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 is derived from the fruit of the Bixa orellana (Linn.), a shrub found native in Central America, and cultivated in Brazil, Guiana, Mexico, the Antilles, and India.
To prepare the dyestuff, the seeds and pulp are removed from the mature fruit, macerated with water, and the mixture is left to ferment. The product is strained through a sieve, and the colouring matter which settles out is collected, partially evaporated by heat, then placed in boxes, and finally dried in the sun.
Annatto comes into the market in the form of cakes, and among the different varieties Cayenne annatto is the most esteemed, and is considered to be the richest in colouring matter. It should contain from 10 to 12 per cent, of the pure dye, and not more than 5 per cent, of ash, whereas the amount of colouring matter in the Bengal product is frequently lower than 6 per cent.
In 1848 Dumontal devised a new method for the preparation of annatto, in which fermentation is avoided, and the pulp is simply washed out from the capsules and off the seeds. This product known as bixin is said to be five to six times more valuable than ordinary annatto (Crookes, "Dyeing and Calico Printing").
The colouring matters of this dyestuff were first investigated by Chevreul ("Leçons de Chimie appliquée a la Teinture "), who isolated two substances, one yellow, which was called orrellin, soluble in water, and a second, bixin, which is red and very sparingly soluble.
Bixin, the useful colouring matter, was subsequently examined by numerous chemists, who were only successful in preparing it as an amorphous powder, and its isolation in a crystalline condition was first achieved by Etti (Ber., 7, 446; 22, 864).
Etti digested 1,5 kilos, of purified annatto with a solution of 150 grammes of calcined soda ash in 2,5 kilos, of 80 per cent, alcohol on the water-bath at 80°. The "mixture was filtered and the residue pressed between warm plates, and again extracted with 1,5 kilos, of warm 60 per cent, alcohol.
The alcoholic filtrate was diluted with half its volume of water, concentrated, sodium carbonate solution added, and the crystalline precipitate of sodium bixin was collected after several days, and pressed. The product purified by solution in 60 per cent, alcohol at 70-80° and reprecipitation with sodium carbonate was finally made into a cream with alcohol, and this, when neutralised with hydrochloric acid, yielded crystalline bixin.
A simpler method has been more recently devised by Zwick (Ber., 30, 1972). Well-dried annatto is extracted for twenty-four hours with boiling chloroform, the extract evaporated, and the residue thoroughly exhausted with ligroin. The product is crystallised from chloroform, and after washing with ligroin is repeatedly recrystallised from the former solvent.
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Dyeing Properties.
Annatto is still employed to a fair extent for colouring oils and butter, but is almost extinct as a dyestuff in this country. As the orange-red colour which it yields is extremely fugitive to light, it has at no time been very extensively used. On the other hand, it resists the action of soap and dilute acids very well.
In order to dye cotton, the annatto is first dissolved in a boiling solution of carbonate of soda, and the goods are then entered and left in the bath for a quarter of an hour. They are subsequently pressed out, and washed in slightly acidulated water or alum solution.
For silk, the bath is made up with equal parts of annatto and sodium carbonate; soap is also usually added, and the dyeing is continued at 50° for about an hour, according to the shade required. The colour produced can be rendered somewhat more yellow by passing the fabric through a weak solution of tartaric acid.
Wool is dyed at 80-100° without any addition to the bath.
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