SafflowerCHAPTER XVIII. Colouring Matters of Unknown Constitution.

The Natural Organic Colouring Matters
By
Arthur George Perkin, F.R.S., F.R.S.E., F.I.C., professor of colour chemistry and dyeing in the University of Leeds
and
Arthur Ernest Everest, D.Sc., Ph.D., F.I.C., of the Wilton Research Laboratories; Late head of the Department of Coal-tar Colour Chemistry; Technical College, Huddersfield
Longmans, Green and Co.
39 Paternoster Row, London
Fourth Avenue & 30th Street, New York
Bombay, Calcutta, and Madras
1918

Kaikki kuvat (kemialliset kaavat) puuttuvat // None of the illustrations (of chemical formulas) included.

This dyestuff consists of the dried florets of Carthamus tinctoria (Linn.), an annual thistle-like plant belonging to the Cynarocephalce. A native of Southern Asia, it has been cultivated in China, India, Persia, Egypt, also in central and southern Europe. When in full bloom the yellow florets are plucked, and either at once dried, so as to form an orange-coloured fibrous mass somewhat resembling saffron, or they are first kneaded with water, in order to remove a useless yellow colouring matter, and then pressed into the form of lens-shaped cakes and dried.

Safflower owes its value to an insoluble red colouring matter which occurs only in very small amount, about 0,5 per cent., whereas the soluble yellow colouring matter is said to be present to the extent of about 30 per cent.

The yellow colouring matter may be obtained by first precipitating a cold aqueous extract of safflower with lead acetate and acetic acid and then adding ammonia to the filtrate, i.e. precipitating with basic lead acetate. The second precipitate thus obtained is carefully decomposed with dilute sulphuric acid, and after removing the lead sulphate the filtrate is evaporated to dryness with exclusion of air. It is thus obtained as an amorphous substance, having acid properties, a bitter taste, and a peculiar odour. It is of a very unstable character, and on exposure to air seems to oxidise, becoming brown and partially insoluble in water. According to Schlieper, its composition is represented by the formula C₁₆H₂₀O₁₀; according to Malin, it is C₂₄H₃₀O₁₅. This product is apparently a glucoside or contains a substance of this character, for after digestion with boiling dilute sulphuric acid, the solution yields to ether a small quantity of a crystalline yellow colouring matter (Perkin, private communication).

Carthamin or carthamic acid is the name given to the useful red colouring matter, which, although insoluble in water, is readily soluble in alkaline solutions. To obtain it, safflower is well washed with slightly acidified water to remove the yellow colouring matter, then it is steeped for some time in a cold dilute solution of sodium carbonate. If the alkaline solution be now acidified with acetic or tartaric acids the carthamin is precipitated in so finely divided a condition that it cannot be successfully collected. This difficulty is, however, obviated by making use of the fact that carthamin is readily attracted and removed from its acidified solution by cellulose. Hence bleached cotton is immersed and moved about in the alkaline solution, which is at the same time gradually acidified with tartaric or citric acid.

In this manner the carthamin is slowly precipitated and is at once attracted by the cotton, which thus becomes dyed red. After washing the dyed cotton with slightly acidified water, the colouring matter is dissolved off by means of a dilute solution of sodium carbonate, from which the carthamin is thrown down, on the addition of tartaric acid, as a bright- red precipitate, which is now in a purer and more granular form. Further purification is effected by dissolving the dried precipitate in alcohol and reprecipitating with water.

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Previous to the discovery of safranine and of the eosins, safflower was frequently used for the production of brilliant pinks or reds, chiefly on cotton or silk. The mode of dyeing is practically the same as that already given in describing the process of obtaining carthamin. The safflower in bags is well washed with cold water, in order to remove the yellow colouring matter, and the red colouring matter is then extracted by a treatment with a cold dilute solution of sodium carbonate. In this solution the material to be dyed is worked about, at the same time adding "lime juice" (citric acid) gradually until in slight excess. Safflower extract is applied in a similar manner.

Dyers usually gave the washed safflower several successive treatments with alkali, employing at first weak and afterwards strong alkaline solutions. The weak solutions give the brightest and purest tints; hence very delicate colours were dyed with these alone, whilst full colours were first dyed with the inferior extracts, and then "topped" or "bloomed" by a dyeing in the purer solutions. The shades obtained from safflower were at one time considered to be the finest and most delicate a dyer could produce. On the other hand, they were not only expensive but had the disadvantage of being extremely unstable.

Safflower is a very weak dyestuff, for 4 oz. are necessary to dye 1 lb. of cotton light pink, 8 oz. for a rose-pink, and about 1 lb. to produce a full crimson.

It is now rarely, if ever, employed in Europe as a dyestuff, but large quantities are still cultivated, more especially in India, and used for dyeing and pigment manufacture in the East.

Carthamin was sold in a more or less pure condition as a thin aqueous paste, under the name of safflower extract or safflower carmine, but this product is now difficult to obtain in Europe. On the other.hand, considerable quantities are still manufactured in Japan, where it is very largely employed as a cosmetic. Carthamin ground up with starch, talc, etc., is used as rouge.

For other references, v. Dumas, Annalen, 27, 147; Liebermann, Ber., 7, 247; 8, 1649; Dobereiner, J. Phys. Chem., 26, 266; Salvetat, Ann. Chim. Phys., (3), 25, 337; J. pr. Chem., 44, 475; Dufour, Ann. Chim. Phys., 48, 283.