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.
In the preparation of madder-lake extraction of the madder with boiling water was avoided, in order not to dissolve those impurities which would cause the production of a less brilliant lake. It was usual, first of all, to decompose the glucoside of the madder, and thus increase the actual colouring matter, by a steeping in slightly tepid water and allowing the mixture to ferment for twentyfour hours, then to wash with cold water and extract with alum solution at 60-70°, employing about equal weights of madder and alum. The hot filtered alum solution of the colouring matter was precipitated as an alumina lake by adding sodium carbonate, and the precipitate was washed.
Another method was to precipitate impurities from a hot filtered decoction of madder by adding a small quantity of lead acetate, then filter, add a solution of alum, and precipitate with sodium carbonate.
Matters could be so arranged as to precipitate basic aluminium sulphate instead of aluminium hydroxide, namely, by adding an insufficiency of sodium carbonate to the cooled solution of alum and colouring matter, and then boil the mixture.
Garancine was preferable to madder for preparing madder-lake, since it does not contain any of the colouring matter in the form of glucoside (ruberythric acid), and the soluble impurities have also been for the most part removed. Thus 1 kilo, garancine was repeatedly extracted for several hours with 20 litres of boiling water containing 0,25-0,5 kilo, alum, and the solution filtered hot through flannel. On cooling, the colouring matter separated from the filtrate as a flocculent precipitate. This was collected and dissolved in ammonia, and the filtered solution precipitated with alum, or stannous chloride, or a mixture of both. The colour intensity of the lake varied with the proportions of ammonia and precipitant employed. A method similar to that described for madder could also be employed in preparing madder-lake from garancine.
Bright carmine-red lakes could be obtained if, in the preparation of madder-lake, an ammoniacal solution of cochineal-carmine was employed for precipitating the alum solution, instead of the sodium carbonate. This method was adopted to render the lower qualities of madder-lakes more attractive. Cheap qualities of madder-lakes were also prepared sometimes by extracting mixtures of madder and Brazilwood with sodium carbonate, and precipitating with alum or a solution of tin.
So-called "crystallised madder-lakes" were such as contained a certain quantity of potassium or sodium sulphate, etc.
"Madder-pink-lake" was simply madder-lake diluted with about seven parts of "blanc fixe" (precipitated barium sulphate).
Madder-lake is entirely, or for the most part, soluble in caustic potash and soda. If chalk or other diluent was present, this remains undissolved. Boiled with dilute sulphuric or hydrochloric acid, the lake is decomposed, the colouring matter being liberated in the form of a flocculent or crystalline precipitate. In dilute ammonia, pure well-made madder-lake is not soluble (distinguishing test from cochineal-carmine). Up to within a few years ago, a rose-coloured lake was still being prepared from the madder preparation known as "Kopp's purpurine" (loc. cit.), and was considered to possess certain characteristics as a paint, which up till then had not been found in other materials.
References. - Colomb, Bull. Mülh., 12, 307; Dingl. poly. J., 73, 47; Persoz, Traite de 1'Impression des Tissus, 1, 507; Merime, ibid., 1, 505; Robiquet and Colin, ibid., 1, 505; Khittel, Polyt. Zentr., 1859, 81.
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