Unlike the animal fibres, _cotton_ has little or no affinity for the

basic colours; hence the cotton dyer makes use of the fact that cotton

has a natural attraction for tannic acid, and that the latter forms

insoluble lakes with the bases of basic colours. Previous to dyeing,

the cotton is prepared with tannic acid by steeping in a cold solution

of the latter for several hours; cotton pieces are run at full width

through a solution containing 2 to 6 oz. per gallon of tannic acid,

and after being evenly squeezed are dried on steam cylinders. The

cotton is then worked in a solution of tartar emetic or stannic

chloride, so that the tannic acid absorbed by the fibre may be fixed

upon it as insoluble tannate of antimony or tin. Although the tannic

acid is thus united with metallic oxide, it still has the power of

attracting the base of the colouring matter, and there is fixed upon

the fibre an insoluble colour-lake, namely, a tannate of antimony and

colour-base, which constitutes the dye. In this process the tannic

acid is called the _mordant_, the tartar emetic acts as the

_fixing-agent_ for the tannic acid, and the cotton as finally prepared

for dyeing is said to be _mordanted_. The proportions employed,

reckoned on the weight of cotton, may vary from 2 to 10% tannic acid,

or the equivalent in a decoction of sumach, myrabolans, or other

tannin matter, and 1/2 to 3% tartar emetic. After mordanting and

fixing of the mordant, the cotton is well washed and dyed in the cold

or at 60 deg. C. for 1/2 to 1 hour with the necessary colouring

matter. Applied in this manner, basic colours are moderately fast to

soap, but generally not to the action of light.

_Linen_ is dyed in the same manner as cotton. Jute is dyed without any

previous preparation, since it behaves like a tannin-mordanted fibre,

attracting the basic colours direct.

The basic colours, to which class most of the earlier coal-tar colours

belonged, are remarkable for their great colouring power, and in most

cases for the brilliancy of the colours they yield. With the exception

of certain dark colours, they are fugitive to light. It is interesting

to note that only one vegetable colouring matter is at present

recognized as belonging to this class, namely, the yellow dyestuff

barberry bark and root (_Berberis vulgaris_) which contains the

alkaloid berberine.

The following is a list of the more important basic colours derived

from coal-tar:--

_Red._--Magenta, safranine, rhodamine, pyronine red, rhoduline red,

rosazein, induline scarlet.

_Orange._--Chrysoidine, phosphine, acridine orange, tannin orange.

_Yellow._--Auramine, benzoflavine, thioflavine T, acridine yellow,

homophosphine, rhoduline yellow.

_Green._--Malachite green, emerald green, imperial green, China green,

brilliant green, Victoria green, diamond green, methylene green, azine

green.

_Blue._--Methylene blue, new methylene blue, toluidine blue, thionine

blue, indamine blue, Victoria blue, night blue, Nile blue, turquoise

blue, marine blue, indoine blue, metamine blue, Capri blue, indazine,

metaphenylene blue, paraphenylene blue, toluylene blue, indigene,

indol blue, diphene blue, setopaline, setocyanine, setoglaucine,

Helvetia blue.

_Violet._--Methyl violet, crystal violet, ethyl purple, methylene

violet, mauve, paraphenylene violet, rhoduline violet, methylene

heliotrope.

_Brown._--Bismarck brown.

_Black._--Diazine black.

_Grey._--Methylene grey, nigrisine, new grey.

DIRECT COLOURS.--The characteristic feature of the dyestuffs belonging

to this class is that they dye cotton "direct"--i.e. without the aid

of mordants. Two distinct series of colouring matters of this group

may be distinguished--namely, _Direct Cotton Colours_ and _Sulphide

Colours_.

(a) _Direct Cotton Colours._--The colours of this class are frequently

called the Substantive Cotton Colours, Benzo Colours, Diamine Colours,

Congo Colours. Considered from the chemical point of view, they are

mostly alkali salts of sulphonated tetrazo colours obtained by

diazotizing certain diamido compounds, e.g. benzidine,

diamido-stilbene, &c., and uniting the products thus obtained with

various amines or phenols. The first colouring matter of this class

was the so-called Congo red, discovered in 1884, and since that time a

very great number have been introduced which yield almost every

variety of colour. The method of dyeing _cotton_ consists in merely

boiling the material in a solution of the dyestuff, when the cotton

absorbs and retains the colouring matter by reason of a special

natural affinity. The concentration of the dyebath is of the greatest

importance, since the amount of colour taken up by the fibre is in an

inverse ratio to the amount of dye liquor present in the bath. The

addition of 1 to 3 oz. sodium sulphate and 1/12 to 1/3 oz. carbonate

of soda per gallon gives deeper colours, since it diminishes the

solubility of the colouring matter in the water and increases the

affinity of the cotton for the colouring matter. An excess of sodium

sulphate is to be avoided, otherwise precipitation of the colouring

matter and imperfect dyeing result. With many dyestuffs it is

preferable to use 1/6 to 1/3 oz. soap instead of soda. On cotton the

dyed colours are usually not very fast to light, and some are

sensitive to alkali or to acid, but their most serious defect is that

they are not fast to washing, the colour tending to run and stain

neighbouring fibres. Their fastness to light and washing is, however,

greatly improved by a short (1/2 hour) after-treatment with a boiling

solution of copper sulphate (3%), with or without the addition of

bichromate of potash (1%). _Wool_ and _silk_ are dyed with the direct

colours either neutral or with the addition of a little acetic acid to

the dyebath. On these fibres the dyed colours are usually faster than

on cotton to washing, milling and light; some are very fast even to

light--e.g. Diamine fast red, chrysophenine, Hessian yellow, &c. Many

of the Direct Colours are very useful for dyeing plain shades on union

fabrics composed of wool and cotton, silk and cotton, or wool and

silk. Owing to the facility of their application, they are also very

suitable for use as household dyes, especially for cotton goods.

A few vegetable dyestuffs belong to this class, notably Turmeric,

saffron, annatto and safflower, but they all yield colours which are

fugitive to light, and they are now of little importance. _Turmeric_

is the underground stem or tuber of _Curcuma tinctoria_, a plant

growing abundantly in the East Indies. It dyes cotton, wool and silk

in a bath acidified with acetic acid or alum, yielding a bright yellow

colour which is turned brown by alkalis. _Saffron_ consists of the

stigmata of the flower of _Crocus sativus_, which is grown in Austria,

France and Spain. It dyes a bright orange-yellow colour. _Annatto_ is

the pulpy mass surrounding the seeds of _Bixa orellana_, a plant which

grows in South America--e.g. Brazil, Cayenne, &c. It dyes cotton and

silk in an alkaline or soap bath an orange colour, which is turned red

by acids. _Safflower_ consists of the dried florets of _Carthamus

tinctorius_, which is grown in the East Indies, Egypt and southern

Europe. Cotton is dyed a brilliant pink colour by working it in a cold

alkaline (sodium carbonate) extract of the colouring matter, while

gradually acidifying the solution with citric acid (lime-juice).

The Direct Colours which are derived from coal-tar products are very

numerous indeed; they are largely employed, and occupy a very

important position among dyestuffs. The following list includes the

principal coal-tar colours of this group:--

_Red._--Congo red, brilliant Congo, benzopurpurine, brilliant

purpurine, deltapurpurine, diamine scarlet, diamine fast red,

rosazurine, salmon red, erica, Titan pink, St Denis red, Columbia red,

naphthylene red, Congo rubine, acetopurpurine, dianol red, thiamine

crimson, geranine, brilliant geranine, Columbia fast scarlet, benzo

fast scarlet, thiamine red, diamine rose, Dongola red, rosophenine.

_Orange._--Congo orange, benzo orange, toluylene orange, mikado

orange, brilliant orange, Columbia orange, diamine orange, pyramine

orange, benzo fast orange.

_Yellow._--Chrysamine, cresotin yellow, diamine yellow, carbazol

yellow, chrysophenine, Hessian yellow, curcumine yellow, thiazol

yellow, thioflavine S, oriol, mimosa yellow, Columbia yellow, cotton

yellow, chloramine yellow, direct yellow, diamine fast yellow, diamine

gold, sun yellow, stilbene yellow, chlorophenine, oxyphenine.

_Green._--Benzo olive, Columbia green, benzo green, diamine green,

direct green, diphenyl green, oxamine green, eboli green.

_Blue._--Azo blue, benzoazurine, brilliant azurine, sulphon-azurine,

diamine blue, benzo indigo blue, benzo black blue, Chicago blue,

Columbia blue, Erie blue, Zambezi blue, benzo cyanine, Congo blue,

diamine sky blue, brilliant benzo blue, benzo chrome black blue,

oxamine blue, diphenyl blue, diamineral blue, diaminogene, benzo fast

blue, diazo indigo blue, brilliant chlorazol blue.

_Violet._--Hessian purple, Congo Corinth, heliotrope, Congo violet,

diamine violet, Hessian violet, azo violet, benzo violet, violet

black, diamine Bordeaux, chlorantine lilac, diphenyl violet, triazol

violet, Columbia violet.

_Brown._--Benzo brown, Congo brown, toluylene brown, diamine brown,

cotton brown, Hessian brown, terra-cotta, mikado brown, catechu brown,

wool brown, Columbia brown, Zambezi brown, benzo chrome brown, direct

fast brown, direct bronze brown, chloramine brown, triazol brown,

toluylene brown, dianol brown, Crumpsall direct fast brown.

_Black._--Diamine black, Columbia black, Nyanza black, Tabora black,

Zambezi black, chromanil black, benzo black, benzo fast black, direct

blue black, Pluto black, oxydiamine black, diamine jet black,

polyphenyl black, union black, triazol black, Titan black, cotton

black, oxamine black.

_Grey._--Benzo grey, benzo black, azo mauve, diaminogene, neutral

grey.

(b) _Sulphide Colours._--These dyestuffs are only suitable for dyeing

the vegetable fibres, since they must be applied in a strongly

alkaline bath. The dyestuff Cachou de Laval, discovered in 1873, was

the first member of this group, and was obtained by melting a mixture

of sodium sulphide and various organic substances--e.g. bran, sawdust,

&c. In recent years numerous other dyestuffs have been added to the

list, namely, grey, blue, green, brown, and especially black colours,

by submitting certain definite amido compounds of the aromatic series

to a similar treatment with sodium sulphide or sodium thiosulphate,

and subsequent oxidation. The mode of dyeing with these colours is

based on the fact that they are soluble in an alkaline reducing agent,

and if the cotton is worked in the solution, subsequent oxidation

develops the colour, which is fixed upon the fibre in an insoluble

condition. The material is boiled for about one hour in a solution of

the colour (10 to 15%), with the addition of sodium carbonate (1 to

10%), common salt (10 to 20%), and sodium sulphide (5 to 30%); it is

then washed in water, and may be developed by heating in a bath

containing 2 to 5% of bichromate of soda, and 3 to 6% acetic acid. A

final washing with water containing a little soda to remove acidity is

advisable. The sulphide colours are remarkable for their fastness to

light, alkalis, acids and washing, but unless proper care is exercised

the cotton is apt to be tendered on being stored for some time.

The following list includes some of the most important of the colours

of this class:--

_Yellow._--Immedial yellow, pyrogene yellow, sulphur yellow, thion

yellow, thiogene yellow.

_Orange._--Eclipse phosphine, immedial orange, pyrogene orange, thion

orange, thiogene orange.

_Green._--Pyrogene green, Italian green, eclipse green, pyrol green,

immedial green, katigene green, thionol green.

_Blue._--Immedial blue, immedial sky blue, eclipse blue, katigene

indigo, pyrogene blue, sulphur blue, thion blue, thiogene blue.

_Violet._--Katigene violet, thiogene heliotrope, thiogene purple.

_Brown._--Pyrogene brown, pyrogene yellow, Cachou de Laval,

thiocatechine, katigene black brown, eclipse brown, immedial brown,

katigene brown, dianol brown.

_Grey and Black._--Pyrogene grey, Vidal black, immedial black,

katigene black, anthraquinone black, St Denis black, amidazol black,

cross dye black, eclipse black, carbide black, thiogene black,

sulphaniline black, sulfogene black, pyrogene black, dianol black,

sulphur black, thion black, kryogene black.

This class of colours is continually increasing in number, and for

certain purposes in cotton dyeing the group has acquired great

importance.

DEVELOPED COLOURS.--This group includes certain azo colours which are

developed or produced upon the fibre itself (usually _cotton_) by the

successive application of their constituent elements. It may be

conveniently divided into the following sub-groups:--Insoluble Azo

Colours, Developed Direct Colours, Benzo Nitrol Colours.

(a) The _Insoluble Azo Colours_ are produced as insoluble coloured

precipitates by adding a solution of a diazo compound to an alkaline

solution of a phenol, or to an acid solution of an amido compound. The

necessary diazo compound is prepared by allowing a solution containing

nitrous acid to act upon a solution of a primary aromatic amine. It is

usually desirable to keep the solutions cool with ice, owing to the

very unstable nature of the diazo compounds produced. The colour

obtained varies according to the particular diazo compound, as well as

the amine or phenol employed, [beta]-naphthol being the most useful

among the latter. The same coloured precipitates are produced upon the

_cotton_ fibre if the material is first impregnated with an alkaline

solution of the phenol, then dried and passed into a cold solution of

the diazo solution. The most important of these colours is

_para-nitraniline red_, which is dyed in enormous quantities on cotton

pieces. The pieces are first "prepared" by running them on a padding

machine through a solution made up of 30 grms. [beta]-naphthol, 20

grms, caustic soda, 50 grms. Turkey red oil, and 5 grms. tartar emetic

in 1000 grms. (1 litre) water. They are then dried on the

drying-machine, and are passed, after being allowed to cool, into the

diazo solution, which is prepared as follows: 15 grms. para-nitraniline

are dissolved in 53 c.c. hydrochloric acid (34 deg. Tw.) and a

sufficiency of water. To the cold solution a solution of 10-1/2 grms.

sodium nitrite is added while stirring. The whole is then made up to

1200 c.c., and just before use 60 grms. sodium acetate are added. The

colour is developed almost immediately, but it is well to allow the

cotton to remain in contact with the solution for a few minutes. The

dyed cotton is squeezed, washed, soaped slightly, and finally rinsed in

water and dried. A brilliant red is then obtained which is fast to soap

but not to light. If the para-nitraniline used in the foregoing process

is replaced by meta-nitraniline, a yellowish-orange colour is obtained;

with [alpha]-naphthylamine, a claret-red; with amido-azo-toluene, a

brownish red; with benzidine, a dark chocolate; with dianisidine, a

dark blue; and so on. The dyed colours are fast to washing and are much

used in practice, particularly the para-nitraniline red, which serves

as a substitute for Turkey-red, although it is not so fast to light as

the latter.

(b) _Developed Direct Colours._--The primuline colours were the first

representatives of this class and are derived from the yellow dyestuff

known as primuline, which dyes cotton in the same manner as the direct

colours. The primuline yellow thus obtained is fugitive to light and

of little practical value, but since the colouring matter is an amido

base it can be diazotized in the fibre and then developed in solutions

of phenols or amines, whereby azo dyes of various hues may be

obtained, according to the developer employed; thus, [beta]-naphthol

develops a bright red colour, resorcin develops an orange, phenol a

yellow, naphthylamine a brown, &c. The _dyeing_ of the primuline

yellow is effected by boiling the cotton for one hour in a solution of

primuline (5%) and common salt (10 to 20%). The diazotizing operation

consists in passing the dyed and rinsed cotton for 5 to 10 minutes

into a cold solution of nitrous acid--i.e. a solution of 3/4 oz.

sodium nitrite per gallon of water, slightly acidified with sulphuric

acid. The diazotized material should not be exposed to light, but at

once washed in cold water and passed into the developer. The

_developing_ process consists in working the diazotized material for 5

to 10 minutes in a cold solution of the necessary phenol, and finally

washing with water. The only developer of any practical importance is

a solution of [beta]-naphthol in caustic soda, which produces

primuline red. The primuline colours are best adapted for _cotton_

dyeing, and the colours obtained are fast to washing and to moderate

soaping, but they are not very fast to light.

If _cotton_ is dyed with other direct colours containing free amido

groups, the colour can be diazotized on the dyed fibre exactly in the

same manner as in the case of primuline-dyed cotton, and then

developed by passing into the solution of an amine or phenol, or by

treating it with a warm solution of sodium carbonate. In this manner a

new azo dye is produced upon the fibre, which differs from the

original one not only in colour, but also by being faster to washing

and other influences. A treatment with copper sulphate solution after

development is frequently beneficial in rendering the colour faster to

light. Some Direct Colours, indeed, are of little value, owing, for

example, to their sensibility to acids, until they have been

diazotized and developed, the usual developers being [beta]-naphthol,

resorcinol, phenol and phenylene-diamine.

The following Direct Colours, after being applied to cotton, may be

submitted to the above treatment, the colours produced being chiefly

blue, brown and black:--

_Blue._--Diazurine, diazo blue, diamine blue, diaminogene.

_Red._--Rosanthiene.

_Brown._--Diazo brown, diamine cutch, diamine brown, cotton brown.

_Grey and Black._--Senzo blue, diazo blue black, diazo black, diamine

black, diazo brilliant black.

(c) _Benzo Nitrol Colours._--These are certain Direct Colours, dyed on

_cotton_ in the ordinary manner, which are then developed by passing

into a diazo solution--e.g. diazotized para-nitraniline, &c. The dyed

colour here plays the part of a phenol or amine, and reacts with the

diazo compound to produce a new colour. The process is similar to the

production of the Insoluble Azo Colours, the [beta]-naphthol which is

there applied to the fibre being here replaced by a Direct Colour. The

colour of the latter is rendered much deeper by the process, and also

faster to washing and to the action of acids. The dyestuffs

recommended for application in the manner described are: Benzo nitrol

brown, toluylene brown, direct fast brown, Pluto black, direct blue

black.

_"Topping" Direct Colours._--The direct colours possess the remarkable

property of precipitating the basic colours from aqueous solution. Use

is frequently made of this property for "topping" cotton dyed with

direct colours either with a view to obtain compound shades or to

brighten the colour. Thus by dyeing cotton first yellow in chrysamine

and then dyeing it again in a cold bath of methylene blue a brilliant

shade of green results. If, on the other hand, a direct blue is topped

with methylene blue, its brilliancy may be enhanced.

MORDANT COLOURS.--The colouring matters of this class include some of

the most important dyestuffs employed, since they furnish many colours

remarkable for their fastness to light, washing and other influences.

Employed by themselves, Mordant Colours are usually of little or no

value as dyestuffs, because, with few exceptions, either they are not

attracted by the fibre, particularly in the case of cotton, or they

only yield a more or less fugitive stain. Their importance and value

as dyestuffs are due to the fact that they act like weak acids and

have the property of combining with metallic oxides to form insoluble

coloured compounds termed "lakes," which vary in colour according to

the metallic oxide or salt employed. The most stable lakes are those

in which the colouring matter is combined with two metallic oxides, a

sesquioxide and a monoxide--e.g. alumina and lime. In applying

colouring matters of this class the object of the dyer is to

precipitate and fix these coloured lakes upon and within the fibre,

for which purpose two operations are necessary, namely, _mordanting_

and _dyeing_.

The _mordanting operation_ aims at fixing upon the fibre the necessary

metallic oxide or insoluble basic salt, which is called the _mordant_,

although the term is also applied to the original metallic salt

employed. In the subsequent dyeing operation the mordanted material

is boiled with a solution of the colouring matter, during which the

metallic oxide attracts and chemically combines with the colouring

matter, producing the coloured lake _in situ_ on the fibre, which thus

becomes dyed. The mode of applying the mordants varies according to

the nature of the fibre and the metallic salt employed, the chief

mordants at present in use being salts of chromium, aluminium, tin,

copper and iron. The method of mordanting _wool_ depends upon its

property of decomposing metallic salts, and fixing upon itself an

insoluble metallic compound, when boiled in their solutions. This

decomposition is facilitated by the heating and by the dilution of the

solution, but it is chiefly due to the action of the fibre itself. The

exact nature of the substance fixed upon the fibre has not in all

cases been determined; probably it is a compound of the metallic oxide

with the wool-substance itself, which has the character of an

amido-acid. The mordant most largely employed for wool is bichromate

of potash, since, besides being simply applied, and leaving the wool

with a soft feel, it yields with the various mordant-dyestuffs a large

variety of fast colours. The wool is boiled for 1 to 1-1/2 hours in a

solution containing 2 to 3% bichromate of potash on the weight of the

wool employed. During this operation the wool at first attracts

chromic acid, which is gradually reduced to chromium chromate, so that

the mordanted fibre has finally a pale olive-yellow tint. In the

dyebath, under the influence of a portion of the dyestuff, further

complete reduction to chromic hydrate occurs before it combines with

the colouring matter. Not unfrequently certain so-called "assistants"

are employed in small amount along with the bichromate of potash--e.g.

sulphuric acid, cream of tartar, tartaric acid, lactic acid, &c. The

use of the organic acids here mentioned ensures the complete reduction

of the chromic acid on the wool to chromic hydrate already in the

mordant bath, and the pale greenish mordanted wool is better adapted

for dyeing with colours which are susceptible to oxidation--e.g.

alizarin blue. For special purposes chromium fluoride, chrome alum,

&c., are employed. Alum or aluminium sulphate (8%), along with acid

potassium tartrate (cream of tartar) (7%), is used for brighter

colours--e.g. reds, yellows, &c. The object of the tartar is to retard

the mordanting process and ensure the penetration of the wool by the

mordant, by preventing superficial precipitation through the action of

ammonia liberated from the wool; it ensures the ultimate production of

clear, bright, full colours. For still brighter colours, notably

yellow and red, stannous chloride was at one time largely employed,

now it is used less frequently; and the same may be said of copper and

ferrous sulphate, which were used for dark colours. _Silk_ may be

often mordanted in the same manner as wool, but as a rule it is

treated like cotton. The silk is steeped for several hours in cold

neutral or basic solutions of chromium chloride, alum, ferric

sulphate, &c., then rinsed in water slightly, and passed into a cold

dilute solution of silicate of soda, in order to fix the mordants on

the fibre as insoluble silicates. _Cotton_ does not, like wool and

silk, possess the property of decomposing metallic salts, hence the

methods of mordanting this fibre are more complex, and vary according

to the metallic salts and colouring matters employed, as well as the

particular effects to be obtained. One method is to impregnate the

cotton with a solution of so-called "sulphated oil" or "Turkey-red

oil"; the oil-prepared material is then dried and passed into a cold

solution of some metallic salt--e.g. aluminium acetate, basic chromium

chloride, &c. The mordant is thus fixed on the fibre as a metallic

oleate, and after a passage through water containing a little chalk or

silicate of soda to remove acidity, and a final rinsing, the cotton is

ready for dyeing. Another method of mordanting cotton is to fix the

metallic salt on the fibre as a tannate instead of an oleate. This is

effected by first steeping the cotton in a cold solution of tannic

acid or in a cold decoction of some tannin matter, e.g. sumach, in

which operation the cotton attracts a considerable amount of tannic

acid; after squeezing, the material is steeped for an hour or more in

a solution of the metallic salt, and finally washed. The mordants

employed in this case are various--e.g. basic aluminium or ferric

sulphate, basic chromium chloride, stannic chloride (cotton spirits),

&c. There are other methods of mordanting cotton besides those

mentioned, but the main object in all cases is to fix an insoluble

metallic compound on the fibre. It is interesting to note that whether

the metallic oxide is united with the substance of the fibre, as in

the case of wool and silk, or precipitated as a tannate, oleate,

silicate, &c., as in the case of cotton or silk, it still has the

power of combining with the colouring matter in the dyebath to form

the coloured "lake" or dye on the material.

The _dyeing operation_ consists in working the mordanted material in a

solution of the necessary colouring matter, the dyebath being

gradually raised to the boiling point. With many colouring matters,

e.g. with alizarin, it is necessary to add a small percentage of

calcium acetate to the dyebath, and also acetic acid if wool is being

dyed. In wool-dyeing, also, the mordanting operation may follow that

of dyeing instead of preceding it, in which case the boiling of the

wool with dyestuff is termed "stuffing," and the subsequent developing

of the colour by applying the mordant is termed "saddening," because

this method has in the past been usually carried out with iron and

copper mordants, which give dull or sad colours. The method of

"stuffing and saddening" may, however, be carried out with other

mordants, even for the production of bright colours, and it is now

frequently employed with certain alizarin dyestuffs for the production

of pale shades which require to be very even and regular in colour.

There is still another method of applying Mordant Colours in

wool-dyeing, in which the dyestuff and the mordant are applied

simultaneously from the beginning; it is known as the "single-bath

method." It is only successful, however, in the case of certain

colouring matters and mordants, to some of which reference will be

made in the following paragraphs.

_The Natural Mordant Colours._--It is interesting to note that nearly

all the natural or vegetable dyestuffs employed belong to the class of

Mordant Colours, the most important of these being included in the

following list:--_Madder, Cochineal, Peachwood, Sapanwood, Limawood,

Camwood, Barwood, Sanderswood, Old Fustic, Young Fustic, Quercitron

Bark, Persian Berries, Weld, Logwood_.

_Madder_ consists of the dried ground roots of _Rubia tinctorum_, a

plant of Indian origin. Formerly cultivated largely in France and

Holland, it was long one of the most important dyestuffs employed,

chiefly in the production of Turkey-red and in calico-printing, also

in wool-dyeing. With the different mordants it yields very distinct

colours, all fast to light and soap, namely, red with aluminium,

orange with tin, reddish brown with chromium, purple and black with

iron. Madder contains two closely allied colouring matters, namely,

alizarin and purpurin. The former, which is by far the more important,

is now prepared artificially from the coal-tar product anthracene, and

has almost entirely superseded madder.

_Cochineal_ is the dried scale-insect _Coccus cacti_, which lives on

certain of the cactus plants of Mexico and elsewhere. The rearing of

cochineal was once a large and important industry, and although still

pursued, it has seriously declined, in consequence of the discovery of

the azo scarlets derived from coal-tar. The colouring matter of

cochineal, carminic acid, is believed by chemists to be a derivative

of naphthalene, but its artificial production has not yet been

accomplished. Cochineal dyes a purple colour with chromium mordant,

crimson with aluminium, scarlet with tin, and grey or slate with iron.

Its chief employment is for the purpose of dyeing crimson, and more

especially scarlet, on wool. Crimson is dyed by mordanting the wool

with alum and tartar and dyeing in a separate bath with ground

cochineal. Scarlet on wool is obtained by the single-bath method,

namely, by dyeing the wool with a mixture of stannous chloride (or

nitrate of tin), oxalic acid, and cochineal. It is usual to add also a

small amount of the yellow dyestuff flavine in order to obtain a

yellower shade of scarlet. The cochineal colours are very fast to

light, but somewhat susceptible to the action of alkalis.

_Peachwood, Sapanwood_ and _Limawood_ are usually referred to as the

"soluble red-woods," because of the solubility in water of the

colouring principle they contain. They consist of the ground wood of

various species of _Caesalpinia_ found in Central America, the East

Indies and Peru. They all yield more or less similar colours with the

different mordants--claret-brown with chromium, red with aluminium,

bright red with tin, dark slate with iron. Owing to the fugitive

character of all the colours to light, these dyewoods are now

comparatively little employed in dyeing.

_Camwood, Barwood_ and _Sanderswood_ represent the so-called

"insoluble red-woods," their colouring principles being sparingly

soluble even in boiling water. They are obtained from certain species

of _Pterocarpus_ and _Baphia_, large trees growing in the interior of

West Africa. Their general dyeing properties are similar, a

claret-brown being obtained with chromium mordant, a brownish red with

aluminium, a brighter red with tin, and purplish brown with iron.

Their chief employment is in wool-dyeing, for the production of

various shades of brown, being best applied by the "stuffing and

saddening" method above described; but since the colours are fugitive

to light, they are now very largely replaced by alizarin. A brown on

wool is obtained by first boiling for one to two hours in a decoction

of the ground wood (50%), and then boiling in a separate bath in

solution of bichromate of potash (2%) for half an hour. These

dye-woods are also employed by the indigo-dyer, in order to give a

brownish ground colour to the wool previous to dyeing in the indigo

vat, and thus obtain a deeper, fuller blue. The colouring matters

contained in these dyewoods have not been exhaustively examined.

_Fustic_ is a yellow dyestuff, and consists of the wood of the dyer's

mulberry tree, _Morus tinctoria_, which grows in Cuba, Jamaica, &c. It

is still an important and largely used dyestuff, being cheap, and the

colours obtained from it being satisfactorily fast to light and other

influences. With chromium mordant it yields an olive-yellow or

"old-gold" shade; with aluminium, yellow; with tin, a brighter yellow;

with iron, an olive-green. It is chiefly employed in wooldyeing along

with other dyestuffs, and furnishes the yellow in compound shades. Two

colouring principles exist in Old Fustic, namely, morin and maclurin,

the former being the most important, and generally regarded as the

true colouring matter.

_Quercitron Bark_ consists of the inner bark of an oak-tree, _Quercus

tinctoria_, which grows in the North American States. It dyes somewhat

like Old Fustic, but gives with aluminium and tin mordants brighter

yellows, for which colours it is chiefly used. The colouring principle

of Quercitron Bark is called quercitrin, which by the action of

boiling mineral acid solutions is decomposed, with the production of

the true colouring matter termed quercetin.

So-called _Flavine_ is a commercial preparation of Quercitron Bark

consisting of quercitrin or of quercetin; it is much used by

wool-dyers for the production of bright yellow and orange colours.

Wool is dyed in single bath by boiling with a mixture of Flavine (8%),

stannous chloride (4%) and oxalic acid (2%). Flavine is used in small

quantity along with cochineal for dyeing scarlet on wool.

_Persian Berries_ are the dried unripe fruit of various species of

_Rhamnus_ growing in the Levant. The general dyeing properties are

similar to those of Quercitron Bark, the orange colour given with tin

mordant being particularly brilliant. The high price of this dyestuff

causes its employment to be somewhat limited. The colouring matter of

Persian Berries is called xanthorhamnin, which by the action of

fermentation and acids yields the true dyestuff rhamnetin.

_Weld_ is the dried plant _Reseda luteola_, a species of wild

mignonette, formerly largely cultivated in Europe. Its dyeing

properties resemble those of Quercitron Bark, but the yellows with

aluminium and tin mordants are much brighter and purer, and also

faster to light. It is still used to a limited extent for dyeing a

bright yellow on woollen cloth and braid for the decoration of

military uniforms. Quite recently the colouring matter of Weld,

namely, luteolin, has been prepared artificially, but the process is

too expensive to be of practical use.

_Logwood_ is the heart-wood of _Haematoxylon campechianum_, a tree

growing in Central America. It is the most important natural dyewood

at present employed, being largely used for dyeing dark blues and

black on silk, wool and cotton. With chromium and aluminium mordants

logwood dyes a dark blue, and even black; with tin, a dark purple; and

with iron, black. The colours are only moderately fast to light. On

wool the mordant is bichromate of potash; on cotton and silk an iron

mordant is employed. Before use by the dyer the logwood is ground and

aged or oxidized, by allowing moistened heaps of the ground wood to

ferment slightly, and by frequently turning it over to expose it

freely to the air. By this means the colouring principle haematoxylin

which logwood contains is changed into the true colouring matter

haematein. The constitution of this colouring matter has been recently

discovered; it is very closely allied to the brazilin of peachwood,

sapanwood and limawood, and is also a member of the [gamma]-pyrone

group of colouring matters.

The importance of the above-mentioned natural dyestuffs is gradually

diminishing in favour of mordant dyestuffs and others derived from

coal-tar. Fustic and logwood are perhaps the most largely used, and

may continue to be employed for many years, no satisfactory artificial

substitutes having hitherto come into the market.

The _Artificial Mordant_ Colours are well represented by alizarin, the

colouring matter of the madder root, which was the first natural

dyestuff prepared artificially from the coal-tar product anthracene

(1868). For this reason many of these colours are frequently referred

to as the Alizarin Colours. At the present time, however, there are

numerous Mordant Colours which are prepared from other initial

materials than anthracene; they are not chemically related to

alizarin, and for these the term Alizarin Colours is therefore

inappropriate. The property, which Mordant Colours possess in common,

of combining with metals and producing lakes, which readily adhere to

the fibre, depends upon their chemical constitution, more particularly

upon the general and relative position in the molecule of certain side

atomic groups. In alizarin there are, for example, two characteristic

hydroxyl groups (OH) occupying a special (ortho) position in the

molecule, i.e. they are next to each other, and also next to one of

the socalled ketone groups (C:O). In other Mordant Colours there are

carboxyl (COOH) as well as hydroxyl groups, which are all-important in

this respect. In addition to this, the general dyeing property is

influenced by the constitution of the molecule itself, and by the

presence of other side-groups, e.g. NH2, HSO3, &c., which modify the

colour as to solubility or hue. Hence it is that the members of this

group, while possessing the mordant-dyeing property in common, differ

materially in other points. Some, like alizarin, are not in themselves

to be regarded as colouring matters, but rather as colouring

principles, because they only yield useful dyes in combination with

metallic oxides. According to their constitution, these may yield one

or many colours with the various metallic oxides employed, and they

are used for cotton as well as for wool and silk. Other Mordant

Colours, e.g. many of the Direct Colours and others, are capable of

dyeing either the vegetable or animal fibres without the aid of a

mordant; they are fully developed colouring matters in themselves, and

possess the mordantdyeing property as an additional feature, in

consequence of the details of their chemical constitution, to which

reference has been made in the foregoing paragraphs. As a rule these

yield, at most, various shades of one colour with the different

oxides, and are only suitable for the animal fibres, particularly

wool.

In the following list, the most important artificial Mordant Colours

are arranged according to the colour they give in conjunction with the

aluminium mordant, unless otherwise indicated. Some of those named

here dye the animal fibres, even without mordants; some are Direct

Colours possessing mordant-dyeing properties, others are sulphonic

acid derivatives of Alizarin Colours, suitable for wool but not for

cotton.

_Red._--Alizarin, anthrapurpurin, flavopurpurin, purpurin, alizarin

Bordeaux, alizarin garnet R, alizarin maroon, alizarin S, cloth red,

diamine fast red, anthracene red, chrome red, chrome Bordeaux,

salicine red, erio chrome red, emin red, milling red.

_Orange and Yellow._--Alizarin orange, alizarin orange G, alizarin

yellow paste, alizarin yellow A, alizarin yellow C, anthracene yellow,

galloflavin, alizarin yellow GG, alizarin yellow R, diamond flavin G,

chrome yellow D, Crumpsall yellow, fast yellow, diamond yellow, benzo

orange R, cloth orange, carbazol yellow, chrysamine, milling orange.

_Green._--Coerulein, coerulein S, alizarin green S, fast green (Fe),

naphthol green (Fe), Dioxin (Fe), Gambine (Fe), azo green, gallanil

green, alizarin green G and B, acid alizarin green, alizarin cyanine

green, alizarin viridine, diamond green, chrome green, Domingo green.

_Blue._--Alizarin blue, alizarin blue S, alizarin cyanine, anthracene

blue, brilliant alizarin blue, alizarin indigo blue S, gallanilic

indigo, acid alizarin blue, brilliant alizarin cyanine, alizarin

grisole, alizarin sky blue, alizarin saphirole, gallanilide blue,

delphine blue, gallamine blue, celestine blue, chrome blue, gallazine

A, phenocyanine, coreine.

_Purple and Violet._--Gallein, alizarin heliotrope, anthraquinone

violet, chrome prime, gallocyanine, chrome violet, anthracene chrome

violet.

_Brown._--Anthracene brown, chromogen, cloth brown, diamond brown,

alizarin brown, fast brown, alizarin acid brown, chrome brown,

palatine chrome brown, erio chrome brown.

_Black._--Alizarin black, diamond black, alizarin blue black, alizarin

cyanine black, alizarin fast grey, chromotrope, chrome black, erio

chrome black, anthracite black, acid alizarin black, anthracene chrome

black.

A brief description of the application of a few of the more important

of the above colouring matters will suffice.

_Alizarin_, _Anthrapurpurin_ and _Flavopurpurin_ give somewhat similar

shades with the different mordants, namely, brown with chromium, red

with aluminium, orange with tin, and purple with iron.

In _wool_-dyeing they are applied along with other Mordant Colours on

chromium mordant for the production of a large variety of compound

shades, browns, drabs, greys, &c., the presence of acetic acid in the

dyebath being advantageous. When alum and tartar mordant is employed,

for the production of reds, it is necessary to add a small amount (4%)

of calcium acetate to the dyebath, in order to neutralize the strong

acidity of the mordanted wool, and to furnish the calcium of the

colour-lake fixed upon the fibre, which is regarded as an

aluminium-calcium compound of the colouring matter.

In _cotton_-dyeing the above colouring matters are chiefly used for

the production of so-called Turkey-red, a colour remarkable for its

brilliancy and its fastness to light and soap. These properties are

due to the preparation of the cotton with oil, in addition to the

ordinary mordanting and dyeing, whereby there is fixed on the fibre a

permanent and stable lake, in which aluminium and calcium are combined

with alizarin and some form of fatty oxy-acid. In the older processes

employed, the preparation of the cotton with oil was effected by

passing the material several times through emulsions of olive oil and

potassium carbonate solution; at a later date, and even now in the

case of cloth, the cotton is first impregnated with hot oil (Steiner's

process), then passed through solutions of alkali carbonate. After the

preparation with oil or oil-emulsions, the cotton is "stoved," i.e.

heated for several hours in special chambers or stoves to a

temperature of about 70 deg. C., during which operation the oil is

decomposed and oxidized and becomes indelibly attached to the fibre.

The oil-prepared cotton is steeped in cold solutions of basic

aluminium sulphate or acetate, washed, dyed with alizarin, and finally

boiled for several hours with soap solution under pressure in order to

brighten the colour. In the more recent and much more expeditious

"sulphated-oil process," castor oil is employed instead of olive oil,

and before use it is submitted to a treatment with sulphuric acid, the

sulphated oil thus obtained being finally more or less neutralized

with alkali. The cotton is impregnated with this sulphated-oil

solution, dried, mordanted with aluminium acetate, dyed, dried,

steamed and soaped. The operation of steaming plays an important part

in brightening and fixing the colour-lake on the fibre. In these and

all other Turkey-red processes, the oil, probably in the form of a

fatty oxy-acid, acts as a fixing agent for the aluminium and enters

into the composition of the red lake, imparting to it both brilliancy

and permanency.

_Alizarin S_ is a sulphonic acid derivative of alizarin, and since it

is much more soluble, it readily yields level colours. Silk is dyed in

a similar manner to wool, the fibre being mordanted by the ordinary

methods and then dyed in a separate bath.

_Diamine Fast Red_ is applied to cotton as a Direct Colour, with the

addition of soda or soap to the dyebath. By treating the dyed colour

with a solution of fluoride of chromium, its fastness to washing is

materially increased. Wool is dyed in a similar manner, sodium

sulphate being added to the dyebath, and the dyed colour treated with

fluoride of chromium or bichromate of potash. On wool, the colour is

so extremely fast to light and to milling that it may well serve as a

substitute for alizarin.

_Alizarin Orange_ is employed in the same manner as alizarin. In

wool-dyeing it is usually applied on chromium mordant for browns and a

variety of compound shades in combination with other Alizarin Colours

and dyewood extracts, less frequently on aluminium mordant.

_Galloflavin_ is used in wool and silk dyeing on chromium mordant as a

substitute for fustic and other yellow dyewoods, to furnish the yellow

part of compound shades.

The alizarin yellows, R and GG, anthracene yellow, diamond flavine,

chrome yellow, diamond yellow, carbazol yellow, chrysamine, &c., are

Direct Colours with mordant-dyeing properties. They also serve as

substitutes for fustic in wool or silk dyeing, and are dyed either on

a chromium mordant, or first in an acid bath and afterwards saddened

with bichromate of potash.

_Coerulein_ is employed in dyeing wool, silk or cotton with aluminium

or chromium mordants, either as a self-colour or for compound shades.

With aluminium mordant the colour is a moderately bright green, more

particularly on silk; with chromium mordant, an olive-green. Coerulein

S is the more soluble bisulphite compound of the ordinary coerulein.

It is applied in the same manner, care being taken, however, to dye

for some time (one hour) at a temperature not exceeding 60 deg. C.

until the bath is nearly exhausted, and then only raising the

temperature to the boiling point. Without this precaution coerulein S

is decomposed, and the ordinary insoluble coerulein is precipitated.

The colours obtained are very fast to light.

_Fast Green_, _Dioxine_ and _Gambine_ are chiefly of use in

calico-printing and in wool-dyeing. With iron mordant they yield

olive-greens, which on wool are extremely fast to light. Cotton is

impregnated with ferrous acetate, dried, aged and fixed with silicate

of soda, then dyed in a neutral bath. Wool is mordanted with ferrous

sulphate and tartar (3% of each) and dyed in a neutral bath.

_Acid Alizarin Green_, _Alizarin Cyanine Green_ and _Diamond Green_

all dye wool direct in a bath acidified with acetic or sulphuric acid,

and the dyed colour may be afterwards fixed or saddened with

bichromate of potash, or they may be dyed on chromium-mordanted wool.

The first method is very useful for pale shades, since the colours are

very level or regular.

_Alizarin Blue_ is a dark blue dyestuff which, owing to the fastness

of the colours it yields, has for many years been regarded as a worthy

substitute for indigo in wool-dyeing. It is applied in the same manner

as alizarin, the chromium mordant being alone employed. Alizarin blue

S is the soluble sodium bisulphite compound of alizarin blue; it

corresponds, therefore, to the above-mentioned coerulein S, and in its

application the same precautions as to the temperature of the dyebath

are necessary. The fastness of the dyed colours to light, milling and

acid satisfy the highest requirements.

_Alizarin Cyanine_, _Anthracene Blue_ and _Brilliant Alizarin Blue_

were discovered later than the above-mentioned alizarin blues, and,

owing to their greater solubility and other advantages, they have

largely replaced them as substitutes for indigo. They are dyed on

chromium-mordanted wool, silk or cotton, and yield dark purplish or

greenish blues, according to the particular brand employed. The

fastness of the dyed colours to light, and general durability, are

very satisfactory, but in fastness to milling and acids they are to

some extent inferior to alizarin blue.

_Celestine Blue_ and _Chrome Blue_ dye purplish blue and bright blue

respectively, and are dyed in the ordinary way upon a chromium

mordant. The colours they yield are inferior to the Alizarin Colours

in fastness to light, but on account of their clear shades they are

often used for brightening other colours.

_Brilliant Alizarin Cyanine_, _Alizarin Viridine_ and _Alizarin

Saphirole_ are true Alizarin Colours, and possess the same fastness to

light as other colours of this class. Unlike most of the Alizarin

Colours, they are capable of dyeing wool satisfactorily without the

aid of a metallic mordant--namely, with the addition of sulphuric acid

to the dyebath, in the same manner as the Acid Colours. If necessary,

the dyed colours may be treated with bichromate of potash. The colours

thus produced are very fast to light and very level, hence these

dyestuffs are valuable in the production of the most delicate compound

shades, such as drabs, slates, greys, &c., which are desired to be

fast to light. Alizarin saphirole dyes clear blue, the colour produced

being much more brilliant even than those of brilliant alizarin

cyanine.

_Gallein_, _Gallocyanine_, and especially _Chrome Violet_, dye

somewhat bright purple shades, and are hence frequently employed for

brightening other colours, but they are only moderately fast to light.

They are applied in the usual manner on a chromium mordant.

_Anthracene Brown_ is largely employed in the production of compound

shades. It dyes a dark, somewhat reddish, brown on chromium mordant,

the colour being very even and extremely fast to light.

_Alizarin Black_ is dyed on chromium mordant in the same manner as

alizarin, and is used as a self-colour or in combination with other

Alizarin Colours.

_Diamond Black_ is very useful for dyeing good blacks on wool, fast to

light and acids. The wool is first dyed with the addition of acetic

and finally sulphuric acid. When the dyebath is exhausted, bichromate

of potash (2%) is added, and boiling is continued for half an hour

longer.

The _erio chrome colours_ (black, brown, red, &c.) are applied in wool

dyeing like diamond black.

_Chromotrope_, of which there are several brands, is an Acid Colour

which is applied to wool in an acid bath in the usual manner. The red

or purple colours thus obtained are saddened in the same bath with

bichromate of potash and changed into black, the colouring matter

being oxidized and simultaneously combined with chromium.

MISCELLANEOUS COLOURS.--Under this head there may be arranged a few

dyestuffs which, although capable of inclusion under one or other of

the foregoing groups, it is more convenient to treat of separately.

Indigo, Aniline Black and Catechu, for example, might be placed in the

class of Developed Colours, since they are all developed on the fibre,

and indeed by the same method, namely, by oxidation.

_Indigo_ is one of our most important blue dyestuffs, which has been

employed from the earliest times. Indigo, being insoluble in water,

would be of no use in dyeing if it were not capable of being rendered

soluble. This is effected in two ways, corresponding to which there

are two methods of dyeing with indigo. One method consists in

dissolving the indigo in very strong sulphuric acid, whereby it is

converted into indigotin-disulphonic acid (Indigo Extract), which is

readily soluble in water. This substance belongs to the group of Acid

Colours; hence it is applied to the animal fibres, wool and silk, by

boiling in a solution of the colouring matter slightly acidified with

sulphuric acid. The second and most important method is based on the

fact that under the influence of reducing agents (i.e. substances

capable of yielding nascent hydrogen) indigo blue is changed into

indigo white, which is soluble in alkali, the solution thus obtained

being called a "vat." If textile materials are steeped in a clear

yellow solution of the reduced indigo and then exposed to air, the

indigo white absorbed by the fibre is oxidized and reconverted into

indigo blue within and upon the fibre, which thus becomes dyed blue;

this is the so-called "indigo-vat" method of dyeing. Comparing the two

methods, the "indigo-extract" method is only applicable to the animal

fibres, and although it gives brighter colours, they are fugitive to

light and are decolourized by washing with alkaline solutions; the

"vat method" is applicable to all fibres, and gives somewhat dull

blues, which are very fast to light, washing, &c.

_Cotton_ is dyed by means of the "_lime and copperas vat_," the "_zinc

powder vat_," or the "_hydrosulphite vat_." In the first-mentioned vat

the ingredients are quicklime, ferrous sulphate and finely ground

indigo; the lime decomposes the ferrous sulphate and precipitates

ferrous hydrate; this quickly reduces the indigo to indigo white,

which dissolves in the excess of lime present. The ingredients of the

zinc powder vat are zinc powder, lime and indigo; in the presence of

the lime and indigo the zinc takes up oxygen from the water,

liberating the hydrogen necessary to reduce the indigo, as in the

previous vat. The constituents of the hydrosulphite vat are

hydrosulphite of soda, lime and indigo. The requisite hydrosulphite of

soda is prepared by allowing zinc powder (13 lb.) to act upon a cold

concentrated solution of bisulphite of soda (17 gallons of sp. gr.

1.225), taking care to avoid, as much as possible, access of air and

any heating of the mixture, to prevent decomposition. The solution

thus obtained is thoroughly neutralized by the addition of lime; and

after settling, the clear liquor is used for the vat, along with

indigo and lime. Here again the hydrosulphite takes up oxygen from the

water and liberates the necessary hydrogen. It is found convenient to

prepare, in the first instance, a very concentrated standard of

reduced indigo, and to add as much of this to the dye-vat as may be

required, along with lime and a little hyposulphite of soda. The

advantages of this vat are that it is easily prepared and that there

is very little sediment; moreover, it can be employed in dyeing wool,

as well as cotton, and it is now very generally in use. The vat

usually employed for dyeing _wool_ is the so-called "woad vat," which

differs from the foregoing in that the hydrogen necessary to reduce

the indigo and bring it into solution is furnished, not by the action

of chemical agents, but by means of fermentation. The ingredients of

the woad vat are indigo, woad, bran, madder and lime. The woad here

employed is prepared by grinding the leaves of the woad plant (_Isatis

tinctoria_) to a paste, which is allowed to ferment and then partially

dried. It serves as the ferment to excite lactic and butyric

fermentation with the aid of the bran and madder, the necessary

hydrogen being thus evolved. Excessive fermentation is avoided by

making timely additions of lime; sluggish fermentation is accelerated

by additions of bran and slightly raising the temperature. When the

reduction and complete solution of the indigo is effected, the vat is

allowed to settle, and the woollen material is immersed and moved

about in the clear liquor for half an hour to two hours, according to

the shade required, then squeezed and exposed to the air in order to

develop the blue colour on the fibre.

_Thioindigo red_ is an artificial colouring matter belonging to the

indigo series and comes into the market in the form of a paste. It is

used in dyeing in exactly the same way as indigo, yielding shades

which range from a somewhat dull pink to a full claret shade of red.

The colours obtained are remarkable for their fastness.

_Indanthrene_. This colouring matter, which is also sold as a paste,

is an anthracene derivative, being formed by the action of caustic

potash on [beta]-amidoanthraquinone. It is reduced by hydrosulphite of

soda yielding a blue vat, in which cotton and other vegetable fibres

are dyed in the same way as in the indigo vat. Since a fair amount of

caustic soda is necessary for the setting of the vat, the dyestuff is

not suitable for animal fibres. Indanthrene yields on cotton reddish

shades of blue which are extremely fast to all external influences; in

fact the colour is so fast that when once fixed on cotton it cannot be

removed again from the fibre by any known means.

Other vat colours belonging to this series, which are similarly

applied, are flavanthrene (yellow), viridanthrene (green),

fuscanthrene (grey-brown), violanthrene (dull violet) and melanthrene

(grey to black). The _algol colours_ resemble the indanthrene colours

in their properties and application.

_Aniline Black_ differs from other dyes in that it is not sold as a

ready-made dyestuff, but is produced _in situ_ upon the fibre by the

oxidation of aniline. It is chiefly used for cotton, also for silk and

cotton-silk union fabrics, but seldom or not at all for wool. Properly

applied, this colour is one of the most permanent to light and other

influences with which we are acquainted. One method of dyeing cotton

is to work the material for about two hours in a cold solution

containing aniline (10 parts), hydrochloric acid (20 parts),

bichromate of potash (20 parts), sulphuric acid (20 parts), and

ferrous sulphate (10 parts). The ferrous sulphate here employed is

oxidized by the chromic acid to a ferric salt, which serves as a

carrier of oxygen to the aniline. This method of dyeing is easily

carried out, and it gives a good black; but since much of the

colouring matter is precipitated on the fibre superficially as well as

in the bath itself, the colour has the defect of rubbing off. Another

method is to impregnate the cotton with a solution containing aniline

hydrochloride (35 parts), neutralized with addition of a little

aniline oil, sodium chlorate (10 parts), ammonium chloride (10 parts).

Another mixture is 1.8 part aniline salt, 12 parts potassium

ferrocyanide, 200 parts water, 3.5 parts potassium chlorate dissolved

in water. After squeezing, the material is passed through a special

oxidation chamber, the air of which is heated to about 50 deg. C. and

also supplied with moisture. This oxidizing or ageing is continuous,

the material passing into the chamber at one end in a colourless

condition, and after about 20 minutes passing out again with the black

fully developed, a final treatment with hot chromic acid solution and

soaping being necessary to complete the process. In this method,

employing the first-mentioned solution, chlorate of copper is formed,

and this being a very unstable compound, readily decomposes, and the

aniline is oxidized by the liberated chlor-oxygen compounds. The

presence in the mixture of a metallic salt is very important in aiding

the development of the black, and for this purpose salts of vanadium,

cerium and copper have proved to be specially useful. The chemistry of

aniline black is still incomplete, but it would appear that there are

several oxidation products of aniline. The first product is so-called

emeraldine, a dark green substance of the nature of a salt, which by

treatment with alkali yields a dark blue base called azurine. The

further oxidation of emeraldine yields nigraniline, also a dark green

salt, but the free base of which has a violet black colour. The latter

becomes greenish under the influence of acids, especially sulphuric

acid, and this explains the defect known as "greening" which is

developed in ordinary aniline blacks during exposure to air. By a

supplementary oxidation with chromic acid such a black is rendered

ungreenable, the nigraniline being probably changed into the more

stable chromate of nigraniline.

_Catechu_ is a valuable brown dyestuff, obtained from various species

of _Acacia_, _Areca_ and _Uncaria_ growing in India. The wood, leaves

and fruit of these plants are extracted with boiling water; the

decoction is then evaporated to dryness or to a pasty consistency.

Catechu is largely used by the cotton dyer for the production of

brown, drab and similar colours. It is seldom employed for wool.

Cotton is usually dyed by boiling it for about one hour in a decoction

of catechu (100%) containing copper sulphate (5%). After squeezing,

the material is boiled for about fifteen minutes in a solution of

bichromate of potash (1/4 oz. per gal.), then washed and dried. By

repeating the operations two or three times deeper shades are

obtained. During the boiling with catechu the cotton attracts the

active principles catechin and catechu-tannic acid, but it thus

acquires only a pale brown colour; in the bichromate of potash,

however, these are oxidized to form insoluble japonic acid, which

permeates the fibre, and a deep brown colour is thus developed.

Catechu browns are fast to a variety of influences, e.g. washing,

alkalis, acids, &c., but less so to light. Catechu has been recently

much employed, in conjunction with copper sulphate, for dyeing the

so-called khaki-brown on woollen material for military clothing. On

silk, catechu is much used for weighting purposes in dyeing black.

MINERAL COLOURS.--Those include Chrome Yellow, Iron Buff, Prussian

Blue and Manganese Brown.

_Chrome Yellow_ is only useful in cotton-dyeing as a self-colour, or

for conversion into chrome orange, or, in conjunction with indigo, for

the production of fast green colours. The cotton is first impregnated

with a solution of lead acetate or nitrate, squeezed, and then passed

through a solution of sodium sulphate or lime water to fix the lead on

the fibre as sulphate or oxide of lead. The material is then passed

through a solution of bichromate of potash. The colour is changed to a

rich orange by a short, rapid passage through boiling milk of lime,

and at once washing with water, a basic chromate of lead being thus

produced. The colour is fast to light, but has the defect of being

blackened by sulphuretted hydrogen.

_Iron Buff_ is produced by impregnating the cotton with a solution of

ferrous sulphate, squeezing, passing into sodium hydrate or carbonate

solution, and finally exposing to air, or passing through a dilute

solution of bleaching powder. The colour obtained, which is virtually

oxide of iron, or iron-rust, is fast to light and washing, but is

readily removed by acids.

_Prussian Blue_ is applicable to wool, cotton and silk, but since the

introduction of coal-tar blues its employment has been very much

restricted. The colour is obtained on cotton by first dyeing an iron

buff, according to the method just described, and then passing the

dyed cotton into an acidified solution of potassium ferrocyanide, when

the blue is at once developed. A similar method is employed for silk.

Wool is dyed by heating it in a solution containing potassium

ferricyanide and sulphuric acid. The colour is developed gradually as

the temperature rises; it may be rendered brighter by the addition of

stannous chloride. On wool and silk Prussian blue is very fast to

light, but alkalis turn it brown (ferric oxide).

_Manganese brown_ or _bronze_ is applied in wool, silk and cotton

dyeing. The animal fibres are readily dyed by boiling with a solution

of potassium permanganate, which, being at first absorbed by the

fibre, is readily reduced to insoluble brown manganic hydrate. Since

caustic potash is generated from the permanganate and is liable to act

detrimentally on the fibre, it is advisable to add some magnesium

sulphate to the permanganate bath in order to counteract this effect.

Imitation furs are dyed in this manner on wool-plush, the tips or

other parts of the fibres being bleached by the application of

sulphurous acid. Cotton is dyed by first impregnating it with a

solution of manganous chloride, then dyeing and passing into a hot

solution of caustic soda. There is thus precipitated on the fibre

manganous hydrate, which by a short passage into a cold dilute

solution of bleaching powder is oxidized and converted into the brown

manganic hydrate. This manganese bronze or brown colour is very

susceptible to, and readily bleached by, reducing agents; hence when

exposed to the action of an atmosphere in which gas is freely burnt,

the colour is liable to be discharged, especially where the fabric is

most exposed. In other respects manganese bronze is a very fast

colour.

_Dyeing on a large Scale._--It is not possible to give here more than a

bare outline of the methods which are used on the large scale for dyeing

textile fibres, yarns and fabrics. In principle, dyeing is effected by

allowing an aqueous[1] solution of the dye-stuff, with or without

additions (alkalis, acids, salts, &c.), to act, usually at an elevated

temperature, on the material to be dyed. During the process it is

necessary, in order to ensure the uniform distribution of the dyestuff

in the material, that the latter should either be moved more or less

continuously in the dye liquor or that the dye liquor should be

circulated through the material. The former mode of operation is in

general use for hank, warp and piece dyeing, but for textile fibres in

the loose condition or in the form of "slubbing," "sliver" or "cops"

(see SPINNING) the latter method has, in consequence of the introduction

of improved machinery, come more and more into vogue within recent

years.

_Loose Material._--Cotton and wool are frequently dyed in the loose

state, i.e. before being subjected to any mechanical treatment. The

simplest method of effecting this is to treat the material in open

vessels (boilers) which can be heated either by means of steam or direct

fire. Since, however, a certain amount of felting or matting of the

fibres cannot be avoided, it is frequently found to be more advantageous

to effect these treatments in specially constructed apparatus in which

the dye liquors are circulated through the material.

[Illustration: FIG. 1.--Dye-vat for Yarn.]

[Illustration: FIG. 2.]

_Yarn._--Yarn may be dyed either in the hank, in the warp or in the cop,

i.e. in the form in which the yarn leaves the spinning frame. The dyeing

in the _hank_ is carried out in rectangular dye-vats constructed of wood

or stone like that shown in fig. 1, in which the hanks are suspended

from smooth wooden poles or rods resting on the sides, and are thus

immersed almost entirely in the dye liquor. The heating of the vat is

effected either by means of live steam, i.e. by blowing steam into the

dye solution from a perforated pipe which runs along the bottom of the

vat, or by means of a steam coil similarly situated. In order to expose

the hanks as uniformly as possible to the action of the dye liquor, they

are turned by hand at regular intervals until the operation is finished.

Washing off is effected in the same or in a similar vessel, after which

excess of water is removed by wringing by hand, through squeezing

rollers or, what is generally preferred, in a hydro-extractor

(centrifugal machine). The drying of the dyed and washed yarn is

generally effected by suspending it on poles in steam-heated drying

chambers. Yarn in the _warp_ is dyed in vats or "boxes" like that shown

in fig. 2, through which it is caused to pass continuously. The warps to

be dyed pass slowly up and down over the loose rollers in the first box

B, then through squeezing rollers S into the next, and the same thing

occurs in the second (also third and fourth in a four-box machine) box

A, whence they are delivered through a second pair of squeezing rollers

S1 into the wagon W. The boxes may contain the same or different

liquors, according to the nature of the dyestuff employed. Washing is

done in the same machine, while drying is effected on a cylinder drying

machine like that shown in figs. 8 and 9 of BLEACHING. Latterly,

machines have been introduced for dyeing warps on the beam, the dye

liquor being caused to circulate through the material, and the system

appears to be meeting with considerable success. Large quantities of

yarn, especially cotton, are now dyed in the cop. When the dyed yarn is

to be used as weft the main advantage of this method is at once

apparent, inasmuch as the labour, time and waste of material incurred by

reeling into hanks and then winding back into the compact form so as to

fit into the shuttle are avoided. On the other hand the number of fast

dyestuffs suitable for cop dyeing is very limited. In the original

cop-dyeing machine constructed by Graemiger a thin tapering perforated

metallic tube is inserted in the hollow of each cop. The cops are then

attached to a perforated disk (which constitutes the lid of a chamber or

box) by inserting the protruding ends of the tubes into the

perforations. The chamber is now immersed in the dye-bath and the hot

liquor is drawn through the cops by means of a centrifugal pump and

returned continuously to the dye-bath. This principle, which is known as

the skewer or spindle system, is the one on which most modern cop-dyeing

machines are based. In the so-called "compact" system of cop dyeing the

cops are packed as closely as possible in a box, the top and bottom (or

the two opposite sides) of which are perforated, the interstices between

the cops being filled up with loose cotton, ground cork or sand. The dye

liquor is then drawn by suction or forced by pressure through the box,

thus permeating and dyeing the cops.

[Illustration: FIG. 3.--Dye-jigger.]

_Pieces._--Plain shades are usually dyed in the piece, this being the

most economical and at the same time the most expeditious means of

obtaining the desired effect. The dyeing of piece goods may be effected

by running them through the dye liquor either at full breadth or in rope

form. The machine in most common use for the first method is the

Lancashire "jigger," which is simple in principle and is shown in

section in fig. 3. It consists essentially of a dye-vessel constructed

of wood or cast iron and containing loose guide rollers, r and r, at the

top and bottom. By coupling up the roller B with the driving gear the

pieces which are batched on A are drawn through the dye liquor and

rolled on to B. A band brake (not shown in the figure) applied to the

axis of A gives the pieces the required amount of tension in passing

through the dye-bath. As soon as the whole of the pieces have passed

through in this way from A to B, the machine is reversed, and roller A

draws them back again through the bath in a similar way on to roller A.

This alternating process goes on until the dyeing is finished, when the

goods are washed off, squeezed and dried. The jigger is especially

useful in cotton piece dyeing, one great advantage being that it is

suited for what is known as a "short bath," i.e. a bath containing a

minimum amount of dye liquor, this being of great importance in the

application of dyestuffs which do not exhaust well, like the direct

colours and the sulphide colours. The padding machine is similar in

principle to the jigger, the pieces running over loose guide rollers

through the mordant or dye solution contained in a trough of suitable

shape and size, but on leaving the machine they pass through a pair of

squeezing rollers which uniformly express the excess of liquor and cause

it to be returned to the bath. The padding machine is used more for

preparing (mordanting, &c.) than for dyeing.

[Illustration: FIG. 4.--Dye-vat for Piece Goods.]

For the dyeing of pieces in rope form a so-called "dye-beck" is used,

which is a machine of larger dimensions than the jigger. Across the

dye-bath is attached a winch W (see fig. 4), by means of which the

pieces, sewn together at the ends so as to form an endless band, are

caused to circulate through the machine, being drawn up on the front

side of the machine and allowed to drop back into the dye liquor on the

other. This form of machine is particularly suited for the mordanting

and dyeing of heavy goods. Washing off may be done in the same machine.

The drying of piece goods is done on steam-heated cylinders like those

used for the drying of bleached goods (see BLEACHING).

The operations which precede dyeing vary according to the material to be

dyed and the effects which it is desired to produce. Loose wool, woollen

and worsted yarn and piece goods of the same material are almost

invariably scoured (see BLEACHING) before dyeing in order to remove the

oily or greasy impurities which would otherwise interfere with the

penetration of the dye solution. Silk is subjected to the process of

discharging or boiling off (see BLEACHING) in order to remove the silk

gum or sericine. Cotton which is to be dyed in dark shades does not

require any preparatory treatment, but for light or very bright shades

it is bleached before dyeing. Wool and silk are seldom bleached before

dyeing. Cotton, wool and union (cotton warp and worsted weft) fabrics

are frequently singed (see BLEACHING) before dyeing. Worsted yarn,

especially two-fold yarn, is very liable to curl and become entangled

when scoured, and in order to avoid this it is necessary to stretch and

"set" it. To this end it is stretched tight on a specially constructed

frame, placed in boiling water, and then cooled. Similarly, union

fabrics are liable to "cockle" when wetted, and although this defect may

be put right in finishing, spots of water or raindrops will give an

uneven appearance of a permanent character to the goods. To avoid this,

the pieces are subjected previous to dyeing to the so-called "crabbing"

process, in which they are drawn under great tension through boiling

water and wound on to perforated hollow cylinders. Steam is then blown

through the goods and they are allowed to cool.

Theory of dyeing.

With respect to the question of colour, we meet with two kinds of

substances in nature, those which possess colour and those which do not.

Why this difference? The physicist says the former are bodies which

reflect all the coloured rays of the spectrum composing white light--if

opaque, they appear white; if transparent, they are colourless. The

latter are bodies which absorb some of the spectrum rays only,

reflecting the remainder, and these together produce the impression of

colour. A black substance is one which absorbs all the spectrum rays.

The fundamental reason, however, of this difference of action on the

part of substances towards light remains still unknown. All substances

which possess colour are not necessarily dyestuffs, and the question may

be again asked, Why? It is a remarkable circumstance that most of the

dyestuffs at present employed occur among the so-called aromatic or

benzene compounds derived from coal-tar, and a careful study of these

has furnished a general explanation of the point in question, which

briefly is, that the dyeing property of a substance depends upon its

chemical constitution. Speaking generally, those colouring matters which

have the simplest constitution are yellow, and as the molecular weight

increases their colour passes into orange, red, violet and blue. In

recent years chemists have begun to regard the constitution of nearly

all dyestuffs as similar to that of Quinone, and some even believe that

all coloured organic compounds have a quinonoid structure. According to

O.N. Witt, a colourless hydrocarbon, e.g. benzene, becomes coloured by

the introduction of one or more special groups of atoms, which he terms

the colour-bearing or _chromophorous groups_, e.g. NO2, -- N:N --, &c.

Benzene, for example, is colourless, whereas nitro-benzene and

azo-benzene are yellow. Such compounds containing chromophorous groups

are termed chromogens, because, although not dyestuffs themselves, they

are capable of generating such by the further introduction of

salt-forming atomic groups, e.g. OH, NH2. These Witt terms

_auxochromous_ groups. In this way the chromogen _tri-nitro-benzene_,

C6H3(NO2)3, becomes the dyestuff _tri-nitro-phenol_ (picric acid),

C6H2(NO2)3(OH), and the chromogen _azo-benzene_, C6H5.N : N.C6H5, is

changed into the dyestuff _amido-azo-benzene_ (Fast Yellow), C6H5.N :

N.C6H4(NH2). These two dyestuffs are typical of a large number which

possess either an acid or a basic character according as they contain

hydroxyl (OH) or amido (NH2) groups, and correspond to the Acid Colours

and Basic Colours to which reference has already been made. Other

important atomic groups which frequently occur, in addition to the

above, are the carboxyl (COOH) and the sulphonic acid (HSO3) groups;

these either increase the solubility of the colouring matter or assist

in causing it to be attracted by the fibre, &c. In many cases the free

colour-acid or free colour-base has little colour, this being only

developed in the salt. The free base rosaniline, for example, is

colourless, whereas the salt magenta (rosaniline hydrochloride) has a

deep crimson colour in solution. The free acid Alizarin is orange, while

its alumina-salt is bright red. It may be here stated that the

scientific classification of colouring matters into Nitro-colours,

Azo-colours, &c., already alluded to, is based on their chemical

constitution, or the chromophorous groups they contain, whereas the

classification according to their mode of application is dependent upon

the character and arrangement of the auxochromous groups. The question

of the mordant-dyeing property of certain colouring matters containing

(OH) and (COOH) groups has already been explained under the head of

_Artificial Mordant Colours_.

The peculiar property characteristic of dyestuffs, as distinguished from

mere colouring matters, namely, that of being readily attracted by the

textile fibres, notably the animal fibres, appears then to be due to

their more or less marked acid or basic character. Intimately connected

with this is the fact that these fibres also exhibit partly basic and

partly acid characters, due to the presence of carboxyl and amido

groups. The behaviour of magenta is typical of the Basic Colours. As

already indicated, rosaniline, the base of magenta, is colourless, and

only becomes coloured by its union with an acid, and yet wool and silk

can be as readily dyed with the colourless rosaniline (base) as with the

magenta (salt). The explanation is that the base rosaniline has united

with the fibre, which here plays the part of an acid, to form a coloured

salt. It has also been proved that in dyeing the animal fibres with

magenta (rosaniline hydrochloride), the fibre unites with the rosaniline

only, and liberates the hydrochloric acid. Further, magenta will not dye

cotton unless the fibre is previously prepared, e.g. with the mordant

tannic acid, with which the base rosaniline unites to form an insoluble

salt. In dyeing wool it is the fibre itself which acts as the mordant.

In the case of the Acid Colours the explanation is similar. In many of

these the free colour-acid has quite a different colour from that of the

alkali-salt, and yet on dyeing wool or silk with the free colour-acid,

the fibre exhibits the colour of the alkali-salt and not of the

colour-acid. In this case the fibre evidently plays the part of a base.

Another fact in favour of the view that the union between fibre and

colouring matter is of a chemical nature, is that by altering the

chemical constitution of the fibre its dyeing properties are also

altered; oxycellulose and nitrocellulose, for example, have a greater

attraction for Basic Colours than cellulose. Such facts and

considerations as these have helped to establish the view that in the

case of dyeing animal fibres with many colouring matters the operation

is a _chemical_ process, and not merely a mechanical absorption of the

dyestuff. A similar explanation does not suffice, however, in the case

of dyeing cotton with the Direct Colours. These are attracted by cotton

from their solutions as alkali salts, apparently without decomposition.

The affinity existing between the fibre and colouring matter is somewhat

feeble, for the latter can be removed from the dyed fibre by merely

boiling with water. The depth of colour obtained in dyeing varies with

the concentration of the colour solution, or with the amount of some

neutral salt, e.g. sodium chloride, added as an assistant to the

dye-bath; moreover, the dye-bath is not exhausted. The colouring matter

is submitted to the action of two forces, the solvent power of the water

and the affinity of the fibre, and divides itself between the fibre and

the water. After dyeing for some time, a state of equilibrium is

attained in which the colouring matter is divided between the fibre and

the water in a given ratio, and prolonged dyeing does not intensify the

dyed colour.

Some investigators hold the view that in some cases the fibres exert a

purely physical attraction towards colouring matters, and that the

latter are held in an unchanged state by the fibre. The phenomenon is

regarded as one of purely mechanical surface-attraction, and is compared

with that exercised by animal charcoal when employed in decolourizing a

solution of some colouring matter. Some consider such direct dyeing as

mere diffusion of the colouring matter into the fibre, and others that

the colouring matter is in a state of "solid solution" in the fibre,

similar to the solution of a metallic oxide in coloured glass. According

to this latter view, the cause of the dyeing of textile fibres is

similar to the attraction or solvent action exerted by ether when it

withdraws colouring matter from an aqueous solution by agitation.

Latterly the view has been advanced that dyeing is due to precipitation

of the colloid dyestuffs by the colloid substance of the fibre.

In the case of colours which are dyed on mordants, the question is

merely transferred to the nature of the attraction which exists between

the fibre and the mordant, for it has been conclusively established that

the union between the colouring matter and the mordant is essentially

chemical in character.

From our present knowledge it will be seen that we are unable to give a

final answer to the question of whether the dyeing process is to be

regarded as a chemical or a mechanical process. There are arguments and

facts which favour both views; but in the case of wool and silk dyeing,

the prevailing opinion in most cases is in favour of the chemical

theory, whereas in cotton-dyeing, the mechanical theory is widely

accepted. Probably no single theory can explain satisfactorily the

fundamental cause of attraction in all cases of dyeing, and further

investigation is needed to answer fully this very difficult and abstruse

question.

Conclusion.

The poisonous nature or otherwise of the coal-tar dyes has been

frequently discussed, and the popular opinion, no doubt dating from the

time when magenta and its derivatives were contaminated with arsenic,

seems to be that they are for the most part really poisonous, and ought

to be avoided for colouring materials worn next the skin, for articles

of food, &c. It is satisfactory to know that most of the colours are not

poisonous, but some few are--namely, Picric acid, Victoria Orange,

Aurantia, Coralline, Metanil Yellow, Orange II. and Safranine. Many

coal-tar colours have, indeed, been recommended as antiseptics or as

medicinal remedies, e.g. Methyl Violet, Auramine and Methylene Blue,

because of their special physiological action. In histology and

bacteriology many coal-tar colours have rendered excellent service in

staining microscopic preparations, and have enabled the investigator to

detect differences of structure, &c., previously unsuspected. In

photography many of the more fugitive colouring matters, e.g. Cyanine,

Eosine, Quinoline Red, &c., are employed in the manufacture of

ortho-chromatic plates, by means of which the colours of natural objects

can be photographed in the same degrees of light and shade as they

appear to the eye--blue, for example, appearing a darker grey, yellow, a

lighter grey, in the printed photograph.

Since the year 1856, in which the first coal-tar colour, mauve, was

discovered, the art of dyeing has made enormous advances, mainly in

consequence of the continued introduction of coal-tar colours having the

most varied properties and suitable for nearly every requirement. The

old idea that the vegetable dyestuffs are superior in fastness to light

is gradually being given up, and, if one may judge from the past, it

seems evident that in the future there will come a time when all our

dyestuffs will be prepared by artificial means.

AUTHORITIES.--Macquer, Hellot and le Pileur d'Apligny, _The Art of

Dyeing Wool, Silk and Cotton_ (London, 1789); Bancroft, _Philosophy of

Permanent Colours_ (2 vols., London, 1813); Berthollet-Ure, _Elements

of the Art of Dyeing_ (2 vols., London, 1824); Chevreul, _Recherches

chimiques sur la teinture_ (Paris, 1835-1861); O'Neill, _The Chemistry

of Calico Printing, Dyeing and Bleaching_ (Manchester, 1860);

_Dictionary of Calico Printing and Dyeing_ (London, 1862);

Schutzenberger, _Traite des matieres colorantes_ (2 vols., Paris,

1867); Bolley, _Die Spinnfasern und die im Pflanzen- und Thierkorper

vorkommenden Farbstoffe_ (1867); Crookes, _A Practical Handbook of

Dyeing and Calico-Printing_ (London, 1874); Jarmain, _Wool-Dyeing_

(1876); O'Neill, _Textile Colourist_ (4 vols., Manchester, 1876);

Calvert, _Dyeing and Calico Printing_ (Manchester, 1876); Moyret,

_Traite de la teinture des soies_ (Lyon, 1877); O'Neill, _The Practice

and Principles of Calico Printing, Bleaching and Dyeing_ (Manchester,

1878); Girardin, _Matieres textiles et matieres tinctoriales_ (Paris,

1880); Hummel, _The Dyeing of Textile Fabrics_ (London, 1885);

Sansone, _Dyeing_ (Manchester, 1888); Witt, _Chemische Technologie der

Gespinnstfasern_ (Brunswick, 1888); Benedikt and Knecht, _The

Chemistry of the Coal-Tar Colours_ (London, 1889); Hurst, _Silk

Dyeing, Printing and Finishing_ (London, 1892); Noelting and Lehne,

_Anilinschwarz_ (Berlin, 1892); Knecht, Rawson and Loewenthal, _Manual

of Dyeing_ (London, 1908); Steinbeck, _Bleichen und Farben der Seide

und Halbseide_ (Berlin, 1895); Gardner, _Wool-Dyeing_ (Manchester,

1896); Rawson, Gardner and Laycock, _A Dictionary of Dyes, Mordants,

&c._ (London, 1901); Gros-Renaud, _Les Mordants en teinture et en

impression_ (Paris, 1898); Georgievics, _The Chemical Technology of

Textile Fabrics_ (London, 1902); Paterson, _The Science of Colour

Mixing_ (London, 1900); Paterson, _Colour Matching on Textiles_

(London, 1901); Beech, _The Dyeing of Cotton Fabrics_ (London, 1901);

Beech, _The Dyeing of Woollen Fabrics_ (London, 1902); _The Journal of

the Society of Dyers and Colourists_ (Bradford, 1885-1908) and the

publications of the colour manufacturers. (J. J. H.; E. K.)