Cotton colouring matter

Cotton and wool, even non-mordanted, are dyed in a dye bath containing sodium sulphate dyed natural wool gives up its Substantive colour in a slightly alkaline medium to white cotton. . . colouring matters... 

Every cotton fibre consists of a single cell, filled with air and albumin residues, breakdown products of protoplasm. It also contains certain colouring matter. 

Basic colouring matters are those the solutions of which are decolorised by mineral acids and give a coloured precipitate with tannin (best in presence of sodium acetate). When acidified with sulphuric acid and shaken with ether, their solutions give up nothing to the solvent. They dye animal fibres in a neutral bath or one faintly acid with acetic acid, without a mordant, and they dye cotton in a tannin bath. Mineral acids remove them completely from the fibres on which they are fixed. 

Acid colouring matters give solutions which are not decolorised by mineral adds and are not precipitated by tannin. When their solutions, addified with sulphuric acid, are shaken with ether, the latter dissolves the colouring matter and leaves a residue when evaporated. They do not dye wool and silk in a neutral bath but do so in an acid bath (with sulphuric add) they are little suitable for cotton. 

Mordant colouring matters dye wool or cotton in neither a neutral, nor an add, nor an alkaline bath, but act only in presence of a metallic mordant. 

With each of these four groups the procedure is as described later. In the first place, however, the colouring matter is investigated with reference to its tintorial properties by means of dyeing tests on non-mordanted cotton or wool, on wool mordanted with aluminium sulphate and cream of tartar, on wool mordanted with chromium fluoride and cream of tartar, on cotton mordanted with tannin and then with tartar emetic, on cotton mordanted with aluminium acetate and on cotton mordanted with chromium acetate. 

The colouring is fixed directly on cotton (substantive colouring matter) ThtazoU colouring matters... 

Dyeing Test.—The two colouring matters are then used to dye equal quantities of wool, silk or cotton yarn or fabric, according to the uses for which the colouring matter is intended, the colours obtained being compared. 

In this connection it must be borne in mind that in some of these extraction tests on naturally coloured and raw cotton, flax, wool, hair, etc, an appreciable quantity of yellowish-brown colouring matter is removed, and that raw silks of a natural yellow or green colour exhibit special behaviour if subjected to some of these tests, eg, to treatment with concentrated acids ... 

Green s method includes two series of tables, one for colouring matters fixed on wool and the other for those fixed on cotton. The former series may serve also for the examination of dyestuffs on silk and the latter for those on the other principal vegetable fibres, excepting that small variations are necessary in both cases for certain groups of colouring matters. 

In the sodium acetate test the cotton remains coloured after about a minute with a saline colouring matter and after about two minutes in the case of dyes on saline mordants. 

Colouring matters which are neither acid nor basic are reduced and oxidised on the cotton itself. The resistance to reduction exhibited by certain azo-colouring matters, especially those formed directly on the fibre, is overcome by addition of very small quantities of suitable colouring matters or other reducing bodies, such as indulin scarlet, alizarin or anthia-quinone, which increase the activity of the hydrosulphite. The use of anthraquinone is preferred because it does not dye cotton, while addition of it in minimal quantity to the hydrosulphite solution and slight acidification with acetic acid yields a reagent (hydrosulphite B X) which causes reduction in every case. 

Stripping test for acid colours. Some direct or " salt dyestuffs are partly decolorised by dilute ammonia and hence might be regarded as add colouring matters. To avoid this error it is useful to add, when this test is made, a piece of mercerised white cotton. With an add dye, the cotton remains white, or is scarcely coloured, and then becomes white again when boiled a second time with dilute ammonia. 

Test for salt colouring matters. A piece of the fabric is boiled in the soap or sodium carbonate solution in presence of white mercerised cotton to see if the cotton remains coloured. 

For the Identification of Artificial Organic Colouring Matters on Cotton... 

Chryso idine, which was discovered by Witt, is one of the few basic azo-dyestuffs, and like all basic colouring-matters dyes cotton mordanted with tannic acid. Its principal application is in cottondyeing, especially for shading purposes. It gives a yellowish-orange colour. 

The commercial products known as Catechu and Cutch are prepared by evaporation of aqueous extracts of the wood of Acacia catechu and allied species, common in India. Gambler is a similar preparation , its exact composition has not been investigated. Catechu serves technically both as a colouring-matter and as a tannin, and is largely employed in cotton-dyeing and in tanning. 

Longmore, J. (1886). Cotton-seed oil Its colouring matter and mucilage, and description of a new method of recovering the loss occurring in the refining process. ]. Soc. Chem. Ini. (Lond.) 5, 200-206. 

Raw cotton contains, in addition to cellulose, the usual constituents of a vegetable cell. These are oil and wax, pectoses and pectins, proteins and simpler related nitrogen compounds, organic acids, mineral matter, and natural colouring matter. Cotton yarns or piece goods may contain, in addition, adventitious dirt, size, and machine oil. The approximate composition of raw cotton is as follows ... 

The chemical constituents of flax are the same as those of cotton, namely, cellulose, proteins, pectins, oil, wax, mineral salts, and natural colouring matter. When purified, cellulose derived from flax is identical with that of cotton. The total extent of the impurities can be as high as 25 to 30 per cent and they are mainly pectins and pcctoses. Their complete removal presents some difficulty. 

M ht scouring operations in which these surface-active compounds are commonly used varv according to the nature of the fibre and the amount and composition of the impurities to be removed. In the case of cotton the cellulose of w hich it is composed is stable to dilute solutions of alkali at the boil. I he imphrities which must be removed are natural oils and waxes, proteins, pectic substances, natural colouring matter, and adventitious dirt. The basic principle of cotton scouring is to boil the goods for several hours at atmospheric, or under elevated, pressure with a 2 per cent solution of sodium h) droxide. 

The methods used for the cellulosic regenerated fibres are the same as those for cotton, with the exception that there is less colouring matter to remove and the severity of the process can be decreased. Thus 1 g per litre of available chlorine will always be sufficient and bleaching must be carried out cold with sodium hvpochlorite. A 015 to 0-3 per cent w/w hydrogen peroxide liquor is used and approximately lb per 100 lb of sodium chlorite would be required. The amount of alkali must be reduced when bleaching... 

Considerations relative to the Wool, Silk, and Cotton, as Objects of the Art of Dying [n c] on the various Preparations, and Mordants, requisite for these different Substances and on the Nature and Properties of Colouring Matter. Together with some Observations on the Theory of Dying in general, and particularly the Turkey Red. ... 

Colouring matter of Indian cotton flowers, Ooaaypium herbaceum, Linn, and other Q. species and of Hibiacua aabdariffayliian. Yellow needles. M.p. 311-13° (310-14°). 

Crude Gottorirseed Oil.—The deep colouring matter of crude cotton-seed oil, together with the mucilaginous and resinous principles, are removed by refining with caustic soda lye. 

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