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DYEING

made distinctly acid with acetic or sulphuric acid. Silk is usually dyed in a hath containing “ boiled-off liquor ” {i.e., the spent soapliquor from the operation of scouring) neutralized or slightly acidified with acetic or tartaric acid, ior a full colour use 2 or 3 per cent, colouring matter, enter the wool at a low temperature, heat gradually to near the boiling-point m the course of | hour and continue dyeing for i hour. Owing to the slight solubility of many Basic Colours, it is important to take the precaution of filteiing the colour solution into the dyebath through a flannel filter, also to neutralize the alkalinity of calcareous water with a little acetic acid, to prevent decomposition of the colouring matter and precipitation of the colour-base. „ .. . ,, 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 one or two hours ; it is then worked for half to one hour in a cold 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 vnovdcint, 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 per cent, tannic acid, or the equivalent in a decoction of sumach, myrabolams, or other tannin matter, and ^ to 3 per cent, taitar emetic. After mordanting and fixing of the mordant, the cotton is well washed and dyed in the cold or at 60° C. for ^ to 1 hour with the necessary colouring matter. Applied in this manner, Basic Colours are moderately fast to soap, but not to the action of light. Another method of mordanting cotton for dyeing with the Basic Colours is to impregnate the fibre for a few minutes with a warm solution of soap, or of so-called sulphated-oil (1 lb per gallon), then dry and work for hour in a cold solution of aluminium acetate (gallon at 1 -045° sp. gr. to 20 gallons water), and finally rinse in water. The cotton is thus mordanted or prepared with a substance analogous to oleate of alumina, in which the oleic acid acts as the real mordant and combines with the base of the colouring matter subsequently applied, while the alumina acts as the fixingagent for the oleic acid. The ultimate compound fixed upon the dyed fibre is an oleate of alumina and colour-base. The dyes thus obtained are brighter than the colours dyed on. tannin mordant, but they are not so fast to soap, and are also fugitive to light. Linen is dyed in the same manner as cotton. Jute is dyed without any previous preparation, since it behaves like a tanninmordanted 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 organic base berberine. _ The following is a list of the more important Basic Colours derived from coal-tar:— . Bed. —Magenta, Safranine, Ehodamine, Pyronme Eed, Magdala Eed. _ m • Orange.—Chrysoidine, Phosphine, Acridine Orange, lannm Orange. Yellow.—Auramine, Benzoflavine, Thioflavine T. Green. —Malachite Green, Emerald Green, Imperial Green, China Green, Brilliant Green, Victoria Green, Diamond Green, Methylene Green, Azine Green. Blue.—Methylene Blue, Toluidine Blue, Thionine Blue, Indamine Blue, Victoria Blue, Night Bine, Nile Blue, Turquoise Blue, Marine Blue, Indoine Blue, Induline, Nigrosine, Meldola Blue, Metamine Blue, Muscarine, Capri Blue, Basle Blue, Indazine, Metaphenylene Blue, Paraphenylene Blue, Toluylene Blue, Indigene, Indol Blue, Diphene Blue. Violet. Methyl Violet, Crystal Violet, Ethyl Purple, Methylene Violet, Mauve, Paraphenylene Violet, Ehoduline Violet. Brown.—Bismarck Brown. Black.—East Black. Grey. —Methylene Grey, Nigrisine, New Grey. ^ 1 J x ^ 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. Three distinct series of colouring matters of this group may be distinguished—namely, Benzidine Colours, Janus Colours, and Sulphide Colours. (a) Benzidine-Colours.—The colours of this class are frequently called the Substantive Cotton Colours, Direct Cotton Colours,

Benzo Colours, Diamine Colours, Congo Colours. Considered from the chemical point of view, they are alkali salts of sulphonated tetrazo colours obtained by azotizing certain diamido compounds, e.g., benzidine, diamido-stilbene, &c., and uniting the product thus obtained with various amines or phenols. The first colouring matter of this class was the so-called Congo Eed, 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 suitably concentrated solution of the dyestuff, when the cotton absorbs and retains the colouring matter by reason of a special natural affinity. The addition of 1 to 3 oz. sodium sulphate and ^ to ^ 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 & to J 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 hour) after-treatment with a boiling solution of copper sulphate (3 per cent.), with or without the addition of bichromate of potash (1 per cent.). Wool and silk are dyed with the Direct Colours in the same manner as cotton, or as with the Acid Colours, adding 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 Eed, 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. 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, lurmeric 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 orangeyellow colour. Annatto is the pulpy mass surrounding the seeds of Bixa orellana, a plant which grows in South America—e.^., 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 :— Bed.—Congo Eed, Brilliant Congo, Benzopurpurine, Brilliant Purpurine, Deltapurpurine, Diamine Scarlet, Diamine Fa,st Eed, Rosazurine, Salmon Red, Erica, Titan Pink, St Denis Led, Columbia Eed, Naphthylene Eed, Congo Eubine, Geranine, Brilliant Geranine. Orange.—Congo Orange, Benzo Orange, Toluylene Orange, Mikado Orange, Brilliant Orange, Columbia Orange, Diamine 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. . Green.—Benzo Olive, Columbia Green, Benzo Green, Diamine Green. , . c. i i. Blue.—Azo Blue, Benzoazurine, Brilliant Azurinc, Sulpnonazurine, Diamine Blue, Benzo Indigo Blue, Benzo Black Blue, Chicago Blue, Columbia Blue, Erie Blue, Zambesi Blue, Benzo Cyanine, Congo Blue, Diamine Sky Blue, Brilliant Benzo Blue, Benzo Chrome Black Blue. Violet. —Hessian Purple, Congo Corinth, Heliotrope, Congo Violet, Diamine Violet, Hessian Violet, Azo Violet, Benzo Violet, Violet Black, Diamine Bordeaux. Brown.—Benzo Brown, Congo Brown, Toluylene Brown Diamine Brown, Cotton Brown, Hessian Brown, Terra Cotta, Mikado Brown, Catechu Brown, Wool Brown, Columbia Brown, Zambesi Brown, Benzo Chrome Brown, Direct Fast Brown, Direct Bronze Brown, Chloramine Brown. ™ i m Black. —Diamine Black, Columbia Black, Nyanza Black, la bora Black, Zambesi Black, Chromanil Black, Benzo Black, Benz Fast Black, Direct Blue Black, Pluto Black, Oxy Diamine Black, Diamine Jet Black.