen 
recognises the acid from gum benzoin by the presence of caieeholy 
which he detects by converting the acid into a sodium salt, drying, 
and shaking with ether. The ether being separated and evaporated, 
the residue is dissolved and the catechol recognised by its reducing 
action on cold ammonio-nitrate of silver and other reactions. 

Inorganic impurities will be left as a residue on igniting the 
sample of benzoic acid. Chalk dissolves readily with effervescence 
in dilute hydrochloric acid. Oypsum dissolves with difiiculty, and 
the solution gives a white precipitate with barium chloride. 
Asbestos, day^ &c., are insoluble in dilute hydrochloric acid. 



Dork acid differs from the foregoing adulterants hy dissolving 

n hot alcohol to form a solution which when kindled bums with 

I florae green at the edges. (If this indication be obtained it 

_«bould be confirmed by repetition on the residue left on dissolvinjj 

e sample in ether, as chloTobenzoic acid might also give rise to a 

tQ-edged flame.) 

Hippiiric acid when present may be detected by the charring 
1 smell of burnt feathers on heiiting the sample ; by its incom- 
» solability in other ; by its charring when boated with strong 
nlphuric acid ; and by the evolution of ammonia which occurs 
nkon the sample is ignited with soda-lima. The last reaction 
Btjr be employed quantitatively in the absence of ommoniAcal 
The proportion of hippuric acid may be approximately 
mined by agitating the sample ^vith dilute hydrochloric acid 
I petroleum ether or chloroform, when the benzoic acid dia- 
Hves ; but any hippuric (or succinic) acid remains. Samples of 
jsoic acid containing hippuric acid usually have a urinous odour, 
i re^lden or char when heated. 
Saiiei/lie acid may be detected by the production of a violet 
loration with excess of ferric chloride. 

t Cinnamie aeid is said to be often present in considerable pro- 
3 the acid prepared from benzoin. It is best detected by 
I reaction with manganous salts (see page 32), and by the 
Wll of bitter-almond oil produced on warming the sample with 
"^horic acid and potassium bichromate, Cinnamie acid lowers 
melting point of benzoic acid (page 32). 
f CStlorinaled compounda may bo detected by dissolving the 
mnple in alcohol, moistening some asbestos with the solution, 
igniting it, and placing a beaker moistened with silver nitrate over 
the flame. If chlorinated products were present, a milky deposit 
I' of ailver chloride will be produced. 

SfUJctr IB recognised by its insolubility in ether, ready solubility 
I cold water, and by the blackening which occurs when the 
mple ia heated with strong sulphuric acid. When present in 
mtjty it may bo detected by the taste of the sample, and in 
lUot qoantity by the taste of the residue left undissolved by 
T or chlorofonn. 

J-amjnoniac is readily detected by shaking the sample with 

1 wat«t, when a solution ia obtained which, on addition of 

mtic nitrate, gives white curdy cldoride of silver insoluble in 

"c acid. This proves the presence of a chloride only ; the pre- 

" in that sal-ammoniac is present is confirmed if the sample 

ammonia on treatuient in the cold with caustic alkali. In 

9 of sal-ammomoc and other ammoniacal salts, the soda- 


lime test for hippuric acid is inapplicable, unless the sample be 
first shaken with cold, moderately concentrated hydix>chloric acid, 
in which ammonium chloride dissolves, while hippuric acid is 
nearly insoluble. 

Essential oU, which is very commonly present in the acid made 
from gum benzoin, causes the sample to turn brown when warmed 
with strong sulphuric acid. Resinous and oUy matters may also 
be detected by dissolving the sample in warm solution of soda, in 
quantity just sufficient for its neutralisation, when such impurities 
will remain undissolved, together with any chalk, asbestos, <&c.^ 

The odour of benzoic acid to some extent indicates its origin 
from urine, &c.; but the acid from benzoin is sometimes imitated 
by mixing the product from other sources with gum benzoin, and 
subliming the mixture ; or by adding vanillin to artificial benzoic 
acid. According to Hager, this factitious product may be 
detected by a mixture of solutions of ferric chloride and potassium 
ferricyanide. With the natural acid from benzoin, the colour of 
this reagent is changed from yellow to blue in from 1 to 3 seconds ; 
while with the product obtained by subliming the artificial acid 
over resin, from 20 seconds to 2 minutes are required. 

Traces of sulphuric and hydrochloric acids are frequently present 
in benzoic acid, owing to the mode of preparation. 

All the principal Pharmacopoeias require that medicinal benzoic 
acid shall be prepared from gum benzoin. 

Metallic Benzoates. 

The metallic benzoates are mostly ciystallisable and soluble in 
water and alcohol, but insoluble in ether. Some of them, such as 
the sodium and barium salts, are withdrawn from their solutions 
by animal charcoal, and calcium benzoate is decomposed by it, so 
that free benzoic acid can be extracted by ether. 

^0. Jacobsen {Jour, Chem. Soc., xlvi. 1168) has recently inyestigated 
the nature of the substances accompanying benzoic acid prepared from gum 
benzoin. On treating such acid with solution of sodium carbonate, an oil 
remains undissolved, smelling of vanillin and of phenol. This may be 
separated by distillation into three fractions. The first boiling between 200° 
and 210** consists of methyl benzoate and guaiacol, which can be separated 
by cold dilute caustic soda. The second and smaller fraction (boiling between 
285** and 245°) when shaken with water yields up catechol, while acetyl-guaiacol 
remains undissolved. The third and largest fraction (boiling between 280** 
and SSO"* C.) contains benzyl benzoate, benzophenone, and benzoyl-guaiacol, 
with traces of vanillin and other bodies. On saponification with alcoholic 
potash, and agitation with water and ether, benzyl alcohol and benzophenone 
pass into the ethereal layer, while the alkaline solution contains benzoic acid 
and guaiacoL 



Benioie acid dcicompoees carbonates in aqueous solution, bat 
ttrhcn A current of carbon dioxide is passed tlirough an alcoholic 
l:Jk>lutioii of potassium benzoate, potaesium carbonate separates out. 

Conunercial benzoates arc liable to contain mueh tbe same 

E'impvmties aa benzoic acid (page 14), especially Mppnric and 

MoTobctwoic aeide, ittii.pkaleg, and chlorides. The two former 

tiinpurities may be detected by acidulating the aolntion of the 

■ bencoKta with hydrochloric acid and agitating with other. Benzoic 

EjUid chlorobeDEoic acids pass into the ethereal layer, while hippuric 

L3 undissolved in the aqueous liquid. The clilorobenioic 

^d may then bo detected by allowing the bulk of the ether to 

repomte spontaneously, adding alcohol, igniting, and testing the 

iducta of combustion foi hydrochloric acid, as described above. 

SnDiUH Rknzoatb, KaCjHjOj+l aq., cryatalHses in colourless 

The salt is soluble in W parts of water at 15° C, if tha 

Idd used for its preparation were pure, but has a lower but vaiying 

Dlubility if chlorobenzoute or hippurate be present. 

LmnuM Bbnzoatg forms a crystalline powder or small Ehining 

K«nlcs, soluble in 4 parts of cold or 25 of boiling water, and in 12 

L^rta of colli or 10 of boiling alcohol. It is liable to contain much 

rihe BBine injpurities as sodium benzoate (see above) and lithium 

[' >«itiate (toL i. page 464). 

CALCnm Benzoatb crystallises in granules or feathery needles, 
[.lUd is leas soluble in hot water than in cold. 

Maxoanous Benzoate is soluble (distinction from cinitamate), 
Fkrbio Benzoate is obtained as a flesh-red precipitate by mixing 
v-tolutions of neutral benzoates of ferric chloride. It is decomposed 
E'^ washing with water into a soluble acid and insoluble basic salt 
CupBto Beitzoatk, Cu(CjH50j)j+2 aq., crystallises from hot 
raler in light blue needles or plates united in spherical 
t is one of the most insoluble of the benioates. 
Lead Benzoate is crystalline aud difficultly soluble. 

I Benzoic Ethers. 

I £tbtuc Eknzoatk, CjHj.CtHjOj, is n liquid of a 
matic smeU, boiling at 212 . It is used in compounding arti- 

^a] fruit essences {see vol. i page 163), and is prepared by 
■olving 3 parts of benzoic acid in 2 of nearly absolute alcohol, 
d poeaing hydrochloric acid gas to saturation. The liquid is then 
illed and the distillate poured into water, the separated ether 

UOg collected, dried with calcium chloride, and rectified. 
Ukhsvl Bb.nzoatb, CjHj.CjHjOj, occurs naturally as a con- 

Bituenl of Peru and Tolu balsiuus (page 38). It has a specific 
vity of 11227 at 19°, and solidiHea in a freezing mixture 
VOL. m. TAltT L B 



to a compact mass of lustrous crystals, which melt at 21 ^ It boils 
at 323* C. 

Aldehyde. Benzaldehyde. Hydride of Benzoyl. 
CyHgO = C7H5O.H. = CgH5.C0.H. 

Benzoic aldehyde forms the major part of the essential oils of 
bitter-almonds and cherry-laurel, and is now extensively manu- 
factured synthetically.^ 

Pure benzoic aldehyde is a thin, colourless liquid of great 
refractive power, and peculiar, very agreeable odour, like that of 
bitter-almond oil, and a burning aromatic taste. Its specific 
gravity is 1-0636 at 0' and 1-0504 at 15' C.,and its boiling point 
180**. It is soluble in about 300 parts of water,* and is nuscible 
in all proportions with alcohol and ether. 

Exposed to the air, benzoic aldehyde absorbs oxygen greedily, 
and is converted into a crystalline mass of benzoic acid, 
CyHgOg.* It is also oxidised by boiling with chromic acid mixture, 
or manganese dioxide and sulphuric acid; but is only slowly 
attacked even by boiling nitric acid. 

Heated with solid caustic alkali, benzoic aldehyde evolves 
hydrogen and yields a benzoate. By treatment with water 
and sodium amalgam, it is reduced to benzyl alcohol^ 

Like all true aMehydes, benzoyl hydride forms crystalline com- 
pounds with the acid sulphites of the alkali-metals. The sodium 
compound has the formula C7HgNaS03. Benzoic aldehyde also 
responds to the other general reactions of the aromatic aldehydes 
(voL i page 164). It differs from aldehydes of the fatty series 
in being permanent in presence of alkalies, and in not reducing 
Feliling's solution. Ammonia converts it into white, crystalline 

^ Benzaldehyde is prepared on a large scale by boiling 2 parts of benzyl 
chloride, CsHb.CHjCI (formed by the action of chlorine on hot toluene), 
with 3 of lead or copper nitrate and 10 of water for several hoars in an 
apparatus famished with a reflux condenser; the operation being conducted in 
an atmosphere of carbon dioxide. Half the liquid is then distilled off, and the 
oil separated from the aqueous distillate. The product may be purified by 
conversion into the acid sulphite compound. Another method consists in act- 
ing on benzidene dichloride, CQH5.CHCI2, with water and caustic soda 
or milk of lime, under pressure, or with glacial acetic acid and zinc chloride. 

' The solubility is often stated at 1 in 80, or ten times the true amount 

* The oxidation is much retarded by the presence of hydrocyanic acid, which 
consequently is sometimes added to the artificial oil. 

^ Bbnzyl Alcohol, CQH5.CH3.OH, is a colourless liquid of 1*051 sp. 
gravity, boiling at 204'', and insoluble in water but readily soluble in alcohol 
and etiier. Oxidising agents convert it into benzoic aldehyde and benzoic acid« 



Sjato-benjiamidB,' (CoHB,CH)gXj, melting at 110°, which is 
wived hy acids into ammonia and benzoic aldehyde. 
I Bomoic aldehyde is used as a scent and flavouring tigent ; for 
tducing benjaldehyde or mulBchite green ; and as the starting 
^nt of eevera] other synthetical products. 


L The natural bensoic aldehyde results from the maceration oi 

■ttor-abuonds with water, with subsequent distillation. Both - 

Bet- and bitter-almonds contain a uitrogenised body called 

uygdalin, which nnder the influence of a ferment coiled 

9 e, present in the WHcr-almond only, is split up into 

aldehyde, liydrocyanic acid, and glucose.* 

HeTNO„ + 2Hj,0 = C,H,0+HCN+2CaHijOB. 

" "iO to 200 parts of bittor-almonds are required for the 

tduction of 1 part of the oil. Crude natural oil of bitter-almonds 

} a density varying from 104 to TOTS (never more), and con- 

i addition to benzoic aldehyde, benzoic and 

lljrdroujanio acids, benzoin, C^jHijOj, beniimide, 

Vdbensaldehyde c y a n h y d r i n, CeH5.CH(0H).CN,» the 

■ 1 corresponding to mandelic acid, CoH5.CH(OH).COOH 

U&Hr, C/u^m. Soc, xxxvl 719). On fractional distillation, hy- 

Dcyanic acid passes over first, and then tolerably pure benzoic 

' ihyde. Benzoin is a solid camphor-like body, and occura most 

' 1 samples of oil of high density, in the preparation or 

ification of wliich a high temperature has been employed. 

i givea a purple colour with strong sulphuric acid. Bitter- 

1 oil gives a crimson coloration with strong sulphuric acid, 

ng brownish on exposure to the air. If the crimson liriuid 

the Bramatio aldehydes bohgve in n similar manner witli aaitnonia, 
M difftirinx from the aldehydes of the fatty serios, 

• Flilokigor «tntcB that cliBrrjf-lHorel leaves which have lieon exposed to fireat 
'i do not yield eithur honzoic aldehyde or faydrocyanic acid on diatillation 
h watar, tjie ferment nppareiitly being killed. 

> O. L I n d a [Pharm. Jour., [3], iviii. 637} helicves that the action of the 

>r aynaptaac of the hi ttfr-nlmond ii limited to the formation from amrg- 

g1ui:oM gnd this cyanhydhn, which lattec on anbeequont distillatiou 

or ii partially split op into th« bonzoic aldehyde and hydrocyanic acid, 

f wbich the bttur is lolabk in water. H^nce tlin distilled oil coiiaiBta chiefly 

aldehyde with from 20 to 30 per cent, of benzaldehyde cynnhydrin 

h fa«a (Htoaped deeoiuposition, F i 1 e t i Btste9 that cherry -iaurol ail oou- 

M body. 

I Juooriiagto Til d sit, cherry-laurel oil consists of benzoic aldeh}'de, loss 
n 1 per cent, of hydmcyanic acid, ■ volatile oil eon vertiblo into benzoic add 
y oaidation and which is poMibly benzyl alcohol, and minute ignautities of 
a oJorooi miu ^Flumn. Jmtr., [8], y. 7flll. 


be poured into water the red colour disappears, and a yellow 
precipitate is produced, which sometimes takes the form of 
globules. The usual proportion of hydrocyanic acid in 
crude almond-oil is from 4 to 6 per cent, but it sometimes reaches 
a much larger amount. Of course the presence of hydrocyanic 
acid renders the oil poisonous ; indeed, it is several times as strong 
in hydrocyanic acid as the B. P. acid. Hydrocyanic acid may be 
removed from bitter-almond oil by agitating the sample with 
mercuric oxide and water, or with lime and ferrous chloride, 
followed in either case by distillation of the oily layer. 

Commercial Oil of Bitter- Almonds often contains hydro- 
cyanic acid, which is a natural constituent of the crude oil 
from almonds, and is sometimes added to the artificial oil to retard 
oxidation. The artificial oil is liable to contain chlorinated 
products. In addition, oil of bitter-almonds is liable to adulteration 
with alcohol and nitrobenzene. 

Hydrocyanic acid may be detected in bitter-almond oil by 
agitating the sample with water, and applying the tests for 
hydrocyanic acid to the aqueous liquid. Ferric chloride and 
ferrous chloride or sulphate should be added, and then solution of 
soda. On acidulating the liquid with hydrochloric acid, a bluish- 
green coloration or prussian-blue precipitate will be formed if 
hydrocyanic acid be present An aliquot part of the aqueous 
solution may be employed for the determination of the hydrocyanic 
acid by precipitation or titration with nitrate of silver. 

A preferable method is to dissolve 1 gramme of the oil in 5 cc. 
of alcohol and dilute with water to 50 cc. Excess of ammonio- 
nitrate of silver is then added, and the mixture well agitated for a 
few minutes. The solution is then slightly acidulated with nitric 
acid, and the precipitated cyanide of silver collected, washed, 
dried, and weighed, or ignited in the air and the resultant metallic 
silver weighed. 5 parts of silver cyanide (nearly) or 4 of metallic 
silver correspond to one of hydrocyanic acid. 

Chlorinated products may be detected by passing the vapour of 
the sample together with hydrogen through a red-hot tube, as 
described under "Chloroform" (voL i page 178), or the alcoholic 
solution of the sample may be inflamed, and a beaker moistened 
with silver nitrate solution held over the flame, when white silver 
chloride will be deposited. 

Alcohol reduces the density of bitter-almond oil. It may be 
approximately determined by shaking the sample in a graduated 
tube with water or glycerin, and noting the reduction in volume 
of the oily layer. 

Nitrobenzene, CgH^NO^ is occasionally used as an adulterant of 



Pftter-olmond oil, and h&s even been sold aa a substitute under tke 

a of "artificial essence of bitter-almondB.'' Nitrobeuzene had a 

jBeneity of ri86, and hence is heavier than bitter-almond oil, from 

Vbich it also diflers in not yielding benzoic acid when a current of 

s passed through it. 

The following method niay he employed for the detection and 

Ipproximate estimation of nitrobenzene in bitteivalmond oil. 

Blntrodnce some clean sand or emery into a wide-mouthed flask, 

rmd then add a known weight (about 10 grammes) of the 

Kaunple to be tested ; next add 40 c.c. of a saturated aqueous 

Baolution of acid sulphite of sodium (NaHSOJ, agitate briskly for 

I few minutes, nud then shake with ether free from alcohol. The 

; aldehyde forms a compound with the sulphite, while any 

hltrobenzene dissolves in the ether. The upper layer is withdrawn 

I pipette, more ether ailded, and the agitation repeated. The 
^pe>tte being again used, the united ethereal liquids are evaporated 

it a gentle heat, and the residual nitrobenzene is weighed. The 
getbod is only roughly approximate. If the quantity of nitro- 
e small, or there be any doubt as to its identity, four or 
drops should bo dissolved in alcohol, anil heate<l for some 
me with hydrochloric acid and granulated zinc. The nascent 
^dngeu reduces the nitrobenzene to aniline, CflHjN. The 
'" '< filtered through wet paper, rendered alkaline with solu- 
D of soda,^ ogitfflted with ether, and the ethereal layer removed 
shnken with water and a few drops of dilute hydrochloric 
pd. The ether is separated, and a dilute solution of bleaching- 
rder is cautionsly added to the aqueous liquid, when, if 
robenzene were originally present, a violet colour (mauve) will 
I developed. The process requires tj) be skilfully conducted, 
Ilia method may be conveniently used for distinguishing bitter- 
tnond oil from nitrobenzene, but not for detecting the latter in 
( of the former; when this is required, the sulphite and 
Bier process must be previously used for their separation.' 
f The following method for detecting and approximately 
tecntining nitrobenzene in hitter-almond oil is due to Maisch. 
J-DisBolve 1 c.c. of the sample in 13 c.c of absolute alcohol, and 
ltd ^ gramme of fused caustic potash. Boil the liquid till it is 
'iduoed to about 4 c.c, and leave it to cooL If the sample be 
crystals form, but a brown colour is slowly developed. 
pie residual liquid is entirely soluble in water. In presence of nitro- 

' WLvn the nltrobeniEnB occare id igaantity, bleaching-powdar may be 

B to the Sltoreil liquid aher nearly neutraliaiag it nitli soda. 
* K«*t other utcntUl oils i^aa also b« Mpsrated from tiydrida of benzoyl by 

II of vnd sodiam sulphite and other. 


benzene, brown crystals of azo-oxybenzene, Ci^iqI^^^^ ^^-^ 
formed, which are insoluble in water, and may be collected, dried 
by pressure, and weighed. 

M. Boyveau states that an artificial oil of bitter-almonds is 
occasionally met with having a density of 1*029 to 1*030. Its 
odour is more acrid than that of the natural oil, as may be 
observed by moistening strips of paper with the oil and exposing 
them to the air. To distinguish the natural from the artificial 
product, Boyveau adds 1 c.c of the oil to an equal measure of 
concentrated sulphuric acid. The two liquids are shaken together, 
when the natural oil acquires a beautiful currant-red colour, which 
in a few hours becomes a more intense and darker red, the mixture 
remaining perfectly clear. Benzoic aldehyde from the cJierry- 
laurel takes immediately a dark-red tint, without first passing 
through the delicate currant-red shade observed with bitter-almond 
oil. The mixture thickens somewhat, but remains perfectly fluid 
and clear. The oil from peach and apricot kernels behaves some- 
what similarly, but gives an evanescent currant-red tint changing 
to a very dark red. Artificial afmond-oU first takes a red tint, 
and then immediately becomes brown, loses its transparency, and 
thickens ; becoming a solid brownish mass in the course of twenty - 
four hours. By the loss of transparency and production of the 
brown colour, an admixture of 25 per cent, of the artificial oil in 
the natural oil of bitter-almonds is said to be recognisable. 

Essence of Bitter-Almonds is the name given to a solution of 
one part of the commercial oil of bitter-almonds in three of 
rectified spirit. It is employed as a flavouring agent, for which 
purpose it should be quite free from hydrocyanic acid. Almond 
flavour is a solution of one part of the oil in seven of rectified 
spirit. The proportion of alcohol in these preparations is best 
determined by fractional distillation. 

Bitter-Almond Water is a solution of bitter-almond oil in water. 
It is not a preparation of the British Pharmacopoeia, but is officinal 
in several other countries. Its strength is uncertain, however 
closely the specified directions for preparation are adhered to. It 
always contains hydrocyanic acid, the proportion of which may be 
determined with silver nitrate, after adding sufficient hydrated 
magnesia to leave the sample slightly opalescent. The mixture 
should be left at rest for half an hour and then titrated '\vith 
decinormal silver nitrate, using neutral potassium chromate as an 
indicator. The use of basic acetate of magnesium is said to be 
preferable to that of magnesia (Beckurts, Jour, Soc. Chem, 
Ind,y vi. 567; Linde, Jour, Chem, Soc,, Hi. 1143). Bitter- 
almond water should retain its characteristic odour after the 



tnorni of nil the hydrocyanic acid by tho above process or by 
■ibition witli excess of silver nitrate. 

f Laurel WafT (Aqua lauro-curan), prepared by diatilling Inurel 

MVes with water,' and Ckernj Watir, from wild cherries, are pre- 

' rations very gimilar to bitter-almond water; but the latter 

8 milky immediately on addition of ammonia, which is an 

, not produced on laurel water till after tho l.ipae of aome 

AcetophenOIld. Benzoyl Methide. Phenyl-methylketone, 

This body results from the reaction of benzoyl chloride on 
ic-methyl, or by distilling a mixture of hcnzoate and acetate of 

I Acetophenone ciyataUises in largo lamintE^ melting at 14° to a 
loarless, mobile liquid of about the density of water, boiling at 
It hn& a very persistent odour, recalling that of hitter- 
Biond and cherry-laurel water. It is nearly insoluble in water, 
Bnble in 60 parts of glycerin, and very soluble in alcohol, ether, 
roform, aud petroleom spirit 

lone is neutral and gives no coloration or characteristic 
ion with ferric chloride, hydrochloric acid, or sulphuric acid. 
r oxidation with chromic acid mixture it ia converted into 
Imzoic and carbonic acids. 

cetophenone has very intense hypnotic properties, and has been 
tduced into medicine under the name of " h y p n o n e " 
snn. Jour., [3], xvi. 445, 582), but tlie statements as to its 
a are conflicting. 

■Bippuric Aoid> Eenzoyi-amido-acetic acid. Benzoyl 

CyllaNOa = CsHj.CO.NH.CH2.COOH. 

I This acid replaces uric acid in the urine of herbivorous animals, 

hidi usually contains it to the extent of about 2 per cent. It is 

o found in small quantity in normal human urine, about 1 gramma 

g excreted daily, and ia formed more freely when a vegetable 

t is taken. In the urine of diabetic patients it is frequently 

Mofc in large proportion, and is abunilant in the acid urine of 

ions suffering from all kinds of fevers. Hifipuric aejd is also 

1 in the excrement of the lower animals, except that of birds, 

imcnts on th« produoUon of artiGoinl laurel water, ne Jour. 


which contains the allied substance ornithuric acid, having the 
constitution of a dibenzoyl-diamidoyaleric acid: ^ — 

cScaSi } :CACOOH. 

When benzoic acid is taken internally, it appears in the urine 
as hippuric acid, and hippuric acid may be obtained artificially by 
heating benzoic anhydride with amido-acetic acid (glycocine) or the 
zinc-salt of the latter with benzoyl chloride : — 

C7H5O. CI + C2H2(NH2)O.OH = CyHgO.O.CgHgCNHj)© + HCL 

Toluene, cinnamic acid, quinic acid, and phenyl-propionic acid 
when taken internally are also excreted as hippuric acid. Substi- 
tuted benzoic acids appear in the urine as substituted hippuric 

Hippuric acid crystallises in milk-white rhombic prisms ending 
in two or four facets, the crystals being often grouped in clumps. 
It has a slightly bitter but not sour taste. It melts at 187**5, 
and above 240** decomposes, with an odour of hay or fresh 
urine, and formation of hydrocyanic and benzoic acids 
and benzonitril,*a dark resinous or coaly mass being left. 

Hippuric acid requires about 600 parts of ice-cold water for 
solution, but dissolves tolerably readily in hot water. It is also 
soluble in alcohol, especially when hot. The aqueous and alcoholic 
solutions have an acid reaction. Hippuric acid is but slightly 
soluble in cold ether, but dissolves in acetic ether, and readily in 
boiling amylic alcohol. In chloroform, benzene, petroleum spirit, 
and carbon disulphide it is practically insoluble. 

When boiled for a time (half an hour) with dilute nitric, hydro- 

^ On boiling ornithuric acid with hydrochloric acid it almost immediately 
parts with one benzoyl group and yields benzoyl-ornithine, which on 
further boiling splits into benzoic acid and diamido- valeric acid or ornithine, 
(NU3),C4H7.COOH, a base of strong alkaline reaction and caustic taste. 

* Hippuric acid may be prepared from fresh cows* or horses' urine, which 
often contains sufficient to yield a precipitate on mere addition of excess of 
hydrochloric acid. If not, the urine should be boiled with milk of lime, 
filtered, and the filtrate neutralised, concentrated, and treated with excess of 
hydrochloric acid ; or the neutralised filtrate may be precipitated with ferric 
chloride, and the washed precipitate decomposed by hydrochloric acid. The 
hippuric acid is freed from colouring matter by recr^rstallising it from chlorine 
water, or treating it with bleaching powder and hydrochloric acid. 

' Benzonitril, or Phenyl Cyanide, CgHg.CN, is produced in a variety of 
reactions, but best by heating a mixture of benzoic acid and a thiocyanate. 
It is an oily liquid of 1 '023 specific gravity at 0°, boiling at 191% and having an 
odour like that of bitter-almond oiL It dissolves in about 100 parts of water, 
and is miscible with alcohol and ether. Boiling alkalies convert it into 
benzoic acid, and nascent hydrogen into benzylamine, C7U7.NH3. 



(one, or oxalic acid (or more rapidly if strong hydro cUoric acid 
leil), hippuric ncid undergoes hydroIyBis, the liquid on cooling 
lepositing benzoic acid, while a Ealt of glycocine (aniido- 
acetic acid) remainB in solution: — CgHgNOj+HjO = CjHB03+ 
C^gNOj. Strong alktdies cause a siuiilar change. A similar 
reaction takes place spontaneously in urine containing bippuric 
acid, under the inHuence of the ferments present. Hence only 
perfectly fresh urine will yield hippuric acid. If the urine be 
alkaline, aa is usually the case with that of herbivorous nianiDialH, 
the glycocine first produced splits up into ammonia and acetic 
acid ■.— CjHjNOj + H jO = C^H^Oj, + NH j. 

If hippuric acid be evaporated to dryness with concentrated nitric 
acid, and the residue heated, an odour of nitrobenzene ia evolved, 

Hippuric acid decompoees carbonates, and dissolves zinc with 
evolution of hydrogen. Its salts are mostly soluble and cr}-Gtal!isafale. 
The hippuratea of silver, lead, and copi>er are sparingly aohible. 

When ferric chloride is added to a solution of a hippuratc, a 
cream-coloured precipitate of ferric hippurate is thrown 
down, which contains more or less basic salt according to the 
greater or less dilution of the solution. The precipitate is almost 
insoluble in pure water, but dissolves in free hippuric acid, in 
excess of ferric chloride, and in alcohol. Tlie reaction with ferric 
Baits may be employed for the determination of hippuric acid in 
nrioe. For this purpose, the urine is acidulated with nitric acid, 
heated to boiling to remove carbon dioxide, neutralised with calcium 
carbouah', treated with excess of lead nitrate, and then diluted to 

I blown volume and filtered. An aliquot port of the filtrate is 
Ifb heated and titrated with a solution of neutral ferric nitrate 
^ch has been standardised with pure hippuric add, Tlie 
Ktion is at an end when a drop of the clear liquid gives a blue 
lorstion with potassium ferrocyatiide. The distinction between 
b point and the previous formation of the white ferrocyanide 
'lead is very sharp. 

On treating ferric hippurate or the solution of a soluble hippurate 
with excess of hydrocldoric acid, the hippuric acid separates sooner 
or later in long crystalline needles. These are distinguished from 
Eoic and salicylic acida by their crystalline form; by charring 
a hoated with strong sulphuric acid ; by giving off ammonia 
I ^nition with soda-lime ; and by not being dissolved on agitating 
p aolution with chloroform or petroleum spirit. 
S"©! the detection of hippuric acid in the urine of the herbivora, 
I frasb liquid should be treated with milk of lime, hlterod, 
I filtrate concentrated to a syrup as rapidly as possible, and 
• of hydrocbloriQ add uddoil, when hippuric acid crystallises 


out on standing. If the urine be at all putrid, benzoic acid will 
be obtained instead. They may be distinguished as just de- 

For the detection of traces of hippuric acid in human urine, the 
perfectly fresh liquid should be evaporated nearly to dryness at 
100°, the residue mixed with powdered sulphate of barium, a little 
hydrochloric acid added, and the whole exhausted with rectified 
spirit. The alcoholic solution is carefully neutralised with soda, 
and the liquid evaporated. The residue is mixed with a little 
oxalic acid, and again evaporated to dryness on the water-bath. 
The residue is exhausted with ether-alcohol, the solution distilled 
to a small bulk, boiled with milk of lime, filtered, concentrated, and 
acidulated with hydrochloric acid. Immediately or on standing, 
according to the quantity present, crystalline needles of hippuric acid 
separate, and may be filtered off and purified by washing first with 
diluted hydrochloric acid, and then with a little ether. 

Benzoic Sulphinide. Benzoyl Sulphonic-imide. 



The commercial product which is now becoming known by the 
inappropriate name of " saccharine " is quite a different body from 
that discovered by Peligot, and described under the name of 
saccharin in vol. i page 222. The "saccharine" of 
Fahlborg and List is a benzoyl-sulphimide, and may be 
regarded as an inner anhydride of ortho-sulphamido- 
benzoic acid.^ Thus : — 

Benzoic acid — 

CeHj.CO.OH or CgH,: J ^^ ^^ 

0-Sulphobenzoic acid — 

CeH,(S08H).C0.0H or C.H,: I ^^q^ 

0-Sulphamidobenzoic acid — 

CeH^(S0jNH2).C0.0H. or CgH^: { ^^q^ 

o-Sulphamidobenzoic anhydride or Benzoic sulphinide (Sac- 
charine) — 

CflH,: { l^' } :NH. 

^ To obtain saccharine, tolnene is first heated to 100"* with concentrated 
siilphnric acid, whereby it is converted into a mixture of ortho- and para* 
tolnene-snlphonic acids. The prodact is treated with cold water and w ^alV, 

masufacturk of saccharine. 27 

Sacchfirine forms a white powder of faintly aromatic odour, 
Tolatilising slightly at 100°, and melting at about 200'^ C. witli 
partial duuimposition. It crystalliseE from nn aqueous solution in 
thick fJiort prisms which are difficultly soluble in cold (1 in 1000), 
but moiv readily in boiling water (about 1 in 100). It is soluble 
ill alcohol (1 in 80), glycerin, and moderately so in ether, and is 
removed from its aqueous solutions by agitation with the last 
solTcnt. It dissolves with some difficulty in chloroform and 
beozmc, but b said to be insoluble in petroleum ether. In benzoic 
ftlfieliyde it dissolves very readily. 

Bturcliurine decompoeea carbonates, and forms salts, which are 
soluble in water, of the formula C„H,{SOjXCO):NM. 

Saccharine is remarkable for its intimiidij meeet taste, which is 
probably about 130 times that of cane-sugar,' and is perceptible in 
a solution of 1 iKii't in 10,000 of water. The sweet taste, which 
is associated with a faint and delicate flavour of bitter-almonds, is 
shared by its salU.^ Saccharine is quite uninjurious, even when 
tnkiiu in considemble quantities, but posses unchanged through the 
system, and may afterwards be detected in the urine. It possesses 
luodcrate antiseptic properties, and now receives numerous appliea- 
tions ne a sweetening agent under conditions where sugar would 
be objectionably.^ 

>tid tbe sulatioD of the resultant calcium snlts treated vith soilium carlxinsto, 
Uio llltere'l liquid eraponLted to dryoeu, and the aodium aalts completely 
ilmricateii. Tbc]' are then heated with phosphorus trichloride in u stream of 
cblorino. when *rtAo- and jpam-tolnone aulphonic chlorides are formed, together 
irilli pLofljihorna oxyehlorido and sodium chloride : — 

CtUjlCH,)SOrONa + PCI,4Cl,-C,H4(CH,)30,.Cl + FOCli + NiCL 
Thio nrtbo'tulphoaic chloride ia liquid, and after cooliuK is se)iaratiid from the 
•olid (TjrEtAllised para-corapouod hy a centrifugal machine, cooled by ice to 
MUM tl>* last truces of the latter to ciyatallisa. The ortlio-tolueuesulphoniu 
cUoride ii neit treated with dry smmoDia gas, which convurtd it into o r t h o- 
t«lB«n*-Bulpbiinia-amidr. C,H,(CH,)SO,NH„ and this iasepnnited 
It «mt«r fnim the ammoniuni chloride fotmeil at the aamo time. By treatment 
with potaKium permanganate and alkali, the amide is conTcrted into a salt of 
nrtho-aalpbamidobeDStoic acid, and this on treatment with a dilate 
mineral acid yield* thp corroaponding anhydride, or Bacoliarinc: — 

, B. Allen, P&arm. Jour., [8], jtriiL 436. The statements made 
itinfC III* TeUtive sneetaning jxiwers of saccharine and sugar vary very 
r, iM)||l&g IWim 180 ; 1 to 330 : 1, according tu diOureut obsorvers. 

idiog to E. ^V. OrBTill {Pharm. Jimt., [3|, xviii, 337), the sweet- 
ie Mlta of xaoi^liarine ia greater than that of the dee acid, while the 
h Uitn or the latter is destroyed. 

10 appciars likely to prove especially irekonio to those guJTeriDg 
, and will) couseijuently cannot Lake sugar. 


An aqaeoos solution of saccharine gives no reaction with ferric 
chloride, hut if previously neutralised with soda a brownish-yellow 
precipitate is formed. 

An aqueous solution of saccharine, if not too dilute (1 in 1000), 
gives a characteristic apple-green coloration or precipitate when 
boiled with potassium ferricyanide, a slight odour of hydrocyanic 
acid being produced. The precipitate is soluble in caustic alkali 
and reproduced by hydrochloric acid (D. Sutherland). 

When treated with borax in aqueous solution, saccharine is 
decomposed, with formation of benzoic and boric acids and sodium 
and ammonium sulphates (W. A. Nay lor, Pharm, Jour., [3], 
xviii. 437). 

When heated with hydrochloric acid, under pressure, to 150* C, 
toccharine is decomposed with formation of ortho-sulphobenzoic acid 
and ammonium chloride. 

When a solution of saccharine is evaporated with caustic alkali 
and the residue is heated to 250% salicylic acid is formed, 
and may be detected by rendering the solution of the residue neutral 
or faintly acid, and adding ferric chloride, when the characteristic 
violet coloration will be produced.^ On igniting a mixture 
of saccharine and caustic or carbonated alkali, an odour of 
benzene is evolved, and on dissolving the residue in water 
acidulated with hydrochloric acid, the solution gives a white 
precipitate of barium sulphate on adding barium chloride. For 
quantitative purposes a little nitre should be added during ignition. 
The saccharine represented may be found by multiplying the BaSO^ 
found by the factor 07 85. 

Bornstein has described a test for saccharine, based on the 
formation of a compound analogous to fluorescein. The saccharine 
is isolated by ether and the ether-residue heated in a test-tube 
with a slight excess of resorcinol and a drop or two of sulphuric 
acid. The mixture becomes yellow, red, and then dark green, and 
strong ebullition occurs with evolution of sulphur dioxide, which 
continues for a short time after the removal of the flame. The 
heating to ebullition is repeated once or twice, after which the 
mixture is allowed to cool, treated with water, and the solution 
supersaturated with an alkalL A reddish solution is obtained 
which exhibits a strong green fluorescence, perceptible with 1 part 
of saccharine in several millions of water. The reaction is also 
produced by ortho-sulphobenzoic acid. 

The intensely sweet taste of saccharine and its solutions and 
salts is in itself highly characteristic, as is the formation of sweet 

^ Or the acidulated solution may be shaken with ether, the ether separated 
and evaporated, and the residue treated with ferric chloride. 



vaponrs and sublimate on heating.^ From sugar and other Ewoi?t 
enbetsnces sacchnrme may be separated by agitating the acidulated 
solution with ether. Phosphoric acid is to be preferred for acidu- 
lating the liquid. The residue obtained on evaporating the ether 
will have an intensely sweet taete, and will respond to the testa 
ftir saccharine already mentioned. In the ease of beer, the bitter 
taste of the ethereal extract will overpower the sweet taste of any 
saccharine tliat may be present, but sulphates will be found in 
the residue left on igniting the ether-residue after rendering it 
alkaline with soda (free from sulphates).* 

Clause 5 of the Customs and Inland Revenue Act, 1888, enables 
the Commissioners to prohibit the use of saccharine in beer, at their 
discretion. This they have done (May 1888) till further notice. 

For the detection of saccharine in mine, C. Bchmitt recom- 
m«ntls tliat 100 c.c. ahould be acidulated with sulphuric acid and 
shaken with 50 c.c. of a mixture of equal measures of ether and petru- 
lesm spirit. Aft«r separating the upper layer, and agitating the 
aqueous liquid with another quantity of the ethereal mixture, the 
ether- petroleum is evaporated with a little caustic soda solution of 
the residue heated to 250° and tested for salicylic acid. Of course, the 
alecnce of salicylic acid from the original wine must be first assured. 
CouHBROiAL Sacchabine Is of eomcwhat variable quality. 
According to Salkowalci it is liable to contain a considerable 
quantity of ortho-sulphobonzoic acid, and para-Bulphamidobenzoio 
«cid. The rmdue on ignition ranges from 0'6 to nearly 7'0 per 
cent. The ash consists chiefly of sodium sulphate, and its weight 
inulliplied by 3 may be regarded as roughly representing the sodium 
soiphobenzoate and sulphamidobeuzoate present. In some coses 
the ash has been found to contain distinct traces of iron. Sutherland 
has met with saccharine having a strong odour of chlorine. 

Saccharine should not blacken when treated with cold con- 
centrated sulphuric acid, and even on heating the mixture to 100° C. 
tot ten minutes the coloration should merely he faint brown. 
^^^^ D. Sntherland {Jour. Sot. Chsm. Ind., vi 808) finds the microBCOpic 
^^^■Mlaocs of the lubliniHteliigljly cliaracteristic. 

^^^^■TilB aathor foaad that if » alnglo tablet of saccbarine (contaimng 0*15 
^^^BpD) vera added to a [liut ol beer, tlie presence of Haccliurine could be readily 
^^MtaeUd lij this mothod. That ifl, the b«ar was concootratsd, scidiilatod witli 
[iha«|ihoric acid (though tbia »tep waa UDUeceaaary), agitaUd nith etlier, and 
the riMidan obtaiurd on eraporating the etber tondared alkaline with «oda, 
IgnitBl, and the prwliict t^ted for tulphatea. A blank eipurimont showed 
no Imiv of mlphatei. Tbe lUbseiineDt manipulation ia facilitated if the beur 
bw trro-Icd oitb a alight exeess □( Uad loeUto and Sltored before agitating nith 
•thv. There is no oecssioa to leirioTe the excess of lead ; in fact, the Qs« of 
jhurettcd hydrogeji should be avoided {Aiutlgil, xiii. 105). 



If saccharine be washed on a filter with ether, and the ether 
agitated with ten times its measure of water, ferric chloride shoidd 
not produce in it either a precipitate or a violet coloration. 

The proportions of recU aaccharine present in a sample may be 
found by extracting the aqueous solution with ether, and evaporat- 
ing the ether. A good approximation may be obtained by 
titrating the aqueous solution with decinormal soda and litmus or 
phenolphthalem. 1 c.c. of decinormal alkali neutralises 0*0183 
gramme of saccharine. 

Sugar and glttcose will be left insoluble after repeatedly treating 
the solid sample with ether. A better separation can be obtained 
by repeatedly agitating the acidulated aqueous solution of the 
sample with ether. If, after removing the ether, the aqueous 
layer be found, after neutralisation, to have a distinctly sweet 
taste, the presence of sugar is certain. The quantity can be 
ascertained by Fehling's solution after inverting the sugar, and 
preferably after removing the saccharine by ether ; but saccharine 
does not i*educe Fehling's solution. 

The saccharine pellets and tabloids of commerce consist in some 
cases of nearly pure saccharine. In others they are mixtures of 
saccharine with sodium bicarbonate, starch, <&c. 

"Dextrosaccharine" is the name given by Fahlberg to 
a mixture of 1 part of saccharine with from 1000 to 2000 parts 
of commercial glucose. The product is indistinguishable in taste 
from the best cane-sugar. 


Phenyl-acrylic Acid. 

CgHgOg = C^O.OH = CeH5.CH : CH.COOIL 

Cinnamic acid occurs ready-formed in liquid storax, Tolu and 
Peruvian balsams, and in some samples of ^rum benzoin ; also in 
old oils of cinnamon and cassia, which sometimes deposit it in 
largo prismatic crystals. 

Cinnamic acid may also be prepared synthetically by a variety 
of reactions, including the following : — 

a. By the oxidation of cinnamic aldehyde, CgHg-COH, 
which constitutes the greater part of the oils of cinnamon and cassia. 

b. By the saponification ofstyracin (cinnyl cinnamate) or of 
cinnamein (benzyl cinnamate) : — CyHy.CgHgOg + KOH = 

c. By heating benzoic aldehyde with acetyl chloride in a sealed 
tube to 120^-130" C.:—C7HeO+CjH80Cl = HCl +0^802, 



A By heating benaiic aldehyiie with acetic anhydride ami 
aodiniu acetate : — 2C7HgO + C5tHjO.O.CgHjO = 2C9l4o5+HjO. 

B« part played hy the sodium acetate is obttcure. 
ft By the action of sodium acetate on beuzylene diehloride 
Spared by the action of chlorine on toluene) : — CbH5.CHCI,+ 
!Ha.COONa = 2NaCl + CflHs-CH : CH.COOH +Cn3.C00H. 
He synthetical production of cinimmic acid on a largo scftle has 
imtly act^iiired much interest aa the first step in the formation 
Utificial indigo. 

Cinnamic acid ciystallisea in colourless, monocliuic prisms or 

laminsB having a specific gravity of 1'247. It mclta at 133° C, 

and distils with more or less decomposition at about 300*. If 

^^dpwly distilled alone, or more readily if heated with lime, it splits 

^^no cubon dioxide and cinnamene, C^Hg, a small quantity of 

^^^Kilbene, G]tHjj, being also produced.^ 

^^HlCinnamic acid dissolves sparingly in cold wnter, but readily in 
^^Hitliiig water, alcohol, and ether. 
^^BId ita general properties, cinnamic acid presente a close 

^^|n> CiHHAMENE, (tyrolene, Btyrol, or ptienjl-Bthfleiie, (C,B,)CH:CH„ 
«zl«ts in «niall quantity ready- formed in liijajd titorsx (paga 87], aad may lie 
extracted by diatilHn); tbe balsam witb water to wliich carbonata of sudiuni 
bM bfen Added to nentrsltse the free oinnamic acid. Ths hyilrocorbon pasaiis 
over with steam, and colleats as an oil on the anrface of the distillate. 
C^namene may also be obtained eynthetically, anil, aa stated abore, by heat- 
ing dnoamiG ncid alaoe, or in odtnixlure with lime or baryta, The reaution in 
the latter aae is exactly parallel to that by wliich benzi^no ia produced Trout 
bentoic add and methane from aeetic acid, 

CiDUameDe ia a colourless, mobilo liquid, having a pleaannt aromatic 
odour. It remuos fluid at ~ 10° C. aad boils nt 146°, the contents of the 
retnrt being liable to rise suddenly in temperature from farmatioD of nicta- 

nsumbles ethylene in its j>ropGrty of conibiniug readily with 

I, bromine, and iodine. The dihrom'ide, C,H|,Br„ is most con- 

iDlly obtained by adding bromine to a solution of the hydrocarbon in 

ifonn. By oxidation, ciunaniene ia readily concerted into benzoic 

.C,H(, is formed slowly at Che ordinary temperature, and 
a beating ciDnamene in a seated tobe to S00°. It is a trauapnrent, 
photM, odourless solid of high rcfroating power, aoftening ou applicatioa 
•at, when it may be drawn out into threads. On distlllutiou, it is reoon- 
all) danatueoe. Metacinnamcno is insolnble in water and alcohol, and 
7 sparinf^y soluble in ether. 
TILBIMK, or diphenyl-ethylene, (C,Hj)CH,CH(C,H(). crystallises in 
u plalos, mdts at 120°, and boils nt about 308°. It unites with bromine 
to form a dtbromide, C^HuBr^ crystallising in silky ueciLles which melt 



resemblance to benzoic acid, the following being the more ready 
points of distinction : — 

Melting point, 

Boiling point, .... 

Reaction in nentral solution : — 

With ferric salts, . 

With manganous salts, . 

CiDnamio Add. 

las'* -8 C. 

800" C. 

Beoaoic Acid 

i28'-8 a 
249** a 

No precipitate. 


White, becoming 

yellow and crystalline. 

Cinnamic acid is also distinguished from benzoic acid by the 
smell of bitter-almond oil developed on warming it with chromic 
acid mixture. The same odour is produced by boiling cinnamic 
acid with water and lead dioxide, the last body gradually becoming 
yellow and being partially converted into benzoate of lead. 

When fused at a moderate temperature with caustic potash, cinna- 
mic acid is split up with evolution of hydrogen and formation of potas- 
sium acetate and benzoate:— C9Hg02+2KHO = KC2H302 
+KC7H502+H2.^ The presence of an acetate in the product is 
a proof of the existence of cinnamic acid in the original substance. 

Benzoic acid maybe separated from cinnamic acid by crystallisation 
from boiling alcohol. The acids may also be separated by distillation 
in a current of steam, when benzoic acid nearly free from cinnamic 
acid passes over. By careful sublimation, the benzoic acid may also 
be completely separated, as little cinnamic acid volatilises below 200*. 

It is probable that cinnamicacid might be determined in admixture 
with benzoic acid by titration with a standard solution of bromine. 

J. Kachler {ZeUs, /. Chein., [2], vL 59) gives the following 
table showing the melting points of various mixtures of cinnamic and 
benzoic acids. The compound 2Bz.0H+Cn.0H melts at 95* C. : — 

Cinnamic Acid. 

Benzoic Acid. 

Melting Point 

Per Cent. 

Per Cent 























87 1 















' The change is strictly analogous to the fonnation of an acetate and 
palmitate by fusing oleic acid with caustic potash : — 

C18H84O2 + 2KH0 - KCaHjOj + KCmH^O, + H^ 


The metallic einnamaies much resembk- llie bcnzoutes. Thuy 
&n umiuiKjrtant. 

Cizmamic Ethers. 

By the Huljstitution of the basic hydrogen of oinnfliuio add by 
alcohol-raJicals, cinnaniic ethereal salts are obtained, aome of whicli 
I an of iniportauci), 

£tbtl CmsijiATK, CjHg.CgHjO.j, ta proJueeJ by distilling 
laUier cinuamic acid, aluohol, and Btrong sulphuriu acid ; or by 
rating a strong alcoholic solution of ciiinamic acid with hydro- 
lorJc acid gaa. It is a limpid liquid of 130 specific gravity, 
; at 265° C. WhiiQ treated with a mixture of strong nitric 
I anlphiinc acids, avoiding rise of tampertttura, it is converted 
into a mixture of ethyl para-nitrocinnamute and ethyl ortho-tiitro- 
cmoiutial«. Ttio lutter body crystallises in prisms which melt ot 
130', iho para-eoni pound in fine, very thin, slightly yellowish 
aeedles which molt at 13S*'5 C. On heating the mixture of thu 
elJien with alcohol the ortho-compound only is dissolved, and 
~ " ' a cooling in largo yellowish noedloa When treated 
I stning alkali, it is saponified with formation of ethyl alcohol 
ussiam ortho-nitrocinnamate, from which free o r t h o- 
stnnamic acid, CjH,(N0j)Oa, can be obtained by 
in KciiL By treating this bmly with bromine it is converted 
n additive compound of the formula CgH,(N0j)BrjOj, whicli 
' csiefut treatment with caustic soda yields sodium bromide 
the sodium salt nf orthon i tro-phen y 1 propiolio 
It d, (VHsNOj. or CoH/NO,).Cg.COOH. This body, when acted 
ft Rilnuing agent^ such as nascent hydrogen, glucose, or sodium 
ute, yields indigo-blue or indigotin, thus: — 
NOj+H,= C8HjNO + C0g+H30. 

' I by the foregoing series of reactions that the production of 
il indigo on a monufactunng scale has been effected. 
en, CiSNAMATB. Ciunomein, CjII^-CuHjOj. This body 
Mready-fonncd in Peru and Tolu balsams. It may be obtained 
9 admixture of cinuyl cinnamate hy treating the former 
inc« with carbon diaulphide, separating tlie insoluble matter, 
t distilling off tlie solvent from the solution. 
~' '. cinnamate has an ngrconble taste and feeble aromatic 
, nwiinhhng that of Peruvian balaiim, but without the 
pipynuiuatic enndl obBurvable in tho latter. It is commonly 
" ■ as an oily lii^uid which is liable to solidify with 
into a crystalline isomeric body called meta- 
nAmuIn. But when obtained pure by boiling together 
tyl chloridd, nluuhol, and dry sodium cinnamate, it forms short 
!. TAUT I. C 

34 STYRACm. 

shining white prisms which melt at 39* C, and may remain 
liquid for a considerable time even if cooled to 0". Benzyl 
cinnamate has a density of 1'098 in the liquid state, and distils 
with slight decomposition between 225° and 235°. It is nearly 
insoluble in water, but is readily dissolved by alcohol, ether, carbon 
disulphide, &c. 

By long exposure to air and light, benzyl cinnamate becomes 
rancid and acquires an acid reaction. It is readily saponified by 
alcoholic potash, with formation of potassium cinnamate and 
benzyl alcohol, C7H7.OH. 

CiNNYL Cinnamate. Styracin. CgHg-C^HyOg. This body occurs 
together with benzyl cinnamate in liquid storax, and Peru and 
Tolu balsams. It crystallises in tufts of beautiful prisms, which 
are devoid of smell or taste and melt at 44° to a liquid which 
remains viscous long after cooling. It distils without decomposition 
in steam heated to 1 80°. Cinnyl cinnamate is insoluble in water 
and but sparingly soluble in cold alcohol or petroleum ether, but 
is easily soluble in ether or carbon disulphida When treated 
with alcoholic potash it is saponified with formation of 
potassium cinnamate and 

Cinnyl Alcohol, Styryl Alcohol, or Styrone, CgHg.OH. When 
cinnyl cinnamate is cautiously distilled with aqueous potash, a 
milky distillate is obtained, and on saturating it with common salt 
the cinnyl alcohol forms a creamy or oily layer on the surface. It 
may also be extracted from the distillate or the original liquid by 
agitation with ether. 

Cinnyl alcohol forms soft, silky needles having a sweet taste 
and an odour of hyacinths. It melts at 33°, and distils unchanged 
at 250° C. It is soluble in about 12 parts of cold water, a hot 
saturated solution becoming milky on cooling and remaining so for 
several hours, when the cinnyl alcohol separates in crystalline 
needles, very soluble in alcohol and ether. 

Cinnyl alcohol possesses valuable antiseptic properties, being as 
powerful in this respect as thymol. A saturated aqueous solution 
forms a convenient dressing for ulcerated surfaces. 

Cinnyl alcohol is converted by cautious oxidation into cinnamic 
aldehyde and cinnamic acid. With chromic acid mixture it becomes 
hot and yields cinnamic acid, which separates on the surface, 
and on heating this becomes further oxidised to benzoic aldehyde. 

Aromatic Balsams. 

The aromatic '* b a 1 s a m s " are such of the oleo-resinous exuda- 
tions of plants as contain benzoic or cinnamic acid, and yield 
cinnamate or benzoate of methyl or ethyl by dry distillation. Tho 



"balsam" is misapplied to "Camida balsam" aiid "copaiba 
1," which are true turpentines (vol. ii. page 451), and do 
^ contain or yield benzoii; or cinnamic acid. 

e aromatic balsams of practical interest ore gum benzoin, 
t Bource of the bensoic acid of pharmacy; Peruvian 
llsam; Tolu balsam; and liquid storas. The first 
e will be conveniently considered separately, and the others 
njointly under the liead of "Cinnamic Balsams," 
^ Gun Benzoin. Gum Benjamin. Gum benxoin Is a balsamic 
teein obtained from Slt/rax hemoin (and probably some allied 
Bpeciea), a tree growing in the Malay Peninsula and Arclii[)clago. 
Sevaral varieties are known in commerce, those from Siam, 
_3iiioatn, and Penang being the chiel 

a betamn is the finest variety and occurs in tears, or masses 
isiating of loosely agglutiniited tears, of a yellow, reddish, or 
I Dolour externally, and translucent, milk-white, or almond- 
I iuternallj. It sometimes occurs in lumpe of a brownish 
or, which when broken present an amygdaloid appearance from 
• white tears imbedded in the darker coloured resinous matter, 
moM benEoia melts at 75° C. This variety of benzoin is never 
eloped in calico. 

I beTooin has a weaker and less afi^eable odonr than 

t of Siom, It occurs in large rectangular blocks, marked with 

tite inijireffiion of a mat and covered with a white linen cloth. 
When bnjken, few but large white tears are seen in it. It ia 
generally composed of brown resiniform matter with numerous 
'J whit« chips or pieces intermixed, which give it a granitoid 
The white portions melt at 85° and the darker 
itions at 96° C. 

' benxoin closely resembles the Sumatra variety, but 
lally differs from it in colour, and more so in odour, which 
1 suggests that of storax. 
I Gum benzoin always contains more or leas bark and similar 
^Mnttore, and in inferior specimens these are present in very large 
pT»t>ortion. With the exception of these impurities, benzoin 
should dissolve in five times its weight of alcohol The resultant 
tincture from Siam benzoin has a distinct red colour, while that 
J«d by the other varieties is brown or yellowish -brown. On 
of water, the liquid becomes milky, and the odour 
I particular variety is readily perceived. That of 
a benzoin is pleasantly balsamic and similar to vanilla ; Penang 
I often smells like storax; while the odour of Sumatra 
I is fainter, lt!ss pleasant, and distinct from either of the 


Gum benzoin contains several resins, a trace of volatile 
oil, and from 12 to 20 per cent, of benzoic acid. Siam 
benzom also contains vanillin, and the presence of cinnamic 
acid has been observed in all three kinds, though the proportion 
varies considerably, and it is often altogether absent.^ 

The presence of cinnamic acid may be recognised by the odour 
of benzoic aldehyde (bitter-almond oil), developed on adding 
potassium permanganate to the hot liquid obtained by boiling 
the benzom with milk of lime and filtering. Or the tincture of 
benzom may be treated with water, and the liquid filtered from 
the precipitated resin treated with solution of permanganate or 
bleaching powder. Another method is to triturate the benzom 
with lead dioxide and distil the mixture with water. 

The determination of the cinnamic acid may be approximately 
effected as indicated on page 39. As much as 11 per cent has 
been found. 

Gum benzoin usually contains from 12 to 14 per cent of 
benzoic acid, but occasionally 1 8 or 20 per cent is reached. The 
proportion present may be ascertained by the following sublimation- 
process : — The sample is powdered, mixed with sand, and the 
mixture heated in a beaker or earthenware jar, furnished with a 
cap of filter-paper pierced with small holes. Over this is placed 
a cone or hood of stout paper. The benzoic acid sublimes and 
condenses on the inside of the hood, any oil and impurities being 
retained by the diaphragm of filter-paper. 

Another method for the approximate assay of gum benzoin is 
to digest 10 parts of the powdered gum with 6 parts of slaked 
lime and 100 parts of water. After six hours, the liquid is 
boiled, filtered, and the residue washed. The filtrate is con- 
centrated, rendered strongly acid with hydrochloric acid, and 
thoroughly cooled. The precipitated benzoic acid is filtered oif, 
washed with a little cold wator, and dried between folds of 
blotting-paper. The small quantity of acid retained in the 
mother-liquor may be extracted by agitation with chloroform, 
and the residue left by the spontaneous evaporation of the 
chloroform may be added to the main quantity of benzoic acid. 
A preferable plan is to agitate the acidulated liquid at once with 

^ The presence of cinnamic acid, as indicated by the production of an odonr 
of benzoic aldehyde on heating the benzoin with chromic acid mixture, is said 
by M a t e r to be specially characteristic of the Sumatra product He gives 
as specially distinctive characters of Siamese benzoin : — The production of a 
cherry-red colour when sulphuric acid is added to the residue left on evapor- 
ating the solution of the gum in petroleum ether ; the complete solubility 
of the sample in chloroform but not in ether ; and the lower melting-point 



cblorofonn, without ^tering off the precipitated benzoic acid, and 
to subsequently recover the benzoic acid from its chlorofonnic 
solution by the spontaneous evaporation of the solvent, assisted by 
a current of dry air from a bellows. If ether be substituted for 
the chloroform the product will contain a small quantity of water, 
and the determination will be too high. In any case, the benzoic 
acid extracted by chloroform or ether from Siamese benzoin wUl be 
liable to contain vanillin {Jour. Chem, Soc,, xxxvi. 245). 

For an account of the bodies accompanying benzoic acid in 
benzoin, see footnote on page 16. 

CiNNAMio Balsams. 

Under this description are included Peruvian balsam, Tolu 
balsam, and liquid storax. These substances are all closely allied 
to one another, but in their physical properties and quantitative 
chemical composition, they present considerable differences. 

The following table exhibits the more important distinctions 
between Peru and Tolu balsams and storax : — 

BoUnical origiD. 


Coniiatency and 



Ferayian Balsam. 

Uyroxylonj several 

San Salrador, Central 

Viscid, bnt not glo- 
tinons, dark-brown 
liquid, resembling 
molasses; transpa- 
rent and reddish- 
brown in til in 
layers. Gradually 
thickens on ex- 

Bitter and persis- 
tently irritating. 

Agreeable and like 

that of 


Tolu Balsam. 


Columbia, Turbace, 
Tulu, and Venezuela. 

When fresh, yellow, 
transparent, and 
liquid ; changing 
rapidly to reddish- 
brown, and becoming 
solid and friable, or 
brittle; but softening 
between tbe teeth, 
and readily fusing. 
Such samples have a 
granular crystalline 
structure; and crys- 
tals of cinnamic acid 
are visible under the 

Sweetish, aromatic, 
and somewhat irri- 

Aromatic, like lemon 
and jasmine, or sug- 
gesting vanilla ; more 
apparent on warming. 

Liquid Storax. 

StyroT oMcinalis ; 

Asia Minor. 

Brown Ish-yeUow or 
greyish, viscous 
liouid. Under the 
microscope shows 
globules of water, 
tftbular crystals of 
cinnamic acid, and 
fi-eciuently feathers 
of styracin. 

Pungent and bal- 

Sweetish and resem- 
bling vanilla, or 
strong and oppres- 

* According to Bail Ion {Pharm. Jour., [8], iv. 382), Peru and Tolu 
balaams are derived from the same tree, Toluifera balsamumy and the 
differences between the two products are due merely to differences in the mode 
of obtaining them. 



Peruvian Balsam is readily soluble in all proportions in absolute 
alcohol, glacial acetic acid, chloroform, and acetone ; with an equal 
bulk of alcohol and ether it yields a clear solution, which on further 
addition of the solvent becomes turbid and deposits resin. Diluted 
alcohol takes up only a small proportion of the balsam. Ether 
dissolves it. 

Cold petroleum ether only dissolves the cinnamein and cinnamic 
acid of the balsam, but on employing the hot solvent styracin is 
also dissolved, and is deposited in crystals on cooling. Carbon 
disulphide acts in a characteristic manner. Agitated with three 
times its weight of the cold solvent, the greater part of the balsam 
is dissolved to a colourless or slightly coloured liquid, from 10 to 
16 per cent, remaining as a reddish-brown, sticky liquid, adhering 
firmly to the sides of the glass, while the solution may be readily 
poured off. 

Tolu Balsam is readily soluble in alcohol, ether, chloroform, and 
solution of caustic potash ; but benzene, petroleum ether, and 
carbon disulphide have little action on it, owing to the compara- 
tively small proportion of cinnamic acid and cinnamic ethers 

Liquid Storax contains water and various impurities. "With the 
exception of these foreign matters, it is soluble in alcohol, ether, 
or chloroform. With an equal weight of warm alcohol it yields 
a turbid solution having an acid reaction. This solution, when 
filtered and evaporated, yields not less than 70 per cent of the 
original balsam as a brown semi-liquid residue, which constitutes 
the "Prepared S t o r a x, B. P.," and is completely soluble in 
ether and carbon disulphide. It is soluble in benzene, but only 
partially soluble in cold petroleum ether. On heating it dissolves 
more freely, and the solution deposits crystals of cinnamic acid and 
styracin on cooling. 

The details of the chemistry of the cinnamic balsams requires 
careful revision, though the main constituents of these products are 
satisfactorily identified. They are all closely allied to one another, 
consisting essentially of the benzyl and cinnyl ethers of benzoic 
and cinnamic acids, mixed with resinous oxidation- products of 
these ethers, free benzoic and cinnamic acids, and the hydrocarbon 
cinnamone. The leading or characteristic constituents of Peru 
balsam may be said to be the cinnamein or benzyl cinnamate 
(page 33) and styracin or cinnyl cinnamate. Free benzyl 

^W. A. Naylor (Pharm, Jour,, [3], viiL 624) has described a specimen 
of spurious Tolu balsam sold as genuine by a large firm, which contained no 
cinnamic acid or cinnamein, and was wholly soluble in carbon disulphide, 
chloroform, ether, and hot alcohoL 


>bol is also present. In Tolu balsam, on the other hanij, the 

irtion of resin is very large ; but of the ethers benzyl benzoate 

lominatcs, and cinnyl benxoate and cinnamate exist in but 

proportions. In liquid storax of Mexican origin, pbenyl- 

i cinnamate exists iu considerable quantity; two isomeric 

ihol-like bodies called a- and ^-storosinol, to which the 

fonnda CjgHj^.fOH), is attributed {Ber., is, 274); and the 

cinnainic ethers of these bodies. 

In many cases there is reason to believe tliat tlie bodies detected 
in the cinnamic balsams have been decomposition-products due to 
the nietliods of analysis employed. The following method may be 
ado|tled for the recognition of the principal constituents of aromatic 
The substance is dissolved in two or three parts of 
ler, and filtered from any insoluble matter. The solution is 
ited with an equal measure of normal solution of caustic soda, 
alkaline liquid withdrawn, and the agitation repeated with a 
fteeh qunntity of caustic soda solution. If desired, the total 
acidity of the balsam can be deduced from the titration of an 
aliquot part uf the alkahne liquid.' The ethereal layer is then 
washed with water, and distilled ot a gentle heat, the residue of 
neutral ethers, &c, being weighed. The residue is then frac- 
tionally distilled. 

The first fraction will contain any einiiamene which may be 

prceent, tha next being rich in benxyl dleohol, which may be 

extmcted by agitation with water and will yield benxoic aldehyde 

and atdd by oxidation. Cinnyl aicohol and henxyl benzoat^ pass 

ov«r next, and at a higher temperature bemyl cinnanuite and 

dimyl beruoate and einnamate may be obtained. These ethers 

suffer more or less decomposition unless the distillation is con- 

:ted in vaeuo, and hence the last fractions consist largely of 

^il, which can be removed by agitating the distillate 

sodinia carbonate solution. The alkaline liquid separated 

_ im the ethereal aolution should be saturated with carbonic acid, 

wbich precipitates much resin. The liquid is filtered, concentrated, 

antl t^u1ted with hydrochloric acid, when a bulky precipitate is 

obtainwl representing the free henzoie and einnamic aeiilg of the 

Thuse bodies may be identified by their ordinary reactions, 

Lheir approximate separation, one-half of the precipitate may 

boiled with milk of lime and the liquid filtered and allowed to 

>me cold, when the sparingly soluble calcium cinnamate is 

litcd in shining nee-dlos, the more soluble benzoate remaining 

volution. The methods indicated on p^e 32 may also bo 

Or the minple may be dinolved in pther ani] the solution diluted with 

ihol and titrated wilb aUiiJai'tl caustic gods and pbeuol-phthalvlii. 

suffer ni 
^^^buted I 

^^Hsptn tb< 


utilised for the separation of the two acids. When an exact 
determination of the free acids of a balsam is desired, it is better 
to agitate the ethereal solution with sodium carbonate instead of 
with caustic soda, as the latter reagent is liable to cause some 
decomposition of the ethers. 

Except for purposes of research, it is rarely necessary to make 
so full a proximate analysis of a balsam as is indicated above, but 
a determination of the percentage of total ethers, of free acids, and 
of resin is of value for judging of the genuine nature of Peruvian 
balsam, which is very liable to adulteration. 

Adultbrations of Peruvian Balsam. 

Peruvian balsam is liable to adulteration with the cheaper 
cinnamic balsams (Tolu and storax) ; copaiba and gurgon balsams ; 
colophony ; an alcoholic solution or extract of gum benzoin ; 
alcohol ; and even with fixed oils, especially castor-oil. Hence the 
examination of Peru balsam for the detection of these adulterants 
is of some importance.^ 

All the usual adulterants of Peruvian balsam have a lower 
specific gravity than the genuine substance, which varies in density 
between very narrow limits, 1*150 being the maximum and 1*137 
the extreme minimum. Any sample having a lower density than 
1*138 should be regarded with suspicion. 

The presence of alcohol is indicated by the loss of volume 
undergone by the balsam on agitating with water. Small 
quantities may be detected by distilling the sample with water 
and sodium carbonate, and examining the distillate by the iodoform 
and chromic acid tests. 

Much information respecting the quality and purity of a sample 
of balsam can be obtained by a judicious treatment with solvents. 
Thus, on treatment with three times its volume of carbon di- 
sulphide, Peruvian balsam dissolves to a faintly coloured solution, 
1 6 per cent, of residue, at most, remaining as a dark sticky mass 

^ The following references relate to original or translated articles of recent 
date on the assay of the aromatic balsams : — 

E. Basse, Pharm, Jour,^ [3], viL 

F. A. Fliickiger, Pharm, Jour,, [3], 
xii. 45. 

C. Grote, Year-Book qf Pharm,, 

1881, p. 219. 
H. Hager, Year-Book of Pharm, , 

1879, p. 257. 
P. MacEwan, Pharm, Joiwr,, [3], xv. 


R. v. Matterson, Year - Bock of 

Pharm., 1876, p. 188. 
W. A. Naylor, Pharm,, Jour,, [8], 

viii. 624. 
J. Peckolt, Pharm, Jour,, [8], xL 

0. Schlickum, Pharm, Jour,, [8] 

xiii. 821. 
A. Andr^, Jour, Chem, Soc, 1. 181. 



which adheres finnly to the side of the glass, allowing the solution 
to be poured off. Any dark coloration of the latter indicates 
adulteratioiL Petroleum dissolves Peru balsam less completely, 
but for this reason its indications are in many respects more 
reliQ.ble than those obtained with carbon disulphide. Thus cold 
petroleum ether dissolves the cinname'in (benzyl cinnamate) 
of the sample, leaving the greater part of the styracin (cinnyl 
cinnamate), which in its turn can be dissolved by treating the 
residue with ether or hot petroleum spirit. Either of the above 
solvents will dissolve the free benzoic and cinnamic acid 
of the sample as well as the cinnamein, and hence a more accurate 
determination of the latter, which may be considered the essential 
and characteristic constituent of Peruvian balsam, can be obtained 
if the free acids be first neutralised. For this purpose, the balsam 
should be thoroughly mixed with slaked lime and a little water, 
and heated on the water-bath for some hours, small quantities of 
water being added at intervals. The dry mixture may then be 
extracted with petroleum spirit 

A direct determination of the free acid of the sample will 
indicate an adulteration with benzoin. For this purpose the 
balsam should be dissolved in ether and the solution diluted with 
alcohol and titrated with decinormal caustic soda, using phenol- 
phthalem as an indicator. The results are conveniently expressed 
in terms of cinnamic acid. The presence of colophony will wholly 
vitiate the result of the titration. 

The following table shows the densities and behaviour with 
solvents of Peruvian balsam and its adulterants : — 












dpeciflc grayity, 

1-187 to 



•916 to 

1-04 to 


Percentage solnble in) 

three parts carbon di-> 
aolphide, .) 

84 to 90 






Percentage soluble in) 

petroleum spirit (sp. gr. >• 

41 to 68 






•TlOX . . . .) 

Percentage solnble in) 

carbon disulphide after V 

26 to 87 


• •• 

• •• 



preTious treatment, .) 
FBToentsge soluble in ) 


petroleum ether after I 
treatment with lime and i 





to 66 per 




WMvCa^ • / 

Dinolred by ether from) 

residue from last treat* }- 



• •• 



• •• 

ment, . . . .) 

The petroleum spirit solution yielded by adulterated balsam 
gives on evaporation a residue which often has a characteristic 



odour. In the Glennan Pharmacopoeia it is stated that it should 
not have the odour of turpentine, storax, or copaiba, and should not 
give a hiue or greenish-blue colour with nitric acid (sp. gr. 
1 '30-1 *33). P. MacEwan has pointed out that the nitric acid test is 
vitiated unless the petroleum spirit solution he freed from suspended 
particles by filtration, and that the strength of the acid employed 
materially affects the colour obtained. He ohtained the following 
results by allowing 1 drop of the petroleum spirit residue to fall 
on the surface of 10 to 20 drops of the acid contained in a 
porcelain dish : — 

Colour Reaction with Nitric Acid. 

Sp. Gr. 1-42. 

Sp. Gr. 1-80 to 1-38. 

Pure Peruvian 

Balsam containing 

Balsam containing 

Balsam containing 

Pale green, developing 
slowly, the margins 
being violet ; on stand- 
ing the whole becomes 

Pale ffreen, darkening to 
decided opaque green 
(without violet tint), 
changing to brown on 

Immediate bright emerald 

Intense blue. 

The original yellow colour 
of the residue darkens 
or becomes an indistinct 

Reaction the same as with 
pure balsam. 

Gradually bright green 
spots on pale brown 


From these results it is evident that the best results are obtained 
by the use of the strong acid (sp. gr. 1 '42). 

The presence of benzoin will tend to decrease the percentage 
soluble in carbon disulphide, while in the case of all other 
adulterants the proportion of soluble matter is increased. A 
further indication of adulteration is afforded by treating the sample 
with lime and water, drying, and extracting with petroleum spirit. 
Under these conditions, the matter dissolved from genuine Peru 
balsam is tolerably constant at 41 per cent., so that a sample 
yielding sensibly below 40 per cent., under these conditions, may 
be fairly regarded as adulterated, and the proportion of admixture 
can be approximately ascertained.^ Tolu balsam and bemcHn can 

^ The difference in the petroleum extract multiplied by 2 '5 equals the per- 
centage of true Pern balsam present. Some confusion in the interpretation of 
this test would be caused by the presence of copaiba, but the portion of this 



detected with certainty in thia manner, and can be diatinguished 
tittsting the free acid in tlie portion of the origiua] balsam 
lUe in ether or petroleum spirit. 

Various other testa have been devised for the detection of 

Iteiants in Peru balsam, the following being the most note- 

: — According toFIuckiger, iften drops of genuine Peru 

be nibbed in a mortar with O"* gramme of a 1 a k e d lime, 

product remuDS soft, kneadable, or somewhat friable, and 

ly divisible even after long exposure in the water-bath, All 

\9 naual adulterants, except fixed oil, occasion more or less 

hardening of the mass. With 10 per cent, of atnrax, a smeary, 

sticky paste is obtained, becoming of pilular consistence, and in 

hours crumbly ; with two drops of rectified spirit previously 

id, the mixture very rapidly becomes brittle and crumbly. In 

ler case, the odour of storax is well marked. With 10 per 

_ it. of copaiba, a very thin paste is produced, which becomes 

pilular in five minutes and brittle and crumbly in one hour, the 

mlour of copaiba being well marked. With 8 per cent, of colo- 

fiftony ur alcoholic extract of bemo'in, the mass becomes brittle or 

in five minutes, G r o t e finds that to obtain satisfactory 

marked hardening, the sample should be treated with two 

of alcohol before mixing with the lime. M a c E w a n's ex- 

iments with the lime test were luisatisfactoiy. 

ding to G r 1 e, if five drops of genuine Peruvian balsam be 
with 3 e.c. of ammonia of 0'96 specific gravity, the mixture 
brownish-grey, gives very little froth, and does not gelatinise 
)d to stand for twenty-four hours. If 20 per cent, or up- 
of colophtmy be present, a very voluminous froth will be pro- 
ond the mixture will gradually gelatinise, so that in fifteen 
!n^ minutes the tube may be inverted without loss of the 
ts. With 8 per cent, of colophony, the froth occupies twice 
volume of the liquid, but no gclatmisatiou occurs. According 
u m, if an ethereal solution of Peru balsam be shaken 
ammonia (specific gravity 0"96), two yellowish-brown layers are 
j, between which yellowish flakes swim. On separating the 
b1 layer uiid evaporating it, about 80 per cent of the sample 
is obtained as a brown balsamic residue, while the ammonia 
9 flee cinnamic acid, which is precipitated on adding excess 
1 but dissolves on boiling. Benzoin behaves somewhat simi- 
bttt the resins of eolophony and eirpaiba combine with the 

it Mluble in petroleum other ia liqutil and has a di^naitjr itid other 
a npproxiuialinj; to tbosii of oil of tar]>«ntiuc, whilo the p«tn>lenui 
W cxtnK't IVoni PeruviBn balaam conainta almost entirely of cr^ratalliue 
I, vhlch U denser than wntcr. 


ammonia, and on acidifying are precipitated and not redissolved by 
boiling. Castor-oil, on the contrary, passes completely into the 
eUier, so that no sensible precipitate is obtained by acidulating the 
ammoniacal liquid. A mixture of equal parts of storax and 
Peruvian balsam yields a stiff homogenous jelly when the ethereal 
solution is shaken with ammonia. With a smaller proportion of 
storax, more or less separation into layers occurs, but gelatinous 
lumps float in the ethereal solution, and on acidulating the 
separated ammoniacal solution solid resin is precipitated. (P. 
MacEwan did not obtain this reaction.) 

If Peru balsam be rubbed in a mortar with twice its measure 
of concentrated sulphuric acid, a frothing and odour of sulphur 
dioxide will be observed if copaiba (15 per cent) or certain other 
adulterants be present If the cooled mixture be washed with 
cold water, the residue should be at first plastic, and afterwards 
hard and brittle. A smeary consistency points strongly to an 
admixture of castor-oil. If the washed resinous mass be treated 
with two or three times its weight of ether, it should dissolve 
completely, an insoluble residue indicating the presence of storax 
or benzoin. The residue from benzoin amounts to half the weight 
of the drug originally present, and is soluble in alcohol or 
(preferably) acetone ; while if treatment with one of these solvents 
leaves a white residue of styrogenin, soluble in chloroform and 
separating on evaporation in microscopic crystals, storax is present 
7 parts of styrogenin are said to represent 100 of storax. 

Various other suggestions for determining the proportions of 
adulterants in Peruvian balsam are detailed by Schlickum 
(Pluirm, Jour,, [3], xiiL 323). 

Cinnamic Aldehyde. 

CgHgO. ^ CgHy.COH. 

This compound, the only known member of the series, occurs 
naturally in the oils of cassia and cinnamon, of which it constitutes 
the greater part. It may be produced artificially by the oxidation 
of cinnyl alcohol ; by the dry distillation of a mixture of cinna- 
mate and formate of calcium; and by saturating a mixture of 
benzaldehyde and acetaldehyde with hydrochloric acid, thus : — 
CeHs-COH + CH3.COH = HjjO + C6H5.CH : CH.COH. 

Cinnamic aldehyde is a colourless oil, rather denser than water. 
It may be distilled in a vacuum, or with water free from air. On 
exposure to the air, it quickly becomes yellow and resinous, and 
acquires an acid reaction. It rapidly absorbs oxygen, especially 
in presence of moisture, and is converted into cinnamic acid. 
Chromic acid converts it into benzoic and acetic acids. 

on. OF CIKNAMON. 45 

L C mnatnin aldehyde forma a ciyetalline compound with strong 
c acid, whidi is decomposed by the leftat rise of temperature, 
"mmedintely resolved into ita conatituenta oa addition of 

acid Bulphitca of the alkali-metals, ciunamic aldehyde 
s crystalline compounds similar to those formed by henzoic 
i other aldehydes. 
~ L OF Cixifuioir. Oc 07 Cassia. 

le volatile oil of cinnamon is prepared by distilling the chips 

I refuse bark with water. The British and French Phanna- 

only recognise the product from Ceylon einn.imon, while 

nan Pharmacopceia only admits the oil from Chinese 

I (casaia), and in the United States the oil from both 

9 is recognised under the name of oil of cinnamon. Ceylon 

a yields from } to 1 per cent, of oil, and Chinese cinnamon 

t to IJ per cent. 

of CeyUm finnammt is a pale yellow or reddish liquid. 
I red-brown and thicker on ejcpoaure to air, and linaUy 
Lg crystals of cinnamic acid. It has a strong, hut agreeable, 
a odoar, and a sweet pungent, aromatic taste. The speciRu 
gravity is about 1'035, but increases with the a^^ of the oil. It 
letnaina clear at —10° C, but at a lower temperature ( — 20° C.) 
flepaistes a stearoptene, It is readily soluble in alcohol, hut not in 
~i petroleum spirit, and when fresh is neutral to htmue, becoming 
3 by oxidation due to ago or exposure. 

e oU of Ckinete einnanion, commonly known as oil of Ctuvsiu, 
r resembles the Ceylon product, except that its colour is 
er, ita odour less delicate, its taste less sweet, and its specifiu 
' somewhat higher, — usually between 1'055 and 1"065. 
Arp distinction exists between the two oils, or one which 
I enable one to bo detected with certainty in presence of the 

I varieties of cinnamon oil consist chiefly, and sometimes 
wt entirely, of cinnamic aldehyde, but contain, in 
I, small but variable proportions of hydrocarbons, and, 
dd, resin and cinnamic acid. To isolate the 
utmic aldehyde, the oil should be agitated with four times 
I of a saturated solution of acid potassinni sulphite, 
preferable to the sodium salt A ctystallim^ 
I npidly forms, which is separated from the mother-liquid, 
1 Mverai times by trituration with cold spirit, and then 
i at a gentle bent with dilute sulphuric acid. The crystalline 
Dpoiind is thus decomposed, and the liberated cinnamic aldehyde 
' s tneaeorcd, and purihed by washing and drying. 


Oil of cinnamon is sometimes mixed with the oil of cloves or 
of cinnamon leaves. These admixtures are indicated by the acrid 
vapours evolved on heating. According to the German Pharma- 
copoeia, "a solution of 4 drops of oil of cinnamon in 10 cc. of 
alcohol should, on the addition of 1 drop of test solution of ferric 
chloride, give merely a brown but not a green or blue colour 
(carbolic acid, oil of cloves, &c.)/* 

Oil of cinnamon leaves is a rather viscid, brown liquid, having a 
specific gravity of 1*053, and a strong clove-like and faint 
nutmeg-like odour. After treatment with potassa, the odour of 
the oil resembles that of cinnamon. A terpene, e u g e n o 1, and a 
little benzoic and cinnamic acid have been found in the oiL 

H a g e r agitates oil of cinnamon with an equal measure of 
petroleum spirit, which dissolves the usual adulterants. H e p p e 
confirms this, but adds that copaiba resin cannot thus be detected. 

Coumaric Acid. Ortho-hydroxycinnamic Acid. 
CftHgOg = C6H^(0H).CH : CRCOOH. 

Coumaric acid occurs, together with melilotic or hydro- 
coumaric acid, CeH^(OH).CH2.CH2.COOH, in the yellow 
melilot and in the leaves of Angrcecum fragrans. It is most easily 
prepared by boiling its anhydride, coumarin, with potash. 
Coumaric acid crystallises in brilliant prisms, which melt at 196% 
and are easily soluble in water and alcohol. The solutions of its 
alkali-metal salts exhibit a bright green fluorescence. By fusion 
with potash, it yields salicylic and acetic acids, and by nascent 
hydrogen is reduced to melilotic acid. 

CouitfARic Anhydride or Coumarin, CgHgOj, is the odoriferous 
principle of the Tonka bean, sweet woodruff, the flowers of 
Anthroxanthum odoratuniy and several other plants, from which it 
may bo extracted by alcohol. It is now manufactured artificially 
by heating sodium salicylic aldehyde with acetic anhydride and a 
little sodium acetate. On pouring the product into water an oil 
separates which on distillation splits up into acetic acid and 
coumarin. Coumarin crystallises in slender, colourless needles, 
melting at 67*, boiling at 290-291°, and distilling without 
decomposition at a higher temperature. It has a pleasant, fragrant 
odour and burning taste, is very slightly soluble in cold water, but 
more soluble in hot water and in alcohoL It also dissolves readily 
in ether, glycerin, oils, &c., and in strong alkalies. By prolonged 
boiling of the last solution coumaric acid is formed. 

Coumarin exists in the Tonka bean in the proportion of 1 to 1^ 
per cent. It is the odoriferous principle of the scent known as 
** extract of new-mown hay." 




Monocarbobenzoic Acids. Benzene-dicarboxylic 

Three isomeric acids of the above constitution are known, 
differing from each other in their properties and sources. Thus, 
on oxidation with dilute nitric acid, or an alkaline solution of 
potassium permanganate, the three isomeric xylenes, €^114(0113)2, 
yield the corresponding phthalic acids. Hence the differentiation 
of the latter bodies affords, in this as in many other cases, a 
valuable means of distinguishing between allied or isomeric bodies 
of the aromatic series, and of studying their constitution. The 
following table shows the chief points of distinction between the 
isomeric phthalic acids. 


Chief Kmrces and 
mode* of forma- 

dyttalline form. 

MeltiDg point 

Solnbilityin water. 




jletion of chromic 
add mixture. 

Barium laltw 

surer nit. 

Orthophthallc or 

Ordinary Phthalic 



Oxidation of ortho- 
xylene, alizarin, 
purpurin, benzene, 
naphthalene, ana 
naphthalene dichlo- 

Monoclinic prisms 
or nacreous laminee. 


Cold, 1 in 120 parts ; 
boiling, more easily 

1 in 10 parts. 


Completely oxidised. 

Small scales or 
silkv needles, only 
tllghtly soluble in 
hot water. 

Crystalline and 

moderately soluble; 
detonates when 
heated rapidly. 

Metaphthalic or 
Isophthalic Acid. 

p„ jCOOHO) 
^•"< (COOHW. 

Oxidation of meta- 
xylene and colo- 

Slender hair-like 

Above 800*. 

Cold, 1 in 7800; bon- 
ing, 1 in 4eo parts. 


Not affected. 

Crystallises in 

readily soluble 

Amorphous precipi- 
tate; forms Phar- 
aoh's serpents on 

Paraphthalic or 
Terephthalic Acid. 

p„ (COOHO 
^•"« tC00H(4). 

Oxidation of parsr 
xylene, turpentine 
oil, cyinene, euca- 
lyptus oil, &c. 

Amorphous or crys- 
talline powder. 

Sublimes without 

Cold, very slight; 
boiling, sparingly. 

Very slight 
Not affected. 

White granular 
powder or concen- 
trically arranged 
tablets, soluble in 
850 psjrts of cold 

Amorphous precipi- 
tate, blackening in 
the light 


Orthophthalic Acid. 

Ordinary phthalic acid is now manufactured on a large scale by 
converting naphthalene into the tetrachloride/ and heating 
this with 5 or 6 parts of nitric acid of specific gravity 1'36, till 
entirely dissolved, when the excess of nitric acid is expelled, and 
the phthalic acid crystallises out on cooling. It may be purified by 
re-ciystallisation from hot water. The yield by this process is 
about 30 per cent, of the naphthalene used. Phthalic acid may 
also be obtained by treating naphthalene direct with nitric acid of 
1*15 specific gravity, but only about 40 per cent, of the theoretical 
yield is obtained. Many of the properties of phthalic acid have 
already been described. The melting-point according to Lossen is 
184'', while Ador states that the crystals melt at 213'' and the 
powder at 203°, The discrepancies are doubtless due to the fact 
that phthalic acid when strongly heated loses H^O, and forms 
phthalic anhydride. Neither iso- nor tere-phthalic acid 
forms an anhydride. 

Phthalic acid is readily extracted from aqueous liquids by 
agitation with ether or benzene. 

When heated with a single equivalent of lime, phthalic acid 
yields calcium benzoate and carbonate: — 2C8HgO^ + 2CaO = 
Ca(C7H50j)2+CaC08+H20. When heated with a larger pro- 
portion of lime or other strong base, phthalic acid yields a c a r- 
bonate and benzene: — C8Hg04+2CaO = 2CaC03+CgHg. 

By treatment with fuming nitric acid, phthalic acid is converted 
into nitrophthalic acid, C8Hg(N02)0^, but by chromic acid 
mixture it is completely oxidised. 

By treatment with zinc and acetic acid, phthalic acid is 

converted into phthalide, C^H^ -! p^ |0, diphthalyl, 

Cj^jHgO^ being also formed. 

When treated in warm alkaline solution with sodium amalgam, 
phthalic acid is reduced to hydrophthalic acid, CgHgO^,* 
which crystallises in tables, dissolves easily in hot water and alcohol, 
melts with decomposition at about 200°, and is converted into 

^ Naphthalene Tetraoiilouide, CJ0H8CI4, is manufactured by grindiug 
naphthalene and potassium chlorate or bleaching powder with water, making 
the paste into balls, and bringing these after drying into concentrated 
hydrochloric acid. Another method consists in passing chlorine gas through 
melted naphthalene, taking care that the temperature does not rise above 
160-170' C. 

' Meta- and para-phthalic acids are not reduced by sodium amalgam in the 
cold, but on heating they both yield tetrahydro acids, C8H20O4, no inter- 
mediate product being formed {Jour, Chem, Soc,, 111. 370). 



oic acid by treatment with chromic acid, nitric acid, or 
le &n<i water. 

■VTien phthttlic acid is diattUed with aniline it is converted into 
phenyl-thalimide or phthaUnil, CjH40,(NC«H5), a body crystal- 
lising from alcohol in needles melting at 205°, but volatile at a lower 
Iciupcrature, It hfls been recommeDded as a febrifuge. 

Phthalic Anhydride. Phthdic Oxide. 




i COO 
I CO. 


ithalic anhydride is prepared by heating phthalic acid to about 
r in a current of ait or carbon dioxide, when the anhydride sub- 
in long, white, pliant, rhombic needles. It melts at 128° and 
TkjUs at 284'"5 C It is only very slightly soluble in cold but more 
t«atlily in hot water, and is reeonverted into phthalic add by pro- 
longed boiling with water and more readily in presence of alkalies. 
*~* ithalic anhydride derives its chief practical interest from the 
with which it reacts with phenola and their allies to form 
ing matters called pht hale ins. Thus, when reeor- 
nol, Cj'H,(OH)j, is heated with excess of phthalic anhydride to 
atiout 200* C. for half an hour, the mixture acquires a yellowish- 
rtd colour, and contains the anhydride of resorcinol-phthalein. or 
_fii]oreBcein, C^^^igO^. The melt dissolves in dilute caustic 
ammonia with dark red colour, the solution changing on 
ion to reddish-yellow and yellow, and exhibiting after dilution 
IQ jellowiah -green fluorescence, which is visible in solutions so 
to appear colourless by transmitted light. On acidulat- 
ing the solution and agitating with ether, the fiuorescein is taken 
op, and will be uguin dissolved on agitating the ethereal solution 
with soda. If phloroglucol be substituted for reaorcinol a yellow 
liquid is obtained, while pyrogallol yields a blue ; but neither ia 
fluoroscent. The blue colour due to pyrogallol may be destroyed 
by cautious addition of permanganate, which acts only slowly on 
flaareacem. Catechol-phthatein, formed by gently heat- 
ing catechol with phthalic anhydride and a tittle aidphuric 
acid, dissolves in caustic alkali solution with fine blue colour. 
Qninol-phtbalein, or qulnizarin, formed in a similar manner, 
disKolves in alkalies with violet-blue colour. If the solution bo 
acidulatvd with sulphuric acid it becomes red, and the quinizarin 
may be extracted by agitation with ether, and recovered from the 
ethereal solution by shaking with caustic soda, the solution of 
wiiicli acquires a vjolet-blue colour. 

The phthaleins are described more fully in the chapter on 
"Ityes and Coloorijig Matters." 



Ortho-hydroxybenzoic Acid. 


Salicylic acid was originally prepared from s a 1 i c i n, Cj^H^gOy, 
a bitter principle existing in willow-bark. It may also be obtained 
from the oil of wintergreen, which consists essentially of methyl 
salicylate (page 58), by distillation with potash. It is now pre- 
pared on a considerable scale by a process due to K o 1 b e, based on 
the reaction of carbon dioxide on sodium phenate.^ The identity of 
the natural acid with the purified artificial product is fully established. 

When potassium phenate is acted on by carbon dioxide it 
reacts in a similar manner to the sodium phenate in Kolbe's 
process, yielding pure dipotassium salicylate up to 150*; but 

^ The following is an outline of Kolbe's process : — Grade soda lye of known 
strength is exactly saturated by crystallised carbolic acid, and the liquid 
cautiously evaporated till the residue is perfectly dry. It is then subjected to 
the action of a stream of carbon dioxide gas at a temperature commencing at 
100° C, which is gradually raised to 180^ and may reach 220*" or 230** C. 
towards the close of the operation. During this process, carbolic acid distils 
over and ultimately amounts to about half the quantity taken. The residue 
in the retort is basic sodium salicylate, the solution of which on fractional pre- 
cipitation with hydrochloric acid yields impure salicylic acid. The first 
portions thrown down are contaminated with resinous and colouring matters, 
and are rejected. The remainder of the precipitate is washed, recryitallised 
from hot water, and distilled at 170"* C. in a current of superheated steam, 
when it is obtained perfectly white. If carbolic acid containing cresylie acid 
be used, the salicylic acid contains cresotic acid (see page 55), which possesses 
many of the properties of salicylic add ; but for internal medicinal use pure 
salicylic acid should be employed. 

The reaction between sodium phenate and carbon dioxide in the cold results 
in their direct union with formation of sodium phenylcarbonate, 
(CcH5)0.C0.0Na, a white powder decomposed by water into phenol and 
sodium hydrogen carbonate. On heating this compound to 180** it under- 
goes direct molecular transformation in mono-sodium salicylate, 
C«H4(0H).C0.0Na. The formation of phenol and basic salicylate is due 
to the reaction of this salt at a high temperature with unchanged sodium 
phenate:— C«H4(0H)C0.0Na + CeHj.ONa - C,H4(0Na).C00Na + CaHj.OH. 
The more advantageous reaction can be realised on a manufacturing scale by 
treating perfectly dry sodium phenate with the requisite quantity of carbon 
dioxide under pressure (either employing the gas or solid substance), the 
temperature being kept down artificially. On heating the product for several 
hours to 120°-130°, it is transformed into mono-sodium salicylate without 
separation of phenol. Operating in this manner salicylic acid can be obtained 
from half the quantities of soda and phenol which are required if Kolbe's 
process be adhered to (R. Schmitt, Jow, Soc. Dyers, &c., IL 114). 



above that temperature the isomeric para-hydrDxybenzoate Is also pro- 

I'" ed, and at 230° is the sole product. MoDo-potaasium saliuylate 
>ii¥erted into the basic para-hydroxybenzoato and phenol 
iQ heated to 220°, whereas the corresponding sodium ^alt yields 
prtAo-hydroxybenzoate or ealicylate, together with phenol, 
kticylic aeid crystallises from aJcohol in large monoclinic prisms, 
TMuidly occurs as a granular powder, consisting of minute, broken, 
lulor crystals, having a sweetish, acidulous, acrid taste. It has 
leeific gravity of 1"483, niults at 155°-156°, and when gradually 
ted sublimes at about 200° in slender shining needles, but when 
boated rapidly with powdered glass or sand it is resolved into 
phenol and cai'hon dioxide. It volatilises readily in a current 
t steam at 60-80 lbs, pressure, and even vaporises on boiling its 
Mneotia solution. 

T Salicylic acid is a powerful antiseptic, and, owing to its slight 
8 employed for preserving beer, wine, milk, lime and lemon 
1, gum, and other fluids,* 
I Salicylic acid is soluble with tolerable facility in hot water, 
t separates for the most part on cooUng. Its solubility in cold 
ratsr ia variously stated at from 1 part in 300 up to 1 part in 
1000. By the presence of various neutral salts, its solubihty in 
«old vater is increased without its antiseptic value being interfered 
BT w ith.' Salicylic acid is veiy soluble in solutions of borax, a 
B^^ktQpound of the formnla Ka(fiO)2CTHgOg being said to be 
^^^Bwmed. The liquid soon undergoes decomposition. 
^^^K Salicylic acid is soluble in alcohol (1 in 2J), amylic alcohol (1 in 
^^^"f), ether (1 in 2), chloroform and beniene (1 in 80). It may be 

' The n*e of Balicylic acid Eor preaerving articles of food is forbiddan in France 
9 other countries. One pari acid to 10,000 of heer or wine is tbo 
ftutinum proportion necesBary for the preserrittion of the liqoid. 
1 HTsnoxTKAFHTHOic AciD, Or OxjDapbtlioic Acid, C,gH,(OH).CO0H, ia a 
irhich beats the aame retalinn to naphthalene that salicylic acid beats to 
se. It is prodaced by the action of carbon dioxide on perfectly dry 
a alpfan-nnpbthol at 130*. It rorma cnlonrless ncicnlar crystals melting 
It ISG'C. and ruqniriaR 30,000 partsoF cold water foraolation. Ita salts give 
e coloration with ferric chloride. The corresponding acid from beta- 
Hphdiol melts at 235° and gives a violet-black colour with ferric chloride. 
'h varieties of hydroxy aapbthoic acid are said to be powerful antiseptics, 
iding the putrefaction of btood and urine much more perfectly than 
rylioBcid (PAnrm. Jour., [3], xvjiL 637, 823). 
* Miiad wiUi 1 part pnlassinm nitrate, it dissolves in GO parts at cold water. 
It part ammonium citrate, ,, 00 ,, 

3 ports sodium sulphite, ,. BO „ 

2 parts sodium phosphate, ., fiO „ 

!} parts sodium phosphate. .. 12) „ 


conveniently crystallised from hot petroleum spirit Agitation 
with ether or chloroform removes salicylic acid from its aqueous 
solutions. H. T a f f e recommends a mixture of ether and 
petroleum ether for this purpose. 

Heated with water under pressure to 230° C, salicylic acid is 
split up into phenol and carbondioxide : — CyELgOg = C^Hg + 
COg. On heating with concentrated hydrochloric or dilute sulphuric 
acid the change occurs at a lower temperature (140*-150*). 

The distillation of salicylic acid with excess of lime produces 
calcium carbonate and phenol. In aqueous alkalies 
salicylic acid readily dissolves, forming salicylates. The 
salicylates are well-defined salts, and have met with considerable 
application in medicine (page 57). 

Analytical Reactions op Salicylic Acid. 

Concentrated sulphuric acid dissolves pure salicylic acid without 
colour, forming a sulpho-acid. Impure salicylic acid gives a 
yellowish-brown coloration. 

Cold concentrated nitric acid forms nitro-salicylic acid; 
with fuming nitric acid, picric acid results. 

Bromine gives a reaction with salicylic acid indistinguishable from 
that produced by phenol, and the same is true of its behaviour with 
Millon's reagent (vol. ii. page 540). When boiled with excess of 
baryta water salicylic acid is precipitated as a basic barium salt. 

Sodium amalgam gradually reduces salicylic acid in a warm, 
slightly acidulated solution, to its aldehyde, recognisable by its 
odour (page 60). 

Silver nitrate and lead acetate give white precipitates with 
neutral salicylates, but not with free salicylic acid. 

With a solution of cupric sulphate, H. Schultz states that 
salicylates and free salicylic acid give an emerald-green coloration, 
visible in 2000 parts of water and destroyed by ammonia or acid. 

Fehling's solution is reduced by salicylic acid, and under 
favourable circumstances may be employed for its determination. 

On heating salicylic acid or one of its salts with methyl alcohol 
and sulphuric acid, methyl salicylate is formed, having an 
agreeable aromatic odour (see page 58). 

C. 0. Curtman (Jour, Chem, Soc., lii. 185) recommends the 
formation of methyl salicylate for the detection of salicylic acid in 
wine or beer. He directs that 4 c.c. of the liquid to be tested 
should be mixed with 2 c.c. of methyl alcohol (or failing this, 
ordinary alcohol), and then 2 c.c. of pure sulphuric acid cautiously 
added. The liquid is then agitated, heated for two minutes, 
allowed te cool for ten minutes, and then heated just te boiling, 
when if salicylic acid were present, a distinct odour of wintergreen 



2 will be perceptible. With traces, it may bo Decessaiy to allow 
e liquid to cool again, and then beat a tbird time. In examining 
ad milk,&c., by tbia process, tbe eaiuple ahouid be digested 
» botira irith dilute alcohol, and the tlltered liquid coiic«u- 
A and heated as above. 

! aalicylie acid may be determined ollcali metrically, using 
B or phcnolpbthaletn aa an indicator, 

« most delicate reaction for salicylic acid is that witb ferric 

iride, which produces a beautiful violet colour even in 

remely dilute solutions. The colour is destroyed by acids and 

f dlkalies, Tbe reaction i3 greatly more delicate (1 in 100,000) 

D that of phenol with tbe same reagent (1 in 3000). 

" " ' e proposes to employ the above reaction in alkalimetry, 

B neutralising an acid solution to which a trace of salicylic acid 

i ferric chloride have been added, the violet colour becomes gradu- 

f more developed until neutrality is reached, when tbe liquid 

IS reddish -yellow. But P a g 1 i a n i has shown that tbe amount 

lineral acid required for the destruction of tbe violet colour 

« greatly witb the nature of the acid and tbe dilution of the 

d, and hence salicylic acid is ill-suited for use as an indicator. 

For the detection of salicylic acid in milk. U. Pellet dilutes 

SOO c.c with an equal measure of water, heate to 60° C, and treats 

with t c.c of acetic acid and an excess of mercuric nitrate free 

from mercurous salt. The salicylic acid is extracted from the 

liltered liquid by agitation witb ether. A simpler plan, which 

Buffioee for rough purposes, is that of A. R e m o n t, who a;;itates 

[) B.C. of the milk with two or three drops of sulphuric acid, so as 

It break tbe coagulum and produce a nearly homogeneous mixture. 

I shaken with 20 c.c of ether, which after separation is 

rapoiatod, and tbe salicylic acid dissolved out of tbe residue by 

with 10 c.c of rectified spirit. To detect the salicylic acid 

K ^le ethereal or spirituous solution obtained, it is often sufficient 

I shake with a solution of ferric chloride, when the characteristic 

lolet colorotion will be produced. A more delicate and satisfactory 

~ n is to agitate tbe ethereal solution witb weak ammonia, se])arate, 

mporot« the ammoniacat liquid at a gentle heat, and test tbe 

bndue of ammonium salicylate witb ferric chloride. 

[ For tka detection of salicylic acid in tnntt, beer, or urine the 

hoid shcilld be treated with excess of acetate of lead, the filtrate 

dpitated with dilute sulphuric acid, and the liquid again filtered 

i shaken with ether, preferably after ooncentration.' Lime- and 

' Bla ■ recomiuonilB that tbe beonbould be drunk and the arinRt«sUd throe 

hoan ■ftvrwards by addition or ferric chloriile. The reactiou u nid to be five 

M aa delicate with urine as with tbe original beer. 


lemon-juice may be treated in the same way, or may at once be 
agitated with ether. 

H. T a f f e recommends a mixture of equal measures of ether and 
petroleum ether for extracting salicylic acid, as such a solvent does 
not take up water or tannic acid, though somewhat liable to form 
an emulsion. 

Another method of separating salicylic acid from liquids con- 
taining it is by distillation. Wine or beer should be rendered 
alkaline with soda, reduced to one half by boiling, to drive off the 
alcohol, and then acidulated with sulphuric acid and distilled. 
The distillate may be rendered alkaline with soda and concentrated 
to a small bulk before acidulating and shaking with ether, or 
applying other tests for salicylic acid. 

The ferric chloride reaction may be employed for the colorimetric 
determination of salicylic acid in a manner similar to the method 
of Nessler for determining ammonia in water. Instead of using 
an aqueous solution of salicylic acid as the standard of comparison, 
it is preferable in all cases to add a definite amount of salicylic 
acid to a liquid of the same kind as that in which the .salicylic 
acid is to be determined. Thus milk should be compared with 
milk, beer with beer, and urine with urine, and the standard 
specimen submitted to the same treatment as the sample to be 
compared with it. In all cases it is desirable to extract the 
salicylic acid with ether before applying the iron test, as many 
substances weaken the colour-reaction or suppress it entirely, e.g^ 
acids, alkalies, and certain neutral salts, such as phosphates, 
tartrates, oxalates, &c. The ferric chloride solution should be very 
dilute, and must be added gradually till the coloration no longer 
increases. With small quantities of salicylic acid an excess of 
ferric chloride destroys the coloration. 

Commercial Sauctuo Acid. 

The salicylic acid of commerce is far purer than was formerly the 
case, when more or less sodium chloride, phenol, cresotic acid, and 
para- and meta-hydroxybenzoic acids were frequently present. 
Salicylic acid is stated to have been met with in America 
adulterated with acid potassium sulphate, gypsum, starch, sugar, 

The facile formation of definite crystals is a good indication of 
the purity of salicylic acid, the presence of foreign matters in its 
solutions greatly interfering with its crystallisation. When shaken 
up with cold concentrated sulphuric acid, salicylic acid should 
yield a perfectly colourless solution. 

H. K 1 b e gives the following method of testing the purity of 
salicylic acid : — ^Dissolve 0'5 gramme of the sample in 5 or 6 c.c. 



;rong alcohol, pour the cIpaf solution into a watch-glass, and 

f it to evaporate epontaneouely. The residual salicylic acid 

B a ring of beautifully aggregated efflorescent cryatala round 

) edge of the watch-glass. This mass is pure white if the 

1 tested be pure and re-crystallised, but yellowish or yellow if 

i aiiaply precipitated acid be used. If the colour be brownish 

r brown, the sample is unfit for internal use. 

Chloride of sodium and other mineral imjiuritiea will remain on 
]iiitittg the sample, 
Cariifilie aeid is especially liable to he present in sahcylic add 
hich has been auhliraed. It may be detected by nearly neutralis- 
; the sample with sodium carbonate, and agitating tlie liquid 
h ether. On gently evaporating tho ethereal liquid, the carbolic 
1 may be recognised by its smell, taste, and chemical reactions, 
'. Muter gives the following test for carbolic acid in sample? 
f nlicylic acid: — Boil 10 grains in half an ounce of water, 
1, de^t the solution, and add to it 1 minim of a saturated 
a of bicarbonate of potaaaium, KHCOj, 1 minim of aniline, 
) drops of solution of bleaching powder, when, if carbolic 
> present, a deep blue colour will be produced. Another 
r phenol is to treat 5 c.c. of a saturated aqueous solution of 
■ I with a crj-stal of potassium chlorate and 2 c,c of 
c acid. On pouring ammonia carcfuUj on the surface 
i liqnid, a reddish or brownish tint will be developed if 
phenol be present. 

Crbsotic Acm, CoH,(Cn3)(On).COOH, the next homologue of 
tli^Iic acid, is prepared from cresol in a similor manner to that 
i for obtaining salicylic acid from phenol. It closely resemblea 
": acid. Three isomeric modiUcationa are obtainable from 
tl-tar cresol, corresponding to the three isomeric cresols, and 
; respectively at 151°, 163', and 177°. 
pro[»erties of salicylic acid are much modified by the 
i of cresotic acid. Thus, pure salicylic acid requires about 
a of boiling water for solution, while samples containing 
c acid dissolve in 11 of boiling water, or even in a smaller 
JOriion. If to the solution so obtained about one-fifth of alcohol 
\, and the liquid allowed to cool, pure salicylic acid will form 
I distinct crystals not cohering together, while samples 
ng cresotic acid form a network or woolly mass of small or 
ttioct crystals. 
the boiling aqueous solution of impure salicylic acid excess 
[ carbonate of calcium be ndded, and the liquid be filtered while 
Bpantigly soluble salicylate of calcium is deposited as the 
lioD cools. When re-ciystallised and decomposed by hydro- 



chloric acid, this substance yields pure salicylic acid, having 
identical properties with that obtained from wintergreen oil (see 
page 58). If the mother-liquid from the salicylate of calcium 
be further concentrated, another crop of impure crystals may be 
obtained. There remains in solution a very soluble calcium 
cresotate,^ which, on decomposition by hydrochloric acid, gives 
a precipitate of cresotic acid. This, when crystallised from boiling 
water, forms silvery plates, which are mudi more soluble than 
salicylic acid in both hot and cold water. The proportion of 
cresotic acid in commercial artificial salicylic acid was formerly 
probably sometimes as high as 25 per cent., but when pure phenol 
has been used for the manufacture the proportion of cresotic acid 
must be insignificant. 

The violet reaction with ferric chloride is common to saUcyHc 
and the three cresotic acids. 

Isomers of Salicylic Acid. — Salicylic acid has the constitution 
of an ortho-hydroxybenzoic acid. Its two isomers, the m e t a - and 
para-hydroxybenzoic acids, are said to be sometimes 
present in commercial samples of salicylic acid. The following 
table shows the chief differences of analytical value :— 


Fusing point. 

Solubility in water 

Solubility in water 
at 15* C. 

Eeaction with 
ferric chloride. 

Heated in a current 
of dry ammonia 

Antiseptic pro- 



(SaUcyUc Acid). 



Volatilises with 
steam when the 
aqueous solution is 

1 in 1100.2 

1 in 1000. 

Deep violet colour. 

Yields phenol, COj, 



p „ / OHd) 
200' C. 

Not volatile with 
the vapour of water. 

No change. 

Yields ozybenso- 
nitrlL C,H.(OH). 



C-H /^H«) 
210* C. 

Not VolatUe with 
the vapour of water, i 

1 in 680. 
1 in 126. 

Yellow precipitate, 
soluble In excess. 

Yields phenol, CO,. 

None. (?) 

Salicylic acid prevents the precipitation of copper salts by 
alkalies, while its isomerides have not this property. 

^ Excess of milk of lime cannot be substituted for the carbonate of calcium, 
or a sparingly soluble basic calcium cresotate results, which cannot be 
separated from the salicylate. 

* According to Bourgoin {Jour, Pharm, Ckimie, [i\ xxx. 488), the 
solubility of salicylic acid at 0" C. is 1 part in 666, instead of the number 
given in the text, which is due to s t (Jour. Prae, Cfhem., [2], xriL 228). 



ilieylic acid may be partially ieparated from para-hydroxjlwin- 
^^^ 1, which is the isomer most likely to be present in the 
.Cemmerciftl eub&tnnce, by mixing the hot aqueous solution witli 
ezce»a of miUc of lime, when a bmic calcium salicylate eepamtcs 
on cooling. A more exact separation may be effected by drying 
the free acids at 100° C, and agitating with anhydrous chloroform. 
Salicylic acid dissolves readily, but para- and meta-hydroxybenzoii; 
■dda remain chiefly undissolved. 

From benioic acid, pam-hydroxy benzoic acid may be separated 
by trealmcnt with carbon disulpbide, in which the latter acid is 
nearly insoluble. 

Metallic Salicylates. 

Salicylic acid has chornclers intermediate between those of a 
phenol imd an ordinary acid. The hydrogen of tlie carboxyl group 
is replaceable by metals, with formation of the salts of the formula 
C,H.(OH)."C0OM. The hydrogen of the hydroxy! group (phenolic 
hydrogen) is also replaceable by alkali-metals, the basic compounds 
ao produced being converted by carbonic acid into tho monobasic 
salicylates. Salicylic acid is monobasic with all indicators of 

The ordinary or neutral metallic salicylates are well-defined 
salts, and mostly crystal! isable. When heated in the solid etate 
tliey evolve phenol and carbon dioxide. The residue 
usually consists of a basic salicylate, but in the case of the 
potassium compound much para-hydroxybenzoate (page 
56) remains. Secondary products are also liable to be formed.^ 

Solutions of the neutral salicylates give an intense violet colora- 
tion with ferric chloride, and respond to the other reactions for 
salicylic acid (page 52). 

On adding diluto sulphuric or hydrochloric acid to a solution 
of a B.'dicylate, siUicylic acid is thrown down as a bulky white 
precipitate, readily dissolved on agitation with ether. 

SiHilusi Salicylatb, ajJaCjEjOj+HjO, forms small white 
eiyataJlino plates or a crystalline powder permanent in the air, 
odourkus, having a sweeti^ saline and somewhat alkaline taste, and 
uvulml or feebly acid reaction to litmus. It is soluble in 1 J parts of 
cold water, only slightly soluble in absolute alcohol, but soluble in 
8 parts of cold rectified spirit. In boiling water and alcohol it is 
very soluble. Both the alcoholic and the aqueous solution give a 
violBt colour with ferric chloride. On ignition, sodium salicylate 
■ rUeaoUnliihonntaB also evolve plienol wbea bunted, but tha rHBJdne 
mlphals, «t »Df rate if nitrate or carbonate of aodium be a<liltiil 


evolves phenol, and leaves from 30 to 31 per cent, of NajCOj. 
It is completely soluble in ammonia, and the solution does not 
reduce nitrate of silver, even on boiling. Barium chloride should 
cause no precipitate in the aqueous solution, and the precipitate 
with nitrate of silver should completely dissolve on addition of 
nitric acid and alcohol When the solid salt is shaken in the cold 
with 1 5 parts of strong sulphuric acid, no brown coloration should 
be produced. Sodium salicylate is liable to become coloured by 
keeping, especially if exposed to the air. The change of the solu- 
tion may be prevented by the addition of a small proportion (1 per 
cent.) of sodium thiosulphate. 

Fbrric Salicylatb, Fe(C7H508)8, separates, on mixing a strong 
solution of sodium salicylate with ferric chloride, as a brown pre- 
cipitate, which, together with the mother-liquor, rapidly acquires a 
deep violet colour. After washing, ferric salicylate forms a brown 
amorphous body, which yields a violet solution on boiling with water. 

Bismuth Salicylatb, which is used in medicine, is of very 
inconstant composition, the proportion of BijOg ranging from 
35 to 73 per cent. (Pharm, Jour,, [3], xv. 889). 

Salicylic Ethers. 

Several of the ethereal salts of salicylic acid have a practical 

Methyl Salicylate, C8H803=CeH^(OH).CO.O(CH3). This 
ether constitutes the greater part of the natural essential oils of 
Gavltheria procumbens, Bdtda IcTiia, cherry-birch, and some other 
plants, and may be obtained therefrom by distilling the plants with 

Methyl salicylate may also be prepared artificially by distilling 
salicylic acid or a salicylate with methyl alcohol and strong sulphuric 

Methyl salicylate is a colourless, oily liquid (becoming red on 
keeping), of strong and agreeable odour, and sweet, cooling, 
aromatic taste. It has a density of about 1*18 and boils at about 
220** C, the hydrocarbon with which it is associated in gaultheria oil 
boiling about 20" lower. Methyl salicylate is slightly soluble in 
water, and is miscible in all proportions with alcohol and ether. 

On adding a coticentrated solution of caustic potash or soda to 
the oil, combination immediately ensues, with liberation of heat, 
and white crystalline compound is formed, CgH^(0K)C00(CH8), 
which is decomposed by acids with separation of the original oil 
When boiled with strong potash solution methyl salicylate is 
saponified, with formation of potassium salicylate and methyl 


The aquemiB and alcoholic solutions of methyl salicylate give tht- 
characteristic violet coloration with ferric chloride. 

CtmtmprriaJ GauUheria Oil is a name applied indifferently to the 
pnxlncte from the wintergreen and cherry-birch, thouj^h the two 
products aiB not ohsolutclj identical. The true gaultheria 
oil containa more or less (from an insignificant quantity up to 10 
per ceni) of a hydrocarbon isomeric with turpentine oil (boil- 
ing about 200° C), which eomewhat modifies ite odour, density, 
and boiling point. Theoil of cherry-h ireh, on the contrary, 
consists of practically pure methyl salicylate. 

Oaulllieria oil is now BOmetimes employed in medicine ns a aiili- 
etitute for the metallic salicylates. It is liable to adulteration 
with oil of sassafras, alcohol, and chloroform. 

Chloro/orm may be detected by the smell when the sample is 
wnrme-d. Samples containing cWoroform have a high density and 
low boiling point, while the density is diminished by the presence of 
alfohol. The chloroform may be approximately separated and deter- 
mined by fractional distillation, or by estimating the hydrochloric 
seid formed on passing the vapour mixed with hydrogen through 
a red-hot tube. In the portion from which the alcohol and chloro- 
form have been separated by distillation, oil of sassafras may be recog- 
niBwl by its odour after addition of a hot concentrated solution of 
caustic potash, which combines with the gnultheria oil. SatisafroK 
nil may also be detected by adding 3 or 4 drops of nitric acid (uf 
1'3 to l"i sp. gr.) to 4 or 5 drops of the oil. Sassafras oil 
becomes blood-red in colour, and soon changes to a brown or dark 
red amorphous mass. Pure oil of wintergreen is unchanged at 
first, but after some houra it BoUdifies to a mass of colourless 
crystals, consisting ofmethyl-nitrosalicylic acid. 

Artificial methyl salicylate is now prepared of high purity, and 
ap[Kars likely to replace the natumi substance. According to 
C. Bullock, on shaking a few drops of the artificial oil with 
wal«r, a " tinted " mixture is formed which does not separate for 
some time, while the natural nil separatee almost immediatelyin clear 
drop«. The behaviour of the artificial product with water is said to 
bo due t/i the presence ofmethylic ether, (CHj)^O, and when 
tUi« is washed out the separation from water occurs more qnickly. 

PuKSTL SiiicTiATB!. SAtou CoHjCOHj.CO.O.CaHj. This 
body is now manufactured by heating the product of the action 
of carlwn dioxide on sodium phenato with phosphorus oxychloride 
or pentachloride, when phenyl salicylate and metaphosphate and 
chloride of sodium result. Phosgene gas (carljon oxychloride) may 
1^)0 cnhstituted for phosphorus pontachloride {Jour, Soc. 0iem. Ind., 



Phenyl salicylate crystallises in rhombic prisms which melt at 
42*-43* C. It usually occurs as a white crystalline powder of 
very faint aromatic odour, but the dilute alcoholic solution has a 
smell resembling that of wintergreen oil, probably owing to the 
formation of traces of ethyl salicylate. It is almost tasteless, and 
nearly insoluble in water, but dissolves in alcohol, ether, chloroform, 
petroleum spirit, and liquefied carbolic acid. 

The alcoholic solution of salol is coloured violet by ferric 
chloride, while bromine gives a precipitate in the form of long 
needles, consisting of a bro mo-derivative, CigH^OgBr, 
crystallising from alcohol in silky needles which melt at 98°*5 C. 
When boiled with caustic soda, salol is readily saponified, and the 
solution when acidulated with hydrochloric acid gives an odour of 
phenol and a copious precipitate of salicylic acid, which after 
filtration and washing with cold Vater gives with hot water a 
solution rendered violet by ferric chloride. 

Salol should not redden moistened litmus-paper; and when 
shaken with 50 parts of water should give a filtrate which is not 
rendered violet on addition of one drop of ferric chloride, nor any 
immediate change on adding silver nitrate or barium chloride. 

Salol is employed in medicine as a substitute for metallic 
salicylates and wintergreen oiL Being insoluble it passes un- 
changed through the stomach, but in the duodenum is decomposed 
into phenol and salicylic acid, and these products can be detected 
in the urine, which is usually very dark in colour. As an 
antipyretic, antiseptic, and antirheumatic, salol possesses properties 
of value. When applied externally it has no corrosive action, and 
its lower melting point gives it some advantages over salicyhc acid. 

A body analogous to salol may be obtained by substituting 
resorcinol for phenol. 

Naphthyl Salicylatb, CgH^(0H)C0.0.CiQBL7^^ a body analo- 
gous to salol, has been introduced into commerce under the name 
of *' b e 1 1." It forms small, lustrous crystals, melting at 203*, 
almost devoid of taste, and insoluble in water but soluble in 
alcohol and fatty oils. 

Salicylic Aldehyde. Salicylol. 

CyHeOg = CeH/OH) . CO.H . 

Salicylol was originally obtained by distilling the flowers of the 
meadow-sweet, Spircea tUmaria, with water. It is formed 
by oxidation of the corresponding alcohol, saligenol, 
C(jH^(0H).CH20H, and by the action of oxidising agents on such 
glucosides (e.^., populin and salicin) as yield this alcohol 
by hydrolysia It is also obtained by the action of chloroform on 


a strong solution of phenol in excess of uauBtic soda : — C|jHpO + 
3:*iiH0 + CHClg= (^0,+ 3NaCl + 2H^0. 

Salicylic aldehyde is a colourless oily liquid, of pleasant aromatic 
(hIoot, and having a specific gravity of I'173 at 15°, It boils at 
about 196° C, and distils leadily in a current of steani, It is 
Riodentt«ly soluble in 'Water and veiy readily in alcohol and etlier, 
and b extracted from its aqueous solutions by agitation with the 
latter solvent. Salicylol, like other aldehydes (voL i, p. 164), 
combinia with the acid sulphites of the alkali- metals to form 
crystalline compounds, which are decomposed by dilute sulphuric 
acid with re-formation of salicylol. The tendency to form the acid 
sulphite compound is so strong that salicylol is readily extracted from 
its ethereal solution by agitation with a strong aqueous solution of 
sodium hydrogen sulphite. This reaction is of service for the 
separation of salicylol from salicylic acid, phenol, Sic. 

By cocidation, salicylic aldehyde is converted into salicylic acid, 
which it resembles in the deep violet coloration its solutions 
acquire on addition of ferric chloride. 

Salicylol hns sometimes been termed salicylous acid, from 
its power of dissolving in solutions of alkalies to form crystalline 
tiietallic derivatives. It even decomposes carbonates. 

Salictlohio Acid, C„H„NOj=CeH.(0H).CO.NH.CH5.C00H. 
This acid occurs in the urine after administration of salicylic 
acid, but some of the latter is excreted unchanged. It closely re- 
sembles salicylic acid, but may be separated herefrom by a mix- 
tunt of ether and benzene, in which it is little soluble. 



~ Ortho-dihydroxy benzoic Acid. Ortho-hydroxy- 
salicylic Acid. 

( Oil'" 
^_ CjHaOj = C,HaO(OH)s = CeHg^ OIf=' 

^■r (CO.OH'". 

^^^vntocatechuic acid results from the fusion of various organic 
^^Bbh witli caustic potash. Catechin and maclurin also yield 
phloTOglucol (set! page 84), while many rosins give para-hydroxy- 
benzoic acid in addition, and gum benzoin gives protocatechuic and 
bonioic acids. 

Protocntechuir. acid forms thin monoclinic prisma or tufts of 
needles containing one molecule of water, which is lost at 100'. 
It melttt nt 194° and at a higher temperature is resolved into 
n dioxide and catechol, CaH^(OH)y Protocatechuic acid 


dissolves in 53 parts of cold water, and in 3^ parts at 80*". It 
is very soluble in alcohol, less so in ether, and almost insoluble in 
benzene, even when boiling. It is extracted from its aqueous 
solution by agitation with ether or petroleum ether. 

An aqueous solution of protocatechuic acid is coloured an 
intense bluish-green by ferric chloride (avoiding excess), the colour 
being changed to blue and afterwards to dark red on adding a 
very dilute solution of carbonate of sodium. A neutral solution of 
a protocatechuate gives a violet coloration with ferrous sulphate. 

Protocatechuic acid gives a white precipitate with lead acetate, 
and reduces ammonio-nitrate of silver when heated, but has no 
effect on Fehling's solution. 

Besides the important class of tannins giving green colorations 
with ferric salts (page 78), the following homologues and deriva- 
tives of protocatechuic acid possess a practical interest: — 

Orsellinic Acid (Dihydroxytoluic acid), . CH^C^^ < OH 

( CO.OH. 
OrseUic, Diorsellinic, or 1 p^ f CgH2(CH8).(OH), 

Lecanoric acid, . . . j ^^\ O.cXcCHjXOH^CO.OH. 

C CO.Off ^ 
Vanillic Acid (Methylprotocatechuic acid), . . CgHjK O.CHj^ 




Piperonal (Methylene-protocatechuic aldehyde), 


Guaiacol (Methyl catecholate), C^jH^-j qtt 

Vanillin. Vanillic Aldehyde. Methylprotocatechuic Aldehyde. 


Vanillin is the odoriferous principle of vanilla (the fruit of 
Vanilla aroma^ica). It is produced artificially from coniferin, 
^le^^^s* ^ glucoside occurring in the cambial secretion of all 
coniferous plants, by oxidation with chromic acid mixture (P?uirm. 
Jour., [3], iv. 996); or the coniferin may be split up by boiling 
with dilute acids or the action of emulsin into glucose, C^H^O^ 


and conileryl alcohol, C,|jH,jOj, and the latter product, 
oxidiaed by chromic acid mixture (see alao, Jour. Soe. Chem, Ind., 
Ui. 530). Vanillin is also piwluced by the action^of chloroform on 
an alkaline Bolution of guaiacoi, CoH,(OCHg)OH, a con- 
stitaent of wood-tar creosote (page 66). Vanillin may likewiBC bti 
|iKparrd from e u g e n o 1, CjoH^Oj, a phenoloid body which is 
obtained by treating oil of cloves with caustic alkali, filtering, nnd 
precipitnLing the solution with carbonic acid. The eiigeool is 
treated with acetic anhydride, and the acetyl derivative 
Qxidieed by a very dilute solution of potassium i^rmanganate. 
VThen the oxidation is sufficiently advanced, the liquid is Altered, 
the filtrate made slightly alkaline, concentrated at a low tempera- 
ture, acidulated with sulphuric acid, and the vanillin extracted by 
agitation with ether. 

Vanillin crystallises in stellate groups of colourless needles, melts 
at 80"— 81°, and sublimes when cautiously heated. It has a pleasant 
aromatic taste and oilour resembling vanilla. Vanillin dissolves 
sparingly in cold water, more froely in hot, and readily in alcohol 
and ether. Vanillin has the constitution and cliaracters of an 
aroumtic aldehyde. It forms well-defined bisulphite compounds, 
and also yields crystalline compounds with bases. Heated with 
dilute liydrochloric acid (preferably under pressure to 200°) it is 
resolved into methyl chloride, CHjCl, and proto- 
oat«chuic aldehyde; and when fused with caustic potash 
is converted into protocatechuic acid. 

By exposing moist and finely pulverised vanillin to the air it 
is oxidised tovanillic or metliylprotocatechuic acid, CgHgO^, 
whidi crystallises from ether in white larainse, and gives no 
colour-reaction with ferric chloride. 

Vanillin may bo extracted from aqueous liquids containing it by 
acidulating and agitating with ether. It may then bo separated 
from many substances sinuUtaueously extracted by agitating the 
clherenl solution with a saturated solution of sodium bisulphite 
(see page 21). 

On rubbing together vanillin, resorcinol, and hydrochloric acid, a 
deep bluish-violet coloration is observed, which vanishes after a time. 

Besides ita agreeable odour, vanillin is characterised by the 
blnish-violet colomtion produced in its solution on addition of ferric 
chlorida On heating the liquid, dehydro-divanillin, 
Ci,H,(Oms(COH)j(OCHg)j, separates in fine white needles, melting 
at 304', and sparingly soluble in water, alcohol, other, chloroform, 
and benzene, but readily soluble in alkalies (T i e m a n n. Jour. 
Soc. Ch'tn. Ind., v. 252). 

Vanilla is the fruit or pod of Vanilla jilanifolia, var. aromatica, a 


plant growing in Mexico, Java, Mauritius, &c. Its cultivation has 
become restricted since the artificial production of vanillin. 
Vanillin has been found in vanilla pods in proportions ranging 
from 1*32 to 1*86 per cent., in the Mexican product; from 0*75 to 
2*90 in that from Mauritius; and from 1*56 to 2 '7 5 in Java 
vanilla. These vanillas also contain vanillic acid, which was 
apparently mistaken for benzoic acid by the earlier investigators. 
Their aroma is entirely due to vanillin.^ 

For the assay of vanilla^ from 30 to 50 grammes of the finely 
chopped pods should be exhausted with ether, and the ethereal 
solution concentrated and thoroughly agitated with its own measure 
of equal parts of water and a saturated solution of acid sodium 
sidphite. The ether is separated, and the aqueous liquid, contain- 
ing the whole of the vanillin, treated with dilute sulphuric acid. 
The liberated sulphurous acid is expelled by a current of steam, 
and the residual liquid cooled and again shaken with ether. The 
ethereal solution is separated, distilled to a small bulk, and the 
remaining ether allowed to evaporate spontaneously. The residual 
vanillin is dried over sulphuric acid, and weighed. The process 
gives results from 1 to 4 per cent below the truth (T i e m a n n 
and Haarmann, PJiami. Jour,^ [3], vL 603). Vanillin has been 
detected in assafoetida by the same process. 

Piperonal. Methylene-protocatechuic Aldehyde. 


CgHgOg = CgHg ^ O I . ^g. 

Piperonal is produced by the gradual addition of a solution of 
potassium permanganate to one of potassium piperate. The liquid 
acquires a plesant odour like that of coumarin, and yields piperonal 
on distillation. 

Piperonal crystallises in large lustrous prisms. It has a pungent 
taste and very agreeable odour, melts at 37**, and boils without 
change at 263°. It is sparingly soluble in cold water, but more 
readily in hot, in which it melts, and dissolves very easily in 
alcohol and ether. It behaves like an aldehyde, and forms fi 
compound with acid sulphite of sodium which crystallises in 

^ On the other haod, in the West Indian variety, called vanilUme, the 
vanilla (from '4 to 0*7 per cent ] is associated with another substance, probably 
of aldehydic character (benzoic aldehyde or piperonal). Yanillone has long 
been used for preparing ** essence of heliotrope," but this is now made 
by adding a small quantity of benzoic aldehyde (artificial) to artificial vanillin, 
when, after a short time, the mixture acquires exactly the odour of the natural 
white heliotrope. 

Jaminffi and ia but eligbtly soluble in water or alcohol. lb is not 
olterml by ttqueous alkalies. 

Piperoiial has been recently recommended as an antipyretie and 
antiseptk of moderate power. 

Catechol. PyrOCatechin. Ortho-dlLydrosybenzene. 

^t«cbol ia produced by heating protoeateehuie acid, and 
Dins and allied bodies derived from it. It is also produced 
by the action of an excess of fusing potash on ortbo-phenoisul- 
phonie acid. CeH^{S03H)0H.i It is beat prepared by the action 
of hydriodic acid gas on boiling guaiacol. 

Catechol forms short square prisms or thin pearly plates 
resembling bensioic acid. It melts at 104° and boila at 245°. It 
sublimes readily and condenses in brilliant laminte. The taste is 
^^^^r, and the fumes are pungent and excite coughing, 
^^^B^iocatechin is very soluble in water, alcohol, and ether. It ia 
^^Hncted from its aqueouB solution by agitation with ether. 
^^" Catechol forms unstable compounds with bases. With lime-water, 
an aqneoDs solution of catechol forms a mixture which acquires a 
reddish or brown colour, but remains clear for some time. Caustic 
soda behaves somewhat similarly, the solution becoming, in 
sacceseioD, green, brown, and black. Catechol is not precipitated by 
gelatin or alkaloids. With acetate of lead it yields a white pre- 
cipitate easily soluble in acetic acid. It reduces silver nitrate in 
the cold, and Fehling's solution on warming. 

An aqaeous solution of pyrocatechin gives no reaction with 
ferrous salts. With ferric chloride, avoiding excess, it gives a 
grass-green colour, which, on adding acid carbonate of sodium, is 
changed to a fine vtulet-red, not much altered by boiling but 
restoriid to green by cautious addition of acids. (These reactions 
distinguish catechol from pyrogallol.) 

i-vood moistened with hydrochloric acid mixed with a solution 
kpyrocatecbin acquires a violet-red coloration. Fhloroglucol 
B a similar reaction to pyrocatechin. 

; Methyl Catecholate, CgH^{OH)O.CIIj, boila at 
', haa a specific gravity of I'llT at 13°, is slightly sotuble in 
n, and readily in alcohol and etber. Its analytical reactions are 
I brat obtuned from tbe fraction of beechwood-tar cnioaotc 
t abnul S00°-2D6°. This conaiaU esnentially of guaiacol (vol. ii. 
pap S6fij, Ihe methyl etber of cateclio!, C,H,(0CU,}OU, and on heatiug it to 
tliB boUiiiK jioiat, and psasing in hydriodic acid gaa aa long aa mvthyl iodida 
Uilila otor, cnlMbol ia prnlaced and may be pnriiied by fractiDnal distillation. 

I Vol. m. PART I. K 


practically those of purified wood-tar creosote, of which, with its 
homologues, it forms the greater part (vol. ii. page 565). Guaiacol 
has recently been recommended for the treatment of phthisis 
{Pharm, Jour,y [3], xviii. 537). 


Trihydroxybenzoic Acid. Dihydrozysalicylic 

CyHeOg = CeH2(OH)3.COOH. 

Gallic acid occurs in gall-nuts, sumach, divi-divi, tea, hellebore- 
root, pomegranate, and many other plant-products. It may be 
obtained synthetically by fusing bromoprotocatechuic acid with 
potash, and by several other reactions. 

Gallic acid is commonly prepared by the action of boiling dilute 
acid on gallotannic acid (fi^fiyQ0^'\-^B^^2C^Ji^^ or by the 
hydrolysis of the same body in presence of air, under the 
influence of a natural nitrogenised ferment called p e c t a s e. For 
this purpose powdered gall-nuts are moistened with water and 
exposed to the air for some weeks. The dark-coloured mass is 
washed with a little cold water and then boiled with more water, 
which extracts the gallic acid. 

Gallic acid forms white or light brown crystalline needles, 
containing 1 aq., which it loses at 100* C, or, according to Bot- 
tinger, at 120% It is soluble in 130 parts of cold, or 3 of boiling 
water, the hot saturated solution depositing abundant crystals on 
cooling. The solution has an acid and astringent taste, and decom- 
poses on keeping. Gallic acid is also soluble in rectified spirit 
and in glycerin, and is slightly soluble in ether (1 in 40). It 
may be removed from its aqueous solution by agitation with ether 
or ethyl acetate. 

When heated to a temperature of 210 to 220"" G., gallic acid melts 
and is decomposed with production of carbon dioxide and forma- 
tion of a crystalline sublimate of pyrogallol, C^H^G^ (see 
page 70). If the heat be raised suddenly to 250* C. the results 
are different ; in addition to carbon dioxide, water is given off, 
and in the retort there is found a considerable proportion of dark 
lustrous material, which consists chiefly of metagallic acid, 
(CgHg03 = CgH^02-|-H20). By heating gallic acid in glycerin 
to about 200* C., the theoretical yield of pyrogallol is obtain- 

When heated to about 1 40* C., with four times its weight of con- 
centrated sulphuric acid, gallic acid is converted into rufigallic 



ftcid.' Lowe osbs five parts of sulphuriu acid, and recommends a 
water-bath as the source of heat. The solution first becomes red 
and then purple, and on pouring the liquid into wat«r nearly pure 
rufigallic acid is precipitated. If in the above process a portion 
of the gallic acid be replaced by benzoic acid, the product is a 
trihydroxyauthraquiuone called anthragalloL 

Gallic acid is a monobasic acid, and forms a series of cryatallis- 
able metallic salta. The gallatcs of the alkali-metals arc per- 
manent in B dry state and in acid solution, but in presence of free 
alkali tbey rapidly absorb osygeQ, and become brown with focma- 
tioQ of hunioid products. 

Gallic acid is employed in medicine, as a reducing agent in 
pliotdgraphy, in the production of certain colouring mutters, as a 
hair-dye, &a. It is not a tanning agent. 

AsALTncxL RKACTiosa of Gallic Acid. 

An aqueous solution of gallic acid gives the fallowing re- 
dons : — 

pn addition of ferric chloride a deep blue precipitate is formed, 
li is soluble in excess of tho reagent with green colour. The 

kct colour of the precipitate is much affected by the concentra- 
tion of the solutions. An excess of gallic acid destroys the colour 
and reduces the iron to the ferrous state. Boiling produces a 
I Mi pilar change, 

^^■In the absence of air a solution of ferrous sulphate gives a white 
^^^Kcipitate with gallic acid in concentrated solution, but in dilute 
^^Hntion no reaction occurs. On exposure to air the liquid becomes 
^^Wight blue, and deposits a black precipitate without becoming 

W. H. Inco (PAanit. Jmr., [3], xvii. 462) prepares a neutral 
ferrous chloride by decomposing cupric chloride by iron filings or 

' BcFIOALLio AoiD Or Bufigallal, C,jH,0,, has thaconstitatiaDof ahexahy- 
droxy-anthinqainoDe. It forniaamiill. shining, rediliab-brown crystals 
, COntaininK 2 uj., but beoomes sobydraus i.i 320°, and gnblimea at a higbvr 
lire ID dnDabar-rsd priama. RnfigTtllic acid dissolves spariDgly in 
r, alcohol, and etber. Its aolutjoti gives a brown colaur with caustio 
and ID indigo-blue prediiitaU vitb baryta icater. When bented with 
, it ia reducod to antbracenn, Ci,H,g. 
n jiyrcigBllol ia Tosed with ammonium onaUte it yields ammonium 
rigallate, which daaaolves in water with red colour, and girei the 
tiom :— Pot«rincn ferricyanide and potassium bithromata give 
k brown precipitate insolobls in alcohol. Ferric chloride gives no black 
, and neither sodimn Ditropmaside nor pUtic chloride prodace 
r precipitate or change ot colour. On addiiig a few drops of acetic acid, 
. potassium cyuiido and mcrcurous nitrate, a black predpitate is 
Cans^c alkalies cause a chaoge to brown bat not to blade. 


wire. He adds this reagent to the solution to be. tested for gallic 
acid, and then gradually adds bromine in excess. Operating in 
this manner, gallic acid gives a faint blue colour on first adding 
the ferrous chloride, and this is changed to indigo-blue on cautious 
addition of bromine water or vapour, but the liquid is decolorised 
on adding excess. 

On addition of excess of caustic alkali to a solution of gallic acid 
the liquid turns yellow and ultimately brown and black on 
exposure to the air, from formation of tanno-melanic acid. 
The reaction is accelerated by boiling. On neutralising the black 
liquid with acetic acid and adding lead acetate, a black precipitate 
is thrown down. If sodium bicarbonate be used instead of caustic 
alkali, the liquid becomes indigo-blue and deposits a deep bluish- 
green precipitate, turned red by acids. 

Lime-water in excess produces a white precipitate, changing 
very rapidly to blue. 

Solution of tartar-emetic, K(SbO)T, precipitates white gallate 
of antimony, even from very dilute solutions. The reaction is 
prevented by chloride of ammonium. 

Grallic acid does not reduce Fehling's solution, or only very 
slowly and imperfectly, but it reduces gold and silver solutions 
(rapidly when hot), and decolorises an acid solution of potassium 
permanganate, being oxidised to hydro-rufigallic acid, 
Cj^HgOg. In the absence of other reducing agents, gallic acid 
may be determined by titration in an acid solution with per- 
manganate, preferably in presence of indigo. If tannic acid be 
present it must first be separated by precipitation with gelatin. 

No precipitate (distinction from tannic acids) is produced with 
gallic acid by solutions of alkaloids, gelatin, albumin, or starch, but 
a mixture of gum-arabic and gelatin is precipitated. 

Solution of potassium cyanide produces, with gallic acid, a fine 
red coloration, which shortly disappears, but can be restored by 
igitating the liquid. 

An ammoniacal solution of potassium ferricyanide produces a 
very bright red coloration, destroyed only on adding a laige excess 
of the reagent. 

An aqueous solution of picric acid, to which an excess of ammonia 
has been previously added, produces with gallic acid a red colora- 
tion, changing in a few seconds to a beautiful green. 

Gallic acid gives a somewhat similar and delicate reaction on 
addition of a faintly alkaline solution of arseniate of sodium, when 
the surface of the liquid exposed to the air rapidly becomes deep 

The following table exhibits the reactions of gallic acid in 


taposition with those of gallotannic and pyrogallic acuU, to I 
\ bodies gallio acid presents many points of resembtauco : — 


1 .«»... 




OmIUo Add. 


ftdebUD.. . . 

WlilM or bull 


No change. 





YbUow or red pre- 
dirtUte ol Cu^. 

No clung.; whin 

YeUow or red prf- 
elpiUU Dl Cl1,0. 

<tn» tnHD Uma 


chBiigea Id blue 

In ooncantraled 

In coneenlrmteil 

Ml(>, . . . 



MlalioD hr leut 

trace of FerrlD Hit 

«. VuTie ohlorids, . 


D«eu bina cDlon- 

Ked colour, turning 

jtate: colour do- 

tion, dalrojed 

brawn on beatiiig. 

■Cn>y>d bj boU- 
Bln^took prodp- 


S. fsrrte m«tmto, . 

^■^rt^' >"" 

Purple-black colot^ 

Deep r«d colnm- 

Cfuide. . . 


ooluntion,' ODlf 


deilrojed bj 

ol the raa«cDt 

Urge acta ol 




Kid, . . . 

rapldlj Chang- 

S. Uiat nUet Id ei- 

White prnttpitBla, 


No preclplute; Im- 


colour becoi^g 

ctaloride uid mm- 

•nonia. . . . 

brown lu the air. 

ft. L>»1 KeUte, . 

Iniolable In 


K:SS,"rt : 

While pmlpltolB. 

So qbUlKO. 



No ehaoge. 

nlum chlorlds. 

U. Blinnith Dltnle, . 

?Bl8 yellow pre- 

Dark grecnlrii pre- 




J^ FDMMlum cjiuiUe, 


No pracipitats. 



Bed eolour dl». 


uppenrtog DP 


(tiD'lliiK, bntre- 



lug with Die. 

B the absence of tannin and other interfering matters, gallic 
I may be determined by digesting the sotutJun with a known 
^t of recently ignited oxide of zinc. This is filtered off, 
, dried at 110° C, and reweighed, when the increase of 
^t iadicates the gollie acid taken up. i 

Uio acid may be Beparated from many varieties of tannin by 
^ting the aqueous solution witli ether. When the tnnnin ia , 
" ' I in ether, it may be precipitated by a moderate excess of J 
IS in Lowentbal'e procOHs (page 109), and the gallie acid ' 
I from the filtrate hy ngitating with ether or acetto ether. 


An approximate estimation of the gallic acid may be made by 
titrating the filtrate with standard permanganate in presence of 
sulphuric acid and indigo. 

Another method of separating gallic acid from tannins depends 
on the insolubility of cupric gallate in water, and its solubility in 
ammoniacal liquids. The solution is precipitated by excess of 
cupric acetate, the precipitate washed and digested with a cold 
solution of ammonium carbonate. The solution, filtered from any 
insoluble tannate of copper, is evaporated to dryness, the residue 
moistened with nitric acid, ignited, and the resultant cupric oxide 
weighed. Its weight, multiplied by 0'9, gives the weight of gallic 
acid.^ This method is applicable to the separation of gallic acid 
from gallotannic and quercitannic acids, but the copper salts of 
many varieties of tannin are more or less soluble in ammonium car> 

The solubility of lead gallate in acetic acid affords another means 
of separating gallic and tannic acids. 

PvrogalloL Pyrogallic Acid. Trihydroxybenaene. 

CeHe03 = CeH3(OH)3=CeH3-^ 0H« 


This substance is prepared by heating gallic acid or an aqueous 
extract of gall-nuts to a temperature of about 210'' C, when 
pyrogallol sublimes in prismatic plates. It may also be prepared 
by heating commercial gallotannic acid in glycerin to 200"* C, 
diluting with water, and extracting the pyrogallol by agitation 
with ether. 

When rapidly heated to 250** C. pyrogallol loses the elements 
of water and is converted into a black amorphous mass called 
metagallic acid, insoluble in water, but soluble in alkalies. 

Pyrogallic acid crystallises in thin plates or white lustrous 
needles. It has a specific gravity of 1'463, melts at 131** C.,* and 
sublimes at a higher temperature. It has an acid and very bitter 
taste. Pyrogallol is soluble in less than three parts of cold water, 
and is still more soluble in hot. It is also freely soluble in alcohol 
and ether, but is not dissolved by absolute chloroform. 

The acid properties of pyrogallol are very feebly marked. It is 
an active poison, producing symptoms similar to those occasioned by 

^ The true factor is 0*9126, the difference between this figure and 0*9 being 
a correction for a small quantity of cupric tannate diasolved by the ammonium 

s Often mis-stated as 115-118^ G. 


Pyrogallol is permanent in dry air free from ammoma, but in 
moist or amnioniacal air it gradually darkens, and in aqueous 
solution it tuma brown or black, eepecitJIy wlien the liquid ia 
Iteatud. In presence of ammonia or Kxed alkalies, it ubaorbs 
oxjgeu from the air with the greatest avidity, the liquid becoming 
iwii, and uitimotely almost black ; the colour ia destroyed by 
"c acid. 

■f ehling's copper solution, potassium ferricyanide-, silver nitrate, 
i auric cbJoride are mpidly reduced by pyrogallol, and perman- 
'i decolorised in acid solutions with evolution of carbon 
aide.* With lime-water, or ammonia and calcium chloride, a 
B purple colour ia produced, mpidly changing to brown, but no 
eipitate is formed. This reaction is delicate and characteristic.' 
h ferroua eulphat« a blue solution is formed, rapidly changing 

"The oxiilBtioD of pyrogatlol in acid or neutral eolutiona results in the 
rnofpnrpnrogalloIorpnrimrogalHii, a body of thoformuU 
C„B,^, or C„HitOg. It ia most readily obtaiaed by treating a wlulioD of 
30 puis of pyrogallol in 330 of water with a aolution of 87 parts of polauium 
ferricyBnide in 330 of water. Gaa ia evolved, the solution loBca ita deep 
nul colour, and purpurogallia aeparat€e, the oiidaHon being camptete in aliout 
hatful hour. PurpurogalUa crystalliaes from alcnhol in brown 
ueedlea, melting at 153°, and volatiliaiug at 200° with partial decuui position. 
It disaotrvs with difliculty in nater, but readily in alcohol and ether, and ia 
Minble in alkaliea to form imatable blae compounds. The aodium suit 
«>Dt>ina K*^ aad gives witb barium chloride an almost insoluble precipitate of 
th* barium coiupound. Id strong anlpharic acid, purpurogallin disauivce to a 
liquid which gives an intense violet coloration when a trace of nitrous acid 
or ■ nitrite is added. The colour is fugitive, but the reaction ia said to be 
ileliiaita and characteristic. 

' For eininiuing the behsvionr of pyrogallic acid with lime-water, it la con- 
Tonient to employ a nitrometer. Thia should be filled with mercury, or a 
roMlitly boiled saturated aolution of common salt, which has been previously 
traatcd with ammonium oxalate aad Altered from any precipitate. A Tew cubic 
irsntiiiietTea of the aolution to be tested for pyrogallol is then allowed to enter 
through the tap, and the cup ia rinsed with water, which is allowed to enter in itg 
liini. Ammonia la noit permitted to enter, when a slight brown coloration ia 
□nially [rroduced owing to dissolved oxygen. On now allowing lime-water at 
■slcium chloride to enter, a line but rapidly fading purple colour wiU ba 
■levcliiiiCHl. and thi* will beenormonsly intensiHed on admitting air and ablating 
til* tube; in (act, in the entire absence of oxygen, the blue colour would prob- 
ably nut Iw produced. In the absence of calcium (or.barinni) eompounda 1 
only a brown colour is produced on admitting air. Addition of potaasiun 
femcyanide to the ammoniscal liquid prodacra an immediate dark brown 
oolonllon, apparently owing to the formation of the same oxidation -product 
■a I* pTodncnl by admitting air; but lerrieyauiile prevents the blue reautiou 
with calclnm aalta, probably by immediately forming the more highly oxidised 
brown product. 


to green and red, and with ferric chloride a red coloration is given, 
taming brown when heated. PTrogallic acid does not precipitate 
a solution of gelatin. The aqueous solution of pyrogallol is turned 
brown by nitrous acid. The reaction is very dehcate. 

Pyrog^ic acid might probably be determined by titration in 
acid solution with standard permanganate, or perhaps by means of 
Fehling's solution. A process of determination might probably be 
based on the observation of the volume of oxygen absorbed by a 
solution of the substance after adding alkalL 

Pyrogallic Ethers. 

The volatile fractions of crude wood-tar creosote contain the 
dimethyl ethers of pyrogallol, methyl-pyrogallol, and propyl- 
pyrogallol (vol. iL page 565). Heated with hydrochloric acid under 
pressure, these yield pyrogallol and its homologues. Methylpyro- 
gdllol, CeHj(CH)8(0H^, resembles pyrogallol, melts at 129^ and 
volatilises unchanged. Propyl-pyrogallolf C^m^{C^Lf){OK)p is 
very soluble in water, alcohol, and ether, and melts at 79°-80\ 

The pyrogallic ethers derive their chief interest from the 
remarkable colouring matters (originally discovered by Bunge), 
which can be derived from them by oxidation {Pharm, Jour.^ 
[3], xii. 261, 428; Jour, Soe. Chem. Ind., iv. 152).^ 

^ Thus, if the sodium-derivative of dimethyl pyrogallate (prepared by adding 
soda to its alcoholic solution) be mixed with the sodium -derivative of dimethyl 
methyl-pyrogallate and excess of soda, and heated in the air, a body caUed 
eupittonic acidis formed :— 2C8HioO, -I- C,Hj,0, + 0, - CssH^Ob -»- 8H,0. 
On treating the mass with water, it dissolves with indigo-blue colour, which 
changes to carmine-red when the liquid is acidified. After removing im- 
purities by shaking the acidulated solution with ether, the eupittonic acid 
may be extracted by agitation with boiling benzene. Eupittonic acid is a 
sparingly soluble body which crystallises from alcohol or dilute acetic acid in 
orange needles. It dissolves in ammonia with blue, and in the fixed alkalies 
with purple colour. On adding caustic soda to the orange solution of 
eupittonic acid in alcohol, a beautiful blue coloration is produced, and a 
fiocculent precipitate is formed which gradually changes to a mass of small 
blue prisms having a beetle-green lustre, and consisting of sodium 
eupittonate, CuH,4Na,09. This compound is soluble in pure water, 
but the solution is precipitated by contact with air, and more rapidly by 
passing carbonic acid, and a blue precipitate is also thrown down by addition of 
brine. The eupittonates of calcium, magnesium, barium, tin, and other metals 
may be obtained as precipitates by double decomposition. The first two salts 
are soluble in pure water, the barium compound is a precipitate consisting 
of blue needles, while the lead salt crystallises in pale reddish needles. 
Reichenbach's *' p i 1 1 a c a 1," called by Wichelhaus **eupittone,*' was a 
salt of eupittonic acid. 

Eupittonic acid has the constitution of a hexamethoxyl-aurin. 


Gau-bITk, Ca,H,(,Oj, the phthalein of pyrofpillol, is obtained 
by heating pyrogallol or gallic acid with phthalic anhydride to 
190°-200°. It fonns a brown-red powder, or beetle-green crystals 
which are almost insoluble in water, but soluble in alcohoL It is a 
weak acid, forming with alkalies a blue solution, becoming dirty 
colonred on standing. In ammonia, gallein dissolves with violet 
colour, and the solution girt^ violet precipitates with metallic sails. 

When heated to 200° C. with twenty times its weight of atrong 
snlphuric acid, gallcin loses the elements of water, and is converted 

CcBBi:i.E[H, CgoHgOg, which on pouring tha cooled solution into 
water is obtained as aa amorphous black precipitate. It is nearly 
insoluble in water (which it colours olive-brown), alcohol, and 
ether, but dissolves easily in acetic acid. In commerce, ccerulein 
occurs OS a thick, dark-coloured paste. In alkalies it dissolves 
with beautiful grass-green colour, and the solution gives with 
mordants very stable lakes. With strong sulphuric acid ccenUeiii 
gives a dirty brown colour. On wanning coBralein with ammonia 
C„Hi(OCH|},0|, uid by heatinj; vritli snimonm ia converted into hexa- 
methozj'l-ptraros&iiillne, C„H,g(OCH,)aN„ which dyea silk, snl- 
pburaUil wool, and Unnikted cottou a Qob and pure blae. 

On subjwting thv pyrogallio ethers from wood-Ur cmotiote to mora poworfal 
oxidiring agents thao atmospberic air, such aa dilute chraniic acid miitnre, 
they are tnaverted into quhioui-a; thus, diinothjl pyrogallate yields 
ccRt allgnose, Ci|H„0„ a body which is identical nith Reiubenbach's 
"OBdrirot," It may ba conveniently prepared by adding potnsaium 
bicbrotnate to an acetic solution of the traction of wood-tat ereoaota di<i- 
tUliag between 2S0' and 260° C., when the liquid becomes hot and ia soun 
im«d wiUi neudlea, which appear red in truumitled and a beantifnl steel-blue 
bv rvQectod light. Cienilignone ih insoluble in ordinary aolventa, but dissolves 

Mtttong auli>batiD acid to form a solution of a fine corn-Hower tint, the 
IVUioa being so iotenae that the merest trace of the substance may be 
b neogniaed. In ptjenol it dissolves with red and iu creosote with blue 
tnr, and is precipitated in steel-blue needles un adding alcohol or etber to 
•olntion- By reducing agents it is converted into colourless hydro 
Tulignone, C,aH,,0„ ealubls in alcohol and benzene, and readily 
Mconreitdd into ccemiigBone by oiidising agents. HydroooiruligEono haa 
the oonsliiation of a totromethjl ether of hcKahydroiy-di phenyl, 
b it may be converted by heating with hydrochloric acid to 200° } 
iilignoue is the corresponding q u i n o o e, thus ; — 
Hvdfoooirulignone. Ctorulignone. 

fOCH, fOCH, 

c,hJoch, chJoch, 


and zinc powder, a brownish-red solution is formed, containing 
coBrulin, G^qH^o^^ ^® solution is oxidised in the air, the 
original green colour being restored. It may be employed in dye- 
ing in the same manner as an indigo-vat. 

On treating coBrulem paste with two molecules of sodium 
bisulphite, NaHSOg, a colourless compound of the two bodies is 
formed, which can be removed from the unaltered coerulein by 
extracting with cold alcohoL The bisulphite compound 
of coBrule'in occurs in commerce as a black powder under the 
name of Coendein S. It dissolves in water with greenish-yellow 
colour, and the solution becomes deep green, and sulphurous add is 
evolved. Acids and alkalies effect the same decomposition in the cold. 

Ccerulem and the bisulphite compound are used for dyeing and 
printing cotton fabrics, on which they produce various shades of 
green. The colour is not removed from the fibre by boiling soap 
or caustic alkalies, and is darkened by concentrated hydrochloric 
acid. The most characteristic reaction is that with a warm, acid 
solution of stannous chloride, which turns the fibre brownish-red, 
owing to the formation of c oe r u 1 i a On then washing with water, 
or preferably very dilute solution of bleaching powder, the original 
green colour is restored. 

Galloctanin, also known as solid violet, is obtained by heating 
gallic acid or tannin in alcoholic solution with nitro-dimethyl- 
aniline hydrochloride. It is a crystalline substance with a green 
metallic lustre, slightly soluble in water with violet coloration, 
and in alcohol and dilute acids with carmine-red colour. It 
readily dissolves in alkalies, and forms a series of salts which 
crystallise well, that with aniline forming small green crystals. 
Gallocyanin dissolves in strong sidphuric acid with blue colour, 
becoming a redder shade on dilution. It dyes silk and wool with- 
out a mordant, and forms a beautiful violet-black-lake with oxide 
of chromium, a fact that is now utilised in cotton dyeing. 


Under the name of Tannin or Tannic Acid are known, and to a 
great extent confused, a considerable number of vegetable acids 
having great analogy to each other, but possessing distinct 
individuality. The different varieties of tannin or tannic acid 
agree in the following general properties : — 

^ See footnote on page 107. 


I AciM are* compoimda of carbon, hydrogen, and oxygen 
^ a benzene nucleus. They are amorphous or sut>- 
crvBtalliiie aolids of astringent taste, not fusible or volatile, more 
or less soluble In water, and freely so in alcohol, or a mixture of 
alcohol and ether, and notably in ethyl acetate. They arc nearly 
insoluble in dry ether, and quite so in chloroform, benzene, 
(wtroleum spirit, and carbon disulphide. The tannins are generally 
but little soluble in dilute sulphuric acid. Their aqueous solutions 
give blue-black or green colorations or precipitates with ferric salts, 
and are all precipitated by tlie acetates of lead and copper and by 
stannous chloride. Some tannins are precipitated by taj'tar-cmetic 
and by mineral acids. In some cases the tannin combines with 
tlie ba«e only, but in others, as when cupric acetate is employed, 
the salt enters into combination as a whole. With a solution of 
gehtin, the tannic acids give precipitates analogous to 1 eather, 
quite insoluble in presence of excess of tannic acid, but not wholly 
insoluble in pure water. Tannic acids, or most of them, can be 
oompletely removed from their aqueous solutions by the intro- 
duction of skin or rasped hida The tannic acids are also removed 
bom solution by digestion with cupric or zinc oxide, and they 
reduce Febling'a solution on heating. A delicate reaction for 
tannins (lirst noticed by the author, and apparently general) is the 
de«p red colour produced on treating a solution with potassium 
ferricyanide mixed with ammonia. Tannic acids give insoluble pre- 
dpitates with many organic bases, the rosaniline and cinchonine 
precipitates being among the least soluble; but it is fretiuently 
observable that an alkaloid and a tannin which occur together 
in the same plant do not combine together to form an insoluble 

Tlie most characteristic property of the tannins is the formation, 
by combination with gelatin and gelatin-forming tissues, of the 
ioBolnble compounds which constitute leather. 

All natural tannins are powerful reducing agents, and exhibit a 
marked tendency to absorb oxygen, especially in alkaline solutiotL 
The oxidiition-products are often strongly coloured, 

Ixtractioii of Tannins. 

le different natural titnnins exhibit such differences, in their 
ic&I reactions and behaviour with solvents, that it is not 
ibie to give a general rule for their extraction in a state of 
The following notes indicate the nature of tbe methods 
to bo pursued: — 

The method of Pel ooze for the preparation of gallotannic 
-nutit IB as follows : — The powdered substance is 


exhausted with ordmaiy ether containing alcohol and water. On 
standing, the liquid separates into two layers, the lower of which 
contains tolerably pure gallotannic acid, while the upper ethereal 
layer retains the gallic acid. The tannin obtained by separating and 
evaporating the lower layer may be further purified by dissolving 
it in water and adding to the solution twice its measure of ether, 
when three layers are formed, the lowest of which contains nearly 
pure gallotannic acid. 

A more generally applicable process of extracting tannins is the 
following : — The finely divided substance is exhausted by treat- 
ment with rectified spirit, the solution filtered, and evaporated to a 
small bulk at as low a temperature as possible (preferably under 
diminished pressure). The extract is treated at once with a con- 
siderable proportion of cold water, the liquid filtered and fractionally 
precipitated with acetate of lead. The first and last fractions 
should be rejected, as they are usually contaminated with colouring 
matters and other foreign substances. The tannate of lead is 
washed as rapidly as possible, suspended in water, and decomposed 
by sulphuretted hydrogen. The filtrate is shaken with ether to 
remove gallic acid, separated from the ethereal layer, and evaporated 
in a partial vacuum to the consistence of a thin syrup. The 
remaining water should be removed by exposure over sulphuric 
acid at the ordinary temperature. 

Many tannins (e.^., sumach-tannin and ratanhia-tannin) may be 
purified by agitating with ether to remove gallic acid, saturating 
the concentrated aqueous solution with common salt, and agitating 
it with acetic ether, which removes the tannin. 

Some tannins {e.g., hop- and aldei^tannin) are stated to be 
insoluble in water after isolation, the change being probably due 
to partial decomposition. When the presence of such tannins is 
anticipated, the lead precipitate should be suspended in alcohol in- 
stead of water, before decomposing it with sulphuretted hydrogen. 

Many other vegetable bodies besides tannins are precipitable by 
lead acetate, but they are commonly insoluble in cold water. 

It not unfrequently happens that a single plant contains two or 
more tannins. Thus both oak- and willow- bark contain a little 
gallotannic acid in addition to their own peculiar tannins; and 
myrabolanes and divi-divi contain both gallotannic and ellagitannic 
acids. The existence of several tannins may be detected in some 
cases by fractional precipitation with lead acetate, and in others by 
examining the products of the action of dilute acid. Thus, oak- 
red produced from quercitannic acid is not removed by agitating 
the liquid with ether, while the gallic acid produced from the co- 
existent gallotannic acid is dissolved by the same menstruum. 


Constitution of Natural Tannins. 

From the tanner'a point of view, the natural tannins may be 
ananged in two great classes, name!;, those which produce a 
" bloom," or fawn-uoloured deposit, on leather, and those which do 
not. Tike tannins giving a bloom on leather give a blue-black 
coloration with ferric acetate, while the others afford a green 
colour with the same reagent. To the first of theae classes belong 
tlie tannins of gall-nuts, myrabolanes, divi-divi, sumach, valonia, and 
oak-bark, while the second includes the tannins of catechu, hemlock, 
laich, ratanhia, mangrove, and all the varieties of mimosa. The 
production of the " bloom " is in most iiasea due to the formation 
of ellugic acid, Ci.HgOg, a body allied to gallic acid, 
CfHgOj, of which most of the tannins of the first group may be 
considered to be derivatives. The tannins of oak-bark and valonia 
are either mixturee of two distinct tannins or of anomalous 
character, for they yield both gallic acid and protocatechuic acid, 
Cf KEgO^ ; while of all the tannins which give a green reaction 
with ferric ocetote are derivatives of the latter of these acids. 
Xhese again may be divided into tannins which yield acetic or 

Other fatty acid on fusion with potash, and those which 


haa been shown by H. S c h i f f that the ordinary tannin of 
_ (gallotannic acid) is in great part a glucoaide, and tliat 
under the influence of dilute acids, or of a peculiar nitrogenous 
ferment cjklled p e c t a s c, it splits up into glucose and gallic acid, 
Ihua:— C3^Hj^Oja+4HjO = CoH,jOg-J-4C,E,05. Many other of 
the natural tannins also furnish glucose by the action of dilute 
acids, but in some cases the change occurs with much less facility 
titan is usual with glucosides, Hence it has been suggested by 
Hlasiewetz that the tannins are not true glucosides, but 
tmdies which would be more correctly regarded as giunraides or 
dextrides,' and henc* that the formation of glucose by the action 
of ililat« acids is due merely to a secondary action on the gum or 
dextrin. Some of the natural tannins certainly yield no glucose 
by the action of dilute acid, and in other cases its formation is still 
ma open question. 

The amngenient of natural tannins into classes is therefore 
baaed on the products they yield: — (1) when heated alone, (2) 
when heated with dilute acid, and (3) when fused with caustic 
"", The characteristic products obtained by heating tannins 

ore pyrogallol and catechol; by heating with dilute 

Ionia is liabU to a natural fennentution (ropiaoss). in which large 
tiin or Mme dnular body precipitabU by aluohol are formed. 


acids, glucose, gallic acid, ellagic acid, and insoluble 
amorphous anhydrides called phlobaphenes; and by fusion 
with caustic alkali, pyrogallol, protocatechuic acid, 
acetic acid, and phloroglucoL 

In the table on next page the principal kinds of tannin are 
arranged according to the foregoing principles of classification. 

Certain of the tannins give a blue or black coloration when 
mixed in solution with ferric salts, while others yield a green or 
greenish colour when similarly treated. Speaking generally, the 
tannins which are derived from gallic acid give a blue reaction, 
while those derived from protocatechuic acid afford a green 

The reaction with iron salts ia best observed by adding to an 
aqueous solution of the tannin contained in a test-tube one or two 
drops of a dilute solution of ferric acetate. This may be extem- 
porised by adding sodium acetate to a solution of ferric chloride. 
Excess of the reagent must be avoided, or its colour and oxidising 
action may lead to error. The coloration produced by ferric acetate 
having been observed^ it is advisable to add an excess of ammonia, 
and note any change which may occur. 

If ferric chloride be substituted for the acetate, the general 
results are the same, but in some instances a greenish coloration 
is produced by tannins which give a distinct blue reaction with 
ferric acetate, and are undoubted gallic acid derivatives. This is 
especially the case if the ferric chloride solution contains free 
acid. Hence the acetate is much to be preferred as a reagent for 
tannins. Other reactions of tannins are given on pages 102, 103. 

The following is a description of the best methods of operating 
with a view to the formation and recognition of the decomposition- 
products obtained by the action of heat, dilute acids, and fusing 
potash on the different kinds of tannin. 

Action of Heat on Tannins. 

When a tannin which produces a ** bloom '' on leather (Class A) 
is cautiously heated to about 200*" C, it is decomposed with 
volatilisation of pyrogallol in feathery crystals. On the other 
hand, the tannins which produce no bloom, but red deposits, give 
a somewhat similar reaction, but the sublimate consists of cate- 
chol From oak-bark and valonia, which apparently contain 
a mixture of both kinds of tannin, and hence yield both bloom 
and red colouring matters, both catechol and pyrogallol are pro- 
duced on heating. 

In using the heating test for distinguishing the two classes of 
tannins, the temperature must be carefully regulated, or much loss 


t J I II |l|a 



IS S S l| ' 

ii lit ' iiil.i . , ^i.A ii 

II III' « Ml fiii I I I S|i I 8 1 

I n 

'Ha ■ ' 


Mili an i i s. iii HIS 



1^ i l« 11 

it! ;j 

Il in 1 1 1ll 1 Si 

iji i i i'm 1 I 1 111 ?! lit 

;; I 6 seas a a s sss I = 

:i i' 

=Bqa en ■ >a b ■ 


1- 1 =■ I » 

i |l I 1 I I 

1 1°- 1 1 I s 


will ensue and the recognition of the pyrogallol or catechol will be 
greatly complicated by the formation of metagallic acid and other 
secondary products. A better result is obtained by mixing the 
substance with several times its weight of sand or powdered pumice, 
and passing a stream of coal-gas or carbon dioxide through the 
retort, so as to carry the products quickly out of the heated space. 
A still better and more convenient plan ia the following, based on 
an observation of T. R Thorpe {Chem, Netcs, xliii. 109): — 
About 1 gramme of the sample should be heated with 3 cc. of 
pure glycerin to a temperature of 190" to 200* C. for twenty 
minutes. After cooling, the product is treated with about 20 c.c 
of water, and the liquid shaken with an equal measure of ether 
without previous filtration. The ethereal layer, which contains 
the pyrogallol and catechol, is separated from the aqueous liquid, 
evaporated to dryness, and the residue dissolved in 50 cc. of warm 
water. The filtered solution is divided into several portions 
which are respectively tested with lime-water, ferric chloride, and 
ferric acetate (see page 69). These reagents readily distinguish 
catechol from pyrogallol when unmixed, and will suffice for the 
recognition of the one in presence of not too large a proportion of 
the other. It must be remembered that the production of pyro- 
gallol may have resulted from the presence of gallic acid in the 
original substance, if the tannin had not previously been purified 
therefrom in the manner indicated on page 76. Catechol,. on the 
other hand, may be a product of the decomposition of catechin 
and other bodies allied to and associated with tannins, unless 
care has been taken to remove them previously. As a general 
rule, however, catechins and catechol-derivatives only occur in 
quantity with catechol-tannins, and the same is true of gallic acid 
with regard to pyrogallol. 

The characters of pyrogallol and catechol have already been 
fully described (pages 65 and 70). 

Action of Dilute Acids on Tannins. 

As already stated, many tannins are resolved on heating with 
dilute acids into glucose, and either gallic acid, ellagic acid, or 
an amorphous, insoluble, red colouring matter or phlobaphene, 
according to the nature of the tannin. Other tannins yield these 
products without glucose being simultaneously formed. As a rule, 
the action of dilute acid on a tannin results in the formation, apart 
from glucose, of a single decomposition-product belonging to the 
aromatic series (e.g., gallic acid, ellagic acid, phlobaphene, &c.), but 
in some cases two or more of such bodies are producible from a 
tannin of apparently homogeneous nature (page 79). 



I nitri 

'o ascertain whether a tannin yields glucose by hydrolysia, it 
firat be carefully freed from any admixture of ready-formed 

'hydrates by precipitation with neutral lead acetate, or satura- 
tion of the aqaeous solution with salt and removal of the tannin 
by agitation with acetic ether, in the manner indicated on page 76. 
The wnstied lead salt, or the tannin left on evaporating the acetic 
ether, ia then heated to 100° C. for some hovtrs, with dilute 
hydroclitoric acid, in a seated tube or firmly closed bottle. (Mere 
boilin}{ with the dilute acid, replacing loss by evaporation, is 
mlBcient in most cases, especially for qualitative purposes.) After 
cooling and opening the bottle, the mixture should bo allowed to 
etand for some time in the cold, to observe whether any simringly- 
Boluble decomposition-product separates.' In such case, the pre- 
cipitate should be filtered off, and any traces remaining in solution 
removed by agitating the filtrate first with acetic ether and then 
with ordinaiy ether. The aqueous liquid is boiled, neutralised 
with soda, precipitated with basic lead acetate (to remove any 
tnces of tannin or colouring matters), the liquid again tiltered, the 
excess of lend removed by dilute sulphuric acid, the filtered liquid 
■^in neutralised by soda, and heated to boiling with Fehling'a 
solution, when a yellow or red precipitate of cuprous oxide will 
prove the presence of glucose. 

The preeipitale produced on cooling the product of the action ot 
dilute acid on the tannin may consist of lead chloride (if the lead 
compound has been used), ellagic acid, or a phlobaphene. The lead 
chloride may be removed by washing with boiling water. If the 
residue has a pale yellow or fawn colour, and is but slightly soluble 
in cold alcohol, it probably consists of ellagic acid, which is 
soluble in ammonia and hot alcohol, and dissolves readily in strong 
nitric acid with intense crimson coloration, A red residue, readily 
luble in cold alcohol, will consist of a phlobaphene, which 

he reprecipitated on diluting the alcoholic solution with water, 

may be further examined by fusion with caustic potash. 
The ethereal layer, obtained by shaking the filtrate from the 
dUgic acid and pidobaphones with ether and acetic ether, will con- 
tain gallic a c i d, if any has been produced by the treatment of 
the tannin with dilute acid. For its recognition the ethereal 
solutioa should be evaporated to dryness, the residue taken up 
with cold water, and the solution filtered. The filtrate will give a 
fine red coloration with potassium cyanide, if gallic acid has been 
'.ueed. The reaction may be conlirmed by treating another 

n jiiKv^nt mbaequent uiarcD ot error, it is ilesirablo to get rid of rdj 
rormcd gallio >cid, by repeatedly ugitAtiag the solation of the tonnm 

oth«r before precipitatipg with letd acetate 



portion of the filtrate with an aqaeons solution of picric acid, 
followed by ammonia^ when a reddish coloration, changing to a fine 
green, will be produced if gallic acid be present 

In many cases it is not necessary to employ so elaborate a pro- 
cess as the for^;oing in order to distinguish the class to which a 
tannin belongs. It is frequently sufficient to boil the tannin or 
its infusion with dilute hydrochloric acid for some time, replacing 
the acid lost by evaporation* The solution is then diluted and 
allowed to cool, when eUagic acid and phlobaphenes will separate, 
and may be filtered off and separated by treatment with cold 
alcohol as already indicated. 

Gallic acid has already been fully described. Ellagie 
acid is considered on page 92. 


Chemically, the phlobaphenes are anhydrides of the 
respective tannic acids from which they are derived, or, in other 
words, they are formed from these tannins by the loss of one or 
more molecules of water. In this way they are produced by the 
action of dilute acids on tannins, and may also be formed in many 
cases by pouring alcoholic or highly concentrated aqueous solutions 
of the tannins into cold water, under which circumstances a part of 
the tanuiu seems unable to assimilate water and the phlobaphene 
se^virates as a red precipitate. Phlobaphenes exist ready-formed 
in most tanning materials capable of producing them, and may be 
dissolved out of these or the dried extracts thereof by means of 


The phlobaphenes are red or brown amorphous bodies, oifficultly 
soluble in pure or acidulated water or in pure ether, but soluble in 
water containing ammonia, and freely soluble in spirit Some 
phlobaphenes are so sparingly soluble in water, even when boiling, 
that the character may be utilised for the determination of the 
corresponding tannin. This is especially the case if, after heating 
with hydrocliloric acid, the liquid be evaporated to dryness and the 
residue treated with water. The decomposition-products then 
often remain almost entirely undissolved, but not wholly so, for, 
though mostly insoluble in pure water, they are dissolved more or 
less by solutions of sugar and other substances. The phlobaphenes 
are also dissolved by dilute alkedies and alkaline carbonates, and 
by borax, which last substance is said to be used in the preparation 
of some tannin extracts, and has been suggested as a means of 
rendering phlobaphenes available for tanning. The solubility of 
the phlobaphenes in water depends much on their degree of hydra- 
tion, many tannins giving a whole series of anhydrides, of which 
those containing only one molecule of water less than the original 


tannin are quite soluble in water, while the higher members of the 
series become less and less soluble aa they lose water. The soluble 
pblobaphenes are the colouring matters of tanning materials, and 
behave like the tannina themselves, precipitating gelatin and 
combining with hifle to form leather.' 

In many cases {e.g., gambler) it ia certain, and in others it is 
probable, that the tannin itself is merely the first anhydride of the 
series, and is derived from a catechin which is itself white, cryatol- 
Usable, and destitute of tanning properties'. 

The pblobaphenes somewhat resemble the rosins in their 
analytical characters, as, for instance, their solubility in alcohol and 
slight solubility in water, and in their behaviour when fused with 
cnnettc alkali; but they are distinguished from the resins by 
dissolving in dilute ammonia. "With gelatin, ferric acetate, and lead 
acetate the pblobaphenes usually react like their respective tannic 
acids. Occasionally a so-called tannin is mot with (c,_7., hop- 
tannin), which is not precipitated by gelatin, while the phlobaphene 
therefrom is precipitated. 

Phlobnphenea are yielded by the tannic acids from the bark of 
the onk, elm, horse-chestnut, willow, birch, fir, and acacia, as well 
as by the tannins from rhubarb, male-fcm, wine, Ac. According 
to Grnbowaki, the pblobaphenes from the tannins of the oak, 
ratanliiu, and tormentilla are not merely analogous to but actually 
identical with chestnut-red {see Quercitannic Acid, page 94), 

Action of Fused Alkali on Tannins. 

■VVheu tannins are subjected to the action of caustic alkali in 
a et(it« of incipient fusion, they are broken up with formation of 
products varying with their constitution. Thus all the tannins 
yielding catechol on dry distillation, that is, all those which give 
a greet! colour with ferric acetate — and valonia and oak-bark 
tantiiiiB in addition — give protocatechuic acid when fused 
with caustic potash. On the other hand, those tannina which give 
pynigallol when heat«d alone yield gallic or ellagic acid when fuxed 
with cAiistic alkali.' In each cose the reaction consists in the 
eCmbuition of COj. 

■ Hi Di lock -hark yirlda a seriea of auch bodici, of which the lowor memliera 
■m licop-rcd Kilublit Unnini, and tlia higher form the red aeditueut which 
(>rciir> in homlnck extracl. It is not pouible to dei:oIoriM Lemlock oxtract 
dithoul at Ihe Mmo tioiB Kt^atiy reducing its touning pavers, thou(;h by 
preparing riu] cnDrvntraUuf; it at n lov Ceuiiiersturo the proportiaa of insoluble 
kl|th«r BDhyilridia farmed Biiy W kept at n minimum. 

* Tbo roLitluiuhiji of these prodncts of thv deoom posit ion of tanuinBisahown 
gJliB folloiTUig formulK ; — 


The tannins which yield protocatechuic acid on fusion with 
alkali may be further subdivided according to the secondary pro- 
duct formed simultaneously, one class giving acetic or some other 
fatty acid, and a second a body called phloroglucol (page 85).^ 
A third class, including the tannins of the alder and hop, give 
both acetic acid and phloroglucol, but this peculiarity is not 
improbably due to the coexistence of two distinct tannins.' All 
those tannins which yield acetic acid instead of phloroglucol on 
fusion with potash give notable proportions of glucose on heating 
with dilute acid, while some, and probably all, of the phloroglucol- 
tannins give no sensible quantity of glucose. 

To recognise the presence of a phloroglucol-tannin without 
employing the tedious method described on next page, K. B. 
Procter mixes 5 c.c. of water, 1 c.c. of a saturated solution of 
commercial nitrate of aniline, and 1 c.c. of a very dilute solution of 
potassium nitrite. To this liquid is added 1 c.c of a solution con- 
taining as nearly as possible | per cent, of the tannin to be examined. 
If phloroglucin or a phloroglucide-tannin be present the liquid will 
gradually become yellow or orange, and will deposit a cinnabar-red 
precipitate after standing for a time not exceeding one hour, but 
many other bodies give precipitates which may lead to mistaken 
conclusions. Thus the reaction is produced by oak-bark infusion, 
which is not supposed to contain a phloroglucol-tannin, and gall- 
tannin, pyrogallol, and other substances give similar but browner 
precipitates. A sharper distinction may be obtained by employing 
more dilute solutions, but it is preferable, when possible, to act on 
the tannin with fusing potash and examine the products. 

The fusion with potash may be conducted either on the original 
tannin or on the body produced by treating it with dilute acid. 
When convenient, the lead salt may be substituted for the free 

rOH(i) rOH<>) 

Protocatechuic acid p xr I 0H(«) p^ Catechol p „ J 0H<«* 

(Dihydroxybenzoic acid) ^«"M H ~ ^'^«" (Pyrocatechin), «"« 1 H 

CO.OH<^) " " Vh 


Gallic acid p it J ^H pr^ Pyrogallol p rr 

(Trlhydroxybenzoic acid) ^«"n OH ~ ^"«"(Pyrogallic acid)^«*^« 



^ The formation of these products is due to a reaction allied to saponification, 
thus : — 

CisHioO. 4- KHO - KC7H5O4 + CjHgO,. 

Morintannic PoUMium Phloro- 

Acid. Protocatechuate. glucoL 

' The fusion of gallic acid with caustic soda is said to result in the formation 
of a small quantity of phloroglucol (Jour* Chem, Soc„ xliv. 60). 



c acid. The sepamtion of recognition of protocatochuic nnd 

; or pyrogallic acids when mixed is v^iy troubleaome, and 

e it appears better id moet cases simply to aim at the isolation 

B);ognition of pUoroglucol. The foUowing ia the method 

aJly prescrihed for thta purjwse: — 20 grammes of the tannin, 

lobaphene, or lead salt ia boiled with 150 c.c. of solution of 

istic potash, of 1*3 specific gravity, for two or throe hours, and 

i liquid then concentrated with continital stirring till it becomes 

', the alkali undei'going fusion.' The product ie cooled, and 

1 with dilute sulphuric acid in quantity siifBcient to render 

t whole distinctly acid when cold, the liquid is filtered from the 

sulphate and other solid matters, and the filtrate is 

[ with sodium bicarbonate till ita wine-red reaction with 

9 (or absence of red coloration witb methyl-orange) shows 

he sulphuric acid is neutralised. The liquid is then shaken 

il times with ether, and the ethereal solution evaporated. The 

le contains phloroglucol, recognisable by its sweet taste and 

ictions with ferric chloride and fir-wood. If necessary, it may 

k purified from protoeatcchuic acid by precipitating the aqueous 

ion with neutral lead acetate, the filtrate being extracted with 

jvaporated after sejuirating the excesa of lead by sulphur- 

1 hydrogen. 

ROGLUCOL. Phtxirogluciv. CgHgOg. This substance is 
■ with pyrogallol and hydrosyquinol, and is generally 
symmetrical trihydroxybenzeno, but 
a evidence in fovour of a difiVrcnt constitution.* It is possible 
t oxistfl in both forms, one of which is readily converted into 
It other, Fhlorofrlucol forms small plates or, rhombic tablets con- 
ning 2 aqua. It becomes anhydrous at 100°, and melts at 318° 
ueat»l rapidly, but at 209° or even 200° if slowly heated. -At 
^er temperature it sublimes without odour, and solidifies again 

hloroglucol is sweeter than cane-sugar. It ia soluble in water 
[ nlcuhol, and readily in ether, and by agitation with tho last 
snt can be removed from its aqueous solution. An aqueous 
n same cases, soch as that of phloretin, it ia sulHcioet to boil ttio alib- 
a with caustic potash lolution, m desnrib»t in the text, omitting the 
eqnent svaporation and fusion, 

i1 Triliydraij'beDitiDe. Modified Formula of Phloroglucol. 

[c/\ CI 


solution of phlorogluciu ia mot precipitated by any metallic salt 
except basic lead acetate. Xt ifl oclouied deep violet by feiric 
chloride, and reduces Fehling's solution and ammonio-nitiate of 
silver. In concentrated aqueous solution it is converted by bromine 
into tribromo-phloroglucol, CeH^BrgO^ which imme- 
diately separates in long needles, the liquid emitting a powerful, 
tear-exciting odour. 

When dilute solutions of phloroglucol and nitrate of toluidine 
or aniline are mixed, and a very dilute solution of potassium nitrite 
added, the liquid gradually becomes turbid and of a brownish- 
yellow colour, then orange-red, and finally a vermllion-red precipi- 
tate is produced. The reaction is extremely delicate. 

If a freshly-cut slip of deal be moistened with a dilute solution of 
phloroglucol (^ per cent), and subsequently with dilute hydro- 
chloric acid, it acquires an intense violet pr red colour. The 
reaction is very delicate.^ 

Gallotannic Acid. Tannic Acid. Tannin. 

Gallotannic acid occurs in gall-nuts in proportions commonly 
ranging from 60 to 77 per cent, and is usually prepared there- 
from by the method of Pelouze described on page 75,^ 

A preferable and more modem plan is to extract gall-nuts with 
a mixture of 12 parts of ether and 3 of alcohol, 12 parts of water 
being added to the extract, and the alcohol and ether removed by 
distillation. The residual aqueous solution is then filtered and 
evaporated, the product being further purified by solution in water 
and treatment with animal charcoal 

Pure gallotannic acid may also be obtained, according to Schiff, 
by extracting gall-nuts with anhydrous ether to which 5 per cent 
of alcohol has been added. 

As prepared by Pelouze's process, tannin yields more or less 
glucose or an analogous body when treated with dilute acids (the 
amount obtained varying from to 22 per cent), gallic acid being 
formed at the same time. Hence ordinary tannin is commonly 
regarded asaglucoside of gallic acid and represented by 
the empirical formula Cj^HjgOjj^j which would yield 23 per cent 
of glucose on hydrolysis. As prepared by SchiflTs process, how- 

' The coloration is readily obtained with infusion of gambier and probably 
of other phloroglucol tannins, but is also given by catechol (page 65). 

' A further purification may be effected by fractionally precipitating the 
aqueous solution of the product by acetate of lead, the first and last fractions 
being rejected. The lead tannate is then treated with a quantity of solution of 
oxalic acid insufficient for its complete decomposition, and the liquid filtered 
and evaporated, first at 100** C. and subsequently in vacuo. 



r, gfdlntannic acid yields little or no gluooHe on treatment with 
acid, and hence is not n glucoside, though agreeing in its 
ler characten with the pri^duct obtained hy Pelouie's method. 
appeare probalile, therefore, that the latter contained an adraixtnre 
sctunl glucoee, oi of a glucoeide brought into solution by the 
iter pieaent, junt as oak-bark tannin is liable to contamination by 
IffiTuIiu or the lievuloae formed therefrom. 

H. Scbiff has obtamed gallotannic acid synthetically by 
drying gallic acid at 110°, mixing it into a thin paste with phos- 
"loras oxychloride, and heating the mixture first to 100'' and then 
130° C. Much hydrochloric acid ia evolved, and the gallic acid 
converted into a yellow powder, which should be washed with 
ler and diasolved in water. The unchanged gfdlic acid is 
iwed to crystallise out, after which the solution ia saturated with 
salt, the precipitated tannin is washed with brine and 
ItBSolred in ether alcohol. The product thus obtained gives all 
reiictionB of purified gall-tannin, but is perfectly reconverted 
ito gallic acid on boiling with hydrochloric acid, without the 
ilion of any trace of glucose or ellagic acid. 
It may now bo considered fully established that pure gallotannic 
acid or tannin from galls has the composition C^^HjoO,, and in 
constitution is the first anhydride of gallic acid, or 
digftllic acid. Its relation to gallic acid and some other 
iiUied bodies is shown by the following formuJie : — 

OalUo acid. Trihydroxy- ) ^q f CoHj(OH)j 

benzoic acid, j ( OH. 

Gallotannic acid. Digallic 1 p^ f Conj(OH)g 

acid, J ^ t O.CaH,(OH)j.C0Oa 

acid co|«C«n^OH), 

"^"^ ^"lO.C,lIj(OH)pCOOH. 

,„ . ., n/, f O.CflHa(OH)j-^0 

„„ i C,Hg(OH), 
nm, . . , . uu j o.CeHi(Ot;H8),.COOH. 

- fc«H,(on), 

■ ^"^ j O.CaH,(O0H3). 

dcadd,. . . C0{W0">' 

UTcitanoic ncid (I), 

„,, (C,H,(OCIl,>, 

^" 1 0.0,H,(OH)(0CFy.C00H. 


The foregoing formula for gallotannic acid explains satisfactorily 
the following reactions : — 

1. The formation of gallic acid by hydrolysis: — C^^Lifig 
+H,0 = 2C,He05. 

2. The formation of gallamide and ammonium gallate 
in almost theoretical proportions by boiling gallotannic acid with 
aqueous ammonia in an atmosphere of hydrogen: — 

CeH2(OH)8.CO.O.CeH2(OH)2.COjjH+ 2NH3 
= CeH^OH)3.CO.NH2+ CeH,(OH)8.C02.NH^. 

3. The formation of a pent-acetyl-derivative by 
boiling tannin with acetic anhydride for one hour, the five hydroxyl 
groups being replaced by a corresponding number of C^ifi 

4. The formation of t a n n i n, or a body giving all its reactions, 
by heating monobromo-protocatechuic acid with potassium gallate 
and alcohol:— CeH2(OH)3.COOK+BrCeH2(OH)j.COOH = KBr 
+ CeH2(OH)jj.CO.O.CeH2(OH)2.COOa 

Pure gallotannic acid forms a colourless amorphous mass, light 
yellowish buff-coloured scales, or brittle vitreous masses. It 
becomes yellow in the light even if air be excluded* The taste is 
strongly astringent, and the reaction acid. When heated it darkens 
with or without fusing, and at 215° decomposes with volatilisation 
of water, pyrogallol, and carbon dioxide, while a residue of m e t a - 
gallic or melanogallic acid, C^H^02, is left. This last 
substance is the sole product when tannin is rapidly heated to 
280°, and is a black, amorphous, tasteless mass. 

Gallotannic acid is soluble in 6 parts of cold water, and more 
readily in hot. It is precipitated from its concentrated solution 
by dilute hydrochloric or sulphiuic acid, common salt, and 
potassium chloride and acetate, but not by sodium sulphate or 
nitric acid. Skin and other gelatinous tissues remove it completely 
from its aqueous solution. 

In absolute alcohol gallotannic acid only dissolves sparingly, but 
it is soluble with great facility in hydrous alcohol. In absolutely 
dry ether free from alcohol tannin is almost insoluble, but if 
water be gradually added the tannin first coagulates and then 
deliquesces, and after a certain proportion of water has been added 
the liquid separates into three layers. This happens when 100 
grammes of tannin is treated with 150 c.c. of ether, and 100 c.c 
of water added. The lowest layer is a concentrated aqueous 
solution of tannin; the middle layer contains some tannin and 
much water ; while the uppermost layer consists of ether holding a 
little tannic acid in solution. 



Gallotaimic scid is practicably insoluble in chlorofonu, bensene, 
petroleum ether, and carbon disulphide. In acetic ether aiid in 
glvcerin it dissolves readily. 

WliBii taken internally gallotannic aeid appears to b« converted 
into gallic acid, which may afterwards be found in the blood and 
arine. Tannin diffusea but slowly in aqueous eolution, but may be 
diitlysed from its eolution in alcohoL 

Gollotannic acid is readily oxidisable. It reduces the salts of 
►Id, silver, mercury and copper, penuanganates, &c. Nitric acid 
" iy oxidises it, with formation of oxalic acid; and chlorine, 
IB, iodine, and chromic acid act violently. 
^Gallotonnic acid decomposes carbonates and acts as a monobasic 
Its solution in caustic alkali rapidly oxidises, and acquirea 
a blown colour. The gallotannates are amorphous and 
diRicalt to prepare pure. Most of them are insoluble. 

One of the most important and characteristic reactions of gallo- 
tannic acid is the formation of a white (or buff-coloured) flocculent 
prpcipitate with a solution of gelatin. The precipitate, which is 
the basis of leather, and is sometimes called tannate of 
g (? I a 1 1 n, is not completely insoluble in pure water, but is 
wholly insoluble in presence of excess of tannic acid. ^Vhen 
freshly formed it ia often extremely finely divided, and passes 
lOgh the closest filter, but becomes coagulated by adding 
loniuni chloride, alum, and certain other neutral salts. 
>ddod to a dilute solution of gallotannic acid, ferrous sulphate 
no change, if free from ferric salt, but produces a white 
lipitatc in a concentrated solution. With ferric chloride tannin 
' ices a bluiah-lilack precipitate of ferric gallotannate 
:), the colour of which is destroyed by boiling or reducing 
lt8L Addition of hydrochloric acid in excess dissolves the 
Ipitate, which is reproduced on adding sodium acetate. Ferric 
ita behaves like fenic chloride. 
Ilotaunic acid ^ves no reaction with a solution of cupric 
mlphate, bnt on adding excess of ammonia it is completely pre- 
cipitated. The reaction may be employed for its determination. 
Fchling's solution is reduced bygallotannicacidon beating. 

With tartar emetic and soluble salts of lead and bismuth, gallo- 
tAnnic oeid yields white insoluble precipitates. With lime-water 
nnd with ammoniacal barium chloride it yields a white precipitate, 
turning Idue on exposure. 

" >taDmc acid ia not precipitated by calcium acetate from a 

veiy slightly acidulated with acetic acid, and the liquid 

clear oven after adding twice its volume of alcohol (seiiom- 

Trom tnrttnted, citrates, oxalates, malates, &c.). 


With an ammoniacal solntion of potassium ferricyamde, gallo- 
tannic acid produces a deep red colour changing to brown, even in 
very dilute solutions. The reaction, which was first observed by 
the author, is very delicate, but the colour is destroyed by a laige 
excess of the reagent. A somewhat similar reaction is produced 
by gallic acid. 

Ammonium molybdate yields with tannin a red coloration, which is 
yellow in very dilute solutions, and is destroyed on adding oxalic acid. 

Gallotannic acid may be determined with considerable accuracy 
by oxidation with a standard solution of permanganate (page 109). 

Gallotannic acid may be extracted from its acidulated aqueous 
solutions by repeatedly agitating with ethyl acetate free from 
alcohol, and may thus be separated from tartaric, citric, malic, and 
other vegetable acids, but not from gallic acid. In the case of 
ink, sufficient oxalic acid must be added wholly to change the 
colour of the liquid. 

Some of the foregoing reactions furnish important distinctions 
between gallotannic acid and gallic acid and pyrogallol, which in 
many respects it closely resembles. Others seem to distinguish it 
from the different varieties of tannin. The table on page 69 shows 
the reactions of gallotannic and gallic acids and pyrogallol in juxta- 
position. The comparative reactions of gallotannic acid and other 
tannins are given on pages 102, 103. 

Commercial Gallotannio Acid is often far from pure. It 
frequently contains more or less glucose, chlorophyll, volatile oil, 
and gallic and ellagic acids. Starch has been met with to the 
extent of 25 per cent, and in more than one instance the author 
has known it to be entirely substituted by gallic acid, either 
intentionally or accidentally. 

Glucose may be detected by precipitating the solution of the 
sample with basic acetate of lead, and heating the filtrate with 
Fehling's solution. A glucoside may be detected by the same 
method, after boiling the solution with dilute sulphuric acid for 
ten minutes, and neutralising the liquid with soda.^ 

If chlorophyll be present, on shaking the sample with an equal 

^ According to J. £. Saul (Pharm, Jorwr,,, [3], xvii. 887), a very delicate 
test for glucose, by which it can usually be detected in samples of oommercial 
tannin, Is to agitate about 0*01 gramme of the sample with 3 cc water, and 
then add three drops of an alcoholic solution of thymol. 3 cc of concen- 
trated sulphuric acid should then be poured in so as to form a separate layer 
below the aqueous liquid. Under these circumstances, tannin containing 
sugar yields a turbid deep rose-coloured solution, while gallic acid remains 
untinted, or merely develops a very faint pink tint in the sulphuric acid 
layer ; and pyrogallol yields a dull violet solution. 


reight of water and the sanje volume of ether the ethereal Inyer 
"1 be coloored more or less grccniBh. 

GallotaQnfu acid ehould be wholly solubJe in alcohol If a 
nidue be left it should be examined for etareh. 
Miwrral imjmriiies will be indicated by ignition. As a rule, 
merciot tannin leaves a very insignificant proportion of aah, 
b'4 per cent, being apparently the miLximuni proportion recorded. 

Gallic acid may be detected in commercial tannin by leaving 

' i aqueoue BOJution of the sample in contaat with a piece of 

Bttatmed skin, and agitating the liquid from time to time. If the 

Lnin be pure it is entirely absorbed, and the liquid becomes 

inpid, and no longer givee a coloration with ferric chloride ; the 

ntrary being the case if gallic acid be present. 

A test which ie said to be shorter than the above, and at the 

me time capable of detecting traces of gallic acid in taunin, has 

1 dBBcribed by S. Young {CheTn. News, xlviii. 31). The 

mple is dissolved in a little water, ether added equal in measure 

p ^out one-third of the water used, and the whole well shaken. 

D standing, three layers are formed. The ethereal or uppermost 

p removed, evaporated, and the residue dissolved in water and 

ted with potassium cyanide, when a strong red coloration will 

B obtained if the sample contained even a trace of gallic acid. 

a midiUe layer contains still more gallic acid, while the lowest 

hueooa layer is almost free from it. By repeating the agitation 

' li etJiet several times a complete saporation of the gallic acid 

D be effected. 

f A determination of the actual gallotaTmio aeid present in the 

merciol article is best made by Lijwenthal's permanganate 

^thod. Tlie residue of " not tannin " does not appear always to 

iet entirely of gallic acid, glucose being probably present in 

The following results were obtained by T. Maben 

■ Jour., [3], XV. 852), by applying Lowenthal's method to 

tentative specimens of commercial tannin. The witvlure was 

M-mined by drying the samples in vacuo over eulphuric acid.* 

P'' Tlie aathoT found that eommerciii tnnnia varied to the extent of 30 to -10 

D U» Jiower of preclpitatiog acetate of lead, which would rosct with 

h gallic and gollotuinic ocida. 

^'■Aooarding to C. Botting«r (/tnir. Soe. Dyers, ke., July ISB8), even the 

\ eaniitiHniUl tunnia ui not a uniform subatAiuw. When heated to IGO", 

witli conoeutrated hydrochloric add, it givvs olT a gae burning 

b a gnwii-«dged Santa (methyl chloride); &nd nn heating the tnniiiii with 

w of bromine. amaU qnantitiM of products voLitilD with itsatn 

ftpreduoMl. HsTerthelBwauch tanninisalmoBt compIet«1; filed b; hide, and 

' '( jwthiDg but gallic acid when boiled with aqueous cnustic alkiliui. 

i with a mijiturB of pheuylhydraiiiie hydrochloride nnd sodiuju 










Molrton. .... 
S'ot-tuialn (bf d^ennn), 
L«.nln.- '. . . . 











Ellagitaimic Acid. C,«H,gOig. 

This variety of tannin is contained in divi-^Ti and myrabolanes, 
and aa a glucoaide in pomegran&te rind. When boiled with dilute 
acids, or heated with water to' 110° C. in a eealed tube, it loses 
UjO and yields the anhydride, ellagic acid. In its other 
chemical reactions, ellagitannic closely resembles gallotannic acid, 
but yields a light brown precipitate with cupric acetate. 

I^j.Aaic Acid. 


T CbH,(OH)j I ^g;2 } C,E,(OH).CO.OH. 

This acid differs in composition from gallotannic acid by two 
atoms of hydrogen, and is formed when a concentrated aqueous solu- 
tion of that body is exposed for a considerable time- to the air, or by 
its reaction with iodine :— Ci,H„09+Ij = 2HI+Ci,HgO^ Ellagic 
acid is also produced by the dehydration of ellagitannic acid (see 
above), and by the action of oxidising agents on gallic acid. It is 
a constituent of bezoar stones.' Air-dried ellagic acid contains 1 
molecule of water, which it loses at 100° and re-absorbs in moist 
air. When heated to 200° C. it loses H^O, and forms an 
anhydride, Ci^HjOg, which is slowly reconverted into ellagic 
acid by boiling with water. When pure, ellagic acid forms a 
sulphur-yellow crystalline substance, nearly insoluble in water, 
even when boiling, and but little soluble in alcohoL The aqueous 
and alcoholic solutions have an acid reaction. It is but slightly 
soluble in ether, but small quantities may be effectually extracted 
from the aqueous solution by agitation with that solvent. In 

acetate it becomes inteDBel? yellow, cliangiDg to a brownish -yellow coiLgalatad 
mitsa on standing. This reaction is not caiued b; the presence of ■ sugar. 

' Ellagic scid is resdily prepared by pouring a concentrated alcobolic eitnet 
of divi'divi into water. The precipitate ma; be purified b; cryttsUisatian 
rrora hot alcohol. It may aUo be obtained by boiling the aqueons extiacta of 
divi-divi, myrabolanes, pomegranate rind, Ac, with dilute hydrochloric acid, 
and may be purified by solution in alcohol. It may also bo prepared bj heat- 
ing gallic acid withdi^ anenic acid to 160° C, but the product is difficult to 
purify from arsenic It may be obtained from beioar atones (intMtioal concre* 
tions of a Fersiau specie* of goat) by bailing with potash and precipitating 
mth hydrocUorie acid. 



Tliia Toriety oE tannic ai 
it furnis brittle mosaoa o 
aliylitly soluble in ether. 

canstic potash ellngic acid diasolvas with yellow colour, which 
tnpiilly becomes darker, and black crystals of potassium gkuco- 
melanatc separate. Neutral ferric chloride, when shaken with solid 
ellagic acid, is coloured greeniah at first, but afterwards becomes 
inky black. The solution of ellagic acid in hot alcohol haB a pnle 
jcUow colour, and deposits tho acid in sulphur-yellow crystals ou 
cooling. Witli lead acetate ellagic acid yields a precipitate con- 
taining 63 per cent, of PbO, Ellagic add dissolves in fuming 
nitric acid with deep crimson coloration. With the product 
ftom divi-divi, the nitric acid solution retains its crimson colour on 
dilution with water, but when derived from other sources, dilution 
is said to change the colour to orange. 

CaffetanniC Acid. Caffetannin. CuHj^Oj. 

,cid occurs in coffee berries. When isolated 
I yellowish-white powder. It is only 
On boiling cafTetannic acid with dilute 
sulphuric acid, or by exposing its solution in caustic alkali to the 
air, tlie liquid acquires a bluish-green colour owing to the formation 
of the oxidation-product viridic acid. This body is character- 
ised by giving a blue precipitate with lead acetate, and a crimson 
colonr with strong sulphuric acid. On prolonged boiling with 
caustic alkalies, cafTetannic acid yields caffeic acid, C^H^O^ , 
Mbich crystallises from tlie neutralised solution. Wlien fused witli 
Btic potash, cafTetannic acid yields protocatechuic and acetic 
Heated alone, it gives catechoL Ferric chloride gives a 
Iwk green colour with cuSetannic acid, and cinchonine sulphate 
'irhite precipitate, but solution of gelatin is not affected. 

I Qnercitaimic Acid. Quercitanniu.^ 

f According to C. Etti {Jour. Clmrn. Soe., xliv. 994) the tannin 
of oak-bark exists in two forms, namely, as quercitannic 
acid, and as an anhydride of that acid, orphlobaphene.* 
> Qiurcitaniiia aciil is aaiil to be idantical with tho tannins or the elni, 
d black tea. 

h 'QneratSQDia acid may be prepnred from treating oak-bark with oloohol, 
npontiug tbe filtered liijiud, disaolving tlie oitrai:t iu water, and BgiUtiDg 

WMlutioD with acetic ether. The product obtained an aeparstingandevapor- 

atlllg the ethereal Uyer ia contaminated by a brownisb-greua t«rp«iie r«ain 
and with aome of the anhydridea of tho tannin. The resin may be removed 
by trtating the dried extract with ether or benzene, in which it ia readily 
•olublo ; and the pblabaplienes or tannin -anhydrides may bo separated by 
aolving the tannin in ether-nlcohal, or partially by mere solution in cold 
Or the solnhld anbydrides may be precipitated by Batumting the 
•otutioD of the alcabaticextract with comiitoB salt before shaking with 
ia ether. 


Quercitannic acid is not a glucoside, the reactions which formerly 
caused confusion being really due to the presence of I » v n 1 i n, 
which on treating the oak-bark with dilute sulphuric acid was 
converted into IsBVulose. 

Quercitannic acid is amorphous, brownish-red, and readily soluble 
in water and alcohol. When pure, it dissolves completely in ethyl 
acetate, and does not yield anything to pure ether or benzene. 

In very dilute alcoholic solution, quercitannic acid yields a pure 
yellow precipitate with neutral or basic acetate of lead, but in 
aqueous solution the precipitate produced is light brown. "With 
ferric and ferroso-ferric salts quercitannic acid gives a blue-black 
colour, and yellowish-white precipitates with tartar-emetic, gelatin, 
albumin, and alkaloids It is also precipitated by solution of lead 
nitrate, ammoniacal chlorides of zinc and magnesium, ammoniacal 
sulphate and acetate of copper, and by molybdate of ammonium. 
It readily reduces permanganate and Fehling's solution. Accordii^ 
to H. R. Procter, a dilute solution of quercitannic acid does not 
precipitate blood-albumin, and in addition renders it imcoagulable 
by heat, even in presence of free acid. 

According to Etti, quercitannic acid has the composition 
CnHigOg.^ At 130' to 140** it gives up water and yields the first 
anhydride or phlobaphene, Cg^Hj^Oiy, which is brownish-red, 
nearly insoluble in water and in ether, but readily soluble in 
alcohol of all strengths. It exists in the original bark together 
with quercitannic acid, and gives a brownish-red precipitate with 
lead acetate. When boiled with dilute sulphuric or hydrochloric 
acid, the phlobaphene loses 1 molecule of water and yields 
a second anhydride, C^TL^iPiq, from which a third, 
Cj^HjgOig, may be obtained. All these anhydrides are soluble in 
alcohol and caustic alkalies, and are precipitated blue-black by ferric 
chloride. Lowe has obtained afourth anhydride, C^fl^fiip 
which he designates oak-bark red, a name which has he&a 
applied by other observers to the first and second anhydrides. 

Tanners designate the anhydrides simply as ** colouring matter," 
and reject barks containing a large proportion, as they impart too 
red a colour to the leather. 

^ Etti points out the following distinctions between gallotannic and querci- 
tannic acids : — GaUotannie Aeid QuereUatmie Add 

Heated with dilute sulphuric Yields gallic acid, giving Yields phlobaphene or 
add tol40' under presfure, a White precipitate oak-red, giving a brown 

with lead acetate. precipiUte with lead 


Heated with acetic anhy- Fonns aceto- tannins. Yields anhydrides and 

(lrl(][« ' acetylised anhydrides. 

Boiled with aqueous ammonia Yields gallamide and Yields indefinite resinoai 
In en atmosphere of hydro- ammonium gallate. products, 



From the number and mode of formation of these anhydrides, 
together with the evolution of methyl chloride on heating the 
tannin under pressure with dilute hydrochloric acid, Etti concludes 
that qiiercitannic acid is a methyl- derivAtive of digollic or gollyl- 
gnUio acid. Etti also inveetigated a tannic acid of the fonnuliv 
CgjHjjO^ obtained from the hark of a different species of oak. 
This agn^L•d with the other acid in all its properties, except that it 
gave a bluish-green colour with ferric chloride, rapidly changing to 
deep green, and on addition of sodium carbonate first to blue and 
then to red. This variety of taimin yields four anhydrides similar 
in character to those of the acid with 1 7 atoms of carbon. 

Liiwa (Jour. Ckem. Sac, xL 901) gives CjaH^Ojg as the 
fonnnJa of the hydrated tannic acid of oak-bark, and C^Hj^O,] as 
that of die ottk-red. Bottinger (Ber., rvi. 2710) adduces 
evidence of weight in favour of C^H,|,Ojo as the formula of the 
tAnnic acid, and CggH^O,^ as that of the onk-red. He has also 
attributed to the latter the formula (C„H,|,0^)j,Hp {Jwi: Chem. 
Sor., xxxviU. G50). To the tannin of oak-wood be attributes the 
formuU CuH,jOb (Jout. Chem. Soc., liL 584),' 

Aniinal Tannin. 

A body having the character of a tannin haa been extracted from 
core weevils {C'liem. Netcg, Ivi. 1 75). Tlirce per cent, was obtained 
of ■ aubetance forming small reddish-yellow scales soluble in water, 
at<»hol, aqueous ether, &c., and precipitating gelatin, albumin, and 
oLkoloids. It gave a hhiish-black coloration with ferric salts, and 

' II is probable that tlio diacrepsnt statements respecting ths coni position of 
o«k-hark taimraare due Uiibe jircaence of two annlagous bodies. Aconrding to 
r. UaiHct {Jour. Soe. Chem. /mi., lit 6i5) this u actnnUy the cue, both 
tonnilu being prscipttablfl b; gelatin aad oxidissble by permanganate. One, 
which he Imus oak-tannin, ma; be extracted by repeatedly sgitatiDg the 
iafiuian with acetic ether, in vhich the oak-red taunin is insoluble. Ha 
prefers, however, to determine the oak-rod tinnin by precipitation with iodine 
SToIdiag presence of ur. The compound formed contaiD9 7'3 per cent of iodine 
ami VI ei]ual qaantity of iodine is converted into hydriodic acid. An cquid 
qmntilyof theioruaion is treated with kihc olide, and, after twenty-four hoars, 
asd the absence of more tbui traces of tannin in the filtered aolution buing 
prnvAi) by gelatin and fcrricacetats, the non-tannin matters are titrated 
with H drcinormal lolDtion of iodine. By dedncting the amount of iodine, 
reinlrcti by the non-tannin ntsttcrs from that consumed hy an equal menscre 
of thu original iofusion, the iodine which has reacted with the tannins is found, 
uid by subtmcttng fram this twice the quantity of iodine contained in the 
precipitate of iodised oak-red taDuin, the iodine corresponding to the oak 
tannin is oscerlaiaed. Examinod in this manner, Musset found German 
okk-barka to contain from 7 to S per cent, of oak-Uniiiu, and G to 10 per cent 
[•laf Mk-roJ tsnniu. 


on boiling with dilute sulphuric acid split up into glucose, gallic 
acid, and a red phlobaphene. 

Lnpulotazmic Acid. Hop-Tannin. CjfHs^O^ 
The tannin of hope is a glucoside which is easily soluble in water 
and proof spirit, but not in ether. It gives a green colour with 
ferric salts, a dirty green precipitate with cupric sulphate, a yellow 
with lead acetate, and a brownish-yellow precipitate with lime- 
water. It reduces Fehling's solution. Lupulotannic acid yields a 
precipitate with albumin but not with gelatin, unless it be pre- 
viously dried at 100° C, by which treatment it is converted into 
the anhydride or phlobaphene,. CgQH^Ogg, a body coexisting 
with lupulotannic acid in the hop, and having all the characteristics 
of a tannin. It precipitates gelatin solution completely, and 
reduces Fehling's solution. It is soluble in alcohol and in alkalies, 
and is precipitated on acidulating the latter solution. 

Csitecllll-tailllic Acid. Mimotannic Acid. 

The tannins which yield catechol when heated differ from the 
pyrogallol derivatives by giving a green reaction with ferric acetate. 
Like oak-bark tannin, they give insoluble red phlobaphenes or 
anhydrides by the action of dilute acids. Their constitution is in 
most cases only very imperfectly understood, and even the 
composition of them is uncertain. The tannin of catechu is typical 
of this class of tannic acids. 

Catechu-tannic acid, probably identical with the body de- 
scribed as mimotannic acid, is the astringent substance 
contained in catechu (cutch) and gambier.^ It is extracted by 
cold water from catechu, and is also formed by heating catechin 
alone to 130°, with water to 110°, or by boiling it with alkalies. 
Catechu-tannic acid is a dark reddish-brown powder, moderately 
soluble in water, insoluble in ether, but readily soluble in alcohol 
and in acetic ether. It resembles gallotannic acid in many of its char- 
acters, but gives a greyish-green precipitate with ferric salts, and no 
reaction with ferrous salts. It is also distinguished from gallotannic 
acid by giving a dense precipitate with cupric sulphate and none 
with tartar-emetic ; and by yielding catechol and phloroglucol by 
fusion with potash. The aqueous solution is precipitated by gelatin, 
albumin, and dilute sulphuric acid. When treated with hydro- 
chloric acid and potassium chlorate in excess, catechu-tannic acid 
yields a chloro-substitution-product which is turned purple-red by 
sodium sulphite, Catechin gives the same reaction. 

^ It is doabtful whether the tannin of gambier is strictly identical with that 
of catechu. 



Catecliu and yambier contain from 20 to 30 per cent, of a body 
callail ca 1 c h i n, which appears to be the type of a number of 
HimUar bodies occurring ia all or most tannin materiiils yielding 
catechol- ton niiis. A catechin has certainly been recogniHed in 
CuIuTodo c|uebraclio, and the kinoi'n of kino is a. body of BimUar 
nature. The co-existence of several homologous or closely 
analogoufl bodies of the nature of catechin, even in catechu itself, is 
the probable expliutation of the difference in the formula assigned 
to catechin by diB'erent observers. Unless qualified in some way, by 
the term catechin the body contained in catechu (cutcfa) or 
(rajnhier is always understood. 

CATBCHiy may be prepared from ganibier or catechu by digesting 
the powdered substance in cold water to remove the catechu- tannic 
acid, and exhausting the residue with boiling water. Impure 
catechin deposits as the solution cools, and may be redissolved in 

dling water and decolorised by animal charcoal. 
i C&t«chin forms a white powder consisting of silky crystalline 
It melts at 217' C. and yields a suWimate of catechol on 
thot heating. It dissolves readily in alcohol and boiling water, 
inquires 1133 parts of cold water for solution. Agitation with 
ftei or acetic ether extracts it from its aqueous solution, a fact 
vich may be utilised for its purification. Though ' sometimes 
fiUed ca techuic acid, catechin possesses no acid properties, 
Itiough it is soluble in alkalies. The alkaline solution turns brown on 
exposure to air. Catechin dissolves in strong sulphuric acid with 
deep purple coloration. The aqueous solution gives white pre- 
I with lead acetate and mercuric chloride, and reduces 
monio-nitntc of silver, but, unlike the tannins, does not precipi- 
t gelatin, alkaloids, or tartar-emetic; on the other hand, it yields 
Boipitate with albumin. It is oxidised by permanganate in 
of free acid, a Fact which may be utilised for its estimation 
112). Heated under pressure to 140° with dilute sulphuric 
a yields catechol and phloroglucol. With diazobenzene 
■tide) catechin gives a red crystalline precipitate, which is 
blft in alcohol and ether, and dyes wool golden-brown. 

often described as an anhydride uf mimotannic 
i, the tannin of catechu and gambier, but according to Etti 
fe Opposite of this is probably the case. In constitution, catechin 
robably a phloroglucido of tetra- hydrogen ised protocatechuic 
This view accounts for its decomposition by fusing caustic 
i with nvolution of hydrogen and formation of protocatechuic 
and phloroglucol:— C,H,.COUUi2CBH3(OH),-f4H(OH)=. 
I,{OH),.COOH+ 2CflH,(0H^ + 2U^ 
'iJL. IJI. PABT 1. G 





> Insoluble in watei. 

Diffi'rcnt observers, however, are not agreed as to the composi- 
tion of cntecbin. Thus Liebermann and lauchert, who 
prepared a crj-staUised diacetjl -derivative, attribute to cat«chin from 
catechu the formuh CjiILjiOg+SHjO {Joar. Chem. Soe^ iL 53). 

By tho graduated action of heat or dilute acid on catechin it 
may be succt^ssivcly converted into the following anhydrides : — 

f Not acid ; does not pre- 
cipitate gelatin. 
Catechin -red ; Catechu- l^TTrt^Aj -i. 

tannic acid. j ^»^<^^ [ ^"'^^ precipitates 

Di-anhydridc. . ^,^0,, j ^eia'-"'. 

Tri^iihydride, . . Cggll^O^^ 

Catechuretin, 2C„H„Oo=C3gH„Oij 

Kisois, CjjHjjOg, a body resembling catechin, is obtained from 

green or Malabar kino by boiling with dilute hydrochloric acid, 

decanting from the precipitated kino-ted, and agitating with ether. 

AVTien recry stall ised from hot water it forms small colourless prisms, 

which are difficultly soluble in cold water but readily in hot water and 

in alcohol Its solution is coloured red by ferric chloride. Heated 

to 1 20°-! 30° it yields the anhydride, k i n o - r e d, CjgH„0„, and 

this when heated to 160°-170° gives CjgHjoOio. Both anhydrides 

are precipitated by gelatin, but kinoin itself is not When heated 

with hydrochloric acid to 120°-130°, kinoin yields methyl chloride, 

gallic acid, and catechol, and hence probably has the constitutiim of 

a guaiacol or methyl-catechol gallate. 

Tamun-yielding Materials. 

The following table gives the common names of the principal 
tannin -yielding substances used in commerce, together with the 
botanical names of the plants producing them, the parts of the 
plant used, and the usual jiercentage of tannin contained in good 
specimens of each material : — 

of MU.rl.1. ^ 




per cent, ol 

SKSi; : 


ChurcD-lwIl, . 

L>irch-liiirk, . 

Querciu peiluDculalu au<l Q. robur. 
Ab1e> CuwlentU. 
Aliiut aluUncHi. 













Common Name 
of liateriaL 

Botanical Name of Plant 

Fart of Plant 


per cent, of 


Catechu (Cutch), 
Qambier, . 

Sumach, . 

,, extract, 

„ extract, solid, 
„ ,, Uquid, 

Marsh Kotemary, 



Divi-divl, . 


Oall-nnts, . 
Tamarisk galls, 

Acacia and Areca catechu. 

Uncarla gambir and U. acida. 

Rhus coriaria, R. cotinus, &c. 
Castanea vera. 

Aspidospemum quebracho, &c. 
Statioe coriaria. 
Krameria triandria. 
Terminalia chebula and T. belerica. 
Ciesalpina coriaria. 
f Pterocarpus marsupium, and) 
( Drepanocarpus senegalensis. ) 
Quercus infectoria, Ac. 
Tamarix Indica, and T. Africana. 
? (Greece and Asia Minor). 

Extract from wood. 

J Extract from ) 
leaves and small |- 
branches. ) 


Extract from wood. 
Extract from wood. 

Do. do. 

Extract from fruit. 







C. Councler (Jour, Chem. Soc, xlviii. 946) has published 
the following results.^ The method of analysis is not stated, 




Readily Soluble. 

Mimotfa-bark, Tasmania, . 




II II • • • 




„ Victoria, 




II II ... 




Root- bark of Kermes Oak, " GarouiUe " 

\ 10-00 



(wiercus cocci/erau 
Bircli-bark, Friedricnsruh, 

• • • 



Alder-bark, Riesenthal, 




II i> ... 




II II ... 




>* II . . • 




II »i ... 




Willow-bark, Russian, Salix purpurea^ 
„ „ viminatis 




„ „ purpurea, 




„ „ capstca, 




„ „ amygcUUina, 




Quebracho-wood (highest), 
„ (lowest), . 











' In the saroe paper Councler gives some interesting calculations of the price 
per kilogramme of the tannin present in various commercial extracts. Thus : — 


Price per 100 kilos, 
iu shilliogs. 

Percentage of 

Price of tannin per 

kilogramme (=219 

lbs.) in pence. 

Quebracho- wood , 

,. extract, 
Hungariau pine-bark, 

., extract. 
Oak-bark extract, 
CbeHnut-wood. . 
Sumach extract, 







11 ■ 





but was probably von Schroeder's modification of Lowenthal's 

The following results by Kay and Bastow (Jour, Soc, Dyers 
and Col,, iiL 132) were obtained by the assay of tanning materials 
exhibited in the Indian and Colonial Exhibition of 1886. The 
process employed was Procter's modification of Lowenthal's method 
(see page 110). 

Tanning Material 

Percentage of Tannin. 

In terms of Oxalic 

In tAmiR of 
Gallotannic Add. 

Terminalia tomentosa (^lls), 
„ belericA (fruit), 
,, chebula (fruit), 
Ceriops Rosbnrghiana (bark), 
Camia auriculata, .... 
Acacia catechu (extract), 

„ ,, (bark^, . . . 
„ arabica (pods), . 
Areca catechu (nuts), . 

87 -65 






• . • 

• •• 

• •• 

• •• 

Descriptions of a large number of tanning products (barks, 
leaves, kinos, &c.) of New South Wales have been published by 
J. H. Maiden (Jour, Soc. Chem. Ind,, vii 38, 392). 

The results of the assay of a large number of tannin matters by 
Procter's method are given on page 113. 

F. Sim and {Jour, Sftc, Chem, Ind., iil 574) gives the follow- 
ing results of the assay of various tannin extracts by the Lowenthal- 
Neubauer method. 

Extract from 




Soluble in 
Cold Water. 

Quebracho-wood, solid, 
Valonia, solid. 
Oak-wood, liquid, 
Oak-bark, liquid. 
Fir, liquid, . 
Chestnut-wood, liquid. 
Sumach, liquid, . 

• •• 





Dried before analysis. 


Commercial extract 




I. Ishikama has published the following figures showing the 
strength, in terms of gallotannic acid, of various tannin-yielding 
materials of Japanese origin (Chem. News, xlii. 274), 

Percentage of Tannin (in 
terms of Gallotannic Acid). 
Gall-nuts (Japanese), . . . . 68 '8 to 67 *7 
., (Chinese), 77*4 


FVuit ofjlmajinna. 
Bark of Myrica mbra. 

FcrceuUge of Tanoiii (i[i 
termi of QalloUmiic Acid). 

Bind of PomDgraiiii 

Betel-nut, .... 

Oak-bark [Qiiemu dfntata) (inaar), 

QDAUTATirB RscooNiTioif OF Tannino Mateklai*. 

The tuble on next pngo, due to H. R. Procter, shovs the 
behaviour of iufuaions of a number of couiniercial tantiin matters 
Willi various reagents. The infuiiious must bo very weak, not 
exceeding I '002 in specific gravity, or preciijitates may be fonnod 
where mere coloration or clouding la described aa occurring. By 
m<^4n3 of the table, the origin of any simple tannin infusion is aaid 
to be uEcertftinable, but in the case of mixed infusions the indica- 
tions are less reliable. In such cases, colour-reactions are apt to 
mislead, and it is safer to rely on tlie categorical test of precipitate 
OS no precipitate, coloration or no coloration, without regard to the 

In some cases, only negative peciJiarities are recorded, and the 
ial cannot be positively identified in admixture with other 
matters giving positive indications with the same reagents. 
Tbna an infusion of myrabokncs could not he dialingulahed with 
ceiloititj from an infusion of divi-divi, where any other matcriid, 
such as gambler, was present, which gives a deep coloration with 
iccntrated sulphuric acid. 

addition to the reactions described in the table, the identi- 
m of the products of the action of beat on tannins, and of 
treatment with dilute acids and fusing caustic alkali, affords 
Tklaable means of differentiation. 

if not all, of the ordinary varieties of tannin give witli an 
loniacal solution of potassium ferricyanide a deep red colora- 
I, lApidly becoming brownish, especially on addition of excess 

\ extract from a bark yields more ash than that from a wood. 
ash of on oak or pine extract contains manganese and has a 
in colour, or becomes green on being fused with sodium 
late and a little nitre. 

shaking a concentrated solution of quebracho extract with 

ther, the ethereal layer becomes at first green and then brown. 

bark and extract of the American chcstimt oak I^Qufrmm 

i) contains a substance exhibiting, like CBsculin, a powerful 

ence, especially in alkaline solution. 





Boiled with 
equal Tolume 
of *dil. sul- 
phuric acid 


Dilute ferric 

On adding 

r Sol. tartar 

Add ammon- 
ium chloride. 





On adding 


in nitric acid. 

With sodium 
sulphide ex- 
posed to air. 

Add concen- 
trated sul- 
phuric acid 
to one drop 
of infusion. 

Lead nitrate. 

Cobalt ace- 


Uranium ace- 

picric acid 


Pale deposit 
on cooling. 

No precipi- 


Brown pre- 

No precipi- 

light pre- 

Faint cloud- 

Dense dark 

Yellow pre- 
cipitate turn- 
ing greenish. 

Dirty yellow 

Yellow col- 

Yellow col- 

Light yellow 

Buff precipi- 

Yellow pre- 

Dark red col- 

No precipi- 

Brown pre- 

Pale deposit 
on cooling. 

No precipi- 

Dark blue 

Dark red pre- 

Faint cloud- 

Dense pre- 

Slight green 

Dense dark 

Yellow pre- 

Dark greenish 

Yellow col- 

Intense crim- 

Dark yeUow 

Buff pink pre- 

Yellow pre- 

Dark red col- 

No precipi- 

Brown pre- 


Slight pale 

No prodpl- 

Blue - black 

Red - brown 

No precipi- 

Pale predpi- 

No predpi- 

Dark reddish 

Yellow pre- 
turning red- 


Slight pale 
deposit or 
turbidity on 

Pale precipi- 

Bluish black 

Red • brown 

No precipi- 

Whitish pre- 

Slight pre- 

Brown pre- 

Brown pre- 



urkffreenish Greenish pre- 
recipitate. dpitate. 


Turns pur- 

Deep yelloi 

Pale predpl- 

Dirty pink 

Dirty yellow 

Dark red col- 

Brown pre- 

Brown pre- 

Turns red. 

Deep red pre- 
cipitate on 

Brown pre- 

Brown pre- 

Brown pre- 

Dark brown 

No predpi- 

Brown pre* 

Slight red de- 
posit on cool- 

No predpi- 

Blue • black 

Dun red pre- 

Slight doud- 

Pale predpi- 

No pred|^ 

Dark brown 

brown pre- 

Dirty green 

Reddish pre- 

Dark brown. 

Brown pre- 

Dirty yellow 

Grey predpi- 

Dark red col- 

No predpi- 

Brown pre- 







ruich 1 OjmMer ''■ll'iliuiiilo 


Light red de- 

at,, " 

pc»|t on 



VbHow pre- 


Yen™ pre- 

Yellow pre- 

No prtclpl- 

Dull brown 

DirtT men 

Fidi brown 




Dull red pM- 



Dork red pre- 



S«^ pwlpl. 



"tate """''''" 



PalB pnrfpl- 

SKb-Ilt pale 

DenK white 


Painl uIoDd- 


filial elDnd. 

Me iireclpl' 

Slight pre- 


^uu '™''''' 

N.. predpl- 

DNf Wut 

ciplute. ', 



Deep Holet 


P-.le preclpi- 
i.itB turning 

DIHr hron 


Rllght tload- 

Slight pro- 


alilht daud. 


YbIIuw col. 


NO ehuije. 


f^llght red- 



intk tmwn 




D«!p red, no 

Dark hrewn 
IT cHm«on, 




nil.1 preclpl- 


Ko precipl- 


While pre- 






No preelpi- 

FomlB pre. 



No preolpl. 







iMTk red 



Crlmeon col- 
our. Brown 




No predpi- 







Brown col- 






Sumach extracts are distinguished by a peculiar tany smelly and 
yield a high 'ash. 

The following are detailed descriptions of certain tannin matters. 
The methods of assaying them for their content of tannin will be 
described in the sequel 

Catechu or Cutch is the dried extract from the wood of the 
Accusia caiechu and allied species. It is very similar in nature to 
gambier. Cutch, however, produces a hard red leather-like 
Mimoaa, and generally occurs in more or less brittle, splintery masses. 
Gambier occurs in light, porous brown cubes, more or less 
adherent, or in blocks measuring 2 feet X 1 foot X 9 inches, soft 
internally and wrapped in matting. Terra japonica is a trade- 
name, now somewhat obsolete, for both cutch and gambier. 

In addition to a large proportion of a variety of tannin 
(catechu-tannic acid), catechu contains 30 or 40 per cent, of 
catechin (page 79), which is deposited on cooling a boiling 
aqueous solution. 

Catechu is not unfrequently adulterated, starch, sand, clay, and 
blood being among the materials employed for the purpose, and 
Jessart states he has met with an admixture of 60 to 70 per cent 
of ferrous carbonate. Catechu should not yield more than 5 per 
cent, of ash. Starch may be detected by treating the sample with 
alcohol, boiling the insoluble residue with water, and testing the 
cold liquid with iodine, which gives the well-known blue colour in 
presence of starchy matters. The presence of ordinary tannin- 
matt ei's is indicated by the modified colour which the sample gives 
with ferric salts, pure catechu giving a decided green. Blood may 
be detected by treating the sample with alcohol, and drying and 
heating the residue in a tube, when ammonia and most offensive 
vapours will be produced. Aqueous solution of catechu should 
give with albumin or gelatin an abundant precipitate ; with salts of 
tin and lead, yellow precipitates of various tints; and a brown 
precipitate with bichromate of potassium. It should take a 
decided brown hue with alkalies, and give a greenish colour with 
ferric chloride. Good catechu yields at least half of its weight to 
ether and should be entirely soluble in boiling water, the latter 
solution depositing catechin on cooling. Catechu does not wholly 
dissolve in cold water unless it has been previously modified by 
age or exposure to damp. 

An aqueous solution of Pegu cutch gives dense precipitates with 
bromine-water and cupric sulphate, neither of which reagents affects 
gallic, gallotannic, or pyrogallic acid. In dilute solution, Pegu cutch 
does not precipitate potassium bichromate, but gallotannic acid 


I The proportion of tannic acidin catecbu ia best determined 
inthol's gelatin- pemianganBte procesB (page 1 10). The pro- 
Moa of catechin may be roughly deduced from the Tolumo 
of permnngtmate decolorised after removal of the mimotannic acid 
by means of gelatiu. More accurate results are obtainable by 
empluying a motlerate excess of gelatin, removing the catechin 
from the filtrate by agitation with ether, evaporating the ethereal 
liquid, dissolving the residue in vorm water and titrating with 

KiKo generally occurs in irregular black fragments, but it is aUo 
met with in round cakes. Thin slices are often transparent and 
of a reddish colour; the powder is red. Kino should be com- 
pletely soluble in hot water, forming a red liquid which gradually 
becomes turbid. Kino is sometimes adulterated, the usual 
■ophiatications being dragon's blood, pitch, catechu, and ratanhia 
extract. The last substance may be distinguished from kino by 
tonching a fmgment of the sample with the tongue ; kino remains 
rcd<li«h- brown, but ratanhia extract takes a fine bronie tint, which 
lu«tfi Bs long as the surface of the fragment ia wet. The itsb of 
kino should not exceed 3 or 4 per cent. 

Divi-Divi is composed of the l*an-like pods of Ctxealpina 
niriaria, a small tree found in the neighbourhood of Maracaibo 
and other parts of South America. The pods are about tlitee 
inches long, brown or blackish in colour, and generally folded up 
or bent into the shape of n letter S. The best pods are thick and 
'tshy, and of a comparatively pale colour. Deep brown pods with 
patches have been gathered when wet, or subsequently 
1 to damp, which injures them considerably. 
B is a generic name applied to those excrescences on plants 
i by the punctures of insects for the purpose of depositing 
^, G:klls are the most valuable and important of all tnnnin 
' Nut-ijedh, t/ak-galU, Al^ipo or Turfefy-ijallii are tlie 
iduce of the female of an insect called eijnxps (gall-wasp), which 
a the buds on tlia young branches of the Quercun inftxtoria 
thor species of oak. The eggs therein deposited soon hatch, 
e the bad loses it« nntural growth and swells out to the siie 
1 huel-nut. When perfect, the insect punctures a hole and 
H. Good gall-nuts should not be so pierced ; tbey should be 
', and of a freoh green or blue colour ("green galls "). If the 
act baa escaped, Utey are yellow and inferior (" white galls "). 
t MTnplaof glll-nnts ftntlyscd byGuibourt contained: — tannic acid, SS'O; 
k acid, 3*0 ; eilsgia and Inleo-gnltic acid, S'O ; chlorophjU and Tolatil« oil, 
etive matter, 2'G; gum, 2'5; lUrch, 3'0-, woody fibre, lU'Si 
r, albumin, and nsh, I'S; water, II'S percsut. 


The best oak-galls contain 60 to 70 per cent, of gallotannic acid, 
and about 3 per cent, of gallic acid. 

Worm-eaten galls are sometimes doctored by filling the holes 
with wax. The fraud may be detected by immersing the galls in 
boiling water, which melts the wax and renders the holes visible. 
Exhausted galls are occasionally coloured by washing them with a 
solution of ferrous sulphate, which is readily detected by its 
chemical reactions. 

Knoppem are galls formed from immature acorns of several 
species of oak, and are largely used for tanning throughout Austria. 
In a large number of samples of Austrian galls of the year 1 884, 
Eitner found from 28 to 35 per cent, of tannin, the moisture being 
about 12 per cent. (Jour. Chem, Soc,, xlviii 947). 

Chinese and Japanese gall-niUs are a production of the Bhus 
seinialata. They are very light and hollow, and distorted by 
numerous protuberances, and are completely covered by a thick 
velvety grey down. Chinese galls are much used for the prepara- 
tion of tannin, of which they contain about 70 per cent English 
galls from the common oak are much inferior to the foreign 
varieties. They are smooth, brown, and slightly speckled with 
pale brown excrescences. The Japanese are smaller, paler, and 
generally more esteemed. 

Myrabolanes are the fruit of several species of Terminalia. In 
size and shape the myrabolane resembles a slightly shrivelled plum. 
As imported, myrabolanes contain from 3 to 7 per cent of 
moisture, and have about 10 per cent, of ash on ignition. The 
tannin is chiefly contained in the dried pulp enclosing the stone. 

Good myrabolanes should be of a pale bulf colour, plump, or but 
slightly shrivelled, and free from worm-holes or blackish stains or 
blotches. They should be hard and firm, and when broken with a 
hammer should form a light-coloured dry powder and irregular 
fragments. If they crumble between the fingers to a dark coloured 
dust, or flatten under the hammer, they are inferior. The stones 
contain very little tannin, and hence their proportion should be 
ascertained by breaking 50 nuts with a hammer, clearing the stones 
from any adherent pulp, and weighing them separately. They may 
constitute from 23 to 52 per cent of the whole fruit. 

Ground myrabolanes should be light in colour, dry, and free from 
a saline or an intensely bitter taste. When slightly moistened and 
rubbed in the hand they should adhere very tenaciously to the skin. 

Myrabolanes are sometimes mixed with earth, sand, nvx vomica^ 
betel-nuts, and a variety of seeds and berries. They may also be 
adulterated with finely-ground divi-divi, wild galls, and old and 
worthless sumach. On scattering the powdered substance on a 


SCMACE. VAL0.V1A. 107 

sheet of paper, and extLiniiiing it ivith n lens, it will be reci^- 
niseil by the fragments of its brown, flat, smooth pea-like eceds, 
which from their hardness and smoothnesB, escape being crushed 
to powder. The leaf st&lks of sumach are readilj distinguished 
from the torn, irregular fibre of the myraljolftnea. 

SimAOH, or Shumac, consists of the leaves, leaf-atalks, and small 
twigs of several species of Jthug. It is sometimes sold whole, 
Aometiines coarsely bruised, but more commonly in fine powder. 
The beat Sicilian sumach gives a bright green powder wliich has a 
plcAsant tea-like odour. The second quality is reddish-yellow ; and 
Spnnish sumach has usually a fawn-colour. 

Sumach should be quite dry, and free from cakes or lumps, the 
presence of which shows the sample has been exposed to damp 
and will probably have become seriously deteriorated. The colour 
should be bright. If dull, the sample is probably damaged by long 
kMping, or is mixed with sumach of inferior quality. 

Sumach sometimes contains a notable proportion of earth or 
10 per cent, of ash is sometimes left on ignition. 

ValoXia consists of the ncom-cnps of certain species of oak, 

lielly exported from Smyrna, but also obtained from other parts 
of Asia Minor, as well as from Greece and the Grecian Archipe- 
lago. They should be of a bright drab colour. If dark they have 
witfcred from damp, and will be deteriorated in quality. 

Determination of Tannin. Assay of Tanning 

A great number of methods have been descibcd for determining 
tannin and assaying tannin-yielding materials,' In many instances 
the unthors have ignored the fact that gallic acid, while reacting 
ID many respects like tannin, does not form stable insoluble com- 
pounds with gelatin and albumin, and hence is valueless for the 
purpose of tanning.* 

' The tnetbmls of aisHjing laan in -fielding niateriHlB have been ably 
oxuninai] by H. R. Procter, and it is Iitrgalf from hia [inbliahed descrip. 
tinoi that the m&ttor in the t«at is derived. It may bo added that thn whole 
trtiele on tumina, mbstantiolly in its present wordiag nnd. ahnpe, has been in 
tmniisrript unce the early part of 1884, when Mr Procter kindly nndertook 
ila {leniial and correclion, and vrith the author's coniKnt incorporated some 
pt-rtionsoflt labia vnlnable Trrl-Bimk of Tanning {E. k F, N. Spon., 1885), 
The proofabeett have also been receotly eabniitted to Mr Procter. 

' A little coniidBrstion of the sobject will show that a genenJ method of 
dFtarmiuiiig the tannin in all kinds of tanning matters is not likely to he 
iltrlMd. The problem ia comparable to that of devising a fteDrrnl and simple 
tni-thud of detorniiniiig the metala forming coloured aalts,— say copper, iron, 
]■ r 11 iiini, i.oliall, and nickel, — iu presence of line, olnraimvirn, and lead, the 




Sahpli.vo of Tannino Mateuau U often a troublesome opcni' 
tion, and together with the difficulty attending complete exttactlaii 
is a fertile source of error. 

When available, a ateel-mill is the best means of loughljr 
pulverising most tanning mnterials. With the exception of barks, 
the grinding can be effected by a disintegrator with fine scnens, 
taking great care to prevent the escape of dust. Barks may be 
sampled by cutting each fragment with a small circular saw or nup 
driven by a lathe, and collecting the dust. 

In the absence of the foregoing appliances, bark and valonia may 
be cut with strong shears, and myrabolanes broken roughly with t 
hammer. In sampling vnlnnia care must be taken to get a doe p«>- 
portion of the beard, and in taking myrabolanes it must be remem- 
bered that the bad berries are light and work towards the top of the 
bag. The sample being partially reduced by one of the above means, 
the moisture (usually 15 to 16 per cent.) must be detennioed by 
drying at 100° C, and the thoroughly dried sample further giouud 
by passing it through a colfee-milL The ground sample must be 
again dried before weighing for aDalysis, as it is very hygroscopic. 

The Extraction ok Tannin-uattebs is better effected by treat- 
ing the sample at once with a. large quantity of water than by 
repeated treatment with smaller quantities. 10 grammes weight of 
vnlonia or myrabolanes, 20 of oak-bark, or a corresponding weight 
of other tanning material is placed in a fiask of at least 1^ litres 
capacity and covered with 1 litre of cold distilled wat«r. This U 
raised to ebullition (great care being necessary at the momutt of 
boiling to prevent frothing up and boiling over), and the liquid it 
kept boiling briskly for half an hour, a funnel being placed in the 
mouth of the flask. The liquid is then allowed to cool, rloMd 
with the solid residue into a litre flask, which is filled with cokl 
water to the mark, and the solution well shaken and filtered. If 
the solution is obstinately turbid it may be clarified by agitation 
with kaolin, followed by re-filtration. With tannin-matters whidi 
are opt to deposit eilagic acid or red anhydrides (pbobaphenesX 
higher results are obtained if the solution is cooled rapidly and 
filtered at once than if it is allowed to stand f or twenty-f our hoUR. 
Hence, in this respect, a uniform practice is desirable. If Gto 

salts of which nre unually colourless. It is enay to aeparate uoppsr from line, 
iron fram alumiDiuni, atid nickel from Uad, but thei-a U no method which will 
s«puste cop[>er, iron, ajid aickel at uue openitton from zino, ■lamintum, and 
lend. If, in addition, it were extremely diffictiU to obtain some of Ibtm 
metala iu it Klato of purity, and thay were lishle to chaoge by the actimi «[ 
rtogents, the prahlem would be rendered still more difficult Yet this Gurlv 
repmenti the pogJUoQ of the chemistry of the tunaius. 


titration ia not to be performed &t once, 0'5 c.c. of glacial acetic BCid 
nhould be added to check oxidation. In dissolving exiracts, it ia 
desirable to pour them into water actually boiling, as many 
become permanently insoluble if iirst mixed with water at too low 
a tflmperatUTD. 

Of the numerous methods which have been devised for the assay 
of tannin- matters, nearly all those worthy of detailed description 
an based on the principle of precipitation of the tannin by a 
solution of gelatin or its alisorption by a gelatinous sulistance. In 
some cases the weight of the precipitate formed, or the increase in 
the weight of the solid gelatinous substance has been ascertained, 
bat a preferable plan is to ascertain the qiiantity of tannin precipi- 
f comparing the liquid after the treatment with the original 
d solution. This is done by Hammer by taking the speoilia 
j; by Simand and Weiss by weighing the solid matter left on 
ration ; and by Lowenthal by determining the volume of 
Urd permanganate solution decolorised by the solution before 
oval of the tannin. These methods, which appear 
J enough in principle, are in practice surrounded with very 
isiderable difficulties, especially when considerable quantities of 
"o acid are present. 

I Ohdation-method op Tajintk Assay. 
a process, which woe first worked out by Lb wen thai, is 
on the fact that tannin is oxidised in acid sohitiona by 
^nate, though the slowness of the oxidation and the want 
I definition of the end-reaction render the method unsuitable 
t modification. By addition of a considerable quantity of 
> the oxidation of the tannin is controlled, and the end- 
1 is rendered perfectly definite. As solutions of coramorcial 
Q-matters contain other osidtsable matters .besides tannins, it 
I separate these and titrate a second time, in order to 
I the volume of permanganate actually required by the 
I preaent. This separation may be effected by digestion with 
pingB. or more conveniently by a solution of gelatin, the use 
!» was first suggested by Estcourt. 
Q practice, Lowenthal employs a mixed solution of gelatin and 
mon salt, to which a small quantity of sulphuric or hydrochloric 
's added. In using this form of the process it is generally 
wry to let the mixture stand several hours in order to obtain 
T filtrate, besidoB which the gelatin remaining in solution (or 
i associated impurity) has a slight tliough generally negligible 
pacing action on the permanganate. In some cases, even after 
etanding, filtration is very tedious, and it has also been 
ed by F. Siraand (Jour. Chem. Soc., xlii. 1237X that a 


certain proportion of the tanno-gelatin precipitate, varying with 
the acid and kind of tannin present, remains in solution, and 
hence that the results obtained by the process are below the truth. 

On account of the objections to Lowenthal's process as commonly 
conducted, H. R Procter has recently proposed a modification 
of it (/our, <St)<r, CA^/k Ind^ iiL 82), in which the excess of gelatin 
is removed by saturating the liquid with common salt, and the filtra> 
tion is facilitated by addition of kaolin. A perfectly clear filtrate 
wholly free from tannin, and nearly so from gelatin, is thus obtained 
without difficulty. The following are the details of the process : — 

a. 10 grammes of a sample of sumach or valonia, or 20 grammes 
of finely -ground bark, are exhausted by boiling with water in the 
manner described on page 108, and the infusion allowed to cool 
and diluteil to 1 litre. 5 c.c measure of this solution is run into a 
}x>rcelain basin and diluted to 750 cc. by addition of distilled or 
good drinking water, and 20 cc. added of an indigo solution, a 
litre of which contains 5 grammes of the purest indigo-carmine,^ 
and 50 c.c of concentrated sulphuric acid. A solution containing 
1 gramme of poUissium permanganate per litre is then dro])ped 
in very slowly with vigorous stirring, until the liquid becomes trans- 
ivirent, when the addition is continued more cautiously, with occa- 
sional i>au$es, until the clear yellow liquid appears of a faint pink 
colour on the margin. The titration is repeated, the measures of 
l>ermiuiganate required in the two cases being added together and 
called a. 

In employing the oxidation-process, it is essential that the 
volume of permanganate rei]uired by the tannin should in no case 
exceed two-tliirds of that reduced by the indigo. If the result of 
the titration shows that this proportion has been exceeded, the 
experiments must be repeated with a smaller quantity of the tannin 

6. 50 cc. of the tannin solution should be mixed in a flask with 
28*6 cc. of a freshly made and filtered solution of gelatin * (2 grm. 

^ The iudigo-carraine (sodium sulphindigotate) most be of such quality that 
the solution when oxidised by permanganate is a pure yellow colour, fh>m a 
trace of brown or orange. Any contamination with indigo-purple, which gives 
brown oxidation -products, is quite fatal to the accuracy of the analysis. A 
suitable material for the purpose may be obtained from Mawson & Swan, 
of Newcastle-on-Tyne. The indigo solution should be of such strength that 
20 c.c, diluted to 760 cc with water, shall require from 14 to 16 c.c of 
standard permanganate for its oxidation. 

' 2 grammes weight of Nelson*s or other good gelatin is allowed to swell in 
distilled water for a few hours, then melted by immersing the flask in boiling 
water, and the resultant solution made up to 100 cc 


per 1 00 C.C.). After slinking, the liquid is saturated with common 
E&lt,^ which increaaea the volume to 90 c.c. 10 c.c of dilute eul- 
[ihuric acid (containing I volume of the concentrated acid in 10) 
sliould next be added, and then about 10 granunea of pure kaolin 
or barium sulphate. The flask should now be vigocomily shaken 
for ■ few minutes, and the hquid passed through a diy filter. Tliis 
is effecttd mpidly, and the filtrate ia perfectly clear. Two quantities 
of the filtrate of 10 c.c each ( = 5 c.c of original infusion) are 
then treated with indigo solution, and titrated with standard per- 
maugauate as before, the result being called b. The difference 
(o— li) between the measum of permanganate employed for the two 
qoantities of unprecipitated tannin infusion (n), and that decolorised 
by Uie two portions of the filtrate, gives the volume of jiemiaoganate 
•olution decolorized by the tannin in 10 c.c of the original 

c. 10 cc. of a decinonnal solution of oxalic acid (6'3 grammes of 
ciystalliacd oxalic acid, CjHjOj+2HgO. per litre) is diluted with 
distilled water to about 500 c.c, warmed to about 60° C, 20 c.c, 
of pare dilute sulphuric acid added, aud standard pemuuigauate run 
in with constant stirring till a pink coloration, remiuning jiermiiuent 
fur a minute, shows that oxidation is complete. The volume of 
periitan^'uiiate consumed, which is called c, is evidently that 
rttijuired for the oxidation of 63 milligrammes of crystallised 
oxalic aciiL 

The proportion f :(a— ft) = 63 ; jt will give the number of 
miUigrammes of oxalic acid corresponding in reducing power to the 
hmnin in 10 cc. of the infusion assayed. If 10 grammes of the 
Bample were extracted and the solution made up to 1 litre, 10 c.c. 
of the infusion represented O'l gramme of the tanning material, and 
hence the number of milligrammes of oxalic acid will lie the jicr- 
eeiUage of lanrtin esy/regsed in terms of erytiaUited oxalic aeid. It is 
fnujuontiy convenient to express the results of the assay in this way, 
mtce what is reijuired in practice is not the absolute weiglit of 
the rarione materials, but their comjiaraiive richness iu 

^B. Hunt {Jmr. See. Chrm. Jnd., iv. 263) bu shown that the e 
itity ofalliBcoramenJedby Prottar L-ousBi the |irt-ripilutionorB not»l)le 
^MnUty of gillie wiit when much is pre«ent. HeiiPe, ha prerera to mk 50 cc. 
^th« tKDiiin solution ffith 2G c.c, or ft 2 por OHDt aohitionofgcslntia, ondlhL'n 
«dil 8G c.c i)( ■ sstaratcd solutinu ot common talt contaiuiDg GO cc of strong 
■nlpIiuHo will per litre. KaoUn 1b next BddaJ, snd the mixture veil ogilaied 
and fill«r*<il. and iu ■)! other rraiwcU Proctrr's method of operating ia ulhered 
to. llunl'i modjfleatiou ia approiimataly a rFturn Lo Luwenthkl't ori^iiiil 
■Bethod, mad intradu»» iU attcndaal error. Heiica HiiDt'i made of workinj; 
only to b« raoommeuded in prestnm of much gallic acid, 


tannin. It would of course be of interest to express the results of 
tannin-assays in actual percentages of tannin, but unfortunately the 
different varieties of tannic acid have different reducing powers, and 
the expression of the results of the assay of oak-bark or cutch in 
terms of gallotannic acid would be more objectionable than the 
expression of assays of all kinds of tannin-matters in terms of 
oxalic acid.^ The actual reduction-equivalents of the different 
kinds of tannin are very imperfectly known. Neubauer states 
that of gall-tannin at 41 '57; that is, 41 *57 grammes of gall- 
tannin possess the same reducing power on permanganate that is 
possessed by 63 grammes of crystallised oxalic acid (C^^O ^213^0% 
or 56 grammes of iron in the ferrous state. This is tantamount to 
the statement that 41 '57 grammes of gall-tannin decolorise a volume 
of permanganate solution yielding 8 grammes of available oxygen. 
Neubauer's equivalent for gallotannic acid has been confirmed by 
Ishikawa (Chem. New8,xhi. 274), who found 41*688 as the 
figure for the tannin of Kibnshi^ or Japanese gall-nuta 
Councle r and von Schroeder, on the other hand, find 
the equivalent to be only 34*25.^ For oak-bark tannin, 
Neubauer gives the equivalent 62*36, which is confirmed by 
Oser's figure, 62'35, and approximately by that of Simand, 61*1. 
The reduction-equivalents of other varieties of tannin are almost 
wholly unknown.^ Osers and Neubauer's figures for oak-bark 
tannin show a reducing power nearly identical with that of oxalic 

^Yon Schroeder has suggested the use as a standard of commercial 
gallotannic acid, the moisture in which has been determined by drying at 95* 
C. , and which has been proved to contain not more than 5 per cent of non- 
tannin matters unprecipitable by hide or gelatin ; dividing the result obtained 
by 1 '05 to allow for the slightly higher reducing power of the impure tannin. 
Procter has proposed to employ gallic acid [for standardising the permanganate, 
as it is readily obtained pure, and is oxidised in presence of indigo in a 
manner very similar to gallotannic acid. 

^ This discrepancy has been shown by von Schroeder to be duo to the 
different manner in which the permanganate was added in the titration, 
Neubauer employing the "drop method," while Councler and von Schroeder 
added the solution in successive quantities of 1 c.c. with a short interval 
between each addition. This modification seriously effects the volume of the 
standard solution consumed (see page 116). 

' The figures recorded byGiinther are so remarkably at variance with 
those of the observers quoted in the text, that there is probably some undis- 
covered error. His results were : — gallotannic acid, 16*25; sumach tannin, 16*6 ; 
catfetannic acid, 17*0; oak-bark tannin, 16 0; kinotannic acid, 14*0; 
ratanhia-tannin, 17 to 18*5 ; and tormentilla-tannin, 17*5. He also gave some 
figures for mimotannic acid and catechin, which when corrected for an error of 
calculation are 2*77 and 2*66 respectively. Lehmann, in checking these ex- 



aciii ( = 63), and bence, in the presfiHt stiiU' of the subject, the 
R<sulte of the titration may be conveniently oxprosaed in torma of 
oxalic Held. An alternativo plan is to atnlo the strength of the 
tnnnin-inatter in terms of " o.xygen conaumed." Each 1 c.c. of u 
lolution Iff piitasaium perroan^'auate (containing 1 gramme of the 
mU i«-'r litre) which mny havo heen decolorised by the tannin, 
represents 0'000253 of "oxygen consumed," or 0'00199 (practically 
0*002] greoimc of crystallised oxalic acid. Keubauer's oqiuvaletit 
fur gjiU-tttnnin is practically two-thirds of the bark and oxalic acid 
figorea. Thefirst figcro ia applicable to gftllB.niidiirohaldy to divi-diri, 
euniacb nod myraholitnes ; the second to oak-barks, mid probably 
to oak-wood, valonia, chestnut extract, Ac. Gallic arid consumes a 
greater volume of permanganate than the tannin from which it is 
derived. Hence, as commercial tannin is often largely contamin- 
ated with gallic acid, it not unfrequently sjiows over 100 per cent. 
of Uuinin irfaen assayed. 

According to Cech {ZeiUchr. Aiial. Chem., viL 134), no inter- 
ferenoe in the estimation of tannin by permanganate ia produced 
by the presence of acetic acid, citric acid, tartaric acid, malic acid, 
cuifl-siignr, dextrin, gum, fat, caffein, or urea, provided the solution 
\m properly diluted. 

It cannot be too clearly nnderstood that the permanganate and 
atl other processes tor the assay of tannin-niattuts are merely com- 
[luatire, and give results worthy of acceptance only when they are 
uaed for comparing the qualities of samples of material of the same 
cbaiBcter- Thus, bark may he compared with bark, valonia with 
valoDtn, and cutch with cuteh, but all cross comparisons are trtia- 
tfoHino ; and wonld be so even if the exact percentage of tannin 
could be calculated, since the practical and commercial value of 
tatming materials docs not depend on the quantity of tannin only, 
but on the colour and quality of the leather, though the same 
ptncesB should give absolute results of at least approximate 
accuracy when applied to different materials containing the same 
Taripty of tannin. 

Tlie fallowing figures hy Procter show the results to be expected 
when appljing the permanganate process to tlie assay of variuua 
tannin -matte 18. The determinations were made by the method 
alrewiy described. 

parlmonta, ronnd the equivalent 3'S7 Tor mimcituinic acid nnd S'42 for catdcliiD. 
Hute ii eviduatly gomctlime gnvnly wrong hero, for it would rranit in ■ 
taiuplF i>r ouMh wliivli a)iow«I flS i<«r cent, or l&tniiii vxpreswd ia IdmiH ot 
nlkUc acid Iwing sUtnt In coulain only 2'i]7 per («iiL ori^totliii-tanaic acid, 
tlioaj{ii n ikr larger proportiuu than that could be actuaUy prepared 




Valonia ; good Smyrna, 






Huugarian larch extract, . 




Chostnnt-wood extract (sp. gr. 
Pegu catch, 
Spent liquor,^ . 

1 -205) 

In terms of Oxalic Acid. 


29 '1 percent 


Other oxidisable 

2*8 per cent. 
2 1 

The permanganate process has been applied by A. H i 1 1 to the 
determination of tannin in tea {Anaiysty vi 95). The average 
proportion of tannin, in terms of oxalic acid, found in the thirty- 
two samples of tea examined was 14*8 per cent., the extreme 
results being 6'18 in black Assam tea and 26*90 in a black caper 
tea. Other determinations of the proportion of tannin in tea have 
been made by 0. K e 1 1 n e r {Jour. Chem, Soc.^ Hi 73) and J. F. 
G e i s 1 e r (Analyst, ix. 220). 

The following figures are due to B. Hunt (Jour. Soc Chem. 
Ind,, iv. 264). They show the insoluble matter and total extract 
of various commercial tanning materials, together with the oxalic 
acid equivalents of the total oxidisable matters, and of the tannin 
as precipitated by Procter's and Hunt's methods.^ The difference 
between the results obtained by these two methods is attributed by 
Hunt to the precipitation of gallic acid by the saturated brine 
employed by Procter, 

^ The results of the assay of the spent liquor are instructive. The liquor 
originally contained from 10 to 15 per cent, of the tannins from oak-bark, 
valonia, myrabolanes, gambler, hemlock, &c. , which contact with hide had 
reduced to the small proportion of 0*12 per cent. That a portion had not 
been absorbed but decom|)Oscd is shown by the large accumulation of oxidis- 
able impurities (equal to 11 per cent, of oxalic acid). Spent liquors are very 
pale in colour, as also are the filtrates from the gelatin precipitation, a fact 
that proves that the colouring matters present in tanning materials resemble 
tannin in their behaviour to hide and gelatin. 

For the method of examining tan-liquors, see page 125. 

' Hunt states in the same paper that treatment with gelatin and salt does 
not remove all that is of tanning value from solutions of gambler and allied 
materials, and hence he recommends the removal of the tannin in such oases 
by means of purified skin -shavings. These he adds in the proportion of 5 
grammes to 100 c.c. of a 1 per cent gambler solution, and after twelve hours 



^ a a_ M 

In terms of Oxalic Acid. 



Total Ex- 

Total oxi- 







<* Pore tannin,** . 

• •• 

• •• 




EngUth oak-l>ark, 






Canadian hemlock-bark. 






larcli-bark, . 






MangTOTe-baik, . 






Alderbaak, . . 












• ■• 











Turkish blue galls. 






img^ : 











DiTi-^vi, . 






Fbmegrmnate rind, . 






Tormentil root, . 











Pore Indian tea, 






Pore dilna tea, . 






Catch, . 






Oiiiii Kino, . 






Hemlock extract 
Oak-wood extract, 

• •• 





• ■« 





Chestnut extract, 

• •■ 





Qaebracho extract, . 
Thin -liquor (sp. gr. 

• •• 





1-090X . . 
Spent Uqnor (sp. gr. 

• •• 






• •• 





A few years since, the permanganate process of determining 
tannin was submitted to a careful examination by a commission of 
German chemists. After reviewing earlier methods, they recom- 
mended the following modifications of the permanganate process 
for general adoption : — 1. That the permanganate solution contain 
10 grammes of KMnO^ in 6000 c.c. 2. That the indigosoltUion 
should be made by dissolving 30 grammes of air-dry sodium 
sulphindigotate in 3000 c.c. of dilute sulphuric acid (1:3), 3000 
CO. of water added, the whole shaken till dissolved, and the liquid 

filters and titrates the filtrate with permanganate in the usual way. The 
following results were obtained : — 


Total Extract. 

In terms of Oxalic Acid. 

Total oxidis- 
able Matter. 

Absorbed by 

Cube gambler, . 
Baiawak ,, . . . 
Bale „ . . . 




43 70 


filtered. 20 c.c. of this solution in 750 c.c. of water should be 
used in each titration, and should reduce about 10' 7 cc. of the 
permanganate solution. 3. Hide powder is substituted for the 
ordinary gelatin solution. It must be white, and in a fine woolly 
state of division, and should yield to cold water no substance 
capable of reducing permanganate.^ 

Instead of adding the permanganate solution drop by drop, 
the commission recommend (with very doubtful advantage) that an 
addition be made of 1 c.c. at a time, and the mixture vigorously 
stirred for five or ten seconds after each addition. As soon as the 
liquid has become bright green, two or three drops at a time 
should be cautiously added with stirring, till the liquid is pure 
yellow. The results obtained by the " 1 c.c. method " differ con- 
siderably from those obtained by the ordinary or " drop method," 
which was that employed by Neubauer and Oser for the deter- 
mination of the reduction-coeflScients of tannins. It has, how- 
ever, been 8ho^vn by H. R. P r o c t e r {Jour, Soc. Chem, Ind,, v. 79), 
that the results are more influenced by the rapidity of mixing thaii 
by actual time, and that the 1 c.c. method, while it always gives a 
higher consumption of permanganate than the drop method, is even 
more affected by variations in stirring.^ 

To determine the oxidisable matters " not tannin,'* 50 cc of the 
infusion should be digested in the cold with 3 grammes of the hide 
powder (previously moistened with water, and well squeezed in 
linen). The liquid is frequently agitated during eighteen to twenty- 
four hours, and is then filtered, and 10 c.c. titrated in the usual way. 

F. S i m a n d has recommended the use of the purified gelatinous 
matter of bones as acting more quickly than hide powder (Jour. 
Soc, Chem. Ind., i. 509). Tubular bones, freed from joints and 
marrow, are crushed and soaked for two days in a 5 per cent, 
solution of soda, then thoroughly washed with water, reduced to 

^ Hide powder of suitable quality is prepared by Dr Roth of Berlin, and is 
obtainable from Messrs ilawson and Swan, of Newcastle-on-Tyne. 

' Procter points out that the limit of the reaction is not a complete oxidation 
of the organic matter, but only a partial one of the bodies more readily oxidis- 
able than indigo ; and hence towards the end of the operation, when the 
indigo has become scarce, the permanganate is partially consumed in further 
oxidising the products of the normal reaction ; and that this is least the case 
when the permanganate is added slowly and rapidly mixed with the liquid, so 
as to bring it into immediate contact with the remaining indigo. Procter 
obtained very uniform results by the use of a stirrer consisting of a perforated 
porcelain disc, which was worked up and down in the beaker by means of 
attached glass rod ; and the results were still further improved by attaching 
a capillary jet to the point of the burette, and allowing the permanganate to 
run in steadily throughout the titration. 


smaUer pieces, and trented with dilute hjdtochlorie acid until 
softened. They are then a^^in washed, and passed through it 
small grinding machine while etilt wet. The comminuted maas 
is treated with very dilute hydrochloric acid, tlioroughly waahed, 
preased and dried. 

E. It (Jo'ir. C/icm. Sac. Ind., vi. 51) suggeatB the use of ferric 
iicetate instead of gelatin for precipitating tannin. The process 
had only been tried on goll-tonnin, and F. G a n 1 1 e r (Jour, Chem. 
&K., liv.) duubt« its accuracy in this case. 

Other operator have recommended tlie use of an ammoniacal 
solution of copper for removing the tannin. This modification ia 
not capable of general application. Sumach, however, is a tanning 
mntetiAl which may be ndvautegeously precipitated by nmmonio- 
cupric ncetiite, with titration of the solution by permanganate and 
indigo before and after the treatment* 

N. H. Darton (Jottr. Ajtier. Cliem. Si>c., May 1882) employs 
aimuonio-sulpliate of copper in the following manner: — Twenty 
gnuumea weight of hemlixk-barir, nr an equivalent amount of other 
tanning material, is extracted first with cold and then with several 
iiuonlititui of boiling water. The mixed infusions are treated with 
2.^ e.c. uf dilate sulphuric acid (1 : 10), the iii^uid filtered, and the 
filtrate rendertil slightly alkaline with ammonia, any precipitate 
being filtered off, A further quantity of 25 c.c. of dilute sulphuric 
.wid is then added, and the liquid made up to 1 litre. 100 cc. of 

kfiiis solution is treated with on equal measure of a solution of 
OUpric sulphate (containing 1^ per cent, of the salt), to which 
mfflcieut ammonia has been added to dissolve tlie precipitate first 
formed. The liquid is passed through a dry filter, and a definite 
measure of the filtrate neutralised and titrated for "not tannin" 
with indigo and (lermonganate in the usual way. H. K Procter 
stAtes that the preliminary treatment with acid and mumonia is 
onncce-nanry in the case of valonia (and probably in that of oak- 
bark), and that the process gives results practically identical with 
tbo improved gelatin method, while it is much less troublesome. 

(With eh^inut extract the results are satisfactory, provided the pre- 

Kltaiinary treatment be omitted, as this removes 75 per cent of the 
' Utter precipitttble by gelatin, and cutch behaves similarly. On 

Wlbe other baud, a sample of larch extract which tanned well, and 
lowed Id pur cunt, of tannin by the gelatin method, gave no pre- 

1 By tlilB iirocun, I. Mncagno Ifihtna. Newt, xlL flS) found tlwt the 
■rlor liilii uf siuDuch leavi:8 wns GUnaiJcrtibly richer in tanuiu tbim tliu 
«r. tha |<ro[iorliuii in old loavea beiug less thau in yonug. Tho reaults 
lu 8 77 |i«r cent, of taDuis in the bwsr side of old, lo 26 'S2 p«r cent. 
ta tilt mperior aide of young leavra. 


cipitate with the ammonio-cupric solution. This peculiarity would 
allow of the estimation of valonia-tannin in presence of larch- 
tannin, and the same principle might be utilised in other cases. 

When applicable, the copper process has the advantage that the 
precipitate may be washed with a solution of ammonium carbonate, 
dried, and weighed. Or the precipitate may be ignited, the 
residue moistened with nitric acid, and re-ignited, and the cupnc 
oxide weighed. Its weight, subtracted from the weight of the 
precipitate previously found, gives that of the tannic acid with 
which it was combined, or the latter may be found by multiplying 
the weight of CuO by 1*034. This factor probably applies only 
to gallotannic acid. 

A. Carpen^ {Jour, Chem, Soc,, xxviii 1054) recommends, for 
the determination of the tannin in wine, the use of a solution of 
ammonio-acetate of zinc containing a laige excess of ammonia, 
which reagent has the property of forming with ceno-tannin a 
tannate of zinc quite insoluble in water, in ammonia, and in excess 
of the reagent itself ; while it gives no precipitate with alcohol, 
malic or tartaric acid, tartrates, glycerin, gelatin, albumin, or the 
iron salts of organic acids. With gallic and succinic acids, glucose, 
and salts of aluminium it forms precipitates soluble in excess of 
the reagent and in ammonia. 

On treating the wine with an excess of ammoniacal zinc acetate, 
a precipitate is formed consisting of zinc tannate mixed with a 
small quantity of colouring matter. The wine is heated nearly to 
boiling to agglomerate the precipitate, which, after cooling, is 
filtered off and washed with a little boiling water, to remove 
adherent colouring matter. The precipitate is dissolved in dilute 
sulphuric acid, and the solution so obtained titrated with standard 
permanganate and indigo, as described on page 110. The results 
by this method are stated to be very accurate, when applied to 
wine, but Kathreiner found that with ordinary tannin-matters the 
figures were very inconstant. 

Determination op the weight op tannin absorbed by hide. 

Instead of precipitating or absorbing the tannin from an 
infusion by means of gelatin, and ascertaining the difference in the 
reducing power of the liquid before and after the operation, several 
operators have proposed to note the difference in the solid matter 
contained in the ^liquid. In doing this there is considerable 
practical diflSculty. Thus the gelatinous matter must be so pure 
that it will not yield to water sufHcient soluble matter to vitiate 
the result ; the solution must be very dilute, or the whole of the 
tannin will not be absorbed ; and special means must be taken to 
bring the gelatin in contact with the tannin, as otherwise the 



Miler portions become swollen and impervious to the liquid, at 
Iv^aat within any reaaonable time. The lost difficulty may be 
avoided by using finely-powdered hide to absorb tho tannin, and 
adding it in small successive portions at intervals of ten or twelve 
huure, wliereby the portions ftret added arc made to do the greater 
[lort of the work, and the later additions effect the removal of the 
last of the tannin from the liquid. A more 
rapid plan ia that of U. R. Procter, 
who optTutes as follows : — A piei* of stout ■" 
f^'toM tube about 4 inches long and 1 int^h 
in diameter (lig. 1), ia fitted in one end 
with a perforated cork carrying a sypln^n 
tube, tho huger leg of whieh ia from 1 '2 
to 16 inches in length. The end of the 
Aort«r limb prqjecbs through the cork, 
and is covered with a little tuft of cotton 
wool and a piece of niuelin to prevent tlie 
hide powder from passing into it. Tho wide tube is 
filled with about 5 grammes of hide powder, which is 
well shaken hut not rammed in, and the open end ia then 
eovered by a circle of muslin, which is secured by an me 
ia-rubber band. The wide tube is then immersed O ' 

) CO. of the tannin infusion (which should not 

Uin less than 1 per cent, of tannin) contained in a . 

r, and when the hide |)Owder is thorougUy soaked ^' 

rphon is gently sucked so as to cause the liquid to pass over into 

k placed to receive it. When a volume of 50 c.c. has collected, 

uld be evaporated to dryness at 100° and the residue weighed. 

of the original tanuin infusion is similarly eva^iorated to 

, when the difierence between the weight of the two 

8 will be the weight of tannin, &c,, absorbed by the hide 

3 C.C. of the infusion. The ligui'e thus obtained requires to 

Bcled by the result of a blank experiment on hide and 

[ water alone, for even the most carefully prepared hi<le 

a residue of 30 to 40 niilligrarames from 5 grammes. Tliis 

I, which ia perhaps the most rational yet devised for assay- 

' tanning materials, is unfortunately wanting in accuracy in 

e of much gallic acid, which Procter found to be absorbed 

e from a 1 per cent, solution to an extent equal to 78 per 

t the whole ; an unstable compound with gelatin being 

itly formed which in practical working would have been 

nuoU; decomposed by the escess of tannin. Hence, for the 

Bling materials containing much gallic acid, the oxida- 

1, in which a solution of gelatin is employed, is to bo 


preferred to that of absorption by hide.^ The hide process is in 
constant use at the Vienna VersucJis-stcUion fur Leder-indiutrie, 
where the error due to the presence of gallic acid has not been 
found of much practical moment. The rejection of the first 30 ac 
of the filtrate reduces it considerably, and also greatly lessens the 
effect of the soluble matter in the hide powder. 

H. Dieudonn^ (Jour, Soc. Ghent. Ind,, v. 549) has proposed 
to ascertain the density of the infusion before and after the absorp- 
tion by means of a delicate hydrometer, instead of weighing the 
residues obtained on evaporating equal volumes to dryness. He 
uses a special hydrometer, on which 1° Baum^ is divided into 
hundredths (!), and he gives a table of densities of solutions of 
gallotannic acid. The trifling saving of time eflTected by ascertain- 
ing the density of the infusions, instead of evaporating them to 
dryness, would be more than counterbalanced by the uncertainty 
that all tannins have the same solution-density as gallotannic add.^ 
The suggestion is practically a revival of the obsolete process of 
Hammer. According to this observer, for concentrations below 
5 per cent., gallotannic acid has a solution-density of "004. Above 
that strength the increase is slightly more rapid, a 10 per cent 
solution having a density of 1*0406, and 15 per cent, of 1*0614, 
while a 20 per cent solution has a density of 1*0824. Hence 
each O'l gramme of gallotannic acid present in 100 c.c. of its aqueous 
solution may bo regarded as increasmg the density by 0*0004. 

Under oitlinary circumstances, the direct observation of the 
increase in the weight of the hide, or other gelatinous substance 
employed, is impracticable, but purified catgut has been used, with 
apparent success, by A. G i r a r d for the estimation of the tannin 
and colouring matter of icine^ {Jour, Soc, Chem, Lid,, i. 464). 

^ According to T. C. Palmer {Jour, Soc DyerSy <fcc., iii. 175), sumach 
extracts give too high a result by tlie gelatin precipitation process, owing to 
the CO- precipitation of pectinous matter. The error may be avoided by first 
dissolving the extract in alcohol, evaporating the filtered liquid, and re- 
dissolving the residue in water. With such treatment, at any rate if repeated, 
the precipitation process gives results agreeing with the al:>sorption method. 

2 If any such method be adopted, the use of a Westphal balance is preferable 
to that of a hydrometer. By comparing the original and filtered infusion side 
by side far better results might bo obtained, and if the experiments were acconi- 
l>anied by determinations of the solid matter corresponding to the densities, 
observed, a useful series of tables might be constructed. 

* Thick catgut (violin string) previously freed from oil by treatment with 
ether, is the best material to use, the quantity employed for 100 cc. of wine 
being from 3 to 5 grammes, according to the character of the sample. The 
catgut is weighed, softened by soaking in water for five hours, and immersed 
in the wine for twenty or forty-eight hoars, or until the liquid is completely 



CBSR Mxiaooa of deteb^ining Tannins, 
! direct weighing of the precipitate produced by gelatin in . 
uutiou of tannm was firet suggested by Sir H. Davy, who 
stntcd that the precipitate contained 40 per cent, of gallotannic 
acid. The method has been more recently employed by Stoddart, 
Macognu, Gtinthcr, Johansen, Lehmann, and others, who differ 
wi(]«lj in their statements as to the composition of the precipitate.' 
It undoubtedly variea greatly in composition acooiding to the 
strength of the solutioQ and other circumstances, boaidea which it 
is solnblo in excess of gelatin solution and very difficult to vaah 
£re« from alum or other salts employed to crnille it. The variable 
, jittture of the precipitate is liable also to vitiate the resulU obtaint'd 
^^^tuploying a gelatin solution toIu metrically, to say nothing 
^^Ke difficulty of ascertaining the end of the reaction. But 
^H^mann has shown that the liquid may be diluted within 
|^Bu> limits without notably affecting the result, while the 
WSrification of the liquid can be effected by adding powdered 
glnsa or barium stdphate, and vigorously stirring. He dilutes the 
tannin infusion with an equal volume of saturated aqueous solution 
of ammonium chloride, and titrates with a 1 per cent, solution of 
gelatui in cold saturated ammonium chloride. The end of the 
reaction is ascertained by filtering a few drops of the liquid and 
testing it with a solution of gelatin on a watch-glass placed on a 
black surface, Catechu-tannic acid is said to give good results in 
this way, 1 cc of the gelatin reagent representing 0'139 gramme 
I ^ the tanniji. Johansen recommends that a little chrome^um 
Mbjl^ be added to the animontuni chloride solution. 
^^■nodifled method of determining tannin by precipitation with 

^^Hprised. The catgat is then rcmovod, washed two or tbreo tioiea witli 
P^M, pressed between folds of blotting paper, ilried at 35' to 40° C. is ^u 
"pan distil and aftenr&nU at 100° in a veaael wbich can be closed. The 
InonaM ill wnight girea the quantity of colouring and astringent matteta in 
ein]>lc7ed for the test This prooesa apjieara to be too alow for the 
onlinuj tannin-niatten. 

iming the iiredjiitate to eontaiu 40 per Mnt. of taanin, tUcagno 
with tuioach pretty constantly 63 par cent, of the reanlta yielded 
i&gftRste. GUnther found that 100 parts of gHlatin precipitateJ 77 of 
eid, 132o[catecha-tanniD, 130 of kino, ISO to 182 of ratanhla, 130 
III Mk-bark, or 16S of tormeatilla-tanQic aciJ. 100 parta of gelatin combined 
itStli ISO of dry gallotBnnic acid, according to Johansen, sad with 130 of 
.tanaie acid according to Lehnanii. Quite recently, C. Bottinger 
the Jvecipitute prodoced by gallotanntc acid to contain IS'S percent. 
I, oorrMpnndiug to 34 percent, of tannin; while oak -bark tannin gave 
coBtainiug S'd jicr cent, of nitrogen, correapondiiig to 487 per 
in {Jour. Chcm. &k., Ut. 614). 


gelatin has been leccntl^r described by Collin and Beaoist 
(Jour. Soe. Dyerr, ^e., iv. 62), and apiware to merit a caisful 
trial, Thej employ an aniline dje in <iDnjunction with gelatin, 
and operate in presence of calcium acetate.' The end of the 
operation is indicat«d by the decolorisation of the liquid, the dj« 
being precipitated together with the gelatin. 

A solution of tannin is mode by dissolving 5 grammes of diy 
and absolutely pure tannic aciil in water, adding 0'5 e.c of a 10 
per txai. solution of mercuric iodide dissolved in its own weighted 
potassium iodide, and diluting the liquid to 1 litre. A weight of S 
grammes of g e 1 a t i n is dissolved in 1 litre of hot distilled water, 
tlie liquid boilej, and sufficient white of egg added to make it dear. 
Aft«r cooling, 0'6 c.c. of the mercuric iodide solution b added 
and sufficient caustic soda to render the liquid slightly alkaline, 
60 grammes' weight of pure and dry calcium acetate is dimolved 
in 1 litre of water, and the filtered liquid treated with a few drops 
of the mercuric iodide solution. This appears to act as a perfect 
preservative of the solution, no alteration being perceptible even 
after four months. 

For the assay of tannin infusions which are not coloured, t 
1 per tent, solution of pure methylene blue is used. For coloured 
tannins or extracts either a 4 per cent solution of Nicholson's bine 
BB, or a 1 per cent, solution of blue-black NBL 

For the determination a ilaak is used, having a capacity of about 
60 c.c, and a neck 3 cm. in diameter. 1 c,c of gointin solution, 
two drops of blue solution and 6 c.c of calcium acetate are 
measured into the flask, which is then filled to the neck with 
distilled water at a temperature of 76° to 80° C, by means of a 
burette capable of delivering at 40 drops to I u.c' A little of the 
standard solution of tannin is added, when the ftask is closed and 
slinken. A precipitate is formed which rapidly rises to the surface of 
tlie liquid, and the addition of the tannin is continued drop by drop 
with agitation between each addition until the solution becomes 
colourless. The process is then repeated with a solution of the 
tannin- matter to be assayed, which, if aeid, should previously he 
nearly neutralised by the cautious addition of caustic soda. 

' The iwe of magenla ax an incUcntor wag previously BUggHSted by Wngnii^ 
but wm found useless from the fact that it wis freely obborbcd by th« pred{ii- 
tate of tamuto of gelatin. 

' The ttuthora uacJ specislly conBtracted Uiretles. An ordinwy bontle 
with glasa-tap noald anawer the purpose, if a Bpecial nozxle of drnwn-ont ^ut 
tube were attached to it by india-rubber tubing. AppareDtl]' it would not bt 
difficult to modify the manipulation so as to employ Inrger cjaantities or nion 
dilute Bolutions, and thus avoid the necessity of using a spedal burette. , 


The method bus been tried under Tarious conditiona, Altera- 
tions in the strength of the tannin solutions; the presence of other 
organic muttere, such ob lactates, butynites, gallatea, and gallic acid; 
itnd nil the salts that aceompany tannin as it occurs in commerce, 
have little or no influence on the results. Tlie operation is only 
ajKiilt when a large proportion of gallic acid is present, and this 
difficulty can be got rid of by adding a known measure of tho 
eUindurd tnnnin solution to the solution to be assayed, and subee- 
(jnently making the requisite correction. 

A method of assaying lea, originating with the author {Chem. 
Xewg, xxix. 169, 189), was based on the precipitation of tho 
tannin from a hot solution by a standard solution of lead acetate, 
the end of the reaction being itscertained by filtering a few drops 
of the liquid and testing it with amnioniacal ferricyuniile (page 90). 
The method was selected partly because the indications included 
Kuy gallic acid which might be present, and henco is not suited for 
the assay of tanning materials without some modification.^ 

R. Jackson (Gkem. N«m, 1. 179) has proposed to a^tate 
tannin infusions with lead carbonate, filter after a few hours, and 
cidcalate the tannin from the loss of gmvity, assuming a 1 per 
cent, solution of all kinds of tannin to be t'0036. 

In G e r I a n d's process, the tannin is precipitated by a standard 
solution of tartar-emetic (2'611 grammes per litre), in presence of 
ammonium chloride, which prevents the co-precipitation of gallic 
acid. The assay of gumaek by this method yielded J. Macagno results 
which were constantly two-thirds of those given by titration with 
pennangonate. The tendency of the antimoniol solution to change 
' be obviated by the addition of methylated spirit to the 
a (or probably by carbolic acid). Some tannins (e.g., those 
of catechu and horse-chestnut) are not precipitated by tartar- 

Richards and Palmer (Silliman'e Anwr. Jour. Seienee, 
[3], xvi. 196, 361) substitute acetate for the chloride of ammonium 
in Garland's process, and ascertain the point of complete precipita- 

> M. TilloD {/our. Soe. Chem. Ind., ri. 3S6) states that gullic acid is 
not giTedjiilAted ly lead acetate, but the author has proved that only a miuute 
tnue remaiiu in loluticiii. It soems [irobahla, as sugguated by Guyard, that by 
tulng k >oliition of itcvtate of lead containing a considerable qnuitity of free 
4cetic acid it might iie poaaihlB to proci]iitjite tannic acida (and colmu'ing 
nuittar) while leaving gallic acid is Bolutiao, and then, by treating the l«ad 
pradpitato with ililute snlphnric acid, a soIulioD would be obtained in whieh 
the tannic acid conld be deterniine<] by indigo and permanganate. This 
dlrtctjon ueinB to the author the most hopeful one in which to work with a 
■r ot devtaing a npid and direct process for the determination of tannins, 


tion of the tannin by testing a drop of the clear supernatant liquid 
on a hot porcelain plate with solution of sodium thiosulphate, which 
will produce an orange precipitate if the antimony is in excesa 

The estimation of tannin by precipitation with an ammoniacal 
solution of copper has already been described. 

A. Casali {Jour. Soe. Dyers, ^c, L 66) has proposed to 
determine tannin by precipitation with a solution of ammonio- 
eulphate of nickel. A volume of solution (1 cc.) which will, 
precipitate 00 1 gramme of gall-tannin is stated to be equivalent 
to 0*01497 of oak-bark tannin. 

F. Becker has described a method of determining tannin by 
precipitation with a solution containing 5 grammes of methyl-violet 
per litre (Jour, Soc. Dyers, ^c, L 180). 60 cc. measure of this 
solution is dilated with 450 c.c. of water at 50* C, and a 1 per 
cent, solution of pure gallotannic acid run slowly in, with continual 
stirring, until the colouring matter is completely precipitated, a 
point readily ascertained by filtering a small sample. A similar 
experiment is then made with an infusion of the tanning material 
to be tested. The process is said to be well adapted for the assay 
of sumach, and would probably be foimd useful in most cases where 
the tannin is intended to be employed in dyeing. 

Ostermeyer, improving on a suggestion of Wagner, ha** 
proposed to determine tannin by a standard solution of cinchonine 
coloured with magenta, the end of the reaction being indicated by 
the pink tint acquired by the solution {Chem, News, xL 181). 
Gallic acid is not precipitated by cinchonine. Some observers 
report unfavourably of this process, and state that in certain cases the 
liquid acquires a red tinge long before the tannin is precipitated. 

F. Joan {Jour, Soc. Chem, Ind., v. 179) has described an 
ingenious process of determining tannin, based on the volume of 
the infusion requisite to render a solution of iron opaque. The 
operation is conducted in a beaker 8 J centimetres in diameter, 
placed in a good light on a black cloth, having on it a small circle 
of white paper about 5 cm. in diameter. 5 c.c. measure of a 
solution of iron, containing 1 4 grammes of ferric chloride and 10 
c.c. of hydrochloric acid per litre, is run into the beaker, and 200 
c.c. of water added. A O'l per cent, solution of tannin is then 
dropped in with constant stirring. The operation is finished when 
the disk of white paper is wholly invisible after the liquid has 
come to rest, which in the case of pure gallotannic acid occurs 
when 11 '6 c.c. of the solution has been added. In comparing 
tanning materials with this it is simply necessary to take care that 
the infusions are approximately of the same richness in tannin, 
and this may be attained by extracting 1*5 gramme of European 


bnrk, l-Q of African bark, 0"6 of Quelimcho, 05 of euiuach, or 
0*35 gmmme of catecliu, and diluting the liquid to 100 c.c Tho 
ileterniiiiatiiiii can be niitdc very rapidlj, and is said to bo accurate 
U> J per cent By eubsequently repoating the exi>eriment with n 
aolutiou which haa been treated with hide, the error uaueeJ by 
gallic acid may be eliminated. 

E. Durion (Ffar-Bmih Pharm., 1886, iii.) has proposed to 
ilotemuoe tnnnin by adding acetic acid ami ferric chloride to the 
infosion, tuid then dropping in a etandard solution of bleaching 
powder (5 grammos per litre) till the colour of the liquid changes 
suddeidy to a roee-brown tint. Sugar was found not to affect the 
leealt, but gallic acid is ignored. 

F. Mueset {Chem. NewB,]L 42) haa described a raethod of 
titmting tannin by oxidation with iodine. 100 c.c of a 1 percent. 
ut bark is treated with 20 c.c of decinornml solution of iodine (12'7 
fjnuunies per litre), tlie flask filled to the neck with warm air-free 
water, and carefully closed. After twelve hours, the free iodine is 
reduced by atandard thiosulphato solution, which should be added 
eotnowhat in excess, and the liquid titrated back with docinormiU 
iodtnc and starch. By operating in a similar manner on a solittioa 
which has been treated with gelatin, the disturbing effect of gallic 
acid and other "not tannin'' matters is ascertained, and can be 
allowed for. 


Besides determining the tannin and oxidisable substances in tan- 
liquors, it is frequently desirable to obtain further information as to 
the proportion and nature of tho free acids present. It is an error 
to Bupjiose tliat the principal free acid of tan-liquors is gallic acid, 
AS this is not present in pure bark- yards. The most abundant acid is 
usually acetic, though butyric, lactic, and other acids produced by 
fennentation arc frequently present. 

Thft total free add may be ascertained by titrating tho filtered 
liquid (previoDsly clarified, if necessary, with kaolin) with lime- 
wat*^. The end of the reaction is indicated bj the production of 
a permanent turbidity, showing that the acids which held the 
calcium tiunato in solution are neutralised. By titrating another 
portion of the liquor with limo-water, using methyl-orange as an 
indicator, the pmiwrtion of strong acids capable of producing 
"plumping,'' or swelling of the leather, will be roughly ascertained. 
Sulphuric acid is sometimes added for this purpose. 

A more accurate and elaborate method of assaying tan-Iiqnors 
haa been described byKohnstein and 8 i m a u d (Jour. Chein. 
Sor„ xlviiL 935). To determine the volatile orffanie adth 
' "" ----- --- i measure of theliquoris 


30 C.C., the residue made up with water to the original bulk and 
again distilled, and the process repeated till the total distillate 
measures 300 cc, when it is titrated with standard caustic alkali 
and phenolphthalein, and the acidity expressed in terms of a c e t i c 
acid. By adding sulphuric acid and water to the contents of the 
retort, and again distilling and titrating the distillate, the combined 
acetic acid may be determined. 

Another portion of the liquid (80 or 100 c.a) is shaken with 
3 to 4 grammes of freshly-ignited magnesia, quite free from 
carbonate and lime. The mixture is left for some hours with 
frequent agitation, when the brown or dirty green colour will have 
disappeared, and the filtered liquid will be nearly colourless, neutral, 
and free from tannin. The magnesia in solution is determined 
in an aliquot part of the filtered solution, and will be equivalent to 
the total free acids of the liquor, exclusive of the tannic acid, 
which is completely precipitated together with the colouring matter. 
Another portion of the filtrate is evaporated to dryness, and the 
residue gently ignited. The ash is moistened with carbonic acid 
water and dried. It is then boiled with distilled water, and the 
solution filtered. The magnesia remaining insoluble corresponds 
to that which existed in the solution as magnesium salts of organic 
acids, and may be determined gravimetrically as pyrophosphate, or 
dissolved in standard acid and titrated with alkali and methyl- 
orange or litmus. By dividing the percentage of acetic acid 
previously found by 3, and subtracting this figure from the 
percentage of MgO, the weight of the latter corresponding to the 
non-volatile organic acids of the liquor will be found ; and 4*5 
times this amount will be their equivalent of lactic acid. 
The magnesia contained in the aqueous solution of the ash is 
equivalent to the free sulphuric acid originally present 

The liquors of a set of seven handlers, in a Continental upper- 
leather tannery in which larch-bark was used, showed, by the above 
process, in grammes per 100 cc. : — Total acids reckoned as acetic, 
from 0-20 to 0*68 ; volatile acids, 0*05 to 0*46 ; and fixed organic 
acids reckoned as lactic acid, 0*05 to 0*59. 

Writing Inks. 

Writing inks are either coloured liquids, or liquids containing a 
finely-divided precipitate in suspension. 

Ordinary writing ink was formerly always made from a decoction 
of galls, to which green vitriol was added. Of late, the com- 
position of writing inks has become far less constant, aniline and 
other dyes beiAg frequently employed, and other metallic salts 
substituted for the ferrous sulphate formerly invariably used. 


he table following showa tbe general composition of black 
inks, anJ sufficiently indicates the nature of the subatancea 
a sought for by the analyst : — 














Oklla.. . . 



La«winil. . 









« iKin niinga. 







SagnJ,' ; 

SB 1000(7) 

Vlntvu. . . 

Wakr. . . 






^^Pbe best black ink ia a tanno-gallate of iron, obtained by adding 
■B infusion of nnt-giiUa to a solution of ferrous sulphate (copperas). 
The galls contain gallic and gallotannic acida, both of which are 
aerviccabld. On coming in contact with fetroua salts in concen- 
tnt«d solutions, these produce white precipitates which turn black 
on exposure to air. With ferric salts, blue-black precipitates are 
at once produced. A amoll quantity of gum is added to retain the 
pracipitato in suspension. To ink intended for copying by pressure 
a small addition of sugar or glycerin is also made. 

Sumacti is sometimes used instead of gulls, and somo of the nut- 
gall inks contain a little acetic acid, added as vinegar. 

Some of the gallic inks receive an addition of indigo-carmine or 
eulpbindigotic acid. Aniline dyes ore frequently used as a whole 
or part of the colouring matter of both black and coloured inks. 

According toR. Bottger, an excellent black ink may be pre- 
pared by dissolving in water 1 part of pyrogallol, 3 of ammonium 
viuiaiiate, and 3 of finely powdered gum-arabic. Another highly 
tvcommendMl ink is made with nigroaino (an aniline black), 
potassium bichromate, and gelatin. 

Logwootl ia a frequent constituent of ink. It gives the original 
ink a darker hue, and itself contains tannic, besides the colourmg 
nmatoxylin. Logwood and alum form a frequent 
IB of purple uiks. 

i very cheap and perfect ink is obtained by dissolving 24 parte 
attract of logwood in 1000 of water, and adding 2 ports of 


neutral potassium chromate. This ink is a deep black liquid, 
which, unlike that made with gallic acid and iron, contains no 

Sulphate of copper is sometimes added to ink, with questionable 

Indelible ink usually owes its permanency to an admixture of 
finely-divided carbon, tx) which indigo is sometimes added. It is 
kept in suspension by gluten, an alkaline solution of shellac, or 
other similar means. 

In analysing ink, the total solid residue should be determined 
by evaporating 50 c.c. to dryness on the water-batL The residue 
thus obtained is first weighed and next ignited, the odour produced 
on heating being carefully noted; sugar or shellac may thus be 
detected. The weight of the ignited residue is then taken, after 
which it is mixed with magnesia and caustic soda, and ignited in 
platinum. The mass is extracted with hot water, the solution 
filtered, and the filtrate acidulated with acetic acid. In presence of 
a chromate, the liquid will have a yellow colour, and will give a 
chrome-yellow precipitate on adding acetate of lead. The preci- 
pitated PbCrO^ may be collected and weighed, or the chromate 
formed determined volumetrically by a ferrous salt. The residue 
left on treating the fused mass with water should be boiled with 
hydrochloric acid, the liquid filtered and examined for iron, copper, 
aluminium, &c., in the usual way. By precipitating the solution 
with a large excess of ammonia, the iron and aluminium may be 
roughly separated from the copper, which remains in solution and 
communicates a blue colour to the liquid. 

For the detection of organic colouring matters^ a portion of 
the ink should be strongly acidulated with hydrochloric acid. A 
blue colour, unaffected by the acid, but destroyed on adding 
bromine water or bleaching powder, shows the presence of indigo. 
If Prussian blue be present, the ink will probably turn brown on 
addition of soda, and the filtered liquid will give a deep blue pre- 
cipitate with ferric chloride, after being acidified with hydro- 
cliloric acid. A black colour, not destroyed by acids or alkalies, 
nor bleached by chlorine or bromine, is pretty certain to be due 
to finely-divided carbon. An ink prepared with ammonium vana- 
date and galls is turned blue by acids, but is unaffected by alkaliea 
Its colour is altered but not bleached by chlorine. Aniline-black 
is not affected by alkalies, but is turned dark green by acids; 
bleaching powder renders it gamet-red. Logwood inks are turned 
red or yellow by hydrochloric acid, while those containing galls 
only are almost wholly decolorised by the same reagent. 

Some inks have a great tendency to become mildewed; this 



may be prevented by a small addition of carbolic or salicylic acid. 
Ksanntial oils are somotimiis need for the eame purpose. 

CoLOURRD Inks do not usually contain tannic acid, and hence 
their discussinu in out of place in tliis section; tn many instnucee 
tfacy are nothing but solutions of coal-tar dyes. The following 
exaroploa will suffice to give a general idea of their composition : — 

Aa/. — Brazil wood, with stannous chloride or cream of tartar 
and alum ; cochineal or carmine dissolved in ammonia or sodium 
silicate ; aniline red. 

—Prussian bine dissolved in oxalic acid ; aniline blue, 

fiujH. — Aniline violet. 

—Acetate of copper and cream of tartar ; chrome alum ; 

BARKiNO Inks are all closely analogous in composition, and their 
y requires no special description. They usually consist of nitrate 
r coloured with sap-green, ivory-black, indigOjttc; or ammonio- 
* silver mixed with sodtum carbonate, sometimes with sul- 
phate of copper added. In Redwood's ink, tartrate of silver is sub- 
stituted for the nitrate. Rcade's ink is ammonio- tartrate of silver. 
pRiNTttto IxK is made by suspending lampblack in Unseed oil, 
k more or le^ nwin oU, rosin, turpentine, itc, 


Hn ehemico-legal cases it is sometimes of importance to ascertain 
e nature of the ink used, to compare it with specimens of writing 
of known history, and to ascertain the relative ages of the writings, 
A minute inspection should first be made with a magnifying power 
of about 10 diameters, and any peculiarities of colour, lustre, 
»hi»dB, &C., duly noted, and where lines cross each other which lie 
uppermost. The examination is oft«n facilitated by moistening the 
paper with benzene or petroleum spirit, whereby it is rendered 
U-traasparent. The use of alcohol or water is inadmissible, 
yalnable information is often obtainable by treating writing or 
r ink-marks with reagents. Some inks are affected much 
I mpidly than others, though the rate of change depends 
{(tfKtly on the age of the writing. Kormal oxalic acid (63 
grnuimHS jter litre), or hydrochloric acid of a corrcs|)onding 
Mtrength, should be applied to a part of the ink mark with a feather 
or tamel-hair brush (or the writing may bo traced over with a quill 
pen), and the action observed by means of a lens, the reagent being 
allowed 1(1 dry on the paper.' Recent writing (one or two days 

V^Tha tnthor sanjneiluil h; this treatment in deteoring on alteration in nreixipt 
n which B flguro 1 hnd been altered to 4. The ndded m«rk, as 
■■ IbrKWl lignatare acniu the stamp necessitatpd lij the clinngH, faded out 

' tr trmtmeul with dilute hydrochloric acid. 


old) in gallic inks is changed by one application of oxalic acid to 
a light grey, or by hydrochloric acid to yellow. Older stains 
resist longer, in proportion to their age, and a deeper colour 
remains. Logwood ink marks are mostly reddened by oxalic acid, 
and alizarin marks become bluish, but aniline inks are unaffected. 
With hydrochloric acid, logwood ink marks turn reddish or reddish- 
grey, alizarin marks greenish, and aniline ink marks reddish or 
brownish-grey. The treatment with acid should be followed by 
exposure to ammonia vapours, or blotting paper wet with ammonia 
may be applied. Thus treated, marks in logwood ink turn dark 
violet or violet-black. The age of ink marks very greatly affects 
the rate of their fading when treated with dilute ammonia, the 
old marks being more refractory. The behaviour of ink marks 
when treated with solution of bleaching powder is often char- 
acteristic, the older writings resisting longer, but unless the 
reagent be extremely dilute, writings of all ages are removed 
almost simultaneously (R. Irvine, Jour. Soc. CJiem, Ind^ vi. 
807). Hydrogen peroxide acts more slowly than bleaching solution, 
but gives more definite results. After bleaching the mark by 
either reagent, the iron of the ink remains mordanted on tiie 
paper, and the mark may be restored by treatment with a dilute 
solution of galls, tannic acid, or acidulated potassium ferrocyanide. 
The same reagents may be used for restoring writing which has 
faded from age alone. 

Where ink marks have been erased or discharged by chemical 
means, traces of the treatment are often recognisable. After 
effecting the erasure, the spot is often rubbed over with powdered 
alum or gum sandarac, or coated with gelatin or size. The bleach- 
ing agents most likely to have been used are oxalic, citric, or 
hydrochloric acid, bleaching powder solution, or acid sulphite oi 
sodium. Moistened litmus paper will indicate the presence of & 
free acid, and in some cases treatment with ammonia fumes wil^ 
restore the colour. The presence of calcium, chlorides, or sulphate^ 
in the water in which the paper is soaked will afford some indicatio^^ 
of bleaching powder or a sulphite having been used. Potassiui:^^ 
ferrocyanide will detect any iron remaining in the paper. Exposmr^ 
to iodine vapour often affords evidence of chemical treatment^ aa^ 
other methods of examination readily suggest themselves. 

The application of reagents to writing in black ink has bee 
recommended by W. Thomson for the identification of han( 
writing {Chem, News, xlii. 32). 


the middle of this century, nearly all the colouring 
tDatt«[S used for dyeing were either such as existed ready-formed 
in the vegetable or animal kingdom, or were producilile from 
lia tnnil products by very airaple chemical proceSBes. In a few 
, however, as when chromate of lead or prussian blue was 
an insoluble precipitate in the fibre, the dyes were 
itly of artificial origin. Now, the vast majority of tlie colour- 
I matters used aa dyes — aa distinguiabed from mere paints or 
mente — are products of otganic Bynthesis, being in almost all 
obtained, by u series of highly scientific processes, from. 

c acid and aurin are the oldest of the coal-tar colonrs, but the 
SMl'tsr duloDr iuduBtry amy W said to date from 1856, whao Perlcin an;ideat- 
allj discovered the Tiolet dye called ma are, la the course of an iaveatigation 
luritig u lis object the synthoaia of quinine. In 1880, rosaniline or mn- 
genta fireC became of commercial importance, owiog to the aimaltaneouB 
ittKorery of the arsenic acid process bj Medlock and Nicholaoa. Phenyl- 
>t«d bluea were first produced by Ginird and De Lsire in the Bame year, 
but their insolubility reodered their application limited until Nicholson, in 
IMS, discovered a method of renderiaK them soluble by conversion iato 
■ ulphonic acids. The firat aio-dye, amido-szobeuzeiie, was introduced by 
SimptoD, Maule, & Nicholson in 1863, under the Dame ofaiiiliDB yellow, 
and in the same year the methylated and ethylatcd rosanilines, known as 
■ Hofnaun'i violets, were manufactared by the same lirBi. Aniline 
h)aek, a'BO. was discovered by Lightfoot in 1863. Azo-dipbeuyl blue, the 
llnrt o[ colouring matters now known as i nd ulinee, appeared in 1S61, as 
tlm did dbitronaphthol or Manchester yellow. !n 1868, triamido- 
uobenKine or Bismarck brovn was Grat made, and in the same year 
Cenpiet's nitrobenzene process of manufacturing msgcDta was intro- 
duced. In 1868, Graebe and Liebermann announced their discovery of the 
fionatitntton of aliiari □, and in the following year this colouring matter was 
tnit manuractiired from anthracene. Gallein and fluorescein were 
diacovored iu 1871, and in 1874 tetiabromflnorBsceiii was introdaced as a dye 
hj Caro, under the name of eosi n. Diamido-azoVienzene or chrysoidinc 
»aaintr<.lucedhyWittiiil87S. Met hylene blue and acid magenta 
l«w« iatroductd by Caro in 1877, and in the same year the fugitive aniline 
jrallow was rendered valuable and stable by Gi^saler, by coaveTaiou into ■ 


The term aniline dye is in popular phraseology regarded 
as synonymous with coal-tar dye, but this definition is far 
from accurate. Picric acid and its allies, aurin, the various eosins, 
alizarin and anthrapurpurin, indigo, and many other important 
colouring matters are now strictly coal-tar dyes, though they cannot 
by any straining of the term be appropriately described as aniline 

G r a e b e and Liebermann have enunciated the rule that 
all coloured organic compounds {e.g., quinones, azobenzene deriva- 
tives, nitro-com pounds, &c,) are decolorised by reducing agents, 
and from this they infer that the colouring matters either contain 
elements with incompletely saturated affinities, or that certain of 
the atoms are present in more intimate association than their 
retention in the molecule necessitates. 0. Witt has formulated 
the conclusion that the tinctorial nature of aromatic compounds is 
the consequence of the presence together of a colour-giving or 
chromophoric group, such as NOg, GO, or N : N, and a s a 1 1- 
forming group, either OH or NHj. The common proposition that 
all bodies containing, for instance, an NO^ and an OH group are 
coloured, does not hold true. Upon the nature of the salt-forming 
group depends the character of the colouring matter, those con- 
taining OH being usually acids, while all basic colouring matters 
contain at least one NHj group, either intact or substituted. 

Basic Golourino Matters are always employed in dyeing in 
the form of one of their salts, the hydrochloride being the usual 
form of combination, though the acetate, nitrate, and other com- 
pounds are employed in certain cases. Golouring matters of 
distinctly basic character, which lose their colour on coming in 

sulphonic acid. In 1878, the tropseolins, fast-red, naphthol- 
scarlet, and other sulphonated azo-colours were first manufactured ; and 
malachite green dates from the same year. In 1879, the first of the 
secondary azo-dyes appeared under the name ofBiebrich scarlet Th0 
analogous crocein scarlets, discovered in 1881, are fast exterminating 
the cochineal industry. The synthesis of indigo was effected by Baeyer iis. 
1880, and indophenols were introduced by Koechlin and Witt in 1881* 
In 1888, Caro's process of manufacturing colouring matters of the roaanilin^ 
group by the aid of phosgene gas was patented. Congo-red, the first o^ 
the numerous class of benzidine dyes, which dye cotton without a mordant, wa^ 
patented by Bottger in 1884, and this was followed in the same year by o h ry 
samin. In 1885, azo-blue and benzazurin appeared, and in 1886 th^ 
benzopurpurins were patented. Numerous other dyes are constantly 
appearing, and in many cases they exceed in fastness, brilliancy, or cheapnei0 
those already in the market (For an interesting paper by R. Meldola, 
from which most of the above information is derived, see Jour, Soc Arts, May 
28, 1886 ; or J<mr, Soc Dyers, <l^, il 95.) 



contact with acids, cannot be employed in dyeing, except certain 

ve ry weak bases, which are absorbed by the fibre as such, and not ' 

^^the form of their salts. Amido-ozobenzene (aniline yellow) is an 

e of this, for its salts are decomposed by water, and hence, ' 

D silk is dyed bj an acidulated solution of its hydrochloride, 

1 is then washed with water, the free base only remains on the 

In the free state, the colour-bases are usually colourless, oi' 

By slightly coloured. Most of them can be converted into 

inble acid colouring matters (sulphonic acids) by treatment with 

mg sulphuric acid. 

I CoiiOUBtNO KIattbrb, like all acids, contain hydrogen 
' I readily replaceable by metals with formation of salts. 
B hydrogen may form part of a bydroxyl group, OH, as in piuric 
a sulphonic group, SO,H, as in helianthin ; of an imido 
Wp, KH, as in aurantia; or of a carboxyl group, COOH, as in 
p scarlet obtained from salicylic acid. Those colouring matters 
li owe their acid properties to the hydroxyl group are yerf . 
I acids {e.if., alizarin, auriu) ; but the acid characters ai'R I 
tRtlerably intensified by the introduction of haloid or nitro- ' 
tops. Thus the eosins and nitrophenols have much stronger 
1 characters than the fluorescein and phenol from which they 
I derived. The acid colouring matters (excepting sulphonic 
3s) are insoluble or only sparingly soluble in water, but dissolve 
I dilate alkalies. In other words, their alkali-metal salts are • 
pible, and this solubility increases with the number of hydroxyl | 
rapa, hut if the hydrogen of the OH be replaced by alkyl 
ncali) the resultant compounds are rendered less soluble or 
■Dluble in water. Many of the acid colouring matters unite 
1 metallic hydroicides (e.g., stannic, ferric, chromic, aluminiu) 
Hfonn insoluble compounds ciilled lakes. 
KSoLrBOHic AoiDS may be derived from either basic or phenolic 

rors, and arc obtainable either by the action of sulphuric acid | 
k B ready-formed colouring matter, or by the direct transformation I 
a previously prepared sulphonic acid into a colouring matter. The , 

mic group, SO,H, is not a chromophoro, and has so liltio 
■oeiice on the colour that the original and the sulphonated dyti 
t DsnnUy of exactly the same colour. The sulphonic acids are 
lally soluble, and can be employed in acid baths, and volatile 
iring matters (i*.^., aniline yellow) can be rendered non-volatile 
I oolpbonation. The salts of the sulphonic acids are generally 
Those derived from aio-dyes have usually the colour of 
It free sulphonic acids, and are taken up by the fibre as salts ; 
pile the aalts of the sulphonated basic dyes have iisually a dull, 
Icfinite colour, and in these cases it is the free sulphonic t 


which is taken up by the fibre, or rather which is retained by it 
Thus, alkali-blue is absorbed by the fibre as a salt, the free sulphonic 
acid being subsequently liberated by immersion in an acid bath. 

Neutral Colouring Matters are rarely met with. Indigo is 
the most notable example, but the special means employed in using 
it sufficiently indicate its exceptional character. 

Relations of Golonring Matters to Fibres. 

While the chemist defines dyes and colouring matters as acid, 
basic, and neutral, the dyer classifies them according to their 
behaviour with fibres. Thus, excluding indigo, aniline black, 
Prussian blue, and a few other colouring matters which are pro- 
duced by some chemical reaction occurring within the fibre itael^ 
dyes may be classed as substantive and adjective. 

Substantive Dtes are absorbed directly from their solutions by 
the fibre, and combine with it without requiring the intervention 
of a mordant The animal fibres {e.g., silk and wool) possess great 
affinity for most of the coal-tar colours, and in many cases absorb 
them so completely that the liquid is rendered colourless. Many 
colouring matters are taken up by animal fibres more readily 
from an acid than from a neutral bath; and in such cases the bath 
is usually acidified (** soured '') by sulphuric, acetic, or tartaric acid. 
If sulphuric acid be used, sodium sidphate is generally added 
lUso, as the resultant acid sulphate of sodium has less action on 
the fibre than free sulphuric acid. Some dyers add acid sodium 
sulphate as such, instead of forming it in the dye-bath.^ In wool- 
dyeing, sodium or magnesium sulphate is often added to the bath, 
to reduce the solubility of the colouring matter, and obtain faster 
and more even colours. In order to avoid an uneven or " cloudy " 
appearance, silk is usually dyed in a weak soap-bath made with 
Marseilles or good olive-oil soap. If an acid bath is required, 
boiled-ofiF liquor is used, together with sulphuric or acetic acid. 

It is generally assumed that in substantive dyeing a chemical 
combination ensues between the colouring matter and the fibre. 
But in some cases, as when wool is dyed with alkali-blue or cotton 
with indigo, a colourless neutral substance is absorbed by the 
neutral and indifferent fibre, and is only converted into a coloured 
body by a subsequent chemical reaction, namely, the liberation of 
the free sulphonic acid in the first case, and oxidation to indigo-blue 
in the latter. 

The " ingrain colours " produced on cotton by means of pnmidin 

^ Care must be taken not to employ the impure acid sodium sulphate known 
in commerce as "nitre-cake," as nitric acid has a very injurious action on 
many colouring matters. 



brd a remarkable extimple of the building up of a. <!yc witliln ] 
ft Gbre. 

( Cotton shows but little tendoncy to combine with coal-tar dyea, 
Ecpt these known as the benzidine colours, which dye it I 
ithout requiring the ^ency of a mordant. On the other hand) 
dlolose, vegetable parchment, and the various modifications of 
i^llalose poasoss considerable aSiinity for coal-tar colours. 
I AwscnvB I>TBtNO. MoKDANTB.— In the great majority of cases, 
and other vegetable fibres can only be dyed through the inter- 
IDtioii of a mordant. Sometimes the mordant acts by forming an . 
lolable compnnnd with the colouring matter, acconling to a , 
USnite chemical reaction ; and in other cases simply serves as a 
idiiun on which the colour acts as a substantive dj'e. Albumin 
B in this way, as also many substances in a state of fine divisiun, 
teh aa calcium phosphate and carbonate, silica, &c., when pro- 
ptsted on the fibre. In some cases, colouring matters which 
e themselves been fixed on the fibre act as mordants for others. 
I the bemsidine dyes may be employed for mordanting the 
aniline dyes on cotton. Several useful combinations .ar« 
IB obtainable. 

■The proteida resemble silk and wool in their affinity for coal-tar ' 

, and hence albumin, &c., are employed in calico-printing, 

•olution of albumin mixed with the colouring matter is printed J 

I the cotton fibre. On steaming, the albumin is coagulated and J 

t colour beeomes fixed. 

iTatinin acts as a mordant for basic dyes, as it forma with thom 
luble tannatcs.' These compounds are soluble in acetic acid or 
lol, and if the solutions thus obtained are thickened with starch 
■ dextrin and printed on cotton, the t&nnate becomes fixed and 
nlable on steaming the goods. Better results are obtained by 
Iploying in conjunction with the tannin and colour-base i 

illiu salt (e.f/., tartar emetic, stannic chloride, lead acetate, &u.) 1 
_^b]e of reacting to form an insoluble taonate. 
The use of oil in dyeing turkey-red is a familiar example of the ] 
application of oil mordants, which are generally employed in con- 
junction with inorganic mordants, 

^^PjTho tann*tM of the colour-boaiiB ma; bo flitharaoluhU or ittsatublp, accord- 
^^E to tha [iroportioni used, the Following buiiig the ijQuatities reituired to I 
^HEn intolobla Uke», acconling to J. Koecbliii: — 
^™ Dye. Tnnnie Acid. Soda Crystals. 

MAgeoU.. . . i 5 2 

Malachite grwn, .4 Ti 1 

Pam*, ... * a I 

Urthjrl green, .4 10 * 


Silica, sulphur, and metallic ferrocyanides and sulphides (e.^., 
of zinc and tin) act as useful mordants for certain dyes. 

On soda being added gradually to a solution of lead acetate or 
aluminium sulphate, avoiding the formation of an actual precipitate, 
a basic compound is formed which is decomposed by cotton fibre 
into a still more basic one which remains fixed and insoluble, and 
a soluble acid salt. The complete fixation of the mordant can be 
effected by immersing the cotton in a dilute solution of soap or 
alkaline carbonate, or by washing it with hard water. Wool has 
a greater affinity than cotton for metallic hydroxides, and hence 
alum is partially decomposed by wool with liberation of sulphuric 
acid. Chemical equilibrium is soon reached, but if a tartrate be 
added the absorption of alumina proceeds much further, as tartaric 
acid is liberated instead of sulphuric acid. 

The acetates of iron (ferric), aluminium, and some other metals 
undergo decomposition when heated, with formation of free acetic 
acid and insoluble basic acetates. Hence these metallic acetates act 
as valuable mordants which become perfectly fixed by steaming. 
The thiocyanates have recently come into use for a similar purpose. 

Classification of Dyes and Colouring Matters. 

The arrangement of dyes and colouring matters in groups with a 
view to their convenient description is preferably based on their 
chemical characters. In certain cases, however, the dyes defy 
simple classification, and in others a strict adherence to a systeiKX 
produces inconvenience. The colouring matters still obtained from- 
natural sources are also best considered in the same sectioi^* 
however different they may be in chemical nature. 

The following arrangement is that adopted in this work for th^^ 
description of the dyes and colouring matters and the methods (^^ 
recognising them : — 

1. Nitro-colouring matters. — Example. Picric acid. 

2. Nitroso-colouring matters. — Ex, Resorcin green. 

3. Aurin and its allies. — Ex, Rosolic acid. 

4. Phthaleins. — Ex. Eosin. Gallein. 

5. Azo-colouring matters. — Ex, Helianthin. Congo-red. 

6. Rosaniline and its allies. — Ex, Hofmann's violet. 

7. Safranines and Indophonols. 

8. Colouring matters from anthracene. — Ex, Alizarin. 

9. Sulphuretted and unclassified coal-tar dyes. 

10. Colouring matters of natural origin — Ex, Archil. Indigo. 

11. Recognition of dyes and colouring matters. 

12. Examination of commercial colouring matters. 

13. Examination of dyed fibres. 



Nitric acid acta very violently on phenol and eimilar bodies, and 
by the direct reaction or indirect means a number of bodies may 
be obtnined, some of which are colouring matters of considerable 
commercial importance. 

The resulting nitro-com pounds contain one or more atoms of the 
redical nitryl, (NOj), in place of the hydrogen of the original 
sabfitance. They are crystjilline bodies, usually more or less 
yellow in colour, only slightly soluble in cold water, and not 
soluble to any great extent in boiling water ; but they are readily 
soluble in olcobol and ether, and are removed by the latter solvent 
from their acidulated aqueous solutions. 

The nitrophenols and their allies have marked acid 
properties, readily decomposing metallic carbonates, and furnishing 
% Borira of salts all or nearly all of which are more or less soluble 
in water, and often form crystals of great beauty, ranging in colour 
taaa a pale yellow to a line crimson. The salts of the nitro- 
phenols and their allies all deflagrate with greater or leas facility 
when ignited, and many of them detonate on percussion, the more 
highly nitrated compounds («.</., the picrates) exploding with 
considerable violence (page 141). 

In cases where the nitro-hody is the product of a limited 
nitration, it may lie converted into the corresponding a u 1 p h o n i c 
■ cid by treatment with strong sulphuric acid; but this is not 
possible when, as in the case of picric acid, the number of nitiyl 
atoms in the molecule is at the maximum. The sulphonic acids of 
the nitro-colonring matters are stable bodies, readily soluble in 
water. The Eutro-colouring matters as a class dye wool and silk 
yellow or orange, but have no affinity for cotton. Their acid 
characters are welt marked and stronger than the phenoloid bodies 
from which they are derived. They dissolve in concentrated 
sulphuric acid to form yellow or colourless solutions. Strong re- 
ducing agents, such as stannous chloride and hydrochloric acid, 
convert them into the colourless amido-derivatives. Pibres 
dyed with nitro-colouring matters, or aqueous solutions of the bodies 
themselves, are but slightly altered by hydrochloric acid, while 
■mmoniit and caustic soda tend to darken or redden the colour. 
With fibres dyed by nitro^jolouring matters in acid baths, the 
colour may subsequently be partly removed by boiling water. 
These reactions serve to distinguish the nitro-dyes from other 
yellow colouring matters. Thus phosphine is turned lighter, 
while the yellow aio-dyes are reddened by acids. Phosphine, 
^■in, is extracted from its alkaline aqueous solutions on agitation 


mTfio-coLou&raa uattbes. 

with ether, but the nitro-compoiinds are not dissolved by ether 
tmder similiu' conditions. In presence of dilute sulphuric acid ir. 
excess, the eirople nitro-dyea {e.g., picric acid, dinitrocresol, dioitro- 
naphthoi, and aurantia) are extracted by ether, but the aulpbonic 
acids {e.g., naphtbol yellow S) are not dissolved, in this respect 
resembling the yellow azo-dyea (except chiysamin^ 

The following is a list of the principal nitro-colouring matters: — 

Vlctorik Tellow ; 

luw; Nipb 


Naphlhol ycUaw 
s.: NBphlholvel- 

n.; BrilllBot Tel- 
low, (?tge 1U.) 
CltRmlD. (P^ie 

Annul tin; BUckl^ 

Mlitiu« of K or N> 

Sodlmn or otbar 



. (0(ON«):OC(IOri 



■ {&ssa 

Besides the colouring matters in the foregoing table, the follow- 
ing obsolete or nearly obsolete dyea belong to the nitro-group : — 




Cittnctan uid liode of 


produced b7 uUon kI 


PaUtlme onoge 




fl«kc«. malUng ot aCT. 





The following sections contain detailed 
principal nitro-colouring mattere. 

Picric Acid. 

Para-diortlio-trinittophenoL Trinitropher 

CoHjNjOj = H.O.Con,(NOj)3 = C^U^ 

F mbetance, formerly called carbazotic acid, is the 

t of the action of nitric acid on a large number of 

B coDtatning a benzene nucbus, just as oxalic acid is the 

Bit of the oxidation of many bodies of the futty series. 

'c acid is obtainable from indigo, aloes, gum-resins, wool, ailk, 

f Kcric acid was formerly prepared by the direct action of nitric 
D phenol, but is now made by first dissolving the phenol in 
; sulphuric acid and then acting on the resultant phenol- 
ionic acid by eKcess of nitric acid.' Mono- or diuitro- phenol 
f result if the action be not carried sufficiently far.^ According 

f Pkric Mid it DO* mannfactured on a large ecitle by aixiiig eijual iiarts by 
tt of aiTatslIiBed Darbolic acid and concentrate J sulphuric aciJ. This ig 
o 100° until n sample is found to be completely soluble in water, when 
wble equivalent of nitric acid of 1'3 ap. gr. ia allowed to Saw in, the whale 
igMUtinnRlljagitHted. In some works, the phenol -Bnlphunic acid, eligbtly 
1 inlfl strong nitric acid. On cooliug, tlie product forms a 
9, which is filtered olT, draiu^, and washed with culd water. It 
n pariSeil by crystal liMtion from boiling water coDtainiog O'l per cent. 
Mlpharic acid ; or the hot solution of tlie crude acid ia exactly neutralised 
b •odium carbonate, the liquid filtered to separate resin, and i^xccss of 
■odiimi esrbonato added to the filtrate, when almost the whole of the sodium 
fiicnte «parate«. This salt Is decomposed by sulphurie or hydrochloric acid 
•ad the picric acid ciystalliaed, Bodiutii sulphate is sonietinies added hefoni 
ci7«t«lligation. aa an adulterant 

* The Gnt product of the action of nitric acid on phenol is a mixture of 
paia-moDOnitrophenol, C,H«(NO,}.OH, with the isomeric ortho- 
derivatire. These bodies are best obtained by adding sutbcieat water to 
patr phanol to prevent it from aolidifyiog on cooling, and then adding the 
ramltSint hydrous phenol drop by drop to a well-cuolcd mixture of two parta 
of nitric acid of I'Si sp. gr. and four parts of water. A heavy bromine-like 
oil Mpanlea, and on prolonged standing acts to a crystalline niasB. This 
eonaialB o( a mixturo of ortho< and para*nitraphenol. with sonie unaltered 
pbend. The higher the temperature has been allowsd to rise the larger the 
proportion of tho ortiio-modiScstiou formed. The product is washed with 
', and then distilled in a current of steam, when the ortho-uitru- 
lol dijuolTea over, and may thus ho separated from tho para .modification, 



toT. Whitaker {Jour. Soe. Dyers, ^c, iv. 87), if the sulpliuric 

acid uBed for aulphonatioa contain nitrous compounda the picric 
acid ha« a brownish colour instead of being pure yellow. 

Picric acid forme pale yellow, ciystalline needles or ecales, of on 
intensBly bitter taste and 1777 specific gravity. The pure add 
melts at 122° C. and the commoa at a lower tempemture to a 
browniah-yellow oil, which at a higher temperature partially sub- 
limes, and boils with formation of yellow, bitter, suffocating vapouts. 
The lower melting point of impure picric acid is probably due to 
an admixture of dinitrophenols or of a nitrocreeol. Hence the 
melting point of picric acid is a test of its purity. 

When strongly heated, picric acid burns rapidly with formation 
of an intensely black smoke. It is commonly stated tu be liable 
to explode when strongly heated, but this is doubtful, and ia 
opposed to the direct experiments of D u p r ^ and A b e L On 
the other haiid, picric acid can be detonated by a blow, a chai^ 
which is not volatile, and msj be obtained from tbe contents of the diltJUiag 
Husk by ooolini; aud ret-'rystuttiaiiig Truiu bailing water. 

A meta-moDonitropheaol is obtainable from tuet«-iiitruuliiie bj tha actiaa 
of nitroiu acid. 

On wBrniiu([ the ortho-monotiitraphenol mth nitria acid of I '86 sp. gr., 
violent action enaues and anotljur nitro-gronp is aasiinilated, a product bting 
obtained which is chiefly a mixture of diortho-di ni trophenol and 
ortho-para-dinitrophenol, C,H,(NO,VOH. (The Utiot body ia >U 
obtained by the further uitratJOD of para-mononitTophiinol.) The prodocl i* 
washed with cotil water, and then boiled with water in a Haak throngh which 
a current of »t*ani is paased, to roroove unaltered mono-nitrophmol. It b 
then boiled with water and eicesa of boriam carbonate, and the Mlnti<ui 
filterod. On coolin;; to 10% the barium salt of diortbo-dinttropliciwl 
cryatalliseB out, wbils the corteaponding ealta of Drtho-para-dinitruphanol and 
picric acid remain iu aolulion. A better separation of the barium nlia of ths 
isomerio dinitrophsnola can be obtained by reoti&e<l fpirit, in wliivb tbo ortho- 
pata-aalt diusolves with moderate ease, while the diortlio -com pound is bmtIj 
'insoluble. Salkowski converla the mixed barium aalCa inlo potaodutn 
salts by potassium carbonate, and removes the greater part of the ortho-pan- 
salt by oryHtallisatian ; then heaU the mother-liquor to ^iO'-M' C aut 
pracipitatea with barium uhloride, which throws down the diortho-oompouiid. 
This is wished with cold water and purified by recrystollisBtion. From tluur 
salts the dinitrophenols may be obtained free by adding exceas of (Uluto 
snlphuriu acid and agitating with other. The etbereal layer leavM th* 
iiitrophonol on eTspoiation. 

A meta-mononitroplienol ia obtainable by indliect means, and ylaMi en 
treatoiont with nitric acid three isomeric di- and two tri- nitrapbenoU (rbleh 
are not identical with those produced by the direct aotiou of nitric add a* 
phenol. By tbe action of boiling cuncentrated nitric acid tlie mnu-dinittv- 
phenols are conveited into trini troteiorcinoL or atyphniii •• 



or 5 graba of fiilniinat« of mercury eufltciiig to detennine the 
ext>lrieian. The di-tonation of one charge will cause tlie dHtona- 
tion of neighbouring quantities, and even wet picric acid can he 
exploded hy this means. Metallic pictates, and notablj' picrate of 
load, or even an imperfect mixture of picric acid with oxide or 
nitrate of lead, will detonate violently when heated, and the explosion 
will induce the ilctonatjon of neighbouring quantities of picric acid 
ot picrates.' This property of the picrates has led to their employ- 
ment in several detonating and explosive mixtures (see page 143J. 

the prop«rtiea of the uitropheDols at proMBt 














Aimoit colonrtDu prftmi 
urdAthinpUtei: not 
tolaUle wlC^ •team. 


F»1b jtUnw prUmii: 
reullly VQl>tllg wltb 



t-OT PU»^>TthO' 



airi»t«l, yell owljh-« hit* 





Slender, ihcirt, bright 
rcUo* DeedloL 



Slender. ihorl, p«]e 

yeUow ncedUi: «!»■ 




Long, colaurleu. (llky 
nea11»; out *olatU. 



BmBU j>eUow Deedlsi. 


(-or p.r*dlnttt.o- 



Pule yellow UinliiM or 





■ iOi nUm." 
WIUO ullny neMUa. or 





White oecdlei. 

■ At midday on Jane 33, 1887, a fire, followed by a violent eiplonon, 
ooeamd at the worka of Hosara Boburta, Date, & Corapanf, Combrook, 
Uaiichesler, manufacturera of pkrio aotd. Ooe loaD ffu killed, the works 
wiini cniiipletely destroyed, aod much damage wu done to the uuiglibouriiig 
buildings. The venlict of the ooroner'a jury was based ou the eviJenco o( 
ColoDvl Mnjendie, chief inapectnr of enploHives, and was to the eOeut that the 
fir* waa canaed by forbidden aoiokinj;, and that the fire ignited picric aoid and 
|i[}iargc DT other oxidising agent which had beta aecidvnlaily miiml and fused 
owioic (« the negligent manner in which they were stored, and so caused the 



Picric acid is soluble in about 15 parts of boiling water, but it 
requires 26 parts at 76*" and 86 at 15*" G. The solution is intensely 
bitter, bright yellow, and reddens litmus. In a stratum one inch 
in depth, the yellow colour of a solution of 1 part of picric acid 
in 30,000 of water is distinctly visible. The yellow colour of 
picric acid solutions is intensified by neutralisation with an 

Picric acid is readily soluble in alcohol, ether, chloroformf 
benzene, petroleum spirit, &c.; the last four solutions being colour- 
less or nearly so. Such of the above solvents as are not miscible 
with water remove picric acid more or less perfectly from its 
aqueous solution, or that of a picrate which has been freely 
acidulated with sulphuric acid. Ether is preferable to chloroform 
for this purpose. 

All the above solutions of picric acid, including the aqueous, 
dye silk, wool, skin, and other nitrogenous organic matters a 
yellow colour of a slightly greenish shade.^ The stain is not 
removable by water, but soap or alkali partly destroys it. AniTnal 
charcoal absorbs a large quantity of picric acid from its aqueous 

Picric acid forms a series of well-defined crystallisable metallic 
salts and also combines with organic basea With certain hydro- 
carbons it forms characteristic crystalline compounds of the 
formula X, CgH3(N02)80, in which X represents a molecule of the 
hydrocarbon. The reaction has been utilised for the purpose of 
distinguishing hydrocarbons, especially those of the anthracene 
group (see vol. ii. page 524), and the formation of the naph- 
thalene and acridine picrates has been suggested as a means of 
identifying picric acid. 

Detection and Determination of Picric Acid. — ^The yellow 
colour and extremely bitter taste of the aqueous solution of picric 
acid, the deepening of the yellow colour on adding excess of 
alkali, and the power possessed by the solution of the free acid of 
dyeing immersed wool or silk yellow, are themselves important 
indications of its presence. In the presence of other colouring or 
interfering bodies, the picric acid may be extracted from the 
aqueous solution by agitation with ether or amylic alcohol, after 
strongly acidulating with sulphuric acid. The picric acid may 
then be recovered by evaporating the ethereal solution, or agitating 

^ Picric acid is used as a dye for silk and wool, bat is employed to modify 
the shades of other colours rather than as an unmixed dye. Thus with methyl- 
greeu it gives a yellow-green, with indigo-carmine or aniline-blue a deep green, 
and with magenta a very fast scarlet Since the introduction of the yellow 
azo-dyes the employment of picric acid has decreased. 


it witli solution of caustic soda, when it will pass into the aJkaline 
li(|iiid. The extroctiou of picric acid from an acidulated solution 
by ether, benzene, or amylic alcohol may be made quantitative. 

Picric Bcid may be titrated with ease and accuracy by standard 
cnnstic alkali and phenol -phthalein (P. Kay, Joxir. Soc.. Dyers, ^c, 
W. 84). The process is applicable to the ethereal or benzene 
aolntion of picric acid if this be first diluted with alcohol 

Ad aqueous solution of picric acid ia not precipitated on adding 
neatial Irad acetate, but basic or ammoniacal lead acetate gives a 
bright yellow precipitate even with very dilute solutions of picric 

Kcrie acid ia not precipitated from its aqueous solution by 
cupric sulphate ; but the ammonio-sulphate produces a bright green 
precipitate, which is insoluble in ammonia, and is decoiupoaed by 
washing with water. A solution containing 1—10,000 of picric 
acid gives a distinct precipitate with ammonio-sulphate of copper 
in twenty-four hours. 

If a solution of picric acid be treated with zinc and dilute 
Bolphuric acid, a turbid yellowish-red solution is obtained, which, 
when poured off from the excess of zinc and mixed with alcohol, 
develops a green colour, changing through blue to a violet, 

£y the action of tin and hydrochloric acid in a warm solu- 
tion, picric acid is compleUly reduced to the colourless hydro- 
chJoride of triamido-phenol, CaHjfNHjVOH. In alkaline 
■olutions, the reduction does not proceed so far, picramic acid, 
C^g(NOj)j(NHg).OH, being the product, This reaction occurs most 
readily by imsaing sulphuretted hydn^en through a saturated 
alcoholics solution of picric acid neutralised with ammonia. Dark 
nd crystals of ammonium picramate are ileposited, from which the 
e acid may be prepared by dissolving in hot water and adding 
"i acid. Picramic acid forms beautiful red needles, almost 
nlable in water even when hot, but soluble in alcohol and etlier. 
« silk and wool brown.* 
BVtbs precipitate be decomposed hy dilute sulphnric acid, aod the (i1tFr«l 
II Tendeted ntDmoniac&l anil evaporated to dryuoas, n reaidae ia olitained 
VDB a deep brown colour on iisnting with potaasium cyamdo. This 
If difltiu)^istiea picric add from qacrcitroD and sach othiir vegetable 
W oolouriag matters as are precipitated by Insic lead acetate. 
■ e. Tnrpio baa patented (No. 10,665, 1887} the use, aa a substitute for 
|[lltipowdcr. of die product resalting from the reduction ol picriu acid liy boiling 
ilia aqnooti* Hoi u lion witb metallic due or iron. When acetic acid is also added 
i» rormed, and this, or its sodium aalt, in admiiLnire with nitre, 
• powerful detonating expEosive. Mixtures containing (torn 30 to fiO 
t, of picramic acid, or 25 to 53 of sodium piiirnmate, are recommeniled, 
» of the French explosive miliniU bos not been nude publio. 

which cryBtalli 
green lustre, 
hot water. 


Wh^n a solution of picric acid is boiled with a strong soln- 
cyanide, a deep red liquid is piuducod,' owing 
of potaesium iao-parpurnte, a IkxIjt 
in amall reddish-brown plates with a lieetle- 
md is slightly soluble in cold but more KadQy in 
reaction with ammonitun chloride, it givee 
ammonium iao-purpura t e, NH,,CsH,N;,Oj, or artificial 
murexide, which iu a slightly acid bath dyes silk and wool a 
lieautiful brown-red colour. It was formerly employed niuler 
the Dame of "grenat aolnble," but is not now used. On adding 
bttriura chloride to a eolution of either of the above salta s 
vermilion-red precipitate is formed, consisting of barium iao- 
purpurate. True iso-purpuric acid is very unstable and i> 
practically unknown. 

Picric acid, when boiled with a strong solution of aalcnnit 
hypochlorite (bleaching powder), gives off pungent and tear- 
exciting vapours of chloropicrin, C(NOj)Clj. 

Picric acid forms highly insoluble compounds with many of the 
vegetable alkaloids,* and the insolubility of the cinchonine aalt 
has been employed for the determination of picric acid. A solu- 
tion of cinchonine sulphate acidulated with sulphuric acid is 
aiided to the picric afid solution. The precipitate of picrate 
of cinchonine, CjoHj,N(0(CgHgN30,)i, is waahed with cold 
water, rinsed off the filter into a porcelain crucible or diali. the 
water evaporated on the water-bath, and the reaidual salt weighed. 
The yeUow, intensely bitter alkaloid, berberine, is said to 
precipitate picric acid bo perfectly that, on mixing the jiicric and 
. nikaloidal solutions in equivalent proportions and filtering, tht 
filtrate is colourless and perfectly free from bitter taste. 

Borne of the colour-bases from coal-tar form extremely inaolaUe 
pici^tes, and have been employed by Kay and Appleyard 
{Jour. Soe. Dyerg, ^e., iv. 83) for the determination of picric acid. 
but its composition is not improbablj' indicated Ly tliat of Uie fortgmng 
mixtares ; or perhnps haa S conoectioii with another patent of tliD tame 
inveulot (No. 10,667, 1887), wlm hae proposed the um, u exploslvM, gf 
chtoro-picrin, bromo- chloro- and iodo-diuitroplieDolB. bromo-dioitrobeaum^ 
chlDm-trinitTobeDzenc, and tclraDitro-chloronaphthaleDe. 

' Aniline yellow of commerce diraolvoa in water with redder colonr than 
picric acid. It is not altercKl by potassiani i-j-aoide, but is turned purple l>y 
hydrochloric acid. 

' The cinchona dkaloida, the opium bKses (except morphine and pHoda- 
morphine), the Mrychiua alkaloids, vontrioo, berbtrine, and tome Dthi»« mn 
caniplelcly precipitated by picnc acid from theil dilute golntions, if addalatad 
by sulphuric acid, bnt not in presence oF 1^ hydrochloric acid. CaSUnc 
aud the glucosidea are not precipitated by jnoric acid. 



For tliis purpose they prefer the dye known as n i g h t-b 1 u e, which 
is the iiyiirociiloride of tetramethyltolyltriamido-diphenyl-naphthyl- 
carliinol. The commercial product is purified by precipitating the 
■rquetms solution with ammonia, washing well with watpt, and 
dtying the precipitate over strong sulphuric acid. A weighed 
quantity of the base is dissolved in acetic acid ajid tlie solution 
diluted to a known volume. Fur the titration, a known volume of 
the night-blue solution i^ measured into a llnsk, and the solutioo 
o( picric ocid nm in from a burette. 485 parts of the night-blue 
base uorreepond to 229 of picnc acid, the picrate, which forma a 
dark precipitat*, liaviug the formula Cj,H^N3,CgHj(N0g)„0H. 
The picric acid solution should contain 1 gramme of the sample 
per litre, and by compnring the volume of the solution used with 
the raeasiuo of a solution of pure picric acid employed in a 
pnidlel experiment, the proportion of impurity may be readil.V 
ascartitined. The end of the reaction is very shaiply delined, an 
by tilting the flaak on one side, so that a portion of the clear 
liquid may run into the neck, it is eosy to observe whether the 
solution retains any blue colour, A very alight excess of picric acid 
sufficient to produce a marked yellow tint. If desired, a portion 
the liquid may be filtered for the better observation of its 

r, but this la rarely necessaiy. 
Crystal violet, the hydroclUoride of hexomethylros- 
intUne, may be substituted for the night-blue in the above 
ptoceaa. 443'.') parte of this colouring matter, when dissolved in 
water, react with 229 parts of pure picric acid to form a picrate 
of the formula C^H„N8.CaH,(NO()gOH. This precipitate is 
lulent, and when in suspension exlitbite such a powerful 
Ippety reflex that the liquid containing it appears brown by 
iflect«d light. 
The picratos of rosaniline, safranine, methyl- violet, and mala- 
;n are also nearly insoluble in water, but not sufficiently 
to Bender the bases desirable substitutea for night-blue or 
" violet in the above prwess. 
Of the com]>ounda of picric acid with solid hydrocarbons, that 
naphthalene, C„Hg+CoHs(NOj)30, is aUuost the only 
precipitated when the cold alcoholic solution of the hydro- 
is mised witli a <!old alcoholic solution of picric acid. It 
atelhit*! grou|js of KoUen-yellow needles, melting at 149° C. 
furmatiou of naphthalene picrate may bo employed to dia- 
ib picric acid from aimilor nitro-compounds. 
Acddinfi hue Wm suggested by Anschtite (Jour. S"C Cliem. 
Ind^ iiL 234} na u suiluble reagent for the determination of picric 
■cid, ttie hydrochloride being used as a precipitant for metallic 
VOL. llL TAKT 1. K 




picrates and a solution of the free base in benzene for the picric 
acid compounds of hydrocarbons. 

Picric acid has been used occasionally to communicate ai bitter 
taste to 6eer, less than 1 grain per gallon being amply sufficient 
for this purpose. The employment of picric acid as a "hop- 
substitute " is objectionable, as it has distinct poisonous properties, 
and rabbits and dogs have been killed by doses varying from 0*06 
to 0*60 gramme. The most delicate or satisfactory method for the 
detection of picric acid in beer is to concentrate 100 cc. by 
evaporation to about 30 cc ; then acidulate with sulphuric add 
and agitate with ether or petroleum spirit. The ethereal solution 
is separated and evaporated. The residue is dissolved in hot 
water and the solution heated on the water-bath for some time 
with a small quantity of white Berlin wool, which in presence of 
picric acid will acquire a yellow colour. The author has readily 
detected 1 part of picric acid in 100,000 of beer by this method. 
Amylic alcohol has been proposed as a substitute for ether, but, 
in the opinion of the author, is not so satisfactory. By first 
precipitating the beer with neutral acetate of lead and filterings 
the colouring matter of the beer may be removed and the indica- 
tions made more delicate. As a confirmation, the dye may be 
removed from the wool by warming it with dilute ammonia, 
filtering, and evaporating the filtrate to a very small bulk on the 
water-bath. On then adding a few drops of potassium cyanide 
solution, and heating, a distinct red-brown colour will be produced 
in presence of picric acid;^ or the ammoniacal extract may be 
treated with zinc and hydrochloric acid and the solution diluted 
with alcohol, as described on page 143. 

It is evident that the method just described is applicable to the 
detection of picric acid on animal fibres, such as sUk or wool. 

Commercial Picric Acid. 

The picric acid of commerce is generally crystallised. Though 

now of much better quality than formerly, it is still liable to contain 

impurities, and occasionally is intentionally adulterated. Thus 

sodium sulphate is sometimes added before crystallisation, and 

.oxalic acid and sugar are said to be occasionally met with. 

The melting point of pure picric acid is 122*" C, and the 
best commercial samples do not melt below 121*'. A lower 
melting point indicates the presence of dinitrophenol or a fUtro- 
cresol. The first impurity is due to imperfect nitrofication and the 
latter to the employment of a carbolic acid of low melting point 
(therefore containing cresol) for the manufacture. The melting 

^ A roagb colorimetrio determination of the amount of picri^ acid present 
may be based on the depth of colour produoed. 


point of picric acid is beet observed by placing a minute fragment 
■>f the sample on the BUrface of some clean mercury contained in 
a porcelain crucible or small beaker. The latter is covered with 
AD inverted funnel or bottomless flask, through, the neck of vhich 
n thermometer passes and is held by a perforated cork in sui^ a 
poeition that the bulb may be entirely immersed in the mercury, 
without touching the side or bottom of the beaker or cruuible. 
The latter is now heated on an iron plate, and the temperature at 
which the fragment of picric acid liquefies recorded as the melting 
point By employing several fragments and repeating the experi- 
ment after allowing the mercury to cool a few degrees, very fairly 
conconlant results are obtainable. 

More rapid, and for technical purposes quite as satisfactory, 
reeults are obtainable by determining the solidifying point 
of the sample. This is effected by melting 8 or 10 grammes of 
tlte picric acid in a snmll test-tube, which is then fixed by means 
of a perforated cork in the month of on empty, sbort-neckod Hask. 
The melted picric acid is continually stirred with a thermometer, 
while the temperature is carefully watched. At a certain juint tlie 
morcnry ccaees to fall, remaining stationary for fully half a minute, 
or even rising again slightly, This temperature, which is perfectly 
tlofinitc, is recorded as the solidifying point of the sample, 

The following figuresj obtained in the author's lahorat-ory by the 
examination of six samples of commercial picric acid, show the con- 
stancy of the results yielded. It will be observed, while the 
ntiidifying point is always several degrees lower than the melting 
point of the same sample, the difference between the two results ia 
not a constant figure : — 



■ "'" 



lis, ue 

H7-S. UT-6 

ll^ lis, iiB-fi. it&. lis. 

lU. lis, Il«, us, USB, 113,113. 

llH'fi! Ill'G. 

117, 117, UB, 118, 118. 117, 118, 118. 118: 



I'icric acid of good quality does not melt when boiled with 
'•ice its weight of water. If fusion occur, it is probably due to 
*^e presence of nitrocresols, which for some purposes are 

fh« bust commercial picric acid is completely soluble in IS 
"**<■ Urn iwl^t of boiling ireXer, or leaTM only a trifling qaanti^ 


(0*5 per cent) of granidar imparity. Picric acid of inferior 
quality leaves a melted globule when similarly treated. The 
scientific advisers of the French Crovemment call this insoluhle 
matter " dinitrophenol " (!), apparently without any evidence of its 
nature, and reject, as unsuited for the manufacture of melinite,^ all 
picric acid which leaves a glohole amounting to more than 1 per 
cent, of the sample. The test is made hy treating 10 grammes of 
the acid with 150 cc. of water, and heating the liquid to boiling 
in a flask with gentle agitation, till the globide of insoluble matter 
1)ecomes transparent and ceases to diminish perceptibly in bulL 
This ])oint is reached in about ten minutes from the commence- 
ment of ebullition. The test must not be much prolonged, or the 
so-called "insoluble matter" will partly dissolve. The critical 
point is by no means well defined, though with care and experi- 
ence fairly concordant results are obtainable with some samplei^ 
while others behave very erratically. When the operation is 
considered to be complete, the liquid is aliowed to cool slightly 
and poured off from the globule of '* dinitrophenol," which is 
then washed with cold water, dried by means of filter-paper, and 

Any resinous matters will also be left insoluble on dissolving 
commercial picric acid in boiling water. The separation will be 
more perfect if the hot solution be exactly neutralised with caustic 

Besides being soluble in 15 parts of boiling water, picric acid 
of good quality dissolves completely in 10 parts of alcohol, while 
any metallic sulphates or nitrates will be left insolubla 

General impurities and adulterations may be detected and 
determined by treating 2 grammes of the finely-powdered sample 
with 50 cc. of ether. The picric acid dissolves, while any picrates, 
nitrates, oxalic acid, boric acid, sodium sulphate, alum, sugar, &C., 
will be left insoluble, and, after removal of the ethereal liquid, 
may be readily identified and determined. For the detection and 
determination of water and oxalic acid, 50 cc. of warm benzene 
may be advantageously substituted for the ether. Sugar and boric 
acid may be separated from the other impurities by treating the 
residue insoluble in ether or benzene with rectified spirit If boric 
acid be present the alcoholic solution will bum with a green flame. 
Sugar may also be sought for by neutralising the aqueous solution 
of the sample by sodium carbonate, evaporating to dryness, and 
extracting with proof-spirit, which will dissolve any sugar and 
leave the sodium picrate insoluble. 

Sulphuric, hydrochloric, and oxalic acids, and their salts, may be 

^ See footnote on page 143. 


detected by sdcliug solutions of barinm, BilTer, and calchim, 
reapecliTcly, to the warm, filtered, aqueous solution of the sample, 
0*2 per cent, of SOj, aa estimated by precipitation ae barium 
anlphate, ia the maximum proportion allowed by the French 
Government in picric acid intended for the manufacture of 
u^Uinite. Free tulphuric acid mif^ht be delected by dissoWing 
Uie sample in warm beniene, agitatiog the solution with warm 
water, removing the benzene layer, and again agitating the aqueou3 
liquid with benzene, till all yeUow colour is removed. On tbeu 
titrating the aqueous liquid with standard alkali, the volume 
leqnircfi for neutralisation will corresiwnd to the free sulphuric or 
other mineral add of the sample. 

It is possible that commercial picric acid ocuasionally contains a 
nitrophmol-wipktmie acid. Such an impurity would be indicated 
hy the presence of sulphates in the residue obtained on igniting 
the sample after neutralisation with a fixed alkali. TJio e.\piosive 
cbaraeter nf the picmtee prevents the direct application of Ibis 
method, but ignition of the picric acid in admixture with 
■ luge excess of lime or magnesia would probably answer, or 
the sample might be dissolved in alcohol together with some 
ammoninm carbonate, and the alcohol burnt in a lamp con- 
nected with an apparatus similar to that employed for deter- 
mining the proportion of sulphur in coal-gns. (See Analifst, 
xiii. 43.) 

If the process of nitrofication has been imperfect, the rcsultaiit 
pjcric acid will be liable to contain dinilropkeml (see above). This 
impurity towers the melting point of the sample. The calcium salt 
is leas snluble than calcium picrate, and if present in sufficient 
qnaittity may be separated from the latter by fractional crystaJ- 
hsation, or by precipitating the hot saturated aqueous solution 
of llie sample with excess of lime-wat«r. 

The most promising, if not the only method of determining 
amall proportions of dinitrophenol in picric acid is by treating the 
tqueous solution of the anmple with bromine, as proposed by the 
author (J/yv.r. Sor. Di/err, ^e., iv. 84). With dinitropbeuol 
the following reaction occurs:— C«Hg(NOj)gOH + Brj = HBr+ 
Cglljltr(NO^),0H. With picric acid, bromine reacts as follows : — 
C„H,(NO5)a0H+ Br, = HBr + HNO, + CaHjBr(NO,),OH.' In 
aaeh eaae two atoms of bromine enter into the reaction, with 
formation of a bromo-dinitro phenol (the same in each case) and 
one molecule of bydrobromic acid. But in tbe case of picric acid 
nitric acid is formed in addition, and hence the acidity of tbe 
liqnid nt tlie end of the reaction would be greater the larger the 
K footnote OD psgellS, referring to bramo.dinitrDphenol us nn eijitosive. 



proportion of picric acid prasent. If the bromo-dinitroplienol and 
excess of bromine' were removed by agitation with etiier or 
similAt solvent, the acidity of the aqueous liquid could In: 
ascertained with great accuracy by titration with staudonl 

The author found the reaction between bromine and diiutro- 
pheuol to occur inatantaneouBly, but in the caao of picric acid it 
was gradual. In twelve hours it was complete, but in the couise 
of a few minutes almost nothing. This fact enables the reaction 
with bromine to be utilised for the direct determination of the 
dinitrophenol, instead of for its indirect estimation (by determining 
the picric acid), as when the acidity is ascertained. The following 
method of operating was found by the author to be the moet 
satisfactory ; — 1 gramme of the sample of picric acid is dissolved 
in about 100 c.c. of warm water. A saturated solution of 
bromine in water is diluted with twice its measure of water in a 
large tapped and stoppered separator, and from this run into a 
Mohr's burette. From this burette, a definite volume of the 
bromine solution, which is approximately of I per cent, strengtit, 
is run into a flask and an equal measure into another similar 
flask, both of which are immediately closed. The picric acid 
solution is then poured into one of the flasks, the last dro[)8 rinaed 
in without delay, and then an excess of a solution of potassitim 
iodide at once added to the contents of both flaska. The liberated 
iodine is then determined by titration with a decinormal aolution 
of sodium thiosulpbate (hyposulphite) in the usual way.* From 
the diilerence in the volume of the solution required in the two 
experiments the amount of bromine which has reacted with the 
dinitrophenol is easily found, Dinitrophtmol reacts with 86'd6 
per cent, of bromine, taking up 43'48 per cent. Monomtrophen^, 
if present, which is improbable, would react with 230'2 per nnL 
of bromine, taking up 116'1 per cent, to form the compouad 
CeHjBrj(NOj).OH. The author has verilietl these reactions by 
experimenta on specially prepared mono- and dinitrophenol. When 
the process is applied to commercial picric acid the results are 
liable to be somewhat in excess of the truth, owing to slight 
action of the bromine on the picric acid itself. 

Commercial picric acid often contains particles of a red colour. 
These are often attributed to the presence of dinitrophenol, but 

• 1( preferreil, before oitracting with eth«r the ckctm of bromin* inay ba 
got rid of by Hdding jiotasaiQiii iodide Had tlien suQiuleut Bodium tliiomlpliaM 
to react with the iodine Ut>erated. 

■ The aotbor fouDd iodine to Ira wholly without octtoa on sclntioiia of Mut 
>■, <U^ or tri-nitropIieooL 



II "^^J 
F whei 

I an obBervation of T, Whit alter (Jour. Soe. Dyera, ^e., 
) it is not improbable that they consist of a nttfoiojihenol. 
Mbtaluo PicaATKa, 

Aa a nile, the picrates are posseted of but tittle eolubiJity, 
They are yellow in colour, and crystallise well. Many of tbeiii 
fxplode violently when heated or stnick, and hence thoy are 
mployed in admixture with metallic chlorates or nitrates for 
Ebe blasting charge of shells. (See footnote on page 143.) 

Pataatiurn jiieraie, CflH3(N0j)g.0K, forms long yellow needles 

when a strong solution of picric acid is neutralised by carbonate 
or hydroxide of potassium. The salt retiuirea 288 of cold or 14 

Iparta of boiling water for Bolation, and in alcohol is nearly 
^Holublei. The aqueous solution is much more strongly coloured 
j^n n a solution of free picric acid of corresponding strength. 
When heated, potoEsiuni picrate becomes red and explodes like 
■Uipowdor, and when strongly stnick it detonates violently. 
K Sodium pierals is readily soluble in pure water, but nearly 
■■olable in solution of carbonate of sodium. 
WAvimonitim picrate crystallises in rhombic scales which ore 
lomewhat more soluble than the potaaaiiim salt. It has been 
sii^eatod for use as an antipyretia 

Lfod jneraie crystallises in brown needles soluble in 119 parts 
o f cold water. In admixture with nitre it is employed as an 
[plosive. A rough mixture of picric acid with rud lead or 
tonatea violently when strongly struck, 

[ Nitrophenol-sulphonic Acids. 

^ The mono- and diuitro-derivatives of phenol are, like phenol 
Kilf, acted on by strong sulphuric acid with formation of 
Biphooic acids. If a mono-nitrophenol be sulphonatod, the 
I be converted into a dinitiophenol-sulphonic acid by 
Bful nitrofication, but if the treatment with nitric acid be 
Mhed to an extreme the product is invariably picric acid, the 
|]phonic group being eliminated. 

\ The Bulphonated nitrophenola furnish two classes of salts : — 
i^ ioliit in which only the hydrogen of the sulpho-group is 
Iplaced by metals, and tMutic «alt» in which the hydrogen of the 
hydroxyl group is also repl.iced. The former salts are yellow, but 
tfao latter are red, and often of great beauty, 

Flavalrin. The commercial colouring matter known under 
Ibis name is the ammonium salt of diuitrophenol-para- 
sulphonio acid, CBH,(S0j,NH()(NO,)a.O(NHJ. It is pro- 
duced by the cautious action of nitric acid on mononitrophenol- 
ulphonic acid, and the conversion of the product into an 



aromoniuTn s&lt, Flavaurin forme a. yellowish-red powder which 
BweUa up like a " Phnraoh'a eerpent " wlien heatwt. Tho aqueou 
solution is yellow, anil is changed to wine-red by hydro^oric 
acid. With caustic soda the solution is dftrkeiied, and amnionia 
is evolved on heating. On boiling the alkaline liquid with line 
duet it tumB brown, and is then decolorised, air restoring the bmwn 
cojoui', Flavaurin dissolves in strong sulphuric acid with wine-red 
Rolour, the solution becoming colourless on dilution. 


When the mixture of isomeric ctesols, CaH,(CH3).0H, from 
coal-tar, formiitg the fraction of the phenolic bodies boiling at 
about 200° C, is treated with nitric acid, the orthocresol and 
paracreaol are converted respectively into dinitro-ortho- 
ere sol and dinitro-paracresol, respectively. The mota- 
creRoE, which is the moat abundant of thtt isomeric cresola, is, on 
ihe other bond, converted into trinitro-melacresol, melting 
at 160°. The isomeric dinitrocresola can be separ&tf'd by taking 
fidvanlage of the difference in the aoluhitity of their barium salt& 
They may also be obtained by acting on the corresponding tnltiidineB 
in ice-K;old hydrochloric acid solution with eodinra nitrite, whm 
diazotoluene ch 1 oride^ CoH/CHs)N : NCI, ia forme.!, and 
if this be [Kinred into hot nitric acid the dinitrucroBoI ia 
fonued, and crystallises out on cooling, 

DiNiTROCKBfioia, C^Hj(CH3)(NOj)j.OH, in their physical and 
general properties closely resemble picric acid, but are volatile and 
more readily explosive. The salta of dinitro-orthocresol are 
generally yellow ; but those of the para-compound are usually red, 
and soluble in water with more or less orange colour. 

Victoria ykllow is a mixture of the s o d i U m salts of dinitro- 
ortho- and dinitro-para-creaol, CflHj(CH3XNOj)yONa. 

Gold tellow b the corresponding potassium salt, and closely 
resembles victoria yellow. 

The dinitrocresylates form soluble reddish-yellow powders which 
dissolve in strong sulphuric acid with pale yellow colour. 
They are violently explosive in a dry state, The dinitrocnsjl- 
ates closely resemble the picrates, but on adding hydrochlorie 
acid to tbe cold aqueous solution the liquid is decolorised ; or if 
siiSicicntly concentrated, yields a precipitate of free diuitiucrasol in 
pale yellow needles, and the liquid obtained on filtering in the 
cold is colourless, whereas that yielded by a picrate has a mnrktwl 
yellow colour. Similarly, hydrochloric acid decolorises a tiaeuii 
dyed with a dinitrocresylate, the yellow colour being restored bj 
washing. Warm wal«r removes victoria yellow from tbe Hhn, 



^^ 6oluf 
^^n«d liqn 

and the eolation is decolorised by hydrocliloric ncid aa described 

Solutinns of victoria yellow are unchanged by caustic sods and 
lia, but on boiling with potaaaium c^nide yield a brovn- 
liquid sirailar to that produced with picric acid. 
According to H. Fleck, dinitrocresol aud its ealta can be 
distinguished from picric acid by wBrmiog the concentrated solution 
for a few minutes with hytirochloric acid, and then adding a 
^gment of metallic zinc After standing in the cold from half 
an boor to two hours, tho liquid will become a beaalifiil blue if 
picric acid be present, or a bright blood-red with dinitrocreBol. 
Mere traces of these colouring matters are said to be recognisable 
by the test. In examining farinaceous foods for diuitrocresol, &c., 
the substance should be exhausted with alcohol, and the test applied 
to the residue obtained. 

The salts of dinitrocresol are very Irritating as well us fugitive, 
and hence are not now used as dyes. 

The salte of dinitrocreBol have been employed, under the name 
<»f " eaffron-Burrogatc." for colouring butter, cheese, macaroni. Sec 
~ this purpose they are very ill-suited, as tliey have distinct 
proportiee. T. Weyl {Ber., xx. 2836; xsi. 212) found 
it doses of 0"054 gramme for every kilogramme in weight of the 
ixperimented npon, suspended in milk or water and poured 
ly into the stomach, in the case of dogs prodnced vomiting 
iwed by difficnity of breathing, and finally severe cramp in the 
imities, the m^'ority of cases terminating fatally. Adminis- 
tered to rabbits, in doses of 0'54 gramme per kilogramme, dinitro- 
cresol caused convulsiene, paralysis of the pupil, and great dithculty 
in breathing, death ensuing from suffocation in twenty to thirty 


The two modifications of naphthol, C^^Hj.OH, yield on nitro- 
6cation bodies analogous to those obtained by similar means from 
phennl and cresol. The d i nitro-deri v ati ve of alpha- 
naplitltul is the most important. 

I)rNrrROALPHANAPHTH0L, Gj|,Hj(NO,)j.OH, is obtained from 
a-naphthylamine, a-C^oHj.NHj, by converting it into the diazo- 
chloride, which on treatment with nitric acid yields the correspond- 
ing dinitionaphthoL It may also be obtained by dissolving a- 
Ml^thol in coQcentnted sulphuric acid, diluting the resulting 
nlphonic acid with water, adding nitric acid, and heating gently, 
' en the dinitro-derivative is deposited in minute yellow needles. 

C product may bo jmritied hy converting it into its calcium or 


salt, which after retry atallisation is decomposed by tax 

Oinitronaphthol forms yellow needles, meltiDg at 138° C^ &d<I 
somewhat readily volatile. It ia nearly insoluble in water, but 
soluble in alcohol and ethor. It closely reserablea picric acid, and 
forms a series of beautiful and well-cry slallised talle yielding 
golden yellow solutions, which are decolorised by hydrochloric acid, 
a yellowish-white p[«cipitAt« of the free acid being produced, 
soluble in ether. Ammonia is without action. Cnustic potash 
and soda produce orange -red precipitates in strong solutions. 
Potassium cyanide and ammoninm sulphide i«act as with picric 

The eodium talt of dinitronaphthol forms readily soluble gUtt«r- 
ing needles containing Ci(,Hj(NOj)yOSa+HgO, and deflogiatos 
when beateil The ammonium gait bums olf quietly when heated, 
and is soluble in alcohol. The ealcium mil forms yellowish-red 
crystals of the formula [C,„Hs(NOj)jO]jCa-f 6H,0. 

The potassium, sodium, ammonium, and calcium salts of dlnitro- 
naphthol have been extensively employed as colouring mattets 
uuder the names of 

Naphthalbnk Ybi4X)w ; Naphthol Yellow ; Mabcbsster 
Yellow ; Martius' Yellow ; Gold Yellow. In an acid bath this 
tx)dy dyes silk and wool (but not cotton) a brilliant yellow colour, 
free from the greenish reflection peculiar to fobrics dyed with 
picric acid. Owing to the volatility of dmitronaphthol (which is 
liberated by the acid of the bath), the colour marks and rube off, 
and hence the employment of naphthalene yellow as a dye has 
much diminished. 

Naphthol yellow is very commonly adulterated with dextrin and 
sodium giitphaie, the proportion of the latter admixture some- 
times reaching 50 per cent. It ia sometimes adulterated with 
picrif aciil, to detect which a sample should be dissolved in water, 
the cold solution acidulated freely with hydrochloric acid, and the 
liquid filtered. If picric acid be present the filtrate will Lave i 
marked yellow coloiu", and the acid can be obtained in crystals by 

Naphthalene yellow may be distinguished from picric acid by 
boiling wool in the acidified solution, washing it, heating it wili 
am monio .sulphate of copper, and a^ain washing. When a fibre or 
fabric dyed with picric acid is boiled with the alkaline copper 
BotutioD it turns bluish-green, but if naphthalene yellow Itas bt«u 
used an olive-green tint results. 

When a material dyed with miphthot yellow is wrapped in 
white paper and Leated to 120° C. in an air-bath, part of tlii 



yellow colour U tEansferred to the paper. Hot water or hot 
dilute amiDOiua diasolvea out the colouriug matter, and the yellow 
scdutioii IB decolorised by hydrochloric acid, a yellow -white 
precipitate being produced (distinction from picric acid). 

Naphthalene yellow ia sometimes employed for colouring butter, 
cheese, macaroni, mustard, saffron, &c., for which applications its 
marked jioisoiious characters rentier it very unfit' (see i>age 153). 
Tlie detection of hutter-colorants will bo described under 
*■ Annntto." 

Hhjochbybin, or San gold, is the commercial name of an unstable 
colouriugmatter consisting of the sodium sal t of tetianitro- 
n a p h t h o 1, C,oH3(NOj),.ONa. 

INitronaphthol-sulphonic Acids. 
"When 111 ph anil plithol is warmed with excess of fuming sidphuric 
id it yields a trisulphonic acid, which on subsequent 
treatment with strong nitric acid yields, on cooling, crystals of 


The product is purified by recrystallisation. It forms long yellow 
dies, readily soluble in worm water, but insoluble in ether. 
e characters distinguish it from picric acid, diuitro-naphthol, 
Its salts are easily crj'stollisable, said to be non-poisonous,' 
I dye wool aud silk (but not cotton) a bright yellow colour, 
Aicli ia fast in the light, non-volatile, and does not mark or 
For these reasons the salts have largely replaced picric 
fwd and the dinitro-napbtholates. 

fonns an orauge'yellow precipitate on mixing a strong solution 
of the free acid with one of potassium sulphate. It is sparingly 
oluble in cold, but readily in hot water. By boiling it with 
5 hydrochloric acid the free Bi'id, or, according to some, an 
( Mlt, C,oH,(S03KXNOj)jOH, is formed. 
\ The sodium and ammonium salts of dinitronaphthol-sulphonic acid 
t freely soluble, but the barium and lead salts only sparingly so, 
1 Tlie talts of dinitronaphthol-sulphonic acid are yellow or orange. 

' Cmnpuntively small doses of naphthaleoe yellow are said to cauaa 
ID breathing, a considerable rise of t«iD|wmtur« (without coDvulBionii), 
I ullimalely death (Cimp. rend., ISSS, p. 101). According to Wcyl 
, xxi. 21S1), Martiiw' yellow i» well tolorated, by rabbits, bat sniatl duscs 
A fatal to dogs, A dog weighing SStiO grammus, to wbiuh a doss of D'S 
LB of diaitranaphlhol was given on two successiFo clays, and I grntniDS 
• sodium ult oa the third day, died on tho fourth day. Less than I 
le given subcutaneously caused the death of a sinulardag. On the other 
if uiplitbol yellow S proved innacuoiu to dogs iii four times theM amounts. 


On heating, they swell up and emit sporka, bnt do not deflagrate. 
The solutions are yellow or brownish -yellow, becoming pale yellow 
on adding hydrochloric acid, but no precipitate is produced, and 
the diluted acid liqnid is not dceoloriBod by agitation with ether. 
(distinction from picric acid, &c.) With caustic soda an orange- 
yellow precipitate is fonned, soluble on warming. In etronc 
sulphuric acid the dinitronaphthol-sulphonatos dissolve with pale 
yellow colour. In other reactions they resemble Manchrater 
yellow, but do not volatilise or colour their paper envelope it 
120' C 

Napbthol YbllowS; Naphthol Yellow; Citronin;' Acid Yellow 
S; Brilliant Yellow; ifcc, are names giveji to the potassium, sodiuni, 
aimnonium, and calcium salts of dlnitronaphtbol-sul phonic ncid. 
The free acid is also met with under the name of "naphthol 
yellow " (Levinstein), 

Commercial naphthol yellow 8 varies much in character. Soma 
qualities are practically pure, while others contain sodium sulpbal« 
and chloride in notable quantity. C. B a w s o n {Jour. Soe, Dytn, 
^e., iv. 83) has proposed a method of assay depending on the pre- 
cipitation of the colouring matter by a solution of uigbt-blue, wbidi 
ismadeby dissolving 10 grammes in 50 c.c. of glacial acetic acid, and 
diluting the liquid to 1 litre. The naphthol yellow is used aa a 
solution containing 1 gramme per litre. The latter solution it 
added to 10 c.c. of the former imtil on filtration of a portion of the 
liquid it is foiuid to have a faint yellow colour. The method it 
similar to that described for the determination of picric acid 
deacribed on page 144. Two molecules of night-blue react with 
one of nnphtho! yellow. 


On treating diphenylamine with nitric acid it readily yields 
nitro-snbstitution products. The tetranit ro-deri vat its, 
[CjHj(NO,)j],NH, mixed with a Uttle of the d i n i t r o-p r o d u c t, 
forms the colouring matter known as "Citronin."' On wanning 
diphenylamine or methyl-diphenyl amine with nitric ocid, it 
yields h e x a n i 1 1 o-d iphenylaminc, a body of strongly acid 
character, melting at 238°, the ammonium xUt of which constitulos 
the " aurantia " of commerce. 

AuEANTiA, or Imperial Yellow, [C8Hj(N0,)Jj,N(NHJ, form* a 
reddish-yellow crystalline powder, or browniaU-red crystals which 
decrepitate on heating and sometimes deflagrate slightly. Aunatta 

' The name citraniD is used bath for implithol yellow 8 ami the product 
obtaiiiod b7 acting ivilh nitric acid oD dipbenyloiiuiHi, oa obo for tJie aw-dyi 


uily soluble in vater to fono a aolutioB which, ia red when 
eentretad, but yellow when diluted. On addition of hydro- 
btic add, the aqueous Bolution yields o Bulphui'-y allow flouculent 
cipitatfl of free hexanitro-diphenylflmine, and on filtering a ] 
Rlly colourless liquid ia obtained. The precipitate dissolves on , 
"tatinn with ether. An acid solution of stannous chloride also 
(treoipitates the free ncid, but the yellow precipitate becomes dark 
brown on boiling. Copper salts also turn the solution of aurantia 
brown. Solutions of aurantia are darkened or reddened by 
iBtii; alkalies, and if concentrated a dark red precipitate is pro- 
Solid aurantia is not changed in colour by strong sulphuric 

K]On the fibre, hydrochloric acid turns the colour due t« oumntia 
'igliter yellow. Ammonia and caustic soda produce but little . 
taga. The dark brown coloration produciad on warming with 
a chloride ia the most characteristic reaction of anranlia. 


■ By treating an m)uetius solution of phenol with potassium nitrite 
i acetic acid, a body is formed which was formerly supposed to 
nitroBo-phenol, CaH,(NO).OH. but which more recent re- 
search has ahowu may more correctly be regarded as quinon- 

I, CsUjO(NOH), or CflH J | 

( S.OH. I 

QciNONoxnre is liest prepared by treiiting phenol dissolved in ' 
' "rty parts of water with rather more than the theoretical quantity 
f nitrOHuJ phonic acid, prepared by passing nitrous fumes into 
Dantrated aujphnric acid. The crystals which separate ara | 
d off without delay. Quinonoxime forms a green solution in 
i wnter, separating in nearly colourless needles by rapid cooling, 
Bin thin, brownish -green plates if the liquid be cooled slowly, 
Bdiseolves in alkalies with brown colour, and on acidulating tha J 
Wution separates as a nearly white amorphous precipitate, soluble I 
in alcohol or ether with green colour. 

Quinonoxime, if moist, rapidly turns brown on exposure to [ 
air. Wlien heated to 120°-13'o" C. it decomposes with slight ' 

tanalion. By ferricyanides in alkaline solution it is oxidised 
■ paranitro phenol. When quinonoxime is dissolved in 
^nol, strong sulphuric acid aJdod, and the liquid warmed to 
mi 40* C, a dark chorry-red or brown aolution is obtained, 


which on addition of water yields a flocculent brown precipitate, 
known as " Liebermann's phenol dye-stuff." This body dissolves 
in alkalies and sulphuric acid with fine blue colour, and has the 
formula, CeH4(OH).N:(O.CflH6)2. 


CftHg < I . This body, which forms the commercial 

HO.N ) ( N.OH 

colouring matter known as reamxin green or solid green, is obtained 
in a manner similar to quinonoxime, substituting resorcinol for 
phenoL It forms yellowish-brown or green plates, or a greyish- 
brown powder. It dissolves with difficulty in cold water, but 
readily in hot. It deflagrates slightly when heated to 11 5^ 
Dinitrosoresorcinol has acid characters. It decomposes carbonates, 
and to some extent acetates, and forms a series of alkali-metal 
salts, of which the nori&al are soluble, and the acid, of the 
type CaH202(NOH)(NONa), are sparingly soluble, green, crystalline 

By the action of resorcinol and sulphuric acid on dinitrosoresor- 
cinol, azoresorufin is formed, a body which is analogous to 
the Liebermann's dye-stuff (see above) obtained in a similar 
manner from phenol^ 

AzoRKSORUPiN, C24Hi^N207,^ is a substance which crystallises 
from hot hydrochloric acid in small, garnet-red prisms. It is 
nearly insoluble in water and alcohol In strong sulphuric acid, 
azoresorufin dissolves with bluish -violet colour; with alkalies, 
particularly in alcoholic solution, it forms a carmine-red liquid 
with a splendid cinnabar-red fluorescence. This colour is so 
intense that azoresorufin may be used as a delicate reagent for 
alkalies, 0'000004 gramme of caustic soda being sufficient to pro- 

^ In practice, 1 part of resorcinol is dissolved in 5 parts of strong sulphnric 
acid, and the solution gradually treated with 8 parts of a nitrosulphonic acid 
made by gradually dissolving sodium nitrite in twenty times its weight of 
strong sulphuric acid. The fine blue solution is heated to 140** till violet, 
when it is cooled and diluted with water. The precipitate may be purified, if 
desired, by treating it with sodium carbonate, evaporating the solution to 
dryness, and treating the residue with alcohol, which dissolves the sodium 
compound of the colouring matter . 

^ Azoresorufin was formerly called diazo-resorufin, a name which 
suggests without warrant, that it contains the diazo-group— N:N — ; 
whereas its true constitution is probably expressed by the formula : — 


ox ,H.c^ roH 

or •^•^•HnoH 


(luce ihtt reaction. Ite extreme sensitiveneas to alkalies renders 
azotesorufio unsuitable for dyeing, but this objection Joes not 
extend toite bromo-defivativo. 

HfMil/rom-asoivearufin (1) ia produced by adding bromine to 
a BoIutioD of OKoresarutiii in caustic alkali. On acidulating the 
eoliition 'with hydrochloric acid the colouring matter is preci- 
pitated, and may be purified by cijstalliaation from toluene. It 
may be converted into the sodium or ammonium salt, the 
latter of which constitutes the colouring matter known as 

Fluobbscknt Kesorcih Blub, or Bleu flw^rescent. This dye 
stuff crystallises in j^en lustrous needles, which are but slightly 
Boluble in water or strong alcohol, but more readily in proof-spirit. 
The solutions are blue by transmitted and red by reflected light, 
and give a brown precipitate of hexahromresorufin on addition 
of & strong acid. 

Fluorescent blue occurs in commerce as'a 10 per cent, paste in 
which bcetle-grecn crystals of the colouring matter may he recog- 
nised. It readily dyes silk in a neutral soap bath, the colour 
produced being blue, with a alight admixture of red and grey, 
and a characteristic red fluorescence, easily visible in artificial 
Kght. It is perfectly fast to light, washing, and acids, but 
unmonia and soda strip the fibre, forming blue solutions with 
itrong red fluorescence. Strong hydrochloric acid changes the 
colour of libres dyed with reaorcin blue to brown. 

LACMom. Another blue colouring matter, sometimes called 
" resorcin-blue," can be obtained by slowly heating together 
too parts of reaorcinol, 5 of sodium nitrite, and 5 of water. At 
IlO' C. a vigorous reaction occurs, ammonia is evolved, oiid the 
■tiixtiire becomes red ; when the melt is further heated to 115°— 
120' till the evolution of ammonia cesses, and the colour changes 
to blue. The mass is then dissolved in water and the solution 
filtered and precipilated by hydrochloric acid. The product is a 
glistening brown powder, which is insoluble in chloroform, benzene, 
or petroleum spirit, easily soluble in alcohol, wood spirit, and 
ftniflie alcohol, and less soluble in water and ether. The colour- 
ing matter was named by its discoverers (Traub and Hock, 
Jmtf. Soe, Chem. Iiul., iv. 297) 1 a c m o i d, owing to its behaving 
to acids and alkalies in a manner analogous to litmus, with the 
Colouring matter of which they suggested rt might be identical. 
& T. Thomson, however, has shown {C%em. Nemg, Hi. IS 
and SI) that well-marked ditfercnces exist, lacmoid being far less 
Bvnaitlve to weak acids than is the case with litmus. In this 
»espoct lacmoid resembles helianthin (methyl -orange), for which it 
BBMgfc^lwbrtitntwt Tith adwntaea in cwtniii caaaa. Thua it ii 


superior to all oiher indicatore for deteiminiiig the carbonates of the 
earth-metals (temporary hardness of water, Chem. News^ zliz. 34). 
In most cases, lacmoid paper is preferable to the solution, which when 
used should be made with proof-spirit and of 5 per cent strengtL 
Lacmoid paper can be employed in cases where the dark colour of 
the liquid renders methyl-orange unsuitable. Thus, bichromate of 
potassium, K^Cr^O^ and the corresponding salt of sodium are 
exactly neutral to lacmoid, the chromates of neutral constitution, 
MjCrO^, being strongly alkaline in reaction. An admixture of 
1 per cent, of K2Cr04 can be detected and estimated in Kfirfij 
by means of lacmoid paper, if, after immersion, the paper be 
washed to remove the strongly coloured liquid. The bodies re- 
presented by the following formulse are also neutral to lacmoid : — 
FeS04, FeCl^ CuSO^. CuCl^ ZnSO^, HjBOg, HgAsOj, KH,AsO^ 
NaH2P04, NaHSOg. (Compare helianthin, phenolphthalei'n, congo- 
red and litmua) 

Naphthol Gkeen B is the sodium-ferrous salt of 
nitrosobetanaphthol-sulphonicacid (Schafifer's acid)^ 


( NO. Fe. NO ) 

It forms a dark green powder, which leaves, on ignition, a residue 
containing iron and sulphides. The colouring matter dissolves in 
water with yellowish-green coloration, the solution being unchanged 
by hydrochloric acid, but rendered bluish-green by alkalies. In 
concentrated sulphuric acid, naphthol green dissolves with yellowish- 
brown colour, the solution becoming yellow on dilution, and 
then giving a blue coloration or precipitate both with ferro- and 


By heating phenol with oxalic and sulphuric acids a yellowish- 
red colouring matter is produced, which is known in commerce 
as aurin or rosolic acid. The nature of the reaction 
was long misunderstood, but later researches have shown that at 
least two homologous bodies had been previously confounded, 
namely : — 

AuriHi or Pararosolic Acid, Ci^^Hj^Og, or 

( C,H, ) ( C,H,(OH) . 
t 0- / ^ 1 CjH,(OH) ' 




Rosaurin, Eosolic Acid, or MethyI-aurm,CjoH,jOj, or 
( C,Hs(CH3) 1 p f C„H,(OH) 
to l^tCfllUOH). 

The formula expresaiug tlie formation of aurin is; — 

3CaHflO + CjH.;,* )j = C,bH j.Oj + C H^Og + 2HjO . 

Aurin and rosaurin may also be obtained by the nction of 
nitrous acid on pararoeaniline and rosaniline respectively : — 
Ca,HuS30 + 3HN03 = CjoH,BOj+4HjO+3Nj. 

Or a dilute solution of aniline bydroehloride may be treated 
with sodium nitrite, when diazorosaniline chloride U foniieil, 
and then on adding sulphuric acid and boiling lOBolic acid is 

Conversely, when aiirin and rosaurin are heated with aqueous 
ammonia under pressure to 200° C. they are reconverted into 
pararosaBtline and aniline respoctivelv : — Cy,H,jOj+3NH^= 
C„H,oNsO + 2HjO. 

From these reactions it appears that aurin and lOBSurin are 
derivatives of triphenylm ethane, CH(CsH5)a. 

Pure aurin may he obtained from the commercial product liy 
passing ammonia gas through a saturated alcoholic solution of the 
lntt«r, when steel-blue crystals of ammonium aurate, 
CjjH]jO.(ONHj)j, are deposited, the impurities remaining in 
solution. The washed precipitate may lie decoraposed by dilute 
hydrochloric or acetic acid, or simply exposed to the air, when 
ammonia volatilbes and pure aurin remains. 

When pure, aurin forms crystalline needles having an 
wlamontine lustre and the colour of chromic acid, or else of 
a darker shade with a blue or grcenisb-blue reflection. Aurin is 
fusible, but not volatile without decomposition. 

Commercial aurin or rosolic acid contains an atom or two of 
water, and is a dark amorphous substance with a beetle-green 
lustre. The powder is red. 

Aurin and rosaurin are but slightly soluble in water, though 
their solutions having a red dish -yellow colour. They dissolve 
very readily in hot alcohol, somewhat more sparingly in cold, 
and are also moderately soluble in glacial acetic acid, phenol, 
cn-ueote, and in ether, but are insoluble in benzene and carbon 

Aurin and rosaurin dissolve readily in solutions of ammonia and 
filed nlkaUes to form solutions whieh are bluish-red when dilute 
and yellowish-red when concentrated. A characteristic change in 
the absorption -8 jwctrum occurs on dilution. 

Aurin and rosaurin have the property of combining both with 



acids and bases. The former componnds are the more definite ; 
but ether extracts aurin and rosaurin from its acidulated solutions 
and not from its alkaline solutions. 

Solutions of aurin are decolorised when heated with sodixmi 
amalgam, or caustic soda and zinc-dust, colourless hydraurin, 
CjgH^gOg, being formed. The alkaline solution is also decolorised 
by heating with excess of potassium cyanide, and on cooling and 
acidulating white crystalline flocks of hydrocyanaurin, 
C^oHjgNOg, are thrown down. 

Yellow Corallin. This colouring matter is prepared by 
treating 8 parts of pure phenol in the cold with 3*2 parts of 
strong sulphuric acid, and after some hours adding 4' 8 parts of 
oxalic acid, and heating the whole to 110° for twenty-four hours. 
In addition to aurin and methyl-auriu, more or less oxidised 
aurin, CigH^gOgp and pseudo-rosolic acid or corallin- 
phthale'in, Cg^H^gO^, are also produced, and a sublimate of 
phenyl oxalate has been observed to be formed. The melt 
is poured into water and purified by treatment with boiling water. 
The product is yellow corallin, and forms a brown resinous sub- 
stance haying a green metallic lustre. It contains about 20 per 
cent, of aurin, besides crystalline derivatives of rosolic acid, and 
resinous bodies. Its reactions are identical with those of aurin. 
The soluble sodium salt of red corallin is also called "yellow 

Red Corallin or Peonin is prepared by heating two parts of 
yellow corallin with one of strong ammonia to 120**-! 40* C., when 
one of the hydroxyl groups is replaced with formation of the 
substance, Cj9Hj302(NH2), which is precipitated on pouring the 
liquid into water and acidifying. The product is " spirit soluble " 
red corallin ; " water soluble " corallin being the ammonium salt. 
The first forms lumps with a metallic lustre ; the latter a brownish- 
red porous mass, soluble in concentrated sulphuric acid with 
yellow colour. The red aqueous solution of the ammonium salt 
is unaltered by alkalies and precipitated yellow by acids. Rasic 
lead acetate and aluminium acetate produce orange or yellow 

Eupittonic acid (page 72) has the constitution of a hexa- 

Detection of Aurin, &c. 

Aurin and its allies are readily recognised by their physical 
characters, and by dissolving in strong sulphuric acid with yellow 
colour, no vapours of bromine or iodine being evolved on heating, 
either with or without the addition of manganese dioxide. If not 
readily soluble in water alone, they dissolve in dilute ammonia 



with non-fluoresMnt purple-red colour, which is not removed by 
agitation with ether. On acidulating, the ted solution is changed 
to yellow, a yellow precipitate being formed in etrong solutions. 
Tlib is readily aoluhle in ether, with yellow colour, and on 
3«pnrotiiig the ethereal layer and agitating it with aniniunia the 
latt«r ac<)uire8 a deep red colour. Solutions of aurin ate imme- 
diately decolorised hy hypochlorites, or by boiling with zioc^ust 
and ammonia, the red colour being restored in the latter case on 
adding potassium ferri cyanide, 

Auriii and its allies are not now used in dyeing, aa the yellow 
or orange-red shades produced are veiy perishable. The colouring 
matter ou printed fabrics is turned yellow by acids, and readily 
removed by ammonia, the solution being purple-red. On acidu- 
lating this liquid with acetic acid, and licating in it a tuft of 
gun-cotton, the latter is dyeil yellov- 


The pbthalems are 
aci<l or iLnhydride on 
moderate temperature 
one of phtholic acid 
„„ iCO.OH p„,.,. „_p„ (CO.C„H,.OH 

The product, pbonol-phtbalein, has the constitution of 
a dibydroxy-dipbenyl-phthulide.' 

At a liigher temjierature, by the reaction of one molecule ol 
eadt body, oxyanthraquinonc, a derivative of anthracene, 
is formed : — 

bodies produced by the reaction of phtlmlic 
phenols, with elimination of water. At a 
two molecides of the phenol react with 
)T anhydride, a "phthalein" being fotmed. 



1 CO.OH , 
I CO.OH '' 

C,Hj.OII = C(,H, f ^^ } CoHg.1 

,OU + 20H5,. 

As a class, tlie phthalems are weak acid bodies, nearly insolulUe 
in water, but soluble in alcohol and readily so in ether. Their 
salts with the alkali-metals are soluble and strongly coloured. By 
the nctifn of nascent hydrogen, the phthaleins assimilate IIj and 
iu« oonrerled into the corresponding phthalins, which are 
Dotnurlexs bodies absorbing oxygen from the air with re-formation 
ot phthale(ns. The phthaleins of phenol, resorcinol, and pyrogallol 

' Arisirtliiig t'l •liothBT viuir of its* constitution, phenol -phthiilein is ■ 
deri«Uip oT triphenyl-raethane, C(C,H,)jH, ami hance is allied lo 



are the most important. The following table shows the constitu- 
tion of those of greatest practical interest : — 

Commercial Name. 

Chemical Name or Nature. 


FlnoresceKn (page 166). 
ChiTioliii (page 166). 
Eodna (page 169). 

Bhodamine (page 178). 
CcDruleiCn (page 78). 



Anhydride of reaorcinol> 

Sodium salt of henxyl- 

VariouB derivationi of 
fluoresceltn; e,g.y Cyan- 
osin, the potassium 
salt of methyl-tetra- 
bromo • dichloro-fluores- 

... • 


Anhydride of pyrogallol* 

c A{88:8^8§: 




Phenol-pllthaleiLII. Dihydroxy-diphenyl-phthalide. 

r TT n — r TT i CO.CgH^(OH).' 
^20^14^4 - v>6^4 1 CO.CeH^(OH).' 

As stated on page 163, phenol-phthalein results from the 
reaction of phenol on phthalic acid or anhydride ^ 

Phenol-phthalein is not used in dyeing, and derives its chief 
interest from the magnificent pink coloration which its solution 
acquires by the action of alkalies, the smallest trace of which may 
thus be detected. On the other hand, the weakest acids destroy 
the colour, so that such bodies as potassium stearate, potassium 
cyanide, and sodium bicarbonate (NaHCOj) are neutral in their 
reaction to it 

The same is true of cold aqueous solutions of the bodies repre- 
sented by the following formulae : — KHCOj, Na^SgOg, Na^SO^ 
NaHS, NajjHPO^, Na^HAsO^ NaNOg, K^CrO^, K,C,0^ 
KNaC^H^Og, NagCgHgOy. In all these cases the point of neutrality 
is indicated extremely sharply, and the same remark applies to 

^ Five parts of phthalic anhydride, ten of phenol, and fonr of concentrated 
sulphuric acid should be heated together to 120° C. for 10 hours. The product 
is boiled with water, and the residue dissolved in dilute soda. On filtering the 
liquid, the anhydride remains behind, while the phcnol-phthaldji itself is pre 
cipitated on treating the filtrate with acetic acid and a little hydrochloric 
acid. It may be purified by dissoMng in alcohol, boiling with animal charooal, 
and reprecipitating by diluting the liquid with boiling water. 



the titntion of acetic, butyric, and valeric acids. No small 
tulvantage poaaessed by phenol- phthalein is that it reacts perfectly 
Id alcoholic and even ethereo-alcoholic solution, and hence allows of 
the accurate titration of many insoluble organic acids, including 
palmitic, stearic, oleic, linoleic, ricinoleic, the acids of colophony 
(pinic, pimaric, sylvic), &c. The alkaloide have generally no 
marked alkaline reaction on phenol-phthaleui, and hence the 
amount of acid in salts of morpihine, quinine, ciuchonine, 
quinidine, brucine, aniline, and urea, operating, if necessary, in 
slcohotic solution, can be ascertained by titration with Btaadanl 
acid, just 03 if no organic base wore present. 

The value of pheaol-phthalein as an indicator of neutrality is 
completely vitiated by the presence of ammonium salts. 

Phenol. phthalein is readily soluble in alcohol. A 1 per cent. 
solntion keeps perfectly, and a few drops are Hufficiont for each 

Further information respecting the use of phenol-phthalein as 
an indicator of neutrality will be found in the section on 
" Xiitmus.'' 

Fluorescein. C^HijOs = CaH^ ] 

[C0.C6Hg(0H)| ■ ■ 

This body is the anhydride of resoruinol-phthale'in, 
CggHjfOg (see lust page). It is prepared by heating three parts 
of phthiitic anhydride and four of resorcinol to SOO'-SIO" for 
one hour, or till no more steam is evolved and the melt has 
become solid.' The product is purified by solution in soda and 
addition of phosphate of sodium and chloride of calcium to the 
■olution, when the phosphate of calcium carries down the im- 
purities, and the fluorescein may be precipitated by acidulating the 

Fluorescein forms an nmorphous yellow precipitate which 
becomes cryatalliue and yellowish-red on standing or drying, and 
then contains CjoHijOj+HjO. It is nearly insoluble in cold 
water, more readily in acidulated, and sparingly in hot water, to 
wlitcli it imparts a yellow colour. Wliun freshly precipitated it 
dissolves readily in alcohol and ether, but ia nearly insoluble in 
beuiene and chloroform. The ethereal solution is pale yellow and 
Don-fluorescent, while the yellowish-red alcoholic solution shows a 
green fluorescence. 

Fluorescein is a feeble acid, dissolving in alkalies with dark red 

1 For B v»Iii«bU deacription of tlio nunufactuw of fluorescein aud ooaiu 
djM, BM B paper by 0. Muhlhausor, Jour. Soc. Dyert, A«., iil 28, 63, 
tniuUuJ from Dinglcr'i Falyt. Jinintal. 


colour. The strong alkaline solution is not fluorescent, but on 
dilution it changes to reddish-yellow and yellow, and then exhibits 
a magnificent yellowish-green fluorescence, similar to that of 
uranium glass, and gives an absorption-spectrum with a broad 
dark band in the green. Even if the solution be so dilute as to 
appear colourless by transmitted light, the green bloom is still 

When a solution of fluorescein in caustic soda is heated with 
zinc-dust the liquid becomes colourless and contains fluorescin, 
^20^14^6- ^^ filtering from the excess of zinc and exposing the 
liquid to the air, it gradually re-acquires its reddish colour, owing 
to the absorption of atmospheric oxygen and re-formation of 
fluorescein. Or if the colourless liquid be acidulated and agitated 
with ether, the fluorescin is dissolved, and on evaporating the ether 
is left as a colourless varnish, soluble without coloration in soda to 
form a liquid which rapidly turns red in the air from formation of 
fluorescein. The oxidation is immediate on addition of a fem- 
cyanide to the alkaline liquid. 

riuorescein dyes silk and wool yellow, but the colours are not 
fast. It forms insoluble lakes with silver, lead, &c., which com- 
pounds are not poisonous, and hence may be used for colouring 
toys, india-rubber good?, &c. 

Benzyl-fluoresobin, C2oHjq08(OC7H7)OH, is produced by 
heating benzyl-resorcinol with phthalic acid and strong sulphuric 
acid. Its sodium salt constitutes the dye-stuif known as 

Chrysolin or Uranin.* A reddish-brown powder possessing a 
greenish reflex. Its aqueous and alcoholic solutions are yellowish- 
brown, and exhibit a remarkable green fluorescence, which dis- 
appears with formation of a brown-yellow precipitate of benzyl- 
fluoresce'in on addition of acids. The precipitate is soluble 
in ether. The aqueous solution is darkened by alkalies, and the 
solid dye dissolves in strong sulphuric acid with yellow colour, 
and yields a yellow precipitate on dilution. With stannous 
chloride and with lead salts, chrysolin gives brilliantly coloured- 
lakes. It dyes silk or wool a fast yellow, and is employed im^ 

^ The beautifully fluorescent fountain shown by I. Levinstein, in th^ 
Chemical Section of the Manchester Jubilee Exhibition, was fed by wate"= 
containing 1 part per million of fluorescein. The intensity of the fluorescenc 
may be employed for tracing the course of underground rivers and deteotioc^ 
the pollution of the water of wells by sewage, &c. By this means an nndc 
ground connection was proved to exist between the Danube and the Ach, 
small river flowing into Lake Constance. 

3 The name u ran in is also applied to the sodium salt of fluoreacein ^ 
methyl-fluorescein. It forms a yollowish-brown powder, the aqueous soluticvK^ 
of which fluoresces yellowish-green. 

tDn-djoing for topping quertitron-yellov 
a a mordant. 

lUe ijuetti troll itaelf 

Babstituted Flnoresceins. Eosins. 

ies of ictereatinR and prscticiiUy imjiortant colouring 

nuitlere can be obtained by subatituting the halogens, nitryl, or 
the alcohol-radicals for some of the hydrogen atoms of fluorescein. 
The following is a tabular list of Bonie of the mofo important | 
bodiua of thia class : — 

p „ (CO.C,H,BrOK«\. 
"-■"t i CU.L';u,BcON'a ) "■ 
y. „ fOOCHSt.OKIn 
'■'"' \ CO.C.HfldOK / "■ 

i.„ /CaC.HBr.OKa 1 
*-•"' t00.C,H(NlWa0S»/ 

run f IXi.C.HBr.OKI, 

i."i<-i, Ico.C.HBriOK/' 

■•"'VcO.C.BBfiOr /" 

nn /OO.C,HBr,l>0H,\ 

•"><-T«lcO.C.HIIrdJK / 

Pyrdstn J or K. 
ErythrtMin B. 

UDROHFLUORBSCbTn, or Acid Eosin, C^H^rfif, ia prepared 

idunlly adding 24 parts of bromine to 10 jmrts of fluorescein 

nlved iu eight times its weight of atrong alcohol. When half 

I Uut bromiiie has been added changes from reddish-brown to a very 

dark browu colour, This marks the fonnation of the dibromo- 

tlerivative,' which is easily soluble in alcohol. Oneonliuuing 

I addition of bromine the tetrahrom fluoresce in scparutes as a 



brick-red crystalline precipitate, which is washed with a little 
alcohol and then with water. An alternative method of prepara- 
tion is to mix a solution of fluorescein in caustic soda with a 
solution of the calculated amount of bromine in caustic soda, and 
then acidulate the liquid with hydrochloric acid, when the 
tetrabromfluoresce'in is precipitated. 

Tetrabromfluorescein closely resembles fluorescein itself. It is 
nearly insoluble in water, and its reddish-yellow solution in 
alcohol is not fluorescent (distinction from fluorescein). It is a 
well-defined dibasic acid, the salts of which are decomposed by 
mineral acids, but only imperfectly by acetic acid. 

By cautious treatment with caustic potash, acid eosin yields the 
potassium salt, C2QHgBr^05K2+ 6aq, which is known in com- 
merce as soluble eo«fw,and forms a red powder or brownish-red crystals 
with a blue or yellowish-green reflection. It is not easily soluble 
in absolute alcohol, but dissolves completely in two or three times 
its weight of water to form a reddish-yellow solution. This on 
dilution becomes rose-coloured and exhibits an intense yellowish- 
green fluorescence, which is rendered still stronger by the addition 
of alcohol. The absorption-spectrum shows a broad dark band in 
the green, destroyed by mineral acids, but not by acetic acid. On 
adding hydrochloric acid the solution becomes yellow, and on 
heating gives a yellow precipitate of tetrabromfluorescein, which 
may be extracted by ether and removed from the ethereal solution 
by agitation with an alkali. 

The sodium salt of the tetrabromfluorescein is an article of 
commerce under the name of Eosin C, or in the form of garnet-red 
crystals as Eosin B extra. It closely resembles the potassium salt 
The ammonium salt, known as Eosin By of a red appearance, 
is prepared by the direct action of ammonia gas on tetrabrom- 

By the addition of a soluble salt of eosin to solutions of t^e 
heavy metals, sparingly soluble or insoluble lakes are obtained as 
precipitates. Silver gives red, and zinc, cobalt, iron, manganese, 
bismuth, and tin reddish-yellow lakes. 

A bright vermilion lake may be obtained by mixing the solution 
of eosin with starch or kaolin and precipitating with alum. If 
excess of alkali be previously added to the solution, the precipitate 
obtained is carmine-red, and with still more alkali a pink lake 
results. For yellowish shades sulphate of zinc or magnesium should 
be used in conjunction with alum. 

Vermiltonette is a brilliant lake obtained by precipitating eosin 
by lead acetate. Lighter shades are obtained by adding soda. A 
very bright vermilion-coloured product is obtained by stirring up 


red-lend with an alkttlino solution of eosin and then adding lead 
acetate to complete precipitation. Basic chromate of lead (cliome- 
red) gives even a brighter red than red-lead. Vermilionette some- 
times contains a considerable proportion of b^irium eulphato or 
other diluent. 

Tbtr4Iodfi,cobbsck(N, or Iodbosin, C^U^lfi^ ia prepared hy 
mixing solutions of fluOTesceui and iodine iu caustic soda, and 
then adding acetic acid. Its alkaline salts are sold as eoxin 
Uiie-ahade (soluhle in water), eosin J, enjthrtmn, erythronin B, 
pyroein B, iodeonn B, dianthin B, and goltible priniroge} The sodium 
salt ia hrown-red and the ammonium salt light brick-red. Their 
aqueous solutions are not flitoroaccnt (distinction from the 
brominated eosins), and on treatment with zinc-dust and ammonia 
the iodine is eliminated and a colourless solution of fluorescin - 
obtained, turning red on cxjmsure to air, with foimation of 
n (see page 166). 


;, is produced by the action of dilute nitric acid on tetrabrom- 
dissolved in glacial acetic acid, or by acting with 
rbmine on dinitroEuorescem in alcoholic solution. The salts are 
known in commerce as sa/roinn, eosin scarlet, daphnin, and eoidn 
BN. The potassium and sodium salts are dark brown or green 
powders, while the ammonium salt is red. A mixture of bromonitro- 
fiuorescein with the di- and tetra-nitro-derivatives is known as 
iutfrienne. Jiubeosin is a nitrochlorofluorescein, obtained by the 
action of nitric acid on anreoem, which ia itself a chlorinated 

substituted fluoresceins hitherto described the replaced hydrc^en 
belongs to the resorcinol residue, but eosins may also be prepared 
in which the hydrogen atoms of the phthalic acid residue are 
replaced. Thus when dichlorphthallc acid reacts on resorcinol a 
dichlorofluorescein is obtained, and by brominating or 
"[Dating this body other colouring matters result. Mone Bengals 
I phloxin are dyes of this kind, the former being the potassium 
wdinm salt of totraiodo-dichlorofluoresceln, and 
i latter the potassium salt of tetrabromo-dichloro- (or' 
chloro-) fluorescein (page 164). Cyanogin is the 
a salt of the m e t h y 1 or ethyl ether of p h 1 o x i n. 
OF BCB8TITDTED FluobbscbInh. The methyl and 
h;l ethers of tetrabromfluorcscein are obtained hy heating 
's with methyl or ethyl alcohol and sulphuric acid, by heating 
leso names are applied to the alkaline salta of ■ di-iod- 


acid eosin with methyl or ethyl bromide, or by brominating 
fluorescein in hot alcohol, when etherification and bromination 
occur simultaneously. The potassium salt of ethyl-tetrabrom- 
fluorescein is a red crystalline substance with a greenish reflex. It 
has found a considerable application in silk-dyeing, and is known 
as sptrit-eosin, ethyl-eosin, rose JB,, spirit primrose^ &c. Methyl- 
eosin is of very similar character. 

Methyl- and ethyl-eosin are sparingly soluble in water and 
insoluble in absolute alcohol, but they dissolve easily in proof- 
spirit, the dilute solutions having a beautiful fluorescence. 

Benzyl-fluorescein, or chrysolin, has already been 
described (page 166). 

Reactions of the Eoems. 

In referring to the various substituted fluoresceins, the 
systematic names are inconveniently long, while the commercial 
names are not always sufficiently distinctive. In such cases the 
terms bromeosin, iodoeosin, ethyl-eosin, &c., may be used with 

The fluorescence of the eosins is most intense in alcohoUc 
solutions (preferably containing a little free ammonia). It is 
strongest in the eosin-ethers (eosins soluble in alcohol), and then 
in bromeosin. Nitrobromeosin (safrosin) is but slightly fluorescent, 
but somewhat more so in presence of ammonia, while iodeosin 
does not fluoDfe&ce at all in aque )i s >^1 but little in alcohoHc 

The absorption-spectra of aqueous and ammoniacal solutions 
of the eosins have been studied by C. H. Bothamley 
{Jour. Soc. CJiem. Ind., vi. 422), and exhibit some interesting 

The eosins dissolve in cold concentrated sulphuric acid with 
yellow or orange colour, which generally becomes darker on 
heating. Bromeosin and nitrobromeosin are turned dark red,, 
and on adding water a new colouring matter separates out in dark, 
flakes. On heating iodeosin with strong sulphuric acid, iodine is^ 
liberated, and bromine vapours are evolved from brominated eosins^ 
especially if manganese dioxide be added. 

On adding hydrochloric acid to solutions of the eosins, th^^ 
corresponding free substituted fluoresceins are precipitated. Ir^ 
all cases the precipitates are soluble in ether, and on agitating th^^ 
separated ethereal solution with soda or ammonia the eosin passe^^ 
into the alkaline liquid with characteristic colour, and usually 
with fluorescence. 

The following table shows the comparative characters of tL 
principal substituted fluoresceins: — 





Colour ol 

ot XolutloD. 

Colour pm- 

duued on 





SalDblB in 

II infflclcmt 



Yellow. On 

Oruge - jrel. 

wMff: not 

ly dilote, 

imen: but 

■ddlng UnO, 





trom flbM 


In dilute tol- 



Soluble in 

None or tri- 



•In J. 





or wltbout 
MnO„ rlotat 



Solsbla In 


or blulrii- 






lidding MnO, 


with roUow 

Soluble In 


Uuht or yel- 



adding MnO, 


■nd beotlng, 



lib ■ brown 

hj w»ter, 
bnl not li; 



inuBOiu, not 



l»lh In 

mtit and 


ether ° wltil 




MnO,, violet 

jdlow col- 

rxr ^ 








K^d pred- 


Mlnblr Id 

plteta, or 

ntar. nil 


yellow nm- 

■olted by 









Strong green- 



Yellow utu- 

■oluble In 

nMlll; In 




weik ■l«>. 



bol. Filirlc 





lu w»ler; 

yrtlow »lu. 


•olnhle In 
week alcu. 


tlon. Br 
Yellow; yel- 

clpiUted red 
on «ldlng 

Yellow or 


Yellow, Hoc 






uulcnt; nuor- 

RBenedikt (Jo^ir. Sor, Chem. //id., ii. 170) has published 


Bystematic scheme for the examination and idc^ntification of the ^^H 

WioM oosin dyes. Besides noting the 8oInl>ility of the substance, ^^1 

Bbvoloor and the fluorescence of the solution, imd the shade ^^^| 



produced on silk, he notes the behaviour of the colouring matter 
when reduced. For this purpose, Benedikt directs that a few 
drops of a moderately concentrated solution of the dye should be 
diluted with water, and shaken in the cold with small quantities 
of zinc-dust and ammonia. All cosins are rapidly decolorised by 
this treatment The docoloriaed and filtered solution usually 
reoxidises very gradually on exposure to the air, but mor« rapidly 
if it be well boiled till a copious precipitation of hydrat«d oxide 
of zinc occurs, and the liquid be then treated with sufficient 
hydrochloric acid to dissolve this precipitate, and an excess of 
ammonia again added. Another means of discrimination em- 
ployed by Henedikt consists of treating a little of the colouring 
matter with a strong solution of caustic potash (I'S sp. gr.). 

By the reduction-test, Eosin G (bromeoain) gives a nearly colour- 
less filtrate immediately after treatment with zinc and ammonia, 
being reduced to colourless tetrabromSuorescin. Aft«r boiling tlie 
liquid and treating with aaid and ammonia as described above, the 
solution becomes cherry-red or crimson, with yellowish-green 
fluorescence ; or, in other words, the original colouring matter is in- 
formed. With potash solution, bromeosin gives in the cold an 
orange-red solution, which on boiling becomes purple-red, violet, 
and pure blue, with a etnmg green fluorescence. If the boiling 
has been continued long enough, the cbarautets are unclianged \rf 

Eosin J (iodeosin) loses its iodine when treated with idnc-dnst 
and ammonia, and is converted into colourless flnorescin, which cm 
oxidation, boiling, &c., is converted into fluorescein, the solution 
of which is reddish-yellow with a strong green fluorescence. The 
production of a highly fluorescent solution from a non -fluorescent 
one by reduction and subsequent oxidation is highly characteristic 
of iodeosin. On boiling with potash, eosin B first turns purple- 
red and then blue-violet, with a feeble green fluorescence. On 
dilution, the liquid becomes purple-red, 

Sa/nmtt (nitrobromeosin), on treatment with iinc-dnst and 
ammonia, is reduced to colourless fluorescin, and the NO^ groups 
ai« simultaneously reduced. The filtered liquid oxidises again 
with great rapidity, with formation of a cherry-red, uon- fluorescent 
solution. With potash, safrosin becomes lighter and yellower, and 
on boiling turns olive-green, without fluorescence. When a little 
solid safrosin is heated on platinum foil, it swcUa up enormously 
after the manner of a " Pharaoh's serpent," 

The epiril'Holuble eonine behave with zinc and ammonia like 
bromeosin. They are insoluble in strong potash solution in the cold, 
but on boiling the reactions of bromeoain are gradually produced. 



The eoaine are often found in admixture with other colouring 
matters. Thus nepaline and imperial scarlet are mixtures of eosins 
with naphthol-yellow (gee page 154), and aiccine ia a, 
mixture of safrosin and a u r a n t i a. Huch mixtures yield acarlets 
which are employed as cochineal substitutes. Naphthol-yellow and 
aurantia differ from the eosins in yielding colourless solutions by 
treatment with zinc and hydrochloric acid, which solutions do not 
^ain become coioured on ex|K)sure to air, either with or without 
the addition of ammonia or sodium acetate. When heated, the 
nitio-compounds deflagrate without disengaging coloured vapours. 
To induce deRsgration it is somotimes necessary to mix the sub- 
stance with a little oxide of lead. 

AurtH and its allies present a somewhat close analytical re- 
semblance to the eoains ; but their ammoniacol solutions are not 
fluoreeeent, and no bromine or iodine vapours ore evolved on heating 
the substance with sulphuric acid and manganese dioxide. 

The eosins produce on silk and wool all shades of colour from a 
reddish-orange to a cherry-red and purple, The yellowish shade is 
produced by eosin G, and the bluest by bengal red. For dyeing 
cotton with eosins, the fabric is mordanted with alumina or tin 
for yellow shades, and with lead salts for blue shades. The 
colours produced are not so fast aa those on wool or silk, and are 
affected by light. 

The eoains soluble in water are slightly removed when fibres 
dyed with them are treated with warm water, especially if a tittle 
.. UDliionia be added. Spirit -soluble eosins are not affected by water, 
^^gt are dissolved from the fibre by alcohol, which leaves the eosbs 
^^nible in water. Concentrated potash solution acts as on the 
^^^Bd dycB, warm solution of bleaching powder discharges the 
^^B^r, and sulphuric acid turns the fibre yellow or orange. 
1 Hydrochloric acid and acidulated stannous chloride decolorise or 
turn the fibre yellow, 

Phthale'lns from Amidophenola. 

Very recently, several colouring matters have appeared in 
commerce which are obtained by the reaction of ph thai ic anhydride 
on amidophenola or their allies. The representative member of 
this group of bodies is : — 



( N-(C,Hs). 
1 by heating, for several hours at 200°, t 



This body is 

jholic ODhydride with two of diethyl-meto-amidophenoL The 


commercial product is a hydrochloride of the baae, and forms a 
red powder, readily soluble in water with fine crimson colour 
and a characteristic yellow fluorescence, which disappears on 
heating the solution to about 90** and is restored on cooling. 
Acids turn the colour of the liquid somewhat yellower, and alkalies 
slightly bluer. Tannic acid, in presence of sodium acetate, gives 
a bright crimson precipitate of rhodamine tannate which is not 
fast to light, but if tartar-emetic be also present the compound 
precipitate formed resists light very well. With stannous chloride, 
an aqueous solution of rhodamine gives a characteristic cinnabar- 
red precipitate, which, while still in a fine state of division, transmits 
a bright blue light (R K n e c h t. Jour. Soe, Dyers, ^c, iv. 96). 
In strong sulphuric acid, rhodamine dissolves with yellow colour, 
changing to red on dilution with water. Bhodamine dyes silk 
and wool a pink colour, with a marked orange fluorescence. The 
dye stands light and soaping fairly well It may be mordanted 
on cotton with turkey-red oil, or tannic acid and tartar-emetic 
The colours obtained are fluorescent. 

QuiNOLiNB Yellow. By heating quinaldin with phthalic 
anhydride and chloride of zinc, a phthalein is formed of the 
composition: — 


The product forms a yellow powder, which is insoluble in water, 
but difficultly soluble in alcohol, to form a yellow solution. In 
strong sulphuric acid the dye dissolves with yellowish-red colour, 
the solution giving a flocculent yellow precipitate on dilution. By 
sulphonation, quinoline yellow yields a disulphonic acid, 
the sodium salt of which contains CgH4:(CO)2:CH.C9H4(SOgNa)2N, 
and is known as water-soluble quinoUiie yellow. It forms a bright 
yellow powder, dissolving easily in water with intense yellow 
colour, which is unaltered by dilute acids but is turned somewhat 
darker by ammonia. The dye is not applicable to cotton. On 
silk and wool, in a bath acidulated with sulphuric acid, it yields 
very pure shades of yellow, which stand light fairly welL 

AzoEOSiN is a colouring matter of which the composition and 
mode of manufacture have not been made public. The com- 
mercial product forms a scarlet powder, readily soluble in water 
with scarlet colour, but without fluorescence. Ammonia turn** the 
solution orange, and hydrochloric acid produces a crimson pre- 
cipitate. In strong sulphuric acid the dye dissolves with deep 
cherry-red colour. On wool, azoeosin produces a brilliant scarlet, 
which stands light well, and is not easily affected ly soaping 
(E. Knecht, Jour. Sac. Dyers, ^c, iv. 96). 



Of Ute years a Beriea of very brilliant and fast dyes bavB uome 
into use, which are generically known as azo-dyes, 

All these subatancea contain the divalent group — N ; >[ — . If 
both of the frc<j bonds be eatUtied by the radical phenyl the 
Bubstaace known aa aKO-benzene, C^Hs.N' iN.CgHg, results; or 
if tho two radicals bt! not identical a "mixed" azo-compound 
reetilts, such aa may bo typified by benzeno-azo-toliiene, 
CgUs.N : N.CjH^. 

Azobenzene. C^Hj-X^fCaiip. 

Tliia body is prepared by the reduction of iiitrobenzenu with 
naaceut hydrogen. Acetic acid and iron may be employed aa the 
reducing agent, or prefembly au alkaline reagent, auch as zinc and 
alcoholic potash, siHlium ataimite, or sodium Hraalgam. If aodium 
nmalgntu be employed, the interniediatn product azoxy- benzene 
ia first obtained, while too-long continued treatment causes the 
formation of hydraaobenzene and the isomeric body b e n z i - 

fne, and the former of these may in turn be converted into 
iline. These bodiea form a continuous aeries, thua : — 
Nitro-benzene, CflHaXOg X 2 = C,.H,oN,0, 

Aaoxy-benzeiie, . . C,^,flNalJ 

Azo-benzene, .... C,jH,oNj 

Hydrazo-benzene, . . . (^ijHijN, 

Amido-benzene(aniIino),ConjN x 2 = CijIIuNj. 
By treating aniline with potassium penuangauate, the reverse 
series of reactiona may bo obtained, at least ao far as oxidation to 
jwoxy-benzcne ; and among the aerondary prodncte ia found aniHne 
tilaek, which has tlio same percentage composition as azo-benzene. 

Azjobenzune cryatalliaes in large yellowish-red laminsB, sparingly 
soluble in water, but readily in alcohol and ether. The alcoholic 
solution hH3 an intenae yellow colour, but no dyeing powers. Azo- 
benzene melts at 6d°'S, and diatils at 293'. Treated in alcoholic 
solution with sulphuretted hydrogen, it ia converted into hydazo- 
tiouzeue. With bromine, azobenzene forma the ailditivo cora- 
jwund CigHjoBrjlVj, and with nitric acid reacts to form mono- and 
di-nitro-dorivativea. NilTi}-as)bemene, C^^.^^C^^'SO^, can 

1 The Ratlior is inilolited to Frofiissor B. Mildola for au ailTance-sbci-t 
of hia artlcio on " Aio. Colouring UnlUrg," contributed to Thorixi'B Dictionary 
of JWAnual CbemiatT^. A very oomplelo list of tlia aio-dyes, with their 
fonauliK aud chemical reactions, has been publiahed b; Schuttz and 
JnUn* (C:knni*A< Indiutrit, 1387). 


be reduced to amido-azobenzene, CgH5.Nj.CgH^(NHj), and this 
on treatment with nitrons acid and warm water yields o x y a z o - 
benzene, CgH5.N2.CgH^(OH).^ These bodies dye silk or wool 
orange or yellow, but offer little resistance to the action of acids. 

Diazobenzene Compomids. C^B.^.lii : N.x. 

When the free bond of the second nitrogen atom of the group 
— N : N — is satisfied by a simple atom or an acid or basic group, 
instead of by a hydrocarbon radical, the substance is said to be a 
"diazo- compound." Thus the body represented by the 
formula C^H^.N : N.Cl is called d i a z o-b enzene chloride,* 
and is the ^pe of a large number of interesting bodies. 

Free diazobenzene is not known, nor does the hydride, 
CgHg.Njj-H, appear to be obtainable. The hydroxide, 
CgH^.N^-OH, is a highly unstable, explosive, yellow oil, which reacts 
with acids to form a highly interesting series of salts. They are 
mostly colourless, crystalline bodies, which turn brown rapidly on 
exposure to air. They are readily soluble in water, spaiingly in 
alcohol, and are precipitated from their alcoholic solutions by etiier. 
Most of them are unstable, and decompose with explosion when 
heated or struck. The chlorochromate explodes more violently 
than nitroglycerin. By many reagents they are decomposed in a 
peculiar manner, usually with evolution of free nitrogen, as in the 
following examples: — 

1. CeH5.N2.Br+H20 = CJH5.0H + N2+HBr. 

DlAzo-bromide Phenol 

2. aH5.N2.NO8 + C2H.OH = CgHsH + N2 + HNO3 + CoH^O . 

DUuo-nitntte Alconol Benxene Aldehyde 

3. CeH5.N2.HSO^ + HI = CgHgl + N2+H2SO^. 

Diazo-acid Bolplutte Phenyl iodide 

4. C-H5.Nj.Cl + CujjClj = CgH.Cl + Nj + CuClj.* 

Dlazo-chloiide Phenyl chloride 

5. CjH5.NBr:NBrs+ CjHj.OH = C,H.Br+ Nj+ CjH^O + 2HBr. 

Biazo-perbromide Phenyl bromide 

Dtazobenxene Chloride, CgH5.N2.Cl, is obtained in solution by 
gradually adding sodium nitrite to an ice-cold, dilute solution of one 
molecule of aniline and two of hydrochloric acid, the liquid being 

^ This body is preferably called hydroxy-azobenzene. It must not 

C H N 1 
be confounded with azoxy-benzene, n'u'^^r r 0. 

' Hence azobenzene, CeH5.N : N.CgH^, is diazobenzene phenylide. 

* By substitating caprous bromide, iodide, or cyanide for Uie chloride, th^ 
corresponding haloid compoands of phenyl may be obtained. The cyanide 
reacts with caustic potash to form potassium benzoate, CfHsCOOK, anc^ 


well rtirred during tlie addition. The conclusion of tha reaction 
18 knoivii hy the evolution of nitrous acid, recognisable by its 
turning blue a piece of paper moistened with a solution of 
potassium iodidu and Etiircli and held over the liquid. l)iiizo- 
ItKOzene chloridH ia only known in solution, which undergoes 
decoiupoailion when heated, but it forms crystulline conipouuda 
with ptatiuic and stannic clUorides. 

Dlazohemene Nitrate, C(H,.Xj.NOj, is prepared by passing a slow 

stream of nitrogen trioxide gas <prepnred from starch or arsenioue 

osido and nitric acid) into a paste of aniline nitrate and watcr,^ 

cooled l>j immersion in a mixture of ice and salt, until the 

xidition of caustic alkali to a sample quantity no longer liberates 

aniline in oily globules, The liquid is filtered, and the diazo- 

bciizcne nitrate precipitated from the filtrate by adding three volumes 

of alcohol and some ether. Diaiobenzene nitrate separates in yellow 

needles which are readily soluble in water, and slightly so in 

alcohol, hut insolnhlc in ether. In the dry state, when gently heated 

or struck, it explodes more violently than fulminating mercury, 

uul hence should be presented under ether. 

^^^■Acid Diazobenzene Sulphalc, CoHj.Nj.HSOj. is obtained by 

^^■Ming diluted sulphuric acid (1 : 2) to a concentrated aqueous 

^^Bvtion of tlie last salt. Alcohol (3 volumes) and ether arc then 

^^BHed, and the heavy liqiud which separatee redissolved in strong 

I alcohol and precipitated by adding ether, the process being repeated 

till the sulphate separates in a crystalline form. The salt forms 

■ vliito, deliquescent prisms, which decompose in the air and 
tonat« at about 100°. 

iokmtzene-mljihtntK Aeul, C^^<\,^ >:N. Thisboay.of 
Udk Uiree modifications exist, is not well named, as it is really tho 
I iWiliydride of the true sul phonic acid, CbH,(S03H).Nj.0H. 
The para-compound, which is the only one of practical importance, 

■ JB obtained by adding rather more than the calculated quantity of 
^inm nitrite to a eolutioa of eulphaoilic acid (para-amidobeuzene- 

. acid), C8H,(S0jH).NHg. in dilute caustic soda, and 

g the mixture into cooled, dilute sulphuric acid. Tlie diazo- 

C acid separates in white ciystals, insotuhle in cold water, 

E readily soluble at 60'-70", It is decomposed by water at a 

(her teni|)cniture, with formation of para-phenolsul phonic acid 

5), while iioiling alcohol converts it into henzcne-sul phonic 
I, C«Hi.SO,H. 

pIA«i-A)iii>oB&Ni!BNB, CglliN iN.NH.Cgllj. This body ia formed 

1 nitrous gas is passed into a solution of aniline in alcohol, 

■ TOL. in. TART t.^^^^^^^^ 


and may be regarded as resulting from the action of aniline (amido- 
benzene) on diazobenzene hydroxide: — C(jH5.N2.0H+NH.H.C(jH5 
= CeH5.N2.NH.CgH5 + H20. Diazo-amidobenzene is also formed 
when a cold concentrated solution of diazobenzene nitrate is 
dropped gradually into strong ammonia or mixed with aniline; 
or by adding a solution of diazobenzene chloride to aniline kept 
cool, and treating the product with sodium acetate, when the 
diazo-amidobenzene is thrown down as a yellow precipitate. It 
may be obtained more directly by adding gradually a cooled solution 
of sodium nitrite to a mixture of one molecule of aniline and one 
of aniline hydrochloride, when it is precipitated. Diazo-amido- 
benzene crystallises in golden yellow scales, melts at 9V, and 
detonates at a higher temperature. It is insoluble in water, but 
is dissolved easily by ether, benzene, or hot alcohol. 

Diazo-amidobenzene does not readily unite with acids, though 
a chloroplatinate is obtainable. By nitric acid containing nitrous 
acid, diazo-amidobenzene is converted into diazobenzene nitrate; 
by strong hydrochloric acid into aniline hydrochloride, phenol, and 


When diazo-amidobenzene is heated in the dry state in presence 
of aniline and a little aniline hydrochloride, it undergoes a mole- 
cular transformation into amid o-a zobenzene or aniline ydlotc, 
identical with the body obtained by the reduction of nitro- 
azobenzene i^— CoTIft.N2.NH(C6H5) = CeH5.N2.CgH^(XHj). 

It is important to notice the leading differences between diazo- 
amidobenzene and the metameric body amido-azobenzene. Thus 
the latter is a well-defined base, which on heating with an acid 
forms a salt which gives a red colour to the aqueous solution; 
while the former when similarly treated is decomposed into phenol, 
nitrogen, and aniline (hydrochloride). 

If (instead of aniline) a solution of meta-phenylenediamine * be 

* Diazobenzene chloride reacts with the secondary raonamines to form 
diazoamido-substitution products. Thus with diethylamine, diethyldi- 
azo-amidobenzene results : — CgH5.N2.Cl + HN(CaH5)2— CgHj.N^N(C,H5), 
+ HCl. With a tertiary monamine a diflferent reaction results, a substituted 
amidoazo-compound being formed. Thus diazobenzene chloride and dimethyl^ 
aniline give the hydrochloride of dimethyl-amido-azobenzene (page 180), 
C,Hb. Nj.C1 + CjHjNCCHs),^ CgHj.Na. C8H4.N(CH5)2.Ha. The primary amines 
of naphthalene react in a similar manner. 

* Meta-phenylenediamine, CgH4(NHa)„ may be obtained by the reduction 
of dinitrobenzene, C0H4(NO2)s> produced by treating benzene with a 
mixture of fuming nitric and strong sulphuric acids. 250 grammes of iron 
filings are shaken in a flask with 15 c.c of hydrochloric acid, 50 grammes of 



- CcH,(NHj).Nj.CaHj(NH,)^ 

(loured into a very dilute solution of diairobeniiene chloriile, the 

by ilruchloride of diamido-aKobenzene or chrysotdtne wpur- 

^■bs as a sparingly soluble precipitate :— CBHj.N^{;i + CaH^(NU2) 

^^V'On adding potassium nitrite to a solution of u neutral 

^^flUt of meta-plienyleneJinmine, a brown precipitate (or in very diluta 
sotatioDs, a brown coloration) is prudui^ed, wliiuli is due to the 
fi'rmation of triamido-aiobenzene or phenylme-iffown, 
tLH,(SII,), N5.C(Ha(N Hj)^. 

^^|^bii9 tbe ttireo ainido-ozobenKcnes are related to each other in 

^^^■l following maoner : — 

^^^UsiDO-AZOBEyzENB, or iiuilino-yellow liaac, CgH(|.X2.C(,H^(NHj) 

^^^^DiAHiDo-AzoBENZENE, or chrysoidiue Imae, CoHj.\j.CoHj(NH2)i 

^^^■rRiAMiDO'AHODENzBNB, or phenyl- 

^^^V ene-brt>wu base, j 

I AifiLiNKYBLLOW, C(Hj.Nj.C9H,.NHj,HC], also called spiW/-i/eWow, 

Is the hyilrochloride of amido-azolwnKeno, and can be obtained by 
mixing dilute aqueous aolutions of azobenzone chloride and aniline 
In the pure state it forms bluish-violet, lustrous needles, soluble in 
w»l<>r with yellow colour turned to a line red by acids. In strong 
sulphuric acid it dissolves with brown colour, becoming red on 
dilution. (.)a heating the aqueous solution of aniline yellow, the 
free hasc is precipitated. Free amido-azolwnzene is also completely 
]>rccipi tilted from its salts by ammonia, and may then be taken up by 
itffitatioii with ether. In the pure state it forma yellow crystals, which 
melt at 120° and volatilise unchanged. It is insoluble in water, 
but soluble in alcohol. Acid solutions dye silk red, the salt itself 
bciuf; taken up, but on washing with water the salt is decomposed 
and the base imparts a yellow colour to the Hbre. Aniline yellow 
is not fast, and easily volatilisea when the fibre is steamed. Hente 
it is not now used as a dye, but forms the starting point in the 
— inufacture of other aniline colouni and of indulines. 

CHRYSolniNE, CeH5.Ns.CaHj{NHs)3.HCl, is the hydrochloride of 

Itrobcoimo Uiffii thoroughly mixeJ with thu filings, and boiling wsler 

Ud. A violent ni'Moii oocurB, which mast be mainlained by the gradual sddi- 

s o( another GO gmmmea of dt nitrobenzene, and tlie reactioo is completed 

vj boiling tho liqaid for a few minutes. The solution is thou uiado ilkaliiie 

by adding lime, ftlterod, and the phenyleuediaimne extracted from the filtrate 

by aplation with olhor. 

Phrnylenediamitie melts at ft3° and boils at 277° C, U is sparingly soluble 
in watur, bat very eolnble in atrjihol and ether. Its sotiitions are alkaline, and 
it bchavea as a di-aeid base, the liydrochtoride being C,Ht(NH,)„2HCI. 
OrChn- and para-pheoyteDediimiue do not reset with disiobeniuna com- 


diamido^obenzene (page 179). It usuaUy occurs in the form 
of a reddish-brown crystalline powder, or blackish-green or dark 
violet crystals having a metallic reflex. It is soluble in boiling 
water and absolute alcohol. The hot concentrated solution forms a 
gelatinous blood-red mass on cooling. The brown or orange- 
coloured aijueous solution is turned red by excess of hydrochloric 
acid, dyes wool orange-yellow, and gives with alkalies a bright yellow 
precipitate of the free base, melting at 1 1 7" '5 C, and slightly soluble 
in water, readily in alcohol and ether. Strong sulphuric acid 
dissolves chrysoidine with reddish-brown or orange colour, which 
turns almost scarlet on heating (distinction from pfaosphine), and 
cherry-red on dilution. Chrysoidine is used in combination with 
safranine to produce a scarlet on mordanted cotton. 

Phenylenb Brown. CeH^(XH2).Nsj.CeIl3(NH2)^2HCL This 
colouring matter, which is also known by the name of Bismarck 
brown, vesumnCy Manchester hrotcn^ cinnamon hrownj leather 
brown, canelle, &c., is the hydrochloride of triamido-azobenzenc 
(page 179).^ The commercial product forms a dark brown powder 
always containing more or less common salt, and on solution in 
water often leaves a residue of insoluble impurities. The aqueous 
and alcoholic solutions are brown, and do not become gelatinous 6n 
cooling, but the liquid is tiuned red by a large excess of hydro- 
chloric acid, though imchanged by slight excess. This reaction is 
very characteristic. Ammonia and the fixed alkalies give a volumin- 
ous brown precipitate of the free base, which is somewhat soluble 
in boiling water, and more readily in alcohol, and when purified 
by recrystellisation forms small yellowish-red crystals which melt 
at 137**. Phenylene-brown dissolves in strong sulphuric acid 
with reddish-brown coloration, becoming orange-red on dilution. 
The aqueous solution gives a brown precipitate with basic lead 
acetate (distinction from chrysoidine, orange), and is decolorised by 
treatment with a hydrochloric acid solution of stannous chloride. 

Phenylene-brown dyes wool a brownish-orange. It is much 
used for dyeing leather. On cotton it is mordanted with Turkey- 
red oil, or by tannin and tartar-emetic. 

times called biiiter yellow, is the dimethyl-derivative of aniline 

^ Phenylene-brown is prepared on a large scale by reducing a known weight 
of diuitrobenzone with finely-divided iron and a little hydrochloric acid, 
and then boiling with water and milk of lime. The solation is filtered from 
the precipitate of iron oxide, and treated in the cold with the quantity of sodium 
nitrite and dilute hydrochloric acid requisite to react with the meta*pheDyl- 
enediamine, when the colour forms immediately, and is salted oat and 
collected on filters. 



illow. Wlien pure, it crystalliaes in aniall yellow platea, meltinR 

and its hydrochloriilp forms purplp-rod hair-like 

iiles. It is insoluble in water, but dissolves witli red coloration 

hydrochloric acid; and in strong sulplmric acid with yellow 

Jour, turning red on dihitiim. Its alcoholic solution has been 

icommended by B. Fischer (Anatynl.x. 153) as an indicator 

in alkalimetry, in preference to methyl -orange, which is th(t 

nmmonium salt of its sul|)honic acid (see page 187). 

PHKNYii-AMiDO-ABOBBUZiiNK, CoHs.H'j.CjHj.NH{CaHj), is pro- 
duced by acting on diplienylamine by diuKobenzene chloride in 
alcoholic solution. Its sulphonate is descrihEd on page 189. If 
meta-diazobensoic acid he Biilwtituted for the diazobenzcne chloride 
product is 
' ich is a yellow colouring matter used under the name of Jaun-: 
'iile ot/osI yellow (for soap). It fomia a sparingly soluble brown 
the solution of which is little changed by alkalies, but 
langee to a reddish -violet Ijy acids. In strong sulphuric acid it 
lives with violet colour, becoming magenta-red on dilution. 


When potassiuui pliwiale ia added to a solution of diazobenieno 
:tnte, hydroxj-az I) benzene is produced according to the 
reaction: — 
H,JrJ^.N0j+CBH5.0K = CBlVN:N.CaH,.0IH-KX0,. 
i same body results from the reaction of ainido-a2o1>cDzene 
b Ditrous acid, or when azobenzene-sulphonic acid is fused with 
nititic potash. The corresponding derivatives of resorcinol, 
"lol, Ac., can be obtained by similar means. 
)lioxT-AZOBi!N ZESK, or Phenol- A2OBaNZENE,C5Hj.Nj.C„Hj.0H. 
t prepared by dissolving 30 parts of potasainm nitrite in 
K)0 parts of water, and adding the solution to 20 parts of phenol 
' of aniline nitrate dlasolTed in 2000 parts of cold water. The 
d is filtered after a few hours, and the precipitate trcateii with 
inio, which leaves resinous matter undissolved. The hydroxy- 
e is precipitated from the filtered liquid by hydrochloric 

I Hjdroxy-ajiobenzene crystallises in yellow ish-retl rhombic prisma, 
Beltinft at 152°-154° C". It is only slightly soluble in water, 
Tot reftdily in alcohol. It has marked arid characters, is readily 

iduble in alkalies, and forms a series of metallic salts. The silver 
^mponnd b a yellow precipitate which detonates at 100". 

Hydroxy-azobenxene is not employed as a colouring matlor; but , 


its sulphonate has been used imder tlie name of Trqpceolin Y 
(pages 184, 186). 

Mbta-dihtdrozt-azobsnzens, or E£sobcinol-azo-benzene, 
CgH5.N2.CgH3(OH)2. This body is formed by the action of 
diazobeuzene nitrate on an alkaline solution of resorcinoL It 
forms red needles, melts at 168**, and is readily soluble in alcohol 
In commerce it occurs as a brown powder, under the name of 
Soudan G. It is partly soluble in hot water, with yellow colour, 
the solution giving a bright brown precipitate with hydrochloric 
acid. In alkalies it is soluble with brown colour, and with con- 
centrated sulphuric acid it yields a yellowish-brown solution, 
giving a brown precipitate on dilution. 

The acid potassium and sodium salts of the sulphonic acid 
of resorcinol-azobenzene occur in commerce under the name of 
Chryso'in, Tropcbolin or R, &c. 

Betanaphthol-azo-bbnzbnb, CgH5.N2.CiQHg.OH^. Obtained 
by the action of diazobenzene nitrate on an alkaline solution of 
betanaphthol. Under the name of Soudan /, it occurs in com- 
merce as a brick-rod powder, insoluble in water, but soluble in 
alcohol with yellow colour. Concentrated sulphuric acid dissolves 
it with magenta-red colour ; and on dilution the solution gives an 
orange-yellow precipitate. 

The sodium salt of the corresponding sulphonic acid 
forms the colouring matter known as Crocein orange or ponceau 

Soudan II is homologous with Soudan I, being produced by 
the action of a diazoxylene compound on betanaphthol.^ 

Alphanaphthol-azo-naphthalene, CiqH7.N2-C5ioH^-OH*, occurs 
in commerce mider the name of Soudan broivn. It is an insoluble 
brown powder, dissolving sparingly in dilute alkalies. In concen- 
trated sulphuric acid it dissolves with blue coloration, a brown 
precipitate being produced on dilution with water. 

Carminaphtha is a colouring matter isomeric with Soudan 
brown, being produced by the reaction of diazotised betanaphthyl- 
amine on an alkaline solution of betanaphthol. It is a reddish- 
brown powder, i insoluble in water, but soluble in alcohoL It 
dissolves in strong sulphuric acid to form a magenta-red solution, 
which on dilution gives a brownish-red precipitate. 

Sulphonated Azo-Compounds. 

The amido- and hydroxy-derivatives of azobenzene and its 
analogues have marked dyeing properties, but owing to their 

^ Soudan III is the commerciAl name of a colouring matter of the tetrazo. 



sparing solubility in water it is found conveniont to sulplionatt.' 
them. Tliis is effected by treatment with fuming sulphuric acid ; 
or, inatend of sulphonating after diazotising, which leasona the 
yield of colouring matter, the aniline or other amine is first 
eulphonated and thea dinzotised, and the diozo-sulphoniu acid 
formed is then tauBed to react with other amines or phenols, 
ncconling to the character of the dye required. In this manner 
sulphtinilic acid, CjHj(S03H)'.NHg. and naphthionic 
acid, C,oHg{S03H)".NHj", form the starting points of im[iortant 
series of ozo-colouring matters. When diamtised, these two 
bodies are convertod respectiyely into diazohenzene-sul- 
{iboiiie acid (page 177) and diaEonaphthaleno-aol- 
phanic acid. By the reaction of the former of these with 
■niline, acui yellow is obtained, while with dimethyl-aniline 
helianthin ia the product. With phenol in alkaline solution, 
the sodium salt of phcnyhdiazoheuKene-atil phonic acid ia obtained, 
knowu commercially as tropiwlm ¥; with resorcinol the analogona 
ekrytviH or trojxeoHn results; alpha-naphthol gives Puirrier'a 
oramje I, or tropaolm 000 No. 1 ; while betanaphthol yields 
Poirricr's orawje II or mandarin. 

In the cose of the foregoing colours it is always the amine which 
is Bulphonated, On the other liand, if the ]>henol be first 
8iit[ihonatcd, and then caused to react on a diazotised chloride, 
bodies are obtained which are isomeric with the former, but possess 
very different colouring and other properties. Cforein vi-ange 
(page 184) is a dye of this class. 


^^^HRrhcn diiuobenzene-aulphonic acid (obtained by mixing solutions 

^^^^■nlphauilic acid and sodium nitrite) acts on amides or alkaline 

H^^Dtions of phenols, a aeries of colouring matters are obtained, 

■bulging from yellow to deep orange, and called tropseolins, 

bf«au8o the shades of colour they produce resemble those of the 

flowers of TrojxKoluin majw. Tbey usually occur in commerce 

■s sodium salts, and are diHtinguished according to their shades, 

ln>p»ulia y being the most yellow, and then tropteolins 0, 00, 

and so ou, aa the shade becomes redder.' The shade of colour 

U^teeomes Tedder by the substitution of toluene, xylene, or cumeno 

^ bpniene, and hence some of the higher homologues arc con^ 

i in the section on "azo-reds" (page 191). 

^(1 following is a list of the yellow and orange dyes of this 

R uf commercial importance : — 

k valuable papuc by 0. UuhlliHuur, on the rnaaurscture of tlu' orangu 
1^ will Iw found ia the Jour. Soe. Djiert and Caloric, iii. ISb. 




Chemical Name or 



Acid yellow; Fast 

yellow. (Page 


nelianthin ; 
Methyl orange; 
III. (Page 188.) 

yellow; Orange 
IV ; Tropajoun 
00. (Page 189.) 

Metanil yellow; 
Orange MN. 
(Page 190.) 

Brilliant yellow; 
Acid yellow 
00 ; Orange N. 
(Page 190.) 

Aioflavine; Azo- 
yellow. (Page 


Tropieolin Y. 
(Page 188.) 

TropsBolin R or ; 
Resorcln yellow; 
ChrysoKn ; Chry 
Beolin. YellowT. 

TropBJolin 000 
No.2;» Oninge 
II. /3-Naphthol 
orange. Man- 
darin G. (P. 188.) 

Croceln orange. ^ 
(Page 188.) 

OranKeG;^ Orange 
yellow. (Page 

Oranse No. 3 (not 
(Page 188.) 

K or Na salt of Amido- 
phonio acid (and 
disulphonic acid). 
Sulphonated aniline 

Am or Na salt of 
azobentene sul* 
phonic acid. 

K or Na salt of 
sulphonic acid. 

Na salt of Diphenyl- 

C,H4(S03Na).N : N.CgH^.NH,. 

Na salt of Diphenyl- 
Bulphonic acid. 

A mixture of Nitro- 
derivatives of di- 

C,H4(S0,Na).N : N.C,H4.N(CH,),. 

CgH/SOaKynN: N.CgH4.NH(C,H4). 

C,H4(S0,Na)(«.N : N.C,H4NH(C«Hft). 

C,ea(CHaX80jNa).N : N.CeH4NH(C.H»). 

Na salt of Phenol-azo- 
phonic acid. 

Na salt of Resorcinol- 
sulphonic acid. 

Na salt of Betanaph- 
para-Bulphonic acid 

Na salt of Benzene- 
sulphonic acid. 

Na salt of Benzene- 
disulphonic acid. 

Na salt of Meta-nitro- 
phonic acid. 

C,n4(S0,Na)(*).N :N.C,H4.(0H)(«). 
C,H4(S0,Kay*).N :N.C,H,. | ^g[*J 

C»H4(30,Na)(0.N :N."CioH«(OH)^. 

„ (SOjNaa 

PH N\C H ^(SO,Na>i 
CeH4(N02)(»).N : '^•C,»H4 {^^^*^ 


Nearly ob- 

Seldom , 
met vita. 

Homo- ! 
are red. 

Not often 
met with 

1 Orange /, or TropcBolin 000 No. i, the corresponding dye from a-naphthol. Is 
obsolete. Orange R, or mandarin G R, and Orange S R, are homologues of Orange II, 
being derived from toluidine and xylidine respectively, instead of from aniline. 

a TropcBolin 0000, the corresponding dye from a-naphthol, is obsolete. Orange OT 
and Scarlet OR are homologues prepared respectively from toluidine and xylidine instead 
of aniline. 

3 Ponceau f G is isomeric with Orange G, and Ponceau G T and R T are homologues 
from toluidine. (See also page 192.) 

The following table shows the general character and reaction of 
more important orange and yellow sulphonated azo-dyes : — 


















•3 • — 

•0 22 


a . 

s ^ 


> « 





Is II 








3 is 

O 0O 









o o o» 








a si's 

















5^1 V* 

St O S u §p 

® ft 











U 9 


s o 

O >» 


o S a 
o :: 9 


I- a 




6 O 




82 S2-J 
11 III 







•a S'a 2 


p^ .» ^^"^ JJ CL -^ 





m » 





o o 








o S w 

•5ft % 

II. s 








If llg 

1^ " 

S ® !: 

j5 o 













Ml dj 

•3 . 

'^ ft 









test way of effecting the reduction of the yellow or orange 
I is to warm the solution of the colouring matteT with zino- 
1 hydrochloric acid, the actiou in an animoniacal solution 
hnewhat alow. Reduction with aiaaionium eulphiile, in 
ser described on page 21 1, may soinctuaea he conveniently 


lolluwing is a detailed description of some of the more 
it sulphonated azo-yellows and oranges ; — 
Tkllow. FahtYbllow.' (Seepage 184.) When aniline ia 
with fuming aulphmic acid, para-amidobeujcene- 
linic aciil (sulphanilic acid) is oblainetl. On diwolving 
I large qnuntity of water and adding sodium nitrite and hj- 
Icacid, diaEobcnzeno-aulphonic acidrceultn. On 
the solution with uniting, removing the excess of the LalUr 
xhloric acid, aud adding common salt, the a m i d o - a x »- 
ne-8ulphonic acid, CflH,(SO,H).N,C,H,{Siyy 
I as a yellow precipitate, and forms the notid j/^lfa 8 of 
e.* It is also prepared by heating aniline yellow with 
tee to four parts of fuming sulphuric acid. The eom- 
product known as acid ydhvD is prepared hy diHmiving 
ihouic acid in sodiuni carbonate and precipitating Um 
by common salt. The potnssium salt is also employed, 
low is a yellow powder, readily forming a yellow Mlntian 
f, but only ajwiringly soluble in alcohol. On kciduUUng 
»us solution with hydrochloric acid the free eulpbonie icid 
B down in the form of minute needles, sotablc in exam vl 
lone acid with reddiah-ydlow colour, appewing erinwiB ia 
tta, the change being probably due to Ibe looMliaa of 
ihloride. Acid yellow is not precipitalwi by WHOT iJa or 
kalies, nor by bsisic lend acetate. It is i««dpiUt«d by 
chloride, but not by calcium chloride. Bii)|Atiric acid 
I the solid ilye with yellow colour. Ziac-doat decoloriMs 
ion, but the filtered ti<iiiid recovets iu yelluw colour on 

sed mn yellow dye for wool ami rilk.and is 
I the tnanufitcture of Biebriek tearliil (page 197), 

The lioniolnguo 

9 In ahails, ud b known ss 




Hblianthin. Mbthtl Orange. Poirrier's Tropaeolin D. Orange 
III.^ Gold-orange. Mandarin Orange (page 184). These names, 
among others, are applied to the ammonium or sodium salt of 
or parasulphobenzene-azodimethylaniline, CgH^(S03Hy*^Nj^**.CgH4. 
N (0113)2^**, a body produced by the action of dimethyl-aniline on 
diazobenzene-sulphonic acid. Helianthin forms an orange-yellow 
powder, readily soluble in hot water, but only sparingly in alcohol. 
The aqueous solution is orange-yellow, and is not precipitated by 
alkalies. On adding hydrochloric acid to a hot, concentrated 
aqueous solution, the free sulphonic acid is precipitated in 
microscopic needles, which soon change to small, strongly lustrous 
plates or prisms having a violet reflection. Concentrated sulphuric 
acid dissolves helianthin with reddish or yellowish-brown colour, 
the solution appearing yellow in thin layers. On copious dilution, 
the liquid becomes a splendid red. With most reagents, helianthin 
behaves similarly to acid yellow, but basic acetate of lead throws 
down the whole of the colouring matter as an orange-yellow pre- 
cipitate. Sodium chloride or magnesium sulphate added to a 
dilute solution of helianthin precipitates the colouring matter in 
microscopic crystals* 

Silk and wool when immersed in an acid solution of helianthin 
are dyed a fiery orange. The dyed fibre is turned red by hydro- 
chloric acid, and yellow by strong sulphuric acid, but alkalies 
produce no change. 

Methyl-orange now receives extensive application as an indicator 
in alkalimetry. The yellow colour which it imparts to aqueous 
and alcoholic liquids is changed to red by a strong acid, but is 
wholly unaffected by weak acids. Thus the titration of sodium 
carbonate by sulphuric or hydrochloric acid can be effected in the 
cold, if helianthin be used as the indicator of neutrality, the 
carbonic acid liberated having no effect on the colouring matter.* 

The following acids are wholly unindicated by methyl-orange, 
and hence the base of their salts can be titrated by hydrochloric 
acid in the cold just as though the acids were absent : — carbonic, 
hydrocyanic, hydrosulphuric, arsenious, silicic, boric, oleic, stearic, 
palmitic, carbolic, &c. With oxalic, acetic, butyric, succinic, 
lactic, tartaric, and citric acids inaccurate results are obtained, but 

^ Orange III is a name which is also applied to a colouring matter patented 
by Roussin and Poirrier, and having the constitution of a sodium salt of 
metanitrobonzene-azobetanaphthol-disulphonic acid (see page 184). 

^ The delicacy and applications of methyl-orange and other indicators in 
volumetric analysis have been described in a series of valuable papers by R. T. 
Thompson [Jotir, Soc. Chevfi, Tnd,), 


sulphuric, hjdrachloric, and nitiic acids givo sharp cnd-reactiooe. 
Tha following salts are neutral to methyl-ontDge, and hence their 
formation ia an end-point of titrations in which ttiey are produced: — 
Na,Sj()„, KflHSOg, NaiyO,, CaH^{PO^)j, NaHjAsO^. Kfitp,. 
Metiiyl-orange can be used to detect freencid ia alum, ferrous sulphate, 
tupric chloride, &c. The earthy carbonates in hard water (which 
occasion the so-calleil " temporary hardness") may be at once deter- 
tuinci by titrating the water with o, mineral acid and methyl-orange. 

Ethijl-ijraiige ia preferred by Wieland to its lower homologue 
at an indicator of neutrality. LacmoTd, cochineal, coogo-ied, and 
dimethyl-amidoazobenzene behave much like helianthtn. 

Methyl-orange is not applicable aa an indicator in presence of 
nitrous acid or nitrites, which compounds decompose it. 

OiPHENYLAUiNB Yellow (pagos 184, 185). This colouring matter, 
the Ti-i^xEiitin 00^ of 5L Witt, and Poirrier'a iirange MN, also 
knuwn aa yotd-orarv/e, anid-i/eilino D, dipfienylamine-'jrawje, /cut- 
tfdiatp, and Majiciiester-yellaai (Perkin), ia a phenylated acid yellow. 
The free sulphonic acid is ohtaiued by the action of diazobenzene- 
sulphonic acid on diphenylamine. The diphenylamine is added in 
thift form of powder to the solution of the dtazobenzene sulphonic 
acid (dinwitiaed eulphaniUc acid) and the mixture agitated for 
some hours, till the reaction is complete. It forma steel-grey 
needles, very sparingly soluble in water with pink coloration. 
It is a powerful acid, forming weO-delined salts, almost oil of 
which are remarkable for their insolubility.^ The commercial dye 
is s potassium or sodium salt, and forms an orango-yellow crystal- 
line powder, or golden-yellow dichro'ic crystals, often arranged in 

) form of a fan. It ia readily soluble in hot water, but only 
y sparingly in cold water or alcohoL Ycry suiall quantities of 

leial salts precipitate it from its solutions. The hot aqueous 
llitttion is yellow, and unchanged by caustic alkalies, but turned 
iddisb-violet by hydrochloric acid, and on cooling a violet prc- 
'pibite is fonned. Calcium and barium chlorides give yellow 
e precipitates. In strong sulphuric acid, the dyo dissolves 
piith violet colour, becoming redder on adding water, while a 
-grey precipitate ia produced. 

A tiitro-derivntire occnni in cnnimerco Dnder th« same nami;. 'Wlieii tlia 

Intioii ia reduval with zino and hydrochlorio aci<l and filtcmd, the tiller. 

IT U •tained browD. The solid nbstani'e 'lefloKratea and girei off yellow 

wwhen belted on plaCiniini fail (see AEaflavine). 

■ Tbo trimetliytaniiuB salt is tlio only ono eonily soluble iu cold 

~ iniliaeialt when treated «itli an «cess ot boiling ajiiliue 

h-suddenly traoaformed into i n d u 1 ! n e, CuH,,N„ a Line colouring natter 

la with pbcnyl-amtdn-uobiinHn«. 


When reduced with an acid solution of stannous chloide, tro- 
pseolin 00 yields sulphanilic acid and para-amido-diphenylamine, 
which may be extracted by ether after adding excess of caustic 
soda to the solution. 

Diphenylamine yellow gives a fine golden-yellow on silk or wool 
The fibre is turned blue-violet by sulphuric and red-violet by 
hydrochloric acid. 

TropsBolin 00 may be substituted for methyl-orange as an 
indicator in alkalimetry, a faint trace of strong mineral acid turn- 
ing the dilute solution red, while carbonic and other weak acids 
have no eifect.^ 

Metanil yellow is isomeric with diphenylamine yellow. BriUiant 
yellmoy acid yellow 00, yellow N, and orange N are names given 
to the homologues of diphenylamine yellow. Two distinct isomers 
are met with (see page 184). 

Luteoline is a higher homologue from diazotised metaxylidine- 
sulphonic acid. It is now nearly obsolete, but occurred as a 
difficultly soluble orange-yellow powder. The hot aqueous solution 
deposits crystals on cooling, gives an orange-yellow precipitate with 
soda, and a violet precipitate with hydrochloric acid. In strong 
sulphuric acid the dye dissolves with yellowish -green colour, a 
violet precipitate being formed on dilution. With calcium chloride, 
luteoline gives an orange precipitate, which on boiling becomes red 
and crystalline. 

AzoFLAViNE is produccd by the nitration of diphenylamine 
yellow, and is a mixture of more or less mono-, di- and tri-nitro- 
diphenylamine with the body C6H4(S03H2).N«.CeH^.NH(CgH4N0j). 
It forms an ochre-yellow powder, soluble with difficulty in cold 
but readily in hot water. The aqueous solution is yellow, changing 
to brownish on addition of hydrochloric acid. When reduced in 
animoniacal solution it becomes yellow. Barium chloride gives a 
slightly soluble crystalline precipitate, but no change results with 
calcium chloride. The solid dye dissolves in strong sulphuric 
acid with magenta-red colour, changing to yellowish-red, with a 
yellowish-brown precipitate, on dilution with water. When heated 
on platinum foil the dye forms **Pharoah's serpents," and gives ofT 
yellow vapours. After reduction and filtration, brown spots are 
produced on the filter paper. 

Curcumein^ Azoflavine S or 2, Azo-yellow^ Cttrontne B or 2 B, 
Indian YetlmVy and Nexo yellow, are names applied to varieties of 
azoflavine. They must not be confounded with the eUrontn of 

' Tropseolin 000, or naphthol-azobenzene-sulphonic acid, behaves in a 
precisely opposite manner, being turned red by a trace of alkalL 



Brooke, Simpson, tind S[)iller(page 15C), or with eurcumin S or surt- 
i/dlniv, which is the sodium salt of azcKixystilbene-dieulphonic acid. 


The ecarlete, ponceaus, and clarots derived from azobenzcne and 
it8 oUicB are aiDong the most iraportant of Lhe colouring matters 
from conl-tar- The ready production auJ fast chnructer of crocein 
scarlet and allied dyes seem not unlikely to cause the extinction 
of the cochineal industry. The general methoil of producing the 
nio-reds may be eseraplified by the process of preparing j-y/idine-retl. 
For tliis purpose, xylidino, CgHj(CHj)2NHj, is dissolved in 
twice tho quantity of hydrochloric acid necessary to combine with 
it, and after copious dilutiou of the liquid with ice^old water a 
solution of the calculated quantity of sodium nitrite is gradually 
ndd»l with constant stirring. The resultant (neutml) solution of 
diazoxylene chloride is allowed to flow into a dilute amiuoQiacal 
solution of sodium betanaphtholdisulphonnti?, when ammonium 
chloride and xijlidinescarlei or sodium xylene-azobota- 
naphtliol-alph a-d iaulpbonate are produced : — 
= NH,Cl + C,H3(CHs)yNj.CioH,(SOjNa)j.OHS. 

After standing, tlie liquid is boiled, filtered from resinous 
iiULtter, and the colouring matter precipitated by addition of salt.' 

The following table contains a description of some of the more 
important azo-dycs of which xylidine scarlet is the type. The list 
is by no means a complete one, and new colouring matters of the 
same class are being continually produced. The commercial tiamcs 
of tho dyes are often confusing, the same chemical compound 
teceii-ing different names from its several makers, while on the 
otlier hand identical or very similar names are commercially used 
to diatiuguiah dyes of distinctly different chemical nature. 

' Owing to the futility with whioh Jiozu-componiids rpnct with phenoloids 
and tbrir iiulphopic «cids in alkaline Bolution, it is ["osaiblo to produce azo^dyei 
(lil«ctly on thn Rbre by immersing the goods alternately or simultaneously in 
a wlntion of naphthol and the diszosalt, and then devrlopiag the coluur in an 
alluline Inth. The methoiI is especially applicable to cotton, whirh does Dot 
take op Kady-fbniiDd nzo-dyn. Another method of operating is lo employ 
th« Ditrite reqnirHil Tor ilinzotiaing in the rorin of an amiDODiuin salt, wlien on 
hwling the goods this is defompowd in the prwimce o( tlio phonoloid and 
amines and thus prodnrea the azo-colourin rilu. The cnluoring nintter knows 
«« primuliiu ean be diaxotiied in the fabric, and on subsequently immersing 
the goo<lB in ail nlkuliiie solution of resorcinol or nnphthol tlio szo-dyc is 
iti^*elo|>ml (jwRB SOB). The property posaeaied by Iho hyilroijnio.dyvs of ibrm- 
ing DOluhle compounds vitb acid sulphite of soilium which are decomposod by 
but ia also utiliaal. A'anxine. C,lli(S0,Na].NH.N(NBS0,).C„H,.01Il9, u a 
nbatanoe of tliia claw. 




Archil snlMtitate. 
Naphthionic Red 


Cochineal Scarlet 

Scarlet O T. 

Wool Scarlet R. 

Ponceau K. Scar- 
let R. 
XyUdine Scarlet. 

Ponceau 2 G and 

Scarlet 2 O and 


Ponceau 3 R. 

Anisol Red. 
Anisidine Pv.u- 

Phenatol Red. 
Coccinin. Coccin. 

Cocoinin B. 

Bordeaux O. 
Claret O. 

Crystal Ponceau 

Fast Brown N ; 

Acid Brown ; 


Roccelline. Fast 

Red A. Rubi- 

dine. Ceraaine. 

Fast R^d C. 
Azorubin S. 

Crocein Scarlet 
7 B extra. 

New Coccin. 
Brilliant Pon- 

Fast Red D. 


C6H|(CH,).N : N.CoHs { ^* 

CeHiCCHsXX : N.CioH8{^/3 


enH,(CH,)2.N :N.CioH4 {^*^ 

I C5H(CH3),(CHj)^N:N.CioH4{^^^^*^ 

CH^CH,\'r:i:.l:.; : N.CioH^iy ^ 
I CeH4(0CH,).N : N.C,oH4 {^^^*^ 


N:N.C,oH4 j^ 




Isomeric with Bordeaux O. 


CioH(t(SOaNa)*. N*:N*.C,oH6.0H* 

I C,aHe(SOaNa)*.N^ : N^.CioHe.OH^ 

y CioH«(SOaNa)* 



^ CioH«(SO,Na)*.N : N.CioHej ®^»| 

|. CioH«(SO,Na)M^:N«.C,oH^{^^^f*^ 


\ CioH«(SO,Na)*.N : N.CiqH^ {^^^J 

(See jMge 194.) 

From naphthionic 

From C acid. Homo- 
logue is scarlet 4 R. 

From S acid. Homo- 
logne is scarlet O R. 

From Nevile's acid. 

From R Salt 

From R Salt Iso- 
mers of yellower 
shade from O salt 
Ponceau O, and 
scarlet O. 

From O salt Isomers 
from R salt 

From R salt 
From R salt 
From R salt 

From R salt 

From O salt Bluer 
shades from R 

From y acid. 

From naphthionic 

From naphthionic 

From naphthionic 
acid and Nevile's 

From naphthionic 
and B acids. 

From naphthionic 
acid and Q salt 

From naphthionic 
acid and R salt 


Brown paste ;n 

C!nnabar>red ; 
soluble in be 
to yellow-red I 

Scarlet powder 
tion orange>f[ 

Brown -red i 
difflcoltly I 
bronzy cryit) 

Brown-red powd 
utiom yellowii 

Scarlet powdsr; 
soluble ; red 1 

Brown-red i 
Fine red sohit 

Dark re<l powdc 
tion ctittTf-tt 

Brownish-red ] 
solation chen 

Fine red solvtic 

Dark red powdc 
tion cherry-re 

Solution daret < 

Red-brown gl 
cr]mtals; solu 

Dark brown i 
solution 1 

Solution reddisl 
forms lnt>w 
when rapidly 

Brown powde 
genta-rod sol 

Scarlet-red ] 
sparingly soh 

solution magi 



n of Aqoeoitt 


With Hy- 

Ked flakes. 

Brown oily 

red flakes. 


No change. 

e. No change. 


Beaction of Dye with 
Solphuric Acid. 

' No change. 

No change. 

>t Darkened. 




with excess, 
brown cry- 
stalline ppt 

Brown ppte. 














or cherry- 




Yellow-brown Violet, 

Brown jelly. 

No change. 

No change. 





On Dflution 




Bed flakes. 
Oily drops. 


Bed solu- 

Brown pre- 





Brown ppt. 






Frodnets of Beduction with 
Zinc of Ammonia. 

Nitranfline and diamidonaph- 
thalene sulphonlc acid. 

Toluidine and amido-a-naph- 
tbol suiphonic acid. 

Toluidine and amido-/3-uaph- 
thol suiphonic acid. 

Xylidine and amido-a-naph- 
thol suiphonic acid. 

Xylidine and amido-a-naphtbol 
disulphonic acid. 

Amido-i8-naphthol disulphonic 
acid and xylidine. 

Amido-^-naphthol disulphonic 
acid and cumidine. 

Amido-/i-naphthc^ disf«^*>honic 
acid and ethyl-xy 

Amido-/3-naphtbol disulphonic 
acid and anisidine. 

Amido-/^-naphthol disulphonic 
acid and phenatidine. 

Amido-Z^naphthol disulphonic 
acid and methyl anisiulne. 

Amido-Z^naphthol disulphonic 
acid and a-uaphthylamine. 

Amido-a-naphthol and a-naph- 
thol-amtne suiphonic acid. 

Amido-a-naphthalene sui- 
phonic acid, and amido-/3- 

a-naph thy lamine suiphonic 
acid and amido-a-naphthol 
suiphonic acid. 

a-uaphthylamine suiphonic 
acid and amido-/^napbthol 
suiphonic acid. 

a-najphthylamine suiphonic 
acid and amido-/3-naphthol 
disulphonic acid. 


BaClj and CaCU, amor- 
phous precipitat««. 

BaCl^ and CaClg, pre- 
cipitates app€»aring 

BaClj, brown, sparingly 
soluble precipitate. 
CaCls red precipitate 

BaCU, brown ppte. 
CaClj, red precipitate 
formed gradually. 

BaCl«, flocculent pre- 
cipitate. CaClj only 
precipitates strong 

Na«CO| in strong solu- 
tion gives pale brown 

CaClj, red crystalline 

MgS04 gives crystal- 
line ppte. in strong 




The dyes of tlie clnss of which xylidine scarlet is tlie type 
are very numerous, and are being continually added to. 
chnracters of the dyes are materinlly dependent on tUeir deriration 
fmm alpha- or beta-Daplithol, and the exact nature of the isomeric 
uaphthol-sul phonic acids employed also notably affect the oolonr 
and other properties of the dye. The letters R and G (the initial 
letters of the words rolh and ijelb), appended to the commercial 
names of the scarlets and other azo-dyes, have reference to the 
eodium salta of the respective isomeric beta-naphtholdiaulphonic 
acids used for their production. "Salt G" yields the yellow 
shades, and "salt B " the red shades of the azo-dyes they are 
employed to produce. Similarly, where beta-naphtholmonosn]- 
phonic acid is used, the characters of the resultant dyes depend tu 
some extent on the isomer employed, whether " Schiiffer'a acid," 
" Bayer's acid," or other modification.' 

' When betanaphthol is heated with twke its weigbt of strong salphiiria 
acid (sp. gr, 1-34S) to aboat SO* C., nntil complclely sulphnnitcd, tbo duet 
product ia a manosuIphoniD aciil known as Schiiffer'a acid ("luiid S"|. 
When betauaphthol is added (gradually to twice its nei|;ht of Btrong snlpharie 
acid (sp. gr. 1-84G), taking care that the temperature does not rise «baT« 
BO* to eO° C, Schiiffer'a acid «nd an isomeric ncid, betknaphtbol- 
alphasulphonic acid, often known as Bayer's acid ("•cidB"),«n 
formed in about equal qnnntitj. The use of s temperature at 3D* C. fot 
preparing Bayer's acid has tieea patented. Schiiffer'a and Bayer's suids inaj b« 
Rvparated by conrertin;; them into sadinm salts and treating the dry proilnet 
with alcohol, in vihich liijiiid the salt of betanaphlhol.alph&antphanic acid ■■ 
by far the moat readily solnble. Anotbcr method of separating Bayer'a aod 
from Scbaffer'B and another isomeric said to be present is based on the diSorent 
facility with which the three acids act on certain aTo-componmla. Tboi hj 
treating the alkaline solation of tbs mixed sulpbonic acidi witli a pni_ 
regulated qaantity of tetnuo-dipheny), the unnamed aoid and Sohafler*! acid 
are precipitated na claret-coloared dyes, while Bayer'a acid remains in solution 
in the requisite purity for the mannfacture of crocnn scarlet, for which 
purpose the isomeric acida are not available. A napht hoi -Eulph ante 
distinct from, and giving shades redder tbsn, either the above acids, is said to | 
be obtainable by a procssa described in Patent No. 15,7S1, of 1685 {Jour. 
DytTt. itft, ii. 199). 

When betanaphthol ia heated with three tjmea ita weight of eoncoutrUtd 
^Uphtuic acid (I'SiEsp. gr.) to 100° or 110" C, it is converted into a mUtara 
of two iwimeric dinulphonic acida. To iieparaCe these, tbe liqnid should 
be diluted, neutntliaeJ with milk of Umc, and filtered after allowing suffioiaDt 
time for the precipitated calcium sulphate to crystal! iae. TheliltrDtiiia trtaliHl 
with sodium enrbonate, and the filtered liquid evaporat«d to dryuesa. From 
(he mixture of the isomeric sodium salts obuined, "salt Q" can be diamlvod 
by alcohol, while "aalt R" ia left insoluble, According to J, W«\ 
{Jour. 866. Chan. Ind., iv. 339), the isomeric acids can b« separitMl hj 
ttMting the solution of their acid sodium hIU with brine, when aalt B 



Xtlidch Red, or Scabl.etR, obtained as described on page 191, 
forms a scarlet-red powder, readily soluble in water or acetic acid, 
but less so in glycerin or alcohol. Its aqueous solution is un- 
changed by alkalies or dilute acids, and girea scarlet lakes with 
the acetates of lead and aluminium. Barium chloride precipitates 
it more perfectly, oven in the presence of acetic acid. Xylidine 
scarlet dyes animal tibrea without a mordant in a slightly acid 
bath. When fixed by means of a barium salt, it withstands the 
action of boiling water very AvelL The colour does not stand 
soaping, but is fast in the air, and resists the action of light fairiy 
well, though it fades slowly when exposed to direct sunshine. 

Xylidine red and allied colours are freqnently adulterated with 
derfrin, which may be separated by treating the sample with 
snfficient alcohol Tarry matters are sometimes precipitated on 
acidulating the solution of the dye with acetic acid. 

FiST-BRnwN N. By the action of alphanaphthol on diazotised 
naphthionic acid a compound is obtained having a naphthalene 
nncleua on both sides of the chain, and of the folloHdng formula; — 
C,oH,(S{.)3N'a)".N^C,oH„(<>H)». This colouring matter, like others 
of similar constitution, dyes wool brown in an acid bath. It forms 
m ditrk brown powder soluble in water to form a yellowish-brown 
Bolution, changed to brownish-red by soda and giving a brown 
pretipitaUi with hydroclJoric acid. In strong sulphuric acid the 
dye dissolves with blue colour, a brown precipitate being formed 
on dilution. 

An isomeric colouring matter from alphanaphthol and diaiotised 
beta-naphthylamine-Bul phonic acid gives a brownish-red solution, 
tumei] mngenta-red by soda or dilute acids. It is soluble in 
strong sulphurio acid with blue colour, giving a reddish- violet 

Cipitat« on dilution, 
&l«t brown colouring matters are described with the tetrazo- 
!([««• 199). 
■Uheii oal. while ult O remuDs in solntioQ. (Tlio some process is uid 
to be »ppli™blo tn the spparaCion of SchilTer'H and Bayer's nionosulphontc 
■tidi.) Another beta a a p h t h □ 1 -d isa I phoD i c arid {y) haa been 
dMCribed and patented by Oaiu Bud Hofftnau (Jour. Soc. Chem. Iiid., iii. B67 ; 
17131, and ii used for the production of cryntal pamxau B £, hj rMCtlon in 
■olntion with diazoiiaad o-napbtbyUmino. 

1* extreme actiou of famiog aulphuric acid on betanapbtfaol, a 
Iphonic acid is obUinable. 

mannfscture of anlphoaic icids and nitroaul phonic aciila from alphs- 

bocu receally patented by II. Caro. Other BuIphoaLc aciila of 

■nd beta-naphthol and of the napbtbylamiueB have bean described and 


Secondary Azo-Compounds. Tetrazo-Dyes, 

Amido'Bzobenzene may be regarded as a primiuy amine, since 
it contaiuB the group NH^. When this is attacked by nitrous 
acid the diazo-reaction occurs, and a diftio-agobonsene 
compound is formed: — C6Hj,.NyCaH^NHsHCl + NaK0„+HCl 
= Conj,.Nj.C9Hj.NyCl+S8Cl+2H,0. The product contft'ins the 
— N:N — group in two places, and is called a secondary 
azo- or tetrazo-compound.' By reaction with phenols 
in presence of alkalies, these tetnizo -compounds yield pradocU 
of which several have received practical applications, aa they 
usually possess a colouring power superior to that of tha azo-dyos 
of similar colour but simpler constitution. They are Kindennl 
soluble by sulphouation, the SO3H group being often introduced 
into both chaius. Thus by ditiKotietng acid yellow, and actiiij; 
with the product on sodium betanaphthol-alphasulphonate 
(Bayer's salt), sodium betanaphtbolsulphonate- 

n i uiij, or eroeeim gcarlel, is obtained, according to the following 
equation ; — 

WHjCl + CflH^{S0j.NH/.N':K'.CflH^.N';J)-.CaHj(S03Na).0H». 

CrooBTn Scarlet 3 B, or Potieeau 4 RB, formulated above, 
is a dye of considerable practical importance. It fonua a red- 
brown powder, soluble in water with scarlet-red colour. The 
solution is turned violet-red by alkalies, but not precipitated except 
in very concentrated solutions. With hydrochloric acid it yields ft 
yellowish-brown precipitate. With barium chloride it gives a 
red precipitate, becoming dark violet and crystalline on boiling. 
With calcium chloride the dye gives a flocculent red precipitate, 
which on boiling the liquid suddenly becomes brown and crystaUise. 
When reduced with line in ammoniacal solution crocein scorlot ia 
decolorised, but tlie liquid acquires a yellow colour on eKpctmiC 
to air. The solid dye dissolves in strong sulphuric acid vrith 
indigo-blue colour, and on dilution a yellow-brown precipitata is 
formed, soluble in more water to a red solution. 

Crocein Scarlet 7 B, or Poneeaa 8 RB, is honiolo<goua with 
the last (containing two ti>luene- instead of l>en:£oue- residues) and 
resembles it generally, but after reduction with zinc and ammonia 
the colourless liquid does not again become yellow on exposure to 
air. The hot concentrated aqueous solution, when treated with 
' Tertiary Aro-Ctnnjxiuiidt, coatainiiig three — !N:N — groups, hare Ims 
prepun'd (R. Meldola. Jour. Chem. Soe., xlUl 436), but tliey ha** lltllt 
tlnotorial value. 




peeinm sulplmte ftnd allowed to stand, deposits 
g silky needles of the magnesium salt. 
I PoscKAB H. Extra is a diaulphonated crocein acarlet : — 

^Orseillin 3 li is the metameric compound from alphanaplitbol 
phonic scid. 
BiKOOiCH SoARLffT, Ponceou S R, or aiobetixeiu' red, is a mixture of 
i searlfl or double marlet, CBH,(S03Na).Nj,CnH,.Ni.CioHg.OH», 
pb the oorresponding d i a u 1 p h o n a t e, C|,H^(80jNa)''.N':N', 
^S0jNa)'.N':K".C,(,Hg.0H8. It is a reddish-brown crystaltine 
hrdec, forming a yellowish-red Holutjon, The hot aqueous Bolution 
f Biebrich scarlet becomes gelatinous on cooling. Dilute acida 
I flooculent brownish-red precipitate in strong solutions, but 
the dye is not precipitated by alkaliea. (According to some, a 
browutsh-red precipitate.) With zinc and ammonia the solution 
of Biebrich scarlet is decolorised, but on exposure to air the liquid 
BotUBS yellow and gives the reactions of acid yellow. The 
i dye gives a green solution in strong sulphuric acid, and on 
^Dg water the colour chimgBs to blue, then to violet, and lastly 
Birty-brown precipitate is formed. 
'virleUS B, S R, and 4 R are varieties of Biebrich siMirlet, 

or Poneeau SS extra, is metameric with Biebrich 
Irlet, the betanaphthol being sutphonated instead of the amine, 
■ :— C,HJ.N:N''.CflH,.N':N.C^(|H^(SOsNa)"5.0H^oraMbenzeDe- 
tben^!ene-betanaphthol-diaulphonate of sodium. It is a brown 
r, soluble in water with magenta-red colour. The solution 
] a violet precipitate with hydrochloric acid, and is turned 
liah-violet by soda. 

' •ilHmii eroeein M is a dye of the same corapositior 
li sodium betanapIithol'^-Bulphonic acid instead of salt R. 
fs S light brown powder, forming a cherry-red solution, which is 
turned brown by soda, and gives a brown precipitate with hydro- 
sfaloric acid. 

^Jizocixnn 7 B and Croeein B are colouring matters from alpha- 
ihtliol analogous to scarlet 8. Azococcin 7 B is a difficultly 
ilUe brown powder. The magenta-coloured solution gives a 
wntoh-rod precipitate with hydrochloric acid, and with soda 
wlet-red precipitate soluble in water. Crocein B is brown-red, 
ultly soluble to a magenta-coloured solution which is pre- 
tated violet by hydroclilorio acid, and gives a violet coloration 
I ooda. Archil red is homologous with scarlet 8, containing 
b xylene- instead of two beniene-roaiduos. 
"^ EC TrntAKo-DTEB are characterised by their behaviour on re- 
With tin and hydrochloric acid, or other acid reducing 



agent, the decomposition is complete ; but when treated with zinc 
and ammonia only partial decomposition ensues, and the decolorised 
and filtered solution usually acquires a yellow colour on exposure 
to air, the colourless hydrazo-compound formed being oxidised to 
acid yellow and amido-azobenzene or some allied body. (See 

A further distinction between the various red tetrazo-dyes con- 
taining a naphthol nucleus is to be foimd in their behaviour when 
treated in the solid state with strong sulphuric acid, as is shown 
in the following table: — 


Colour with Sulphuric 

Products of Bednctioii. 


On Dilution 
with Water. 

In Alkaline Solvtiaa. 

In Add Sohitioo. 




Blue, brown, 




and brown 

and amido-hydim- 

anlphanilic add, 
and para-diamido- 



phonic add (oxi- 
dising with ywow 




Fast scarlet 


Blue; then 
blue - red 




zene and amido- 


to scarlet. 


sulphonic acid(oxi- 
diung with yellow 



Violet ppte. 


disulphonic acid 

Sulphuric acid, 

Scarlet S. 


aniline, ana para- 

8S extra. 

and amido-azo- 



Brilliant cro- 


Blue-violet ; 

• ■• 

• •• 



and red or 
brown ppt 
on further 



Brown fsh- 

■ ■ ■ 




red ppte. 



Violet ppte. 

• •• 



Sulphuric add, 


scarlet 8 B. 


ppte., and 

aHBulphonic add 

then red 

and amido-hydrazo- 

sulphanllic add, 
and para-diamido- 


benzene sulphonic 
acid (oxidiung to 


acid yellow). 




• • • 

• •• 

scarlet 7 6. 

Orseillin 2 B. 



• •• 

• •• 

Ponceau S 



• ■ ■ 

• •• 





From tkis table it appears tlmt (A) when the aulphonic group 
(SOgll) exists iu the benseDe nucleus or nuclei only, as iu Biebrich 
scarlet, a green coloration is produced ; (B) whcu the naphthol 
nucleus ia alone sulphonatod, as in scarlet S, the dye dissolves in 
strong sulphuric acid with violet colour ; while (C) when both the 
benzene and naphthol or naplithatene residues ore sulphonated, as 
in the crocein scarlets, a blue coloration is obtained.' 

Soudan III, or Amido-aioltenzene-azobetanaphthol, CoHj.N^ 
CjH,.Nj.C,DHg.OH.* This ia the only unaulphonated tetrazo-dye 
of comuietcial interest. It forms a brown powder insoluble in 
water, but soluble in alcohol. It dissolves in concentrated sul- 
phuric acid with bluish-green colour, becoming blue on addition of 
water, and giving a red precipitate on further dilution. 

Tbtraso-Bbowhs mostly belong to the class of bodies sometimes 
called diaaso-compounds, the constitution of which is 
iBp poaed to be somewhat different from that of the onhnary 
mpounds. The following colouring matters of this class 
t ia commerce : — 

t hrown (Bayer), . 


CbH,(OH)j. -^ j^ . N.cX(SO,Va: 

'■ t N : N.CioHg(SOjNa)/' 

C»H,(NH,),, I jj . N.c"„H„{SO,Na) 


t brown (Mcater). C.^,(OH) : | ^^ ^ N.c'HjicH'SsolNa) 

JORCIN Browx. C,Hj(CH,)i,.N,.C(Hj(OH),.Ng.C,H,(SO,Na). 
■ compound is one of the few tetrazo^colours not containing 
ihthalene nucleua. It is a brown powder, soluble in water to 
|own solution which is but slightly changed by soda, but yields a 
a precipitate with hydrochloric acid. The solid dye dissolves 
rong sulphuric acid with brown colour, and on dilution with 
1 1> brown precipitate is formed. 
!&cip Bbown G ia the type of several similar bodies obtained 

' AMRcrmN 2 S, produced by reacting on diiuotised acid yellew with 

KvriU'* ■-nBgihtbol-an] phonic acid (torn Da^itliianic scid (and hincc d dye of 

ckaa C) Bppiwn td I>i> itn oicsption to tliia nUe, for it diBaolrea iu eidphnrio 

il ttilh green colour, beooming liluo on dUiition. 


by introducing an amine residue instead of a phenol residue. It 
is prepared by the action of diazobenzene chloride on chrysoidine- 
sulphonic acid. It dissolves in strong sulphuric acid with reddish- 
brown colour, becoming yellowish on dilution with water. 

Acid Brown R is a similar dye prepared by the action of 
diazotised napthionic acid on chrysoi'dine. It is a brown powder, 
forming a brown aqueous solution which is unchanged by alkalies, 
but precipitated brown by acids. In strong sulphuric acid the dye 
dissolves with a dirty olive colour, and on dilution gives first a 
reddish and then a brown precipitate. 

Fast Brown G is a brown powder, forming a reddish-brown 
solution. Dilute hydrochloric acid gives a violet precipitate, 
soluble in excess with violet colour, or in water with brown colour. 
Alkalies turn the aqueous solution cherry-red. Strong sulphuric 
acid dissolves the solid dye with violet colour, becoming yellowish- 
brown on dilution. 

Fast Brown of Meister, Lucius, and Briining is homologous with 
the last dye, and forms a dark brown powder soluble in water with 
brown colour. Alkalies turn the solution reddish-yellow, and dilute 
acids give a violet precipitate. Strong sulphuric acid dissolves the 
dye with violet colour, becoming red on dilution. The colour 
produced on wool is a brownish-red. 

Naphthol Black or Azo-Black contains Ci0Hg(SO3Na)jJ^j. 
CioHe.N2.CioH4(OH)^(S03Na)2, and results from the action of salt R 
on diazotised amido-azonaphthalene-disulphonic acid. It forms a 
readily soluble black powder, yielding a dark blue-violet aqueous 
solution, precipitated red-violet by hydrochloric acid, and giving with 
alkalies a blue precipitate soluble in much water. Precipitates are 
yielded with barium and calcium chlorides, as also by solutions of 
iron and other heavy metals. The dye dissolves in strong sulphuric 
acid with dark green colour, becoming blue on dilution. Kaphthol 
black dyes silk and wool a blue-black in a slightly acid bath. 

Wool-Black is a similar dye produced by the reaction of 
diazotised amido-azobenzene-disulphonic acid on paratolyl-beta- 
naphthylamine,'and has the formula, CgH4(S03Na).N2.C6H3(SO3Na). 
Kg-CioHe-N 11(07117). It gives a violet precipitate with soda, and 
a red-violet precipitate with hydrochloric acid; and dissolves in 
strong sulphuric acid with blue colour, yielding a brown pre- 
cipitate on dilution.^ 

^ Both wool>black and azo-black are employed as indigO'Bubstitutes in wool- 
dyeing. They are fairly fast, and can be applied in the simplest possible 
manner, namely, by simply immersing the wool in an acid bath of the dye, 
bat the colour is apt to bleed in the milling process. 


.fczo-Dyes from Benzidine and its Analogues.' 

During tlia Inst few years a yruup of naw coal-tar ilyaa hitve 
been introduced, which possess the characteristic property of dye- 
ing cotton in a. neutral or alknline bath without a mordant, a 
peculiarity previoualy confined to a few natural colouring matters 
(&_7,, turmeric, aafflower, annutto). The new dyes belong to the class 
of tetrazo- or secondary azo- compounds, but differ from those pre- 
Tiously described (page 196 piuu?.) by containing two benzene nuclei 
in the nzo-group, being derived from diazo-di phenyl (diazotieed 
ti^nzidine) or ita analogues. They all contain a sulpho- or corlwxyl 
group, Jind occur in cotamerce as sodium salts. 

When an alcoholic solution of nitrobenzene is treated with 
caustic soda and zinc-dust, azobenzene, CgHj.Nj.C„Hp, is 
formed. Tliia body ia converted by boiling with zinc-dust into 
byJrazo-benzene, CgIl5.NH,NH.CaH[i, and this on treatment 
with strong hydrochloric acid is converted by a molecular change 
into b e n E i d i n c, which is precipitated on adding excess of 

Benzidine has the constitution of a diomido-diphenyl in which 
both the NHj groups occupy the para-position. When the di- 
hydrochJoride Ib treated in acid solution with nitrous acid or sodium 

R'te it is diazotised, forming te trazo-diphenyl dichloride, 
cding to the following equation : — 
J C,H,NH,'.HC1 . ,„„„ -,T,nj.l C,H,.N;N.CI 
y reaction with aromatic amines or phenols, or their deriva- 
tives, the tetrazo-di phenyl dichloride forms the series of colour- 
ing matters known as the benridine dyes, of which conyn- 
r»i is the type. To produce this substanc*, the solution of one 
molecide of tetrazo-diphenyl dichloride is added to a well-cooled 
solution of tvro molecules of sodium naphthionate, and then 
Bodium acetate added: — 

r CBH,.Nj.CioH5(SO,N"a).NHj 
" 1 CflH4.Nj.Ci(,H4(SOjNa).Nn^ . 
3ie reaction requires several hom« for its completion, and occurs 
diatinct staj^es, an intermediate product being first obtained. 
9 of general occurrence under similar circumstances, and by 

eiyvalasble iNiper on the BvDzidino Slid Allied ColonrB. from vhich much 
hi text U derived, lias heea pabtished by G. U. Hunt 
Dyen, lb^, iv. 14). 


taking advantage of the fact it is possible to combine one molecule 
of diazotised benzidine or an analogous body with two different 
phenols, amines, &c. Thus eango corirUh is obtained by first reacting 
on one molecule of tetrazo-diphenyl dichloride with one molecule 
of sodium alphanaphthjlamine - sulphonate, and treating the 
intermediate product thus obtained with sodium alphanaphthol- 
sulphonate: — 

-non- 1 c,H,.N^C,oH,(SO,Na)-.OH'. 

By processes similar to those employed for the preparation of 
benzidine, the homologous base tolidine, (NH2).CgHg(CH,). 
CgH3(CH3).(NH2), can be prepared from nitrotoluene, 
CgH^(CH3)(N02); and when diazotised, tolidine yields tetrazo- 
ditolyl dichloride, homologous with the similar product 
from benzidine. This body reacts with phenols, aromatic amines, 
&C., in the same way as its lower homologue. Bemopurpurin and 
azo'blue are examples of colouring matters thus obtained. 

By first sulphonating paranitrotoluene, and treating the product 
with zinc-dust and caustic soda, it is converted into d i a m i d o - 
stilbene-disulphonic acid, and this when diazotised in 
hydrochloric acid solution yields the dichloride of tetrazo- 
stilbene-disulphonic acid : — 

f f CH.CgH8(S08H).NH2 ^TTTH^^ 
U CH.C6H8(S03H).NH2^^^^2 

-4H 0+ 1/ CH.CeH3(S03H).N2.Cl 
-4±i2U-i- 1^ CH.CeH3(S03Hj.N2.Cl . 

This body can react with phenols, amines, &c., to form colouring 
matters, of which brilliant yellow SLiidihe Hessian purples are examples. 

Similar colouring matters are obtainable from d i a m i d o- 
fluorene, Ci3Hg(NH2)2. 

As already stated, all the colouring matters of the class under 
consideration dye cotton in a neutral or slightly alkaline bath, 
without the aid of a mordant. In practice, the cotton is boiled in a 
solution of the dye rendered alkaline by soap and sodium phosphate or 
carbonate. Borate, silicate, and stannate of sodium are also used. 

The benzidine dyes can also be used for wool, but an alkaline 
bath is an objection. With some of them a bath acidulated with 
acetic acid can be employed. The colours produced on wool by 
the blue and violet dyes of this class are always much redder in 
shade than are given by the same dyes on cotton. The colours on 
wool are faster to light than those on cotton. 


AUullDe Baln- 

IDUutlKd > 

1 BnlpbaoUle 


1 NiphtUooic 


phonic add. 

[ihonli: idd. 
1 ^-uphthyl- 

1 DtuotlKd 

t MMhri-D 

' IMuaU* 

' 1 DUiotlHd dll '^ 
mmtdo-dl- I 

1 ?fiiphUi jl- ' j 
untDe tnt- 
phonio Kill. J 

I Niphlbol nil- 

ulildtDe dl- 

Colour pro- 

l<:sH,.Nj Ci„H((H03!H).NUjS 

\ C^^0C,H^N9.CMH,(80iNaJ.NH(CHi) 


Homologns ot chrrumlnB O. 

iMnwr of beniopiirpurln 1 




Obtained by the 

Alkaline Solu- 
tion of 

purm B. 

ponn 6 B 

Diamine red 

Congo 4 B. 




Congo B. 

Corinth B. 


From Di- 





Hessian Bed. 

B, P, D. 

Purple N. 


( 1 Diazotised 
2 /}-uaphthyl- 
phonic acid. 

1 Diazotised 

1 Naphthionio 

1 BesorcinoL 
( 1 Diazotised 

1 /}-naphthyl- 


phonic acid. 
1 Ethyl-/}-naph- 

thvlamine h- 

sulphonlcacid. ) 

1 Diazotised 


2 a-naphthol 

solphonicacid. ) 


Formula or Chemical Nature. 

Isomer of benzopurpurin 4 B. 

Homologue of deltapurpurin G. 
Isomer of deltapurpurin 5 B. 



Ethyl-derivatire of rosazurin O. 
Homologue of brilliant oongo O. 
Homologue of oongo corinth. 


1 Tetrazo-stn- 
bene disul- 

Ehonic acid, 

1 Tetrazo-stil- 

bene disul- 
phonic acid. 

2 Salicylic acid. 

1 Tetrazo-stil- 

bene disul- 
phonic acid. 

2 Kiaphthiouic 


1 Tetrazo-stil- 

bene disul- 
phonic acid. 

2 /3-naphthyl- 

1 Tetrazo-stil- 

bene disul- 

phonic acid. 
1 o-naphthyl- 

1 /}-naphthol. 

it CH.CeHs(S08NaXN2.iC8H^OH)p 


lie hydrogen of 
brilliant yellow 

the OH grou 
replaced by me 

It Cfl.C«H8(S03NaXl!f2^.C6Hs(OH)P.COONa 
^ I CH.CeHs(SOsNa).N2i.C6H^OH)P.COONa 


ups of ^ 
thyl or \ 


/jCH.C6H8(SO,Na).Nj.CioH8(808Na)".NHj" > 
"((CH.CeH8(S08Na>.Na.CioH8(SO,Na)*.NH,» j 

Isomers of Hessian red. 

( icH.C«H3(SOjNa).N2.CioH6.NH3^ 



Colour pro- 
duced on 

Bright red. 
















The preceding tables show the constitution and reactions of the 
more important dyes from benzidine and its analogues. The table 
on last page has been mainly compiled from the recorded observa- 
tions of E. K n e c h t and G. H. Hurst {Joiur, Soe. Dyers, ^c, 
V. 14). 

The colouring matters named in the foregoing tables may be 
distinguished from all other azo-dyes by heating a piece of 
unmordanted cotton in the aqueous solution. The cotton is then 
removed to a warm solution of soap, which will strip the dye from 
the fibre unless the colour be derived from benzidine or an 
analogous diamine. 

The dyes from benzidine, &c., can be fixed on silk from a bath 
containing soap and phosphate of sodium; and mixed silk and 
cotton goods take the colour well and evenly. 

The benzidine dyes act as mordants to the basic aniline dyes, a 
fact of which the practical application is evident. 

In their general reactions with sulphuric acid and reducing 
agents the ben.juine and analogous colours resemble the other 
azo-dyes (page 210). 

Besides the dyes mentioned in the foregoing tables, there are 
a few other colouring matters of peculiar constitution, such as 
azarine and primidin, which can be conveniently considered in 
the same section, and are described in detail on page 209 ef aeq. 

The following is a detailed description of the more important of 
the dyes from benzidine and its analogues : — 

Chrtsaminb, or Flavopheninb, is produced by the action of 
tetrazo-di phenyl chloride on sodium salicylate. It forms a yellow 
powder, sparingly soluble in cold but readily in boiling water. 
The solution has an orange colour, changed by caustic soda to an 
orange-red, from which acids precipitate tetrazodiphenyl- 
disalicylic acid in orange flakes soluble in ether. Strong 
sulphuric acid dissolves the solid dye with deep magenta colour. 

Congo-Red forms a brownish-red powder, readily soluble in 
water to produce a blood-red solution. Very small quantities of 
dilute acids turn the liquid to a beautiful blue, a precipitate of 
the free sulphonic acid being formed in strong solutions. 
Alkalies restore the red colour, and salts of neutral constitution, 
such as alum,^ ferrous sulphate, cupric sulphate, &c,, do not act as 
acids. Hence it has been proposed to employ congo-red as an 
indicator of neutrality, but it has been shown by R. T. 
Thompson (Jour, Soc. Chem, Ind., vi. 195) that its delicacy 

^ R. T. Thompson finds that congo-red is incapable of indicating with 
certainty the presence of 0*2 per cent of salphuric acid in alum, or even of 
giving a trustworthy reaction with 0*5 per cent. 


has boen overrated.' While not wliolly unaffected by weak acids, J 
such as carbonic and sulphydric, it faUs to indicate the presence of ' 
acetic acid in presence of twelve timea the quuitity of sodium 
acetate. Congo-fed dissolves in strong Bulphurio acid with slate- 
blue colour, which is not changed by dilution. Congo-red dyes 
cotton a bright crimson-red, but the colour is far from permanent. 
Exposure to light and air for a short period dulls the colour, which . 
is restored to its original brightness on soaping. After longer 1 
exposure to light, the colour cannot be thus restored. On wool 1 
the colour is rather more scarlet, brighter, and more stable than o 

EESZoPimpimm 4 B is the next higher homologue of congo-red, 1 
It forms a dark browniah-red powder, soluble in water with orang8*> 
red colour, which is unchanged by alkalies, From strong solutions, 
dilute acids throw down the free sutphonic acid as a 
reddish-hrown precipitate resembling ferric hydroxide. Strong 
sulphuric acid dissolves the solid dye with pure blue colour, a 
blue precipitate being formed on dilution. In a bath contuiuing 
soap or alkaline carbonate, beniopurpurin dyes cotton a fine scarlet. 
^^^lie colour is almost unaffected by dilute acids, and is much faster 
^^B light than congo-red. 

^^B BBHzopnRPURiN B is isomeric with the lost named dye, nnd is 
^^tepared by the reaction of diazotised tolidine on jS-naphthyl- 
tmine-sulphonic acid ^ in presence of alkali. It is a brownish-red 
powder, not very soluble in water. The aqueous solution ie 
reddish-brown, unchanged by alkalies, and precipitated brownish-red 
' y dilute acida. It dyes cotton a colour approaching turkey-red in 
kt of brilliancy. Acids turn the dyed fibre blue, the colour i 

Ing restored by alkalies or washing. 
I Dbltapokpurin CI is isomeric with congo-red, and like its homo- 1 
me Deltaytirprtrin 6 B \a obtained by the use of the so-called 1 
^odiRcation of ^-naphthylamine-sulphonio acid.' The delta- 
rpurius dye cotton a bright scarlet. Deltapurpurin G B is dis- 

P ChrywmiinB is probablj the only cnnimorcuil ■zo-dye wliieh is extracted by I 

~ a icidulstcd aqueous soludon with Mher. 

f Tbe sulphonic acid is the «a c&Iled fi-mod if ic&ti on, obtained (miisd 1 

"a m- and 7-iiu)meride3) by besting £-nap!ithylamui4 iritb 8 parts of I 

ic add (96-»r per cent of H,SO() to 100°-105'' C. for six hours, or by I 

SchaOer's ^-naphthal-sulphonio aciil with ammonia. 

* The B-naphthyl»miBB-B-8U I phonic acid, used for the produo 

a of thn dtllaparpaTint, is prepueit by healing 3'iuiphth?laniini; nulphats -J 

" " ir 8 pftTts of strong sulphuric acid {!'8*£ apociKc gravity] lo 150° (X I 

IT 1 1 hour. The a- acd f- sulpbonio acids of ^-naplithylaDiine are said U 

nifonued into the ^-modificatioD by this treatment 



tiiiguished from its ieomer diamine red S B^ and from D dfUa- 
jmrjnirine 7 B hj not being precipitated from its oi^ueouE solution 
by acetic acid, and by forming a soluble calcium salt. 

Azo-Bn;a is closely related in constitution to benzopurpurin, 
the two NHj groups of the latter being replaced by two of OH. It 
forma a bluish-bloc^ powder, readily soluble in water with fine 
violet colour, which is changed to crimson by caustic alkalies anil 
restored by dilute acids, In the concentrated solution, hydro- 
chloric acid produces a violet-blue precipitate, but dilute acetic 
acid occasions no change. Conceutrated sulphuric acid diseolro) 
the dye with pure blue colour, the solutiou giving a violet 
precipitate on dilution with water. In a boiling hot balli 
containing soap and sodium phosphate, azo-blue dyes cotton » 
violet-blue colour, fast to soap, and unaffected by acids. 

Bbnzo-azuren R forms a dark blue (almost black) powdeii with 
a slight hronie reflex. It dissolves rsaiiily iii water with deep 
violet-blue colour, changed by caustic potash to a red-violet W 
crimson. Dilute hydrochloric acid produces a dark violet pre- 
cipitate. The dye dissolves in strong sulphuric acid with purt 
blue colour, Benzo-azurin dyes cotton a dark shade of blue. Tht 
colour is remarkably fast to light, and unaffected by acid^ but 
is reddened by alkalies. 

Benzo-azurin G differs from the last named dye in not 
being precipitated from its solution by dilute acids, the colour 
being simply darkeued. On cotton it dyes a brighter tolour 
than the lost, and on wool gives a pleasant and useful shade of 

BntuJANT Tbllow forms a readily soluble brown powder. The 
solution is orange, changed to scarlet by alkalies, and gives a bine- 
black precipitate with dilute acids. It dyes cotton and wool a 
very bright orange shade of yellow, quite fast to light Adds 
change the colour fibre to blue, and alkalies redden it ; eottping 
turns it a shade redder, but there is no bleeding. 

On treating brilliant yellow with soda it forma a red basic salt, 
and on ethylating this body it is converted into 

Chrtsophbnihb, This forms a light orange powder, partially 
soluble in water. The solution is unchanged by alkalies, but gives 
ft dark brownish-red precipitate with acids, In a neutral bath it 

' Prepared by actiug on diuzntisml tolidine iu Mlbaline noliillon nith 
B-naphthylamine-F-Bulphonicncid. This is pn'pjiml hy ^MItlj 
tliL' aodium wit of a-aii|)hthalenc-difiulj)bonic itcid with four tiiuiw lia wcigbt 
of GO per cent, caiistiu khIii at 200° C, unUl diuxynn[ihthitIeno bc^s ta Iw 
formed. {S-naphthol.F-aulphonic acid is formnd, and on helling thit wtUi 
'a nudcr prexiurc the ooneBpondinj; amiilo-aoid is obtained. 


ilj-M both wool and cotton a bright yellow, unatFected by dilute 
ncids, itlkaliee, or soap. 
^^—AxARiNE is a colouring matter of peculiar constitution, boin^ 
^^^■esented by the following formula:— - 
^H <n i CbKj,(OH}.NH.N(SO,NH^).C,oH(|.OH 

l^r * 1 CaHs(OH).NH.N(S03NHj).C,oHB.OH 

I It is produced by diaaitising d lam ido-dihydroxy ben zoaul phone, 
SO^CoHj(OH).NIIa)^ and causing the product to react with 
betonapbthol. The azo-K:ompound formed is then treated with acid 
sulphite of ammonium or sodium, which formB a compound of the 
niiture shown above. The employment of nzarine is an application 
of the fact that many aKo-compounds which are themselves insoluble 
combine with the acid sulphites of the alkali -metals to form com~ 
pounds which are soluble in water and unafiected hy dilute acids, but 
which under the influence of heat are decomposed into a bisulphite 
of alkali~metal and an insoluble azo-dye. The reaction is capable 
of bein^ used in calico-printing. 

Azarine occurs in commerce in the form of an orange-yellow paste, 
doaely resembling alizarin paste. It is sparingly soluble in water, 
but dissolves readily in alkalies with IJuish-violet colour. The 
nqueoua solution is yellow, and yields an orange-yellow precipitate 
with hydrochloric acid, and with caustic soda a violet precipitate, 
which dissolves to a red solution on heating. On heating the paste, 
Kulphur dioxide is evolved, and the colour uliangos to scarlet. 
Strong sulphuric acid dissolves azarine paste with magenta-red 
colour, a reddish-brown precipitate being formed on dilution. 
Azarine forms alumina-lakes of a line red colour with a shade of 
violet. It is very fast to soap and chlorine, but is affected by light. 
Prjhttlin is a colouring matter the constitution of which has 
not yet been made public, except to the extent that it is an 
amido-sulpbonic acid (A. G. Green, Jour. Soc. Dj/en, 
^e., iv, 39). The commercial product is a yellow powder, which 
is very soluble in hot water. The very dilute aqueous solution of 
primnlin exhibits a blue fluorescence. In a 5 per cent, neutral 
Imth at a boiling temperatiue, primulin dyes cotton a lemon- 
yetlow colour, whicti is tolerably fast to scouring, entirely unaffected 
by alkalies, and turned a golden yellow by acids. The alhnity of 
the fibni for the colouring matter is increased, and conseijueutly 
iltiB[iet shades may be obtained, by addition of sodium chloride or 
sulpliate to the bath. Beducing agents produce no cliange, but 
" B colour is attacked by oxidising agents, such as bleaching powder 
3 acid. By the latter the shade is changed to olive, 
e boiling solutions of hypochlorites turn the colour to orange- 
aw, which is very fast to all agents. 
'"OL. ril. PAKT 1. 


Since primulin contains an amido-group, it is capable of being 
diazotised, and this operation may be readily performed on the 
dyed fibre by passing the washed material through a dilute 
solution of sodium nitrite (3 to 5 per cent.) acidulated with 
sulphuric acid. If the fabric be then again washed and immersed 
without delay in a developing solution of one of the naphthols, 
naphthylamines, or their derivatives, various shades of yellow, 
orange, scarlet, or maroon may be obtained. The colours so 
obtained are termed ingrain colours, and are characterised by their 
extraordinary fastness to scouring, milling, acids, <&c., being said 
to be only equalled in this respect by alizarin and its congeneis, 
and to far exceed the ordinary benzidine dyes. 

Oeneral Analytical Reactions of Azo-Dyes. 

The great majority of the azo-dyes are sulphonated, and more 
or less soluble in water. In no case is a sulphonated dye removed 
from its aqueous solution by agitation with ether, whether the 
liquid be alkaline or acid. There are a limited number of 
xmsulphonated azo-dyes, such as chi^soidine and bismarck brown, 
from which the free base may be extracted by agitating the 
alkaline solution with ether. Chrysamine, on the other hand, is 
an unsulphonated azo-dye of acid character, and is removed from 
its acidulated aqueous solution on agitation with ether. 

The azo-dyes are stated to be non-poisonous. On addition of 
hydrochloric acid to the concentrated aqueous solution of a 
hydroxy azo-dye, a precipitate is usually produced if the colouring 
matter contain only one SO3H group, as in that case the free 
sulphonic acid often is insoluble or sparingly soluble in water. But 
when the free acid contains two sulphonic groups it is soluble 
in water, and hence is not precipitated when the solution of the 
dye is acidulated,^ TropsBolin 3 gives a purple precipitate 
soluble in excess of hydrocldoric acid, and some of the scarlets 
behave similarly. 

The caustic alkalies and ammonia do not usually produce a 
precipitate in solutions of the sulphonated azo-dyes; but they 
often change the colour, owing to the replacement of the hydrogen 
of the hydroxyl groups.^ 

^ This statement does not apply to the benzidine dyes, almost all of which 
are precipitated by dilute acid. 

' Thus a mere trace of alkali changes the dilute solution of maodarin from, 
yellow to crimson (exactly the opposite being true of methyl-orange). 
Scarlets 6 and R and crocein and biebrich scarlets show a similar leactioiB. 
but are far less sensitive than mandarin. Ammonia is almost without actiQiV' 
on solutions of scarlets 2 R and 3 R. 



! concentmteil sdlutions of ninny of the tmo-djee are pre- 
tnted by barium and calcium ohloridea, and in some cases the 
letionB are of analytical interest. The ozo-dyee ae a. ctase are 
arkable for the striking colorations pcotluced when tlie eolid 
» trc.ited with concentrated fiiilphuric nciil, as was first 
|nted oat by J. Spiller (Chvm. A'ewg, x\ii. 191). To apply 
5st it 18 merely necessary to a few graina of the solid , 
uicB in a test-tube or porcelain cmciblo with strong sulphuric 
Very frequently, useful information can be gained by 
serving the spectrum of the coloured liquid obtained. In the 
case of the tetmzo-dyes the colour of the solution in strong 
sulphuric acid is an important indication of the constitution of the 
Ij matter (nee page 198). 
^mong the most characteristic reactions of the azo-dyes is their 
Uiviottr with reducing ngenta, the moat generally Biiitable re- 
tnt for the purpose being hydrochloric acid and zinc or solution 
I stannous chloride. Thus the amido-Hzo-compouuds are split up 
into B primary amino and para-diamine, amido-azoben- 
Mue yielding aniline and paraphenylenc-diamine ( para-di ami do-ben- 
.10):— CoUj.N:N,CeHi.NH,+2H,= C«Hj.NHj+CaH,(NH3V 
rBimilarly, when heliantliin ia reduced it yields the ammonium 
iof Bulphanilic acid (amidobenzenu-sulpbonic acid) and 
nethyl-paradiamidobenzene ; — 

CflH (803NH,).N:N.C8H^.N(CHj,) 
= CflH,(S03NUJNIIa+HjN.CjH,.iV(CHa)j . 
e best way of affecting this reduction is to heat the lielionthin 
Ifthe water-bath with amuionium sulphide until the orange colour 
tppeara. The ammouiacol liquid is agitnled with ether, and the 
I layer separated from the aqueous liquid containing am- 
~mbniutu sulphanilate. The ethereal solution agitated with moist 
hydrated oxide of lead (to get rid of sulphide), filtered, and 
evuporatiid, leaves free dime thy l-paradiamido-benaene. Thia base 

(ll« at 41° and boils at 267*. It forms asbestos-like needles, 
ich when pure are unchatiged on exposure to air, hut otherwise 
D red or violet. It ia readily soluble in water, alcohol, chloro- 
D, and benzene, but less so in ether or petroleum ether. Ii may 
purified by conversion into the sulphate and crystalbsing the 
salt from abaolute alcohol. On treating the free base or a suit 
with a hydrochloric acid solution of sulphuretted hydrogen, a 
ientlid blue coloration ie produced, nip-ihylene blue being formed. 
1 acid solution of stannous chloride reduces the hydroxyazo- 
■ in a similar maimer, the products being u primary amine and 
B^ldophenol. ThuB oxyazobeniene yields a n i I i u e, CgU^NHj, 


iuid para-amiJophenol, CbHj(NHJ.OR MflnOarin split* 
up similarly into sulphanilic acid, C,H„(S03U)NH„ and 
^ntidobetanaphthol, C,oHjj<NH,)OH, When the naphthol 
group is sulphooaled, the amidonaphtbol-sulphoDic ncid decom- 
poses into amido-naphthol and free sulphuric acid. Thus xylidine- 
red is decomposed as follows :— CgHjfCHaJ.NiN^C.oH/SOjNnVOH 
= +2H30CaH,(CHj),NHj,+CioHfl(NHj).OIH-2NaHSO^. With 
an alkoliue reducing agent, such as ammonium sulphide or zinc and 
aimnojiia, the am idonaphthol-disu] phonic scid does not undetgo 

Secondary azo-dyes split up in a similar manner under the 
action of reducing agents. Thus with metallic tin or staimous 
chloride and hydrocliloric acid, biebrich suarlet yields sulphan- 
ilic acid, paradiamido-benezene, and amidonaphthoL With an 
alkaline reducing agent, such as zinc and ammonia, biebrich scailet 
undeigoea a modified decomposition, resulting in thp formation 
of amidohydrazo-benzene sulphouate and amido-nnphtbol, thus: — 
C„H/S03N"a).N:N.C,H,.N:N.CioH,.OH + SHs 
= CoH/SOaNa).NH:NH.CeH^.NHj+CjoH,(NH,).OH . 

On exposing tbn decolorised liquid to the air it rapidly acquires 
a yellow colour, from the production of sodium amido-«so- 
beuzene-sulphonato or acid i/ellow. Other tetrazo-dyea bebare 

Congo-red, the typo of tbe benzidine dyes, on reduction yields 
benzidine and a dinmidonaphthalene-sulphonic acid, CjuHj(SO,H)* 

It will be seen that the investigation of tbe behaviour of the ato- 
dyes with reducing agents aflbrds a most valuable means of recog- 
nising them and ascertaining their constitution. Tbe bases result- 
ing from the treatment can be extracted from the alkaline liquid 
with ether,' and if more than one be produced they can be separated 
by fractional distillation or crystallisation of their salts. Tho 
isolation and identification of the amidophenols is very difficult, 
especially as some of them ore very readily afl.^cted by air. Hence 
it is preferable, when it is desired to obtain tbem in a pur« 
state, to evaporate tbe neutralised solution to dryness, and faeat 
the residue with anhydrous sodium carbonate. 

The following table gives some of tbe leading characters of certun 
of the bases produced by the reduction of commercial azo-dyes: — 

' Whenever nn amidonsphtbol-Bulphonio ncid Ji a product of tbe rviluetioB, 
it decomposes into bd amidouaphthol and free Bulphurie ociU, if a 
reducing "gfit he employed ; but is not decomposod, and lienco does oot {an 
into th« edier, nhen sniiDoniara sulphide ii used aa the reiluclng ognuL 







Point "c 

Utlier L'liinctcm. 


£=^ } 

Sparingly aolublo. Vlalet 


colour with bluahlug aol- 


Brown coltmi wltb bleaching 

h^-lalnidlna. \ 



dilution. Colour .ol«bl? 
in Mlwr. and changed to 
I>ink by dllale acetic acid. 

—""•"' * 




changing to red. 

.™»»,,. > 

odour. Tom. SSlt on 



HO ■ 

eyHHure, Fed, aud other 

Nearly iuoluble platea. 

Dew blue coluur on add- 




ing to lu Bolutlon In pan 

aulphurlc acid a trace ol 


Small luitnjiu pUtsa, bo- 




... - 

flparingly mluble taUuta. 

UnOi and dilute H^Oj^ 
Baailyaoluble. OKeimethyl 





SffiS""'- } 




or H^ In hydrochloric 
acid, ^pagem. 
Calonrleai nialea, rapidly 
turning bro-n-'AlkSuM 
aolollon becomaa vlidet 




qulnoue with oildlalnB 
agenta. With blea.;bing 

On^^'SSl^DB ^""aUaUiw 
MluUon with air, a dirty 
green colour il produced. 




cal UDOunt ol s-naphlba- 

Ou aglUlbw Ibe alkaUne 
•Dlutlon with air. prrmau- 



and imn nam anliible in 
alcohol topuregnmn eol- 
ntion. Brand feci, jrlve 
yellowlih or green \m- 

ffS '• "™- " 

Flat plateatumlrg green In 


the air. K.HOgl.e,d«p 



green and lirown. i^, 
glm deep lirown colour, 
and then nearly black 





Rosaniline, a base of which the salts are usually known in com- 
merce as fuchsine and magenta, was one of the first — ^and still is 
one of the most interesting and important — of the basic colouring 
matters obtained from coal-tar. It is the type of a large number of 
bodies, not a few of which are or have been of practical importance. 
Many of them dye silk and wool without the aid of a mordant^ 
and by suitable means they can also be fixed on vegetable fibres. 

Kosaniline and its allies are derivatives of the hydrocarbon 
triphenylmethane, obtained by the action of benzene on 
chloroform, in presence of aluminium chloride : — H.C'Cl3 + 
3CeH5.H = 3HCl+(C6H5)8;C.H. By oxidation of the hydrocar- 
bon with chromic acid in glacial acetic acid solution at 100° C. 
(vol. ii. page 626), triphenyl-methyl alcohol or tri- 
phenyl carbinol, (C5H5)3C.OH, is obtained. On the other 
hand, when slowly added to cold fuming nitric acid, triphenyl- 
methane is converted into the trinitro -derivative, (€5114X02)3011 
Tliis may be oxidised by treatment with chromic acid to the 
corresponding carbinol, (CgH4N02)3:C.OH, which when partially 
reduced by zinc-dust and acetic acid is converted into p a r a r s - 
aniline, (0^114X112)30.011. Hence, pararosaniline has the con- 
stitution of a triamidotriphenyl-carbinol, while its 
liomologue rosaniline is methyl-pararosaniline or 

Pararosaniline. Rosaniline. 

OeH4.NH2 ( 0,H,(gH3).NH2 

O5H4.NH2 J O6H4.XH2 

0,H4.NH2 ) C«H4.NH2 

OH (oh 

By the action of reducing agents the bases lose oxygen. Thus 
rosaniline yields leucaniline, (C7HgNH2)(CeH4NH2)2:CH, and 
pararosaniline the lower homologue triamido-triphenyl- 
methane, (CeH4NH2)3:CH. The salts of these bases are colourless. 

Pararosaniline and rosaniline are well-defined bases which 
react with acids to form salts, with elimination of the elements of 
water. Thus with hydrochloric acid, rosaniline reacts in the follow- 
ing manner : — OgoHj^NjO + HCl = OgoH^gNg-HOl -f- HjO. In con- 
stitutional formulae the reaction must be expressed as follows '} — 

^ The formula for rosaniline hydrochloride given in the text shows one 

nitrogen atom as exercising pentavalent functions, and is generally regarded as 

th<! most probable. An alternative view of the constitution of magenta is :— 

pj CeH4.NH, 
^^ aH4.NH, 

( C^H„(CH3).NH, 
) C9H,.NH, 

r c^n^(CH.).NiL 

? CH.NH,, 
( C„H,.N]Ii.Cl 


ul the amido -derivatives of di- . 
siTiiilarly with acids. 

On account of this |)cculiar behaviour, the constitution of 
rosaniline and ite allies was formerly misunderstood, but for 
rt-'presontinij many of their reactions the formulae of the anhydrides 
luay lie conveniently used. 

When a mixture of one molecule of parti- toluidine with two of 
aniline is treated with an oxidising agent of moderate power, such 
na arsenic acid or mercuric chloride or nitrate, pararosaniliue 
resulte ; and when a molecule of ortho- toluidine is suhstituted fur 
the second molecule of aniline, rosaniline is produced, according 
to the ociuationr— CH,°.C,H4.NH2+CaH(,.>lHj+CH3°.C„H,.NH, 
+ Oj = Ca„H,|NjO + SH^O. 

By treatment with nitrous acid, rosaniline and pnrorosaiuline 
are converted into tosaurin and aurin respectively, white, on 
tbe other hand, by heating rosauriu and aurin to 120'^ with strong; 
ammonia the reverse a<!tion ocicurs, and roaaniline and pararosaniline 
are respectively obtained (see pmge 161). 

Rosaniline and pararosaniline are themselves colourless, but 
their salts are remarkable for the intense crimson-red colour of 
their solutions. Kosaniline hydrochloride forms the commerciid 
ilyo known na mat/enla or /uafmni', ; while acul mageiita is a 
mixture of tlio sodium salts of several rosaniline-anlphonic acids. 

From the residues of the manufiicture of rosaniline the less 
hydrogeniaed haaes chryaaniltne, CiBHmNj. and chryao- 
toluidine, C^H,yN,, are also obtainable. They are romark- 
ftblo for forming ulraost insoluble nitrates, and the hydrochlorides 
constitute the commercial product known as phiMpkine or aniline 
rimnge. Sa/raniiie and tbe indtdinm ure also secondaiy products 
i>f the manufacture of rosaniline. 

By heating a salt of rosaniline with aniline, one, two, or three 
atoms of hydrogen in the original base may be replaced by the 
radicnl phenyl, with the formation of m o n o -, d i -, or lastly, t r i- 
phenylrosauiline, CjoH,g(CBH5)jNaO. These substituted pro- 
ilucts biiwmo more intensely blue with each rejilacement of the 
hydrogen atoms, ho that tbe salts of the mono-ilerivativo are reddish' 
violet, those of diphcnyl-rosoniline bluish-violet, while the tri- 
phenyl&teid base yields salts of n nearly pure blue {Blea de 
Parti, page 224). 


The dye known as 'liph'-nylamine-btw U of similar conatitotion 
to Paris blue, \mrtg the hydrucliloriJo of triphonylporaroe- 
aniline. It is obtained by heating dipheuylsQiino with oxolii- 
neid: — 3{C«H,)jSH4-C,HjO, = 3HjO+CO + C,^n(C8Hj),K, 
The dye aniline, obtained by heating aurin with aniline and buotuii' 
acid, ia apparently an impure kind of diphenylamine blue. By the 
action of methyl chloride or ethyl chloride on diphenylamine blin.'. 
or by using methyl- or etbyl-diphenylaniine in the process iif 
manufacture, eubstitution- products are obtained, the hydrochlorides 
of which are known iu commerce aa jnethyl bluti and ethj/l IJur. 
They dye a purer blue shade than the unsubstituted diphenyl- 
amine blue. If a mixture of diphenylamine (plienylaniline) and 
pbenyltoluidine (instend of the former base only) be heated with 
oxalic acid or carbon hcxachloride, tripbenylrosaailiDe, 
C»H,5(C„Hs),Ns, is obtained. 

Just as several of the atoms of rosaniline and pararosanilint- 
may be replaced by phenyl or tolyl, so may the radicals ethyl ot 
methyl be substituted for one, two, or three atoms of the hy- 
drogen ill rosaniline. The replacement ia efTe'cted by bwting 
magenta or free rosaniline with alcoholic potash or soda and 
chloride or iodide of methyl The Hofmatm'i viiM* so obtainal 
range from RRK, the very red, wliich is chiefly a salt of m o n »< 
methyl-roaaniline, CmH„(CH,)N30, to BBB, the blm-sl 
shade, consisting of the highest substitution-products.' Similar, but 
not identical, dyes may be obtained by introducing the methyl or ethyl 
ndica] into aniline or diphenyl-amine before submitting the Utt«'i 
to the action of oxidising agents. Methyl violet is thus produced. 

The colouring matter known ae jiialachile 'jr»-n or bcnalde- 
hyde green differs from all tho preceding in the fact that only 
two insteatl of all three of the phenyl groups of the trijihenjl 
carbinol are amido-aubstitutod. Thus malachite green in a salt 
of t e tramethy t-diamido-triphenyl-carbinol, aiid 
hrSlianl grtm, helrrlia yrawt, /an! t/rceji, and re»orHn purple hav' 
an allied constitution. 

Many of the basic colouring matters of the rosaniline grauj' 
are convertible into more readily applicable dyes by s u 1 p It o n s- 
tion. The sulphonuted dyes thus obtained are readily solublr, 
and dye silk and wool in acid baths. Usually they are Dol 
readily Kxed on cotton, except o/Ao/t btu». in which the basiv 
character of tho Paris blue from which it is derived is not wholl]' 
destroyed by conversion into a mono-aulphonic acid. 

' It ia a curious fitct that while the sulistitulMl roaanilinea twcont btau 
with «iuh replace uiant of tho hyilrogon nUiins by pbenyl, tolyl, methyl, "r 
Mhyl, rliL' i^oloiir of the Bulistituted inauvrina folluws Ihv mnrw rale. 


217 I 

1 some oases, as in that of acid magenia, the eulphonated dye | 
tioa the hjdroxyl group of the rosoniline from which it is I 
derived, and hence is of the carbinol type. In other cases, as fnr 
inabuice in alladi-btue, the eulphonated dye appears to lose the 
elenients of vater, just aa the basic dye does on comhining with I 

racid. This is illustrated by the following examples, which ' 
oe to indicate the foruulx of the whole class : — 

Aciil Maijmta, 




1 NH, 

-j CgH^.NH(C„Hj) 


k.The colouring mattera of the rosaniline group may be con- j 
Miently classified as aniline red, aniline blues, aniline violets, 
Uine greens, and associated dyes. This arrangement will be 
Dptcd in their description. 
Kosaniline. Aniline Bed. Triamidotolyl-diphenyl-car- 
binoh Ca,Hs,N30 = (CBlI«NH,>i,(CjngNHa)C0H. 

Rosaniline is the artiRcial organic base the salts of which form 
the magnificent dyeing materials known as amHru^-red, magmta, 
fuehsine, aixileme, rulnne, and by otlier more fanciful names. 
The colouring matter is produced whenever a mixture of anihne 
and toluidine is heated to about 180° C. with an oxidising agent of 
moderate power. A. "W. Hofmann showed that the presence 
of both aniline and toluidine — which coejcist in commercial aniluie 
oils — was essential to the production of the colour, and represented 
th e reaction thus :— C,HiN + 2C7HgN + O, = C„H,BNi,+ 3Ha0. 
J recent researches of E. & 0. Fischer have shown 
I Iha tree base contains oxygen, and on reacting with acids loses 
E elements of water (page 2 1 4). 
i groat number of methods of oxidising aniline oil for the 
idliclion of rosaniline have been employed and patented, but 
r thre« are in general use, namely : — the arsenic acid, the 
! nitrate, and the nitrobenzene processes.* According to 

EAofiotdlng to Boiisdikt, add magenta is a mixture of ths locliuni ults of , 
>■ anil di-mlpbonAtcd roEinlliTie. 

ling to the arnmif acul procem, 100 p«rW of " »nililiii oil for red " 
" "8 ports of araonic acid of 76' Bnumi^ for oigiit honra lo a 


the oxidising agent employed, and the subsequent treatment, the 
product may be the hydrochloride, nitrate, acetate, or other salt of 
rosaniline, but the first is now by far the most commonly met with. 

Free rosaniline can be obtained by precipitating a solution of 
either of the commercial salts of rosaniline by excess of ammonia. 
If a boiling solution of the hydrochloride be employed, a reddish 
crystalline precipitate is produced, and the colourless liquid deposits 
on cooling a further crop of crystals of the pure base in colourless 
needles and plates, which have the composition C20H21N3O or 

Rosaniline is a non-volatile, colourless, bitter substance. Heated 
in boiling water it melts, and dissolves to the extent of 0*3 per 
cent., a portion being deposited on cooling. In alcohol it dissolves 
in the proportion of about 1 per cent. In ether, rosaniline dissolves 
to form a colourless solution, which dyes silk crimson, and gives 
a fine crimson colour on agitation with dilute acetic acid. In benzene, 
rosaniline is said to be insoluble, but it is very soluble in aniline. 

temperature somewhat exceeding the boiling point of aniline, in a boiler fitted 
with a condensing tube. Water and a part of the aniline employed distil 
over. The residue is boiled with water, and the liquid filtered from the in- 
soluble matter, which contains mauvaniline, violaniline, and some 
chrysaniline. The solution, which contains arseniate and arsenite of 
rosaniline, chrysaniline, excess of arsenic acid, and resinous sab- 
stances, is treated with a large excess of common salt. Sodium arsenite and 
arseniate and rosaniline hydrochloride are formed, and the last of these, being 
sparingly soluble in strong brine, separates out. The precipitated colonriDg 
matter is dissolved in water and purified by crystallisation or again precipitated 
by the addition of salt. The mother-liquors yield an impure magenta, known 
as cerise or geranium. The arsenic is recovered by treating the waste-liquors 
with lime, when arsenite and arseniate of calcium are precipitated. The 
resinous matters may be used for the production of the colouring matters 
known as grenadin and maroon. 

A very pure nitrate of rosaniline may be obtained by oxidising aniline oil 
with Tnercurie nitra^y and this may be converted into the hydrochloride by 
double decomposition with common salt. 

Instead of using arsenic acid, nitrobenzene and ferrous chloride are some- 
times employed. The latter body is oxidised by the nitrobenzene, and the 
product in turn oxidises the aniline, so that it acts as a carrier of oxygen. 100 
parts of aniline oil are treated with two-thiids of the amount of hydrochloric 
acid required for neutralisation, and 50 parts of nitrobenzene added. The 
mixture is heated, while from 8 to 5 parts of iron filings are gradually added. 
Tlie eubsequent operations are the same as in the arsenic acid process. The 
bye-products contain much induline, but no chrysaniline. 

A valuable article on the manufacture of magenta has been published by 
P. S c h o o p in Dingier' s Polytechniache Journal, cclviii. 276, and translated 
in t/our. Soe. Dyers, dec, ii. 118. 


RosimUine loses no water at 100° C. When heiited alone to 
nUiut 130°, it is dccomiiosed. I! tbo free base or one of its SEiltB 
Iw henttii with water under pressure to nbout 240' C, phenol and 
Miimouia are produced, with other products ; but if the water be 
acidulated with hydrochloric acid, or if the rosnniline be heated 
Willi concentrated hyilriodiu aeid, it is completely reaolved into 
uoiline and toluidine. 

Salts or Rosanilinb. Roaaniline is a well-defiii'i'd and powerful 
>itt8e, capable of coinhininf; with either one, two, or three equivaleute 
of an acid. The tri-acid salts are brownish-yellow, both in 
the solid state and in solution, and arc readily soluble in water 
and alcohoL The di-acid salts are little known and difli cult 
topnpare. The mono-acid salts, typified by ordinary mai/^a, 
um the most interesting and important. They nre stable crystalline 
bodies having a beetle -green metallic lustre, and are mostly 
nuluble in water and alcohol, formiiij^ violet-red, non-fluorescent 
solutions uf high tinctoritd power. Their solutions dye ailk and 
wool a niagniticent crimson colour, without the aid of a mordant, 
Hnd by proper means the colour nmy be fixed on vegetable fibres, 
Vormerly, English-made mwjcnia was generally rosaniline acetate ; 
ttie French article known as roseine consisted of the hydnichloride ; 
while the nitrate was known as nibinA or azaleine. 

RiiaaniUne Acetate, CapHj^N^iCnH^Oj, forms magnificent crystals 
with a beetle-green reHeotion, which are apt to turn brownish-red. 
It is one of the soluble of the salts of rostmiline, and also 
dissolves freely in alcohol. The acetate was formerly the most 
commonly occurring salt of rosaniline, hut latterly has been supcr- 
acdnl by llie hytlrochloride. 

Rimaniiine Chnrnmle is a brick-red, nearly iuFoluhle powder. 

HoHaniliite IJydnichloride, or Hydrochlorate of Rosaniline, 
Cj^(gNa,UCl. This compound, which constitutes the ordinary 
magenta, fwAnw, or rogeine of commerce, crystidlises in vety 
emuU, deliiiuescent rhombic plates, which ore somewhat aparinnly 
Muluhlo in puro wnter, but more ntadily in acidulated water and in 
alrahol. It is also soluble in amylic alcohol, but insoluble in etiier. 
RoMuiline hydrochloride combines with platinic chloride to form 
an uncryetailisable chloroplatinate. With concentrated 
hydmchloric ncid, rosaniline hydrochloride yields brown needles of 
thP triftcid anit, C«H,9Na.3HCI. This body dissolves in a 
little water with brown colour, but on dilution splits up into hydro- 
chloric aewl and the mono-acid salt, the re-torniation of which is 
indictttcd by the change of the colour of the solution to crimson, 

fiomtnilitie Nitmte, CguHmXn.HNOg, constitutes the commercial 
a known as amlnne and nthiite. It is not often met with. 


JiDsanilittt! Pifrate forms magnificent reddieh needles, nearly 
insoluble in water. 

RomnSiTte Sulp/uife much resembles iLe hydrochloride. 

RomnHine Tannate has a pmctii^ importance in dyeing, » 
its insolubility in wnter affords a means of fixing the colouring 
matter on vegetable fibres, and of recoverbg rosaniiine Itom spent 
dye-liquors. It dissolves in alcohol, wood spirit, and ac«tic add. 

Maobnta. Fuchhine. AKiLiyn Rkd. These names, as alsn 
ruheiite, rimeine, asileine, Ac., are used to signify the salts of 
rosanilino 09 occurring in commerce. Formerly, tlie Snglisli' 
made product generally consisted of rosaniline acetate, 
and was known as magenta; the French article calleil ruwiw 
consisted of the hydrochloride; while the nitrate wu 
known as ntleinc or aaileijic} Sow the hydrochloride has to a 
great extent superseded the acetate and nitrate of rosaniline, niA 
the distinction is no longer observed. The following reactions an 
common to all the commercial varieties of magenta. 

Magenta usually occurs in beetle-green crystals or as a dark- 
green crystalline powder. It dissolves in water with magniiicaiit 
crimson colour without fluorescence. The dilute aqueous ind 
alcoholic solutions of magenta exhibit characteristic ahsorpticn* 
spectra, having a well-defined black baud between the Fraunhof*r 
lines D and E. 

Solutions uf magenta dye silk and wool without a moidauU 
The colouring matter is partially removed by boiling water, wMa 
soap removes it completely. 

Caustic alknlicB, ammonia, baryta, lime, and magnesia decompote 
solutions of magenta, free rosaniline being precipitated in ■ 
crystalline and nearly colourless state. If magnesia bo nsed,* and 
the operation conducted in a boiling hot liquid, so that some of thft 

' Magetita-mokt or /uehtine f ib a mixtare of TosanJline and maavanJIiM 

CffrtK U ■ ealonriug matter conttining magenta, and ia used in djaisg 
broWDs. The mather-liqQoTs from which maf^ntii hu been ulMdoal contain' 
phosphine, unprecipilated mageats, aad a brown ooloariag matter. They tn 
trented with milk at litup, and t]>e precipitate aeparaled, diiuolTSd in aditn- 
Ikted water, and salted out. The oerise obtained fornii an unorphoua b 
mata, with a vitreoua fracture. 

JfarooH and grenadiit are farown colouring matters obtained by pnti^riai 
the reainoas inatteis formed in the manufacture of magenta. 

Cardinal and amaranlh consist of mixtures containing magenta •■ tha el 

* If one of the other bases mentioned in the text beaubatituted for magne 
it should be added gradually, and only in sufficient iinantity to afTnit tx 
dacompositiDii. as indicated by the di'coluritjiliuu of the solution. 


libemted Tosaniltnc may rcmaiu in solution, nud the liquiil be then 
tillered out of contact with air, a colourless filtrate is obtained. 
Un passing carbon dioxide, or the air exhaled from the lungs, 
through this colourleM solution of roanniline, a crimson coloration is 
produced, owing to the formation of ros&uiline carbonate. 
The reaction constitutes a delicate test for carbon dioxide. 

If a solution of magenta be treated with excess of soda or 
animotiia and then agitated with ether, the liberated rosaniline 
dissolves. The aeparnted ethereal solution is colourless, but dyes 
silk a fine crimson, and on slinking with dilute acetic acid yields a 
crimson solution. 

Excess of strong hydrochloric acid turns magenta solutious 
yellow or brown, owing to the formation of a triacid salt, 
which is decomposed on copious dilution, or on adding a solu- 
tjou of sodium acetate, with restoration of the original crimson 

Reducing agents, such as zinc and acetic or hydrochloric acid, 
stannous chloride, sulphurous acid, &e., decolorise solutions of 
magenta with formation of colourless salts of leucaniline, 
C,o^„Ng. This base differs from the products resulting from the 
Nduction of safranine, magdala-red, and certain other colouring 
matters, in not being reconverted into rosaniline by atmospheric 
oxygen. On the other hand, oxidation of leucaniline to rosaniline 
con be effected by manganese dioxide, chloranil, and similar agents. 
Strong oxidising agents, such as permanganates, hypochlorites, 
otid chlorine, decolorise solutions of magenta. Oxidising agents 
of moderate power produce new colouring matters, a yellowish-red 
product known as aniline-scarttt being formed by the action of 
hydrogen peroxide or lead nitrate. Chromic acid acts on magenta 
wiUi formation of a brown colouring matter. 

Aldehyde and alcoholic solution of sheUac convert magenta into 
blue colouring matters. 

Solid magenta dissolves in strong sulphuric acid with yellowiah- 
brown colour, becoming violet-red on dilution with water. 

Dbtbctiok of Mao£NTA. \Viien perfectly pure, magenta is not 
poisonous, but as occurring in commerce it frequently contains 
•nenic, and hence is unsuitable for colouring confectionery, 
ayrups, wine, &c. Its use for such purposes is absolutely foi- 
bidden in some countries. 

The detection of magenta is based on the foregoing reactions, but 

rder to apply these satisfactorily it is usually necessary to 

e the colouring matter more or less perfectly. 

ir tlie detection of magenta in ivine or other coloured liquids,' 

10 frotb of wiue vol(iur«d with mBgeota bos a distinct violet tint. 


about 50 ex. of the sample should be treated with excess of baryta 
water, heated to boiling, and filtered. The filtered liquid is then 
cooled and shaken with ether, which will take up the rosaniline. 
The ethereal solution, though colourless or nearly so, will com- 
municate a violet-red colour to dilute acetic acid, and the resultant 
solution will exhibit a characteristic absorption-spectrum.^ On 
evaporation to dryness, the ethereal solution will yield a residue 
soluble in strong hydrochloric acid with yellow-brown colour, 
changed to violet-red on dilution, and permanently decolorised by 
warming with zinc. If a thread of white silk or wool be placed 
in the ethereal solution, and the ether allowed to evaporate, the 
rosaniline will be taken up by the fibre, which will acquire a 
crimson colour when moistened with dilute acetic acid. A fairly 
approximate colorimctric determination of the magenta present may 
be obtained by comparing the tint with those of standard specimens 
of wool or silk prepared in a similar manner with known quantities 
of the colouring matter. 

A modification of the above test consists in rendering 50 cc of 
the wine slightly alkaline with ammonia and boiling the liquid with 
a little white wool till all the alcohol and ammonia are expelled 
The wool is then removed, washed with water, and at once heated 
with a few drops of caustic soda solution till dissolved. After 
cooling, about 5 c.c. of water and the same measure of alcohol are 
added, and the liquid is shaken up with 10 c.c. of ether. The 
ethereal solution is then separated, and examined as already 

An alternative process for the detection of magenta in wine is to 
warm 50 c.c. with a strong solution of lead acetate, filter, and tu\d 
one drop of acetic acid to the filtrate. This is next shaken with 
10 c.c. of amylic alcohol, which will remain colourless if the wine 
be pure, but will be coloured red in the presence of magenta^ red- 
violet by archU^ and yellow by rosolic acid. If the amylic alcohol 
be separated and agitated with dilute ammonia, it will be de- 
colorised, the ammoniacal liquid acquiring a bluish- violet colour if 
archil and a red-violet if rosolic acid be present, while magenta 
communicates no marked colour to the ammonia. 

Of late years, the use of ordinary magenta for colouring wine has 
been to a great extent superseded by that of other coal-tar dyes, 

^ In the Paris Municipal Laboratory, where a large number of wines are 
examined, it ia usual to test for basic coal-tar dyes, including ordinary magenta, 
by adding enough baryta water to render the wine slightly alkaline, and then 
shaking with amylic alcohol or acetic ether. The upper layer, either imme- 
diately or after acidulation with acetic acid, will be coloured if a baric dye be 


ospectally the aulphoiiated rosnniline known as acid magimla (page 
236). To detect this colouring matter, J. Heri {Anali/M, xi. 
175) recominends that from 30 to 50 c.c. of the wine, or prefer- 
ably 100 c.c. previously conuentraltHi to that volume, should be 
treatuit with half its measure of a cold saturatod solution of 
lua^niisiiiui sulphate, and then from 10 to 20 c,c. of a strong 
solution of caustic soda stirred iu. The precipitate of maguesium 
hydroxide carries down with it all the natural colouring matter of 
the wine, and also most of the ortilicinl colouring mattera, except 
nrchil and sulphonated magenta. If the filtrate be not colourless, 
or at most merely yellowiah-red, the treatment with magnesium 
sulphate and soda shoultl be repteated. A colourless or yellowish 
filtrate having been obtained, il is ar.idukted with dilute sulphuric 
ncid, when if acid magenta or other sulphonated dye he present 
the li']uid will rc-.icquire its original violet-red colour, and from the 
de[ith uf the tint an approximitte estimate of the amount present 
can be made. If art'bil be present, the alkaline filtrate will be 
bluish, becoming litmus-red on addition of acid. If the excess of 
acid be nearly neutralised, and the coloured liquid be shaken for 
some minutes with peroxide of lead and filtered, a colourless liltrate 
will be obtained if the previous coloration was due to archil, 
while in the case of the acid tnaijmta the red colour remains, and 
■U intensity indicates the amount of the dye present. 

The gelatinous precipitate of magnesium hydroxide is next 
stirred up with hot water, and the liquid separated by decantntiou 
or filtration.' The precipitate ia then mixed with sand, dried at 
100", and exhausted with ether. The ethereal solution will con- 
tain any ordinary magenta present in the original wine, and can 
be examined in the manner already described (page 222). Her/ 
mentiouB a dye called eamifine which is extracted together with 
the ordinary magenta, but dyes wool reddish-brown and is left as 
a reddisb-brown residue on evajHirating the ethereal solution. The 
dyed wool becomes yellow when treateil with strong hydrochloric 
^^uld, and colourless on adding ammonia. 

^^^E& If ODly the natural colouring matter cf tbo wine be present, or bilbarg 

^^H^lwtn uied, this liquid ti yoUowUb-browu ; vcith archil, dark violet ; wilh 

^^^Bwau, onion or ponceBu red : with autiaaitu, {inle red or dark jellow ; and 

^^TrWi niaicoliM bordelaite, jellowi»h-rad or reddiah- brown, giving a violet 

lona when pourud on tbo anrjaus of strong Bulphurio acid. Thia last colouring 

matter i« aaid to be a niiitura o{ Biebrich rod and oldBrberry extract, ir tbe 

eolonred liquid b« agitated with amjlic alcohol, and the solution so abtained 

mtm), Ihe residue will be dark grey or brovniah-grey if only natunil or 

ring nialUis are )iresent ; violet in presooce a( artltil; dirty 

[• witb either onliiwry or acid magenta ; dirty yellow-brown with aMsunn«; 



To detect magenta in wine, K. Kayaer {Jour. Stjc. Chum. 
I'ui., tv. 291) recommends tliat 100 cc. of the sample should be 
Mliaken with 20 c.o. of colourkas amylic alcohol. The lic^uld li 
then diluted with water and the amylic alcohol layer examinH 
with a epoctroscope. If the chotacteristic absorptioD-baiids of 
magenta are observed, another portion of the tiample should be 
treated with gxcoss of ammonia, and shaken with amylic alcohol 
as before, which will be coloured red by ordinary magenta, while 
sulphonated magenta is not extracted from alkaline liquids,' 

In the Paris Municipal Laboratory, for the detection of a^ 
d;ies in n-ine, 10 ax. of the sample is rendered strongly alkalin« 
by the addition of 2 to 3 cc. of a 6 per cent, solution of caustic 
potash; from 2 to 3 cc. of a 20 per cent, solution of mercuric 
iicetate is next added, and the whole well shaken and filtered. 
With pure wine, the filtrate is colourless, and remains so even 
after acidulation with hydrochloric acid, but will be yellow oi 
red if acid magenta or other sulphonated coal-tar dye be present. 

Further information respecting the detection of foreign colouring 
matters in wine will be found in toL i. pages 86 to 88. 

The methods already described fur the detection of magenta in 
wine are applicable to other articles coloured by it. 

The detection of magenta on fibres dyed with it presents no 
difficulty. The colour is destroyed by sodium siUphide, owing to 
its reduction to leucaniline. Alkalies also bleach the colour from 
liberation of rosaniline, which may be extracted by ether (see page 

' It is not avident why free rosauiiine sliould coltinr «mjlio tluohol w statid. 
TLera ia alaoadiaci'Bpancy botween thb processand theeipericuce of J. H<ti^ 
who dooa not tppoar to hare obaervad the extToctioo oF either ordiaaty or leid 
nifgenta from acid aolatione by trentmcnt nith ninylic alcohoL On tin oon- 
trary, he ffnAa that the colour of the wine after the treatment in cherry-rad 
in the presence of ordinnry ■niageTila, reildiflh-Tiolet with aeid magtiUa., dark 
uhen-y-red with Bordamx B ; and j'elluwiah-red with pmttaa SRR. On 
ovipor&ting the amytjc alcohol solution to diynees and testing the ceddiie widi 
reagctitu, Hen obscrred the Eollawing 

Colouring Matter. 

BMidDS iRHd AutUc AlmhoL 







Vide t- red. 




222). Strong liyJrochlorit ncid turns the fnliric yellow or brown, 
the colour being restored by copious dilution. 

Liebmann and Studer (Jour. S<ie. Ckem. Ind., v. 288) 
recommend that 100 c.c, of the wine should be evaporated to 
abont 1 c.c, eaturated with sulphur dioxide, and then precipitated 
with lend acetate To the filtered liquid a drop of aldehyde or 
acetone ia ad<ted, when a violet coloration wOl be produced if 
magenta or acid magenta be present even in the proportion of one 
niiUigraniiiie per litre. The teat is equally applicable to syrups, 
lowDgoB, &e. The treatmeut with lead acetate is not essential. A 
similar method may be employed for the detection of magenta in 
ctidbcar and archil. 

In testing wine for magenta it should always be borne in mind 
that the colouring matter is precipitated by tannin, and hence is 
often present moat largely in the deposit, from which it be ex- 
tracted by treatment with an alkali and agitation with ether. 

I^XAHiKATloM OF CoHMBRCtAL Maoenta. Pure magenta con- 
sists simply of the hydrochloride or other salt of rosaniline, mixed 
with more or less of the corresponding compound of pararosaniline. 
The commercial product generally contains, in addition, mure or 
less water, mineral impurities, resinous substances, and, if prepared 
by the arsenic acid process, a notable quantity of arsenic. Besides 
these imparities, actual adulterants are sometimes present, the 
most usual being sugar, starch, dextrin, sodium sulphate, and 
occtsionolly bronze powder. 

Magenta of good quality being generally well crystallised, 
powdered or imperfectly crystalline specimens are always open 
to suspicion. 

The blue shades of magenta are generally the purest. The 
yellow shades, if made by the arsenic acid process, usually contain 
phofphiw; magenta made by the nitrobenzene process contains no 

A solution of pure magenta is entirely decolorised by sulphurous 
Hcid, while impure samples arc turned yellow or brown ; or the hot 
aqueous solution of the sample may be treated with hydrochloric 
acid, and xinc-dust then gradually added in small quantities at a 
time, till the red colour is destroyed. With pure magenta the 
reduced liquid wiU be colourless, but if c/iri/mmline be present 
it will have a yellow tint. 

Ammiic is sometimes present in commercial mt^imta in con- 

■itleruble proportion, as much as 6} per cent, having been met 

with. It may he detected by Marsh's test. For its determination. 

tlio acidulated solution may be treated with bromine water, excess 

T ammonia added, the liquid filtered if necessary, and mitgnosia 

"KroL. m. VABT i. p 


mixture then added. A precipitate of the ammonio-magnesiam 
arseniate, deposited in streaks in the track of the glass rod used 
for stirring, will be gradually formed if arsenic be present. The 
arseniate may be distinguished from the similar phosphate by 
washing the precipitate or streaks with water, and adding silver 
nitrate, when the arseniate will be turned brown, or the phosphate 

The detection of other impurities and adulterants of magenta 
will be described in the section on the '* Examination of Com- 
mercial Colouring Matters." 

Acid Magenta (page 217), called also magenta S and rtMne S, is 
obtained by heating ordinary magenta with fuming sulphuric acid 
or sulphonic chloride, SO3HCL The product is poured into water, 
neutralised with milk of lime, the solution filtered from the 
calcium sulphate, and the filtrate decomposed by sodium carbonate. 
The calcium carbonate is filtered off and the filtrate evaporated to 
dryness. Acid magenta occurs in grains or powder of a green 
colour and metallic lustre. It dissolves readily in water, forming 
a bluish-red solution, which is nearly decolorised by alkalies with- 
out a precipitate being formed, and nothing is yielded to ether. 
Dilute acids, even carbonic acid, restore the colour, which is not 
materially altered by a considerable excess. In strong sulphuric 
acid, the solid dye dissolves with yellow colour, becoming gradually 
red on dilution. 

According to C. Blarez, all red coal-tar dyes except acid 
magenta, and also all red vegetable colouring matters, are com- 
pletely decolorised when their aqueous solutions are slightly 
acidulated with tartaric acid and digested with dioxide of 

In its behaviour with reducing agents and acetone, acid magenta 
reacts like the basic dye. 

Acid magenta is employed for colouring red wines. Being 
insoluble in ether, either in acid or alkaline liquids, it may be 
distinguished from ordinary magenta, and may be more definitely 
recognised as described on page 223. 

Acid magenta has only about half the dyeing power of ordinary 
magenta, but can be dyed from strongly acid baths, and hence is 
conveniently employed in conjunction with acid yellow, indigo- 
carmine, &c. 

On the fibre, acid magenta is unaffected in colour by a mixture 
of equal measures of hydrochloric acid and water, whereas 
ordinary magenta is turned yellow or brown. The reagent dis- 
solves some of the acid magenta, and acquires a cheny-red 


Aniliae Blues. 

As Btatti! fdreaJy {page 215), tho plipnylatril dfirivittives o 
rosaniline and parnrosaiiiUne dye tOuer shades thnn the iiiiBiibsti 
tilted liuses, and this in proportion to the number of hydrogen 
atoms rHplaoed by phenyl, C^ll.^. Thus the colouring matter 
known as regina motet (page 233) is uhieSy a salt of diphanyl 
nrnnniline, while tho various commercial aniline blues are mostly 
trijibenyhited derivatives; ami Benerlikt statos that hoxaphenyl 
rosanilioe }-ieIde a purer blue than any other colouring matter known. 

Besides a few aniline colours of a somewhat dlHerent nonstitu- 
tion, there occur in eommerce two parallel series of blue dyea, whiuh 
are triphejiylated derivatives of pamrosaniline and rosaniline re- 
spectively. Thus : — 




AllilU blue D. SotabiB Di- 
Mrthyl blirui ro'r cottoE. 

KouniliDB bine. AdIIIub 
bjije. spirit W«.. S^ 

Alklll blue. Solubto bins. 
SoliiblfblUB. Chin. Win. 

The parallel compounds from para-rosaniline and rosaniline 
present a close analytical and general resemblance. In addition, the 

more or less of their lower homologuea (from para-rosaniline), ant; 

hence there ]» no sharp distinction between the two series of dyes 

UiPBB.vvuDdNE Blue or Para-rosaniline Blue is the hydrochloride 

It is prei>ated by heating di pheny lamine, (CoHs),:NH, to 
120*- 1 30" with oxalic acid. The exceaa of oxalic acid is removed 
by washing wiUi water, and unaltered diphenylamlne by Ixilling 
witli bcuxeue, the residue being then converted into the hydro- 
chloride. The comnierLiial dye forms a lirowniah powder, having 
Ml odottr resembling that of di pheny lamine. It is insoluble in 
watOT, ami only sparingly soluble in cold alcohol, but dissolves 
more readily on heating. The solution is turned greenish b> 
bydrcKiidorie acid. A two per cent, solution of the colouring matter 
^in methylated spirit is employed to produce light and very pure 
H|badea of blue on silk. Dipbenylamine blue dissolves in Btron<, 



sulphuric acid with brownish-yellow colour, a blue precipitate being 
produced on dilution. 

The colouring matter known as azaline or azurine is an impure 
hydrochloride of triphenyl-parai*osaniline. 

Colouring matters known as methyl blue and ethyl blue are 
obtainable by the action of methyl or ethyl chloride on diphenyl- 
amine blue ; or by heating methyl- or ethyl-diphenylamine with 
oxalic acid. The products dye silk a still purer blue than that pro- 
duced by diphenylamine blue. One of the purest blues is obtained 
by treating methyl -diphenylamine at 100° with chloranil (tetra- 
chlorquinone), C,jCl402,^ and then further heating to 130*. The 
product is reduced to powder, washed with hydrochloric acid, 
dissolved in alcohol, and precipitated by water. 

RosANiLiNE Blub, also called Spirit Blv£ or Paris Blue^ is a salt 
of triphenyl-rosaniline, containing more or less of the 
corresponding salt of triphenyl-pararosaniline. To prepare it, 
rosaniline (prepared by precipitating a solution of the purest 
bluish magenta with ammonia or lime) is heated to about 180* 
with ten times its weight of aniline and some benzoic acid. The 
excess of aniline, together with the ammonia formed in the re- 
action, distils over. The product is neutralised with dilute 
hydrochloric acid, when aniline hydrochloride dissolves and the 
salt of the new base remains insoluble. This is washed first with 
dilute hydrochloric acid and then w^ith water, and dried and 

The most usual form of occurrence of triphenylrosaniline is as 
the hydrochloride, C2QH,^(CgHg)3N3.HCl, but the sulphate 
and acetate are also met with. The first salt forms a greyish- 
green or brownish powder, which becomes pure blue at 100*; the 
sulphate and acetate bluish-violet, lustreless powders. In cold 
water the salts of triphenylrosaniline are quite insoluble, and 
nearly so in hot. In alcohol the acetate dissolves easily, and the 
hydrochloride and sulphate with more difficulty, to form deep blue 

* Prepared ])y the action of potassium chlorate and hydrochloric acid on 

^ The blue obtained from rosaniline, as described in the text, is of a lower 
price and quality than diphenylamine blue. The less pure products have a 
reddish shade, especially observable in artificial light. The best qualities 
appear pure blue by gas or lamp light, and are sometimes known as blue de 
nuit and hleu lumUrej ])iit must not be confused with the night blue described 
on page 232. These qualities are also known as spirit-blue 5B and 63^ the 
redder shades being described as 28^ 3B^ &c., according to their qaality. 
Spirit-Mue is sometimes further purified by dissolving it in aniline and precipi- 
tating by hydrochloric acid, and by other methods. Such purified products are 
known as opaX blue or basic blue. 

I blu 


eolutione, unchimged or turned greenish by liydrothloric acid, and 

in which slaimoua chloride produces a blue precipitate. A cold 

Icobolic solution of spirit blue becomes brownish-rud with soda 

onift, but at a boiling heat a colourless solution ia produced, 

dilution with water thin yields a white precipitate of free 

pheiiyltosvniline, CjaH,^(CaHj)jNj.OH, wlii''-ii rapidly becomes 

blue in the air. In concentrated sulphuric ticiO, spirit blue ills- 

solves with brownish -yellow colour, and on dilution with water a 

blue precipitate ia produced. 

Spirit blue is employed to produce bright blues on wool. The 

;ides are dyed in a bath containing alum, sulphuric acid, or 

innic chloride. Fibres dyed with spirit blue are nearly 

decolorised by hydrochloric acid, turned greyish .violet by soda, 

and clianged to light blue, fading to colourlciis, by nnimoniu. 

Alcohol 8tri]j8 the fibre even in the cold. 


Diphenylamine blue and spirit blue being insoluble in water, 
their practical application is attended with some inconvenience, to 
ibviate which tbey are frequently sulphonuted, with produc- 
of soluble colouring matters known as soluble bine, wafer blue, 
(see page 224). 

The greater the number of SOgH groups that are introduced 
ito tripbonylrosoDiliuo or its homologues, the wore readily soluble 
products become, but their fastness to light and air, soap, and - 
lea decreases in the same proportion. Hence the higher 
Iphonic ftcida, such as triphenyl-rosaailine tetraeul phonic acid, 


The Buljibonated aniline blues are prepared by beating dipbenyl- 

aniiiie blue and spirit blue with coucentrntwl sulphuric acid, Uie 

:teut of the sulpbonation de[<ondiiig on the proportion of acid 

and the temperature employed. A soluble diphenylamine 

may be prepared directly by heating diphenjlamine-su Iphonic 

with oxalic acid, instead of sulphonating the previously 

ipared triphenjlpararosoniline. 

TiUPHBNiXROSANiUNK-MOKOSULPHosic AciD hus the formula 
,Hu(SO,HKCgUj)jNg, and is formed by dissolving spirit blue in 
sulphuric acid and heating the solution to 30°-35* C. for five 
hours. t)n pouring the resultant brown is h-yeUow solution 
water, the sidpbonic acid is obtained as a bulky blue precipitate, 
ih after being dried at 100° forms small grains having a metallic 
Its alkali -metal salts are soluble in water, but those 
with the heavy metals and alkaline -earth metals are 
i or nearly so. By digesting the washed sulpbonic acid in 
quantity of caustic soda solution somewhat less than that 


required to combme with it, ftnd filtering, b solnticoi <kf (Ik 
sodium salt is obtained, from which tb« solid compoandin^ 
be pnpat^ by wturatiag the liquid with common salt, or evapMtt* 
ing it to dr,vnes3 with addition of a little ammonimn carbanale. 

Sorlitim lrtp/ient/lTntianilin«-moriagui}>h(mate forms Uie coramiatiial 
dye-stutf known as Nich"lson'ii btaf, aikali blue, or aolvii^ Hat. 
It occurs in lumps or powder of a greyish, brownish, or dull blu 
colour. It dissolves readily in hot water, with light brows «r 
bluish colour, which becomes deep blue on adding untie acid, Mid 
on boiling the acidulated liquid the free sulj^ouic acid sepuatM 
as a blue precipitate. Hydrochloric acid products tlie nut 
reaction in the cold, and un filtering a colourless liquid is ubtained, 
unless a di- or trisulphonate be present. Caustic soda turns tlii' 
solution of soluble blue reddish- vinlet, the colour changing un 
boiling to reddish-hrown. Excess of ammonia decolorisot the 
solution. Calcium chloride and stannous chloride produce lilnr 
precipitates. Soluble blue dissolves in strong sulphuric acid wtUi 
fine brownish-red colour, becoming blue on dilution with wat«t. 

If wool be immersed in a hot solution of alkali blue, pnferabh 
containing borax, sodium silicate, sodium carboniite, or anunoni*, 
the nearly colourless suit is taken up by the fihre and cannot b» 
removed by washing with water ; but on eulaequnntly immeising 
the fibre in dilute sulphuric acid the blue colour is developed. 

Cold alcohol readily removes the colour from wool or silk djsd 
with alkali blue. Caustic soda turns the libre a y ell n wish-brown, 
while ammonia immediately destroys the colour. HydrocJilonr 
acid nearly decolorises the iibro, and an acid solution of etaniunu 
chloride destroys it gradually. 

Commercial alkali blue is liable to contain various impurities 
and adulterations. It should dissolve without residue in atwal 
live jMrts of hot water. Sugar, starch, and doxtrin am sometimm 
adde<l, and a considerable proportion of sudium oarbonat*!, sulphsU. 
or chloride is often present. Arsenic is not an unusual contunint- 
tion. Alcohol dissolves the dye and leaves sodium sulphate and 
carbonate insoluble. The dye may be precipitated by saturatin;; 
the aqueous solution with purified conimou salt, whilo sodiuin 
carbonate and sulphate remain in solution. The sulphatu of 
sodium contained in the residue left on ignition represeula that 
formed from the sulphonate, as well as that pre-existing M 
sulphate. Pure sodium td phenyl rosaniline-monosulphoiiat« will 
yield 22'6 per cent, of Ka^SO^ oii fusion vrith sodium carbonatv 
atid nitre. On ignition alone a low n:s\ili is ubluin<^d, the mdiuni 
present heing insufficient to fix all the suljihur, bcaidca w hich 
TOoro or less sulphide and sulphitt' will probably be furmi " ^~ 



Sodiian tnpkeni/lpararosaniline-Tntmosulphonale is known in 
ixtmmerce as alkali blue D. In its reactions it closely resembles 
its homologue from rosaniline, but is nearly insoluble in cold 
water, und in hot water forms a blue solution which has iin odour 
of d i p h e n y 1 a m i II e. 

TiUi'HENn.ROHANiLiNE-DisuLPHONic AciD, having the formula 
C^H„(SO,H)3(CbHj;)3N3, is obtained, together with the triaul phonic 
acid, when triphenylrosaniline hydrochloride (spirit blue) is digested 
with 4 or 5 parts strong sulphuric acid at fiO° C. for five or six 
hours, and the temperature finally increased to 100°~110°. If the 
product be diluted with three or four times the quantity of water 
both Kiilphonic acids are precipitated, but if a comparatively large 
quantity of water be uaed the precipitate consists mainly of the 
disulphonic acid, while the trisulphonic acid dissolves and may be 
obtained as a blue precipitate by treating the filtrate with common 
talt or hydrochloric acid in excess, Tripbenylroaaniline-diaulphonic 
acid is slightly soluble in water, but insoluble in acid liquids, und 
hence U thrown down as a blue precipitate on acidulating the 
solution of one of its salts. Excess of soda turns the solution of 
its salts yellow. The sodium salt occurs in commerce under 
the name of gUk blue, and Bavarian blue DSF consists princi- 
pally of the corresponding derivative of para rosaniline, while 
Blaektey Uw is the sodium salt of diphenyl-tolyl-rosaniline- 
disulphonic acid. 

TBiPBKNTLRoaANiLiNB-TRisiTLPHONia AciD, of the composition 
C|oH,s(SOgNa)g(C8Hj)gNg, is obtained as indicated above. It is 
soluble in water and alcohol. The nodium, ammonium, and ealeium 
talU, mixed with more or less of the corresponding disujphonates, 
form the commercial colouring matters known as wati-r hhi-f., cottmt 
iUue, &c. (jiage 327). The ammonium salt forms dark lumps 
or grains having a coppery lustre; the sodium salt usually 
occurs as dark blue irregukr lumps. China blue is a veij porous 
variety of water blue, obtained by adding carbonate of ammonium to a 
very concentrated and slightly acid solution of the colouring matter. 

Water blue iH more soluble than alkali blue, aud cryataUittes 
from its concentrated hot solution in flakes having a metallic 
lustre. Its solution is not completely precipitated by hydrochloric 
acid, under any circumstances ; and not at all unless a large 
excess of the reagent be used or disulphonatc be present. 
Caustic soda decolorises the solution or turns it reddiah-brown. 
Water blue dissolves in strong sulphuric acid with dark yellowiah- 
red colour, and on dilution a blue solution is formed, sometimes 
9ocomptiniod by partial precipitation. 

" " ) differs from alkali blue in not being taken up by 


required to combine with it, and filtering, a solution of the 
sodium salt is obtained, from which the solid compound may 
be prepared by saturating the liquid with common salt, or evaporat- 
ing it to dryness with addition of a little ammonium carbonate. 

Sodium triphenylrosaniline-monostUphoncUe forms the commercial 
dye-stuff known as Nicholsons bltte, cdkcUi hlue^ or soluble blue. 
It occurs in lumps or powder of a greyish, brownish, or dull blue 
colour. It dissolves readily in hot water, with light brown or 
bluish colour, which becomes deep blue on adding acetic acid, and 
on boiling the acidulated liquid the free sulphonic acid separates 
as a blue precipitate. Hydrochloric acid produces the same 
reaction in the cold, and on filtering a colourless liquid is obtained, 
unless a di- or trisulphonate be present. Caustic soda turns the 
solution of soluble blue reddish-violet, the colour changing on 
boiling to reddish-brown. Excess of ammonia decolorises the 
solution. Calcium chloride and stannous chloride produce blue 
precipitates. Soluble blue dissolves in strong sulphuric acid with 
fine brownish-red colour, becoming blue on dilution with water. 

If wool be immersed in a hot solution of alkali blue, preferably 
containing borax, sodium silicate, sodium carbonate, or ammonia, 
the nearly colourless salt is taken up by the fibre and cannot be 
removed by washing with water ; but on subsequently immersing 
the fibre in dilute sulphuric acid the blue colour is developed. 

Cold alcohol readily removes the colour from wool or silk dyed 
with alkali blue. Caustic soda turns the fibre a yellowish-brown, 
while ammonia immediately destroys the colour. Hydrochloric 
acid nearly decolorises the fibre, and an acid solution of stannous 
chloride destroys it gradually. 

Commercial alkali blue is liable to contain various impurities 
and adulterations. It should dissolve without residue in about 
five parts of hot water. Sugar, starch, and dextrin are sometimes 
added, and a considerable proportion of sodium carbonate, sulphate, 
or chloride is often present. Arsenic is not an unusual contamina- 
tion. Alcohol dissolves the dye and leaves sodium sulphate and 
carbonate insoluble. The dye may be precipitated by saturating 
the aqueous sohition with purified common salt, while sodium 
carbonate and sulphate remain in sohition. The sulphate of 
sodium contained in the residue left on ignition represents that 
formed from the sulphonate, as well as that pre-existing as 
sulphate. Pure sodium triphenylrosaniline-monosulphonate will 
yield 22*6 per cent, of Na2S04 on fusion ^vith sodium carbonate 
and nitre. On ignition alone a low result is obtained, the sodium 
present being insufiicient to fix all the sulphur, besides which 
more or less sulphide and sulphite will probably be formed. 



>ditim triphenylpirarosaniHne-miMosulphimats is known in 1 

tnerce ob alkali blue D. In its renctiona it closely resemblea t 
ita homologue from roaauiline, but is nearly insoluble in cold I 
wat«r, and in hot vrnter fonnii a blue solution which has an odour J 
of li i p h e n y 1 a m i M e. 

Trip BEN VLROHAKiLtMB-DisuLPHONic ActD, bavin^ the formula 
CjnH„{S03H)^(C6Hs).,Ny is obtained, together with the trisul phonic 
acid, when triphetiylrosaniline hydrochloride (spirit blue) is digested 
with 4 or 5 purts strong sulphuric acid at 60" C. for live or six 
hours, and the temperature finally increased to 100°-1 10°. If the 
product be diluted with three or four timea the c]uantity of water J 
both sulphonic acids are precipitated, but if a comparatively large 
quantity of water be used the precipitate consists mainly of the 
disulphonic Bci'l, while the triaulpbonic acid dissolves and may be 
obtained as u blue precipitate by treating the filtrate with common 
salt or hydrochloric acid in excess. Triphenylrosaniline -disulphonic 
acid is eliglitly soluble in water, but insoluble in acid liquids, and 
henee is thrown down as a blue precipitate on acidulating the 
eolution of one of its salts. Excess of soda turns the solution of 
ita Bolie yellow. The sodium salt occurs in commerce under 
tbe name of n7h blue, aud Bavarian blue DSF consists princi- 
pally of the corresponding derivative of paraiosaniline, while 
Blarkleij Hue is the sodium salt of diphenyt-tolyl-rosoniline- 
disulpbonic acid. 

TRiPHBNYtJin8AKti.iNB-TB!auLPHONic AciD, of the Composition 
C»Hu(SOgN«yCjHj,)gNg, ia obtained as indicated above. It is 
soluble in water and alcohol. The eodiiiia, amjiwniunf., and calcium 
tallt, mixed with more or less of the corresponding dieulpbonates, 
form the commercial colouring matters known as weU^ bine, rtitton 
Uk«, &c. (p^e 227). The ammonium sail forma dark lumps 
or gmius having a coppery luatre ; tbe sodium salt usually 
oCGOts as dark blue irregular lumps, China blue is a very porous 
▼ariety of water blue, obtained by adding carbonate of ammonium to a 

' concentrated and slightly acid solution of the colouring matter. 

iiaUa blue is more soluble than alkali blue, and cryatallisea 

1 ita concentrated hot solution in flakes having a metallic 
Its solution is not completely precipitated by hydrochloric 

I under any circumstances ; and not nt all unless n large 
9 of the reagent be used or diHulphonate lie present. 
'i eoda decolorisea the solution or tunia it redd isli -brown, 
r blue dissolves in strong sulphuric acid with dark yellowish- 
and on dilution a blue solution is formed, sometimes 

npanied by partial precipitation. 
tfatm blue diffoi's from alkali bine in not being taken up by 



wool from an alkaline solution, and hence the fibre so treated is not 
rendered blue by subsequent immersion in dilute acid. 

Strong sulphuric acid dissolves water blue from fibres dyed with 
it, with blue coloration, and a hydrochloric acid solution of 
stannous chloride behaves similarly. Caustic soda turns the fibre 
reddish-brown, and ammonia decolorises it immediately. Alcohol 
has no effect on the dyed fibre, even when boiling. 

Water blue is chiefly used for dyeing cotton, being fixed by 
means of tannin, or by alizarin oil in conjunction with aluminium, 
antimony, or tin compounds. It is dyed on silk and wool in an 
acid bath, and in this case is always used in conjunction with 
other colouring matters. 

The colouring matters known as Bavarian blue DBF^ methyl- 
blue My BI for cotton^ &c., chiefly consist of the sodium salt of 
triphenyl-pararosantline'trisiLlphonic acid, and closely resemble the 
homologue, ordinary water blue. 

Blubs from Tetramethyl-diamido-benzophbnons. 

Several interesting colouring matters are obtainable by the 


Chemical na- 




Victoria Blue B. 


C]oHf . 


acid to aoue- 
ous solution. 

Caustic soda 
to aqueous 

Solid dye with 
strong sul- 
phuric acid. 


Hydrochloride of Tetra- 
methyl- phen vl-M. 
diph enyl-carbinoL 

Blue crystalline g^ralns 
or powder with 
bronxe reflection. 

Sparingly' in cold, 
readily in hot, to blue 
solution, gradual W 
depositing reddish 
resinous precipitate 
of free base on boil- 
ing. (Decomposition 
prevented by acetic 

Green precipitate, 
changing to dark 
yellowish-brown ; 
original colour re- 
stored on neutral- 

Darlc reddish-brown 

Keddish-yellow or red- 
dish-brown; on dilu- 
tion, yellow; and on 
adding more water, 
green and blue. 

Victoria Blue 4 B. 

\ C.H,.N(CH,)2 

i C,oH4*.N(CH,XC6Ha).Cl 

Hydrochloride of Penta- 
a-naphtbyl • diphenyl- 

Bronze powder. 

Soluble on heating to a 
bluish-violet solution. 

Same reaction as Victoria 
blue B. 

Violet-brown precipitate. 

Yellowish-brown ; on dilu- 
tion, green and blue. 

Night Blue. 



C ^ C6H«.N(CH 


Hydrochloride of Teti»r 

Brown-violet powder 
with bronze refleo- 

Soluble with fine blue 
colour, becoming 
turbid and precipi- 
tated by boiling. 

Same reaction 
Victoria blue B. 

Pale reddiah-brown 

Orange solution; on 
dilution, blue, es- 
peciallv if nearij 


^^^^ ax:line violets. 233 

Helioii of tetmraethyl-dianiido-henKOplienone oti phenyl-alpha- 
K'^t'iy'^tnuie and ita homologuea in presence of condenaiiig 
agebta. Although the mode of preparation of these dj-ea is 
entirely different from tliat of diphenylamine blue and rosaniline 
blue, the products bear a certain constitutional relutionsbtp to these 
pnxlucts. The preceding tnble (page 232) shows the coropositioii 
ftiid uharactera of the three chief members of the group. 

Victoria and night blues dye wool and silk in a bath acidulated 

aluminium acetate. Sulphuric acid changes the colour of the fibre 
to orange or reddish- brown, but the original blue colour is restored 
by washing. 

Aniline Violets. 

By the substitution, partial or complete, of the hydrogen of the 

Viirious violet colouring matters are obtained, those compounds in 
which the substitution is carried furthest yielding the bluest shades. 
These methylated and ethylated rosanilines (and para- rosooi lines) 

« introduced, constitute the anUitte violets of commerce. The 
iollowing are the most important members of the class : — 







M^vUnllitie 1 
rlol.t. PMHrtolct. , 
(B« pw 3M.) ) 

Crrit^ Tlolai- Violet 1 
8B. 19« p«i. 338.) f 

Ben»l rtolet Violet ) 

ft B. utn. Prnlt ( 

EUifl rlulsL 

Unfminn'i nolel. | 
^rjuU. ■(S«p^' 

rr '^ '^' 'i 

B— tn»ilnl»t. nmr\ I 
Vfolot, Spirit •lolet. [ 

HTdrocUartde of PenU- 

Hydjochloride ol Hsia- 

melbTl-bcniyl-piiriioMn l- 
Hjdfoohlorido ot HeHthyl- 

Hydtochlorida (hydrlodlde 
or nceUte) of THiDsUi;|. 


wn.poundi' '' 
Hrdrochlflrtde (or iDlpbata) 




Commercial Name. 


Soluble regina violet 

Bed violet 4 RS. 
Bed violet 6 BS. 

Acid violet 6 B (Bayer) 




Chemical Mature or Nature. 

Na salt of Phenyl- or Di- 
phonic add. Trisulphon- 
ated spirit-violet Phenyl 
ated acid magenta. 

Na salt of Dimethylrosanlline 
trisulphonic acid. Di- 
methylated acid magenta. 

Na salt of Ethylrosaniline 
trisulphonic acid. Ethyl- 
ated acid magenta. 

Na salt of Pentamethyl- 
benzyl-pararosaniline sul- 
phonic acid. 




The aniline violets are usually greenish powders or crystals with 
metallic reflection, soluble in water to fine violet solutions which 
dye silk and wool violet without a mordant. They can be fixed 
on cotton by tannin and tartar-emetic. The aniline violets are 
decolorised by boiling with potassium cyanide, a turbid solution being 
produced. With sulphuric acid they dissolve with yellow or 
brownish-yellow colour, and present a very close analytical resem- 
blance, as will be seen from the annexed tabulated statement (com- 
piled from the descriptions of Schultz and Julius) of their 
physical characters and chemical reactions. 

Methyl Violet, Methyl-aniline Violet, or Paris Violet 
(page 233), is the hydrochloride or double zinc salt of pentamethyl- 
pararosaniline. It is produced by the direct oxidation of di- 
methylaniline (from dimethyl-toluidine) by cupric chloride :^ — 

3CeH6.N(CH3)3 + 30 = ZTIfi + C^.U.^iCU^,^, . 

A colouring matter known as chloranU-violei, probably identical 
with methyl-violet, is obtained by the reaction of dimethylaniline 
and chloranil (tetrachlorquinone). 

Methyl-aniline violet occurs in commerce as a hydrochloride, 
and also as a compound of this salt with zinc chloride. The h y- 
drochloride forms small crystals, the zinc double salt a 
powder or irregular lumps. Both varieties of the colouring matter 

' Sulphate of copper is treated in solution with a large excess of common 
salt, and acetic acid and dimethylaniline added. The product is moulded into 
cakes which are dried at 40"* to 50** C. These are treated with a quantity of 
boiling water insufficient to dissolve all the common ^t. The aniline violet, 
being insoluble in strong brine, remains as a residue. It is dissolved iu water, 
tbe copper removed by sulphuretted hydrogen, and the colouring matter pre- 
cipitated by treating the filtrate with common salt. It is again purified by 
re-solution and crystallisation or salting out, or is converted into the zinc 
double salt 


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exhibit a green metallic reflection, and are easily soluble in water, 
alcohol, amyl alcohol, and chloroform. 

Dilute solutions of methyl violet are turned pure blue by a veiy 
small addition of hydrochloric acid. With more acid they appear 
green in thin layers, but red and somewhat turbid in thicker 
strata. Excess of acid turns the solution red or yellowish-brown 
fix)m the formation of an acid salt. Ammonia produces a lilac and 
caustic soda a violet-brown precipitate, the solution becoming 
colourless on boiling. 

With chromic acid, methyl-violet gives a dirty violet and with 
stannous chloride a blue-violet precipitate, becoming lighter on 
boiling. Hypochlorites decolorise solutions of methyl violet 

Methyl violet is completely precipitated by soluble fenocyanides 
and ferricyanides, and hence may be conveniently fixed on cotton 
mordanted with potassium ferrocyanide, or in the fibres of which 
zinc ferrocyanide has been previously deposited by double decom- 
position. In this manner methyl violet may be used for printing 
calico. It is also fixed by albumin or tannin, and is used for 
topping goods dyed with iron mordants and alizarin, in order to 
brighten the fast violet thus produced. 

Boiling with water gradually decolorises fibres dyed with 
methyl violet. Hydrochloric acid removes part of the colour and 
the fibre becomes greenish-yellow, but the original colour is restored 
on washing with water. Ammonia decolorises the fibre. Caustic 
soda turns it reddish-violet and gradually decolorises it. Treated 
with a hydrochloric acid solution of stannous chloride, the fibre 
becomes a yellow or greenish-yellow colour. 

Methyl violet is liable to much the same adulterations as other 
aniline dyes. It may be determined volumetrically by precipita- 
tion with picric acid (page 145), the formula of the pi crate 
being C24H27N3.CflH2(N02)30H. 

Crystal Violet is the hydrochloride of h e x a m e t h y 1-p a r a- 
r o s a n i 1 i n e. It is obtained by the reaction of tetramethyl- 
diamido-benzophenone chloride or carbon oxychloride on dimethyl- 
aniline, the reaction in the latter case being : — 

[CeH6.N(CH3)2]3 + 2COCI2 = C1.C[C6H4.N(CH3)2]8 + 3HC1 + CO^ . 

Crystal violet forms long hexagonal prisms or pyramids. The 
crystals have a beetle-green reflection if anhydrous, but a variety 
containing 8 ciqim also occurs, the reflection from which is bronze. 
When heated to 100", the crystals become brown and suffer slight 
decomposition. Crystal violet is soluble both in water and 
alcohol, but crystallises more readily from the former than the 
latter menstruum. The solutions are deep violet-blue, and dye 



wool and silk a. very blue Bhade of viok't. Oii cotton, crystnl 
violet is fixed by tannin and tartar-emetic. 

According to G. Zetter, crystal violet dissolves in strong 
sulphuric acid with orange colour, which ia unchanged on dilution ; 
but according to other obsorvera the solution in sulphuric acid is 
I^JbUow, changing on dilution to green, blue, iind violet. 
^^Hpn adding; pjatinic chloride to a solution of crystal violet in 
^^^big hydrochloric acid, the chloroplatinate is obtained aa 
^^^Arick-red precipitate of the composition, [C,,H,g(CH,)^N,Cl]2 

On healing cryptal violet in a cloBod tube to 3 20" C. with an 
aqueous solution of ammonium sulphide, a leuco-base ia 
formed of the formida Cj^H^iNg, which melts at 173° after being 
purified by crystallisation from alcohol. 

Crystal violet forms a very insoluble picrate, a fact which 
may be utilised for its determination and assay (see page 145). 

Bbxztl Violet (pages 333, 235) is prepared by heating methyl 
violet with benzyl chloride. CuH^.CHjCl, alcohol, and lime or soda, 
in an apparatus furnished with a reflux condenser. A aeries of 
products are thus formed, becoming bluer the greater the number of 
benzyl atoms introduced into the molecule. The commercial product 
ia the liydrochloride or zinc double salt Benzyl violet closely 
resembles methyl violet, but dyes somewhat bluer ahadea. Fibres 
dyed by benstyl violet are turned light blue by caustic soda ; but 
if dyed by methyl violet red-viulet. In both cases, the material is 

I''""''"-ised after a time. 
•Mann's Violbts are of historical interest, being, with the ex- 
I of mauve (page 257), the first aniline violets produced, but 
ave now been nearly superseded by the newer colours, such 
ihyl violet. They are produced by acting on an alcoholic 
n of rosaniline with caustic soda and iodide of methyl 
yL The larger the proportion of alkyl iodide employed, 
enter is the substitution and the bluer the product. The 
ted rosanilines are redder than the eoiTesponding methyl- 

Aniline Ore ens. 

The green colouring matters derived from triphenylmethane 

be divided into two classes, one of which is represented by 

tk]/l great and the other by hfinzaldfhyiie ^een. The former dyes 

derivatives of triani id o-triphenylme thane, while the latter are 

derived from diamido -triphenylmethane. The aulphonated aniline 

greens which are found in commerce are mostly dyes of the latter 




The following is a list of the principal greens from aniline 
having a practical interest: — 

Commercial Name. 

Basic Orsens. Class I. 

Methyl green. 
Paris green. 
Methyianiline green 
(page 240). 

Ethyl green. 

hyl ffre 

Methyl green (Bayer). 

Todine green. 
Xight green (pages 289, 

Spirit-soluble green 
(pages 289, 241). 

Basic Grkkms. Class II. 

Malachite green. 
Benzaldehyde green. 
Victoria green (pages 289, 

Solid green. 

Brilliant green. 
New Victoria green. 
Ethyl green. 
Solid green J. 

Victoria green. 
New solid green. 


Helvetia green. 
Acid green (pages 289, 

Acid green (B.A.S.F.). 

Guinea green B (page 239). 

Acid green (Bayer). 
Light green S or SF (page 

Fast green (Bayer) (page 

Chemical Name or Nature. 

Componnd with zinc chlo- 
ride of hydrochloride of 

Compound with zinc chlo- 
ride of the hydrochloride 
of bromethyl-hexamethyl 

Compound with zinc chlo- 
ride of the hydrochloride 
of Chlormethyl-hexa- 

Picrate of the base of 
iodine green. 

Oxalate of, or compound 
with zinc or iron chloride 
of, the hydrochloride of 

Sulphate (or oxalate) of 

Hydrochloride (or zinc 
chloride compound) of 

Na salt of Tetramethyl- 
binol-sulphonic acid. 
Sulphonated malacliite 

Na salt of Dimethyldiben- 
carbinol-sulphonic acid. 

Na salt of Diethyl-dibenzyl- 
binol-disulphonic acid. 

Na Salt of Diethyl-dil)enzyl- 
binol-trisulphonic acid. 

Na salt of Tetramethyl-di- 
disulphonic acid. 


(C6H4.N( ^_ 
C 4C6H4.N(CH^CH,a 
(C6H4.N((;H3)s.(1 -fZnCls 

C -^C6H4.N(CH8V.^ 

C6H4.N?C - 
I (CeH4.N<C 












) CgH,. N(fc2H5X07H«SO,Ni 




The following table is compiled chiefly from the description given 
by Schultz and Julius {Chemische Indvstrie, 1 888) of the 
physical characters and chemical reactions of the principal green 
dyes in the foregoing list : — : 

I, if 1 1 rum «i 

Is ifillfi slljilliilsi 


PI S' ||s 

Mm ^7 

IP ffl ill 

lU ■Ij ass 

Pi 1 l«l^'; 

it I iW 




"ail ^ ^ si SS| I 

|ii*,|i j |s in I 

|i lis ilsill 


Methyl-Greek or Methtlaniline Green is the most important 
of the basic green dyes of Class L (page 237). It is prepared by 
acting on pentamethyl-pararosaniline (the base of methyl violet) 
by methyl chloride, in amylic alcohol solution, and converting the 
product into the double zinc salt. 

Methylaniline green is the double salt with zinc chloride of 
the hydrochloride of chlormethyl-hexamethyl-pararosaniline,^ and 
has the formula :—Ci9Hi2(CH8)gN3.CLCH3Cl+ZnCl2+HjO. It 
occurs in commerce either in small green needles, in large coppery 
prisms, or as a light green powder. It dissolves readily with 
bluish-green colour in water and alcohol, but is soluble in amyl 
alcohol. This last character distinguishes methyl green (and 
probably the other greens of Class I.) from benzaldehyde green (and 
its allies). Methylaniline green is insoluble in ether or benzene, 
and may be precipitated from its alcoholic solution by addition of 

Dilute acids colour the solution to greenish-yellow, a tri-acid 
salt being formed, but on dilution with water the original colour is 
restored. Hypochlorites destroy the colour of methyl green, and 
stannous chloride and other reducing agents gradually decolorise it. 

On adding a strong solution of caustic soda to one of methyl green 
a resinous precipitate is produced. This precipitate is the free 
base, and contains CigHj2(CH3)gNg.OH.CH3CL It is soluble 
in pure water, and on treatment with moist oxide of silver yields 
silver chloride and the non-chlorinated base, CigHi2(CH3)gN3.0H. 
CH3.OH, is produced. 

As might bo expected from its constitution and mode of forma- 
tion, methyl green readily splits up into methyl chloride and 
methyl violet. The decomposition occurs gradually at 100°, and 
rapidly at 120°-130° C. Hence if filter-paper be moistened with 
a solution of methyl green, and then strongly dried, it will acquire 
a violet colour. This reaction, which is equally applicable to fibres 
dyed with the colouring matter, is characteristic of methyl green 
and its immediate allies (e.g., ethyl green, iodine green). 

The adulterations and impurities of methyl green and other 
aniline greens are described on page 242. 

Methyl green is now rarely used for dyeing wool. When it is, 
sulphur or zinc sulphide is one of the best mordants. Silk is 
dyed in a warm bath, to which picric, tartaric, or acetic acid is 
sometimes added. On cotton, methyl green is fixed by means 
of tannin. 

On the fibre, methyl green may be recognised by the change of 

* This base may be conveniently referred to as ** verdaniline." 



nir on heating strongly. Excesa of hydrochloric acid turna the 
e yellow, but the original colour is restored by washing. The 
s removed by alcohol or acetic acid, the liquid being coloured 
hliiish-grcen. Alkalies and reducing agents decoloriHe the fibre, 

lODiHR Gubbk (pagea 238, 239) presents the closest teseniblsnce 
to methyl green, with which it is homologous. As formerly pre- 
pare, with metliyl iodide, it gave off violet vapours of iodine when 
heated with strong sulphuric acid, but as at present mnuufiictured, 
|, by the treatment of rosanilme with methyl chloride, the dye does 
jn^Mpt give this reaction, 

^^^kf^kin't grenn resembles iodine green, but is precipitAted by 
^^^pium carbonate in the cold. 

^^r6FiiUT-HoLUBUcGRBBN(pa^esS38, 239) is obtained as an insoluble 
I ciystalline picratc by adding picric acid to a solution of iodine- 
green (or methyl^reen I).* It often occurs in commerce as a dark 
green paste, which is nearly insoluble in water but dissolves in 
alcohol. The solution yields the sparingly soluble yellow potassium 
pjcrate on addition of an alcoholic solution of potassium acetate, 
but picric acid may be extracted by agitating the dye with dilute 
sulphuric acid and ether. Spirit green sometimes contains an 
excess of picric acid. This may be detected by placing successive 
quantities of silk or wool in the alcoholic solution of the dye, until 
the colouring mntter is nearly all taken up. If free picric acid be 
present, the libres lost added will be dyed yellow. Free picric 
acid might probably be removed by drying the paste and treating 
it with ether or benjiene. 

^J}KN)ULOBaTnB Gbeen, or Malachite G&bbn (pages 238, 239), 

1 by the reaction of dimethyl-attiline on beuKoldeliyde, 

reby tetramethyl-paradiumido-triphenyU 

e is produced, thus : — 
[a.COH+2C„HjN(CHa), = HjO + H.C(C,Hj)[CflH,N(CH,)(],. 
1 hydrochloric acid solution of the product is oxidised by 
de of lead at 60°-80'' C. preferably with addition of a 
e chloDinil. The lead is removed by sodium sulphate, and the 
1 treated with common salt and zinc chloride, when the 
i xinc compound is precipitatetL 

I duuLle zinc rJiloridi of tetramethyl-diamido-triphenyl- 
inol contains 3Cj3Hj,N^HCl+2ZnClj+2H,0, It forms 
n-yoUow prisms, with a yellowish-green reflection. 
Byicoonling M Benedikt tba picrate (contains nu uhlorine, but P. 
I sltribiites tu it the formula ■- 

■vol. in, PART I. 






The doulde trun eMoriiU (ferrous) also occurs in commerce m 
an inferior quality of benzaldeliyde green. 

TLe nxtUate, CjgHyNpHjCjO^ forma acnlea having a growi 
metallic reflection. 

All the commercial forms of benzaldehyde ^en dissolve eaaily 
in wiiter and alcuhol. They are also Boliible in amylic alcohol, 
which character diatinguishes them from methyl green (and its 

The free Ikub of benzaldehyde green is obtained as a green 
precijiitate on adding on alkali to the solution of one of its salt*. 
The precipitate ia soluble in etiior and petroleum spirit, and after 
crystftlliaation from the latter solvent forms colourleea needles, 
which melt at ISSMSO" C. 

The base of malachite green combines with both one and two 
molecules of picric acid to form insoluble picrates. 

The solutions of benzoldehyde green are bluish-green. By 
concentrated hydrochloric acid they are changed to orango-yellow, 
but the green colour is restored by diltition, Hypodilorilw 
decolorise the solution, and stannous chloride forma a gmn 

Benzaldehyde green may be detected on fibres dyed with it hy 
the orange coloration with hydrochloric acid, restored to gnea by 
washing, and by the decolorisutiou produced by ammonia, soda, or 
soap. From methyl green it is distinguished by not turning violet 
when heated. 

Helvetia Greem is the type of the sulphonated aniline greena, 
the reactions of which have already been described (page 339). 
It differs from benraldehyde green hy giving no precipitate with 
caustic soda in dilute solutions, though strong soda solution pro- 
duces a white precipitate. On the fibre, acid green closely 
simulates benzaldehyde green, but is turned greenlah-yellow by 
hydrochloric acid, the liquid itself becoming yellow; whereaa fibtM 
dyed with bennaldehyde green become bright orange, and pvo np 
very little colour to hydrochloric acid. In each case the original 
green colour is restored by washing with water. From me^yl 
green, hetvetia green is distinguished by the fibres not becoming 
violet when heated. 

Adulterations op Aniline Greens. Iodine-green varies much 
in price and quality, the commercial value not dways following 
the dyeing properties, which in samples of the same price may 
vary as much as 50 per cent. Crystallised greens arc uauiUy 
purer than the amorphous kinds, but not always. Aniline greens 
vary much in tint, yellow shades being duo to picric acid or other 
yellow dye, and green ones to soluble aniline bluo. The latter. 


243 . 

irlien present in nnall proportion, ia best recognised by yeUow 
light. Large amounts may be detected by treating the dye with 
picric acid and glycerin, when the gveen remains insoluble, and 
sny blue admixture moy be recognised by the colour and 
characters of the filtered liquid. If the dye be the picrate of ' 
"verdaniline" mised with soluble blue, mere treatment with 
water is sufficient to detect the admixture. Free picric acid may 
be detected by agitating with water and ether, and a picrate in the 
manner already descrihed (page 2'H). 

Some greens contain accidental admixtures of sodium acetate j 
and black insoluble bodies, besides some aniline violet. Methyl | 
green of good quality dissolves entirely in boiling alcohol. If a ' 
gtBenish- white residue be left, which turns violet when heated, 
it probably consists of the hydrochloride of nonamethyl- 
paraleucaniline, C„H,g(CH3)„(CH3Cl)3. This body is 
often present in considerable proportion in methyl-green which 
has not been purified by alcohol, and la sometimes added as an . 
adult emnt. 

In water, methyl green should dissolve entirely with bluish- 

IBn colour. A residue of green may consist of the picrate, 
ich is entirely soluble in alcohol or dilute caustic soda. The 
leouB solution of methyl green should yield no precipitate in 
cold with dilute soda or sodium carbonate. A precipitate will 
bably consist of the base of methyl- violet, which after separation 
f be rect^iaed by its colour and reactions of its solution in 
Irochloric acid. Its presence is due to defective putiiication of 
colon ring matter. 
Intentional additions of sugar are occasionally made to aniline 
greens, and compounds of ma^esium, lead, and chromium have 
been met with. Arsenic is found in some samples, Zinc chloride 
is a normal constituent of soluble and malachite greens. 

Comparative tinctorial and dyeing tests are also of value for the 
wxamination of aniline greens. 

^Mixed Greens are made by blending yellow and blue colouring 

Such products, or the tissues dyed with them, may lie 

Dined ta follows : — Boil with strong alcohol. Aniline greens 

I completely dissolved, as also are picrates. Any blue residue 

H Gonsiat of indiijo or pniggian blue, which may be distinguished 

■ ftdding dilute bromine water. The indigo will bo bleached, 

^ the Prussian blue remains unaffected. On the other hand, 

vian blue is turned brown by soda, while indigo remaina 

ihonged. If tlte alcohol acquire a green colour, aniline blue is 

At, in which cose the originnl substance or fabric should h« ' 

1 with dilute hydrochloric acid, when a blue residue will be ' 

244 AUfiAMINE. 

left, and the solution can be examined for picric acid and other 

Appendix to the Aniline Dyes. 

In the manufacture of magenta and other aniline dyes, certain 
bye-products are formed, which may be conveniently discussed 
here, although their constitution is unknown or different from 
that of the ordinary aniline dyes. The chief products of the kind 
are phosphine, indvline^ and safranine. The last of these will be 
described in a special section (page 256), while auramine and 
Jlavaniline, on the other hand, though not strictly secondary 
products of the manufacture of magenta, may be conveniently 
considered in the present connection. 

Auramine. Ci^HgiNg.HCl+HgO. By the action of carbon 
oxychloride on dimethylaniline in presence of aluminium chloride, 
tetramethyl-diamido-benzophenone is produced, 
and when this body is heated with ammonium chloride and zinc 
chloride to 1 50°-l 60° C, it reacts to form an imido-tetra- 
methyl-diamido-diphenylmethane. The reactions 
are represented by the following formulae : — 

C0Cls+2C,H5.N(CH3),= 2HCH-C0| c'h^Sh')* ' "^^ 

f C H WCH ■> ( C8H4.N(CHj)j 

CoIcKnIctS: + NH3 = C|C^^.N(CH.), 

The new body is a colourless base, which forms salts of on 
intensely yellow colour, the hydrochloride being the attra- 
mine of commerce. The hydrochloride, sulphate, and acetate are 
readily soluble in water, but the thiocyanate and double zinc salt 
are only very sparingly soluble in cold water. 

Commercial auramine is a sulphur-yellow powder, which 
dissolves somewhat sparingly in cold, but more readily in hot 
water, to form a bright yellow solution. It is also soluble in 
alcohol. The cold aqueous solution is unchanged by hydrochloric 
acid, but on boiling the liquid is decolorised, with re-formation of 
ammonium chloride and tetramethyl-diamido-benzophenone. On 
addition of caustic soda, the aqueous solution of auramine yields 
a white precipitate of the free base. The precipitate dissolves on 
agitation with ether, and the separated ethereal solution is not 
fluorescent, but communicates a yellow colour to acetic acid when 
shaken with it. When treated with zinc and acetic acid, aura- 
mine gives an evanescent green coloration. Alkaline reducing 
agents, such as sodium amalgam or zinc and ammonia, gradually 


wlorise the alcoholic solution of iLuramine, and on adding watei 
I colourle&e reduction-product is precipitated, which when heated I 
nth acetic acid yields a deep blue colour. 
j Aununine produces a brilliant and very pure yellow whea 

rdanled on cotton with alizarin oil or tannin and a salt of j 
lltimony.' The fibre is decolorised both hy acids and alkalies. 

'i the manufacture of aucamine the ammonium chloride be { 

laced by the hydrochlorides of aniline, xylidine, naphthylaraine, 
ied auiamines are obtained, none of which J 
Bpear to crystallise, and which dye shades ranging from yellow i 
D light brown, 

Flavaniline. CmHjjNgfHCl. When HC«taniIide is heated \ 
"with rinc chloride to a temperature of 250°-270° C, it is 
verted into a colouring matter, tlie free base of which has th« I 
constitution of a para-amidophcnyl-j'-lepidin 
y-lepidine-aniline. The reaction consists in the conver- 
sion of acetunilide into the isomeric ortho-amido-aceto- 
phenone, the subsequent conversion of a portion of this into 
jwra-amido-acetophenone, and the coalescence of one molecule of i 

h of these bodies with elimination of water, thus ; — 

|€,HyNH,C{CH3)T = C«H/NHj).C(CHs) : 


IsC,H.(NH,).C(CH.) ; = C,H. | ^5|^™ H NH + ^''''' 

JiiiK(D>aMCii|>'iFnMK<. Para-amidopli^niil-lrpidi'u. 

J Flavaniline is now almost obsolete in commerce. It is a 
pdrochloride of the base, and occurs as an orange-yellow 
Rstalline powder, readily soluble in water with yellow colour. 
! Bolution is unchanged by hydrochloric acid, but on adding 
soda yields a niilky precipitate of the free base, soluble in ether, 
without colour, but with steel-blue fluorescence. In strong aul- 
phuriv acid, flavaniline dissolves with dirty-yellow colour and blue , 
"lotesceuce. Flavaniline dyes wool and silk yellow wjtliout a 
rdanL Silk dyed with Uavoniline exhibits a fine mosa-greeu 

mJiTavaniline S ie a. sulphonated flavaniline. It resembles the 
Jkio dye, but the solution is gradually decolorised by soda without 
^precipitate being formed. In strong eulphunu acid it forma a 

mrless solution, becoming yellow on dilution. 
I Chrtsanilini!. Phobfhine. This colouring matter, also called ] 

' Anmnine i» oiia of the few *rtjScUl yellow dyea which c&il be Ried re, 
W fibre by moana of taDiiin. Hcnoe it may be employed to produce very \ 

■r ibadmi uf nmtiitthite grwn on cottUQ. 


aniline yellow, aniline orange, and leather ydlow, is obtained u i 
eeccmdary product of the manufacture of magenta.^ 

Pure chrysoniline liaa the uouBtitutioa of a diamido- 


The commercial product p/iiifjikine is usually the nitr&te, 
or according to Benetlikt the hydrochloride, of chiy»- 
aniline, mixed with more or leae of tlie correapoadiog salt of the 
homologue ch r jaotol uidine, CjoHj,Nj. 

CommeKialp/t/isphineiorms an urauge -yellow powder, leadQy k1- 
uble if the hydrochloride, but difGcultly if the nitrate, to a mldisb- 
yellow solution. It is also soluble in alcohol Dilute hydrochloric 
acid simply deepens the colour, but with excess of the strong acid > 
dihydrochlorido is precipitated, readily soluble in pure wat4!r. 
Ammonia and soda liberate free cbrysanilineas an amorphooa 
yellow precipitate, which melts on boiling, the liquid being coloured 
pale yellow. The precipitate is soluble in ether. Pbosphine dis- 
solves in strong sulphuric acid to form a reddish-yellow solntion 
which exhibits a Htrong green fluorescence. On dilution, a reddish- 
yellow solution is obtained. 

On adding nitric acid or sodium nitrate to a tolcrabljr concen- 
trated solution of phosphine, the sparingly soluble chrysKniline 
nitrate separates as a red crystalline precipitate. In wbttd 
solutions, the precipitate is produced slowly, and on stirring the 
liquid is deposited in streaks in the track of the glass rod. Under 
the microscoije the precipitate is seen to consist of needles. This 
' The resionUB bye-|)rDduets canMJa chrysanitine, luaaTBiiitiiie, vioUiulinti 
4 little rofiBniline, mid unduliued rttiiiioDs mattera. On balling the mM> 
with dilate bydrochloric acid, rvsins and violaniline Tcmnia insnlablib Bj 
rraotinnal precipitatiDn of the filtered solutian with Iiidd, mnavKiiiliDe, T«t- 
aniliue, und abrysaniline are succenBiTely {iret^ipitated. CbryHaniline may tw 
more easily prepared from the mother-liquors which remain after jiwiapitatiiiK 
the msgonta by salt, in the aiaenic acid procesl. Uore lalt is addvd fa iha 
liquid and then lime, the precipitate treated with iltlute nitrie add, Mid the 
sparingly soluble nitrate of chryssniline precipitated by ailding «iL'«ai of nitrie 
acid to the aolution. The deliberate ayntheais ot cbrysaniline has Immi sll«ct«d 
by bcBtiDg bentoic acid and diphcnylamjiio with line chloride, nltra^itiji 
tlie resultant pheuylacridine, and reducing it to the diimiilo-derivattve!. 
* For further iDrormation nu the cettatiCutioo or t-hrysaniline and Oaraniliiit, 
a interesting lecture by R. Meldola, Jnur. See, Dyen, ife, H. SB, 

from Jow. Soc. Aria, May i 

dimethyl -phenyl acrid ine (Jmir. 

!. Ditn, *c,. 



characteristic reaction, when carefully applied, diatinguislica phoa- | 
phine from other yellow coIouriDg matters, but is liable to fsiil in 
Bolutione of the nitrate, Hence a preferable plan is to liberate tlie 
base by ammonia, agitate with ether, treat the separated ethereal 
solution with dilute acetic acid, concentrate the acetic solution, 
ttnd add sodium nitrate. This mode of operating nxdudes tba 
possibility of confusion with uitro- com pounds, which often i 
yield yellow crystalline precipitates on treating their solutions 1 
■with nitric acid or potassium nitrate. But the nitro^lyes are not 
icted by agitating their ammoniocal solutions with ether, 
igh, unlike chrysaniline, most of them are extracted from their 
bluUted solutions. Nitro-compounda are further distinguished 
f the red or brownish colour developed on boiling wttli potassium 
toide ; whereas phosphine gives a yellow precipitate in the cold, 
1 the liquid acquires a yellow colour on boiling. 
f On treatment with stannous chloride and hydrochloric acid, 
saniline solutions are decolorised, but the yellow colour rapidly 
a on exposing the reduced liquid to the air. 
PWhen heated with 3 or 4 parts of hydrochloric acid to 1 60°— 180* 
L, chryeuiiline is decomposed with formation of ammonium chloride 
KDJd chryaophenol, C,gH,jN/J, in the same way that flav- 
Kuiltne yields flavenol, and aummine tetntmethyl-benzophenone. 

Phosphine behaves to fibt^s lllce the other basic aniline dyes. It 
produces a yellow on silk or wool, and is used in admixture with 
magenta for dyeing silk scarlet On cotton mordanted with aluminium 
acetate it gives a nankin-yellow which will stand soaping. 

Acids redden fibres dyed with phosphine, and after a time the 
colouring matter is removed. Alkalies turn the fibre to a greenish- | 
yellow [laler than the original. Reducing agents decolorise It 

KSIaitvahiline, C,gHj,Nj,U^O, is a base of unknown constitution 
ined in magenta-residues. It must not be confounded with 
B or Perkin's purple, which is related to the safranincs 
Ige 257). It is prepared by boiling the resinous residue from the 
' ; acid process with dilute hyilrochloric acid, and preeipitat- 
t the bases From the hltere<l solution by excess of lime. The 
ihed precipitate is sold as niaroan paste, or is neutralised by 
Khloric acid, and thus rendered soluble in water. If the 
-oon so obtained be fractionally precipitated with 
ion salt, the hydrochloride of mauvoniline is thrown down 
\, while the rosanihne and ehrysuniline salts remain in solution. 
■ product may be purified by ctystalhsation from boiling water, 
Hho hydrochloride of mauvaniline is crj'stalUne, and exhibits a 
'( bronze rcflectioa It dissolves sparingly in cold water, mora ' 


readily in hot, to a blue-violet solution, from which alkalies pre- 
cipitate the free base. It dyes silk and wool a fine and fast violet 

Mauveine, the base of mauvey is another product of the oxidation 
of aniline containing toluidine. It is probably related to the 
safranines, with which colouring matters it will be described 
(page 257). 

Indulines and Nigrosinbs. 

The name induline is applied to a series of basic bodies formed 
by the reaction of amido-azo-compounds on the hydrochlorides of 
aromatic amines (e.g.f aniline), with elimination of ammonia. The 
substances of the induline class occurring in commerce are dark- 
blue or violet dyes, less remarkable for their brilliancy than their 
, resistance to light and atmospheric influences. 

Vtolaniliney C^gH^gNj, the typical member of the class, is a 
base contained in the commercial colouring matters known as 
nujrosine and induline. It is a product of the oxidation of 
aniline (CgH7N + 03 = Ci8Hj5N3+3H20), and may be prepared 
by heating aniline with nitrobenzene and iron filings to 180* C. 
Yiolaniline is often present in magenta-residues, from whidi it 
may be prepared by boiling with hydrochloric acid, which dissolves 
the other bases, and leaves violaniline hydrochloride and resinous 
matters undissolved. On treating these with boiling aniline, and 
filtering, the pure colouring matter separates out on cooling. The 
hydrochloride so obtained is a bluish-black amorphous 
powder, insoluble in water but soluble in alcohol with bluish- 
violet colour. The free base is precipitated in flakes on adding 
an alkali to this solution. 

Violaniline may also be prepared by heating together aniline 
and amido-azobenzene (page 178) in molecular proportions, when 
the new colouring matter is produced with evolution of ammonia: 
— CoHyN-f Ci2HiiN3 = Ci8Hi5N3-f NHj. The dye obtained by 
heating hydrochloride of aniline with amido-azobenzene to 160* 
in alcoholic solution, is called azo-diphenyl blue, and is probably 
identical with induline B. It is distinguished from induline 3 B 
(see below) by its readier solubility in alcohol, its redder shade of 
colour, and the brownish-red colour of the free base. 

By heating violaniline with aniline, or by using excess of 
aniline in its manufacture, phenylated substitution-products are 
obtained, the highest of which is triphenyl-violaniline, 

By increasing the proportion of aniline hydrochloride, a series 
of indulines are obtained, the identity of which is determined by 
the proportions of the reagents and the temperature employed. 

If two parts of diazo-amidobenzene (page 177), one of aniline 

INDULitJES, 249 

hytlrocbloride, and fooi of aniline be mixed and allowed to stand 
for twenty-four houni, to allow of the conversion of the diazo- 
wnido-ftiobeneeDe into the metamerit; body aniido-azobenzone, and 
the mixttire be then heated to 125°— 130°, a more complex reaction 
ensues' and a baao is produced, the hydrochloride of which 
ciystuUiscs from the liquid on cooling. The free base has the for- 
mula CgglljjN^ and forms warty crystalB, soluble in alcohol with 
dark purple colour. The hydrochloride is the indttlitte S B 
of commerce, and forms brownish shining scales, soluble with purple 
colour in aniline or alcohol, and is used for producing delicate fast 
greys on cotton, for which fibre it has some little affinity. 

By inereiwing the proportion of aniline hydrochloride in the melt, 
and raising the temperature to 165'— 170° C., a base is obtained 
of the torniula Cj|,Hjj(CgHg)Nj, which crystallises from aniline in 
needles having a green metallie reflection. The hydrochloride, 
CjoHj,Nj,HCl, is the indulhie 6 B ot commerce, and forms green 
lustrous crystals which readily lose hydrochloric acid. 

Bine dyes of the indnline class are obtained when amido- 
azonaphthalene ie substituted by amido-azobonxene ; but if the 
aniliue be replaced by orthotoluidine or amido-naphthalene, red 
colouring matters are produced. 

The chamcteta and reactions of the various commercial indulinea 
are not strictly identical, hut do not require separate description. 
At n class, the indulines usually occur as bluish-black or brownish- 
black powders, which are insoluble in water but soluble in alcohol 
with greenish or bluish-violet colour, The Alcoholic solution becomes 
pure blue with hydrochloric acid, and on adding soda yields a dirty- 
red or reddish- violet solution or precipitate, the exact reaction 
depending on the nature of dye under examination. In strong 
eulphitrie acid, the indutines dissolve with blue colour, a violet-blue 
precipitate being formed on dilution. Treatment with iinc and 
sminonia decolorises the solutions on warming, but the original 
colour returns on exposure to air. The benzene solution exlkibits 
an intense red-brown fluorescence. 

SiiLPHONATBD Indulinbs. SoLtTBLB Indulines. By treating the 
indulines with strong sulphuric acid, various sulphonated indulines 
are obtained which are soluble in water. The redder shades are 
met with in commerce under the name of fast blue R and leater- 
KiuUe nu/roainc, nnd the bluer varieties aa fast lAue B,fast blut 

' If the UmperftliUTi bs limited to 100*, ths product consiats largely of 
fttot''>>''i"°> '^wI^v^'k b biwie which crystal ILsea trom hot auiline in Btnall, 
gutxt-red plahsH, nolting »t 230°, and forming a violet solution in itrong 
■alphnrio (Did whirh bscomsB luni'e-lilua at 300°, and exhibits a carmine-red 
flanmcsnce on dilution with water. 



greenisk, indidine 3 B ot 6 B, &c. Theee gulphonated indnline* 
occur as cryatAlliue powdeis with a bronze reflection ("iiiduline''),i>r 
as biack, glistening fragments ("nigroeine "). They dissolve in w»ter 
with bluish-violet, and in alcohol wiUi blue colour. HjdrocUiorie 
acid renders the solution blue, Alknlies produce a bninnieh- 
violet precipitate. In sulphuric acid, the eulphouated induliues dii- 
solve with blue colour, changing to violet on dilution with water. Bj 
oxidation they yield q u i n o n e and other products, and by reducing 
agents are converted into unstable leuco-derivatives. 

Soluble indulines are used for the preparation of coloured inH 
and both the soluble and insoluble in the prppamtion uf spiiit- 
vamishes. They are very fast dyea, ond are employed tot pro- 
ducing grey, bluish, and blue-black shades on wool, silk, leather, 
tie, and are used as indigo-subatitutea. In commerce they are mrt 
with under a variety of names, including, besides thosd tixttdj 
mentioned, Blae/dey blue, Guenuey blue, indi'/o-imbgfitutf, bcngalim, 
Coiipier'ii blue, &c 

On the fibre, the indulines are turned somewhat bluer b; 
hydrochloric acid, but nitric acid is almost without action 
(distinction from indigo). Ammonia tmd soda strip the fibre, 
forming reddish-violet sDlutinns, which are decolorisod by liiH 
powder, but the colour returns on filtering and exposing the Uquiil 
to the air. An acid solution of stannous chloride strips the fibie, 
and forms a green solution. Hypochlorites bleach some indulincS) 
and turn others reddish-grey. 

Aniline Black. By the oxidation of aniline under suitable con- 
ditions a very stable black colouring-matter is formed. The mo* 
perfect black is yielded by pure aniline boiling at 182° C. Ortho- 
toluidine gives a bluish-black and paratoluidine a brown-black.' 

The oxidation of aniline to aniline black may be effected bj 
potassium bichromate, permanganate, or chlorate, and by vuions 
other oxidising agents. In practice, a readily changeable metalUe 
salt is employed as a carrier of oxygen, a veiy suitable combioatioii 
lieing a cblonite (preferably that of sodium) and cupric sulphate. 
Ammonium vanadate now receives a large nppiiciition in the 
production of aniline black, as it is readily reduced to vanadituA 
chloride, and this is immediately reoxidJeed to a vanadate by tha 
clUorate simultaneously employed. One part of vanadium will do 

' NAl'HTHAMEiN, Or Nspljtljiiluini Violst, is n coloiiriiLg inatler prodacad bjF 
treating lliu hydrtMbloricie of nlphBDapbthyluaiiie vith ferric cUoridii oi 
uther oxidising ageot. It rarms an amor|)hous, [iur{ile ]irecipitalo, UMolublt 
in water, alkalies, and dilute acida, anil only Bparingly aoluble in a 
bat readily soluble in «ther or acetic acid. In itrang aulpburio add ll 
diawilvea irith blue colour. 



m dutj of 4000 of copper, and aufSce for the production of from | 
KOOO to 20,000 parts of aniline black. Electrolytic oxygen may 

be employod for producing aniline black. 

To producQ aniline black in a pure state, 40 parts of aniline 
hydrocLlocide, 40 of cupric sulphate, 20 of potassium chlorate, and 
16 paxla of anunouium chloride should he diBSoIved in 500 parta 
of water, and the solution heated to about 60° C. The black 
precipitate formed may be purified, if desired, hy boiling it 
successively with hydrochloric acid, alcohol, ether, benzene, and 
chloroform. The prmluct ia the hydrochloride of a base called 
u t g r a n i 1 i n e, which may be obtained in a free state by treating 
the colouring matter with a dilute alkali. 

Xigraniline has the empirical formula CgH^N, and consequently 
possesses the same centesimal composition as azobenzene 
(pago 175), lis molecular formula, according to Nietzki, is 
probnbly CjjHjjNj, According to L i e c h t i and S u i d a, how- 
ever, aniline black is a chlorinated base called emeraldine, 
containing Cj^Hj^CINg, all the salts of which contain chlorine, 
, which cannot be removed even by treatment with argentic oxide, - 
miliue is a weak base, and eombines with two eijuivalents of 
B to form a scries of dark green salts, which are insoluble in 

1 partially decomposed by water. 
3 black is turned dark green by sulphurous acid, and 

r mineral acids also affect it ; but if it be treated with an acid 
I of potassium bichromate the black colour becomes per- 
kent, and is no longer affected by treatment with acids or 
Being agents. According to Liechti and Suida, this un- 
able black is not a chromate of the base, hut the compound 
n oxidation- product with chromic oxide (Cr^Oj). 
By treatment with tin and hydrochloric acid, aniline black is 
paradiamidohenzene, paradiamido- 
^henylamine, and other product& 

~ werful oxidising agents, such as chromic acid mixture, convert 
e block into quinone, CjH^Og. 

liline black dissolves in strong su][ihiiric acid to form 
aphonic acids, which are insoluble in acidulated water, 
1 are therefore precipitated on adding water to the solution. 
'"On protracted washing with water the precipitate dL'isolvea with 
given colour. The alkali-metal compounds of aulphonated aniline 
black dissolve in water with blue-black colour. The solutions are 
dcDoIoriBed by reducing agents {e.g., zinc-powder, glucose), but 
recover their original tint on exposure to air. The fact is em- 
ployed for the preparation of an aniline-black vat. 

pn heating aniline-hlack with aniline acetate, an indulino is 



formed (page 248), the hydrochloride of which crystallises in 
needles having a cupreous lustre. 

Aniline-black differs remarkably from most other aniline colours 
in that it is wholly insoluble in water, alcohol, acids, soap-lye, and 
alkaline solutions. Hence the application of ready-formed aniline- 
black is very limited, and it is usually produced in the fibre 
itself. It yields an extremely fast and pure black on cotton, but 
it is not well suited for dyeing silk or wool. 

On the fibre, aniline-black is easily recognised by its resistance 
to reagents,^ being unchanged by alkalies, and either wholly un- 
changed by acids or turned slightly greenish, the black colour 
being restored by alkalies. Weak oxidising agents have no effect^ 
but if the fibre be treated alternately with strong solutions of 
potassium permanganate and oxalic acid, several times in succession, 
the colour will be destroyed. Hypochlorites change the colour to 
brownish-red, but if the fibre thus treated be' washed and exposed 
to the air it slowly becomes black again. 


The colouring matters of this class are, or can be, obtained bj 
the reaction of nitrosodimethylaniline or its analogues on various 
aromatic amines and phenola The dyes thus produced may be 
arranged under the four heads of safranines, eurhodines, indo- 
phenols, and oxazines. The following table shows the names and 
formulae of the more important colouring matters of these classes. 
Mauveine (page 257) is probably related to the safranines, 
but its constitution has not been ascertained with certainty. 

Commercial Name. 

I. Safranines. 
Neutral Blue. 

Basle Blue. 

Chemical Name or 

Chloride of phenyl- 


Chloride of tolyl-dlme 


fiN*l • 
(CH3>2Np.C6H8:-^ . y:CioH« 


(CH3)8Np.CoHs :{ . * I : C,oH«^.NH(C7H7) 



^ Fibres dyed with logwood black leave on ignition an ash containing iron 
or chromium, as also do madder and tannin blacks. These blacks are reddened 
by dilute hydrochloric acid, and are readily bleached by bromine water or 



merdal Name. 

tnlne B extra. 

mine (page 256) 
uiine T. 
mine extra O. 

HA, Ametliysr. 

Chemical Name or 

dthalene Red. 
tao Red. 
dne (page 257). 


tral Violet 
w page 258.) 

>e page 25S.) 


ithol Bine 

)e IndophenoL 
iced Indo- 
enol (page 

ol Blue. 


Violet (page 

e (page 259). 

ithalene Blue, 
ola'i Blue. 
Blue (page 

arin (page 

Blue (page 

Chloride of paramido* 

Mixture of Tolusafra- 
nine and phenotolu- 

Chloride of xylrl- 

Chloride of diamido- 


flydrochloride of Di- 

Hydrochloride of Di- 

Oxidation-product of 

(Tin compound of) 


Chloride of Dimethyl- 
phenvl ammonium- 
azlne-carbonic acid. 

Methyl ether of Oallo- 

Chloride of Dimethyl- 

Chloride of Dimethyl- 

um betaoxjmaphth- 
Chloride or sulphate 
of Dimethyl-phenyl- 

HjNp.CbH,; ^^^ X:C5H< 

cf ifceH^P.NHj 

HaNp.C6Hj(CH,),: <^' >: C^^CB^ 

cC CA-i'NHs 

(CH,),N5.C6H8 :]'[: CsHj(CH^CH5)« 

d i^ieHj-lPNrf, 

H2N.C10H5 J . I : C,oH« 
cf" C,oH«.NHa 









J > : CioHe 




a.(CH,)8N.CeH, : I JS I • CjH \*OH 

^"^J (6CO.OH 

a.(CH,)3N.C6Hs : (IS 1 : CeH |oH 

^^^ * (CO.O(CHs) 

CL(CF,)jN.CeH, : |'^| : CioH« 





Safranines. The dyes of this class all contain the group: — 

The two unsatisfied bonds are usually united to pheuylene either 
substituted or intact, but in a few cases are satisfied by C^^^ 
In addition, one or both of the nitrogen atoms exercise pentavaleDt 
functions, as will be seen on reference to the foregoing table. 
This constitutes a distinction between the safranines and the 
eurhodines, as in the latter both the nitrogen atoms appear 
to be trivalent (see page 253). 

A general method for the production of the safranines consists in 
the oxidation of one molecule of a paradiamido-base with two 
molecules of a mono-amido-base in a hot, neutral, aqueous solution.^ 
Potassium bichromate is a suitable oxidising agent. The simplest 
member of the class, namely, phenosafranine, is obtained bjr 
oxidising a mixture of paradiamido-benzene and aniline hydio- 
chloride, C^HgNj + 2CqKjN + 20^ = CigHi^N^ + 4H2O . 

The safranines of commerce are the chlorides of compound 
ammonium bases called azoniums. The free bases are but little 
known. Their salts, which usually crystallise well, are red or 
violet dyes, the dilute aqueous solutions of which give no precipi- 
tate with alkalies. On treatment with dioxidising agents they are 
reduced to colourless leucosafranines, which readily absorb 
oxygen from the air, with re-formation of the original colouring 

The safranines mostly dissolve in strong sulphuric acid with 
fine green colour. On gradually adding water, the colour of the 
liquid changes first to bluish-green, and then to a pure blue. With 
still more water, the solution becomes violet-blue, and ultimately 
acquires the colour of an aqueous solution of the dye under examin- 
tion. The green solution absorbs the violet, blue, and red rays of 
the spectrum, and the bluish-green behaves similarly, but absorbs 
the red less perfectly; the blue solution absorbs only yellow light; 
and as by dilution the colour changes to violet and red, the region 
of absorption approaches the green. 

The following Table exhibits the chief properties and reactions 
of the safranines of commercial importance. Their constitutional 
formulae are given on pages 252 and 253. 

^ Safranines are also formed when one molecule of meta- or para-tolnidioe, 
or of methyl- or dimethyl-aniline, is substituted for one of aniline. Both 
molecules of aniline may be similarly substituted by metatoluidine, but with 
two molecules of paratoluidine or of meth}*!- or dimethyl-aniline the formatioD 
of the colouring matter does not take place. 














s a 


a sj 9 




i*« o 


J.*?! • ^ 









^ s 


« o 

e c 








AS s 
■** dja 



























OS a> 

d ^ k 

















The only colouring matters of the saf ranine group requiring further 
description are the following ; — 

Safraninb, Safranine T, Safranine extra G, or Aniline PinL 
This colouring matter, as it occurs in commerce, is a mixture of 
several homologous bodies, of which CigHj^N^Cl, C^Hj^^Cl, and 
C21H41N4CI are the chief. The structural formula of the second 
of these is shown on page 253. Safranine can be obtained 
by various methods, including the oxidation of mauveine, 
C27H25N^C1 ; the treatment of aniline with glacial acetic acid and 
lead nitrate; and by heating amido-azotoluene with toluidine 
nitrate. These methods are obsolete, that now employed being 
usually the oxidation of a mixture of aniline, ortho-toluidine and 
para-toluylene-diamine in molecular porportions. Aniline oil of 
suitable composition is first converted into the amido-azo-compounds 
amido-azobenzene and amido-azotoluene (page 178). When re- 
duced with zinc and hydrochloric acid, the first of these splits into 
aniline and paraphenylene-diamine, and the latter into ortho- 
toluidine and paratoluylene-diamine (page 213) ; thus — 

CeH,(CH3).N2,CeH3(CH3).NH,+ 2H,=CeH,(CH3).NH,+ 

NH3.C<,H3(CH3).im, . 

When the reaction is complete the liquid is diluted, a mole- 
cular proportion of toluidine hydrochloride added, and the mixture 
oxidised by potassium bichromate. The product is boiled with 
milk of lime, and the liquid filtered, neutralised with hydrochloric 
acid, and saturated with salt. The precipitate is purified by solu- 
tion in water, and again salting out. 

Commercial safranine usually occurs as a reddish-brown powder, 
but the pure hydrochloride forms reddish crystals, soluble in water 
and alcohol. The alcoholic solution exhibits a fine yellowish-red 
fluorescence. Caustic alkalies and ammonia change the colour of an 
aqueous solution of safranine to brownish-red, but no precipitate 
is produced unless the liquid is concentrated. The base is best 
prepared by treating a solution of the hydrochloride with argentic 
oxide, filtering, and evaporating the filtrate to dryness. 

Safranine is one of the few colouring matters wliich are taken 
up by animal fibres from alkaline solutions. In alkaline or 
neutral solution safranine also possesses some affinity for cotton, 
but the colour produced is not fast. The best mordant is tannin 
and tartar-emetic. 

On the fibre, safranine is distinguished by being unchanged by 
dilute acid but turned from red to blue- violet by concentrated 
hydrochloric acid. Ammonia and caustic soda remove the colour- 
ing matter without much previous change of tint. The colour is 



L»l on warming the iibre with hydrochloric acid and stannous 

Alcohol atripa fibres dyed with aafranine, forming a red 

which exhibits a reddish-yellow fluorescence, 

LOUAU Rkd. Naphthauinb Red. CgoH^jN^Cl + H^O (see 

253, 255). This colouring matter is prepared by heating 

iphthylamine in acetic acid solution to 150° with a molecular pro- 

" inofldpha-amido-asDnaphthalene (prepared by diazotisingal|>ha- 

itliylftmine hydrochloride). The melt is boiled with a large 

of hydrochloric acid, and the liijuid filtered. The filtrate is 

lised, and salt gradually added, when the rosanaphthylamine 

ipitated as a sparingly soluble hydrochloride, and a violet 

ing matter and excess of napbthylamine i-eniain in solution, 

Faphthaleue red ia characterised by its veiy sparing solubility 

itflT, oven when hot, and by forming a cherry-red alcoholic 

which exhibits a fluorescence of a remarkable ciiinabar- 

colour. This behaviour is simulated only by an alkaline 

lutinn of azoresorufln (page 158) ; but that substance differs from 

naphthalene red in the colour it dyes silk, and in yielding a brown 

precipitate on addition of a stronj; acid. The fluorescence of a 

solution of naphthalene red ia destroyed by ammonia or soda, 

Magilrdn red is employed for producing a fluorescent pink on 
wlk and velvet. It is not used on wool. Neither the shade nor 
fiuoresccuce is altered in artificial light. It is distinguished from 
hy not being stripped from tlie fibre by alcubol, and hy not 
readily afl'ected by alkalies or dilute acids. 
[ADVKtse, C^HjjN,, is of interest as being the base of Perkin'a 
_ I»i aniline violet, or mauEe, the first commercial dye from aniline. 
^6 free base may be obtained by adding caustic ^ali to a boil- 
ing alcoholic solution of the cryatollised acetate. It then separates 
a ft black glistening powder, which is almost insoluble in ether or 
Le,but in alcohol forma a violet solution, which is turned purple 
[ding a dilute acid, or even by carbonic acid, Mauveine is a 
base, decomposing ammonium salts and forming a carbonate, 
iminercial mauve ia usually a sulphate of the base. It is 
almost obsolete, but occasionally occurs as a reddish -violet 
Sparingly soluble iu hot water with violet-red colour. The 
ion is unchanged by hydrochloric acid, but yields a bluish- 
tt precipitate with soda, and dyes silk a reddish -violet. In 
XM of strong sulphuric acid, mauve dissolves with olive- 
colour, changing on adding water to green, sky-blue, and 
ly to o reddish -violet. 


^, N. Witt defines the c u r h o d i u c s as dye-stuffs which 
BfOl. UI. PART L It 

I BUo rci 


are derived from azines by the replacement of an atom of hydrogen 
by an amido-group, thus differing from the safranines, which 
contain two amido-groups, and are the salts of azonium- 
bases (page 264). Neutral violet and neutral or toluylene-red, 
the formulas of which have been already given (page 253), are 
the only dyes of the eurhodine class requiring detailed description* 

Neutral Violet, Ci4Hj^N^,HC1 (page 253), is produced by the 
reaction of nitroso-dimethylaniline on meta-phenylenediamine. 
The commercial colouring matter is a greenish-black powder, the 
dust of which is intensely irritating to the mucous membrane. It 
dissolves easily in water with violet-red colour. The solution is 
scarcely changed by a little hydrochloric acid, but is turned blue 
by excess. Soda produces a brown precipitate. In concentrated 
sulphuric acid the dye dissolves with green (or, according to 
Zetter, dirty violet) colour, which on adding water becomes blue, 
and on further dilution violet. 

Neutral Red or Toluylbnb Red, Ci5HjgN4,HCl (page 253), is 
homologous with the last colour. It forms a greenish-black powder 
easily soluble in water with bluish-red colour, which turns bluer 
and then disappears oil warming with zinc and hydrochloric acid, 
but returns on exposing the reduced solution to the air. In 
alcohol the dye dissolves to a magenta-red solution, which exhibits 
a strong brownish-red fluorescehce. With hydrochloric acid the 
aqueous solution becomes bluer, and with excess pure blue. With 
soda it yields a yellowish-brown precipitate, soluble in ether with 
greenish-yellow fluorescence. In strong sulphuric acid, toluylene 
red dissolves with bluish-green colour, changing to blue and magenta- 
red on adding water. 


When a phenol is substituted for an aromatic monamine in the 
process for the preparation of safranines (pages 254, 256), colour- 
ing matters are produced which are called indophenols. The 
chief member of the class is prepared by reducing nitrosodimethyl* 
aniline in aqueous solution to dimethyl-paraphenylenediamine, 
NH2.CgH^.N(CH3)2, filtering, and treating the filtrate with a 
solution of two molecules of alpha-naphthol in caustic soda. 
Potassium bichromate is next added, and then acetic acid till the 
liquid acquires an acid reaction, when the colouring matter is pre- 
cipitated. Indophenol may also be obtained by the direct action 
of nitro-dimethylaniline on alpha-naphthol. 

Indophenol or Naphthol Blub, CigHj^NgO, prepared as above, 
is a feeble base which probably has the constitution expressed by 
the formula : — 

„ ( C,H,..N(CH,), 
r I C,.H,-,0 


Tbia is bome out by ita reduction by stannoua acetate to a 

Ko-body posaeasing both acid and biisic properties, and 
g the formula :- 
_ (■CeHyN(CH3), 
■„„inniercial in-iophenol N forma a blue paste or dark broivn 
powder, which when dry has a coppery reflection and closely 
reaeniblea some varieties of indigo. When heated it sublimes in 
needles. Indophenol ia quite insoluble in water, but diesolvea in 
alcohol with blue colour, and in strong sulphuric acid with dirty 
yeUo wish-brown colour, the solution giving a brown precipitate on 
dilution. The alcoholic solution is turned reddish-brown by 
hydtocbloric acid, but ia unchanged by alkalies. The alkaline 
solution, DT the solid dye in presence of alkali, is decolorised by 
reducing agents, such as stannous chloride or glucose, so that a vat 
can be prepared from indophenol in the same way aa from indigo. 

Kbsucbd Indofhknol, or Whttb Indophenol, CigH,gNjO, 
ocoure in commerce as a yellowieh-white paste, soluble in pure or 
acidulated water. It is unchanged by hydrochloric acid. In pre- 
sence of aa alkali and air it gradually oxidises to blue indophenol, 
or immediately on cautious treatment with bichromate of potassium 
or n hypochlorite, 

Indophenol is employed as a substitute for indigo in wool and 
cotton dyeing. It forma a lake with chromic oxide. On the fibre 
it is boet recognised by being turned greyish-biown or dark grey 
by treatment with somewhat dilute (10 per cent.) hydrochloric 
acid, while indigo and other dark blue dyes are unaffected. 


(See also page 263.) These colouring matters are pioduced by 
Uie action of phenoloids on a salt of nitroso4imethylaoiline or an 
allied body. All the oxnzines contain the group: — 

■[ a . N(CHa).CaH3; | ^ j : , or ClC„HuNjO : 

i(jALLOCrANTN, or Solid Violet, C,sH^NjObCI (page 253), occure 
unially iu commerce as a nearly insoluble, greenish-grey paste, 
which fonus a bronze powder on drying. The characters of puie 
([kllocyanin are described on page 74. 
r Pbunb, Ci-Hi-NjO-Cl (page 263), is the methyl ether of gallo- 

260 0XAZINE3. 

cyanin, and forms small bronze eiystala or a dark brown powder. 
It is soluble in water and alcohol with bluiah-violet colour. 
Hydrocliloric acid turns the solution magenta-red, and sods, give* 
first a brown precipitate, and with excess of the reagent a nulct 
solution. In concentrated sulphuric acid the dye dissolves with 
corn-flower blue colour, changing to magcnta-red on dilution. 

Mkldola's Elcs, or Nbw Blub (Caaelh), C,sH,jN(OCI (ftgt 
253), called also fast bltif 3 B for eotton and napkthatfw Niti B 
in crystals, is produced by the reaction of twtanapbthol on oitrosodi- 
methylaniline hydrochloride. It occurs in commerce as a dftik 
violet powder with bronso reflection. The dust strongly iirittlM 
the mncouB membrane. In water it is soluble with bliush-vidil 
colour ; in alcohol with blue colour. The violet aqueous M^tioa 
becomea at first green and then colonrlosa when reduced by nac 
and acetic acid, the original colour returning on cxi>ostirB to lii. 
The solution is turned blue by hydrochloric acid, and with uda 
yields a broivn precipitate. In strong sulphuric acid the ilj« 
dissolves with black isli-green colour, becoming iiist bine and then 
violet on dilution. Naphthalene blue dyes cotton noidiiilcd 
with tannin and tartar-emetic an indigo-blue colour. 

MuscARiN, CijHijNjOjCl, introduced by Dumnd and Hagumin. 
occurs in commerce as a brown-violet powder, sparingly aolubU in 
cold but readily in hot water, with bluish-violet ooloor. Tba 
solution is decolorised by heating vrith zinc-dust, but ths tfAmt 
returns on exposure to air. Hydrochloric acid produces a bluiA- 
violet and soda a yellowish-brown precipitate. Tannin precipittM 
the solution indigo-blue. In concentrated sulphuric acid muMUin 
dissolves with bluish-green colour,' the solution turning fltst Um 
and then violet on adding water, and on further dilution givin;^ » 
violet precipitate. 

NiLB Blue is produc«d by the reaction of alpha-naphthylaiiuiH 
on the hydrochloride of nitroso-dimethyl-metamidophenoL U 
occurs in commerce both as the cMoridf, the formula of whi«b hu 
already been given (page 253), and as a mJ/Jtate of the composition 
(C,gHjgN30)jS0j. The sulphate forma a green erysUUlRo powilcf 
with bronze reflection. It is sparingly soluble tn cold water, bnt 
readily on warming, with blue colour. It is also soluble in qJcoIuiL 
The warm concentrated aqueous solution yielda with hydruehlotie 
acid needles of the chloride, which appear violet by tnuumilted 
and green by reflected light. .Addition of soda to the dilnta 
solution (1:1000) produces a red precipitate, solulile in etber to t 
brown-orange solution, witJi dark green fluoreaciincc, Tuiani 
presence of sodium ac«tate gives a prusaian-blne prajpitat^ 
I According to »ome ■athoritiee, rrddiah-rlolM. 


stfuinous chloride a dnrk greenish-blue precipitate, and on warming 
the liquid exhibits a greeu fluorescence, with blue tranamitted light. 
In concentrated sulphuric acid, the dye dissolves with yellow or 
red-brown colour, changing to green and blue on dilution. Wool 
is dyed dire<:tly by nile blue a red shade of blue, and cotton mor- 
danted with tannin and tartar-emetic is dyed blue. The colour 
is not fast to light, and is liable to bleed when milled with eoap, 
but not with soda. 


The coloured derivatives of anthracene are limited in number, 
and even of theBe few have any practical value as dyes. Thoy differ 
materially from the coal-tar dyes hitherto considered, though present- 
ing considerable resemblance between themselves, and several mem- 
bers of the group are colouriug matters of the first importance.' 

The starting point in the production of alizarin and allied 
colouring matters ie commercial antbracene, containing from 50 
to 56 per cent, of the pure hydrocarbon, C^Hj^, or sometimes a 
purer product, obtained by sublimation, is employed. Thia ia sus- 
pended in water and treated with 1 J times its weight of potassium 
bichromate and on equivalent quantity of sulphuric acid, when the 
anthracene is converted into anthraquinone, CnHgOj. The 
product is separated by filtration, dried, ti'eated with strong sulphuric 
add (ap. gr. 1-84), and the mixture heated to 106°-110' C. The 
black product is treated with steam, which is absorbed by the 
inlphitric acid, and as the dilution proceeds the anthraquinone 
crystaltisea out. Boiling water is then added, and the product 
well washed with hot water and solution of soda to remove 
BMOciat«d organic acids, after which it is further purified by sub- 
limation or distillation in a current of superheated steam. The 
product contains from 9G to 98 per cent, of real anthraquinone, 
and forms golden-yellow prismatic needles, melting at 273° C, 
insoluble in water, highly stable and indifferout, and unacted on 
by bases or dilut« acids (see voL iL page 515). 

Anthraquinone has a constitution espressed by the forinul.i 

C^St- { pf) f ^CnH, . When treated with fuming aiUphuric acid 

containing 60 per cent, of the anhydride, it yields authra- 

' The tnonpy valne of artificml aliESrin and the allici! colours is more than 
ODft-thinl ot that of the tnCal coal-tar dyes, aad the piica of aliiano, comparad 
^potatiBlly, U Dot more than one-fourth of what it was in the form of madder 



qutnone-monosulplioiiic acid, the sodium ealt of wbicli 
ii fused for several days at ISO' to 200° C. with caustic soda, and 

BiifEcient potassium chlorate or nitrate to prevent reduction bj the 
hydrogen evolved, yields sodium al izarate,* thus : — 

CflHi:COi:CsH,SOgNa+3H(ONa) = C«H4:CO^;CaH^ONa), 
+Naj80j4-HjO + Hj. 

On dissolving the melt in water and adding hydrochlorio add, 
free alimrin, or ortho ■ dih ydrox y -an thraqniuon*, 
CgH^ : CjOa : CoHj(OH)j , ia precipitated. 

If, in the treatment of the anthmqninonc with fuming solplniDe 
acid, an excess of the recent be employed, instead of the IINK- 
sulphonic acid b Jiefn-diaid phonic acid is the chief product; bat If 
the temperature be increased to 180''-185°, the isomeric tt^/kt- 
disnlphonic acid is the more abundant.' 

On fusing the alpha-disulphonic acid of anthraquinone witb 
causticsoda, it is converted into the sodium salt of a nth raflavic 
acid, while the beta-acid when thus treated yields the isomeric body 
tso-anthraflavic acid. Both these substances are dilij- 
droxy an thraqui nones, like aJiuuin, and dissolve in alkalies with 
yellow colour, but have no dyeing properties. If the fusion of llw 
alpha- and beta-disulphonic acids of aiithraquinone with caus^ 
soda he conducted in presence of an oxidising agent, the pK- 
ducts are the sodium salts of f lavopurpurin and anlhit- 
purpurio respectively. Both these bodies are raluahl* ij*- 
matters, and have the constitution of trihydroxy-anlliri- 
q u i n o n e B, CgH^ : CjOj : CeH(OH)g, the difference between thott 
being due to the positions of the hydrojcyl groups. They are holh 
isomeric with the natural substance purpurin, contained u> 
madder, which has been obtained synthetically by oxidising aliaria 
in solution in concentrated sulphuric acid (jiage 270). Anthrs' 
gallol is a fourth trihydroxy-anthraquinone, obtained by th« 
action of phthalic anhydride on pyrogallol in sulphuric acid boIu- 
lion. (See page 270.) 

Several tetrahydroxyanthrnquinones (i-.g., anlhn- 
chrysone, hydroxypurpurin,rufiopin) are known, while ruf igalli' 
acid (see page 67) has the constitution of a hexahydrozy- 

' It the fumon bo conduoted in the absence of njr, and no oiidiaing iffOit b> 
added, the sodiam compoand ol mono - hydroxy an tfa 

' On converting the mixed product into sodium salts and adding dJoU 
sulphnric acid, the sparingly soloblo moDosuIphonate can be separattdi' 
the eneily soluble acid sodium salts of the two isomeric disnlphonic 


The constitution of anthraquinone derivatives is beat interpreted 
by the aid of the " bensiene-cliaia." 

k^ram represents the conBtitution of anthmquinone, an 
.rbon being situated at each angle, and combined at the 
— ^ ^jBitions with an atom of hydrogen. By the replacement 

of one or more of these hydrt^en atoms by a corresponding number 
•it liydroxyl groups, various hydroxy-derivfttivea of anthraquinone 
are obtainable, and their constitution, bo far as it is known, will be 
understood by comparing the following table with the diagram: — 




















a:lK, ■ 


Aattannllol. . 

noses, . 




B«flwUUc«W (PW BT). . . 

By the oxidation of methyl-anthiacene, C,^HB{CHg), , 
fae» of products parallel to the above maybe obtained. C h ry a o 



phanic acid, C^H, : CjOj : C(CHgXOH), (see page 3Sl),iik 
dihydroxy-methytanthraquinone, wbHe e mo din ia a tiihydmj^ 


Such of the hydroxy-dcrivatiyes of anthraquinoDB as Kodn 
practical application are not known generally by their systeau& 
or descriptive names, but are simply termed " alizarin for Ttit," 
" alizarin for blues," &c. Hence it will be convenient to duscrib* 
fully the characters of true alijarin, and aubaequently treat of tin 
various products known in commerce as " alizarin." 

Alizarin. Ortho-dihydroxy-anthraqtuiione. 


Alizarin exists ready-formed in madder-root (Jtubia tindanan), 
but the proportion of actual alizarin is, except in old mat*. 
small compared with that existing potentially in the form of 
ruberythric acid,' a glucoside which on ateeping the maddei 
roots in water is resolved, under the influence of a peculiar fermajit 
called erythrozyme, into alizarin and dextro-gl' 
according to the following equation ; — 

CiMHagOi,-|-2H,0 = C,.HgO,+2C,H,jOo. 

Various methods of accelerating this change have been 
the most important and rational being to treat the powdered nut, 
previously exhausted with water, with strong sulphuric acid, whid 
splits up the ruberythric acid according to the foregoing equation, 
without altering the resultant alizarin. The product thus obtaind 
was called garancine, but the cultivation of madder as a sonrcc 
of alizarin is now almost entirely abandoned, and garancine and 
similar products have little more than an historical interest. 

Alizarin is now manufactured artificially on a very Urge scale. 
the sole source being the anthracene from coal-tar. IV 
synthesis of alizarin was first effected by G r a o b e and L i e b r r 
mann, in 1868. One of the methods employed in practice haa 
already been described in outline (page 261). The other coffl- 
niercial process, devised by W. H. P e r k i n, consists in converting 
anthracene into dichtoranthracene, C„HbCIs, by the actloii 
of chlorine, and heating the product with sulphuric acid, whetvlif 

1 RDBKarrnaio or BimiANiC Actn, Cf,Hffii„ may ba otitalind hy ubwut- 
iag fr«3h madder-root with wHtcr, addixig iieulral Inul wbkte, fillBri^, ml 
dccom|)i»iug tbe procjpiute of lend raliianate by sulpbiiraltvJ faydnigm, 0> 

evaporating the liquid filtered from the lead * ' 

^Iky a 



a mixture is obtained of the two i 
disalphonic acids deecribed on page 262, with more or lesa 
of the raoiiosulpbonic acid. The subsequent fusion with an alkali 
and an oxidising agent, and decomposition of the sodium salts by an 
acid ie the same as that already described. To obtain pure alizarin, 
% pure monosulphonic acid (free from the diaulphonic acid) must 
be employed,* and hence Perktn'a process ia better adapted for 
die pToduotion of anthrapurpurin and fiavopurpurin thiin true 

Alizarin may also be prepared by heating phthalic anhydride 
with catechol, a reaction which indicates its constitution; — 

CeH,;(CO.OH)j+C8H,:(OH)j = CeH,:(CO)2:CflH„(OH),+20Hs. 

Alizarin crystallises from alcohol in reddish-yellow prisms or 

needles cnntaining 3 aqua, which it loses at 100", It melts at 

369*— 290" C.,' and sublimes at a somewhat higher temperature in 

I Bugsificent orange-red needles. 

' AliEarin is nearly insoluble in cold water, and requires 3220 
paito of boiling water for solution. Cold alcohol dissolves it but 
sparingly, but in boiling alcohol, glacial acetic acid, and glycerin it is 
more soluble. It ia also readily soluble in ether, carbon disulphidc, 
and benzene, and may be extracted by agitation with these solvents. 
In strong sulphuric acid, aliaarin dissolves with dark brownish -red 
colonr, and is precipitated unchanged on diluting the solution with 

Id solutions of alum and aluminium sulphate alizarin is almost 
insoluble, a character which distinguishes it from purpurin, which 
dissolves in boillug alum solution, forming a yellowish-red and 
strongly fluorescent liquid (page 270). 

Alizarin has the characters of a weak acid. It dissolves in solu- 
tions of carbonates of the alkali -metals, apparently without decom- 
posing them, and it also dissolves in a boiling solution of sodium 
acetate, separating ^ain unchanged on cooling; but if the boiling 
be continued (or some time, acetic acid is given off and sodium 
alLcarate remains in permanent solution. With caustic alkalies it 
reacts to form true compounds or alitarates, the solutions of which 

'To obtun pare olizBnn, the !)liie«lisde of commercial alizarin paatemsy be 
diMolvtd in dilnte caostic soda, and the filtered solation treated with barium 
chloride uiil heated to boiling. Barium ati/arate separstfs as a prroipitaCe, 
which ia filtered off, washed, and decompowd by hydrochloric acid. The rre« 
■lizarin is wall waibed, and can be further purified by niblimation or cryatal- 
liaatiou from glacial aeeric acid. 

■ This ia tha melting point of alizarin according to C 1 a a a and W i 1 d- 
'odt Suhunuk gives 232^ as tho malting point. 


266 RKAcno.vs of alizahdj. 

Me violet by tmnsmitted, and purple by reSected, tight. A solll* 
tiou of sodium olizarate give« insoluble, colouied precitntata a 
" lakes " with most metallic solutiona. Tbua with barium umI 
calcium s.tlts it yields purple precipitates (distinction from mono- 
hydroxyanthraquinone) which are soluble in water containing oar- 
bouic acid. With aluminium ajid tin alixarin forme red lakes, and 
has such afHnity for these metals that it is capable of decomposing 
dilute solutioHB of nitrates or chlorides containing th«m. Witb 
ferric salts, sodium alizamte yields a bluck-violet precipitate, but 
with ferrous salts a violet precipitate is formed. An alcoholii; 
solution of free aliwrin also gives a purple precipitate with ferric 

By heating in the solid state with zioc-duet, alizarin b redocnl 
to anthracene, Ci,H,o. If dissolved in weak soda and treated 
in the cold with zinc-dust, tho violet solution becomes ml 
When alizarin is boiled with zinc -dust and ammonia it u 
reduced to a body of the formula C„H||,Oj, to which the name 
antbrarobin has been given.* 

The solution of alizarin in ammonia or carbonated alkali differ* 
from that of purpurin in being non-fluoresceat, but eThibiU a 
characteristic absorption-spectrum, having a well-defined bond in 
the yellow, and another narrower one between the ornnge and r«il. 
There is also another faint band about £,, scarcely distinguUbablfl 
from the general absorption occurring in that region. The absurp- 
tion spectra of the solutions of alizarin in ether and carbon disol' 
phide are not characteristic (compare page 272). 

When boiled with acetic anhydride, alizarin yields a mono- 
ace ty I-de rivative, and on prolonged boiling diacetyl- 
alizarin, CuHo(O.CjH^O),Oj . 

Alizahin-sitlphonio Acid. CnH[|Oj(OH)i(SOgH). This body 

' Ahthrarobik has been recommeodeil in Bkln-dineases ns a sahstitatc fn 
clirysarobin or chiyeophanic acid (p*ge '283), as it is aaid to be \ue liable to pio- 
dnw infl&mmatiou of the cuticle. It ia prepared by boiling commercirU alinnD 
with dac-diut and dilute nminoni*, filtering the ammoDianLl Bolation inU 
hydrochloric acid, and collecting, washing, and diying tlie precipitUc. tbt 
simiUr product trom purpurin is called aHtkrarabin P or T. 

Commerml anthrarobin is a yellowish -whilo powder, permanent in [he 
and insulnblo in wsteranddilnteacids, but readily soluble with browniih-yd 
'colour in dilute solutions of alkalies and alkaline earths, tlie aolutiont bj 
contact with air or oxygen changing to green and blue, and finally to rioltt. 

Antbrarobin dissolves with difficulty in beDianeor clilorofomi, butiswIobU 
with moderate facility in cold, and *ery easily in boiling alcohol. The ako- 
holic Bolntion may be mixed with glycerin withont precipitation. 

CoiamerciDl anthrarobin contains a trace of zinc, but the eotin; luh sbmld 
not exceed 0'3 per cenL 

B formed by heatinjj aluarin with fuming aulphuric acjii until the 
3 completely soluble in wat^j. The liquid is then diluted, 
xud the unaltered sulphuric acid precipitfited^y lime or baryta. 

Alijiarin-Bul phonic add is freely soluble in water, and forma thi 
■eries of salts, according to the number of hydrogen atoms replace 
The salts of the alkali-metala containing one atom of base i 
yellow or orange, and soluble in wlter ; those with two atoms a 
reddiab-riolet; and those with three atoms intensely violet. 

Sodium Aluarin-gidphciruUe, C^fifi^O'H'^^O^a), conatitutea 
the colouring matter known in commerce as alimnn carmine^A 
alwarin jioteder W, and alizarin WS or W$I. It forms a 
yellow powder, easily soluble in water or alcohol with orange t 
brownish-yellow colour. The solution is turned bright yellow 
hydrochloric acid and violet by caustic soda. In strong sulphuric 
acid the dye dissolves with yeUowish-red colour, changing to 
bright yellow on dilution. Alizarin carmine dyes wool mordanted 
with alumina scarlet, while tin mordants give orange and chromium. J 
claret-red shades - but the colours are not so bright as those ol>< 
tained with sulphonatcd azo-dyea 

Bbta-nitboalizarin. CBH,:C,Oj;CflH{NOj){OH)j. By direct * 
treatment with nitric acid, alizarin is converted into phthali' 
acid, CaH,{COOH)3(page47); but by the action of nitric acid on 
alizarin dissolved in g^ial acetic acid or petroleum spirit, be ta- 
-alizarin is obtained. This body, which constitutes the 
> orange of commerce, was formerly prepared by exposing 
loth dyed with alirarin red to nitroun fumes, but is now directly 
ibtained by treating alizarin in nitrobenzene solution with nitric t 
i of 30°— 40° Baumd. When pure, nitro-alizarin forma yelloww 
sedles or leaflets, which melt at 244° C. and sublime at a highei 
mpeimture with partial decomposition. It is nearly insoluble in 
water, but dissolves in glacial acetic acid. The solution in caustic 
aoda is magenta-red, and on treatment with zinc-dust gradually 
becomes blue and then yellowish-brown, the indigo-blue colour r 
turning on exposing the filtered liquid to the air. Other reactions | 
of alizarin orange are given on page 276. 

^-nitro-alizarin derives its cliief practical interest from 
action with glycerol and sulphuric acid,* whereby it is cc 
in dihy droxyanthraquinone-quinoline, 
n blue, according to the following equation : — 

ited. ^1 

ites I 





+ CH.OH = 

'»■( CH : CH. \ 
(.N ;CH. J 

+ 0i+30H,, 

AuzARiN Blce, C,jHjNO^, has the constitutional fornrnJi 
shown above. In the pure state it forma dark blue or brownish- 
violet needles, which melt at 270°, and may be partially Bubllmed 
without decompoaition. In commei'ce, alizarin blue ocoutb U 
minute shining crystals, or as a dark violet paste containing 10 
per cent, of the diy substance. The pure colouring matter con bo 
obtained by boUiiig the dried paste with glacial acetic acid, tlie 
alizarin blue being deposited in crystals on cooling. It is tnsoluhlu 
in water, but dissolves with blue colour in hot alcohol, and a 
sparingly soluble in benzene. 

Alizarin blue eichibits both acid and basic characters, a property 
doubtless due to the simultaneous presence of OH groups and a 
pyridine residue in the molecula With dilute sulphuric acid alizarin 
blue imitoa to form a brown compound, which is decomposed by 
washing with water. In strong sulphuric acid it dissolves witii red, 
and in phosphoric and arsenic acids with reddish-yellow colour. 

In dilate caustic alkalies alizarin blue dissolves with greeniali- 
blue colour, but the solution is precipitated by excess of alkali. 
By treating the solution of alizarin blue in caustic alkali with 
metallic solutions a series of insoluble lakes may be obtaioeil. 
The compounds with lime, baryta, and ferric oxide are greenisb- 
blue, that with nickel oxide blue, and those with alumina and 
oxide of chromium bluish-riolet. 

When treated with zinc-dust in alkaline solution, alizarin blue 
is reduced with red coloration, but the blue colour returns on 
exposing the filtered liquid to the air. Other reducing agents may 
be employed, and the property may be applied for the production 
of an alizarin blue vat, similar to that used in Indigo-dyeing. 
Alizarin blue is too expensive to be used generally as a substitule 
for indigo, and its tendency to form insoluble lakes is not in Us 
favour. The colour is not so fast to light us indigo, but is lem 
readily attacked by oxidising agents, such as hypochlorites, chromic 
acid, and alkaline solutions of ferricyanidea. 

Tha inconvenience attending the employment of 



1 blae cnn be overconie by converting it into a soluble fomi, 
^^ reating the commercial paste with a concentrated solution of 
acid sodium sulphite. After standing ten days or a fortnight, 
the liquid is filtered, and the new colouring matter ohtaincd 
in the solid state by eyaporation at a low temperature or salting 

tLlZARt?! Blue S, or Soluble Alimrin Blue, obtained as above 
ihed, ia the sodium bisulphite compound of dihydroxyanthra- 
one-quinoline. It occurs in commerce as a dark purple or 
olate-hrown powder, which dissolves easily in water with 
yellowish-brown colour. In strong sulphuric acid the solid dye 
dissolves with deep yellow colour, and on dilution with water the 
liquid yields a brownish precipitate. Dilute hydrochloric acid 
changes the colour of the aqueous solution to reddish-yellow, and soda 
turns it bluish- violet. With excess of a strong acid or alkali, the 
bisulphite compound is decomposed with precipitation of the blue; 
bnt the eolation is unaffected by salts of calcium, magnesium, or 
chromium, or by acetic or tartaric acid. On heatmg the aqueous 
solution above 70° C, the bisulphite compound is decomposed, and 
the insoluble blue colouring matter is precipitated. This reaction 
is extensively applied in practice, and the colour produced being 
leu aHected by light than that given by insoluble alizarin blue, the 
soluble variety has almost superseded the older colouring matter 
both in printing and dyeing. 

Soluble alintriu blue is now a formidable rival of indigo in 
wool-dyeing. The wool is firat mordanted by sulphuric add 
and bichromate of potassium, and is then immersed in a bath of 
alizarin blue S, to which sufficient acetic acid has been added to 
neutralise any earthy carbonates existing in the water. The 
colour? thus obtained are said to be as fast as indigo to light and 

On the fibre, alizarin blue is unchanged by soap, soda, or solu- 
tion of bleaching powder. When dyed on wool with a chrome 
mordant, nitric acid produces an orange colour, but otherwise the 
colour is discharged. Dilute hydrochloric solution turns the 
colour to violet, and soda to bluidi-green, while an acid solution 
of Btansous chloride changes the colour to a brownish-yellow. 
When treated with phosphoric acid of 1'436 sp. gravity, alizarin 
blue is dissolved from the fibre with orange colour, and the solu- 
tion, after dilution with water, is turned blue on adding ammonia. 
The abaorption-spectmm of alizarin blue is characteristic, and the 
fact may be utilised for its detection. 
I Alizarin bias ia nov being tried on a large wale in the PruHian army, 
BBn^tieli DBvy, and on the Atlantic liner*. 


Trihydroxyanthraquinones. c,,HgO,(OH), . 

Of the five known boliea of thia constitution (formulat«id on 
page 263) four have a practical interest ae colnuiing matl«ts, and 
are described below. Of hydtoxychryBazin, the fifth dis- 
covered isomer, verj' little is known. 

AnthragalU)l, CoH^:CjO,:C,H(OH),.[OH:OH:OH = al :^1 :^2]. 
Thia body has not yet been obtained from anthracene. It is pte- 
I>ated by the action of phthalic anhydride on pyrogallol in presenw 
of sulphuric acid or chloride of zinc ; — 

C,H, : Cp, : + CBHg(0H)3= CflH^ : C,Oj : CgH(OH),+ Hp . 
It may also be obtained by acting with gallic acid on benzoic uil 
in presence of sulphuric acid : — 
C,HB.CO.OH+CaHj(OH)3.CO.OH = CoH,:C30i;CsH(OH)3+2HjO. 

Anthragallol forms the essential constituent of the ooloun'nit 
matter known as artlhraeene brown. It occuis as a dark blown 
paste, insoluble in water, but dissolving in alcohol with y«Ilo* 
colour. Its other reactions are described on page 276. 

I'UBPURIN. C„H,:Cp,:CflH (OH), [OH:OH:OH = «! -.01 :a2] 
Purpurin occurs to a considerable amount in old mwlder-nml, 
mixed with alizarin, from which it may be separated by treating 
the mixture with a boiling solution of alum, in which alizarin is 
insoluble. Purpurin may also be prepared artificially by oxidiung 
alizarin or quinizarin (page 263) with manganese ilioxidfi and BUl- 
pburic acid. A preferable plan is to dissolve alizarin in atroDg 
sulphuric acid, heat the liquid to ISO'-ISO" C, and gradually add 
dry arsenic acid. When the reaction is over, the liquid is diluted 
with water and the precipitate separated and treated with a hot con- 
centrated solution of alum, the liquid is filtered from the residue of 
unchanged alizarin, and the purpurin precipitated from the filtnte 
by adding hydrochloric acid.' The product may be purified hj 
crystallisation from alcohol. 

Purpurin crystallises from its solution in hot spirit in yellowish- 
red needles or prisms, containing CuHg(OH),0,+HjO. It be^ni 
to sublime at 150° and melts at 153°, but is more readily ileoom- 
posed by heat than is alizarin. In water, purpurin is mon 
soluble than alizarin, and the solution in hot water free from alkali 
has a yellow colour, Purpurin also dissolves in alcohol and ethe». 

In caustic alkalies, purpurin dissolves easily with magenta ot 
purple-red colour. It forms a compound with soda, which crystal- 

' Th^ proportion of purpurin presBnt in the oommercW pMte mny b« dni- 
larly determined by boiling the Mmple with m strong suhition of alau or 
alaminiuiD sulphate, filtering, precipitating the flltrnte by hydrochloric tdil 

' weighing the dried precipitate. 

pcmpunnr. 271 

iiaes in well-dofined long prisms. The olkaluio solutions of puipurin 
become decolorised on prolonged exposure to light. On strongly 
acidulating a solution of purpurin in an alkali with hydrochloric- 
acid, purpurin hydrate is thrown down. The artificial pur- 
purin paste probably eonaiats chiefly of this body. When heated, 
it loses its water of hydration, and changes into ordinary purpurin. 
In warm alcohol it dissolves more readily than ordinary purpurin. 

■When heateil %¥itli aqueous ammonia under pressure, purpurin is 
converted into purpurinamide, Cunj(NH3)(OH)aO^ Owing 
to the formation of this body, an ammoniacal solution of pur- 
purin, if kept for several weeks, loses its power of dyeing mor 
danted doth. On neutralising the solution, the purpurinamide 
furios a dark crystalline precipitate, soluble in alcohol or a largo 
quantity of hot water, but separating again on cooling in long 
crimson needles, which exhibit a deep green metallic reflection. 
It diasolvea freely in fuming nitric acid (sp. gr. 1'5) at the tem- 
perature of boiling water, and on cooling the solution deposits 
luogniGcent scarlet crystals, which are insoluble in water, ether, 
and carbon disulphide, and only slightly soluble in alcohol. 

With acetic anhydride, purpurin forms a trtacetyl deri- 
vative of the composition Cj,H5(OCgHjO)30j, which crystaUises 
in yellowish needles fusing at 190°-193° C. An alcoholic solution 
of purpurin gives with alcoholic lead acetate a dark crimson preci- 
pitate, which dissolves on treatment with an excess of tlie reagent 
to form a fine crimson solution, the spectrum of which shows three 
alworption-bauds. Alizarin when similarly treated gives a purple 
coloration or precipitate. 

An alcoholic solution of purpurin gives with alcoholic copper 
acetate a dark reddish-yellow precipitate, whereas sliuirin, if pure, 
gives a purple solution, but no precipitate, when treated similarly. 
With lime and baryta water purpurin yields purple-red preci- 
pitates, and dyes cloth mordanted with alumina a colour varying 
from scarlet to dark red, without any shade of blue. Purpurin 
a cotton mordanted with ferric salts purple or black. 

i most characteristic reaction of purpurin is its property of 
olving in a hot solution of alum with reddish-yellow colour and 
lish-yeUow fluorescence. The purpurin-alumina lake behaves 
arly. The fluorescence is seen to perfeclion in a liquid prepared 
idding a solution of purpurin in sodium carbonate to one of 
D which has been previously treated with tartaric acid and 
a carbonate in quantity sufficient to prevent precipitation. 
The aboorption-spectrum of purpurin is characteristic. A solu- 
tion of purpurin in alum or alkaline carbonate, if of suitable 
I, gives two well-defined absorption-bands in the green, the 


line D fu from line I 

loss ref niDgible — situated above twice as far from line 
E ' — being particularly sharp and black,* The tibsorption-spectnini 
of the solution of purpurin in carbon disulphide contaiDS four nttaly 
equidistant absorption- bands, of vhich the fiiBl, which is somewhat 
more refrangible than the D line, is the narrowest, the second and 
lliird broader, but very distinct, while the fourth is scarcely di»- 
tinguishable from tho general ab6oq>tion. An otherool wdutlon of 
purpurin is faintly fluorescent, and shows a Tery dark nanww ab- 
sorption-band slightly more reftm^ble than E, and n aocond wider 
and less delinod band at F. 

The detection of alizarin by a similar method is far leas delicate, 
since alum cannot be used to separate it from the accompanybg 
impurities, some of which produce absorption in that part of the 
spectrum in which aQ but the least refmigible of the absorption- 
Ijitnds occur, and this band is not the most intense or charactenstic 
of those produced by aliiarin (Stokes, Jour. Ck«rn. Sik., xu. 219). 

To detect small quantities of alizarin in purpurin, a solution of ite 
colouring matter in caustic soda should be exposed to tlie light till 
^11 the purpurin is destroyed. The liquid is then treat«d wiUi 
dilute sulphuric acid and agitated with ether, alizarin being 8ub> 
sequently sought for in the evaporated ethereal solution. 

F™ "l^r.™" } C.H.(OH>:C,0,:C,H,(OHW...d»p^«M). 
These two isomeric bodies differ from each other and from 
purpurin simply in the position occupied in the molecule by 
the hydroxyl groups. They are produced by fusing hefa-aaibr*- 
quinone-disulphotiic acid and a/jiAa-autbt^iuinone-disulphoQicacid, 
respectively, with caustic soda and potassium chlorate (page 263). 
Ikith are valuable colouring matters, and exist in various brands of 
commercial alizarin. Anthnipurpurin is as important a colouring 
matter as alizarin itself, and used with it increases its brilliancy, 
while alone it gives very brilliant scarlet shades. AUsarin/or rtdt 
consists chiefly of anthiapurpurin, while flavopurpurin gives yellower 
shades. Both colouring matters present a close resemblancfl to 
alizarin, and the general reactions of the commercial pastM are 
shown on page 276. In the following table, the principal distitK- 
tions between anthra- and flavo-pnrpurin are exhibited : — 

' Acconlioj; to H.Morton, the r«rnnpbi1itj of the abwrptiim-liuids of 
a solution of iiuipuria in alum is sensibly aOixted by tiie tempcnliue oTtlw 
Bolntioii and the proportioD of eloTa contained in it. 

^ B; boiling B very small quantity of Ih« root with alum, and obeerTinf the 
iibsorplioD -spectrum and fluorescence of th« fillrred liquiJ, Stoke* detectfd 
purpurit) in upwnrdii of twenty apecies of the fninilf ituAionw, cotnprftlng tb( 
genera Jtubia, A^mla, Oallium, CruciaTialla, and Stherardia. 








Orange oeadlu; »nhjilrou« 

Ooldon - yellow neodlea: 

no alcohol. 

Kully (Oluble in IraiUng 

Easllyiollible even in colli 





r Id boiling iratOT. 

Slight; loliition tnrnirad 

aUght; Bilntloi. remoliui 

OD pnilao)[ea bumug. 

Kuto* """ ''"'''"*'^ 


SUgbU; Hlable with onnge 
colour on boning : Hp«r- 
.taiigiln on cooling. 


I ulDtlan Id itraiig 

Dnll Tlolet coloor. Qbiog- 


ingloOno red-violH on 
■dillng • Inoe at HidlDni 


r kIoUod In caiutic 

Violet rbut redder Ihinw 

Punile {redder ibade tluii 


on dilution, pure red. 

bundi rimnMliug tboH 

Two abJorptfon-lmndH. 


mom nlmngible Ituin 
Ilioae ol AlJuHn, lud 
a chK-acteriiitic broad 
bud in (he blue. 

gt MluUtm Id am- 



r ■DlntlaD In udloDi 



wttb BlcohoUs lolu- 

ReddUb ■ brcwn preolpl- 

Ing -lib violet colour 

Bpw^nglF on bollfag witli 



with red colour. 


Fine Yiolrt colour. 

Bed colormbioD. 

1 a state of almoBt perfect purity, but Bometiraes are very im- ^^H 

1. J e 1 1 i n e k (Ber.. xxi. 2524; J. S. C. Ind., vii T43) states ^M 

. article supplied as pure flavopurpurin by various German ^^M 

makerB sometimes contains as much as 30 per cent, of non- ^^H 

Q mibstancea, chiefly anthrafiavic acid. For the detection ^^H 

1 impurities in commercial Savopurpurin, Jellinek recotn- ^^M 

bat the sample should be dissolved in alkali, aad the solu- ^M 

Bted with lead acetate. The precipitate is well waahed ^H 

The colouring matter ie theu obtained from the alcoholic ^^H 

by fractional ctyatallisation. ^^^| 



Commercial Alizarin. Alizarin Paste. 

Commercial alizarin always occurs in the form of an ochre- 
yellow or brownish-yellow paste, consisting of the solid colouring 
matters in a hydrated state mixed with a definite proportion of water. 

Alizarin paste ordinarily contains 20 per cent, of solid matter. 
The strength is easily ascertained by drying a fair sample at 
100® C. By exposure to this temperature the alizarin is rendered 
anhydrous, loses the slight solubility it previously possessed, and 
becomes wholly unfit for dyeing.^ The residue, after drying, should 
be yellow,— ^not dark brown. After weighing, the residue should 
be ignited at a dull red heat. The ash obtained should not exceed 
1 per cent, of the weight of the dried residue, and should be prac- 
tically free from iron. 

According to Benedikt and K n e c h t, commercial alizarin 
is liable to contain glycerin, turkey-red oil, and other thickening 
agents, for the detection of which they recommend dilution oi the 
paste with water and filtration of the liquid, when a perfectly colou^ 
less filtrate should be obtained, which may contain small quantities 
of sodium chloride and other salts, but should leave no syrupy residue 
of glycerin on cautious evaporation. A practical objection to this 
method of examination exists in the great difficulty, sometimes 
amounting to impossibility, which attends the filtration of alizann 
paste diluted with water. If the presence of glycerin or turkey- 
red oil be suspected, it would probably be preferable to examine the 
Residue left on evaporating the paste to dryness at 100^ 

Besides true alizarin, the commercial paste contains more or less 
of the dihydroxy-anthraquinones isomeric with alizarin, as well as 
several of the mono- and tri-hydroxyanthraquinones. All these 
bodies present a very close general resemblance to alizarin proper, 
but all except the trihydroxyanthraquinones (flavopurpurin and 
anthrapurpurin) are valueless as dyes, and these latter give very 
different shades from those produced by pure alizarin. 

The following method is given by Benedikt and K n e cbt 
for recognising the constituents of commercial alizarin paste : — A 
small quantity of the sample is dissolved in a solution of sodium 
carbonate, and the liquid filtered. The residue consists of 
anthrcLquinone and monohydroacyanthraquinoney which may be sepa- 
rated by means of dilute caustic soda solution, in which only the 
latter is soluble. The filtered carbonate of sodium solution is 
acidulated with hydrochloric acid, and the precipitate boiled 
with milk of lime, which will dissolve any anthraflcme and isoca^ 

^ The same statement applies to alizarin paste which has been frozen, and 
hence it is customary daring severe weather to protect the colouring matter 
from the cold. 



l/traffavie acids with red coloiir.i On filtering and acidulating the 
filtrate these impurities will be reprecipitateJ, ami may be 
collected, wnahed, and weighed. The insoluble lime-lake is 
removed from the filter and decomposed by agitation with dilute 
hydrochloric acid, and the ecparated colouring matter iTashed and 
weighed, or dissolved in ether and recovered by evaporating the 
ethereal solution. The residue thus obtained will coutatn the 
alizarin of the sample, mixed with any anthrapurpurin or flavo- 
purpurin which may be present. According to S c h u n k and 
R d m e r, the detection and approximate determination of these 
three bodies in admixture can readily be effected as followa : — 
The mixture is dried at 100° C, and then placed between two 
glass plnt«!t(, separated from each other by a leaden ring some 
millimetres in thickness. The whole is heated in an air-bath to 
140°— 150°, at which temperature the aUmrin alone suhlimea. 
Un rftising the temperaturo to 170°, a crystalline sublimate of 
mixed Jfavopurpurin and anlhrapurpurin is obtained, the former 
of which assumes tlie shape of fine reddish-yellow needles, while 
the latter sublimes in compact, well-defined rhombic crystals. A 
separation of the two isomers may bo efTccted by boiling with 
benzene, in which only fiavopurpurin dissolves. (See also page 273), 
> Both thcM bodies, ib aUo uonohydroxyantliraqa inane, Me vitlaeleM u 
dyes. Thrir presence in commcrciat aliEsrin may be detected by boiling the 
nmple with milk oE lime and filtering, when a yellow or brownish-red solution 
viU be obtainEd. The following are the chief differences betweea these three 
allied snbstani'es \- — 




Action or beat. 

Snbtlnifli, wlthntit 
Dieltlng. above 286*. 

UtlCa *bo*e 380*, and 

Uella above 300*, 

Artlon of «Ur. 




jMlon of aiincoua 

Separalei Iram hot 
ulntlun In jeltuw 
Uminn or ueedlei. 

lion In long, an- 
hydroai, yaUow 

Sepvalei Irom 

Ujd rated 




ForoH dwp red 

buyta vrater. 

Solable with r«*il.h. 


Eaatly lolubla 
oiih dark red 



unarlf liuulutile 
bol^ nilnUon ^al. 

EoillT aoluble 
■Tth dark red 



Commercial Name. 

Allzariu P, V, VI, 
la, or No. 1. 

AlUarln YCA, X, 
01, FA, 8D0, 
6KD, or No. 10. 

Alizarin 8C (GD), 
RX, RF, SKF, or 
SX extra. 

Alizarin No. 6. 

Alizarin Orange, 
OR, 00, or N. 

Anthracene Brown, 



Alizarin Black. 

Alizarin Blue. 

Alizarin Violet, 
Anthracene Violet. 


Anthracene Green, 
Alizarin Green. 

Solid Violet 

(page 264). 


(page 272). 


(page 267). 

(page 270). 

(Toloorof Paite. 


Sodium bisulphite 
compound of 

(page 268). 

CgoH^oO, (page 73). 

CjoHgOe (page 73). Bhwjk 





Dark brown. 



Dark violet (or 
minute blue 

Violet (or dried 
lumps or crystal- 
line powder of 
dark brownish- 
red or green 

(pas^a 74 and 

SolubiUty In Water. 







(soluble in 






Greenish-grey (or 
when dry, bronze 



soluble to 

ly solnm 

ly soluble. 

with red 



Solable , 







olonr of Solatlon in 

Colour of Solution 

in strong Sulphuric 


Colour on Cotton Mordanted with 

^^«« AmmoniiL 





• •• 

Yellowish-red; on 
dilution, orange- 
yellow precipi- 



Puce or 


than an- 



Reddish-brown; on 
dilution, orange- 
yellow precipi- 


• •• 

• •• 

et (redder 
B ftliarin 


Magenta or cherr>- 
re(l ; on dilution, 


• •• 

• • • 

Ider than 
nre brands). 


Reddish-yellow; on 
dilution, reddish- 
brown precipi- 

Red (with- 
out blue 

Purple or; 



• •• 

Yellowish-brown ; 
on dilution, yel- 
low precipitate. 







• •• 

Brownish-red ; on 
dilution, brown 

• •• 

• •• 


Y yellow or 

• •• 

Reddish-yellow; on 
dilution, greyish- 
white precipi- 

• •• 

• •■ 



• •• 

Dirty yellowish- 
green, changing 
to carmine-red 
on heating with 
evolution of SOs; 
on dilution, 
brownish solu- 
tion and black 

• •• 

• •• 


large ex* 


Crimson-red; chang- 
ing to yellowish- 
red on dilution. 




) indJgo- 
le, becom- 
( dirty on 
inding, or 


Reddish-yellow ; 
unchanged on 



• •• 



Dirty yellowish- 
brown; on dilu- 
tion, reddish- 
brown solution, 
and with more 
water a greenish 
liquid and green- 
ish-black procipi- 


• •• 

■ •• 


• •• 

Cornflower-blue ; 
on dilution, ma- 

• •• 

• •• 



The foregoing table (pages 276, 277) shows the characters of the 
different varieties of alizarin and analogous colouring matters met 
with in commerce in the form of paste. 

Artificial alizarin does not contain purpurin, buf; in the natural 
product from madder more or less purpurin is usually present 

In forming an opinion on the quality of commercial alizarin, the 
performance of a miniature dye-test is very useful, and is best con- 
ducted as follows : — A piece of white calico, some feet in length 
and four inches wide, is boiled in water containing a little caustic 
soda, to remove any stiffening agents. After being thoroughly 
washed, it is immersed in a solution of aluminium acetate (''red 
liquor") of known measure and strength, the time of immersion 
and the temperature being duly noted. The calico is then removed, 
wrung out, and torn into a number of strips three inches wide, 
which are hung on a string to drain. 0*5 gramme of each sample 
of alizarin paste to be tested is then weighed out, and put into 
a corresponding number of wide-mouthed flasks or wide beakers 
of similar size arranged in a capacious water-bath. 1 litre ol 
water at 40"^ C. is then poured into each, and the liquid well 
agitated to facilitate the solution of the alizarin. A strip of the 
previously mordanted calico is then immersed in the contents 
of each flask, care being taken that it is suspended freely so that 
all parts are in contact with the liquid. This is best done by 
attaching it to a thread tied to a glass rod placed across the moutii 
of the flask or beaker. The temperature of the bath is then 
gradually raised, so that it may reach 76° in about an hour and a 
half from the immersion of the cloth, after which the temperature 
is increased to about 90° C. for half an hour longer. The strips of 
calico are now withdrawn, rinsed in cold water, and dried. Each 
strip sliould then be cut into two equal portions, one of which is 
preserved between the leaves of a book or in other situation away 
from the light, while the others are steeped for half an hour at 
about 40°-42° C. in 1 litre of water containing 2 grammes of white 
curd soap.^ The strips are then taken out, rinsed in cold water, 
and put into another bath made with the same quantities of soap 
and water, with the addition of 0*6 gramme of stannous chloride 
("tin crystals"), which is allowed to boil for thirty minutes. The 
strips are then removed, well rinsed, dried, and preserved in the 

Instead of relying on the behaviour of the dye-stuff with a 

^ In some cases, as in the assay of reds, it is desirable to precede the aoap 
treatment by an oil process. This consists in immersing the fabric in a 5 per 
cent, solution of turkey-red oil, again drying the cloth, and then exposing it 
to open steam in a suitable box for one hour. 


single mordant, it is preferable to use a piece of cloth printed in 
five or eix parallel linea with, c.y. (a), strong solution of olumiaiuia 
acetate ; (&) weak aluminium acetate ; (c) strong iron acetate ; (d) 
weak iron acetate; («) miiLtun) of strong solutions of aluminium 
and iron acetates ; (/) mixture of weak solutions of aluminium 
and iron acetates.' 

The shades dyed by commercial alizarin depend much on the 
coinpoaition of the colouring matter. Thus the variety giving blue 
thtultss (ejj., " aliatrin F, or extreme blue shade") consif^ts chiefly of 
real alizarin, In dyeing, it yields with tdumiua mordant a 
bluish but not very brilliant sbB<le of red ; but with a small pro- 
portion of mordant very beautiful shades of pink can be obtained. 
"mu mordanted with iron, it ia used for dyeing and printing fast 
The yellow shades of commercial alisarin (e.y,, ftliEariii GS) 
a a large percentage of anthrapurpurin and f 1 a v o • 
spur in, and but httle real alizarin. Anthrapurpurin yields 
'moat neutral red with alumina mordants ; but flavopui'purin 
I a fiery red containing a cousiderable proportion of yellow, 
i hence the larger the proportion of flavopnrpurin the yellower 
f shade. Iron mordante give with antbmpurpurin and flavo- 
3 violets of little or no practical value, Purpurin does 
I occur in arti6ctal alizarin, hut was a very common constituent 
;he dye from madder, whicli fact was the chief reason of the 
different shades produced by uaturol and artitieial alizarin. 

Detection of Alizarin and its Allies on the Fibre. 

Uizarin and other allied colouring matters are applied in so 

jT wap, and with such a variety of mordants, that it is not 

bible to describe the method of dyeing shortly. As the use of 

's essential, they are not so suitable for silk as the aub- 

itive coal-tar dyes. Alizarin is now used in wool-dyeing, not 

18 a bottoming colour for indigo, &c, but as a self-colour with 

rdants. Thus when mordanted with alum and tartar it gives 

Sne nnls loid scarlets ; with stannous chloride, orange shades ; 

with potassium bichromate, rich claret-browns ; with ferrous sul- 

I pinto, shades ranging' from bluish-violet to black ; with ammonio- 

l^bate of nickel, grey; and with uranium acetate, ahite-blue 

These colours are fast to light and air, ajid resist milling. 

Jlie mordants used in dyeing cotton with alizarin are various 

rnds of calcium, aluminium, iron, chromium and tin, besides 

Die acid and oils. Turkey-red, one of the fastest and most 

• of cloth [iriiiteil in tlia nunoor teooiamenilod, or nny otlinr which 
I b* duired, Dun W obtained liy order from muiy calico •printL-rs. 


perfect of the alizarin styles, is dyed by a complicated series of 
operations, in which the formation of a compound of alumina with 
alizarin and a fatty acid is an essential step. The method of 
operating is substantially that employed in the process of assay 
described on page 278. Treatment with ether changes cloth dyed 
turkey-red to a duU cherry-red colour, and on evaporating the 
ethereal solution a brilliant scarlet fat is left This dissolves in 
hot caustic soda with purplish-blue colour, and on adding hydro- 
chloric acid alizarin is precipitated in orange flakes. Alizarin violet 
may be obtained in a similar manner to turkey-red, the blue shade 
of alizarin being used for its production. . Other violets are obtained 
by the use of an iron mordant 

Turkey-red is but little affected by a dilute solution of bleaching 
powder if free acid be absent, but the other alizarin colours are 
gradually bleached. 

Alizarin is not affected by potassium bichromate, but free chromic 
acid destroys it. Dilute solutions of permanganate (1 per cent) 
and alkaline solutions of ferricyanides are without effect on colours 
produced by artificial alizarin, but purpurin is easily oxidised. The 
last reagent especially is of value for distinguishing colours pro- 
duced by artificial alizarin from those produced by madder, as the 
latter always contains purpurin. Madder-dyed fibres are also dis- 
tinguished by boiling them with a strong solution of alum, when 
the purpurin is dissolved with formation of a reddish-yellow liquid, 
which exhibits a strong greenish-yeUow fluorescence and charac- 
teristic absorption-bands (page 271). 

On exposure to nitrous fumes, cloth dyed with alizarin-red be- 
comes orange, from formation of nitro-alizarin. 

Fibres dyed with alizarin are but little affected when boiled with 
ammonia or caustic soda solution of moderate strength. Alizarin 
red is turned to violet when boiled with baryta water. Dilute 
acids are almost without action. Concentrated hydrochloric acid 
decomposes the colour lakes, and partially or completely removes 
the metallic oxides. The violets are more readily affected than the 
reds, and of the latter turkey-red offers the greatest resistance. 

Cold concentrated sulphuric acid dissolves the fibre of cotton as 
well as the colouring matter. On diluting the solution with water, 
the alizarin, &c., will be thrown down as a flocculent precipitate, 
which may be dissolved by agitation with ether. The separated 
ethereal solution on evaporation will leave a residue, in which 
alizarin and its associates may be recognised by their appearance on 
sublimation, the colour and absorption-spectra of their alkaline 
solutions, &c. 

Fabrics dyed with alizarin are decolorised when boiled with a 



e of two parte of alcohol and one of strong hyilrouhloric 
This reaction distinguishes alizarin htaek from aniline Uach, 
which latter colour ia unaffected, or merely turned greeniab, by 
similar trentment. LngiwfA hlaehi, on the other hand, are de- 
stroyed even by dUute acids, which acquire a red colour. 

Strong acid oxidising ngeuts, such as, nitric acid and ferric cldoride, 
destroy alizarin coloura. 

Chrysophanic Acid. C^Ji^fi^=C^;;RlCR^O^)p^. 

This substance, the nature of which was formerly misunderstood, 
is now recognised as a dihydroxy-methyl-anthraquinono, being homo- 
logous with chrysttzin (page 263). 

Chrysophanic acid occurs ready-formed in rhubarb root, senna 
leaves, tlie wall lichen {Panndia parietina), and some other plants, 
or, at any rate, is readily produced by the oxidation of a Bubstanee 
pre-existing in those plants. This substance has l:he fomitda 
C,^j(0„ and is called chtysophan or chrysarobin, 
chryso] ill anic acid being a product of its oxidation, C3oHjjOj+04 = 
2C,jH,d04-|-3HsO. Many of the statements made as to the 
occurrence and properties of chrysophanic acid really apply to 

The best source of vhrysophanic acid is the commercial product 
known as chrysarobin, or Goa powder,' which consists of the medul- 
lary matters of the st«m and branches of Andira araroba, a. plant 
growing in the neighbourhood of Bahia. The Goa powder ia ex- 
haneted by boiling benzene or petroleum spirit, conveniently in a 
Soxhlet-tube. The filtered liquid, after concentration if necessaiy, 
deposits on cooling pale yellow, warty crystals. These may be 
purified by repeated ciystallisation from glacial acetic acid, when 
^^y^ eubstance ia obtained in small yellow Iamin». 
^^^^Pare chiyBOphnnic acid may be prepared from the chrysophan or 
^^^^^Mrobiu obtained as above by pouring a somewhat dilute solu- 
^^^p of caustic alkali over the substance contained in a large retort, 
ud then passing a current of air over the surface of the liquid 
(Liebormann and Seidler, Pharm. Jour. [3], ix. 897). 
The retort is agitatod so os to renew the surface, and the operation 
ttinned until the chrysarobin ia dissolved, and the solution has 
T uniformly the red colour characteristic of an alkaline 
ion of cbtysopbanic acid. The liquid is then treated by an 
\f and the precipitate washed, dried, and exhausted with petro- 
Bb the BrUviK Pknnaacopaia of 1886 the natural product Goa powder is 
DiUd with tho cryatalline principle extracted therefrom by solvents, 
" being described aa " msdullor; matter,'' and at the Mune 
"iniautaly orystalliue." 



leum spirit (not benzene) in a Soxhlet-tube. On cooling, the 
chrysophanic acid is obtained in beautiful yellow laminffi. 

The following are the chief differences between chrysarobin and 
chiysophanic acid : — 


Action of ammonlA. 

Action of very dilute caiu- 
tic potash solution. 

Action of strong caustio 
potash solution. 

Action of fusing caustic 

Action of concentrated sul- 
phuric acid. 


Undissolved at first On agi- 
tation with air, dissolves 
with red colour. 

Soluble with yellow colour and 
strong green fluorescence. 
On exposure to air, colour 
changes rapidly to red. 

Brown coloration. 
Soluble with yellow colour. 

Soluble with red oolov. 
Soluble with red coloar. 

Soluble <Mth red colour. 

Blue coloration. 
Soluble with red colour. 

The chrysophanic acid of commerce consists of an indefinite 
mixture of chrysophan or chrysarobin with the true chiysophanic 
acid which is the product of its oxidation. 

According to J. A g e m a, commercial chrysophanic acid may be 
purified by dissolving it in chloroform and adding an equal volume 
of rectified spirit, when the pure acid only is precipitated. 

Chrysophanic acid crystallises in golden yellow scales or prisma 
It melts at 162* C, and sublimes at a higher temperature with 
partial decomposition. Exposure to a temperature of 195° con- 
verts chrysophanic acid into a body allied to purpurin, which 
colours alum mordants pomegranate-red and iron mordants a light 
greenish-blue. It is nearly insoluble in water, but dissolves 
sparingly in hot alcohol (1 in 224), the greater part separating on 
cooling. Chrysophanic acid is also readily soluble in ether, chloro- 
form, benzene, petroleum spirit, amylic alcohol, and glacial acetic 
acid, the solutions being yellow or brownish-yeUow. 

When treated with a solution of caustic alkali or ammonia, 
chrysophanic acid dissolves readily, forming a liquid which is 
pink when very dilute, and dark purplish-red in a more concen- 
trated state. The chrysophanic acid is precipitated in yellow 
flakes on neutralising the alkaline liquid. A very small quantity of 
alkali suffices for the production of the red colour. If the red solu- 
tion of chrysophanic acid in caustic alkali be evaporated to dry- 
ness, it turns violet and blue during the operation. The fihns 
deposited on the sides of the vessel especially exhibit this change 
of colour. 

If a solution of chrysophanic acid in ether, chlorofoim, benzene, 


amylic alcohol, or petrolewm spirit be eliaken with solution of Boda, 
the colouring matter passes completely ot partially into the aquQoiia 
liquid, which it coloura pinlt or crimson. Ammonia gives the same 
reaetiou as soda with a solution of chrysophonic acid in ether or 
petroleum spirit, hut docs not readUy extract the colouring matter 
fiom its solution in chloroform or henzene. 

The acid characters of chryaophaaic acid are but feebly marked. 
It forms unstable barium and lead salts, which ai« decomposed 
even by carbonic acid. An ammoniacal solution of chrj'sophanic 
acid is precipitated lilac by acetate of lead and rose colour by 

Chrysophanic acid is not acted on by dilute nitric acid, but 
the strong acid converts it into tetranitro-chrysophanic 
acid, Ci5H5(2sOj)^0^ , a body homologous with chrysamic 
acid, obtained by the action of nitric acid on aloes or chryaaJon. 

When heated with acetic anhydride and acetate of sodium, 
chrysophanic acid yields a diacetyl-derivative. 

Wlien heated with rinc-dust, chiyaophanic acid is reduced to 
methyl-anthracene, C]sH^g, just as alizarin and chrysazin 
yield anthracene, C„Hg, when similarly treatorl. 

Chrysophanic acid possesses decided antiseptic properties, and has 
proved of service in the treatment of certain forms of akin-disease. 
It is said to be somewhat uncertain in its action, a fact which is 
not improbably due to an admiKture of chrysarobin, to the deozi- 
diaing action of which impurity it has been suggested that the 
chiTBophanic acid of commerce owes its chief value.' 

Chiysophnnic acid is said to produce purplish-brown stuns on 
linen or ctitton, which are only removable with difficulty, pro- 
longed immersion of the fabric in a solution of bleaching-powder 
being the best mode of treatment. The author has not succeeded in 
producing these stains except in the presence of an alkali. A solu- 
tion of chiysophanic acid in alcohol, acetic acid, or petroleum 
spirit merely colours linen a light yellow colour. On washing the 
Mnineil fabric with sonp, the purplish -brown stain is readily dc- 

An aqueous or ahwholic solution of chrysophanic acid does not 
dye aillc or wool yellow. 

■ Working on this iilen, Liel»ntinnn (P/uinit. Jovr. [S), xriii. 711, 780) hiu 
attempted to reduce <^itTyBophauic acid to chrysarobin by trentment with ziac- 
dnst autl ummonia, Hd obtained iustvad t Uuco-disricaiiix, tli« lower Iiamo- 
iDguci of wLkh, prepsrud from alizarin and purpuHn in a similar mauUDT, in j, 

DOW commarciallj liDown aa an th rarobin (page 26 S). ^fl 

IXvidently, the productjoa of chrysophanic acid stains on linen may bo J^M 

Idsd by dissolving out the colauring matter and grease with beuzeun. I ^M 



Chrysophanic acid ia eaid to lie liable to adulteration with picric 
acid and other yellow cotonring matters. Inorganic odmixtuiGS 
may be detected by igniting a portion of the sample. Picric aeii, 
if present, would be detected by the yellow coloration the Bomple 
imparts to cold water ; by the yellow crystalline precipitate pro- 
duced on adding potassium carbonate to the alcoholic solution of the 
sample j and by immei'sing a piece of white wool in the hot aqueoiu 
Rolution, which, in presence of picric acid, will be dyed yeUow. Aaria 
or rosolie acid might be detected in chrysophanic acid by treating 
the sample with chloroform or benzene, which woold diseolTs tlie 
chrysophanic acid without affecting the admixture. 

The extraction of the chrysarobtn or ehtysophanic acid pnaent 
in plant-products may be effected by treating the powd6Ti>d sub- 
stance with the ether, benzene, or petrolenm spirit, in the mimnKi 
already described. Goa powder yields fcora 70 to 80 per cent ul 
the active principle, while the proportion of chrysophanic acid 
contained in rhubarb is but smalL According to Dragendoiff, 
the presence of chrysophanic acid in a condition {free) extractftbh 
by cold petroleum spirit is a test of the quality of rhubarb. Good 
rhubarb yields a colourless extract even when left for several d»y« 
in contact with petroleum spirit, while a rhapontic rhubarb ytelde 
an intensely yellow extract. Ac^wrding to Roc hied e r (Ci««. 
iVeuv, XX. 78), the acid from rhubarb generally contains emodiSi 
CijHigOj. This body has the constitution of a tri-hydroxyni^hyl- 
anthraquinone, and hence ia homologous with purpurin. It OCCUK 
to a notable extent in the bark of Rhamans franf/iJa, and TUB^J Ik 
separated from chrysophanic acid by means of ao<liuiti cnrbosBtts 
which dissoivea the emoJin only, with blood-red coloration. It 
forms long, brittle, monoclinic prisms, melting at 215°— 2S0°i 
and ia converted into methyl -anthracene by heating with dnc- 

A body having considerable analogy to chrysophanic aud occnii 
in the root of the Mexican plant Trixts pipiiiahuac or Penaia ^rnfr 
Ucoea. This substance, which has been named pipitiahoic 
acid, has the formula Ci&H^oOg, and dissolves in alkalies with a 
colour resembling that of potassium permanganate (Anschtti 
and Leather, Jour. Chem, Soe., xlix. 709). 


Nearly all the coal-tar dyes of industrial importance havo been 
described in one or other of the preceding sections. The chicX 

lauth's violet. 

exceptions &re the remcirkable sulphuretted dyes of the luethyleuo 
blue dasa, discovered by L a u t h. 

Thio-Colouring Matters from Amido-bases. 

When the aromatic diamijiea are heated with sulphur, buI- 
phuielted bases are formed, which yield violet colouring matters 
OD oxidation. These bodies may bo obtained more simply by 
passing sulphuretted hydrogen through the solution of the hydro- 
chloride of the diamine, and then adding ferric chloride. The 
body thus obtained from para-diamidobenzeue (para-phenylene- 
diamise) is known as 

Lauth's Violet. Ci^Hi^NgSCl. This curious colouring matter 
is the hydrochloride of the base t h i o n i n e. It crystallises from 
a faintly acid solution in thin prismatic needles, having a beetle- 
green lustre. It dissolves slightly in cold but more readily in 
hot water, to form a solution which appears violet-red by trans- 
mitted, and violet-blue by reflected light, It is almost entirely 
precipitated from its aqueous solution by strong hydrochloric 
acid, but on adding excess redissolves with fine dark blue 
coloration. By precipitating a solution of Louth's violet with 
soda or ammonia, the free base, C,gHgNgS, may be obtained as 
a brownish-red or black crystalline precipitate, or from a hot 
solution in small needles with a feeble green reflection. Thionine 
dissolves only slightly even in hot water, but more readily in 
alcohol, to a reddish-violet solution, which exhibits a fine browuiab- 
red fluorescence. 

Thionine and its salts dissolve in strong sulphuric acid with 
fine yellowish-green colour, changing to blue and violet on dilution 
with water. In this reaction thionine exactly resembles the 
safranincs (page 254). 

Lauth's violet is not employed in practice, but the important 
colouring matter known as methylene: blue has the constitution of 
a tctramethyl-thionine hydrochloride. 

MffTHTLBKB Blcb. CigHigNjSCI. This colouring matter may 
be represented by the following formula r — 



It may be prepared by treating dimethyl-aniline hydrochloride with 
sodium nitrite, and then with sulphuretted hydrogen until the solu- 
tion loses its yellow colour and ia covered with a blue scum, when 
ferric chloride or bichromate of potassium is added till the smell 
^ulpbuDitted liy<.lrogeu has disappeared. The liquid is then 


saturated with common salt and zinc chloride added. The pre- 
cipitate is separated, redissolved in water, and again precipitated 
with salt and chloride of zinc. The product so obtained in the 
double zinc salt From it the chloride may be prepared by adding 
strong hydrochloric acid to the concentrated solution. Methylene 
blue may also be obtained from helianthin in the manner described 
on page 211,^ and by various other reactions. 

Methylene blue occurs in commerce as a hydrochloride, but 
more frequently as the d o u b le zinc salt It forms a dark 
blue or reddish-brown powder with a bronze reflection. In water 
or alcohol it dissolves easily with blue colour. The solution is 
unchanged or turned greenish by hydrochloric acid. Caustic soda 
changes the colour to violet, and the addition of strong alkali to a 
concentrated solution produces a dirty blue or violet-black pre- 
cipitate. In concentrated sulphuric acid, methylene blue dissolves 
with grass-green colour, which, on addition of water, becomes fiist 
blue and then violet 

From a solution of commercial methylene blue, the iodide, 
C^^H^gNgSI, is completely precipitated on adding iodide of potas- 
sium, and potassium bichromate also completely precipitates the 
solution as a purple-violet chromate. Methylene blue forms a 
soluble compound with tannin which is taken up by metallic 

Tetramethylthionine Hydroxide^ CjgHjgNjS.OH, the free base 
of. methylene blue, is most readily obtained by treating a solution 
of the iodide or chloride with freshly precipitated argentic oxide. 
On evaporating the filtered liquid in vaciu), the base is obtained as 
a dark amorphous mass which acquires a green metallic lustre when 
rubbed, forms a syrupy solution in water, and dissolves readily in 
alcohol. The solution decomposes various metallic salts, like an 
alkali, but is veiy unstable. 

By treating methylene blue with zinc and acetic acid, or with 
an alkaline solution of sodium hyposulphite, the leuco-de- 
rivative, CjgHjgNgS, is obtained. This body crystallises from 
ether in flat satiny needles, having a penetrating odour resembling 
that of the lobster. It is readily soluble in water, and is extremely 
oxidisable both in the diy state and in solution, methylene blue 
and other products being formed. In acid solution, tetramethyl- 
leucothionine is more stable, and it forms a readily soluble and 
crystallisable double zinc salt. 

The formation of methylene blue afibrds the most delicate and 
certain reaction for the detection of sulphuretted hydrogen in 

^ Mention of the last stage of the process, namely, oxidation of the redaced 
product by ferric chloride, ia accidentally omitted on page 211. 



n«nttnl or acid solution, far exceeding in this respect the reactions 
with lead salta and nitroprassidea. 1 00 c.c. of the liquid to be tested 
H>uld he treated with 2 cc. of fuming hydrochloric acid, and a 
p grains of dimethjl-paradiamido-beniene sulphate (page 211) 
On then adding a drop or two of ferric chloride solution, 
■thylene blue will be formed either immediately or on standing, 
bty milpharett«d hydn^n was previously present. 
"Tethylene blue is a valuable dye for cotton yam and calico- I 
JBting. The blue produced has a greenish shade, especially in ■ 
"Iciol light. The colour is faster than aniline blue, being 
tffected by light and unacted on by neutral soap solution or 
Rlt« hypochlorites. Ammonia is also without action, but alkaline 
» and caustic alkalies remove the colour. On treating the fabric 
b hydrochloric acid, it is turned green and the dye is gmdually 
loved, the acid Uquid remaining green. Stannous chloride and i 
r reducing agents discharge methylene blue more rapidly than , 
nier blue dyes. A three pet cent, solution of potassium bichro- 
mate changes a fabric dyed with methylene blue to violet, and 
hnally discharges it. If the dye was mordanted with tannin, a 
^dark brown colour remains. 

^^KTlie behaviour of methylene blue with reducing agents and the 
^^Kaitivenefis of the resultant leuco-derivatire render the colouring 
^^Htt«r of great value in bacteriological research. " The bacilli of 
^^roerculosifl, glanders, and cholera were first discovered by the aid 
of methylene blue." i 

Ethylene Blue closely resembles methylene blue, but is pre- 
jiared by using diethyl-aniline instead of_the lower homologue. 

Mbthvlknb Ekd, CjflH,gN(S^2HCl, ia a secondaiy product 

obtained in the formation of methylene blue, especially if the treat- 

aieat with eulphuretted hydrogen be too prolonged and much ferric 

^^^nride be used. It remains in the mother-liquor whm the blue 

^^■toecipitcited by the addition of rnilt. It is decolorised by alkalies 

^^^B leducing agents, and turned blue by oxidising agents. A 

^Hmilied methylene blue is obtained from it in practice by treating 

the acid solution tiret with zinc-dust and then with ferric chloiide. 

UncIasBified Coal-Tar Dyes. 

^Of the conl-tur dyes not falling naturally into any of the groups 
idy considered, the following are all which reijuire special 

JiSSTDB Grkkn. CjjHjjWjSjO, This colouring matter, now 
Uically obsolete, ia of intei'est as being one of the first green 
I obtained from aniline. It was prepared by the reaction of 
lyde on magenta and treatment of the product with sodium 


thiosulphate (hyposulphite). It formed an amorphous green 
powder, insoluble in water and but little soluble in alcohol, but 
readily soluble in a mixture of alcohol, water, and sulphuric acid. 

Cakarin. G3N3S3H. This colouring matter, sometimes called 
persulpliocyanogen yellow, is not strictly a coal-tar dye, as it ib 
produced by the action of an oxidising agent, such as chlorine or 
nitric acid, on a thiocyanate (sulphocyanide). It will be considered 
at greater length in the chapter on "Cyanogen Compounds.'* 
Canarin forms an orange-yellow powder insoluble in water, alcohol, 
or ether. It dissolves in alkalies with yellow colour, and on 
addition of hydrochloric acid is reprecipitated from the solution 
in orange-yellow flocks. It dissolves in strong sulphuric acid, bat 
is reprecipitated on adding water. It is employed in calico-printing. 

Thiorubin, a colouring matter made by Dahl & Co., is the 
sodium salt of thio - paratoluidine - azo - betanaphthol - disulphonic 
acid :— NH2.CeH3(CH3).S.CeH3(CH3).N2.CipH^(OH)^(SO,Na)^ It 
occurs as a reddish-brown powder, soluble in water with magenta- 
red colour. Hydrochloric acid precipitates the solution yellowish- 
brown, while soda turns it bluer. In strong sulphuric acid 
thiorubin dissolves with magenta-red colour, the solution giving 
a yellowish-brown precipitate on dilution with water. An acid 
solution of the dye gives a red on wool. 

CuBcmnN S, called also sun-yellow and maize, is the sodium salt 
of the disulphonic acid of azoxy-stilbene, and has the following 
formula : — 

UCH : CeH3(S03Na).N> 

Curcumin S is prepared by heating paranitrotoluene-sulphonic 
acid with caustic soda, and occurs in commerce as a brown powder, 
soluble in water with brownish-yellow colour. The solution in 
strong sulphuric acid is violet, but becomes yellow on moderate 
dilution with water. Curcumin dyes silk and wool reddish-yellow 
in an acid bath. 

Tartrazin is a body of peculiar composition. It has the con- 
stitution of a sodium salt of diazotartaric-acid-diphenylhydrazine- 
disulphonic acid (or diphenyl-parasulphonic-acid-osazon-dioxytar- 
taric acid). 

C,H,(SO.Na).N.H.C.COONa ^^ | C { ^OONa^^^g^^^^^ 

CeH,(SO,Na).N,H.C.COONa °' |c | c^^f*^^^*^"^ 

Tartrazin is prepared by the action in alkaline solution of two 
molecules of phenylhydrazine-parasulphonic acid on one of 


dioxytartaric acid (Jour. Soe. Chem. Ind., v. 437). It forma a 
beaatifoJ orange-yellow powder, soluble in hot water to a golden- 
yellow solution, which if conceutnited deposits u yellow pre- 
cipitate on cooling. On adding alcohol to the concentrated 
aqueous solution a crystalline precipitate is ohtoined. The solu- 
1 is not cliangod by dilute acids, but becomes reddish on 
; caustic soda. Stannous chloride produces a yellow pre- 
tate, soluble in oxalic acid. Barium chloride gives a yellow 
Itjpitate, but calcium chloride occasions no change. Concen- 
aulphuric acid dissolves the solid dye with yellow colour, 
unchanged on dilution. Tartrazin precipitates the coal-tar 
I very completely (W. R. Richardson, Jow. Soc. Dijera, 
,, iii 3), and dyes wool yellow in an acid bath. 
Various other dyes from hydrazines have been recently patented 
{Jaw.&>c.Dyers,^c,m.U2.\v. 109). Thus Mn/*n.jw//ow is obtained 
hj the action of isatin on phcnylhydrazine-parasulpbonic acid, and 
wthreTte-red by the reaction of one molecule of phenanthrene- 
lue on two of aaphthylhydraeine-sulphonic acid. 
tDZOPLAViNB ia the typical member of a series of basic dye- 
fa obtained by the reaction of one molecule of benzaldebyde on 
loluylene-diamine (or other aromatic meta-diamine) and one of 
rdrochloride or sulphate. The product, CjjHyN^,2HCl. consist- 
lot the hydrochloride of tetramido-ditolylphenylmethnne, is heated 
1 hydrochloric acid under pressure, when the hydrochloride of 
hydrodiamido-dimethyl-phenylacridine, CjiH^Ng, is obtained, with 
elimination of ammonia. On exposure to air or treatment with an 
ig agent of moderate power, such as ferric chloride, this body 
aidised to diamido-dime thyl-phenylacridine or 
|K/Zaifin« (compare page 246). The new colouring matter is 

' " K substance soluble with difficulty in cold water, bat more 

nadily on heating. It is precipitated from its aqueous solution 
by dilute acids. In strong sulphuric acid it dissolves with yellow 
colour and pronounced yellowish-green fluorescence. The alcoholic 

Vitiou shows RD intense yellowish fluorescence, which disappears 
the addition of an acid. The free base of benzoflavine ia 
lOriess and insoluble in water, but soluble in alcohol and other. 


■ Xlie dyee occurring uaturallj in animal or vegetable products, or 
can be produced therefrom by comparatively simple means, 
ry numerous and interesting ; and there is no doubt that the 
ds for their extraction or production would have been greatly 



improved of late years had not the coal-tar dyes engrossed the atten- 
tion of nearly all investigators actively interested in the chemistry 
of colouring matters. The use of some of the natural colouring 
matters has greatly decreased, owing to the rivaliy of the coal-tar 
dyes, and the production of some of tbem is nearly, if not wholly, 
a thing of the past Thus the azo-scarlets have greatly diminished 
the consumption of cochineal, while artificial alizarin has nearly 
extinguished the natural dye from madder ; and alizarin-blue and 
the indulines now compete with indigo, which is itself producible 
by complex synthetical processes from the [^coal-tar constituent 
toluene, C^Hg. 

The dyes and colouring matters of natural origin may be con- 
veniently classified under the following heads : — 

Indigo, and allied colouring matters. 

Lichen Dtss, such as orchil, cudbear, litmus. 

Bed DtEB from Woods, &c., as Brazil-wood and logwood. 

Yellow Ybgetable Dtbs, such as saffron, turmeric, weld. 

Chlorophyll and its allies ; and 

Animal Dyes, such as cochineal. 
Of the colouring matters included in the above arrangement, 
madder has already been referred to under the heads of alizarin 
and purpurin (pages 264, 270) ; eJUorophyU and many other 
plant-colours receive little or no practical application, and hence 
need not be specially described ; while the colouring matters of 
blood, bile, urine, &c., will be better considered in the sequeL 


Indigo is the product of various species of leguminous plants of 
the genus Indigofera^ which appear to be indigenous in Cambay, 
but are also cultivated in India, China, Java, and other parts 
of the East, It is also grown in the West Indies and South 
America, and the species Indigo/era argentea is cultivated in Elgypt 
and Arabia. 

Indigo does not exist ready-formed in the above plants, but is 
produced by the decomposition of a glucoside called i n d i c a n, 
CsqH^NO]^, which may be extracted from them by cold alcohol. 

^ The most valued and extensively cultivated species is the Indigtfera 
tinctoriaf but /. dispermay anil, and argentea are also widely grown. Less 
important species are /. hirsuUi^ pseudxy-tincUma, serieeaf cytiwidea, angvsU' 
folia, triplia, glabra^ glatuM, &c. Indigofera tinctoria is grown from seeds, and 
is a herbaceous plant with a single stalk, growing to a height of 8 feet or a little 
more, and about the size of the finger. The value of the crop is almost in pro- 
iwrtion to the abundance of leaves, as the colouring matter exists chiefly is 
that part of the plant 



ao obtnin indigo from the plants, the chopped leavee or twigs 
) completely covered with water. Fermentation sets in, and 
nitinues from nine to fourteen hours, according to the tempera- 
ture. 'When complete, the water is vun off into ehallow vats, where 
it b subjected to agitation to expose it to the air.' The yellow 
liquid thereby assumes a greenish colour, and the indigo separates 
ID Hakes. After standing for ao hour, the blue piUpy indigo is 
separated, and boiled with water to prevent secondaty fermentation 
and the conse^juent formation of objectionable brown products. 
After standing twenty-four hours, the liquid is again boUed, and 
then passed through a coarse filter. The precipitate is separated, 
pressed, and dried slowly in sheds, from which the light is care- 
^inlly excluded,* 

^^Llbe indigo thus obtained varies greatly in quality, both as ro- ^ 
^^H^cte the proportion of blue coloiuing matter it contains and in 
^^B'freedom from objectionable impurities (see page 302). 

Indigo may also be obtained from several plants besides the ■ 
Indigo/era, but these are more generally used directly for dyeing ' 
blue than for extracting the indigo. The most important of these 
iodigo-yielding plants are Itatig tinclona or w o a d, once exten- 
sively cultivated both in England and on the Continent ; Poll/- 
goaam tinetoriwn and Nerium. tinctoriitm ; Agclej/ia* limjens; 
Eupatorium Hncirmwn, one of the Compositffl ; and several species 
of orchids, which, when cut, become blue at the section after 
exposure to the air. 

Woai at pastel is a biennial cruciferous plant. Tlie leaves, of 
tiicb two crops are yieliled, are gathered in the second year, and *' 
B' rapidly washed and dried. They are used directly for dyeing, 
) made into a paste with water, piled in heaps, allowed to 
neat for fourteen days, and then made into small Imlls and drieii. 
I product is sometimes again moistened with water and sub- ' 
jected to a second fermentation, during which ammonia is evolved. ' 
The best woad comes from France. The balls are light, of a green 

I yellowish- green colour, and have a sickly odour. When cut, 
id ehould exhibit a soft, shining surface, and when rubbed on 
in should leave a green mark. It improves by keeping, and 
lie manufacturers consider that the finest shades of indigo-dyeing 
kiot bo obtained without an admixture of woad. 
|Some manabctDran add a little lime-water at tliistitiigo, nbib J. Sayors 
BintndH the addition of ammoDia daring the fermentation. By this means 
tha field of colonriog matter nuy be incTGHaed fully 100 percent {Jour. Soe. 
Dgen, Ac., ii. 111). 
> The hest ijaalitlea of indigo are nmially those msaarMtared by EuropeanB, 
» oiwrate with more care than the native*. 


Isatis tndigotica is cultivated in some parts of China for the 
preparation of a variety of indigo which is sold in the form of 
paste. When dried it appears blackish, and is used in producing 
Canton blue, &c. 

Polygonum tinctorium is also indigenous to China, and yields 
an indigo of superior quality. It is also used for dyeing directly. 
The attempts made to acclimatise the plant in Europe have been 

A substance allied to indican sometimes occurs in urine, and 
gives rise, by its conversion into indigo-blue, to a blue coloration 
of the liquid when left in contact with the air, or when treated 
with sulphuric acid. 

Indican, CgeHg^NO^y, already referred to as the natural gluco- 
side by the decomposition of which indigo-blue is produced, was 
first isolated by E. S c h u n c k.^ It forms a transparent brown 
syrup, from which it is impossible to separate the water without 
causing decomposition. The aqueous solution has a yellow colour, 
bitter taste, and slight acid reaction. When boiled with caustic 
alkali it evolves ammonia. Weak solutions of alkalies and lime water 
produce a bright yellow colour. The alcoholic solution of indican 
gives a bright yellow precipitate with lead acetate, which is 
increased on adding ammonia ; but the aqueous solution does not 
give this reaction. Indican is soluble in ether, but is extracted by 
water from its ethereal solution. 

The most characteristic and important property of indican is the 
behaviour of its solution with dilute acids, by the action of which 
it splits up with formation of indigotin or indigo-blue, 
i n d i r u b i n, and indiglucin. The reaction occurs slowly 
in the cold, but rapidly at a boiling heat, the liquid becoming 
first sky-blue, then opalescent, and finally purple, and on cooling a 
purple deposit of mixed indigotin and indirubin is obtained 
(both of which may be obtained in a crystalline state by sublima- 

^ Schanck hew described the following process for the preparation of indi- 
can : — Dried woad leaves are finely powdered and extracted with alcohol by 
percolation. A little water is added, and the solution concentrated as quickly 
as possible at the ordinary temperature in a current of air. The residual 
brown liquid is filtered from the green i-esidue of fat and colouring matter, 
and agitated with some freshly precipitated cupric hydroxide. The liquid is 
filtered, the copper precipitated by sulphuretted hydrogen, and the liquid 
again filtered. The filtrate, which should be light yellow, is concentrated to 
a syrup at the ordinary temperature in a current of air, treated with cold 
alcohol to remove decomposition-products, filtered, and mixed with twice its 
measure of ether. The filtered liquid yields on evaporation a clear brown 
syrup consisting of pure indican. 

k), while indiglucin remains in solution. Tlio following foniuila 
tesenU the formation of indigotin from indicaii : — 
CaaHs,NO,^+ 2H„0 = CaH.NO + 3C.H,oOfl . 

luduan. ' IndlgullB. ludiflucln. 

[ndigotin or indigo-blne is considered more at length on ) 

Ikoiqo Beiown. If an aqueous solution of indican bo boiled or I 
heated for some time it undergoes a change, and on now treating | 
it with an acid it yields neither indigotin nor indirubin, hut dark f 
brown or biockiah Qocke, consisting of a mixture of two lirown r 
sinous bodies, called by Schunck indiretin and indihumi 
of which only the latter is soluble in alcohol, and to which bodies I 
lattributw the formula CigHjjNOm and CgHgNOj respeetively. 
tuHne, CgHjjNOj, a body [iroduced in the putrefaction of ] 
se, and by the treatment uf various animal substances with 1 
khurie acid, is idea a product of the reaction of dilute acids o 

RjroiRDBiH or Indigo Red, CgHjNO, is obtained with indigotin I 
Kthe decomposition of indiean, especially when oxalic or tartaric I 
■ la used. It may be separated from the indigotin fey boiling 
i precipitate with alcohol. On concentrating and coohug the i 
tholic solution, the indirubin is obtained in long red crystals, 
pluble in caustic alkalies, but reducible by boiling with an alkali 
I BtannooB chloride or glucose to a leuco-derivative, the 
ptdon of which on exposure to air yields purple flakes, which 
. washed, dried, and heated, give a sublimate of beautiful 
BMdlfa. readily soluble in boiling alcohol, and recrystallising as 
Iho solution cools. If a piece of calico be immeraed in a reduced 
alkaline solution of indirubin, and then exposed to the air, it 
birconics dyed a fast purple colour (not blue as with indigdtin) 
which is not affected either by acids or soap, Indirubin dissolves in 
cold concentrated sulphuric acid with beautiful purple colour. On 
heating the solution it becomes lighter and gives oil a little sul- 
phur dioxide. On diluting the solution of indirubin in sulphuric 
acid with water, a li([uid is obtained which dyes cotton, wool, and 
silk a fine purple colour. Indirubin is not affecti-d hy boiling 
with dilute sulphuric acid and potassium bicliromate, a character 
which distinguishes it from indigotin. 

Indioldcin, C^Hj^Og, is obtained from the liquid from which 
the atiove colouring matters have been separated, by adding excess i 
of lead atetiile, filtering, and treating the filtrate with excess of 
Biuraonia. The bulky yellow precipitate thus obtained is decomposed , 
by sulphuretted hydrogen, and the indiglucin piirifiod liy rei>eating ' 
I procBsa or treatment with animal churconl. On eoncentrat- 


ing the colourless liquid or syrup, and adding alcohol and two 
volumes of ether, the indiglucin separates as a pale yellow, 
sweetish syrup, which turns red and blackens when heated with 
sulphuric acid, and yields oxalic acid on treatment with nitric 
acid. It reduces hot Fehling's solution and silver nitrate. 
The solution gives no precipitate either with neutral or basic lead 
acetate, unless ammonia be added. If milk of lime be added and 
the solution filtered, a strongly alkaline liquid is obtained, and on 
boiling this it becomes thick from the formation of a flocculent 
yellow precipitate, which completely redissolves to a clear yellow 
solution on cooling. This reaction may be repeated indefinitely. 
By fermentation with yeast, indiglucin appears to yield acetic 

Indigotin. Indigo Blue. CgHgNO or CjgH^^jOj. This sub- 
stance probably has the constitution represented by the following 
formula:^ — 

Indigotin is the constituent on which the value of commercial 
indigo depends. Besides the natural product as contained in 
indigo, indigotin may be obtained from coal-tar by a series of 
complex reactions described on page 33. The artificial indigo thus 
obtained, or rather the phenyl-propiolic acid which yields indigotin 
on reduction, was recently an article of commerce, but it has not 
been found possible to produce it at such a price as would enable 
it to compete successfully with the natural product. 

Pure indigotin may be obtained by mixing one part of com- 
mercial indigo in fine powder with two parts of plaster of pans, 
making the whole into a paste with water, and spreading it on an 
iron plate. When quite dry the mass is cautiously heated, when 
the surface becomes covered with beautiful crystals of pure indigo- 
tin, which may be removed with a fine spatula. Indigotin may 
also be obtained in a pure state by the oxidation of indigo- 
white, CigHigNjOg (page 296), orindoxylic acid, CgH7NOs, 
or by the reduction of orthonitro-phenyl-propiolic 
acid (page 33). It may also be prepared by heating i s a t i n, 
C8H5NO2, with a mixture of phosphorus trichloride and penta- 
chloride, and reducing the resultant isatic chloride, 
CgH^NOCl, by ammonium sulphide. 

' Baeyer regards the molecule of indigotin as composed of two symmetrical 

halves, CfiA -^^ rC:, and this half-molecule he calls indogeu. The 

indogenides are compounds of yellow or bluish-red colour, and some of them 
yield blue salts which exhibit the indigo spectrum. 


Pare indigotin forma dark blue cryatala exhibiting a eoppeiy I 
reflection and having the form of & right rhomboidal priam. In ] 
the form of powder it is deep blue, and asBumeB a coppery luatre 
when bumiahei Its specific gravity ia 135. Indigotin is not 
fusible, but sublimes at about 390° C., with more or leas decom- 
poeition- In an inert gas it may be volatilised unchanged. 

Indigotin is unchanged in the air at ordinary temperatures, and 
has neither taste nor amelL It is iueotuble in hot or cold water, 
cold alcohol, ether, and fatty and essential oils. Creoaotc, carbolic 
acid, absolute alcohol, amylic alcohol, and carbon diaulpbide dissolve 
K little indiffotin when hot, but it is again deposited on cooling. Ita 
beet solvents are glacial acetic acid, nitrobenzene, and aniline. On 
boiling powdered indigo with aniline it readily dissolves to form a 
blue aoliitlon, which if filtered hot and allowed to cool deposits 
nearly all the indigotin in beautiful crystals, which after being 
washed with alcohol are perfectly pure. Boiling paraffin and high 
boiling petroleum are also solvents of indigotin. The dilute 
solutions have the colour of an alcoholic solution of magenta. 

If a little finely powdered indigotin be treated with glacial 
Hcetic acid and one or two drops of strong sulphuric acid added, a 
deep blue solution is formed, from which the indigotin is precipi- 
tated unchanged on dilution with water. If any fibre be immersed 
in the undiluted solution, and then washed with water, it will be 
iyed blue, 

Indigotin is a perfectly neutral substance, and is insoluble in 
dilute acids and alkalies. 

When subjected to dry distillation, either alone or in admixture 
with an alkali, indigotin yiclda aniline, CgH,N. 

When subjected to the action of OKidiaing agenta, such as dilute 
cid, chromic acid, or chlorine, indigotin is converted, in the 

KDce of water, into a body called isatin^ or indigotic acid. 

|l8*HK, C,HjN0,-C,H4:|*^^.|c(0H). Thifl body is obtained by oii- 
{ indigo by chromic acid, or prererably nitric acid. Powdered iodlgo is 
a a Uiin paste wi(b wBt«r. the laixture heated to the boiling point, 
I nitrio ncid added eaiitiotial}' till tlie blue colour diwppean, wh«D tha 
• i* largely dilated with boiling water sod the liquid tittered. Impure 
1 HjMratej on cooling, and is wiuhed with nmmoniacal wat«r. Isatin 
a daep yellowish-red priimatie crjatats, ipuritigly soluble in uold water, 
E-ftevly in boiling watei and in alcohol The solution Btoina thu Htcin 
', and give* it n diasgreeabte odonr. When heateid, iaatiu melts and 
I, with jiartial dpcompoBition. It forma crystoHine componnda willi 
■ •dd tulphitei of the alksli-iuetaU, and diaaalTea in alkalies to form violet 
M, whicli turn yellow when heated and then coutoiu a lalt of iaat Jc 
Uydrindic acid or dioiindole is Formed by the action of 


Hot and strong nitric acid converts indigo-blue into picric and 
nitrosalicylic acids, some carbonic or oxalic acid being 
simultaneously formed. 

Hydrindigotin. Indigo Whitb. Bsduced Indigo. CkjHijNjO,. 
Wben indigotin is subjected to the action of reducing agents ife 
assimilates two atoms of hydrogen, forming a leuco-body of the 
above composition, the constitutional formula of which is prob- 
ably : — 

^«^*| NH I CH . HC I j^g I C^H^ 

Agr eat variety of substances have the power of reducing indigo- 
blue to indigo-white. Thus in alkaline solution, or presence of free 
alkali, we may use : — sodium amalgam ; zinc, tin, aluminium, and 
phosphorus; ferrous hydroxide; phosphorous, hypophosphoions, 
and hyposulphurous (Schutzenberger's) acids ; certain phosphides, 
arsenides, and sulphides (especially sulphide of arsenic) ; glucose, 
gallic acid, the butyric ferment, &c. The resultant reduced indigo 
is soluble in the alkaline liquid. In acid solutions, indigotin is 

sodium amalgam on this solution. Further reduction in acid solution pro- 
duces oxindole, and this when distilled with zinc-dust yields indole, a 
weak base existing in human excrement. The relationship of these bodies to 
indigotin, isatin, and each other is shown by the following constitutional 
formulee: — 

Indigotin, . 
Isatic acid, 
Oxindole, . 

^•^* I .NH. }^=^{;nh. I^*^* 

CeH^j;^^- }C(0H) 


.CO. CO. OH 




Silver nitrate throws down from alkaline solutions of isatin a red pre- 
cipitate containing C8H4AgNOa. The hydrogen of the hydroxyl group may 
also be replaced by acid radicals, as in acetyl-isatin, C9H4(CsH{0)N0f 
Mono- and di-chlor- and brom-isatins are obtained by the action of 
chlorine and bromine on isatin or moist indigo. Isatin-sulphonic acid, 
C8H4(S08H)N02, is formed by the treatment of indigotin-sulphonic acid by 
permanganate or other oxidising agents in acid solution. It is soluble, and 
difficultly crystallisable. 



I iiiB olu 

less readily, hypoBulphuroua acid (H^SO^ being almost 
only available agent* 

~ rdiindigotra is a greyish-white, amorphous, tasteless, odour- 
Buhstanco, having a silky lastre. Heated out of contact with 
air a small quantity of indigotin sublimes, and a carbonaceous 
is left. In contact with the air at the ordinary tempera- 
ture white indigo gradually becomes blue from oxidation, and 
the action is rapid in presence of moisture. Indigo-white is 
insoluble io water and dilute acid liquids, but dissolves in alcohol 

[ydrindigotin ia soluble in solutions of the alkalies and alkaline 
but its acid characters are very feebly marked, for the 
nee of a textile fabric sufBces to decompose its compounds, 
tho indigo-white uniting with the fibre and alkali being set free.^ 
The alkniine solutions of reduced indigo have a yellow tint, but in 
£ODtact with air they become green and blue and covered with a 
im, and deposit minute crystals of indigotin. Addition 
,n oxidising agent produces the same effect more rapidly, and 
slight rise of temperature causes a similar change. The 
Ication of indigo in dyeing by tlie Vat-process is based on 
■reduction to white indigo, the solubility of the reduced sub- 
ice in alkaline liquids, and its reoxidatton to indigo-blue on 
" ■-* Alkaline solutions of hydrindigotin gives bulky 
ite precipitates with solutions of magnesium, zinc, alumiultun, 
ferrous, mangonous, and stannous salts. The last precipitate 

BA MDveniinit process for tbs prHparation of white indigo condgts in treat- 
^1 part indigo-blue with 3 parts of crystallised ferroui sulphate, S parb 
■kad lime, and 2D of water in a eloaed vesseL The mixture is agitated at 
rvals for wme days, and Snatly allowed to settle. The pale yellow liquid 
B lyphoned off into a bottle filled with carbon dioxide, containlug some 
Btl; boiled hydrochloric acid. The iudigo-nhite is immediately prtcipjtated, 
■ when the battle is quite full it is imniediately closed. After ataudiug some 
^ the liquid is filtered in nn atmogpbero of carbon dioxide or coal-gus, the 
~'|Mtale washed with air-free cold water, and dried in vacuo. 
I alternative proceas is to treat the indigo-blue irith caustic sods and 
h the subseqaent operattona being the same as those already described. 
i inxtantaDeona reduction may bo effected by treating the fiuely powdered 
indigo with a solution of a hyposulphite, obtained by agitating ^iinc-dust with 
1 Mmug salution of acid sulpLite of sodium, and treating the decautad liquid 
vrlth pxec» of canstao Koda. 
i White indigo fonne two compounds with lime, one of which is soluble 
\ ibe ntliet insoluble. 

oant of indigotin is, however, never recovered ; the cause of 

ire, and its investigation would probably lead to means of 

ni^ng it which would well repay the trouble, 


is employed for printing indigo on fabrics. When heated it yields 
metallic tin and a sublimate of indigotin. 

Concentrated sulphuric acid dissolves white indigo with intense 
purple coloration, forming mono- and di-indigotin-sul- 
phonic acids. 


digo-purpuric Acid. CigH^j^Q-^^s^ ^^^ body, also called 
sulphophenicic acid, may be obtained by adding one pari 
of good commercial indigo in fine powder to four parts of ocmcen- 
trated sulphuric acid, and heating the mixture for a short time, or 
until a sample gives a deep blue colour when largely diluted with 
water. Too high a temperature and too prolonged heating most 
be carefully avoided, or the disulphonic acid will be produced. As 
soon as the product is found to be soluble, the mass is thrown iato 
about fifty parts of water, when a beautiful purple precipitate of 
sulphopurpuric acid will be thrown down. This is filtered ofi^ and 
washed slightly with dilute hydrochloric acid. 

Sulphopurpuric acid is almost insoluble in dilute acids and veiy 
sparingly soluble in water, but communicates a bluish-purple colour 
to the liquid. On adding sodium carbonate or acetate to the 
aqueous solution, purple flocks of the sodium sulphopur- 
p u r a t e, CieHgNjOg-SOgNa, are precipitated. This salt is soluble 
in a large quantity of water, and is employed in dyeing under the 
name of indigo-purple or red indigo-carmine. Precipitates are 
produced by solutions of calcium, aluminium, and iron. Caustic 
alkalies produce no effect, but the solution is decolorised by reduc- 
ing agents, such as zinc, sulphuretted hydrogen, or stannous chloride, 
and becomes blue again on exposure to the air. 

Indigotin-disulphonioAcid. SulphoindiqoticAoid. Ci^HgNjO, 
(S08H)2. This acid, also called indigo-sulphuric acid and 
sulphindylic acid, is obtained when the monosulphonic acid 
is heated with eight or ten parts of sulphuric acid, and hence is 
usually formed, to a greater or less extent, together with the mono- 
sulphonic acid, when indigo is treated with concentrated sulphuric 
acid. It forms the sole product when the sulphuric acid amounts 
to fifteen times the weight of the indigo employed. It is best 
obtained by carefully heating the finely pulverised commercial 
colouring matter, or preferably pure indigotin, with ten or twelve 
parts of ordinary strong sulphuric acid (sp. gr. 1*845), or six or 
seven parts of the fuming acid, to a temperature of 50° C. for 
several hours, or until a small sample is found to be entirely 
soluble in water. The product is then cooled and treated with 
about fifty parts of water. On standing for some time, any mono- 
sulphonic acid and certain other impurities will be deposited, and 



the filtered solution will be pure blue.' ,To prepare pure sulpb- 
indigotjc acid, clean white wool or flannel, wliich bas been pre- 
viously thoroughly washed by boiling with soap and solution of 
CArboDste of sodium and then with pura water, is imnnQTsed in the 
solution till the greater part of the colouring matter is taken up, 
It la then well washed to remove the free sulphuric acid, and 
stripped by immeraing it in a weak solution of ammonium car- 
bonate. The blue solution thus obtained is evaporated at a tem- 
perature not exceeding 50° C, and the residue treated with rec^fled 
spirit to dissolve any hyposulphindigotate. The undissolved por- 
tion, consisting of ammonium sulphindigotato, is treated with water, 
the solution precipitated by lead acetate, and the insoluble lead 
salt washed and decomposed by sulphuretted hydrogen. A colour- 
less solution of hydrindigotin-disul phonic acid, C,(HjgN„0^80jH)2, 
nsults ; and on exposure to air this readily oxidises to a blue solu- 
tion of sulphindigotic acid, which may be obtained as a blue 
amorphous mass by evaporating the solution. 

Svdphindigotio acid is decolorised by reducing agents. By 
oxidising agents it is converted into isa t in-disulphonic 
acid, C,jHgNjO,{SO,H)j, a body of an orange colour, on the 
fonnatiou of which several methods fur the assay of commercial 
indigo are based. 

Sulphindigotic acid is decomposed by an excess of strong caustic 
alkali, with production of a yellow liquid; but with dilute alkalies 
it reacts to form sulphindigotates. These salts, when 
solid, have a beautiful bronze-blue colour, and dissolve freely in 
pure water yielding blue solutions. In saline solutions they are 
almost or quite insoluble; and hence, on adding common salt or 
sulphate of sodium to the solution of a sulphindigotate of alknli- 
metal, the latter compound is precipitated in blue flakes. 

Potassium sulphindigotate, C„H8NjOj(S03K)j, is soluble in UO 
parts of water, and the sodium salt somewhat more readily. The 
lead salt is insoluble, and the barium salt very slightly soluble in 
cold, but more readily in hot water. The sulphindigotates of cal- 
cium, magnesium, and aluminium are easily soluble. 

IttDioo Extract, Soluble Indigo. Indigo-carmine. Those 
nafflGs are applied in commerce to more or less pure indigo- 
■nlphonic acids and their salts. The exact nature of the product 
Tsries considerably with the quality of the indigo, the propor- 
tion of sulphuric acid used, the temperature employed in the 
proceas, and the subsequent treatment of the sulphonated indigo. 
' A thiril ndd, cklled bypoaulphiodigo tic acid, b Eaid to be 
temad. bat no tonnuln has been uaigned to it In its roactiouB it clowly 
~ a nilliliiadigotiu a<.^id, but its suits are uoluble in n^ttified spirit. 


With a moderate proportion of acid,tbe mono-sulphonic acid 
(page 298) is the chief product, and this, when converted into the 
sodium salt, is known as indtgo-purple or red indigo-earmine, A 
product of similar composition, known as BoUey^s hlue, is prepared 
by gradually adding 1 part of finely powdered indigo to 10 or 20 
parts of sodium hydrogen sulphate, NaHS04, in a state of fusion. 
The product is dissolved in water, precipitated with common salt, 
and washed with brine. Boiley's blue is a crystalline, light purplish 
mass, soluble in water with beautiful blue- violet colour. Its solu- 
tion in strong boiling acetic acid deposits, on cooling, large pris- 
matic crystals, exhibiting a coppery reflection. It is insoluble in 
alcohol or ether, but readily soluble in hot water. The light trans- 
mitted by the solution is red. With barium and strontiimi salts it 
yields violet precipitates. 

Saxony blite, chemiCy chemic blue, and sour extract are names 
applied to the solution of indigo in sulphuric acid, without any 
neutralisation or subsequent treatment It is not unsuitable for 
wool-dyeing, as the green colouring matter which it generally con- 
tains has no affinity for the wool-fibre ; but for dyeing silk this 
must be removed. For this purpose the acid is usually converted 
into a sodium salt, known as indtgo-^xtrmine. This can be made 
by neutralising the acid with soda-crystals, when the sodium sul- 
phate simultaneously formed precipitates the sodium sulphin- 
digotate, the separation being rendered complete by adding common 
salt. The precipitate may be purified by re-solution in water, and 
again salting out, the process being repeated until the absence of a 
^reen tint in the filtered liquid shows that the objectionable green 
colouring matter has been entirely removed. The purified pre- 
cipitate should then be washed with water until the liquid begins 
to run through blue, when it is drained and pressed. In some cases 
the solution of the sulphonated indigo is at once precipitated with 
common salt, without being previously neutralised. Magnesia and 
chalk are sometimes employed instead of soda-crystals. The 
potassium salt, obtained by precipitating a solution of sulphindigotic 
acid by potassium acetate, is occasionally met with. 

Indigo-carmine occurs in commerce as a dry powder or copper- 
coloured masses having a blue streak, and also as a blue or purple 
paste, which should be free from any green or brown reflection. 
The following figures (page 301) indicate the usual percentage 
composition of indigo pastes. 

The toater is determined by drying 2 grammes of the sample at 
100°, and noting the loss of weight. The dried substance is then 
heated just to redness in platinum, when the residue represents the 
acUine matters, the loss being regarded as organic matter. The 


lignre thus obtained is sometimes reported aa " colouring matter." 
but in reality is mode up of water not driven oif at 100°, sulphuric 
«cid evolved from NaHSO^, organic impurities of the indigo, ifec. 
&a the real colouring uutttir of iudigo-camiine usually ranges from 

■IquUtJ' ) 

3 to 6 per cent, vith an average of about 3 per cent., it is evident 
Uut the organic matter of a sample does not, even appro si mately, 
indicate ita tinctorial value. The indication ia still more worthless 
in presence of deririn and other adulterants. A useful method 
of assaying indigo-carmiuo is to dissolve 1 gramme of the sample 
in a litre of water, and compare the depth of colour with that 
yielded by a standard specimen; but the difference in the shade 
of various makes of indigo-paste often renders this niethoil of 
examination untrustworthy. In such cases the true strength of 
the sample is best ascertained by titration with pei'mangonate or 
hyposulphite, as described on pi^ea 308, 309. 

The presence of the green colouring matter in indigo-paste nmy 
he detected by rubbing a little of the colouring matter on gliiKed 
paper. On drying, the shade will vary from pale blue to a rich 
coppery-purple, according to the mode of manufacturing the paste; 
and if any green colouring matter be preeent, a green border will 
be observed surrounding the blue circle. The test may be modified 
by dropping an aqueous solution of the colouring matter on a piece 
of filler-paper, when the green margin will become evident as the 
paper dries. 

Indigo-ex tracti) should leave no undissolved gritty particles 
when treated with water, but all the common varieties leave a 
dirty greenish-black insoluble residue. Soluble indigo is said to 
be Bometimes adulterated with farina, dextrin, and other inert 
nutters. A general indication of the quality of the sample may 
be obtained by dissolving a known weight in water, adding a little 
alum and cream of tartar, and then introducing successive swatches 
of well-washed white wool or flannel. The value of the sample 

' Prwo F. Craeo 
■ Frwn FUrb. Muil. 

Calvert's valuable work on D]/tiag and Caiko 
ZtU., 17, 131; alMtracted in Jour. Son. Cheia. I-ul., 



will be in proportion to the weifjht of wool dyed to a fituuiud 
shade of colour. The greeu colouring matter already refen«d to 
occurring in some qualities of soluble indigo ia taken ap by wool 
last, or not at all, when the sample is thus treated. 

The more acid varieties of soluble indigo are employetl (or 
dyeing wool and worsted. The neutral is employed for eUlc, and 
is also used for dyeing mixed goods containing cottun, and tot 
printing woollen goods, such as tapestry -carpets, &c. The dyeing 
is effected in an acid bath, to which cream of tartar, 
aulihhate, or alum is sometimes added. 

CouueROiAL IxDioo. — Indigo occurs in commerce in Ininpiar 
fragments of a deep blue colour, usually showing a bronze orpuijJi 
red streak when nibbed with any hard substance, or, lu the case of 
the better kinds, even with the friction of the thumb only. TIk 
fracture of indigo is dull and earthy, and it is practically inMlnUt 
in water or any of the ordinary solveuta, except conoeatnled 
sulphuric acid. 

Indigo varies much in quality according to the cnro taken in iti 
preparation.' The i n d i g o t i n or indigo-blue, which ia the nwl 
valuable and abundant constituent, varies from 30 to (occauoD^f) 
80 per cent., with an average of alwut 45 per cent The only irtl«t 
conatituent of tinctorial value is the indirubin or iodig4- 
red, the proportion of which ia generally between 3 and 8 per wot 
Chlorophyll (more or less altered), a brown colouring maUtf 
called indigo-brown, and a glutendike substance teiaiA 
indigo-gluten, are the other principal constituents, in addilia 
to a trifling percentage of moisture and a variable proportion 
of mineral matter. 

When an indigo of superior quality is required, as ia deainU* 
for making indigo-extract, the finely powdered substance is trwled 
several times at a gentle heat with hydrochloric acid conlniBinc > 
little free chlorine, by which treatment iron, lime, and smne otW 
mineral impurities are dissolved, while the amylaceous uatteia m 
converted into dextrin or sugar, which is removed by suhseqwrt 
woahing with water. The residue is then trealful with 
caustic aoda, which removes chlorophyll and some other 
impurities. The product is known in commerce us rvfined inJigo. 
The same name is applied commercially to a product obtninod by 
reducing finely-ground indigo with ferrous sulphate and lime. 

The technical andlyHa of indigo ia usually limited to deter- 
minations of the moisture, ash, specifiu gr a vi tf, snii 
colouring matter. In some cases the iiidigotia istht 
n 'Wtet African Indigo by Bawson and Ehb 

M. Dyert, <*e., iv. f 

t^^^^r Asew OF 303 ^^H 

on); colouring matter taken into account, but the i n d i r u b i n ^^^| 
onight not to be neglecteil, as it modilies the shade of the blue ^^^| 
produced, and is itself capable of dyeing any fast coloiire. Indigo- ^^^^| 
brown, on the other hand, ia of no practical interest, as in the dye- ^^^| 
vat il forma an insoluble compound with the lime used, and in ^^^| 
making extract is precipitated when the svdphuric acid solution of ^^^| 
the indigo is diluted with water. The methods of determining the ^^^^| 

few can be at once considered both accurate and practical^ ^^^^| 

The moi«lttre in commercial indigo usually ranges from 3 to 8 ^^^^| 

per cent., and may lie determined with accuracy by observing the ^^^H 

loss of weight undergone by the sample on exposure to the tem- ^^^| 

penture of boiling water. ^^^^| 

The auk left on igniting commercial indigo ia a useful cntenoa ^^^^| 

of its purity. In the purest kinds it is sometimes as low as 2 per ^^^^| 

cent., but from 5 to 8 per cent, is a more usual proportion. Some ^^^^| 

of the inferior kinds of indigo, such as Kurpah and Madras, fre- ^^^| 

quently contain from 25 to 35 per cent, of ash. ^^^^| 

Leuchos has recommended the determination of tht spKifid ^^^^| 

yravity as a useful preliminary test of the quality of indigo, and ^^^^| 

gives the following figures in illustration of the relation between ^^^^| 

the specific gravity and percentage of iudigotin : — ^^^^| 











Helen Cooley {A^ner. Jmir. Anal.. Ck»m., u. 130) has 
recorded the specific gravities and percentages of ash and iudigotin 
contained in the following samples of commercial indigo : — 



Speclflc gnilty. 





I Mil 

I -en 






Theee figures do not establish the value of the specific gravity as 
a test of quality, or even indicate that it is a criterion of the pro- 
portion of ash. 

' The ViluBtion of lodifio htt been treated in an eihanstive mBnner by C 
RnwBon {Jour. Soc. Dytn,ix.,\. H, 211), frorawlioae paper mucli ot the 
infomution here given in derived, and to whom the author U indebted for llie 
pHttMkl and comclioQ of this articis on the mbject. 



Starch, sometimes coloured with iodine, is said to be occasion- 
ally employed for adulterating indigo. To detect it, the sample 
should be treated with a cold dilute solution of sodium thiosulphs^, 
and the insoluble residue washed with proof spirit. The starch- 
granules may then be detected by the microscope, or the residue 
may be boiled with water and the starch tested for by adding 
iodine solution to the filtered liquid. 

A useful proximate analysia of indigo, together with a moderately 
accurate determination of the indigotin present^ may be effected as 
follows : — The sample is dried at 100° to determine the water, 
then treated with hot water and the residue dried and weighed 
This gives the matters soluble in water, and the residue is treated 
in succession with dilute hydrochloric acid, dilute caustic soda, and 
alcohoL The loss of weight resulting from each of these treat- 
ments may be determined with advantage, especially the amount 
of matter soluble in alcohol, as this represents the indiga-red of 
the sample.^ The residue after this treatment is dried and 
weighed. Its weight, after deducting that of any ash it may leave 
on ignition, represents the indigotin of the sample. 

C. Tennant Lee {Chem, News, 1. 49 ; from Jour. Ameriean 
Chem, Soc.) has proposed to assay indigo by observing the amount 
of indigotin which can be obtained by sublimation — a method 
which is easy, rapid, and, in his experience, uniformly satisfactoiy. 
For the operation he recommends the use of a shallow, flat-bottomed, 
platinum tray, 7 centimetres in length, 2 wide, and 0*3 or 0*4 
deep. About 0'25 gramme of the finely powdered sample, pre- 
viously dried at 100°, is introduced and spread evenly over the 
bottom of the tray, which is then gradually heated on an iron 
plate. When the surface of the indigo becomes covered with a 
shining layer of crystals, the tray is covered with a piece of sheet 
iron, about 8 or 9 centimetres in length and bent into a slightly 
arched form, so that the highest point may be about 1 cm. 
above the plate. The heat is simultaneously lowered. Purple 
vapours of indigotin are now given off, a portion condensing on the 
concave side of the arch. The heat is now raised slowly, so as to 
maintain a constant sublimation of indigotin, the progress of which 
can be observed by raising the arch. With a 50 per cent indigo, 
the operation is complete in 30 to 40 minutes ; but soft Java indigo 
must be treated with more caution, the sublimation sometimes 

^ As indigo-brown is only with difficulty removed by treating indigo with 
caustic soda, the indigo-red is liable to be contaminated with the portion of 
the brown wliich escaped solution. By treating the impure product with dilate 
caustic alkali, the indigo-brown will be readily dissolved and the indimfaiA 
obtained pure. 



occupying two houra. When all crystals of indtgotia have dis- 
appeared from the dark-coloured surface of the residue, the tray is 
temoved, cooled in a desiccator, and weighed, the loss of weight 
being regarded as tmligoUn. On repoatiug the process the results 
should not vary more than 0"3 per cent. C. R a w s o n points out 
that the author of the above process has not given any ligures by 
which the results obtained ean be compared with those yielded by 
other methods. In his own experience he has found the iigree- 
ment to be in many cases very good ; but, as a rule, inferior quali- 
ties of indigo, containing much matter soluble in hydrochloric acid, 
yield by the sublimation-process results above the truth; whilst, 
on the other hand, rich samples give results which are undoubtedly 
too low. Rawaon obtained diSerentea of upwards of 2 per cent. 
by an alteration in the cover. It seems probable that these 
strictures are justified, but that the process ia nevertheless very 
useful in many cases. If applied to indigo which had been 
subjected to a preliminary treatment with dilute hydrochloric 
uid, and then thoroughly dried, it would probably yield, on sub- 
jection to corefully-regulated sublimation, results of considerable 

Another method of estimating the real indigotin present in 
comracrcial indigo ia baaed on its reduction to the leuco-derivative 
(white indigo), and reoxidation of this by exposure to air. Some 
of the processes for effecting this are tedious and deficient in accu- 
racy, but the following, in one of which the reduction is effected 
by a ferrous hydroxide and in the other by a hyposulphite, are 
recommended by C. E a w s o n. The iron process is conducted by 
treating 1 gramme of the finely powdered sample in a flask with 
S grammes of cryatollisod ferrous sulphate, 5 of caustic soda, and 
tOOOc.c. of water. The fiosk is closed by a cork having three 
perforations, through one of which passes a syphon, while the 
other two are used for the entrance and exit of a current of coal- 
gaa. The contents of the flask are maintained at a temperature a 
little below the boiling point for 1 1 to 2 hours, when the source of 
heat is removeil and the insoluble matters allowed to subside. 
A niensure of 500 c.c ( = i (gramme of the sample) is now syphoned 
off, and the reduced iniligo oxidised by passing a current of air 
through the solution. To complete the precipitation, the liquid is 
Acidified, and the precipitate of indigotin, mixed with indirubin 
and indigo-brown, allowed to subside. The supernatant liquid is 
paued through a weighed fliter, and the precipitation washed several 
times by dccautation with hot water. It is then boiled with alcohol, 
which dissolves the brown and red colouring mattere. allowed to 
^1 to insure the separation of any traces of dissolved indigotin, 


transferred to the filter, washed with rectified spirit, and the pn« 
iadigotin dried at 100° and weighed. 

The following method is preferred hj C. Kawson, as leaving 
nothing to be desired in point of accuracy, and being more rapid 
than any other reduction-process: — 1 gramme of the finely powdn«l 
sample is made into a paste with water, and treated in a flask with 
about 600 c,c of lime-water. The flask is closed by a cork hiring 
four perforations, two of which serve for the passage of a cuirent of 
coal-gas, a third carries a syphon, while to the fourth is fitted a 
tap-funnel. The contents of the flask are heated to S0° C. and 
100 to 150 c.c. of a strong solution of sodinm hyposulphite 
(NaHSOj) introduced through the tap-funnel.' In a few minutes 
the liquid assumes a yellow tint, aitd is maintained at a temperature 
near the boiling point for half an hour. After allowing the insoluble 
matters to subside, an aliquot part of the solution should be removed 
and a current of air drawn through it for about twenty minates, 
when it is acidulated with hydrochloric acid. The precipitatfi 
consisting of a mixture of indigotin and indirubin, is c«Ue(^ on 
a weighed filter, thoroughly washed with hot water, dried at 100', 
and weighed. It is then exhausted by boiling alcohol, whereby 
the indirubin is dissolved, and can bo estimated from iiiei los of 
weight or recovered by evaporating the alcoholic solution. 

Although, with care, the precipitate of mixed indigotin and indi- 
rubin obtained as above may usually be obtained free from impuri- 
ties, in some cases Bawson recommends that the dried precijutttn 
should be dissolved in pure concentrated sulphuric acid at 85* C, 
and an aliquot part of the diluted solution titrated with ^ per- 
manganate, each 1 c.c. of which, according to him, corresponds M 
O'OOIS gramme of indigotin. 

In a method described by H. M. Rau (Jour. Amer, Chem. Sac., 
18S5, 7, 16), which is a modification of one previously suggested 
by Fritsche {Annai. C/iem., xliv, 290), the indigo is reduced 
in alkaline solution by glucose. The operation is conducted in a 
weighed flask of about 8 oe. capacity, fitted with a cork carrying 
two tubes. From 1 J to 2 grammes of the sample of indigo, 3 to 4 

' The sodinni hfposnlplijte, which must not be confouoded with Qu lltia- 
BDlphito, NajSifO,. ia prepared by traating a solatioD at sodium brdnqpa 
sulphite (NaHSO,) with :inc-du9t in a closed Daak. After sUnding aboal mt 
hour, with Dccaaioud. agitation, the lir^uid ia docantcd and diluted with alitn 
of receatl; boiled diatilled water. About 50 gremmes ofalaked Umv •hooM ti* 
next added, the reasel closo], and when the precipitate hia Bubsiiieil tlia«lMr 
liquid is syphoned off and kept under a layer of keroseiu oil, ia a bottlt jn- 
tect«d from the light. 


of pure ^pe sugar, from 6 to 10 cc of n 40 per cent eolution of 
I cn natie soda, 60 c.c. of water, and about 120 cc of rectified spirit 
^^^ employed, and the total weight of the apparatus is observed. 
^^^■B flask is heated in a water-bath for half an hour, and allowed 
^^Bi for another hour. One of the two tubes is then connected 
^^Wfe an apparatus generating carbon dioxide, by which the liquid 
is blown out through the other tube, which is arranged as a syphon, 
and the shorter limb of which is loosely plugged with glass-wool, 
The weight of the liquid expelled is noted, and the indigotiu is then 
precipitated by passing a current of carbon dioxide for about fifteen 
minutes, and this is followed by a current of air to complete the 
precipitation. The precipitate is crystalline, and is readily washed. 
It is stated by Rau to represent the indigotiu and indirubin of the < 
sample, but Rawaon has pointed out (Jour. Six. Dyern, ^c, i. 211) 
that the solubility of indirubin in alcohol renders its precipitation 
improbable, and he has proved by actual experiment that the pre- 
cipitate obtained by Rau's process consista of pure indigotin, yield- 
ing nothing either to cold alcohol nor to ether. 

A volumetric method of determining indigotin has been described 
by L M. Sorton (Amm: Amx: Adv. Science, 1880, p. 358). 
One gramme of the sample is mixed in a mortar with milk of lime, 
and the paste washed into a flask. One gmmme of zincJust is 
added, and water added to a mark on the neck. The flask is then 
a the water-bath for half an hour, closed, and allowed to 
d overaight In the morning the contents are shaken, allowed 
settle, and a volume of 100 c.c. blown out by a neutral gas into 
i^ution of iron-olum. The ferrous salt formed corresponds to the 
^ced indigo in the volume token, and ia determined by titration 
'hk standard solution of bichromate. Helen Cooley (Amer. 
: Anal. Chem., ii. 133) states that the manipulation is simple, 
1 that, with some practice, the method gives good results. 
L variety of methods of assaying indigo have been based on the 
lation of the colouring matter in acid solutioa Thus, potas- 
I permanganate, bichromate, and ferricyanide have all been 
mmended and used to a considerable extent, and bleaching 
|rder solution has also been employed. All these processes are 
D to the objection that the oxidising agent acts on the indigo- 
ten and ferrous salts, as well as on the indigo-red and indigo- 
I, and tiencc tlie results are liable to bo seriously above the 
; but Kawson has pointed out that the errors due to this 
e may be practically avoided by previously precipitating the 
Bulphindigotic acid in the form of the sodium salt, by adding 
common salt to the solution. He recommends the following 
'orking: — I gramme of the sample of indigo in 


fonn of impalpable powder is mixed in a small mortar with about 
its own weight of ground glass. This mixture is gradually and 
carefully added, during constant stirring with a glass rod, to 20 cc. 
of concentrated sulphuric acid (sp. gr. 1*845), which is then heated 
to about 85' C. for an hour.^ The product is then cooled, diluted 
with water to 1 litre, and filtered from indigo-brown and other 
insoluble matters. If the solution bo now at once titrated with 
permanganate the results are liable to be seriously above the truth, 
owing to the presence of sulphurous acid, ferrous salts, indigo- 
gluten or the products of its decomposition, and other oxidisable 
matters. To eliminate this source of error, Kawson recommends 
that 50 cc. of the filtered solution should be treated with 50 cc 
of water and 32 grammes of common salt, which quantity is 
almost sufficient to saturate the liquid. After standing for two 
hours,^ the solution is filtered and the precipitate washed with 
about 50 cc of brine of 1*2 sp. gr. The precipitated sodium 
sulphindigotate is dissolved in hot water, and the solution cooled, 
mixed with 1 cc of sulphuric acid, and diluted to 300 cc This 
solution is then titrated in a porcelain dish with a solution of 
potassium permanganate, containing 0'5 gramme of the solid salt 
per litre,^ the exact oxidising power of which has been ascertained 
by experiment with a solution of pure indigotin. This is made 
by dissolving 0*5 gramme in strong sulphuric acid, diluting the 
solution to 1 litre, and employing 50 cc. of the solution and 250 
cc of water for the titration. The oxidation is regarded as com- 
plete when the liquid, which first takes a greenish tint, changes to 
a light yellow, with a faint pink colour on the margin (compare 
page 110). A correction should be made for the small quantity 
of sodium sulphindigotate which escapes precipitation by the salt, 
and which Rawson finds to be equivalent to 1 milligramme of indi- 

Instead of precipitating the sodium sulphindigotate by salt, as 
recommended by Rawson, it is in many cases sufficient to mix the 

^ The temperature and time recommended in the test should not be greatly 
exceeded. The sulphuric acid employed for dissolving the indigo must be free 
from arsenic and nitrous compounds. The first condition may be ensured by 
well'known means, the second by heating the acid with a few crystals of 
ammonium sulphate. 

^ Rawson states that if the liquid be strongly agitated, by drawing a current 
of air through the solution, the precipitate completely separates in less than 
half an hour. 

' Instead of permanganate of this strength, ^ solution (0*6324 gramme per 

litre of KMn04) may be used. According to Rawson, I cc. of thia oxidises 
0'0015 gramme of indigotin. 


309 , 

Je of indigo with powdered gloss, and treat with hot hydro- 
Ic avid of modertttc strength, filtering, washing the insoluble t 
))ortion with water, drying, and treating with Bulphiiric acid.^ 
WIiethBr or not tliJB treatment be Bubatituted for precipitation of 
the 9al|ihindigotate, it is essential, in order to obtain accurate i 
'ta, that the dilute solution io sulphuric acid sliould he filtered, i 
imove indigo-brown and other organic matters having a reducing I 
m on the permanganate. 

Ither osidising agents, such as potassium ferricjanide or hichro- I 
ite, which have been recommended for titrating the solution of ] 
Iphindigotate, present no advantage over permanganate, and the ] 
' 'reaction is not so well defined. 

ilnstead of assaying the solution of sulphindigotic acid ( 
"lum salt by an oxidiaing agent, a suitable reducing agent may 
substituted. Mulder hss proposed the use of stannous 
iride for the purpose, and Bernthaen and Drews (C/iem. 
xliii. 80) have suggested Schiitzenberger's hyposulphite 
aodium (NaHSO,) for reducing sulphindigotic acid. They find 1 
reductaon to occur in a strictly quantitative manner, according 1 
:the equation ; — 
,H,N,0a(S0;,n),+NaH8O,+ H,0=C„H,,N,Oj(SO,H),+NaHS0,. 
A- J[ ii 1 1 e r has alao recommended the utilisation of this reao- I 
tion, and C. K a w s o n considers that, of all the volumetric 
methods which have been devised for estimating " indigotin," the 
hyposulphite process is capable of giving the most rapid and I 
iurate results, hut considerable care and delicacy are required ii 

If iron be present in the ferric state, the results obtained by 
hyposulphite process will be above the truth, but it is only 
the lower clasees of indigo that this impurity is present, and in 
those cases it principally exists in, or becomes subsequently re- 
duced to, the ferrous state. Of course, treatment of the sample 
with hydrochloric acid, or precipitation of the sulph indigo tatc by 
salt, can ho resorted to if requisite. Neither indigo-gluten, indigo- 
brown, nor indigo-red has any appreciable oxidising ai^tion on 
•odium hyposulphite. Hence the method is one which effects e 
~ lination of lulual indigotin present, and is in that respect 
adapted for the commercial valuation of indigo than a method I 
that of oxidation by permanganate, which also lakes cogniaanca I 
the indirubin of the sample. 

n troaUtuut with ult In Dmitleil, the oolation of the iodigo in sdI- 
ic Mid bIiouU be aomvwliat ililulvil, boitsil for fifteen minutM to drive uS 
^humot add, cooled, >nd dilulcd to 1 litre. 




The use of sodium hyposulphite for reducing indigo in presence 
of ou alkali has already been deacribed. Its application to acid 
solutions of indigo and to the assay of Lndigo-carmine ia coiried 
out by Rawson as follows : — A standard solution of cupric sulphaf 
is prepared by dissolving 1*904 gramme of thi; crystallised sail 
{CuSOj,5EjO) in water, adding 100 c.c. of strong tunmonio (sp 
gr. 0'880), and diluting to 1 litre. 50 cc of this solution is boiled 
in a wide-mouthed flask of about 200 c.c, capacity, to expel air, 
and allowed to cool. The flask ia fitted with a caoutchouc stopper 
pierced with four boles, two of which serve for the entrance and 
egress of a current of coal-gas, while into the other two are fitted 
the noBes of two Mobr's burettes containing the solutions of sodinni 
Bulphindigotate and sodium hyposulphite respectively. The latter 
solution should be of one-fifth of the strength of that emjiloyed 
for the alkaline reduction -process (p^e 306), and the burott« con- 
taining it is attached to the stock-bottle of standard solution in 
such a manner that it can be refilled without introducing air. A 
current of coal-gas (previously caused to traverse a V-tube, charged 
with a mixture of milk of lime and solution of ferrous sulphate) 
is passed through the flask containing the measured quantity of 
copper solution, and the solution of sodium hyposulphite is then 
gradually run in until the liquid becomes nearly colourless, when 
a few drops of indigo-carmine solution are added from the other 
burette, and finally a further quantity of hyposulphite is added 
until the solution assumes a peculiar brownish-red colour. The 
volume of hyposulphite employed, after making a slight correction 
for that requisite to reduce the sulphindigotate, represents tlu 
quantity required to reduce '050 gramme of indigotin, this being 
the amount to which 50 c.c, of the standard cojiper solution a 
equivalent. The strength of the hyposulphite solution having 
been thus ascertained, a measure of 50 c.c. of sulphindigotic acid 
solution, prepared as already described, is introduced into the Bask, 
boiled to expel air, and allowed to cool The flask is then attached 
to the burettes, coal-gas passed as before, and the hyposulphite 
solution gradually added during constant agitation. With purn 
indigotin and the better qualities of indigo, the liquid, when fully 
reduced, becomes of a pale yellow tint, but in the case of inferior 
samples it has a more or less dirty brownish-yellow colour. In 
both cases, however, the end of the reaction is perfectly w«II 

C. Rawson {Joui: Soe. Dijen, ^e., i. 79) gives the following 

figures allowing the results yielded by six typical eaiiiptes of com- 

mercial indigo when examined by the principal of the method) 

^drpady deacribed. The figures (all of which are the means of 


several detennioatione) are valuable as showing the influence of I 
the prraence of impuritiea on the results obtained : — 

















JUgoUn : by iubUn» 




41 W 


38 '» 








l»S^,«HiN»HO. ' 














■SSti. """'•■' 







KMM>t direct 





«7 1S 


tadlcotlB uid indlni- 
Ud ; liter nndplla- 







■ Helen Cooley (Amer. Jour. Anal. Chem., iL 137) gives the ] 
lUowing figures (among others) in illostration of the results yielded 
jf different processes of aaaaying indigo (compare page 303). 

Oude. GDitBtuila. 

IndltottD: byni 

ludlnjrUn ; ani 

RdO and Bill 

iDdlgodD ; tdIiu 

^Kd criticising these results {Amer. Jour. Anal. Chem., it 366), 
j^Bavreon points out that higher figures are to be expected 
y s process which tabes cognisance of the presence of indirubin 
than by nne which is unaffected by this constituent of indigo, and 
he attributes the higher results obtained by the permanganate pro- 
is at least in part to this cause, though over-heating with sul- 
irio acid may also have contributed to the result. In a sample 
EAfric&n indigo he has met with 8 per ceai of indirubin and 33 


The assay of indigo by dyeing swatches of cloth under specified 
conditions is useful in some cases, but the results cannot be com- 
pared in accuracy or delicacy with those obtained by chemical 
methods ; and on assaying a series of samples a repetition of the 
test will very frequently fail to show the same gradation between 
them. The method of operating is to mix 2 grammes of the 
sample of indigo and 1 gramme of lime into a paste with water, 
transfer the mixture to a laige beaker, add 1 gramme of zinc-dust, 
and make up the volume to 600 c.c. The whole is then heated on the 
watei^bath for an hour, and a piece of white calico or swatch of cotton 
yam of known weight introduced. It is then removed, squeezed, 
and exposed to the air till the blue colour is fully developed, when it 
is compared with similar pieces of cotton which have been dyed by 
pure indigotin, or standard indigo, in precisely the same manner. 

A preferable method to the above is to treat 0*5 gramme of the 
sample with 6 grammes of strong sulphuric acid at 85** C. for an 
hour, and dilute the solution to 1000 c.c 10 c.c. of this solution is 
then further diluted with a known quantity of water, and used for 
dyeing 5 grammes of white wool. About *05 gramme of sodium 
sulphate and a drop or two of sulphuric acid may be advantage- 
ously added to the bath before immersing the wool 

A colorimetric test, based on the depth of tint of the sulphin- 
digotic solution, can be made under favoimtble conditions, but is 
valueless for comparing samples of indigo containing variable pro- 
portions of indigo-red and other secondary colouring matters, owing 
to the different shade which the solution possesses in such cases. C. 
H. Wolff {Jour, Soc, Chem, Ind., iiL 516) has proposed to avoid 
this difficulty by observing the absorption-spectrum of the solution 
(1 in 800,000). H. Cooley states that the method gives fair 
results with indigoes of high quality, but is useless for the lower 

Dbtbction of Indigo on the Fibre. The colouring-matter 
deposited in the fibre when a fabric has been dyed in the indigo- 
vat consists essentially of indigotin, but when soluble indigo has 
been employed the dye is taken up in the form of mono- or di- 
indigotin-sulphonic acid. 

Fibres dyed in the indigo-vat are unaffected by hydrochloric 
acid, dilute sulphuric acid, soda, or ammonia. On heating with an 
acid solution of stcmnous chloride the fibre becomes paler, and a 
greenish-yellow solution is formed. Concentrated sulphuric acid 
gives a blue solution, and boiling absolute alcohol also dissolves the 
dye with blue colour, the solution becoming colourless on standing, 
with separation of indigotin. Chloroform, amylic alcohol, glacial 
acetic acid, phenol, and aniline also give blue solutions when heated 



with indigo-dyed fibres.* On carefully heating a fabric which has 
been dyed in the indigo-vat, it givee off purple vapours, which can 
be condensed on the cover of a porcelain crucible to a blue spot. 

Indigo is now frequently used in admixture with other colouring 
matters, some of which are difficult to recognise in presence of 
indigo. W. Len* {Jour. Snc. Dijere. ^c, iii. 127, 140, 150, 
178) states that woollen goods {e.ff., yam) which have been dyed 
with vat-indigo only mnat satisfy the following conditions : — Water, 
even when hot, should not extract any colouring matter; alcohol, 
of fiO and 95 per cent, strength by volume, should not, as a rule, 
extract any colouring matter on gejUly wanning ; oxalic acid solu- 
tion saturated cold, cold iaturated borax solution, 10 per cent, 
alum solution, and solution of ammonium molybdate in two parts of 
water should none of thora, when used boiling, extract any colour- 
ing matter from the fibre - and the borax solution should not be 
coloured red by hydrochloric ncid (campeachy), or give a blue 
coloration or precipitate on subsequently adding ferric chloride 
(pruaeion blue). On the other hand, the blue colour should be 
completely destroyed on warming the fibre with an acid solution of 
stannous chloride or ferric chloride. Glacial acetic acid should 
entirely remove the colour after repeated treatment, and on treating 
the solution obtained with twice its measure of ether, and adding 
water in sufficient quantity to cause the ether to separate, the ethereal 
layer should appear distinctly, but not very intensely, blue, while a 
daposit of indigotin should appear at the junction of the two layers. 
Tlie lower layer should be colourless, and remain so when a little 
concentrated hydrochloric acid is poured into it through the ether. 
On boiling the fibre with concentrated hydrochloric acid, no sul- 
pburette^l hydrogen should be evolved ; and after continued boiling, 
till the fibres are decomposed, treatment of the solution with strong 
Cftustic soda in large excess, warming, and adding a few drops of 
chloroform, no odour of isonitril should be observable (aniline blues). 

Fibres which have been dyed with sulphonated indigo (indigo- 
carmine, soluble indigo) give a greenish-blue solution when treated 
witli liydrochloric acid, and strong sulphuric acid yields a blue 
solutioiL Little or no colour is removed by alcohol. Caustic soda 
turns the fibre greenish, and on boiling with the dilute alVali the 

' Strong lutric acid gives ■ yellow apot on iodigo-dyed goods. Tliia reaction 
li employed as a rough practicsl tent for the quality of indigo-dyod goods. 
The clnth ih Gnt s^wtted with hydrochloric acid, wliich will produce no ubRuj^e 
nilli IndigD, bat will change logwood dyeti to nd. The fabric is then spoIt«d 
vith nitric add, which, if the doth be of good qaality and indigo-dyed, will 

mIuw a yellowtsb-red stain, surrounded by a bluish -green ring. An inferior 
la givee a rod itain and no definite ring. 




dye 18 removed without tlia solution becoming much colooied, until 
it is acidulated, when it blue. Ammonis behaves aimiliu]]'. 
The colour is also removed by boiling with dilut« sodium carbooatD, 
and silk or wool may be dyed blue in the acidulated solatiim. 
Heated with an acid solution of stannous chloride, the fibre is ile- 
colorised. With nitric acid, goods dyed with aulphonated indigo 
behave like those dyed in the inJigo-vat. When boiled with « 
solution of borax (saturated in the cold), goods dyed with indigo- 
carmine are decolorised, while if dyed with vat-ini^o the colour i* 
not affeiited. Indigo^raimine colours the borax solution blue, and 
the liquid is decoloiised when warmed with stannous cblorida ud 
hydrochloric acid. Glacial acetic acid does not remove tlie colour 
from fibres dyed with indigo-carmine. 

The determination of the amount of indigotin fixed on fibres it 
sometimes of interest, since, as a rule, neither the quantity of indigo 
contained in the vat not the exact quality of the indigo used in 
known. The determination may be effected by complet«ly extracting 
the fibre with glacial acetic acid, precipitating the indigotiii bom 
the resultant solution by addition of water, and either at once col- 
lecting and weighing it or determining it by one of the proctnei 
used for the assay of commercial indigo. In some cases it ii 
desirable to remove other colouring matters from the fibre hy treat- 
ment first with cold hydrochloric acid, and then with a boilii^ 
solution of oxalic acid saturated in the cold. Sulphonated indigo IS 
not stripped by glacial acetic acid, but may be removed from the film 
by boiling with borax solution in the manner already described. 

A. R e n a r d (Jotir. Soc. Dyers, ^c, iii. 4) determines the indigo 
on fabrics by a direct application of sodium hyposulphite and lime to 
the fibre. He treats 10 grammes of the fibre with 200 c.c. of asoln- 
tion prepared by adding 2 litres of water and 1 00 c.c of milk of liQu 
to 100 c.c. of neutral sodium hyposulphite prepared from bisulphite 
solution of 1'32 sp. gravity. The liquid is heated to 60° or 70' C 
till the Ubres are decolorised, when a current of coal-gas ia yastoi 
through the flask employed and the contents abakeu til! eveij ti«B 
of blue has disappeared, when the liquid is decanted into a graduated 
cylinder without interrupting the current of gas. After cooling, Hu 
exact volume of the decanted liquid is ob8erved,excesa of hydnx^ilorifr 
acid added, and the precipitated indigotin filtered off aft«r twelve 
hours, washed, dried, and dissolved in sulphuric acid, the r«8iiltaiil 
solution being subsequently titrated with standard hyposulphite, U ' 
described on p. 310. Renard found the amount of imligotin fixeil' 
on cotton fibre to range from 1 to 3 [ler cent. Tlie method ia appU' 
cable in presence of aniline blues, and with an obvious modification 
yrould serve for the assay of fabrics dyed with sulphonated indigo. 

oaring Matters tram Lichens. 

SevBial kinds of Itchons acquire a violet colour under the joint 
uence of ammonia and atmoapheric oxygen. This fact depends 
on the presence of one or two peculiar principles, and was known and 
practically utilised long before it received a satisfactory explanation. 

The colouring matters of industrial importance obtained from 
lichens are three in number, namely : — Archil, orgeille, or orchil; 
cudbear, known on the Continent aa pursea; and litmus or loumeaol. 
The two principal species of lichen which yield archil are Hoeella 
/uei/ifrmui, which furnishes the products from Lima, Angola, Zanzi- 
bar, Ceylon, and Mozambique ; and Rocella lincloria, growing in Cape 
Verde and the neighbouring islands. Chili, &c. The first species 
contains a peculiar principle called erythrin, convertible into 
a red dye by the united action of air and ammonia ; while the 
latter contains, in aildition, a chromogen called lecanoric or 
orcellic acid and itj; homologue eTornic acid. Cudbear 
is obtained from the Swedish lichen, Lemnoria lartarm. 

The value of the various lichens or "archil weeds," from which 
archil and the allied colouring matters are prepared, depends on the 
proportion of orcin obtainable from them. TUa may be ascertained 
■p|iroximatcly by the following volumetric process devised by 
Stenhouae : — 1 granimeB weight of the finely divided lichen 
is macerated three or four times in succession with a dilute solution 
(5 per cent.) of caustic soda, each treatment being only extended 
to a few minutes' duration. The strained or filtered solutions are 
then mixed and titrated with a standard solution of sodium hypo- 
chlorite, which must be gradually added. Ench drop of the hypo- 
chlorite produces a blood-red coloration, which changes to yellow 
in the course of a few seconds. The addition is continued 
cautiously as long as this reaction ia produced. The hypochlorite 
solution must be freshly prepared, and its strength ascertained by 
titration with pure orcin or a lichen of known quality. 

S. Hey maun has proposed to assay archil weeds tor orcin by 
acidulating the solution obtained by macerating the lichens with 
caustic soda and titrating the solution with a hypobromite (see 
papi 319). 

Ebtthhin or Eryturic Acid, C^'K^^O^^ may be prepared from 
SiKetta furi/oTTnis by macerating the lichen in the cold with wik 
of lime. The filtered liquid is acidulated with hydrochloric acid, 
when the erythrin is precipitated as a hydrate of the formula 
2C„H^O,„+3H,0, which Is filtered off and washed. It bo- 
« anhydrous at 1 00° and melts at 1 37' C. Erythrin ia nearly 
' e in cold water, but dissolvos Ln 240 parts of boiling water. 


and is deposited from the hot solution on cooling as a colonrleas 
crystalline powder, only slightly soluble in cold alcohol or ether, 
but more soluble in hot alcohol, from which solvent it ciystallises 
in stellate groups of needles. The solution gives a white precipi- 
tate with basic lead acetate, but none with the neutral acetate. 
With ferric chloride it gives a fine purple or violet coloratioii, 
changing to a brownish-red precipitate with excess of the reagent 
Erythrin exhibits the characters of a weak acid, dissolving in 
solutions of caustic and carbonated alkalies and of the alkaline 
earths, from which solutions it is thrown down as a bulky white 
precipitate on addition of an acid. The ammoniacal solution of 
erythrin becomes red on exposure to the air. 

If the solution of erythrin in alkali be boiled, decomposition 
ensues, the erythrin splitting up into picro-erythrin, C^yfip 
and orcellinic acid, CgHgO^, while on further treatment 
the picroerythrin is decomposed into orcinol, Ot^% 
erythrol, C^H^qO^ and carbon dioxide. These reactions 
establish the constitution of erythrin as the di-orcinillic 
ether of erythrol, and that of picroerythrin as the m o no- 
orcellinate of the same alcohoL The relationship of these 
and allied bodies is shown by the following formulsB :^ — 

Orcinol, CeH2(CH3)(OH)yH 

OrceUinic acid, . . . CeH2(CH3)(OH)2.CO.OH 

^. „. . ., f O.CeIL(CH3)(OH).CO.OH 

Diorcelhnic acid, . . { co.CeH,(CH3XOH), 


Erythrin, ..... HO 5^^*^«^'^ 


Picro-erythrin, . . . tt^ ^C^H^^ 


Erythrol, So z'^*^^*'^ 


' Homologues of these bodies are obtainable from certain lichens. ThM 
homoerythrin, CjiHj40io, has been found in a stunted specimen of 
JRocellia /uc\formis, Evernic acid, CiyHigOy, occurring in Evtmia Pmn- 
astrt;tind usnic acid, C18H13O7, and barbatic acid, C]^,0O^ fooixl 
in Usnea harhcUa^ are homologous with orselHc acid, and split up in a similtf 
manner when boiled with alkalies. 



PiCROEKiTHRiN, CjjHjjOj, IB Only sUghtly soluble iii cold water, 
but very readily in hot, and on cooling the solution is deposited in 
ailky needles or shining plates, melting at 158° C., and having at 
once a slightly sweet and intensely bitter taste. With ammonia, 
ferric chloride, and basic and neutral lead acetate it reacts like 
erythrin. Its behaviour when boiled witli alkalies has already been 

LxoANOBiG, OiBBLUc, or DioRsBLUKic Acib. CiaH,^Oj. This 
Eubatancc bears the same relation to orcellinic acid that tannic acid 
(digltllic acid) bears to gallic acid (page 87). It may be obtained 
by extracting the lichen RocdJa linetaria with ether, evaporating the 
solution, treating the residue with milk of lime, ogttin filtering, 
precipitating the filtrate with sulphuric acid, and ctyBtollising the 
}>recipitated orcellic acid from alcohol. It is scarcely soluble in 
cold water, and requires 2500 parte of boiling water for solution, 
hut dissolves more readily in ali^ohol and ether. It forms pris- 
matic needles containing 1 aipia, which become anhydrous at 100°, 
and melt at 153° C. with decomposition and evolution of carbon 
dioxide. The alcoholic solution of lecanoric acid gives no preci- 
pitate with lead acetate, but yiekis with cupric acetate a pale green 
precipitate after standing. Ferric chloride produces a dark purple- 
Kd colour, and anunonio-nitrate of silver is reduced on heating. 
When boiled with water, lecanoric acid undergoes hydrolysis, and 
is converted into orcellinic acid, CgHgO^. Boiled with 
alcohol it yields ethyl orcellinate (pseudo-ery thrin). 

OiicKLUxicAciD. DihydrosytoluicAcid. CaH,(CHj)(0H)yCO0H. 
|;COOH:OH:CHs:OHj = l:2:i:5]. This substance results from 
the hydrolysis of lecanoric acid (see above), but is best pre* 
pared by heating erythrin on the water-bath with baryta-water, 
tmtil barium carbonate begins to separate. When a sample no 
longer gives a gelatinous precipitate on adding hydrochloric acid, 
tlie liquid is acidulated, when orcellinic acid gradually precipitates. 
It can be crystallised from acetic acid or dilute alcohol in stellate 
masecs, which contain I aqua, become anhydrous nt 100°, and 
molt with partial decomposition at 176° C. Orcellinic acid is 
readily soluble in water, the solution gradually decomposing into 
D r c i n o I and carbon dioxide when boiled alone or with alkalies. 
It is coloured a purple-violet by ferric chloride, and yields an 
amorphous precipitate with ammoniacal acetate of lead. 

Orcellinic acid is characterised by the great facility with which 
it forms ethers. Thus amyl orcellinate is readily formed 
by boiling erythrin (urythrj-I orcellinate) with amy] alcohol, an<l 
etbyl ocellinate, C8H,0,(CjHj), formerly called pseudo- 
in, is always obtained when lichens containing oiythrtu 


are extracted with boiling alcohol It is slightly soluble in cold 
water, more readily in hot water or alcohol, and crystalliseB in 
small needles or plates, which melt at 132^ The aqueous solutkn 
is precipitated by lead acetate. 

Ertthrol, Eryturitk, or Ertthboolucin. C4Hg(0H)^. This 
substance, which has the constitution of a tetratomic alcohol, is a 
product of the decomposition of picroerythrin by alkalies, and exists 
ready formed in the Protoeoecus vulgaris. It ciystallises in 
colourless dimetric prisms, fusing at 120° C. It is readily solnUe 
in water, sparingly in alcohol, and insoluble in ether. Eiythrol 
has a slightly sweet taste, is optically inactive, and does not 
reduce Fehling's solution. When distilled with excess of ttioog 
hydriodic acid, it yields butyl iodide, C^Hgl. By treatment 
with a mixture of strong nitric and sulphuric acid, it is convezied 
into tetranitro-ery throl, C^H^O/NOj)^ a body hafing 
marked explosive properties. By prolonged treatment with nitric 
acid, erythrol is converted into oxalic acid, no mucic acid being 
simultaneously formed. 

Orcinol. Orcin. Dihydroxy-methylbenzene. CeHj(CHgXOH)j". 
This substance, which is homologous with resorcinol, and has tii6 
characters of a diatomic phenol, occurs in a free state in variooe 
species of lichens, and is a decomposition-*product of the varioos 
acids and ethers contained in or prepared from these plants. It is 
best prepared by boiling erythrin (prepared as described on pegB 
315) for half an hour with a slight excess of milk of lime, in an 
apparatus furnished with an inverted condenser, filtering, paning 
carbon dioxide through the filtrate, and evaporating the solution 
nearly to dryness. On agitating the concentrated liquid with hot 
benzene the orcinol is taken up, and can be obtained by separating 
and evaporating the solvent^ while the erythrol remains in the 
aqueous layer. Orcinol may also be obtained by synthetical 

Orcinol forms six-sided monoclinic prisms, melting at 58°, and 
containing CyHgOg+HgO. The crystals effloresce gradually over 
sulphuric acid, and more rapidly when heated to 100°. The 
anhydrous substance melts at about 107°, and distils with some 
decomposition at about 287° under atmospheric pressure, but may 
be obtained pure and colourless by distillation in vaaio. When 
pure, orcin is colourless, but it acquires a pale reddish-brown colour 
on exposure to air. It has an intensely sweety but unpleasant, 
astringent taste. Orcinol is extremely soluble in hot water, but 
much less so in cold. It is almost completely precipitated in fine 
needles when its concentrated solution is warmed with saturated 
brine. Orcin dissolves readily in alcohol and ether, but less 



«uily in hot benzene. The cTyetala deposited from the ethereal 
solution are anhydrous. It is neutral in reaction, but poesesaea 
marlied acid propertiea. It readily decomposes sodium carbonate, 
and precipitates silica from silicates. 

With oxidising agents orcinol yields oxalic acid. With con- 
centrated sulphuric acid it gives a sulphonic acid. When treated 
vrith a solution of bleaching ponder, orcin yields an intense purple- 
ted uoloration, which rapidly changes to yellow. The most minute 
trace of orcin may be detected by this reaction. 

When an aqueous solution of orcin is mixed with ammonia and 
exposed to the air it acquires a deep purple colour, owing to the 
(omiatiou of a body called orcein, identical with the colouring 
matter of archil. If carbonate of sodium or potassium be also 
present, a blue colouring matter is formed which is identical with 
thai contained in litmus. 

If an alkaline solution of orcinol be heated with a little chloro- 
form, it becomes first purple-red and then bright red, and on 
dilution with water exhibits an intense greenish-yellow fluorescence, 
from the formation of homofluoresce'in, CggHggO^. This reaction, 
first observed by Schwartz (BericWe, xiii. 543), is so delicate 
that the compounds which yield orcinol on treatment with alkalies 
can readily be detected by this means in the lichens containing 
them, by simply boiling a few pieces of the plant with a 5 per 
cent, aolution of caustic potash, adding a little chloroform to the 
clear liquid, then warming the solution for ten minutes mure, and 
diluting it with water. 

An aquejjus solution of orcinol is not precipitated by mercuric 
chloride, lead acetate, cupric sulphate, tannin, or gelatin. With 
basic acetate of lead it yields a white precipitate, and with fenic 
chloride a violet-black coloration or red precipitate. 

On addition of bromiuc-water to orcinol in aqueous solution, 
tribromorcinol, CjHjBrjOj, is formed, and the reaction has 
been recommended by Reymann for the quantitative determi- 
nation of orcin and the assay of archil weeds. The process is 
carried out exactly like the volumetric determination of phenol by 
bromination (voh ii. p^e 543). 

Orckln ia the product of the action of ammonia and oxygen on 
orcinol. Liebermann states that two compounds may be thus 
formed, containing respectively CuHjjNOj and CkHj^NjO,. The 
latter substance is the chief product when the ammonia is in excess, 
and 18 less soluble in alcohol and ammonia than the former com- 
pound. Both bodies form brown amorphous masses, having a 
buetle-gruen lustre. Orcein is somewhat soluble in water irith red 

Ipur, but is reprecipitated from its solution by neutral salte of 

320 ARCHIL. 

the alkali-metals. In ether it is insoluble, but dissolves readily in 
alcohol, yielding a scarlet solution. In fixed alkalies and ammonia 
orcein dissolves with formation of splendid purplish-violet solutions. 

Archil, Orchil, or Orseille is the commercial colouring matter 
from Rocella tinctoria and R. fuciformis. It is usually prepared 
by treating the finely chopped lichens with dilute ammonia, and 
keeping the mixture at about 20"* C. till a dark violet paste has 
been formed. This when diluted with ammonia and filtered 
through a press yields blue archil, while on gently heating this till 
the ammonia is removed red archil is obtained. French purple is 
a lake obtained by precipitating the ammoniacal liquid obtained as 
above with calcium chloride. In using it, the colouring matter is 
treated with oxalic acid and boiled with water. The filtered 
liquid, when rendered slightly ammoniacal, dyes silk and wool a 
fine purple colour. 

Archil has lost much of its importance since the introduction of 
the coal-tar dyes, and is now chiefly used in combination with other 
colouring matters to obtain certain shades of brown, and for the 
production of a cheap blue on wool, the material being first lighUy 
grounded with indigo and then passed through a bath of archil, 
when it is dyed a rich purple hue, similar to that produced by 
indigo alone. 

Archil occurs in commerce in two forms, paste and liquor. 
The solid matter consists essentially of the impure orcein in com- 
bination with ammonia. Archil varies greatly in quality, owing 
to differences in the weed employed, the care used in the manu- 
facture, and the presence or absence of impurities. In some cases 
it contains an immoderate excess of ammonia, and in others the 
proportion of solid matter is abnormally low. This can be readily 
ascertained by drying a known weight of the sample at 100'. 
Occasionally the solid matter in archil paste is as • low as 20 per 
cent. Spent weeds, from the manufacture of archil liquor, are 
sometimes added to the paste. 

Archil liquors range in specific gravity from 1*040 to 1'080, or 
even to I'lOO, but the density is no accurate indication of the 
dyeing power, which is best ascertained by a practical dyeing test 
on wool 

Archil paste is sometimes adulterated with other vegetable 
colouring matters. To detect these, J. W. Slater recommends 
that 3 or 4 grammes of the sample should be treated with 100 c.c 
of water, and 50 drops of a solution of stannous chloride in twice 
its weight of water added. On boiling the liquid, a yellowish 
colour only will remain if the archil be pure, but 3 to 4 per cent 
of logwood liquor will yield a greyish-blue, and the colour will be 


h if peach-wood, sapan-wood, or other red wood has beea 
a an adulterant, 
rchil is decolorised by reducing agents, but the colour returns 
ikposiug the reduced liquid to tho nir. Its other reactions and 
tnetliods of detecting it will be gathered from the description 
' i methods of detecting it in wine (vol ii. page 88 ; iii. 222 
g.), and from the following processes of examining the com- 
' J subetance for adulterants. 
:hil is now frequeutly adulterated with aniline dyes, espe- 
f magenta, acid magenta, and metliyl violet, 
". Ciossley (./oor. iSoc. i>i/er«, ^f., ii. 33) determinea bttaic 
' 1 archil by dUuting the sample, if neceaaary, with bot 
', Altering, and evaporating the filtrate to dryness at 100°.* 
I residua is reduced to powder, and a weighed portion is 
digested with sti'ong ammonia, which dissolves the orcem and 
leaves the magenta base. The solution is filtered, and the residue 
is washed with ammonia till no more colouring matter ia removed, 
when it is dried at 100° and weighed. It should be proved to be 
magenta by dissolving it in dilute acetic acid and applying the 
ordinary tests (page 221). Another method for the detection of 
magenta consists in treating the residue obtained by evaporating 
the filtered solution of the sample on filter-paper with two or three 
drops of benzoic aldehyde or aniline oil, when the magenta will 
di«solvo and colour the paper crimson. A faint pink tint is obtained 
with pure archil after a few minutes, but this is not readily mis- 
taken for the immediate and strong coloration given by magenta. 

For the detection of magenta or metliyl- violet in proportions 
KTeater than 1 per cent., E. Knecht (Jour.Soe.Di/fTs,^.,\i. 68) 
employs cotton yam dyed with chrysamine (page 206). This does 
not take up the colouring matter of archil, but is dyed red by 
jonta, and brownish'Ted by methyl- violet. For the determi- 
igentu in archil, Knecht evaporates the filtered li([uid 
ESryneas, extracts the residue with alcohol, filters, and evaporates 
k filtrate. This second residue is heated for about a minute 
I caustic soda, and the insoluble portion allowed to settle. 
in standing a few minutes the liquid ia decanted, and the 
tdue treated with a more dilute soda solution, the process is 
eated as long as the liquid takes up colouring matter. The 
residue is then washed with water and weighed. On subsequently 
treating it with hydrochloric acid, it will ilissolve with mi^enta or 
violet colour, according to its origin, Sofrauine and the azo-dyes 
wnnot he detected iu this manner. 

' T. Fair! ey (Jour. Soc CKern. Tnd., v, 288) treats Mchil parte at onoo 
with Htrting amiQonia, repeating the proceu till all thti orceia is retnovixl. 


Liehmann and Studer {Jour. Soc. Gheni. Ind.y v. 287) 
test archil for magenta by saturating the laigely diluted solution 
with sulphurous acid, when most of the orcein is precipitated. On 
adding acetone to the filtered solution, genuine archil does not 
show any change of colour, but if either basic or sulphonated 
magenta be present the liquid changes in a few minutes to violet 
One-tenth per cent, of magenta in archil gives a strong coloration. 
If the liquid which was saturated with sulphurous acid be boiled, 
filtered, and a piece of cotton, mordanted with tannin and tartar- 
ometic, immersed in the filtrate, only magenta will be fixed on the 
iibrc, and whether it be the acid or basic kind can be ascertained 
as described on page 226. 

C. Rawson {Cliem, News, IviL 165) objects to the foregoing 
methods on the ground of want of delicacy, and recommends that 
an amount of archil paste or liquor containing 1 or 2 grammes of 
solid matter should be boiled with 50 cc. of alcohol, and the 
solution diluted with 100 cc. of water. From 15 to 20 cc 
measure of a solution of basic acetate of lead, of 1*25 sp. gr., i* 
next added, and this is followed after stirring by a similar quantity 
of strong ammonia. With pure archil, the filtered liquid will be 
quite colourless, but if magenta be present it may either be colour 
less or pink, according to the amoimt of ammonia present in the 
solution ; but in either case, on acidulating the liquid the charac- 
teristic colour of magenta will be at once developed, no change 
occurring with pure archil. By a colorimetric test, using for coni- 
j>arison an aqueous solution of magenta containing 0*001 gramme 
per 100 cc. and acidulated with acetic acid, the proportion of 
magentA present may be determined, but in this case the lead 
precipitate must be washed with a mixture of 5 parts of alcohol, 
10 of water, and 1 of strong ammonia. 

The foregoing test also serves for the detection of safranine and 
methyl -violet. On adding acetic acid to the ammoniacal filtrate, 
the liquid becomes bluish-violet, if the latter dye be present. 
Strong ammonia decolorises methyl-violet and magenta, but scarcely 
affects the colour of a solution of safranine, while strong hydrochloric 
acid changes the latter to blue, and turns solutions of magenta and 
methyl-violet yellow. 

F. B r e i n 1 has pointed out {Jour. Soc. DyerSj ^c, iv. 46) that 
various azo-dyes, producing colours ranging from crimson to claret- 
red, are now in the market, under such names as orchil extract, 
orchil-red, orselline, &c., being intended as actual substitutes for 
archil and cudbear, and, being cheaper than magenta, are more likely 
to be used for the adulteration of those colouring matters. Breinl 
gives a very complete list of such coal-tar colours, and a table of 



a hy which they may he recognised. He dividea thom into 
e groups, nccordiDg to their hehaviour with common salt, and 
ti basic acetate of lead (sp. gr. 1*25) io presence of 25 per cent. 
Thus, on saturating the aqueous solution of tlie saniplu 
a unit, the following coal-tar dyefi are completely pre- 
Orsellin BR and orchil red E (Bayer & Ca), orchil red 
Jnd. Anilin und Soda F.), cloth reds B and G (Oehler), Bordeaux 
and Extra (Bayer), Bordeaux B{ActienGe9.fiir Anilin Fab.), 
3 A and B (Bad. Anilin und 8. F.). The following colours 
L almost completely salted out by similar treatment : — Ajjorubiii 
d orchil red G (Actien Ges. fiir Anilin Fab,), amaranth, car- 
" I B (Baypt). magenta, basic colouring matters from magenta 
I and safranine. On the other hand, acid magenta and 
r acid colouring matters from magonta-reaidues, oraeltine R 
1 (HiJchat Col our- works), and red-violet NRS. (Bad. Anil. 
}. F.) are not precipitated by common salt. A filtered extract 
;hU gives a alight precipitate with salt, which redissolves when 
iked with brine. The coal-tar dyes which are not completely 
^rtially precipitated by saturating their solutions with common 
t may be distinguished from archil by boiling with a solution 
made by dissolving 10 grammes of crystaUised stannous chloride in 
a mixture of 25 c.c. of concentrated hydrochloric acid and 50 c.c. 
, of water. When thus treated, a filtered solution of orchil or cud- 
8 decolorised or turned light brown; while acid magenta, acid 
ing matters from magenta-residues, and red-violet NRS, 
» a darker and more bhiiah coloration, and orselUne R and B an 
e bluish-violet coloration. These colouring matters again are 
I partially precipitated when a solution containing 25 p«r cent, 
measure of absolute alcohol is treated with basic lead acetate ; 
nas orchil is completely precipitated under these conditions, 
p the other coal-tar dyes already mentioned are not precipitated 
By these reactions it is always possible to establish the pre- 
e of a coal-tar dye, even if it be not possible to identify it with 

1 admixture of brazil-wood, barwood, or logwood with orchil 

mdboar may be delected by immersing cotton, mordanted with 

> or aluminium (page 278), in the hot dilute solution of the 

^RUpected sample.* After half an hour's treatment the cloth is 

removed, and washed with warm soap solution. The orchil or 

cudbear will produce at most a faint pink colour on the mordanted 

1, and this will be removed by boiling the cotton for a few 

a tfaa colonring matter of barwood is aot readily eitmcled by wator, it 
tt to bon 3 gnuame* nr thn lanpecttA cndbcar Tor 10 minatoa witli 50 o.c. 
>hol, and then dilute tho lolutLon with water to 200 c.c. 


minutes with alcohol, while if logwood be present^ cotton mordants 
with iron will be dyed bluish-grey or black, and if mordanted with 
alumina salts bluish-violet. Brazil-wood will dye the iron mordant 
blackish-brown, and the alumina mordant red 

C. R a w s o n (Jour, Soc, Dyers, ^c, iv. 69) detects azo-dyes in 
cudbear by sprinkling a little of the sample on some concentrated 
sulphuric acid, when the formation of a streak of characteristic 
colours — green, blue, violet, &c.-^K)ften affords valuable assistance. 
To obtain further evidence of the presence of azo-colouring matters, 
he recommends that 5 to 10 grammes of worsted yam should be 
dyed for an hour with about 10 per cent, of its weight in cudbear 
in a bath rendered faintly alkaline with ammonia. A fresh 
quantity of yam is similarly dyed in the partially exhausted bath, 
whereby the greater part of the orcein is removed from the solution. 
Sulphuric acid, equal to 3 per cent, of the weight of the yam, is 
now added, and a third quantity of worsted yam introduced. The 
azo-red is now deposited on the wool in a form sufficiently pure to 
allow of its subsequent identification. It is desirable, though not 
directly necessary, to treat a genuine sample of cudbear side by side 
with the sample. 

Cudbear, called on the Continent Perseo, is obtained by the 
action of ammonia or urine on various kinds of lichen, especially 
Lecanoria tinctoria and Variolaria oi'dna, and hence in its origin 
and properties is very similar to archil, from which it differs mainly 
in being free from all excess of ammonia and moisture, and in being 
reduced to a fine powder. It often contains a considerable pro- 
portion of mineral matter, usually common salt, which is sometimes 
added as an adulterant, but in other cases to reduce an unusually 
rich article to a imiform standard of quality. Grenuine cudbear 
leaves from 5 to 1 2 per cent, of ash. Cudbear is liable to much 
the same organic sophistications as archil, and if it be boiled with 
water the filtered solution may be examined by the same methods. 

Litmus, or toumesoly is prepared from various species of JRocellOj 
Variolaria, and Lecanoria by allowing them to ferment in presence 
of ammonia, as in the manufacture of archil, except that in the 
case of litmus potassium carbonate is likewise added. When the 
mass has become violet, stale urine, lime, and potashes are added, 
and the mass is again allowed to ferment until it assumes a blue 
colour, when it is mixed with chalk or gypsum and a little indigo, 
and made up into small tablets. 

On extracting litmus with cold alcohol, a red colouring matter 
is obtained, which is unaffected by acids, and yields litmus-bine 
and another substance on treatment with water. On evaporating 
this solution, and treating the residue with absolute alcohol and a 

little acetic Hcid, a scarlet colouring matter ia remored, which la 
cbangeil to purple by Hnunonia, while the pure litmuH-blue remains 
behind as a brown powder, soluble iu water to a reddish-brown 
solution, which is turned blue by the slightest trace of an alkaJi. 

As-iliimin, CjHjNO,, the chamcteristic colouring matter of litmus, 
may be obtained in a state of purity, according to De Luynes, 
by digesting 1 part of orcinol with 1 of strong ammonia, 35 of crystal- 
lised sodium carbonate, and 5 of water, at 60°-8O° C. for four or 
tife days in a closed vessel, A blue liquid is thus obtained, which 
la diluted with water and slightly acidulated with hydrochloric 
odd, when a precipitate is fonuod, which, after being washed and 
dried, is regarded as pure azolitmin. So obtained, aswlitmin is a 
blue substance, which acquires a coppery lustre by friction. It is 
nearly insoluble in cold water or beoiKene, but dissolves in alcohol 
with red and in ether with yellow colour. Azolitmin appears to 
have the characters of a weak acid, the salts of which are blue, and 
the potassium compound of which exists in litmus. 

Litmus exhibits a very characteristic abaorption-apectrum. Ether 
extracts it from an acid solution, and forms a yellow liquid, wliich 
absorba the more refrangible end of the spectrum to a point mid- 
way between D and E. On adding a drop of ammonia to the 
ethereal solution the liquid becomes blue, and an absorption-band 
is formed, which commences at d, where it ia extremely black, and 
gradually diminishes to E. On shaking the ethereal solution with 
ammoniacal water, the colouring matter passes into the aqueous 
liquid, and the blue solution shows a well-marked absorption- band 
nt J). Addition of acid now changes the colour to red, and the 
hand at D disappears, the spectrum of the acidified liquid reeembling 
that of GB n o U n, the colouring matter of red wine. 

Litmus ia not employed in dyeing or calico-printing, but ia used 
for colouring wine and vinegar, and In the laboratory ia well known 
OS an indicator of neutrality. Its indications are fairly delicate ; 
but the habit of regarding litmus as an infallible guide to neutrality 
has soriuusly retarded progress in several directions.* Of late 
years thia fact has been more generally recognised, and a number of 
other indicators have been proposed. Of these, two — namely, 
helianlhin or mdhyl-' -range (page 188) and phctwlpktlialein (page 
164) — deserve the fullest confidence, and one or other of them can 
bo oniployed advantageously in place of litmus in a large number 

a the following table, by E. T. T h o m s o n {Joum. Soe. Chem. 
|4tlnaB 1> atill emjilayc J for tli« titration of lima and lemoa Juice, a purposo 
n Uiu o|)inion of the Huthor, it U very ill-iuited, eapeci&IIy if agdEuui 
bouate tw aauti tot tliu tiuiitintisatioii [«ee Aiuilf/il, liv. SB, SO). 



I}id.,vi, 198), is given an epitome of the indlcationB yielded by lit- 
mus, Bs compared with those given by phenolphthalein and methyl- 
orange (which last is affected by strong acids only). The figures 
represent the number of atoms of hydrogen displaced by sodium or 
potassium in the form of caustic alkali, when a compound is fQimed 
having a neutral reaction to the indicator in question. Thus, when 
methyl-orange is used in the titration of sulphurous acid the neutral 
point is reached when alkali has been added in quantity sufficient 
to form the compound NaHSO^j but when phenolphthalein is used 
the point of neutrality corresponds to the formation of the salt 
NajSOj. By a combined use of the two indicators valuable voJu- 
metric determinations can be effected. In employing phenol- 
phthalein as an indicator, it must be remembered that the resolta 
are vitiated by the presence of ammonium salts. In other cases, 
when a blank space appears in the table, it is meant that the end- 
reaction is obscure, and not to be depended on. 

The table shows the basicity of acids with different indicators, 
when titrated in aqueous solution with fixed caustic alkali. 







{ dilute 

} "■ 




Csrbonlc, . . 

P».<»ph«ri.. . 

Sllroiu. . . 
Baric, . 
OirDrulo, . 
Oullc, . , 
Actlic, . . 
Bnlyric. ■ , , 
Bnodnlc . , 

CIWc, . , 






. 1) 

It will bo seen that all indicators behave alike on titrating strong 
mineral acids with fixed caustic alkali ; in the titration of a weak 
acid with a strong base they differ, methyl-orange being most 
Bensitive to alkalies and phenolphthalein to adds, while litmus 


occupies an intermedintc place. Spimking gcncritUy, lacmoid | 
(iWge 159), dimothyUmido-azobeiizenB (page 180), | 
cochineal, nntl c.ongo-red (page 206) behave like mKthyl- I 
unu)^ while turmeric behaves like pheiiolphtbaleiti.^ Phe 
a c e t o 1 i n and rosolic acid (page 161) usually react lik« J 
litmus, except that iji the latter case a sharp neutrality- point is j 
obtained in titratin;,- sulphurous acid when the salt No^SOg is formed. ' 

Red Dyes from Woods, &c. 

A nnm!)cr of red colouring matters of vegetable origin are, or 
have been, used in dyeing. Thus, madder is the root of Hubia \ 


BnUniail Origin,! 







Root oJ RuMa (fne- 

Tnrkej', *>iij«. 





W«>t Indln, 

Meiloo, SwuUi 



pull wood; Pel 

Wood of Ca«(. 
anJ C. Crina. 

BnuU. Pomun- 


C. ",.'>. 


Wood Hi C>e«^ 




8«U4i«oo<l(i«ure Woo-I of Ca-ut 





Wood of Pttraear- 

C«ytDn, Ukdii- 



kvood (pw 

Wood of Saphla 

Siorra Uotw. 




Wwt ca»t of 



Kool of .4nfAt4« 

LflVMJt, South 

Alkmnln. { 


<M«« (p«. 

Flo«pi of Car- 

»«mli Amerti-a, 




IHontm, a herbaceous plant Its cultivation is almost obsolete, 
I ite charactera have already been sufficiently described. Other 
colouring matteiB, as lo'jwml and IrrasU-ieoixl, ore obtained from 
wood of trees of considemblc siw ; while alkaiid is obtained 
n tlie cortical j)arts of a root, and aa^atcer from the flowers of a 
rhna iBlivB RDil milk arc nautrtl to litmns pnpcr, itcongly •IkalJne to 
aoid oi congu-rcil, uid acid tu turiuurit; paper. 


kind of thistle. Tlie preceding table (page 327) shows the origin 
of the more important red colouring matters derived from plants. 

LoowooD or Campeachy (see page 328) is the most important 
of the red dye-woods,^ and is imported in the shape of inegnlar 
blocks, having an average weight of about 400 pounds. The 
colouring matter probably exists in the form of a glucoside, f(V 
when the trees are freshly felled the wood is colourless. By the 
time the logs arrive in this country they have acquired a da^ 
brownish-red colour externally, while the inside is still pale yellow 
or liglit red. The logs are reduced to chips or raspings, which aie 
moistened with water and allowed to ferment^ whereby the glnco- 
side is converted into hsBmato-xylin, and this is partially 
converted into hsBmateinby the action of the air. The product 
is lixiviated with water, and the solution concentrated to obtain a 
htgwood extract. To obtain a good extract, the powder must not 
be too highly oxidised, and the concentration of the solution must 
be conducted at a temperature not exceeding 60° C, or the 
haBmatein will be converted into a dark purple resinous matter 
which injuriously affects the brilliancy of the colour. An inferior 
extract is largely made from campeachy roots. 

Logwood yields very little soluble and colouring matter to cold 
water, ])ut from 14 to 18 i)er cent, of its weight to boiling water. 
The decoction is pale yellow if made with distilled water, but 
blood-red if a calcareous water has been employed. The whole of 
the haematoxylin can only be removed with difficulty by water, 
but alcohol and ether extract it with facility. 

llamiato-xfjUn^^ C^^ifio, is best obtained by treating the 
aqueous extract of logwood, or the finely powdered wood, with 
ether, evaporating the resultant solution to a syrup, adding water, 
and allowing it to stand for some days, when the haematoxylin is 
deposited in crystals, which if prismatic contains 3 aqua^ but if 
granular 1 o/ywa only. A jx^rtion of the water is lost at 100", but 
the whole of it can only bo expelled at a higher temi^erature. 
When further heated, haBniatoxylin fuses, and at a still higher tem- 
j)erature decomposes and leaves a ])ulky carbonaceous residue. 
The crystals of haematoxylin are bright yellow, sometimes brownish 
externally, but the powder is yellowish-white. Its taste resembles 
that of liquorice. 

Haematoxylin is only slightly soluble in cold water, but more 

^ For convenience of classification, logwood is here classed as a red dye-wood. 
Although the colouring matter of logwood is itself red, it is not used in practice 
to produce red shades, but rather violet, blue, and black. 

* This word is often pronounced hsemat-oxylin, but such a practice is open 
to objection. 


readily on beating, and is diaaolved with facility liy alcohol, ether, 
md cnrbon disulphido. It has tlie characters of a weak acid, and 
unites with bases to form tompoiinds which are colourless when 
perfectly pure, but absorb atmospheric oxygen with great avidity, 
twconiiog Gret bluish and finally teililish-brown, from formation of 
h a m a 1 i n and mora advanced products of oxidation. The com- 
pounds of haeniatoxylin with the alkalies are best obtained by 
saturating a cold decoction of freshly-drilled logwood with conunon 
anlt, and graduttlly abiding caustic soda, The precipitate ttrst 
fonned contained the coloured oxidation-products, and should be 
ia[ndly filtered off, and on again adding caustic soda a colourless 
precipitate of the sodium salt is obtained, which becomes rapidly 
colotqvd on exposure to air. 

Ifoutral and basic acetates of load yield, with hematoxylin, 

bluish-while precipitates, which rapidly darken on exposure to air, 

SlannouB chloride produces a permanent rose-coloured precipitate. 

Alum gives a bright rod colour, but no immediate precipitate, 

tlumgb a slight blackish precipitate is formed after some time ; 

^Qtad aluminium acetate yields a fine purple. Hcematoxylin in- 

^Hj^bly reduces chromic acid and potassium bichromate, yielding 

^^H^ bhtck precipitate. 

^^^BoTTuUein, Ciailj,0«, is produced with great facility by the 
^BPRoepheric oxidation of hematoxylin, especially in presence of on 
alkalL It may be prepared by saturating ammonia with hiema- 
toxylin, and exposing the warm solution to tlie air. The liquid 
booomes deep cherry-red, and ultimately deposits granular crystals 
of the ammonium salt of htematein. This, when decomposed by 
Bcvtic acid, yielde free htematein as a bulky, brownish-red 
precipitate, which on drying becomes deep green, and exhibits a 
inet^lic lustre. Hsmatoin yields a red powder, which is sparingly 
•oinble ill cold hut more readily in boiling water. It is sparingly 
aoluble in alcohol and acetic acid and slightly soluble in ether, and 
diasolros in ammonia and the fixed alkalies to form solutions 
which arc nt first blue or purple, but become brown by contact 
with nir. The ummouium salt forms a deep violet powder, 
oonsiating of microscopic, transparent, four-aided prisms, which 
dissolve in water with purplish, and in alcohol with reddish-brown 
colour. The salt loses its ammonia at 100° C, or even at the 
ordinary temperature over sulphuric acid ^n vacuo. Its solution 
yicldn n violet-blue precipitate with salts of cnppar, and a violot 
with stutinous chloride. It reduces silver nitrate, and witli ferric 
aaltA gives u block precipitate. By oxidising agents LffiTnateiu is 
couvertad into brown ulmic bodioa. By sulphuretted hydrogen it is 
decolorised, hut bssmatoxylin i& eaid not to be the product of the 



reduction, though it is certainly formed when sulphurous acid and 
certain other reducing agents are employed. 

HsBmatein is destroyed by hot sulphuric acid, but dissolves in 
the cold concentrated acid, with dark reddish-brown colour. On 
adding two or three measures of glacial acetic acid very gradually 
to this solution, a body of the formula CigHii(SOjH)Og, is thrown 
down as an orange crystalline precipitate. This body, which is 
apparently a sulphonic acid, is insoluble in alcohol, ether, or ben- 
zene, but slightly soluble in strong acetic acid or cold ammonia. 

The reactions of an aqueous decoction of logwood are due to the 
simultaneous presence of both hsematoxylin and hsematein.^ Dilute 
acids turn the solution yellow, but with excess of a strong add a 
red colour is produced. Sulphuretted hydrogen decolorises the 
solution of logwood, and sulphurous and carbonic acids turn it 
yellow. Alkalies and ammonia produce first a red, then a violet, 
and ultimately a brown colour ; while lime, baryta, and most of the 
hydrated oxides of the heavy metals produce blue precipitates. 
Stannous hydroxide behaves as a base and yields a violet lake, 
while stannic hydroxide reacts as an acid and turns logwood solu- 
tion red. Salts of iron yield a bluish-black coloration, a reaction 
which is employed for producing ink. Mercuric chloride yields an 
orange, tartar-emetic a carmine, and bismuth nitrate a fine violet 
precipitate with logwood solution. Alum gives at first a yellow 
coloration, becoming red after a time ; while aluminate of sodium 
yields an abundant bluish-violet precipitate, insoluble in excess of 
alkali. This reaction is said to be so delicate and characteristic that 
by means of it logwood may be detected in a mixed decoction with 
great facility. Another characteristic reaction of logwood is the 
black coloration it produces with bichromate of potassium. A 
good way of applying the test is to boil some white wool in a solu- 
tion of potassium bichromate, containing such an amount of the salt 
as will correspond to 3 per cent, of the weight of the wool. The 
mordanted wool is then introduced in small successive portions 
into the hot liquid to be tested, when it will be dyed black if log- 
wood be present, and the weight which can be thus dyed will be 
an indication of the amount of colouring matter. This method of 
assay takes cognisance both of the actual and potential colouring 
matter present (hsematein and hsBmatoxylin), and, as pointed out 
byL. Siebold {Jour, Soc, Chem, Ind., 1889), is a more rational 
method of examination than any based on the colour produced on 
cotton mordanted with alumina or tin salts. 

* C. E. Avery {Jour, Soe. DyerSf Ac., i. 268) has patented the use of hypo- 
chlorites, nitrates, chlorates, &c., for oxidising hsematoxylin to hsmateini 
and thos getting the full development of colour without ** ageing." 


colouring matter of logwood niiiy be extracted by agitating 
acidulated aqneoiis solution with amy lie alcohol, or, less 
itegeouely, with chloi'oform. Oa shaking the araylio alcohol 
a saturated solution of borax, the colouring matter passes into 
latter, tuid may he isolated by separating the borax solution, 
■ ,ting it, and again shaking with amylic alcohol 

logwood chips or raspings often occur containing 
monual proportion of waler, from 40 to 50 per cent being oeca- 
"lyinet with. 14 per cent, is the average proportion of water 
natural to unfermented logwood, and should be deducted in 
culculiiting the excess. An excess causes fermentation when the 
material is allowed to remain long in heaps, with consequent de- 
:tiou of the colouring matter. 

'ood is Dccasiou^y treated with an alkali, such as lime 
weak soda, or stale urine, with the view of giving it a 
itious strength. If so treated, the wood yielda abundance of 
colour to water, but oxidation and deterioration speedily occur. 
On treating such logwood with a little cold distilled water, and 
Awting a piece of sensitive red litmus paper on the surfnce of 
lif^uid, the paper will be turned blue before its colour is affected 
rough comparative teat of the tinctorial value of logwood 
made by treating 0*5 gramme of each sample with 50 cc, 
ol methylated spirit, agitating at intervals for an hour, and com- 
paring the depth of colour of the difierent tinctures. 

Iji)ffV)iiod adraei is met with in commerce both in a liquid and 

a solid form. The specific gravity is not a reliable indication of 

tho strength of the fluid extract, as it is liable to he raised by 

Ihe addition of salt, glucose, molasses, &c. The solid and paste 

;ts may not only contain salt, but are sometimes adulterated 

brina, cheatnut-bark ejctract, Ac. Treatment of the sample 

ithylatcd spirit, and observation of the intensity of the 

ir of the resulting tincture, is a useftd method of examination. 

. Trimble {Jour. Soc. l^ers, ^c, i. 92) recommends that 

colorimetric assay of logwood extract should be made by treating 

ilume of solution corresponding to O'OOl gramme of the ilri/ 

it with 10 c.c. of water naturally or artiticially containing 

of calcium carbonate " and u solution of O'OOS gramme of 

italitsed copper stdphate. The mixture is brought quickly to 

boiling point, and diluted with distilled water to 100 c.c. 

colour of the solution is then compared with one of pure 

ktoxylin similarly treated, or with a standard sample of log- 

; tract. 

iTha must satisfactoiy method of assaying logwood and logwood 


extracts is by a miniature dye-test with wool and potasdom 
bichromate, as described on page 330. A known quantity of the 
sample should be boiled with water, the solution strained, and 
diluted to a definite volume. A standard specimen must of course 
be treated in a similar manner, side by side with the sample. 

With the exception of indigo, logwood is, perhaps, the most 
important and indispensable of dyeing matters. It does not dye 
cotton without a mordant, and wool merely acquires a useless diab- 
tint. Hence the employment of logwood in dyeing depends an 
the colour-lakes which it forms with metallic oxides. 

With aluminous mordants, logwood yields deep violet-grey 
shades. With ferrous salts it gives a bluish-black, and with ferric 
salts a brown-black shade, while a mixture of the two yields a finer 
black than either separately. With chromates, logwood yields a 
black colour, which on exposure to light gradually takes a 
greenish shade. Logwood is used chiefly for dyeing black in 
conjunction with potassium bichromate. It likewise yields blues, 
which resemble those produced by indigo, but are not so fast. It 
is also likewise in dyeing leather, and in printing calico brown, 
slate, lilac, grey, &c. 

Fibres dyed black by logwood leave on ignition an ash contain- 
ing oxide of chromium, sometimes mixed with alumina or oxide of 
copper or iron. The dyed fabric is turned red by moderately con- 
centrated hydrochloric acid (tannin blacks are altered, but not 
reddened), and if the reddened spot be pressed, while still moist, 
against a piece of filter-paper, it produces a cherry-red stain, which 
turns blue if touched with a glass rod moistened with aluminate 
of sodium. Logwood violets and blues leave on ignition an ash 
containing alumina. With hydrochloric acid they behave like 
logwood black. When placed in milk of lime, and subsequently 
washed with soap, the colour is discharged. All logwood colours 
are readily bleached by chlorine and hypochlorites. 

If a fibre dyed with logwood (especially the blues) be boiled 
with glacial acetic acid the colouring matter is dissolved, and the 
solvent when cold has a rose-red colour, changing to yellowish -red 
on wanning. On adding ether and sufficient water to cause separa- 
tion of an ethereal layer, any indigo will remain in the ether or 
separate at the junction of the two liquids, while in presence of 
any quantity of logwood the lower layer will be reddish-blue. If 
the amount present be insufficient to produce this effect, the log- 
wood will still be detected on adding a few drops of hydrochloric 
acid. This will colour the aqueous liquid a beautiful red, while 
at the same time it will decolorise that portion of the Ic^wood 
colouring matter which was taken up by the ether. In the presence 


hotton-blue or iTi(ligo<carmme, the Eicotic solution should he 
mted from thu ethereal layer and ehaken with amylic alcohol. 
'p dissolves the logwood colouring matter, which can Iw extracted 
gitatiog the araylic alcohol with a saturated solution of borax, 
K-tbuB obtained pure. 

ZIL Wood is derived from the Ciemljnnia Brasiliemeg, a 
I growing in the forests of Brazil (page .137), The rod dye- 
's known in commerce as peack-ipood, eajian-toofKlj Lima~nrood, 
i (page 327), &c, are all the praluets of various species 
fHatalpinia, and yield very similar shade* of colours on fabrics, 
either when employed alone or with mordants. They appeal, also, 
to contain the same glucoside, which is decomposed by peculiar 
ferments or by boiling with dilute acids into a glucose and the 
colouring matter brnzilin, a substance which has been found in 
large crystals in casks in which extract of sapan-wood had been 
kept. The crust obtained in the manufacture of braril-wood 
extract contains much brazilin and its lime-compound. If treated 
with dilute hydrochloric acid, and then boiled with a mixture of 
one part of alcohol and eight of water, a solution id obtained from 
which bTazilin crystallises on cooling. 

Brazilin, C^Hj^Oj, may be obtained from brazil-wood by the 
method employed for the preparation of htematoxylin from logwood 
(page 328). When pure it forms colourless hydrated crystals, 
which become anhydrous at 130° C. It dissolves in water, 
alwhol, and ether. Brazilin presents a. close resemblance to 
hamatoxylin, C,gH,jOg, from which it differs only by an atom 
fosygen.^ On exposure to the air the solution acquires a bright 
^\ colour from the formation of brasilein. This change is 
itly facilitated by the presence of alkalies. Acetyl- and bromo- 
[vatives of brazilin have been obtained. 
a adding chromic acid or potassium bichromate to an aqueous 
ition of bradlin, a dork brown coloration is produced, and a 
> dark crimson lake separates on standing. This substance, 
1 is apparently a compound of brazilin and chromic oxide, is 
Bly decomposed by dilute acid. 

uAein, CigHijOj, is produced by the oxidation of brazilin in 

lline solution, and may be prepared in a manner similar to that 

\ for obtaining b le m a t e i n, Cj^Hj^Og, to which it presents 

i analogy. Braziloin forms minute crystals, having a grey 

The powder is reddish-brown. It is very slightly soluble 

kErjwdiog to K. K p p, brftzilin has the formula CsH„0,, which, if cor- 
I mmld rendvr it [irobxMa thit braziliu ivfta [he rosorcinol «thsr o( 



in cold, but more readily in hot water. The solution is yellowish- 
pink, with a greenish-orange fluorescence. On addition of an 
alkali the solution becomes carmine-red, changing to brown on ex- 
ix)sure to air. With concentrated sulphuric, hydrochloric, and 
hydroromic acids, brazilein reacts to form crystallisable compounds, 
which have greater tinctorial power and are faster on the fibre than 
brazilein itself. Boiling with zinc-dust or acid sulphite of sodium 
reduces brazilein to brazilin. 

An aqueous decoction of brazil-wood, or any of the allied woods, 
becomes yellow or orange on addition of an acid, the shade of 
colour depending on the relative proportions of brazilin and 
brazilein present. If the solution be strong, yellow or red crystals 
will probably separate on standing. With excess of strong hydro- 
chloric acid, brazil-wood solution becomes a bright pink, but the 
coloration disappears on adding water. Ammonia, caustic alkalies, 
and carbonates of the alkali-metals turn the solution crimson-red, 
this colour gradually changing to brown on exposure to air. Potas- 
sium bichromate reacts as with brazilin (page 33). Neutral lead 
acetate gives a shght reddish precipitate containing oxidation- 
products. The filtered liquid dyes a deeper shade than the 
original solution. Basic acetate of lead gives an abundant bluish 
precipitate with brazil-wood solution. 

Brazil-wood and the commercial extract are liable to the same 
kind of adulterations as logwood and its preparations, and may be 
examined by exactly similar methods, except that for the dyeing 
test twice the quantity of brazil-wood should be employed, as it is 
not so rich in brazilin as logwood is in hsematoxylin. 

Brazil-wood is used in calico-printing and dyeing, and yields 
colours similar to those obtainable with cochineal or alizarin. 
Thus when mordanted with alumina it gives red, with iron greyish- 
violet or black, and with a mixture of the two, brown. Stannic 
chloride gives a red, and chromates an olive shade. 

Wlien fixed on fabrics, reds produced by brazil-wood are turned 
violet-blue by alkalies, while acids change them to yellow and red, 
and give a pink solution. They are bleached by chlorine and 
hypochlorous acid, and are discharged by boiling with soap solution 
bluish-red, a character which distinguishes them from the alizarin 
reds. When immersed in succession in hydrochloric acid and in lime- 
water, fibres dyed red with brazil-wood are changed to violet, and the 
latter colour can then be removed by boiling with soap. Concen- 
trated sulphuric acid alters brazil-wood red to deep cherry-red, while 
it changes a cochineal red to an orange-yellow. On ignition, fibres 
dyed with brazil-wood leave a residue containing alumina, oxide of 
tin, &c., according to the mordant employed for fixing the colour. 



Sa.vtal Wood, Babwood, Cauatoub Wood, and Camtoou 
(seo also page 327) differ from Brazil-wood and its allies in their 
more resinous character, aiid aro often known as " close woods." 
They yield faster dyes than tlie " open woods," but the insohi- 
bility of the colouring muttera prevents them from being used in 
the form of extmcts. 

Sajtlaiia, C^^^fi^ OX the colouring prineiple of santal wood, 
Boema to bo identical with that of barwood, and probably with 
that of camwood, It appears to be developed by age, being absent 
from the young branches, but existiug in largo quantity in the 
trunk. The chemistry of santalin is very imperfectly understood, 
nnd the formula is uncertain. Santalin is best extracted by boiling 
crushed suntal wood with water to remove the tannin, heating tin* 
insoluble residue with a solution of borax, and saturating it with 
lime until the colouring matter is entirely removed. The filtered 
liquid is then treated with sulphuric or hydrochloric acid until no 
further precipitate is obtained. The voluminous red precipitate 
ia filtered off and dissolved in boiling ulcohol, when the santahu 
separates as a red ciystalline powder as the solution 000I& San- 
talin is insoluble in water, but soluble in alcohol, ether, and acetic 
acid. It dissolves in ammonia, lixed caustic alkalies, and carbonates, 
phosphates, and borates of the alkali-metals with violet-red colour, 
and is teprecipitnted in red flakes on acidulating these solutions. 

A- Zander {Jour. Soc. Dyers, ^e., iv. 496) has recently pro- 
posed the employment of a san talin-sul phoni c acid. 
Tliis is prepared by treating santal wood, or one of the allied woods, 
with a warm solution of borax, sodium phosphate, or carbonated 
or caustic soda, and precipitating the crude santalin from the 
liquid by means of an acid. The aantaliu is then warmed with 
ordinary concentrated or fuming sulphuric acid, until a sample 
ceases to be precipitated on dilution with water. The product is 
than poured into a cold, saturated solution of common salt, and the 
precipitated colouring matter washed and dried. Santalin-sul- 
phonic acid and its sodium salt occur in commerce as greyish- 
brown powders, readily soluble either in hot or cold water. The 
solution gives no characteristic reactions. It is best applied in an 
ftcid bath containing sodium sulphate, and produces sliades of 
colour much yellower than, but equally deep and fast with, those 
obtained with the original dye-wooiL 

Santal Wood or Sandal Wood (page 327), called also mndetr» 
wood or red eawlen, is imported in large billets, which are very 
dense (sp. gr. I'OH) and compact, and of blackish-brown colour 
«xtemally, while the interior is red. The fibres occur in alternate 
layers running in opposite directions, and hence when planed the 


wood exhibits alternately a poliBhed and a rough tom-up surface. 
Powdered santal wood is lighter than water, has an aromatic taste, 
and an odour like that of orris-root It yields to alcohol about 
16 per cent, of a colouring matter which is insoluble in water. 

Santal wood is chiefly used on the Continent, where it is employed 
' to give a bottom to woollen cloth which is afterwards to be dyed 
with indigo. The fine colour called bleu de Nemoursy obtained in 
this manner, has a purple hue by reflected light. Santal wood is 
also used for dyeing woollen and cotton a dark red, which is 
changed to a rich brown by a chromate-bath. It produces da^ 
browns with sumach and light browns with fustic. 

Barwood is allied to santal wood. It is compact, and of an 
orange colour when polished. It generally occurs in the fonn of 
raspings, as a rough, harsh, and odourless powder. Boiling water 
takes up about 7 per cent, of colouring matter, which on cooling is 
almost entirely deposited as a reddish powder. The colouring 
matter is soluble in alcohol, but the whole amount, averaging 23 
per cent., can only be extracted from the wood by repeated treat- 
ment The colouring matter dissolves in soda or ammonia with 
violet-red colour, and is reprecipitated in red flakes on acidulating 
the solution. 

Barwood is employed to produce mock turkey-reds on cotton, 
which are distinguished from the alizarin-dyed goods by yielding 
part of their colour to soap, and at the same time assuming a purple 
hue. It is also used for dyeing woollens brown and other dark tints. 

Cam Wood or Kamhe Wood yields its colouring matter to water 
much more freely than santal and barwood, but is not sufficiently 
soluble to yield an extract It is used in a manner similar to bar- 
wood, and is regarded as producing brighter and faster colours. 

An alcoholic extract of santal or barwood is rendered opalescent 
by copious dilution with water. The fixed alkalies redissolve the 
precipitate, the liquid acquiring a dark claret colour. Caustic 
alkalies change the original alcoholic solution to crimson or violet, 
while lime water produces an abundant reddish-brown precipitate. 
Dilute acids heighten the colour of an alcoholic solution of santal 
or barwood to a deep cherry-red ; while chlorine decolorises the 
tincture, with formation of an ochreous precipitate which rises to 
the surface of the liquid. The tincture of santal or barwood yields 
with stannous chloride a blood-red, and with stannic salts a 
brick-red precipitate ; with ferrous salts a violet coloration and 
abundant violet precipitate ; with ferric salts an intense brownish- 
red coloration and precipitate ; and with tartar-emetic an abundant, 
dark cherry-red precipitate. Salts of aluminiimi only render the 
liquid turbid, while lead salts give a dark violet, gelatinous pre- 



cipitate. The last two reactions diatinguisli santal- and bnr-wood 
from eatii-wood, an alcoholic extract of which gives a beautiful red 
coloration with salts of alumiDitim, and a bright oraiige~red pfeci- 
pttate with aalte of lead. 

Santal-, bar-, iind cam-wood are chiefly used in wool-dyeing, 
^^tqgether with other dyewoods, Buch as logwood nnd old fustic, for 
^^^ttpducing various shades of brown, olive, drab, &c. They have 
^^■yb a limited application in cotton-dyeing, but are not used for 

^^H Fibros dyed with santal- or bar-wood are not changed by hydro- 

^^Hloric acid, but if of wool nre turned dark olive by nitric acid. 

^^PPcohol is coloured red, as also is an acid solution of stannous 

^HHiloride, the colour of the fibre remaining unchanged. Caustic 

sods and ammonia turn the fibre purplish or brownish without 

yielding a coloured solution. When boiled with ferrous sulphate, 

cloth dyed with santul-wood beconies violet. 

Alkanbt (page 327) consists of the cortical parts of the root of 
Anehttm iinciona. The colouring matter called allMimin may be 
prepared by boiling the root with witter to remove all soluble 
matter, drying it, and then exhausting with alcohol. The solution, 
which has a violet colour, is slightly acidulated witli hydrochloric 
Rcid and evaporated to dryness. The residue is treated with ether, 
which on evaporation leaves the colouring matter as a dark red, 
Ksinous substance. According to Carnelutti and N a s i n i 
{Joitr. Ghent. Soe., xl. 53). the product so obtotned is contaminated 
with n reddish-brown acid. The cotouring matter is best obtained 
pure by extracting alkanet root with dilute potash solution, and 
agitating tlio solution with ether to remove the above-mentioned 
impurity. Ou saturating the alkaline liquid with carbonic acid the 
alkannin is precipitated, and may be purified by solution in ether. 
Al/cmtnin, Awhvfin, ot Anchusfe Acid. This body, of which 
tte formula is probably either Ci^HijO, or CjjH,(0,, is a reddiah- 
hrowu resinous substance of metallic lustre. It is insoluble in 
water, but soluble in alcohol, glacial acetic acid, ether, chloroform, 
carbon disulphide, turpentine, and fixed oils. The alcoholic solu- 
tion is crimson, and is unchanged by exposure to light or continned 
boiling. It gives a blue coloration with alkalies (restored to 
crimson by acids), a bluish-violet precipitate with aluminium 
oceUite, a crimson precipitate with stannous chloride, and a purple 
preoipitate with stannic chloride. Lead acetate produces a blue, 
and iron salts a violet precipitate- Alkannin forms a diacetyl -deri- 
vative which crystallises from glacial acetic acid in brownish -yellow 
grains. Alkannin is evidently a derivative of methyl-an thra- 
, C,^H,,, 09 that hydrocotbon ia formed when the colouring 


matter is distilled with zinc-dust In its tinctorial properties and 
absorption-spectrum, anchusin resembles quin-alizarin. 

The most characteristic test for alkanet and alkannin is the 
absorption-spectrum. The solution in amylic alcohol gives the best 
results, and exhibits three equidistant bands in the blue-green. On 
adding ammonia these give place to two bands, one nearly coincident 
with and theotheronthered side of the D line (compare vol L page 86). 

Alkanet root may be assayed by treating it with ether, which 
should extract not less than 5 per cent, of colouring matter. 
Alkanet was formerly used for dyeing various shades of violet, 
lilac, lavender, and yellow, but has been superseded for such pur- 
pose& It is used for staining wood crimson, and is employed in 
perfumery for colouring oils and pomades. An alkaline solution 
is sometimes used to colour syrups. Tincture of alkanet forms a 
very good substitute for litmus. 

Safflower consists of the bloom or petals of a plant resembling 
the thistle (page 327), indigenous to £gypt and the Levant, and 
cultivated in other countries. It varies much in quality, tiie 
Egyptian being the richest in colouring matter, and after that the 
Indian and Chinese. The colour of good safflower is a fieiy red ; 
a dull red colour is an indication of bad preparation. 

Safflower contains two yellow colouring matters, one of which 
is soluble in cold water, and exists in considerable proportion (26 
to 36 per cent.) ; the other is insoluble in water, but dissolves in 
alkaline liquida Besides these, safflower contains a small propor- 
tion of a red colouring matter called carthamin, which is the 
only constituent of value. The proportion of insoluble yellow 
colouring matter varies inversely with that of carthamin. 

Carthamin, Cj^H^qO^, the red colouring matter of safflower, 
forms only from 0*3 to 0'6 per cent, of the weight of the flowers. 
To prepare it, safflower is washed with cold water till no more 
soluble yellow colouring matter is removed, after which it is treated 
with water and 15 per cent, of its weight of crystallised sodium 
carbonate. The solution is strained from the insoluble portion, 
cotton yam immersed in it, and the liquid acidulated with citric 
acid. The cotton takes up the carthamin and an accompanying 
yellow colouring matter. When washed and treated with a weak 
solution of sodium carbonate, the carthamin dissolves, while the 
yellow dye remains fixed on the cotton. On acidulating the solu- 
tion with tartaric acid, the carthamin is thrown down as a bright 
red, amorphous precipitate, which, when mixed with a little water, 
forms the safflower extract or paste of commerce.^ The product 

^ If the paste be triturated with French chalk and the znixture dried, a 
product is obtained which is employed as a rouge. 


may be further purified by Bolution in akoliol ani! re precipitating , 
it by adding wat«r, 

Carthamio is ioBoIublo in water or ether, but readily soluble in 
alcohol The cherry-red alcoholic solution dyes silk without a 
mordant, and when allovfed to evaporate on glaaa leaves a varnish 
whiuh appears red by transmitted light and a beautiful beetle- 
gret^n by reflected light. On adilition of an ncid, the alcoholic i 
Bolution of lyirthaniin beeomes yellow, and alkalies also turn it ] 
yellow or orange. The colouring matter is consequently very 
imetable, and even undergoes rapid alteration on exposure to air 
or when boiled with alcohol or water. 

Carthamiu has feeble acid characterE. The ammonium aalt 
yields, with stannic chloride, a yellowish-brown precipitate, with 
ferric chloride a brownish-red, and with mercuric chloride a reil ' 

Carthamin dissolves with red colour in strong sulphuric acid, 
probably forming a sulpbonic acid, for the solution is not preci- 
pitated on addition of water. 

Satflower is best assayed by a miniature dyeing operation, and 
by an application of the method already described for detecting 
and separating any objectionable yellow colouring matter. 

Safllower is employed to dye silk, cotton, and linen various 
shades of pink and red. On fabrics dyed with annatto it pro- 
duces a scarlet. The use of safflowcr has much decreased of late 
years, owing to the competition of the coal-tar colours, but it is 
still employed for colouring red tape. 

On the 6bre, a rose, pink, or crimson colour due to safflower is 
immediately turned pale yellow by a single drop of alkali, and iho 
colour is then destroyed by any further treatment. Weak acids do 
not affect the colour, but strong acids, chlorine, and sulphurous acid 
bleach it at once. Alcohol has no action, but ammonia changes 
safflower pink (on cotton) to a flesh-tint, and ammonium sulphide 
decolorises it. 

Yellow Dyes of NatTiral Origin. 

The yellow colouring matters of natural origin which receive 
Wlical applications are all of vegetable derivation. They are of 
f vftrious origin and character, as will bo seen from the tabulated 
|«f the more important on next page. 

number of other vegetable colouring mattera might be 
imerated, including Chiwie yeitow, from Oanienia ffrarulijlora ; 
)fy«ophan, from Goa powder (page 281); the colouring matters 
ibnbarb, barberry root and carrot, and many others. 

H Bark, as met with in commerce, ia a mixture of 



fibres and fine powder of a yellow or buff colour. The articles 
imported respectively from Philadelphia, New York, and Baltimore 
rank as distinct qualities, the first being generally preferred. 

Quercitrin, the yellow colouring principle of quercitron, was 
obtained by Chevreul by boiling the bark with water, and 
allowing the solution to stand, when the quercitrin is deposited in 
crystals. B o 1 1 e y prepares it by boiling the bark with alcohol, 
precipitating the tannin (quercitannic acid) by gelatin, concen- 
trating the filtrate, and recrystallising the quercitrin which separates 



Colouring Principle. 





(page 839). 

Old Fustic ; 
Yellow Brazil 
wood (p. 843). 

Young Fustic : 
Fustet wood 
(page 346). 

Weld (page 

Persian Berries; 
Yellow Berries 
(page 848). 

Saffron (page 

Annatto (page 

Turmeric (page 

Gamboge (page 

Bark of Qtterrut 
nigra or Q. tine- 

Wood of Morus 

Wood of Rhu* 

Leaves, Ac, of 
Reseda luteofa. 

Various species of 

Stigmata of flower 
of Crocu* salivtu. 

Pulpy parts of 
Bijpia Orellana. 

I ndei-ground stem 
of Curcuma tinc- 

Gum resin from 
Oarcinia morella. 

North America. 

South America. 

West Indies ; 
Levant, South 

France, Ac. 

Spain. France, 
Persia, Turkey, 

Austria, Spain, 

Mexico ; South 

East Indies, 
China, Barba- 

Slam, Cochin 
China, Ceylon. 


Moric acid. 

Fostin or 















from boiling alcohol. Quercitrin is most readily prepared by boil- 
ing the prepamtion of quercitron known as flavin with water, and 
cooling the filtered liquid. Quercitrin forms pale yellow, rhombic 
plates, which are odourless, have a somewhat bitter taste, and a 
feeble acid reaction. It is only slightly soluble in cold water or 
ether, more readily in boiling water (1 in 25), and easily in 
alcohol. Ammonia and the fixed alkalies dissolve quercitrin 
readily, with greenish -yellow colour. The ammoniacal solution 
rapidly oxidises, and turns brown on exposure to air. The aqueous 
solution of quercitrin gives a reddish-yellow precipitate with baryta 
water; a beautiful yellow colour with alum; flocculent yellow 



p>recipitates with the acetates of copper and lead ; and an oliva- 
green coloration and gradual precipitate with ferric sulphate. 
Xitric acid colours quercitrin orange-red. 

Quercitrin is a glucoaide, suffering hydrolyais when boiled with 
dilute sulphuric acid, with formation of quercitin and a 
«ugar^like bodj. The formula of quercitrin is somewhat uncertain, 
and it is douhtfal whether different observers have always worked 
on the same body. According to Hlasiwetz and Pfoundler, 
several kinds of quercitrin exist, all of which yield quercitin on 
trcAtmeiit with dilute acids, hut differ as to the kind of sugar 
simultaneously produced. But it seems more probable that quer- 
citin and isodulcite are conetant products of the hydrolysis, though 
the proportions formed depend on the origin of the glucose. Thus 
while rutin, C^^U^O^j, contained in the leaves of lliita graveiiaut 
and Pofyijoniim faf/opymm, splits on hydrolysis into one molecule 
of quercitin and one of isodulcite, quercitin yields one of quercitin 
and fico of i s o d u 1 c i t e (vol. ii. 189), according to the following 

CmH„Ok,+ 3HaO = Cj^HmOji + 2CuHjO^HjO 
(juircilrln. Ijiiercltla. Itodultlte. 

Quetvifin, Cj^HiflO,,,' or its glucoside, is found in a great 
variety of plants. It forms slenderncedles of a bright yellow colour, 
which are tasteless, and insoluble in cold water. Quercitin is but 
slightly soluble even in hot water (1 in 380), hut dissolves readily 
in alc«hol and in acetic acid, and sparingly (1 in 125) in ether. 
In alkalies it dissolves with orange-yellow colour, and a utystalline 
eomponnd, containing Cg,HmO,j,KjO, has been obtained by dis- 
solving quercitin in a concentrated solution of potassium carbonate. 
An alkaline solution of quercitin becomes dark brown when treated 
with sodium-amalgam, the colour gradually changing to yellow. 
The alcoholic solution of quercitin yields orange precipitates with 
eslcium, barium, and lead salts; gives an orange coloration with 
"c chloride, and a greon with ferric chloride. 
citin dissolves in strong sulphuric acid, apparently forming 
ic acid, and the solution dyes wool a fast yellow 
; a mordant. A di-acetyl-derivati ve has also 
D obtained. 

1 1 put of quercitin be treated with 3 parts of caustic potash 
1 1 of water, and the whole evaporated to dryness, the quercitin 
Iplit up with formation of paradatiseetin, CiJIioO^, 
%tC6tic acid, CijHioO;. and phloroglucol. CgH^Oj 
'tig {Jour. Cham. Soc., I. SGI) has givcu reaMOi for doubting the 
My of this (unuuta. 


(page 85). By prolonging the treatment with potash, or by treat- 
ing quercetin at once with the fusing alkali, the queicetic acid is 
further decomposed into protocatechuic acid, C^H^O^ (page 
61), and quercimeric acid, CgH^O^, which latter takes up 
oxygen and again splits up into protocatechuic acid and carbon 

Quercitin is easily decomposed when its acidulated aqueous 
solution is boiled. 

When a dilute alcoholic solution of quercitin containing 
silver nitrate is shaken with three volumes of ether, the latter 
acquires a crimson colour rapidly fading with deposition of metallic 

If an alcoholic solution of quercitin be acidulated with hydro- 
chloric acid and treated with sodium-amalgam, the liquid assumes 
a fine purple colour, and on concentration yields red prisms, which 
dissolve in alcohol and a little alkali with green colour, the solution 
being readily reoxidised with formation of quercitin on exposure 
to the air. 

Besides quercitrin, quercitron bark contains quercitannic 
acid (page 93). 

Flavin is the commercial name of a preparation of quercitron 
produced by acting on the bark with sulphuric acid, and hence 
contains woody fibre with more or less quercitrin, quercitin, and 
isodulcite. In some cases it consists of nearly pure quercitrin, and 
in others of quercitin. A good quality of flavin has about sixteen 
times the colouring power of quercitron bark, but very inferior 
specimens are sometimes met with. Aurantine and '' patent bark" 
are preparations similar to flavin. 

A freshly prepared decoction of quercitron bark is transparent, 
and of a dull orange-red colour, but after a time it becomes turbid, 
gives a yellow crystalline deposit, and the supernatant liquid 
gradually becomes gelatinous and acquires a blood-red colour. A 
freshly made solution is deepened in colour by alkalies and lime- 
water, the latter reagent also producing a brownish-yellow flocculent 
precipitate. Alum brightens the colour, and forms a light preci- 
pitate only. Stannous chloride gives a brown and stannic chloride 
a yellowish precipitate. Gelatin produces a reddish flocculent 
precipitate, and chlorine also precipitates abundant flocks, an excess 
of the reagent decolorising the liquid. Iron salts colour the solution 
of quercitron green, an olive-brown flocculent precipitate being 
subsequently formed. 

Flavin and quercitron bark are chiefly used for dyeing woollen 
and mixed fabrics, tin being usually the mordant employed. Flavin 
is laigely used in conjunction with cochineal or lac-dye for pro- 



diiciDg scarlet. Samples of flavin or quercitron are beat assayed 
by a miniature dye-test. 

Fibrea dyed with quercitron bark yield a yellow solution with 
liydrocliloriD acid, but the colour of the fibie is little affected. 
Caustic alkalies behave similarly. Nitric acid turns the fibre light 
brown, and it becomes olive when boiled with ferric chloride, and 
orange with lead acetate. Alcohol has no action, and the colour is 
little affected by ammonia or an acid solution of stannous chloride, 
though the solution becomes yellow in each cose. 

Old Fustic, also called i/dlow wood (page 340), contains two pecu- 
liar principles, known respectively as morin or moric acid, and 
morintannic acid or maclurin. To obtain these bodies 
in a pure state, rasped fustic is boiled with water and the decoction 
concentrated to a syrup. The crystalline deposit which forms in a 
few days is washed rapidly with cold water and pressed. On treat- 
ment with boiling water, morintannic acid is dissolved, while calcium 
morato remains insoluble. The morintannic acid is obtained by 
concentrating the solution, and crystallising the colouring matter 
from water acidulated with hydrodUoric acid. The calcium morale 
^M decomposed by dilute hydrochloric acid, and the residue taken up 
^■B alcohol, from which solution, on addition of two-thirds of its 
^Blume of water, the morin is deposited in yellow needles.' 
^ft Morin or ifmic Aeid, according to Benedikt and H a 2 n r a, 
probably contains CjgHgOg, It crystallises in colourless neeilles 
containing 1 aqua. It is nearly insoluble in water and carbon 
disulpbide, slightly soluble in ether, and freely in alcohol. In 
solution of caustic alkalies, carbonates, borates, and phosphates, it 
dissolves with yellow colour, and is reprecipitated on addition of 
an acid. Ferric chloride gives an olive-green coloration with the 
alcoholic solution of motic acid, while yellow precipitates are pro- 
duced by salts of tin, lead, zinc, and aluminium, and a dark green 
precipitate by cupric sulphate. If an alcoholic solution of moric 
acid be acidulated with hydrochloric acid and treated with sodium 
amalgam, it acquires an intense purple colour, and if then separated 
from the excess of the amalgam and concentrated, purple crystals 
uru obtained of isomorin, a botly said to be ia 

' Morin may lOao be prepnrod bj muing fnatio extract with an wjual Tolmne 
B tntsT atiil a little bydrochloric acid, docaatiDg the clear liquiil, and repeat- 
the tmatmcnt till the washings are no longer yellow. The residue of crud« 
n to jinssed, powdored, and dried in the air. It is tbeu diaaolred in hot 
)o1, and one-teutb of hot water added, when free moriD separates on 

I obuia 


The solution of this body becomes green on treatment with an 
alkali, and morin is gradually reproduced, in the cold and rapidly 
on boiling. A solution of isomorin, when treated with alum, 
becomes intensely fluorescent, and on dilution appears yellow by 
transmitted and uranium-green by reflected light The alcoholic 
solution of moric acid itself becomes highly fluorescent on addition 
of a minute proportion of alum (1 : 8000), a character which dis- 
tinguishes it from morintannic acid, and has been suggested by 
Goppelsroeder as a delicate test for aluminium. When fused with 
caustic potash morin yields resorcinol, phloroglucol, and 
other products. 

Moric acid presents a close analogy to quercitin (page 341) in 
many of its characters and reactions. 

Morintannic Acid or Madurin, C^^H^QO^+ILfi (page 79), forms 
a pale yellow, crystalline powder, freely soluble in water, and soluble 
also in alcohol, wood spirit, and ether. It becomes anhydrous at 
130" and melts at 200" C. On boiling with concentrated caustic 
potash ley, or heating to 120" with dilute sulphuric acid, it spHts 
up into protocatechuic acid and phloroglucol (com- 
pare page 84). With ferric chloride, morintannic acid yields a 
greenish or greenish-black precipitate. When boiled with hydro- 
chloric acid it yields rufimoric acid, a substance forming 
brick-red crystals and dissolving in ammonia with purple colora- 

On heating a moderately concentrated solution of morintannic acid 
with zinc and diluted sulphuric acid, it rapidly acquires a red colour, 
which gradually changes to orange, and then contains phloro- 
glucol (page 85) and machromin, Cj^Hj^Og. The latter 
body crystallises in tufts of slender needles, only slightly soluble 
in water or alcohol, but more readily in ether. Both crystals and 
solutions of macliromin become blue on exposure to air or treat 
ment with oxidising agents. On adding hydrochloric acid the solu- 
tion yields an amorphous blue precipitate, and with ferric or mercuric 
chloride a beautiful violet coloration, gradually changing to blue. In 
strong sulphuric acid, maclurin dissolves with orange colour, changing 
to intense green on heating. The colour is unchanged by dilution, 
but becomes purple on adding an alkali. The blue substance pro- 
duced by the action of oxidising agents on machromin is said to 
contain C^^HgOs. It is best obtained by the employment of excess 
of ferric chloride, M'ashing the blue precipitate which is formed, and 
after drying and washing it with ether. It dissolves in alcohol 
to form a solution which is decolorised by reducing agents. 

A decoction of old fustic has a bitter, astringent taste. Alkalies 
and lime-water change the colour a reddish-brown. Acetic add 


remlciB the decoction paler and brighter, and salphnric, nitric, and 
oxalic acida produce slight precipitates. Chlorine-water produces 
a alight precipitate and reddish coloration, which is destroyed by 
excess. Alum gives a bright yellow precipitate with fustic decoc- 
tion; stannous chloride, lead acetate, and gektin yield golden or 
orange-yellow precipitates. Ferric sulphate produces an olive-brown 
culonttion, and on standing a brownish- black precipitate falls. 

Old fustic with on alumina mordant dyes wool yellow, and with 
salts of iron olive-green. Brighter colours can be obtained if the 
morintannic acid be first removed by gelatin. The yellows pro- 
duced by fustic become orange on exposure to air and light, and 
hence it is now rarely employed alone ; but when mordanted with 
potassium bichromate, it is largely used for the yellow constituent 
of browns, jet-blacks, and greens. 

Fibres dyed with old fustic become orange on treatment with 
hydrocldoric acid, and yield an orange solution. Nitric acid turns 
them pale yellow. By alkalies and ammonia the fibre is little 
changed in colour, though in the latter case the liquid is coloured 
yelluw. An acid solution of stannous chloride changes the fibre to 
orange, tlie solution being colourless. Heated with ferric chloride, 
the Oolour of the fibre is changed to olive, and when boiled with 
aluminium acetate a yellow solution is obtained, exhibiting a 
bluish-green fluorescence. 

FirsTET Wood or Youso Fcsno (page 340), notwithstanding 
its name, is derived from quite a diji'erent source from old fustic 
It occurs in commerce in small logs or crooked branches, that 
imported from the Antilles and tho West Indies being the finest 

According to J. Schmidt (Jonr. Sof, Dyers, ^c. ii. 1 48), fuslct 
wood contains a substance which is easily broken up by the action 
oithar of dilute acida or alkalies into a kind of tannin (probably 
sumoch-tonnin) and the gluuoside f us tin. The red and brown 
coloiuring matters describiMl by older investigators were probably 
oxidation- products or phlobaphenes of this tannin. The fustin- 
tannido may bo prepared by treating young fustic with water, pre- 
cipttAting impurities by on acetic solution of lead acetate, and ex- 
tracting the filtrate with acetic ether. It forms yellowish- white 
needles, easily soluble in water, alcohol, and ether. The solution 
gives with ammonia a brown, and with potaah a brownish-red colora- 
tion, and reduces Fehling's solution. When dissolved in a little 
worm glacial acetic acid, and the solution diluted with water, 
yctlowi eh -white needles of the glucoside fust in are obtained. 

' I substance is reailily soluble in boiling water, alcohol, and 
inly sparingly in ether. With lead acetate it gives 

346 FISBHN. 

yellow and with cupric acetate a browniflh-yellow precipitate, in 
both cases readily soluble in acetic acid. Ferric chloride gives a 
g^en coloration, changing through violet-blue to red on adding 
dilute soda. When warmed ¥rith dilute sulphuric acid, fustic ib 
gradually decomposed into a sugar and f i s e t i n. 

Fisetin, C^K^fig, may be obtained more readily from the com- 
mercial extract of fustet known as eolimn^ which is prepared by 
extracting the wood with very dilute caustic soda and evaporating 
the solution. Fisetin crystallises from dilute alcohol in small, 
lemon-yellow prisms. It is sparingly soluble in ether, beniene, 
petroleum spirit, chloroform, and boiling water, but readily in 
methyl and ethyl alcohols, and in ethyl acetate. Fisetin does not 
melt below 360**, but may be partiaUy sublimed in small needles. 
Fuming sulphuric acid dissolves it with formation of a sulphonic 
acid. Alkalies and alkali-metal carbonates turn an alcoholic solution 
of fisetin brownish-red, and render it fluorescent The abeorpticm- 
spectrum is not characteristic. An alcoholic solution of fisetin 
gives a brilliant orange-red precipitate with lead acetate, an orange 
yellow with stannous chloride, and a brown precipitate with 
cupric acetate. The precipitates in each case are readily soluble 
in acetic acid. Fisetin reduces Fehling's solution and ammoniacal 
silver nitrate on warming. If an alcoholic solution of fisetin 
be acidified with sulphuric acid and treated on the water-hath 
with sodium-amalgam, the liquid acquires a beautiful purple- 
red colour. 

When heated with glacial acetic acid and sodium acetate, fisetin 
yields a hexacetyl-fisetin, G^^^Q(G^Jd)jd^^ which 
crystallises in white needles sparingly soluble in boiling alcohol, 
readily in chloroform, and melting at 200** to 201* C. 

When fisetin is dissolved in a warm saturated solution of sodium 
carbonate, a sodium derivative, CgjHj^NagOg, crystallises 
out in yellow glistening needles, which turn greenish-black on 
exposure to air. When fused with caustic potash, fisetin yields 
phloroglucol and protocatechuic acid (page 84). 

Fisetin presents a close resemblance to quercitin, from 
which, if the formula of Liebermann and Hamburger for the latter 
be correct, it only differs by C02.^ 

A decoction of young fustic gives a fine orange colour with 
alkalies, and bright orange precipitates with lime and baryta water, 
stannous chloride, and lead acetate. Acids give it a greenish hue. 
Ferric sulphate produces an olive-green, and cupric acetate a dark 
red precipitate. 

^ According to Hlaziwetz and Pfoundler, the formula of quercitio 
ia C^HigOu (compare page 841). 



SToimg fustic gives a fine orange colour with alumina rootdante, 
1 employed in conjunction with cochineal and lac-dye in 
jreing scarlet, the mordants being tartar and stannous chloride. 
It U also used for dyeing leather orange-yellow. The colours ore 
not BO fast aa many vegetable yellows and oranges. 

On the fibre, colours dyed with young fustic are unchanged by 
hydrochloric acid, the solution becoming pale yellow. Soda and 
ammonia turn the fibre reddish-brown, and nitric acid dark brown. 
Alcohol and an acid solution of stannous chloride have no action. 
Heated with ferric chloride the fibre becomes olive. 

Wbu) (page 340) consists of the leaves and other parts of a 
variety of mignonette. Luleolin, the colouring matter of weld, 
probably has the formula CjoHj^Og, and forms small yellow needles 
having an astringent, bitter taste. It dissolves slightly in cold 
and very sparingly in boiling water, but b more soluble in alcohol 
It dissolves readily in alkalies with deep yellow colour, and in cold 
sulphuric acid to form a reddish-yellow solution precipitated on 
dilution with water. Ferric chloride employed in small propor- 
tion produces a green coloration, which changes to brownish-red 
on adding excess of the reagent. Oxidising agents, such as pota(«ium 
bichromate, turn luteolin a brilliant yellow. On fusion with potash, 
Inteolin yields hydrogen, protocatechuic acid, and 
much pbloroglucol. 

A decoction of weld is pale yellow when freshly prepared, but 
soon becomes turbid, and gives a greenish- brown precipitate con- 
taining irun. It is slightly acid, and turns reddish when kept. 
Alkalies change the colour to a golden yelbw, and baryta water 
precipitates beautiful yellow flocks. Alum gives only a alight 
yeUow precipitate, but lead acetate and stannous chloride produce 
ntnindaut yellow precipitates. Gelatin only renders the liquid 
slightly turbid, while ferric sulphate (^ves on olive-brown colora- 
tion, and, on standing, a brown precipitate. Chlorine changes the 
colour of a decoction of weld to brown, and gives a flocculent 
precipitate - an excess of the reagent partially decolorises the 
liquid. Potassium bichromate changes the colour to golden yellow, 
■mil then gives a precipitate in yellow plates. Most acids render 
the lii{uid turbid, but nitric acid deepens the colour, without pro- 
ducing any precipitate. 

An aqueoua solution of weld dyes wool, mordanted with alum, 
n fine daffodil-yellow, which is very fast to light, heat, and dilute 

On the fibre, colours dyed with weld are little ulTccted by 
hydrochloric acid, though the solution is turned pale yellow, 
monia, alcohol, nitric acid, boiling lead acetate, and an acid 


solution of stannous chloride have little or no visible action. With 
caustic soda the fibre is but little affected, but the solution becomes 
pale yellow. 

Persian or Yellow Berries are the fruit of the buckthorn and 
other species of Rhamnus (page 340) growing in the east and 
the south of Europe. They are about the size of peas, shrivelled, 
and yellowish-green in colour. When old or injured they are 
brown or black. The flavour of yellow berries is bitter and dis- 
agreeable, and the odour unpleasant. 

Xanthorkamnin or Chryaorhamnin^ the yellow colouring matter 
of Persian berries, has, according to Liebermann and H o r- 
m a n n, the formula G^^^fi^^ It forms golden yellow crystals, 
and, when boiled with dilute sulphuric acid, or even when simply 
heated to 130**-! 60'' C, it is hydrolysed into rhamnetin and 
the saccharoid body iso-dulcitol (voL i. page 189). The 
following formula expresses the decomposition which is stated to 
occur : — 

C«H«,Oa,+ 5HjO = 2Ci2H„05+ 4CeH,,0, 

XanthorhRmnln. BhamnetlD, Iso-dolcitoL 

Rhamnetin crystallises from water containing sulphuric acid in 
microscopic needles, and from phenol in distinct yellow needles. 

A freshly prepared decoction of yellow berries has a brownish- 
green colour. It is very liable to ferment and become ropy, but 
the change may be prevented by addition of carbolic acid. The 
solution is brightened or rendered slightly turbid by acids, while 
alkalies change the colour to orange. Alum weakens the colour 
without forming a precipitate, and chlorine deepens it to red, or 
with excess changes it to yellow. Acetate of lead renders the 
decoction of yellow berries turbid after a time, and other metallic 
solutions fail to produce characteristic changes. 

Persian berries give bright yellows on wool and cotton with 
alumina or tin mordants. Their use has much diminished. 

Saffron consists of the stigmata of the flowers of Crocus 
tiotivm (page 340), of which from 50,000 to 100,000 are required 
to produce 1 lb. weight. It has an agreeable odour, and a bitter 
pungent taste. 

The chemistry of saff'ron has been recently re-investigated by 
K. K a y s e r (Jour. Soe. Df/ers, ^c, i. 43). The essential oil 
is obtained by distilling saflxon with water in a current of carbon 
dioxide, agitating the distillate with ether, and evaporating the 
ether in an atmosphere of carbon dioxide. It is a very mobile, 
nearly colourless liquid of the terpene class, C^qIIj^ having aa 
intense odour of saffron, and very prone to absorb oxygen and 
become thick and brown. 



If MS'ron be treated with ether, to remove the fat and essentinl 
oil, nml the residua treated with cold water, the colouring matter 
is dissolved. Ou shakiug this solution with purified animal char- 
coal the colour ia rapidly absorbed, and on filtering and boiling thu 
charco&l with rectified spirit, it again passes into solution. The 
red liquid yields c ro c i n on evaporation. 

in, so obtained, according to R. Kayser bos the formula 
_Pro'-*s8' I' f"rms a yollowiah-brown mass, the powder of which 
p yellow. It dieaolves readily in water and dilute alcohol, but 
Vith difficulty in absolute alcohol or ether. Concentrated sulphuric 
acid dissolves it with blue colour, changing to violet, dierry-red, 
and finally to brown. CoQcentmted nitric acid also gives a blue 
coloration, changing to brown, but hydrochloric acid dissolves crocin 
without alteration, 

Qy the action of hot lime or baryta water, or even hot acetate 
of lead solution, crocetin is hydrulysed with formation of a 
glucose, crystalliBing in rhombs, and a body called crocetin, 
CjjIIjjOi,. Tlie latter is best prepared by heating crocin with 
djiuto hydrochloric acid in a current of carbon dioxide, when 
crocetin is precipitated as a red powder, scarcely soluble in water, 
tiut soluble in presence of an alkali with omnge colour, and rcpre- 
cipitttted on adding an acid. 

Pt'crocroein, C^Hg^Oj^, is obtained in bitter prismatic crystal*, 
melting at 75°, and soluble in wa^r and alcohol, on estractiug 
dried saffron with ether for a prolonged time. "When warmed in 
aqueous solution with a dilute acid, lime or baryta water, or lead 
Bcetnte, picrocrocin splits up into a sugar and the terpene of a 
Baflron-odour already described. 

Saffron is too expensive to use in dyeing, but is employed for 
colouring ]»istry, and has a limited use in medicine. It is liable to 
various substitutions and adulterations, which are classified by 
J. M. Maisch (Analyst, x. 300) as those derived from the same 
plant and those coming from other sources. The stigmata of which 
genuine saffron consists become thinner towards the leaves, fermi- 
itate tVi a ydlote Ihread, and three are generally united. Saffron 
ttylei are ]>resent in all saffron of Spanish origin to a greater or less 
extent, and crocus utamerm, dyed so as to resemble the stigmata, 
aro also mot with. Fibres of shredded beef and ham are said to be 
B common adulterant in Italy. Such an addition would be readily 
detected by the microscope, and the smell produced on heating will 
afford a pruliminary indication of their presence. The corolla tubes 
of the crocus, dyed with braxil-wood or santal-wood, are said to be 
frequently nsed for adulterating saffron. Various other coloured 
vegetable pi'oducta are referred to by Maisch, iacluding the 


calendula florete (marigold) dyed by dinitroeresylate of sodium 
observed by J. B i e 1. This fraud may be detected by treating the 
suspected portions of the sample with petroleum ether, which is 
not coloured by genuine saffron, but dissolves the coal-tar colour 
with citron-yellow colour. The colouring matter from gantal-wood 
is not taken up by water, but dissolves in alcohol with red and in 
ammonia with purple-red colour. Brazil-wood will tinge the water 
red in a few minutes, the colour becoming pale on adding acid and 
deeper with ammonia, but the infusion will not be blackened by salts 
of iron. 

Safflotoer and red poppy have also been observed as adulterants 
of saffron. In the latter case the infusion is turned greyish-green 
by ammonia, and bright red by nitric acid. Safflower is said to be 
80 commonly substituted for saffron in some parts of America that 
the genuine substance is unknown {PhamL Jour., [3], vL 950). 

Mineral additions, such as chalk, gypsum, barium and sodium 
sulphate, emery, &c, have been observed as adulterants of saffron, 
being made to adhere by means of honey, glucose, or glycerin. The 
ash of genuine saffron of good quality ranges from 4 to 7 per cent, 
but in samples of Alicante saffron D. Hanbury {Phann. Jour., 
[3], i. 241) found proportions of ash varying from 12 to 28 per 
cent., the excess being due to mineral adulterants. J. Ingham 
has described a sample of saffron containing 45 per cent of mineral 
impurity, besides a quantity of crocus stamens ; J. H a r t a saffron 
yielding 20 per cent of ash, the greater part of which consisted of 
barium sulphate ; and Tanner a sample containing a considerable 
quantity of a red ferruginous earth. M. Adrian has described 
a saffron yielding 26*4 per cent, of ash, containing borate, chloride, 
sulphate of sodium, and carbonate of potassium, the last having 
probably been derived from tartrates. The presence of ammonium 
nitrate was also suspected. K M. Holmes (Pharm. Jowr.^ [3], 
xix. 666) met with an adulterated saffron of excellent odour and 
colour, which immediately coloured water orange-yellow, deflagrated 
like touch-paper on ignition, gave a fusible ash, and yielded the 
brown coloration indicative of a nitrate with ferrous sulphate and 
sulphuric acid. 

G r i s p o found vegetable filaments of unknown origin in 8a£&on, 
together with water, glucose, and barium sulphate. Kanoldt 
examined a factitious saffron that consisted entirely of an alga, prob- 
ably Fttcus amylaceus, which had been weighted with a coloured 
mixture of chalk and honey. 

For the detection of mineral adulterants in saffron, D. Hanbury 
recommends that about 1 grain of the sample should be treated on 
a watch-glass with 8 or 10 drops of water, and then lightly touched 



so u to caase the water to wet it. Genuine saffron will yield 
iramediately a clear bright yellow solution, but if a niineral 
adulterant be present a white powder will irutantly a^arale, ami 
will render the liquid turbid ; and on adding hydrochloric acid a 
perceptible effervescence and disappnarantie of the turbidity will be 
obaerved if a carbonate be present, whereas tlie pollen from crocus 
stamens is unaffected, and its nature can be recognised under the 
microscope. If it be desired to collect the adulterant, the saffron 
should be stirred with water in a funnel closed at the lower end. 
The mineral matter will settle into the stem, and after removing 
the saffron and pouring off the bulk of the water, con readily be 
washed out and further examined. 

If genuine saffron he scattered on the surface of warm water, it 
immediately expands into a characteristic form, readily distinguished 
from crocus stamens, or the florets of salSower, marigold, or arnica. 

According to the German Pkarmaeojxeta, " if 1 part of saffron 
be macerated in 10 parts of water, a yellow-red liquid is obtained 
free from sweet taste, and whici), diluted with 10,000 pnrta of 
water, has a distinct yellow colour. Saffron on being dried at 
100* C. should lose less than 14 per cent, of moisture, and on 
being now incinerated should leave not more than S per cent, of 
ftsk" From this description it appears that 1 grain of saffron will 
colour 7 gallons of water distinctly yellow. 

B. S. Proctor (PAonw. Jour., [3], six. 801) states that saffron 
ia beat assayed, in the absence of other colouring matters, by com- 
paring tlip colour of the infusion with that of a solution of jwtiisaium 
bichromate. 1*4 grammes of this salt, dissolved in 100 c.c. of 
wal«r, is said to furnish a liquid of the same tint as that produced 
by exhausting 0^1 gramme of genuine saffron by several alternate 
treatments with methylated spirit and water, and diluting the 
mixed decoctions to 100 c.c. These solutions are too strong for 
the accurate observation of the colour, and hence should be 
further largely diluted before comparing the tints. I c.c. of the 
bichromate solution should bo measured with a delicate pipette, 
and ililiited with SO cc. of water. To a similar quantity of water, 
in anotiier tube, sufficient of the saffron infusion is gradually 
added from a graduated pipette to render the colour similar to 
that of tho bichromate solution, 

Saffron gives a fine yellow colour on silk, but is now rarely if 
ever used as a dye. It is employed in medicine, and would prob- 
alily he more extensively applied if the price were lower. 

Annatto, occasionally called araotta and rocou (page 340), is 
mainly composed of the pulp surrounding the fruit of Bixa iirellana, 
(pving in the East and West Indies and South America. The two 

352 ANNATTO. BlXm. 

chief kinds which reach England are Spanish annatto, imported from 
Brazil, and the flag or French annatto which comes from Cayenne. 
Brazil annatto occurs in cakes or rolls, is hard and dry, brownish 
on the exterior but red inside, and with a rather agreeable odour. 
Cayenne annatto is a soft paste, of a bright yellow colour. It 
often has a repulsive urinous odour, said to be due to the actual 
addition of urine to keep it moist and impart a richer colour. 

Annatto contains two yellow colouring matters, bixin and 
r e 1 1 i n. 

Bixin, CggHj^Og, the properties and chemical relationships of 
which have been very imperfectly examined, may be prepared by 
digesting annatto at about 80^ C. with rectified spirit and sodium 
carbonate. The filtered liquid is treated with half its measure of 
water and a saturated solution of sodium carbonate. The preci- 
pitate, consisting of the sodium salt of bixin, is purified by re-solu- 
tion in weak alcohol and precipitation by sodium carbonate, and is 
then decomposed by hydrochloric acid. Bixin forms minute 
yellow leaflets which melt at 176^ It is insoluble in water, and 
only slightly soluble in alcohol, benzene, carbon disulphide, or acetic 
acid, but is very readily soluble in ether.^ Bixin forms a sodium 
salt, containing C^HjgNaOg, 2 aqua, which crystallises in lus- 
trous red needles, very soluble in water, but insoluble in alcohol and 
ether. It also yields a compound containing CggHjgNagOg, 2 aqua, 
which forms a dull red powder. 

According to some observers, bixin reduces Fehling's solution 
even in the cold, but according to others it has no action even 
after boiling with dilute sulphuric acid. It dissolves in strong 
sulphuric acid with bright blue colour, and on dilution with water 
a dark green precipitate is formed. 

Ordlin is described as yellow, soluble in water and alcohol, but 
insoluble in ether, and dyeing cloth mordanted with alum yellow. 
It is probably an oxidation-product of bixin. 

Annatto is only partially soluble in water, but more completely 
in alcohol. It dissolves readily but sometimes imperfectly in solu- 
tions of caustic and carbonated alkalies, of borax, and of soap, 
forming liquids of orange or red colour, which furnish orange-reti 
precipitates with acids. It gives orange lakes with alumina and 
ferrous sulphate, a yellowish -bro\yn precipitate with salts of copper, 
and a lemon-yellow with tin salts. Concentrated sulphuric acid 
dissolves annatto with deep blue colour, the colour gradually 
changing to green and violet. On adding water a deep green pre- 
cipitate is formed. 

^ According to some authorities, bixin is insoluble in ether, bat readily 
soluble in alcohol. 



Commercial annatto varies greatly in quality, and is liable to 
various adulterations. According to Wynter Blyth, a fair 
commercial sample contained : — water, 24*2 ; resin, 28*8 ; ash, 
22*5; and extractive matters, 2 4 '5 percent. An adulterated sample 
contained: — water, 13*4; resin, ll'O; ash (oxide of iron, alumina, 
silica, chalk, and common salt), 48 '3 ; and extractive matters, 27*3 
per cent Crace-Calvert gives the average composition of 
inferior Cayenne annatto as : — water, 72*25 ; leaves, 3*85 ; starch, 
mucilage, and woody fibre, 18*30 ; and, colouring matter, 5*60 per 

The following results, obtained by the analysis of commercial 
annatto, have been recorded by W. L a w s o n {Pharm, Jour,, [3], 
xvi. 645). 





No. of 

Mois- 1 






















2 90 





66 00 






• ■• 


58 40 
























Red roll Ash was largely NaCI. 
Red roU. Ash was largely NaCl. 

Red roll. Ash large, chiefly 

NaCl and Fe^Oj. 
Bright red paste. Ash chiefly 

Red roll. 8 per cent, of sand. 

Red roll. Contained iron and 

foreign matters. 
Brown cake. Soluble ash chiefly 

KgCOs, and insoluble CaCOs. 
Brown cake. Very offensive. 

Soluble ash chiefly KsCO^. 
Brown cake. Resembled No. 7. 

Brown cake. Resembled No. 7. 

The resin was determined by drying the samples at 100° (the 
loss of weight being recorded as moisiure)^ and then exhausting 
with boiling methylated spirit. The alcoholic solution was eva- 
porated on the water-bath, the residue dissolved in carbonate of 
sodium, and the solution precipitated by a very slight excess of 
dilute sulphuric acid. The precipitated resin was filtered off, 
washed, dried, and weighed. The ash was determined by ignition, 
and the extractive matter by difference. 

The samples in the form of brown cakes gave on ignition an 
agreeable odour resembling that of good tobacco. Most of the 
red rolls contained abundance of starchy matters, this in No. 4 
being largely replaced by water. The cakes all gave the boric acid 
reaction for turmeric, and all except No. 8 contained large quan- 
tities of chalk. 

VOL. 111. PART I. Z 


Besides containing the adulterants already mentioned, annatto 
is liable to be mixed with ochre, brick-dust, &c 

The colouring power of annatto is best ascertained by a dye- 
assay in a bath containing soap or sodium carbonate. 

Annatto receives a limited application in dyeing and caHco- 
printing, but by far the greater part is employed for colouring 
butter and cheese. 

BMer colourings are now numerous. Among the substances 
employed for the purpose, E. Schmidt (Jour, Chem, Soc^ xlvL 
286) enumerates marigold and carthamus flowers, saffron()), carrot 
juice, and turmeric. More recently the coal-tar colours known as 
coralline yellow and victoria yellow are said to have been used, as 
also dimethyl-amido-azobenzene (page 180). Lead chromate has 
been met with as a colour on the outside of cheese. 

Various methods have been described for the recognition of 
butter-colourings, the process being usually based on the solution 
of the butter-fat in ether or similar solvents, the agitation of thiB 
liquid with alkah*, the precipitation of the dissolved colouring 
matter by an acid, and the application of special tests to the 

To extract na^yhthalene-yellow from butter, the fat should he 
separated from the curd, water, &c., dissolved in ether, and the 
solution agitated with water, to which dilute ammonia is added 
drop by drop until present in slight excess. The naphthalene 
yellow or other added colouring matter,,, annatto, turmeric, 
saffron, &c., will dissolve in the ammoniacal liquid. Turmeric 
will be indicated by the formation of a brownish or reddish stratum 
between the ethereal and aqueous layers before they are thoroughly 
mixed by agitation. 

E. W. Martin {Analyst^ xii. 70) recommends that 2 part.« 
of carbon disulphide should be gradually added, with gentle agita- 
tion, to 1 5 parts of alcohol or wood spirit. Five grammes of the 
butter to be tested, which need not be previously clarified, is 
shaken with 25 c.c. of the solution so obtained. On standing for 
a few minutes, the mixture separates into two layers, the lower of 
which is a solution of the fat in carbon disulphide, while the upper 
alcoholic stratum will be yellow if any artificial colouring matter 
be present. If the butter be but slightly coloured, a larger amount 
should be employed. The alcoholic stratum will give a greenish 
coloration with nitric acid, and a red with hydrochloric acid and 
sugar if saffron be present. A brownish colour with ammonia 
indicates turmericy and a blackish coloration with silver nitrate, 
mariyoJd, If the alcoholic solution be evaporated to dryness, and 
the residue treated with concentrated sulphuric acid, annatto will 



be indicatud hy a greenish-blue, and saffron liy a bliio coloration. 
On adding a fow drops of boi-ic acid solution (or a solution of borax 
to which sufficient hydrochloric acid has Iwen added to distinctly 
reddt^n litmus), and ag'^n evaporating, luitnei'ie will be indicated 
by ft bright browniah-red coloration, changed to blue, gi'oen, or 
Tiolot by cnuatic alkalies, Dinitro-erm'l and ilinitrn-naphlhol will 
be detected by treating the residue with ninmoaia, and adding excess 
of hydrochloric acid, when a light yellow crystalline ptecijiitate 
will bo formed, soluble in ether. The I'osidue obtained, on evapo- 
mting the ethereal Bolution, is soluble in alcohol, and after dilu- 
tion with water the hot solution will dye a fibre of silk or wool 
yellow without n mordant. 

R. W. Moore has pointed out (Anaiyst, xi. 163) that, when a 
butter coloured with earolin is dissolved in carbon disulphide and 
shaken with alcohol, as prescribed by Martin, the alcohol remains 
colourless, while the lower layer is deeply coloured ; but on adding 
a drop at n dilute solution of ferric chloride and again shaking, a 
gradual change is observed, the alcoholic layer becoming distinctly 
yellow and the bisulphide solution of the fats quite colourless, or 
retaining only the pale yellow colour due to the natural colouring 
matter of tbe butter. Excess of ferric chloride must be avoided. 

A. R. Leeds (^nn/^s/,xii. 150) lias described a general method 
for the detection of butter-colourings. He recommends that 100 
grammes of the butter should be dissolved in a tapped separator in 
300 c.c of petroleum ether of about 0'C38 specific gravity. The 
water, &e., are tapped ofii and ethereal solution of the fat and colour 
ing matters washed several times by agitation with water. The 
ethereal solution, poured off from any stearin which mny have 
wpamted on standing, is then shaken with 50 c.c. of n deciuortual 
BoIution of caustic potash (5'6I grammes of KHO )iL'r litre), 
which is usually sufficient to effect the solution of all colouring 
matters capable of being dissolved by dilute alkali.' The alkaline 
solution is separated from the ethereal layer, and very cautiously 
treated with dilute hydrochloric acid until faintly acid to litmus 
paper. The precipitate, consisting of colouring matter mixed with 
a little fatty ncid, is filtered off and washed with cold water. If 
I Jealr ed, it may be weighed. 

^^Bke following table shows tbe reactions of the colouring mattery 
^^Hted in the above manner, when two or three drops of their 

^^^Bven alter ogitttion with caustic alkitU tbe petroleum ethor alwtiys retaiui 
I ftpalo yetlnw colonr, which is uot remorod or Uraencd by rcpeutting tile treat- 
ment with alkalL This h duo to the iiBtTirel or yollowiali colour of Uiu butter 
ud not to oay added colouring D)«tt«ra. It may bo destroyed 
r aeunible cliaage to tlie butter fat. 



alcoholic solutions were treated with an equal measure of the reagents 
(acids) mentioned. 


Reaction with 




Sulphuric Acid. 

Nitric Acid. 

Mixed Salphorio 
and Nitric Adds. 




Indigo • blue, 

Blue, becoming 



No change, or 
merelr dirty 

changing to 

colourless on 

colourleas on 




yellow or bnfvn 
No change, or 

Annatto with 

Blue, becoming 
green, and 

Blue, becoming 



green and 

6nly dirty yel- 


slowly chang- 
ing to violet. 







Violet becoming 
yellow on eva- 
poratiooof the 

Turmeric with 

Violet, chang- 

Violet to red- 

Violet to red- 

Very flne violet 


ing to purple. 





Violet to cobalt 

Light blue. 

Light blue. 

Yellow, changing 

blue, chanc- 

changing to 
light reddish- 

changing to 
light retVdish- 

to diriy yellow. 




Saffron with 

Dark blue, 

Blue, changing 
to green and 

Blue, rapidly 

Yellow, becom- 


rapidly chang- 
ing to reddish- 

chancing to 

ing dirty yel- 







Amber brown. 


with reii fumes 
and odour of 
burnt sugar. 


Carrot wltfj 

Red dish-Tiro wn 

Yellow and de- 

Yellow and de- 

Slightly brown. 


to purple. 






Dark olive green. 

Blue, instantly 


Oreen to yellow- 

not changing 

changing to a 


in colour. 

dirty yellow- 


Light brown. 

Partially de- 


No change. 

Aniline yellow. 





Martius' yellow. 

Pale yell«»w. 

Yellow - red 
precipitate ; 
magenta at 


Yellow preci- 
pitate, which 
when treated 
with ammonia 
and heated. 

Victoria yel- 

Partially de- 

Partially de- 

Partially de- 

Yellow colour 





returns on 

with ammonia. 

The butter-colouring sold as " carottine" is apparently a solution 
of 1 part of annatto in 4 parts of oil, the annatto being partially 
replaced by turmeric for the lighter shades. " Orantia" is a 
solution of annatto and carbonate of sodium in water. 

Carotin, the colouring matter contained in the root of the 
carrot {Dauciui carofa), may be prepared by exhausting the finely- 
divided root with water, precipitating the solution with tannin 



ntid a little sulphuric nciil, nnd exhausting the wnshed precipitate 
with boiling alcohol at 80 per cent. This takes up m n n n i t o 1, 
(!^Hj^O^ and hjdrocarotin, a body closely ruaembliug cho- 
ItiBterin. The residue iuBoIuble in alcohol is treated with 
eatboo disulphide, the resultant solution evaporated, and the 
rusidue treated with absolute alcohol. The solution obtained 
yields, on couccntration, a precipitate of r«rotin as a brownish-red 
eiyslalline substance with a metallic tetlection. Pure cutotiii forms 
riiombic leitduts, which ap])eiir blue in reflected and red-orange in 
traDsmitted light. It is soluble in benzene and carbon disulphide, 
but insoluble in water or hydrous alcohoL Carotiu is decolorised 
by heat or exposure to light It dissolves in sulphuric acid with 
indigo-blue or violet colour, wtiile sulphurous acid also colours it 
indigo-blue. With iodine it yields a derivative of deep green 
colour and metallic lustre. 

Husemann attributed to carotin the formula CigHsjO, Iml 
according to Arnaud this was probably an oxidised product, 
tho pure subslance being an unsaturated hydrocarbon of the 
formula, Cjallssi which he proposed to call carotene. This 
Intter formula is probably incorrect, as no other coloured hydro* 
carbon is known. 

Carotin appears to be a constant and normal product of vege- 
table life, and to be frequently present in the leaves of tlie most 
vigorous plants, and consequently those that are the most intensely 
green, its presence in such cases being masked by the green colour 
of the chlorophyll. It may be detected and approximately estimated 
by carefully drying the leaves in a vacuum dver sulphuric acid, 
digesting in the cold for ten days with petroleum spirit, evaporating 
to dryness in an open dish, and dissolving the residue in a little 
carbon disulphide. The resultant solution is intensely red, and is 
examinetl colorimetricoUy against a standard solution of pure 
crystallised carotin, containing O'OIO giumme per litre. The pro- 
portion of carotin in dry leaves often approaches O'l per cent, 
(it. A. Arnaud, Jour. Sm. Dffov, ^c, iii. 99). 

TcBHERio or Indian Safkbon (page 341) is the tuber or 
underground stem of Curcuma lineloria or longa and C rotttaila. 
Tho colour of the roots externally is generally greyish, but in th" 
interior they are usually a deep yellow.' 

I The jiriDcipal comueicial varietiea of CDrmenc are: — Chiaeat, I'nnsisting 
af nmny cwntral rhizomisa with weU-dcviloped briuiclies; Bnignl, niostly in 
*l«ndar linuchia of a docp rcdilinh tint ; Java, which coiuJstH of rather smalt 
tnbm* &□■! brtnoliea that nn ofton tnnsvi>rac1y and iDDgittuliuuUy cat: Nnd 
Cixkin lurntTu;, io neotionii or slicos o[ > larger tuber, Hiino boiiig marked with 
istliei Luge dpiirciseil ttfin-ji'iirs. 



According to John, turmeric-root contains : — ^yellowish volatile 
oil, 1 ; yellowish-brown resin, 10 to 11; brown extractive matter, 
with dyeing properties, 11 to 12; gummy matter, 1 4 ; matter 
soluble in alkalies, including earthy salts, 57 ; and moisture, loss, 
<fec,, 7 to 5 per cent. The presence of starch is not indicated in 
this analysis, though turmeric-root contains a sufficient proportion 
for iodine solution to change the whole colour from yellow to blue. 

The powder of turmeric has a strong odour and a very bright 
orange colour. The taste is bitter and aromatic. Ck)ld water dis- 
solves but little colouring matter, but boiling water extracts a 
larger quantity. Alcohol dissolves the colouring matter freely, and 
likewise takes up the greater part of the resin. 

Curcumin, C^^Hi^O^, is prepared by F. W. D a u b e by steaming 
powdered turmeric to remove the volatile oil, washing with boiling 
water till the washings are no longer coloured, drying, and extract- 
ing the residue with a'lai^e quantity of boiling benzene. The 
solution is evaporated to the crystallising point, the crystals dis- 
solved in spirit, the solution precipitated with basic lead acetate, 
and the lead compound decomposed by sulphuretted hydrc^n. The 
product is recrystallised from boiling alcohoL Another method is 
to exhaust ground turmeric with carbon disulphide to remove the 
volatile oil and resinous matters, and treat the residue with weak 
caustic alkali. On neutralising the alkaline solution with an acid, 
the curcumin is precipitated, and after drying may be recrystallised 
from ether. 

According to Jackson and M e n k e (Amer, Chein, Jour,, iv. 
77, and Jour, Chem, Soc., xlii. 1107) curcumin may be obtained 
pure by treating ground turmeric-root >\'ith petroleum spirit to 
remove the volatile oil, and then with ether, which dissolves the 
curcumin together with a large quantity of resin. The product is 
purified by crystallisation from alcohoL Thus prepared, curcumin 
crystallises from hot alcohol in stout needles or shining prisms, 
which have an orange or red colour and a beautiful blue reflection. 
Curcumin is odourless when pure, melts at 178** C, and is only 
slightly soluble in water, even when boiling. It is difficultly 
soluble in cold but more readily in boiling alcohol, and is also 
soluble in ether, the solution exhibiting a strong green fluorescence. 
It is also soluble in wood spirit and glacial acetic acid, but only 
slightly so in benzene or carbon disulphide, and is all but insoluble 
in petroleum spirit. Strong sulphuric acid dissolves curcumin with 
fine reddish -purple colour, gradually changing to black from char- 
ring, and the same efiect is i^roduced, though more slowly, by 
strong hydrochloric acid. 

Curcumin dissolves readily with reddish-brown colour in solu- 


lioiie of caustic and carbonated alkalies, and to a slight extent 

when boiled with water and calcium carbonate. The ammoniacal 

solntion gives off ammonia when boiled, and deposits curcumin. 

On adding a large excess of strong alcoholic iiotash to a hot alco- 

il holic solution of curcumin, the potassium salt, CjjHijKjO,, 

L^iyuBtes in globular radiated groups of flame-coloured crystals, 

^^^Beh oasuine a claret colour when dried. The precipitation mav 

^^Btnade more perfect by adding ether, iu which the new compound 

I^^Eliearl; insoluble, though soluble in alcohol and freely so in 

1^ initer- On exposure to air, the alcoholic solution of potasflium 

curcumate assumes a magenta colour, probably frOm oxidation. 

When excess of potassium carbonate is added to a hot solutibu of 

curcumin in absolute alcohol, the acid salt, Ci^H^KO^, is 

fonned, and on adding ether separates in crimson-black Hooka 

resembling magenta. The solution gives coloured precipitates with 

metallic salts. 

JJy treatment with chromic acid mixture cimiumin is completely 
oxidised to acetic and carbonic acids, without any terephthoJic acid 
(page 47) being formed, IJy oxidation with permanganate in alka- 
line solution it yields vanillin (page 62). 

In consequence of the sensitiveness of curcumin to alkalies, tur- 
meric is sometimes used as an indicator of alkalinity. The yellow 
colour is rcstoretl by very weak acids, and hence turmeric has been 
proposed for titrating fatty acids, for which purpose, however, 
phenol-phthalein is better adapted (see vol. ii. 76 ; and R. T. 
Thomson, Jaw: Sue Ghem. Iml, vi. 195). The alcoholic 
solution of turmeric exhibits a well-marked fluorescence. 

The most characteristic reaction of curcumin and turmeric is 
that with boric acid. If on alcoholic solution of turmeric or 
curcumin be mixed with one of Ijoric acid, it becomes of ileep red 
colour, distinct from tlmt produced by alkalies, A convenient way 
of applying the test is to place a small disk of lilter-paper, about 
1 iucli in diameter, in the turmeric tincture, and evaporate the 
latter to diyness at 100*. On the paper is then poured ait ai|ueo<us 
solution of boric acid, or a solution of borax to which sufficient 
hydrochloric acid has been added to render it distinctly acid to 
" iBua, The red colour will probably be nt once developed, but if 
\ will become apparent on evaporating the liquid to dryness, 
low adding a drop of caustic dkali, n very beautiful series of 
B will be produced, green and purple being tlio most pro- 
L aiiunt. On adding bydrocliloric acid a red colour is produced 
which is again turned green and blue on addition of excess of alkali. 
' In isri, the autliDr recommenJed this mode ot opBrKling to eflect the 
Mtiou <tS tnnncric hi mustard (CAcni. A>uu, xxx. llS). 


The reaction of curcumin with boric acid appears to be doe 
to the formation of a substance called by Schlumberger 
rosocyanin, which may be prepared by treating an alcoholic 
solution of curcumin with boric and sulphuric acids. The liquid 
acquires a deep red colour, which changes gradually in the cold, 
and rapidly on heating, to dark red, orange, and finally to yellow. 
Hence the operation should be arrested when a sample is found to 
become blue on adding ammonia. The impure rosocyanin ciystallises 
out as the solution cools. When pure, it forms dark red needles 
with a green reflection, and is insoluble in water, ether, or benzene. 
The alcoholic solution has an intense rose-red colour, but rapidly 
changes. It is turned blue by ammonia, the original colour return- 
ing on adding an acid. The alkaline solution becomes grey on 
exposure to air, and gives blue precipitates with lime or baryta 

Turmeric is not employed alone as a dye for fabrics (except in 
China), but is used to some extent in certain mixed colours known 
as '* sour browns." It is one of the few colouring matters for 
which cotton has a strong attraction. Cotton may be dyed with- 
out a mordant by heating in a bath of turmeric at 60*. Turmeric 
is also employed in paper-staining, and for dyeing wood and leather ; 
also as a colouring for butter, cheese, pastry, &c. It is an im- 
portant ingredient of curry powder. 

Powdered turmeric is sometimes adulterated with starch and 
mineral matters. The ash should not exceed 5 to 6 per cent. 
Common salt is added to turmeric to give it a brighter appearance, 
but interferes with some of its uses. Turmeric should be quite 
dry. If damp it becomes yellowish-brown, and is rendered unfit 
for its chief applications. The characteristics of good turmeric are 
a rich, deep, but bright, orange colour, and a strong aromatic, rather 
pungent odour. Turmeric may be assayed by dyeing equal weights 
of white woollen cloth at 60** C. with solutions of equal weights of 
the samples, using no mordant. The dyed pieces are examined for 
depth of colour, and also held horizontally in front of a window 
and viewed along the surface. In this position cloth dyed with 
good turmeric shows a beautiful golden lustre, on the purity of 
which its value for many purposes depends, as for the yellow cotton 
warps of figured table-covers. 

On the fibre, turmeric is turned reddish-brown by hydrochloric 
acid, or an acid solution of stannous chloride, without the solution 
becoming coloured. Caustic soda and ammonia turn the fibre bright 
reddish- brown, the solution becoming brownish-orange. Alcohol 
extracts the colour, producing an orange or yellow solution with 
green fluorescence. Nitric acid turns the fibre pale yellow. 

'aubogb (pnge 340) is a gnni'resin [iroduced hj trees growing 

arious parts of tbe Malay peninsiita. It ocoitb in cyliiidri<:iil, 

or solid rolls,' longitudinally striated on the surface, and 

distinct or more or less ^glutinated or folded together in 

Externally it is brown ieh-y el low, and is covered with a 

powder, "When broken it exhibits a vitreous or conchoidal 

fmcturo, the fractured surface being opaque, smooth, glistening, 

and of a uniform reddiah-yellow colour. The powder is bright 

j^low, and forms a yellow emulsion with water. Although nearly 

lOut odour at the ordinary temperature, gamboge evolves a very 

'iar emell when heated. Tbe taste is nt first scarcely per- 

lible, but after a time it produces a sharp acrid sensation in the 

Gamboge acts as a dmstic purgative, and is the active 

constituent of a well-known patent pill. 

Oambogin or Gambogic Acid, the resin of gamboge, according to 
hner has the formula CjjHjjOg. It may bo obtained by 
lipitating the filtered alcoholic solution of gamboge by water, 
iting the dried precipitate with ether, and evaporating the 
d solution. It may be obtained less pure by treating the 
original gamboge with ether. Gamboge is a transparent, vitreous, 
brittle resin, breaking with a conchoidal fracture. The colour is 
hyacinth- or orange-red, and the powder bright yellow. It softens 
on beating and melts at TS^-SO" C, soUdifying to a glassy mass 
on cooling. It ia tasteless, and, according to Htu^t, has no purga- 
tive action. Gamboge-resin is readily soluble in alcohol, ether, 
klid chloroform, but is only slightly soluble in petroleum spirit. 
ibogin has well-marked acid properties, decomposing carbonates 
the alkali-metals at a boiling heat. It dissolves in caustic 
lies with orange-red colonr, and is precipitated in gelatinous 
'flakes on acidulating the solution. On adding excess of common 
salt to the solution of gambogiu in caustic soda, the sodium 
salt is thrown down as a red precipitate. 

The leax, the portion of gamboge insoluble in ether hut dia- 
by alcohol, is described by U u rs t as a soft brownish sub- 
, melting readily and having slight bitter taste, and persistent 
after-tnste, with slight purgative action. It is soluble in 
i soda with brownish -yellow colour, being reprecipitated on 
; an acid. 

gwn of gamboge, according to G. H. Hurst, is a transparent, 
lish mass, having a sweetish taste and slightly adhesive pro- 

■• oytJDdrical variety of gHinboge is proiluceil tiy ruDaing tbe jnics iato 
^bocMMiui. On drying, tin: ^lubngo cnntiacta, and conaequeutly boles ore 
n through the iiiiilille of the cjlin Jen. Inrmur ganibogo often occura 
Iar luaaBEa neighing sDveml potimla. 

taa I 




perties. It is soluble in water to form an opalescent solution, 
rendered clear by acids, and which is not precipitated by basic 
lead acetate, ferric chloride, mercuric chloride, borax, or alcohol 
It appears to be a glucoside. 

Gamboge dissolves in alcohol, in ether, and in annnonia. The 
ammouiacal solution produces a red precipitate with salts of barium^ 
yellow with those of zinc, reddish-yellow with lead acetate, and 
brownish-yellow with silver nitrate. 

The following analyses by Christison indicate the composi- 
tion of commercial gamboge : — 



1 ' 

Cake Gamboge 
from Slam. 

Ceylon Gamboge. 

Realn, ... 74 2 
Gum, ... 21-8 
Amylaceotts matter, ' ... 
Woody fibre, . 1 ... 
Moisture, . . ' 4*8 


• •• 













• •• 



• • • 


• •• 


• •• 


• •• 





100-4 i 99-6 






A sample of gamboge recently analysed by G. H. Hurst 
{Pharm. Jour,, [3], xix. 761) contained : — moisture, 2*50 ; mineral 
matter, 1*05; resin, soluble in ether, 66'05 ; wax, soluble in 
alcohol, 4*31 ; and gum, 26*03 per cent.; total, 99*94. 

Commercial gamboge is liable to adulteration with mineral 
matters and starch. The ash should not much exceed 1 per cent 
Starch may be detected by exhausting with alcohol, boiling the 
residue with water, and adding iodine to the cooled liquid, when 
the well-known blue coloration will be produced if starch be 
present. An emulsion, made by boiling the powdered sample with 
water, gives after cooling a green coloration with iodine in the 
presence of starch. It will bo observed that the analyses of 
Christison of cake gtimboge from Siam show a small proportion of 

Gamboge is not employed as a dye. It has a limited use in 
medicine as a purgative, and is employed as a yellow pigment iu 
water-colour painting. 

Dyes of Animal Origin. 

The colouring matters contained in the blood, bile, and urine 
receive no practical application, and, so far as they require descrip- 
tion, will be more conveniently considered in the sequel. Exclu- 
sive of colouring matters, such as murexide and jpitLSsian blue, which 
are prepared by complex chemical reactions from substances origin- 
ally obtained from animals, the only dyes of animal origin which 



pile descriptioa are ericMnfo/, lae-dye, anA kcrmea. Theee are 
1 from tlireo distinct species of n peculiar tribe of insects 
callod CMciwt. 

CocHiSBAi is the female of the Ojcciw earM, an insect which 
]ivo3 and propagates on certain kinds of coctus, especially the nnpel, 
orCaclM opMWdfl. a plfint which grows wild in Mexico, though the 
inaects collected from the cidtivatod plant are the superior. The 
weight of the dried insect is about O'l grain, and hence 70,000 are 
required to produce 1 lb. of cochineal, The two chief varieties of 
cochineal are the white or nilcT <jrain, and the llaek grain. A 
third inferior variety, called the ijranilla, consists of very small 
iDsecte, probably unirapregnated females. The silver gffdn, which 
is the finest kind of cochineal, probably consists of young females 
after impregnation, and the black grain of the mothers after the 
eggs liave been laid. Accordiny to other descriptions, the colour 
_ ' a depends on the method employed for killing and dry- 

gUw insects (see Jour. Soe. Chsin. Ind., I 181). 

minic Acid, C^jHigOju, the colour-principle of cochineal, is 

j^aied by SchUtzenberger by washing the cochineal graina 
(insects) with ether, to remove fat, aud then treating them several 
times with warm water. On treating the filtered liquid with a 
alightly acid solution of lead acetate, the whole of the colouring 
matter is thrown do^vn as a violet-hlue precipitate. Tlio concen- 
trated filtrate deposits otystals of tyrosine, while the preci- 
pilate consists of camiinate and phosphate of lead, with a little 
nitrogenous matter. This is removed by tliorough washing with 
water, and the purified precipitate is susjiended with wann water 
and treated with barely sulfictent sulphuric acid to decompose the 
lead carminate, leaving the phosphate unattached. The solution 
of the carminic acid thus obtained is evajwrated to dryness at a 
temperature not exceeding iC-SO" C, and residue dissolved in 
absolute alcohol, which on evaporation and cooling yields the 
oanninic acid in crystals. It may be further purified by dissolv- 
ing it in ivater, filtering, evaporating, and recryatoUising the residue 
from absolute alcohol or ether. 

Camunic acid \e a, purple substance soluble in water, alcohol, 
carbon disiilphide and benzene, aud slightly soluble in ether. It 
does not melt or decompose at 135" C., and dissolves without de- 
composition in strong sulphuric and hydrochloric acids. Chlorine, 
, anil iodine readily destroy carminic acid, and nascent 
1 rediKes it to a luuco-body, which again becomes red on 
» to air. 

iln of carminic acid, according to Schiitzenbcrger, is 
, but irinsiwetz and Grnbowski obtained potas- 


slum and barium salts corresponding to C^^HigOjo, and found 
that when boiled with dilute acids carminic acid was split up into 
a sugar and carmine-red, a purple-red substance, which appears 
green by reflected light, and is cinnabar-red in powder. It is in- 
soluble in ether, but soluble in water and alcohol with red colour. 

Carminic acid dissolves in caustic alkalies with beautiful red 
colour. Sodium carminate crystallises in purple plates. An 
aqueous solution of carminic acid gives purple precipitates with 
baryta and lime water, barium chloride, lead acetate, and cupric 
acetate ; with stannic chloride, a red precipitate ; and with potas- 
sium oxalate or acid tartrate, an orange-red precipitate. Alumina 
removes the whole of the colouring matter from an aqueous solu- 
tion of carminic acid, yielding a fine red lake, which when heated 
becomes crimson and purple. The addition of aluminium acetate 
or a little acid to the lake produces the same change of colour. 

A decoction of cochineal behaves with reagents somewhat differ- 
ently from a solution of pure carminic acid, owing to the presence 
of phosphates, tyrosine, &c. Acids produce a slight precipitate, 
and change the colour to a yellowish-red, while alkalies change it 
to violet. Lime-water, salts of copper, lead and zinc, and stannous 
chloride free from excess of acid give violet precipitates, while 
stannic chloride gives a scarlet coloration. Ferrous sulphate pro- 
duces a violet-grey coloration and precipitate, and ferric acetate a 
brown precipitate, changing to olive-green. Alum changes the 
colour of a solution of cochineal to red, a precipitate being also 
formed; while aluminium chloride produces a reddish-violet pre- 
cipitate, the supernatant liquor becoming crimson. 

By heating carminic acid or carmine to 200° C. with water or 
dilute hydrochloric acid, or to 140° with strong sulphuric acid, an 
insoluble red body called ruficarmine or ruficoccin is 

Cochineal is somewhat liable to adulteration. A fraud said to 
be commonly practised at certain places consists in removing part 
of the colouring matter by a short immersion in water. After re- 
drying, the partially exhausted material is sold as " black cochi- 
neal," or faced by agitation with talc, sulphate of barium, or sulphate 
of lead, and sold as " white cochineal** On powdering such a 
sample and treating it with water, the mineral adulterant will fall 
to the bottom of the liquid. Black iron sand, to the amount of 
12^ per cent., has been recorded as an adulterant of black Tene- 
riffe cochineal {Jour, Soc. Chem. Ind.y i. 144); and graphite and 
black oxide of manganese are other probable adulterants. Accord- 
ing to L o e w e, genuine cochineal leaves only 0*5 to 0*6 per cent, 
of ash on ignition. 


ullier came the cocbiueal ia subjectad to au atmosphere of 
Lcani, and when the j^ins have swollen and become dump 
a the exudation of an ndhesivo juice they are rotated in a drum 
with the mineral adulterant, of whith they take up from 10 to 12 
]ier cent. On re-drying, the grains ahrink up and assume their 
originnl nppearaneo (Loewe, Pharm. Jour., [3], xiii. 590). 

The specific gravity of cochineal is a useful prelimiiiary test of 
qnality. Heavy samples are always inferior or adulterated. Par- 
tially exhausted cochineal ia always deeply wrinkled, and does not, 
^^^en treated with wati^r, take up moisture equally, so that some 
^^B'the insects or "grains" float, and utiters bticome only partly 

^^KTd delect cochineal in alimentary substances, E, Lagorce re- 
'' eommends that the substance ahoidd be dissolved in water or weak 
alcohol rendered faintly acid with acetic acid. The liquid is then 
agitated with amylic alcohol, which is separated and evaporated in 
presence of water, Tlie arjueous solution obtained is treated with 
n few drops of a 3 per cent, solution of uranium acetate, when a 
beantiful bluish-green coloration or precipitate will be produced if 
cochineal bo present. Acids destroy this colour, with production 
of the orange tint of the c.arminic acid. In the case of wine, the 
amylic alcohol cmpbyed should be mixed with an equal measure 
of benzene, or, preferably, toluene, as otherwise tenolin will also be 
taken op, and will mask the reaction of the cochineal, Ammoniacal 
cochineal, which has been occasionally employed to colour wine, 
produces a rosc-violet or violet-blue lake with uranium oxide. 
Logwood gives a somewhat similar reaction, but may be distin- 
guished from cochineal by other means. 

Cochineal has been ooeasionally adulterated with an extract of 
ImiEil-wood, This may bo detected by treating the decoction with 
^"^ ! of Ume-watcr, which completely precipitates the colouring 
r of cochineal, while if brazil-vrood lie present the filternd 
Pdd will liave a purjile or violet colour. Brazil-wood may also 
letacted by soakiiig cotton in the decoction and then immersing 
1 a warm solution of potassium bichromate, when the tissue 
n oasurae mther a deep colour if brazil-wood be present. 

B essay of cocJiineal may be effected by boiling 1 graninie of 

E powdered sample for an hour with 1 litre of water and 'IQ drops 

\ Batuiated solution of alum. After cooling, the liquid is a),'ain 

e np to 1 litre, and the colour compared with that of a staniUrd 

nmen similarly treated. 

", Lieberman {Jour. StK. Dj/en, ^c, i. 269) recommends 
b the cochineal should be exhausted as completely as possible 
h boiling water, and then precipitated with a slightly acid solu- 


tion of lead acetate. The precipitate is washed with warm water, 
dried, and weighed, and the lead determined in an aliquot jmrt of 
it. By deducting the amount of oxide of lead in the precipitate 
from the weight of the latter, that of the colouring matter is found. 
This method is open to the objection that phosphoric acid and 
other matters are estimated as carminic acid. Hence a more 
accurate result would be obtained by simply igniting the impure 
carminate of lead, and deducting the weight of the residue from 
that of the original precipitate. A still better determination of the 
colouring matter might probably be obtained by treating the moist 
lead precipitate with a slight excess of dilute sulphuric acid, 
filtering from the sulphate of lead, rendering the filtrate strongly 
alkaline with caustic soda, and running in a standard solution of 
potassium ferricyanide until the purple colour of the solution changed 
to a dull reddish-brown. The use of ferricyanide in alkaline solu- 
tion for the assay of cochineal was suggested by Penny; but when 
the original decoction is operated on, as proposed by him, the 
results are not satisfactory. 

Cochineal may also be assayed by a mihiature dye-test A 
suitable bath may be prepared from 1 gramme of finely powdered 
cochineal, 1 gramme of cream of tartar, IJ gramme of alum, and 
1 litre of water. 7 grammes of flannel should first be immersed 
and dyed to a full tone, and a second piece of the same weight then 
introduced, and allowed to remain till the bath is exhausted. 

Cochineal is not used in cotton-dyeing. In dyeing silk it has 
also been almost entirely superseded by aniline-reds, and in wool- 
dyeing the azo-colours have to a great extent replaced it ; though 
many dyers prefer to use cochineal or alizarin colours for all 
scarlets, since these dyes do not bleed and stain the neighbouring 
fibres like the azo-reds. Two distinct red shades are obtained 
with cochineal, according to the mordant used. Cochineal crimson 
is mordanted with cream of tartar and alum, with or without tin 
salts ; while cochineal scarlet is mordanted with stannous chloride 
and cream of tartar or oxalic acid. Cochineal reds on wool are 
fairly fast to light, but become dull or bluish by Uie action of weak 
alkalies or soap, though the bright tone may be restored by im- 
mersing the fabric in water acidulated with acetic acid. A good 
purple colour can be obtained by dyeing wool mordanted with 2 per 
cent, of potassium bichromate in a slightly acid cochineal bath. 

Fibres dyed with cochineal are turned orange-red by hydro- 
chloric acid, the liquid becoming pink. Sulphuric acid turns both 
fibre and solution a bright pink. Caustic soda and ammonia give 
a purple solution. Alcohol has no action, and an acid solution of 
stannous chloride behaves much like hydrochloric acid alone. 


Avimtmiacai cMhiwal ia prepared by leaving ground cochineal 
mtact iritL excrss of anuuonia, when a diemical action occuie 
suits, acuording to Schiitzciibergor, in the fonnatiou of 
amido-coni pound called cumiinamide. After several 
" e the laixturo ia heated to drive off part of the ammonia, 
8 aODt into commerce in tUo form of a thick past?. Instead 
cheating the product directly, it is BoraeUmes mixed with about 
9 per cent, of hydrated alumina, and the whole then heated till 

odour of ammonia can bo oLaerved. 'VVlien cold the mnsa is 
Tioulded into cakes. 

Ammoniacal cochineal u distinguished from carminic acid by 
giving n beautiful purple precipitate (instead of scarlet) with 
"oxymuriato" of tin. The crimson, purple, and mauve colours 
it yields with mordants aro not affected by acida so readUy as those 
produced directly by cochineal. Ammoniacal cochineal is used in 
admixture with ordinary cochineal for producing the bluer shades 

1 pinks. 

wCochineai Carmim or Carmiiw Lake is a brilliant red pigment 
)duced by precipitating a decoction of cochineal by alum 
I atannic chloride. Acid oxalate or tartrate of potassium may he 
d in conjunction with alum, but the employment of a compound 
I tin or aluminium appears to be essential to the production of the 
The employment of a decoction of cochineal itself, and 
rminic acid, is also a necessary condition, the nitrogenised 
httera being essential to its formation. The method by which 
hinenl-carmine is actually produced in practice is kept rigidly 
sample examined by C. Lieberman [J'/ur. S(«'. 
i. 269)contained, after drying, 3'7 per cent, of nitrt^en, 
r 0'25 per cent, of which could be expelled by boiling with 
Bute alkali. The remainder appeared to exist as proteide, or 
iDbably in port as tyrosine.^ The ash was white, and amounted 
I 8'I per cent, 100 parts contained 43 of alumina and 46 of lime, 
n7 of oxido of tin, and small proportions of magnesia, alkalies, 
i phosphoric acid. The composition of the original carmine was 

^ Sevsnil recil>ea, collected from atatiilard works, have been publisbnl by &I. 
Jaohan [PAnmi. Jour., [3], xvi. 611). The English procowUnaid tucon^Bl 
Kboiling 1 lb, of cDcLincnt and \ m. oi putasaium carbouate with 7 galloDB of 
r for IC minuteB, The beat httving beai witbdrawn, 1 oa, of powderoil 
U U sddsd, and tho liqaid stirred and allowed to settle. The clear liquid 
ecanted, { de. of iainglass addod, and beat ajipliod till a coagiiluni forms, 
lU tbu lii^uid is stirrad briskly and allowed to settle. 
V As albuntiu mid gelatin are sometimes employed in preparing carmiae, it 
' ■ not follow that tlio whole of the nitrogon present bad it* origin iu tlic 


probably approximately: — water, 17; mineral matter, 7; nitro- 
genous matters, 20 ; and colouring matter, 56 per cent. ; with 
traces of wax. 

Cochineal -carmine is liable to adulteration with starch, kaolin, 
vermilion, red-lead, chrome-red, &c. These admixtures may be 
detected by treating the sample with dilute ammonia, in which a 
pure sample should be completely and leadUj soluble.^ The 
solution of cochineal-carmine in ammonia yields no precipitate with 
ammonium oxalate, and the precipitate produced on adding an 
acid is a lake, from which the colouring matter can only be set 
free by heating with moderately strong mineral acid. If the 
ammoniacal solution of carmine be heated on the water-bath, with 
constant stirring, until entirely destitute of ammoniacal odour, 
the product is a deep ruby-red liquid which gives no precipi- 
tate with mercuric chloride, and becomes purplish on addition of 
ammonia. Vermilionette (page 168) can be recognised by treating 
the colouring matter with dilute sulphuric acid and agitating the 
liquid with ether, which on evaporation will leave the eosin in a 
condition ready for further examination. 

The following analyses of commercial cochineal-carmine are by 
M. Dechan {Phann. Jour., [3], xvi. fill). The sample was 
treated with dilute ammonia, the liquid filtered, the ammoniacal 
solution evaporated, and the residue dried at 100°, and weighed 
It was then ignited, and the aah weighed to obtain the combined 
aluminium, &c., the loss being regarded as colouring matter. The 
organic matter insoluble in ammonia appears to have consisted chiefly 
of starchy matters. In every case the aah was free from tin, and 
consisted of alumina and lime, with a trace of silica. 2so foreigu 
colouring matter other than vermilion was detected. 

! 1. 





8. 1 7. 


Mftlrtar. 1 82-1 

^K,'"{ss:f=;!';i.; i; 

ether, ivannllbn, 

09 '2 




7-0' 0* 


IS-* «r-r, 

1-4 Ififl 

Carmine is employed by artists, paper-stainers, and fabric-printers. 

' According to M. Declian, tin spirits form with Blebricli scarlet n compound 
wbjcli vi^ry much rescinbles carmine phyeicallj and chnmicatly, being, like 
it, soluble in dilute ammonia and insoluble in water. If Biebrich scarlet be 
preqent, white wool acquires a red-orange tint when boiled in the ammoniacal 
sntution, whi'reOB pure cochineal carmins commnnicateB a reddish -purple shade, 
Biebrich carmine need not be looked for in tlie atuence of tin. 



composed of the female of the Cueetu ilicin, an insect I 
id on the Hex or Qmiftu eacei/fi-a, a slirub growiiig on arid, 
soils in hot climates. The gratua arc about the size of a. pea, 
>ular, and almost smooth. Kermes of good (juality has a, deep red 
HIT, ogreeaWe odour, and rough, pungent taste. The red ooloui'- 
niattcr is soluhlu iu water and alcohol, and is either identical 
i^th or closely related to ttie c a r ni i ii i c acid of cochiueal (page ■ 
S63). The deeoetion is turned yellow or brownish by acids, and I 
violet or crimson by alkalies. Terrous sulphate blackens it, prob- 
ably owing to the presence of a small quantity of tannin from the I 
oak on whicli the insect lives. Kermes dyes fabrics mordanted I 
with alum n Wood-red j with stannous chloride and cream of tartar I 
it gives a ciunnmou-yellowj and with salts of copper and cie&m of 1 
lartur, an oliTo-green. It requires about twelve times as much. | 
kermea as cochineal to produce the same scarlet with a tin n 
dant. Kermes ia but little used in England. 

Lac-Dve is the product of the Cocew larca, which lives on the 
banyan and other trees, on the twigs of which the ova are deposited, I 
From the mature and impregnated female insects a resinous sub- J 
»Uinue exudes which encloses them. The twigs, with the attached I 
resin and enclosed insects, are sold as xtiek-lat: If the resinous con- 
cretion be removed, powdered, and triturated with water, the greater \ 
Iiart of the colouring matter dissolves, and the residue when dried I 
is known as neeil-lae. If this be melted and squeezed tlirough 
cotton, it yields kIwH-Ioh or nhrllac. The following figures by 
lintchett indicate the relative composition of these three lacs; — i 


Uoiiv. . . 


Colauling matter, 





6 '5 

Foteifiti bodies, . 


LOM, . . . 


Sml-lac Sliell-kc. 

^^HtThe exiict method of preparing lac-dye is not generally known, 
PH& it ia proliably 1>nsed on the treatment of stick -lac with a weak 
I- alkaline solution. The composition of the ash points to a preci- 
pitation with alum, or with lime to which some alumina has been 
added, probably to facilitate the ^vashing and working up the preci- 
pitate (com [are H. G. Glasspoole, Pkarm. Jour.,\Z\%a. 741). 
The colouring matter of lac-dye lias been investigated by R. E. 
Schmidt {Jour. Soe. Lh/ere, ifc, iii. 122), who terms it lac- 
At II i c n c i d, and points out its close resemblance to carminic acid. 











370 LAC DYE. 

Laccainic Acid, CigH^jOg, forms a brownish-red ciystalline 
powder or crust, appearing under the microscope in well-formed 
rhombic tables. It melts without decomposition at 180°. It is 
abundantly, though slowly, soluble in alcohol, and freely soluble 
in wood spirit, amylic alcohol, and glacial acetic acid. It is some- 
what less soluble in water, with bluish-red colour, and is insoluble 
in benzene and petroleum spirit. It resembles carminic acid in 
being nearly insoluble in ether, but not precipitated on adding ether 
to its alcoholic solution. It is a well-defined dibasic acid, and in 
its reactions and the absorption-spectrum of its alkali-metal salts 
closely resembles carminic acid; but a difference exists between 
the absorption-spectra of the two substances when dissolved in 
strong sulphuric acid. 

Schmidt gives the following results obtained by the analysis 
of two samples of lac-dye: — 

Moisture (expelled at 100"), . 

Mineral matter, 

Colouring matter, .... 
Other organic matter, .... 

100-0 100-00 

A good lac-dye should be soft enough to be broken with the 
fingers, and should powder readily under the pestle. The fracture 
should be deep in colour, not shining and resinous. When breath- 
ing on, it should emit a strong and peculiar odour. Samples 
which are hard and have a resinous fracture are usually poor in 
colouring matter, and contain an excessive proportion of resin. 
The amount of this constituent may be judged of from the bulk of 
the precipitate produced on diluting the alcoholic solution of the 
lac with water. 

A superior variety of lac-dye is obtainable by treating stick-lac 
with weak ammonia, and adding stannous chloride to the solution, 
when the colouring matter is thrown down as a fine red precipitate. 
A lac-lake is obtained by substituting caustic soda and alum for 
the ammonia and tin salt in the above process. Lac-lake usually 
contains about 50 per cent, of colouring matter, 40 of resin, 9 of 
alumina, and 1 per cent, of impurities. 

Lac-dye gives much the same colour as cochineal, but two or 
three times the quantity is requisite to produce the same effect 
It is prepared for dyeing by mixing it into a paste with stannous 
chloride and hydrochloric acid, and hence the dye and mordant 
are used in the same bath. Lac-reds are considered faster to light 
and wear and to the action of weak alkalies than cochineal teds, 


though they are less brilliant than the latt«r. The two colouring 
matters nre sonietimes employed consecutively or in admixture. 


The numljoT of dyes occurring in trade, and especially of those 
artificially prepared, is exceedingly great, and the difficulty of re- 
cc^ition consequent on their number and close reBcmblance is 
further increased by the practice of calling the same substance by 
Kveral different names. 

The methods of examining colouring matters with the ^new of 
identifying them require considerable modilicBtion when the dye 
already exists on a fibre or fabric, as the mordant and other con- 
ditiona affect its character considerably. Hence the recognition of 
the dyes or fabrics will bo described in a separate section (page 
389). In the ease of a concrete colouring matter it is desirable to 
ascertain the shade it cotmnuutcates to wool or silt;, as the colour 
which a dye will produce on a fibre can scarcely be guessed from 
its appearance in the solid state, and in many cases cannot even be 
predicted from the colour of the solution. 

The great point of resemblance in the generality of coal-tar dyes 
is that they are "substantive colours," or, in otlier words, will dye 
sillc and wool without a mordant. To ascertain whether the dye 
is of this character it is generally oidy necessary to heat a frag- 
ment of white wool or a skein of white silk in a solution of the 
dye ; usually a neutral or faintly acid solution is the best, but with 
alkali-blue (page 230) and a few other dyes the stuff should bo 
heated in the alkaline solution, and then removed and immersed in 
dilute acid, when the blue colour becomes fixed. Alizarin and 
pnrpuriu arc not substantive colours, and hence cannot be fixed on 
wool or silk without a mordant. 

The identilication of a coal-tar dye is much facilitated by a 
judicious employment of certain general reagents, which will suffice 
to dermo the substance as belonging to a certain class. The colour 
or absorption-spectrum of an aqueous or alcoholic solution of the 
dye is also a valuable indication, and water and alcohol may often 
be advantageously employed to effect a separation of mixed colours. 

Tht) following general methods of examination are of service in 
daaufying the coal-tar colours: — 

1. Agitato a small quantity of the dye with dilute sulphuric acid 
and ether. On separating the ether and evaporating it to dryness, 
a ftonublo residue will be left if the dye contained an acid dye, 
8 picric ncid (or a picrato), a nitrocresolate (victoria yellow), 


a nitronaphtholate (manchester yellow), aurin, an eosin, &c. The 
basic dyes are not removed from an acidulated aqueous solution by 
agitation with ether, and hence a complete separation of the above- 
named substances may be effected by a judicious employment of 
this method. 

2. Another indication of the nature of a dye is obtained by 
adding weak caustic soda to the aqueous solution and warming the 
liquid. Basic coal-tar dyes, except those of the safranine class 
(safranine, safranisol), are precipitated, while the solutions of acid 
dyes usually remain clear. 

3. E. Weingartner recommends for the distinction of 
soluble acid from basic dyes a reagent prepared by dissolving 
tannin and sodium acetate in water. The preparation and applica- 
tion of this reagent are described on page 377. 

4. By heating with acetic acid and zinc-dust, most basic coal-tar 
dyes are reduced with formation of colourless leuco-com- 
pounds, from which the colouring matters are reproducible only 
by the employment of moderately strong oxidising agents. The 
azo'dj/es similarly yield colourless hydrazo-compounds, 
but these differ from the leuco-derivatives by regenerating the 
original colouring matters on mere exposure to air. Somewhat 
different results are obtained if an alkaline reducing agent is em- 
ployed, and the method, which is of special value in studying azo- 
dyes, is described at length on page 211 et seq, 

5. J. Spill or {Chem. News, xlii. 191) has shown that treat- 
ment of the sample with concentrated sulphuric acid affords a 
valuable means of recognising coal-tar dyes, which are none of 
them charred by its action, except under very severe conditions. 
To apply the test it is merely necessary to heat a few grains of the 
^olid substance in a test-tube with concentrated sulphuric acid. 
Very frequently, useful information can be gained by observing 
the absorption-spectrum of the coloured liquid produced. The 
property of yieldmg a colourless solution with concentrated sulphuric 
acid, the liquid becoming coloured on dilution, is a characteristic 
reaction of several quinoHne di/es, and does not occur in the case 
of dyes of most other classes. Tabular statements of the reactions 
of various dyes with concentrated sulphuric acid are given on 
pages 171, 185, 186, 193, 198, 205, 224, 232, 235, 239, 255, 
273, 275, 277, 282. 

6. In the case of basic dyes, the determination of the nature of 
the acid often materially assists identification. In most instances 
the basic dyes occur in commerce as hydrochlorides, but exceptions 
to this rule are by no means rare. To detect the salt-radical the 
solution of the dye should be precipitated with ammonia or soda, 



and the filtered liquid acidulated with nitric acid and tested with 
silver nitrate. In some few cases, especially with safranine, the 
base of which is freely soluble in water, this method is not applic- 
able, and it is necessary to add the silver nitrate to the acidulated 
solution of the original dye. Double chlorides of the dye-base and 
zinc may be recognised by the presence of zinc in the ash left on 
incinerating the sample. Common salt is very commonly present 
in dyes, and it is important not to mistake the chlorine existing in 
this form for that existing as the hydrochloride of a basic dye. 
Common salt will be left as a residue on igniting the dye. On 
ignition, the eosins leave residues the solutions of which contain 
more or less haloid salts of the alkali-metals, and hence precipitate 
silver nitrate. But these dyes are not basic, and the colouring 
matter (containing one or more halogens in organic combination) 
can be separated from the pre-existing common salt by agitating the 
acidulated solution of the dye with ether (compare page 385). The 
following is a list of those basic dyes liable to be met with in 
commerce in other forms besides that of hydrochloride : — 

Name ol Dye. 

Formula of Base. 

Form of Combination. 

Magenta ; fuchsine ; roBani- 

line ; aniline red. 
Azaleine; fuchBine. 




Aniline blae ; triphenyl- 



Sulphate ; acetate (in alco- 
holic solution). 







Iodine green ; night green. 



Spirit soluble green. 



Benzaldehyde-green ; mala- 


Oxalate ; zinco-chloride ; 

ferrico- chloride. 

Mauve; Perkln'a purple. 



Nile blue. 






Nitrates, acetates, and oxalates, in a few cases in which they 
occur, can be sought for by the usual methods, in the filtrate from 
the precipitate produced on warming the dye with caustic soda. 
Picrates may be sought for in the same liquid, or the original 
solution may be strongly acidulated with dilute sulphuric acid, and 
agitated with benzene or ether. The mere detection of picric acid 


does not prove that the dye examined was a picrate, as free picric 
acid may have been added to the hydrochloride or double zinc ealt 
of the base. 

Many basic and other dyes are used in the form of mdphomc 
aeidsy and these latter bodies again are usually converted into 
metallic sulphonates. The sulphonates of potassium, sodium, and 
ammonium are the most common, but those of the metals of the 
alkaline earths are occasionally met vnth. Ammonium salts can 
be readily detected by the evolution of ammonia on warming the 
dye with caustic soda. Other sulphonates on ignition will leave 
metallic sulphates or sulphites, in which the metal can be readily 
identified. Of course, the presence of a sulphate in the ash does 
not prove the previous existence of a sulphonate, \mless the absence 
of a sulphate in the original dye has been ascertained. This may 
usually be effected by adding barium chloride to the highly dilute 
aqueous solution of the dye. In the case of a coloured precipitate 
being formed, probably consisting of the barium salt of the sul- 
phonic acid, this should be filtered off, washed, and digested with 
a solution of ammonium carbonate, which will convert a sulphonate 
of barium into barium carbonate, without affecting barium sul- 
phate. On again filtering, and treating the residue with dilute 
hydrochloric acid, any white insoluble matter will consist of barium 
sulphate (compare page 385). 

The ba^eii of many acid dyes can be detected without igniting 
by precipitating a concentrated aqueous solution of the colouring 
matter with pure fuming hydrochloric acid, which almost always 
precipitates the free acid. After filtration, the base can be sought 
for in the filtrate. 

For the detection of the halofjens existing in organic combina- 
tion in the eosins and some other dyes, the substance should be 
dissolved or suspended in water, and the liquid acidulated with 
dilute sulphuric acid and agitated with ether. The ethereal layer 
is then removed, evaporated, and the residue mixed with excess of 
quick-lime, free from chlorides, and then heated to redness in a 
combustion-tube. The product is treated with water, dilute nitric 
acid added in quantity sufficient to etiect solution and leave the 
liquid sliglitly acid, the liquid filtered, and a portion of the filtrate 
tested with silver nitrate. If any notable precipitate is produced, 
chlorides, bromides, and iodides are then sought for in the usual 
way. In the aqueous liquid separated from the ethereal layer, 
metallic chlorides can be sought for directly by means of silver 

Nifro-compoundSt used as colouring matters, are of a yellow or 
orange-red colour. When warmed with metallic tin (or stannous 


chloride) and hydrochloric acid, they are converted into colourless 
amido-compounds, which do not become again coloured on ex- 
posure to air. This behaviour distinguishes them, except acid 
naphthol-yellow, from the eosin dyes, but not from azo-colours. 
The latter, however, are usually sulphonates, and are not removed 
from their acidulated solutions by agitation with ether, as are the 
nitro-compounds, eosins, and most other phenolic dyes. The nitro- 
compounds also differ from the azo-dyes by dissolving in sulphuric 
acid to form yellow or colourless solutions, whereas with the latter 
far more brilliant and striking colours are obtained. The solutions 
of nitro-compounds, or fibres dyed with them, are but slightly 
altered by hydrochloric acid (distinction from yellow azo-dyes, 
which are reddened); while ammonia and caustic soda tend to 
darken or redden the colour (distinction from pliosphine). 

A considerable number of the colouring matters of commerce, 
possessing definite names, are by no means of a simple character, 
but are mixtures of two or more dyes. Mechanical mixtures may 
usually be recognised by spreading the powder on a piece of filter- 
paper and then floating the latter on some water or alcohol con- 
tained in a plate or flat capsule. Marks appear on the paper, and if 
the dye was of a simple character, are all of the same colour. On 
the other hand, if a mixture be under examination, the dye-particles 
dissolve with their re8i)€ctive colours, and the paper appears of two 
or more tints, according to the number of different colouring 
matters in the mixture. This ap|)earance becomes very marked 
when the wet pai)€r is held up to the light. It is even |X)S8ible in 
this way to form an approximate notion of the relative proi)ortions 
of the constituents of a mixture.^ 

When, as often happens with mixtures of azo-dyes, the con- 
stituents are too similar in shade to be recognised when dissolved 
side by side on filter-paper, the |)owdered dye should be sprinkled 
sparingly on the surface of pure, colourless, concentrated sulphuric 
acid contained in a porcelain dish. In many instances the particles 
will dissolve with marked differences in colour. Thus a mixture 
of orange II (mandarin) with crocein scarlet, when sprinkled on 
sulphuric acid, will give carmine-red streaks alongside with others 
of indigo-blue colour. This method of examination is very sen- 

Capillary Analysis of Colouring ^Iatters. 

Another useful method of examining certain dyes consists in 

^ This is sometimes of im{)ortance when it is desireil to distinguish actual 
mixtures from dyes ** ordered to shade/' the latter being mostly of a simple 
character, bat contaiuing a slight addition of another dye, so as to give a re- 
quired shade in dyeing. Thus most cheap violets contain a little magenta. 


dissolving the sample in the smallest possible quantity of alcohol, 
diluting the solution with rather more than its own measure of 
water, and then dropping the liquid on a piece of filter-paper, 
when concentric circles of different tones of colour will be pro- 
duced if a mixture be under examination. Magenta may be con- 
veniently examined in this way for violaniline, mauvaniline, or 
chrysaniline, and the same method may be employed for testing 
aniline blues and violets. 

A more elegant and delicate application of capillary attraction 
has been made by F. Goppelsroeder {J(Mr, Soc. Dyers^ ^c, iv. 
5), who suspends a number of strips of Swedish filter-paper in such 
a manner that the lower ends of the strips dip into a series of small 
beakers containing solutions of the dyes to be tested. The water 
of the solution always rises to a greater height than the colouring 
matter. Picric acid stands next in capillarity, and if the method be 
applied to a mixed solution of picric acid and turmeric, after a 
time three zones may be distinguished. The highest narrow zone 
is produced by water only ; below this there is a broad yellow zone 
containing picric acid ; while in the lowest zone only the colouring 
matter of turmeric exists. On exposing the paper to fumes of 
ammonia or dipping it into weak alkali, the presence of turmeric 
will be indicated by the production of a brownish-red colour, 
while the picric acid zone will disappear. If the lowest zone be 
cut off, the colouring matter dissolved off with alcohol, and the 
l)roces8 repeated with the solution obtained, the picric acid zone 
will be observed to be very narrow and faintly coloured. Interest- 
ing results are obtained when indigo-extract is examined in a 
similar manner. Traces of rosaniline may be detected in magenta 
by the same means. AVhen an alcoholic solution of azuline (page 
228) was examined by the capillary test, Goppelsroeder foimd 
three coloured zones to be produced, namely, pink, violet, and blue. 
In the alcoholic solution of the blue zone, silk was dyed a much 
purer blue than by the original colouring matter. It is evident 
that the method admits of various other applications. 

Although mechanical mixtures are far the most frequent, more 
intimate mixtures are sometimes produced by co-precipitation, or 
evaporation of a mixed solution. In almost all such cases one of tlie 
constituents of the mixture possesses a greater affinity for a fabric 
than the other, and it is this circumstance which forms the prin- 
cipal disadvantage of such mixtures. If a small dye-bath be made 
up with the colouring matter, and small samples of wool or silk 
dyed successively therein until the bath is exhausted, the colouring 
matter, if simple, will give a shading down from one and the same 
colour. But in the case of a mixture each consecutive sample will 



have a different colour, and the first and last samples will be 
entirely different in shade. The division obtained in this way is 
often a very sharp one, and it becomes easy to recognise impurities 
in colour whether due to accident or intention. The test can 
be conveniently conducted in a wide test-tube or small beaker, 
combed wool being the fibre used to withdraw the dye from the 

Tabular Schemes for Eecognition of Colouring Matters. 

Several systematic methods have been described for recognising 
the various commercial colouring matters, especially those derived 
from coal-tar. These schemes have generally the defect of 
describing the colouring matters merely by their commercial names, 
and of being based merely on certain colour-reactions. Bearing 
in mind the great number of dyes now met with in commerce, and 
the rapidity with which these disappear and are replaced by new 
colours, and old ones under new names, no perfect scheme of 
examination can be expected. The best method in many respects 
is that of E. Weingartner {Joiir, Soc, Dyers, ^r., iii. 67), 
who arranges artificial colouring matters in three classes : — I. 
Basic colouring matters soluble in water; II. Acid colouring 
matters soluble in water ; and III. Colouring matters insoluble in 
water. ^ 

The soluble basic colouring matters are then distinguished from 
the acid dyes by a reagent prepared by dissolving 25 grammes of 
tannin and an equal weight of sodium acetate in 250 c.c. of water. 

^ The following table shows the solubility of certain coal-tar dyes in 
water and alcohol, as determined by A. Brunner {Jour. Soc, DyerSf <fcc. , iii. 

Colouring Matters. 

Reference Page. 

Amount Dissolved by 100 parts of 





almost insoluble 


Blamarck browD, 




Ckmdlin, . 




Dahlia blue, . 

• •• 







Btliyl orange, . 


0*02 'almost insolublel 

Ctontian Tiolet, 

• •• 



LnteoUn, . 




Masenta, . 
Sfdfachite green, . 







Manchester yellow, 
Methylene blue, 







Methyl green, . 




Methyl violet, . 








Tropieolin 00, 










This precipitates the basic dyes only. A few drops of the reagent 
are added to a 1 or 2 per cent, aqueous solution of the dye, and if 
any precipitation occur the liquid is heated, as certain sulphonated 
derivatives of triphenylmethane give precipitates at first which re- 
dissolve at a higher temperature. 

The following are Weingartner's tables for the recognition of 
artificial colouring matters. The group to which the dye belongs 
having been ascertained, the colouring matter may usually be 
identified by its si)ecial reactions. The figures in parenthesis after 
the names of the dyes show the pages on which more detailed 
information may be found respecting them. 

Table I. — Artificial Colouring Matters Soluble in IVaUr, Basic Colouring 


The aqueous solution gives a precipitate with the tannin reagent. 

The primitive shade reappears. 


shade does 

not reappear. 


Yellow or 







red (258). 








green (241). 


green (239). 

Methyl Rreen 



blue (285). 
New blue 





violet (234). 


violet (237). 





Crystal Wolet 









Victoria blue 



green (see 



Observations. — After having reduced the basic colouring matter with zdnc- 
powder and hydrochloric acid, the liquid should be filtered rapidly. It is very 
important to neutralise the filtered liquid with sodium acetate, since hydro- 
chloric acid in excess may fonn with the basic colour acid salts, of different 
colour from the neutral salts. 

The primitive shade docs not appear on oxidation with the colouring matters 
in column F, but in certain cases oxidation produces different shades from the 
primitive. When Bismarck brown (vesuvine) and chrysoidine are reduced, 
the di- and tri-amines are formed, which easily oxidise in the air with brownish- 
red colour. It is very important to distinguish this shade from the original, 
which is brown or yellow. After reduction and oxidation methylene-green 
gives a blue shade. 

The oxidation of the reduced solution on the filter-paper may be facilitated 
by gently heating. Some colours oxidiso with such rapidity that the original 
colour returns whilst filtering. 

Methylene-green forms a dark green aqueous solution, which becomes 



quite coloarless on reduction, but into sky-blue in presence of air. The 
solid substance di:$solves in strong sulphuric acid with dark green colour. 

Table II. — Artificial Colouring Matters Soluble in Water, Acid Colouring 


The aqueous solution does not give a precipitate with the tanniu reagent. 


The solution 


The solution is decolorised. 

red. The 

colour of 

the am- 

solution re- 

The original colour reap- 
pears on paper. 

The original colour does not appear. 

appears on 
the paper. 

The aqueous solution is 
acidulated with hydro- 

The colouring matter, when heated on 

._LA£ M 11 


chloric acid, and treated 

platinum foil. 

Alizarin blue 

with ether. 

CcBrulein S 

The ether 

The ether 


Bums quietly, or slightly 




without for- 

deflagrates, giving off 

the colour- 


mation of 

coloured vapours. 

ing matter, 


and the 


Heat a piece of calico, not 

Bolution • 

mordanted, in the aqueous 



ly becomes 


The colora- 
tion of the 
stuff is fast 

The colour 
does not 
resist warm 




to warm 


AuriQ (leo). 


ing matters 





Azo • colours 

Azo - colours 


from ben- 
zidine, &c. 

(182, 191, 196). 










Ohservatums, — a. The reduction of tlie acid yellow, orange, ponceau, and 
claret non -fluorescent colours requires special precautions. The best way is to 
treat with zinc-powder and hydrochloric acid, and afterwards to neutralise 
with sodium acetate, as has already been pointed out The reduction will 
often be too slow if ammonia or acetic acid be used. 

b. It is necessary, as before, to compare with great care the original colour 
with that which is produced by reoxidation, so that their identity or difference 
may not be mistaken. In the reduction of nitro- or azo-bodies diamines or 
amidophenols are formed, which by oxidation give dirty or brown shades. In 
the column K this remark equally applies to erythrosin, for when that colour- 
ing matter is reduced iodine is separated and fluorescin formed. 

e. All the colouring matter not specified in a are reduced by zinc and 



d. When the acid colours are being reduced, the solution, as long as 
zinc-powder is present, should be colourless, or at most slightly yellow or red. 

e. The nitro-derivatives of the azo-colouring matters and of fluorescein can 
be easily recognised by the formation of '' Pharaoh's serpents" on heating a 
small quantity (0*5 grm.) on platinum foil. 

/. In order to find the group NOj with certainty in a yellow colouring 
matter (e.^., picric acid), it is necessary to add a little sodium carbonate. 

g. It is very difficult completely to reduce alizarin S. It is therefore put in 
column L. The colour of the ammoniacal solution more often