Cochineal-carmineCHAPTER XIX. Lakes from Vegetable Colouring Matters

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 this brilliant scarlet lake, cochineal is extracted in tin -lined vessels with a large quantity of boiling water. Certain additions are made to the filtered decoction, and it is then allowed to stand for several weeks, or even months, in shallow vessels of tin or porcelain, during which period the carmine gradually separates in the form of a fine red powder. The additions referred to have varied with different makers, and include the following: potassium binoxalate, acid potassium tartrate (cream of tartar), alum with or without cream of tartar, hydrochloric acid, etc. In all cases the presence of iron must be strictly avoided. The necessary ingredients may also be added to the water with which the cochineal is boiled, in which case the decoction must be filtered hot, since it rapidly becomes turbid on cooling. The addition of gypsum, calcium carbonate, zinc oxide, etc., so usual in other cases, must be avoided, since these render the lake violet.

The manufacture of cochineal-carmine is now very restricted, and the methods employed for producing the finest product have always been kept secret.

According to Alyon and Langlois, 500 grams cochineal are boiled for one and a half hours in 30 litres water containing 25 grams sodium carbonate. The decanted solution is well stirred up with 25-35 grams powdered alum, and then allowed to settle about twenty minutes; the clear liquid is poured off, a dilute solution of isinglass or albumen is added, and the whole is heated until the carmine collects together in the form of a coagulum. After cooling and allowing to settle, the supernatant liquid is decanted off, the carmine is collected on a filter, washed, and dried at a low temperature. The deeply coloured filtrate serves for the production of carmine-lake.

Even alum alone could apparently be used as the precipitating agent, according to an old recipe, but it seems likely that in this case water possessing an alkaline reaction must of necessity have been employed. Boil sixteen parts ground cochineal for ten minutes with about 600 parts of water, then add i part ground alum, boil a few minutes longer, filter the hot solution, and allow the filtrate to stand in shallow porcelain basins. In the course of a few days the carmine is said to separate in the form of a red slimy precipitate, which is collected and dried. The decanted liquor on standing yields a further quantity of carmine of a lower quality; its precipitation is facilitated by the addition of a small quantity of stannous chloride.

The residual cochineal which has thus been only partially exhausted serves for the preparation of carmine-lake.

In other similar recipes a mixture of alum and cream of tartar is used instead of alum only, but in that of Madame Cenette, at one time a celebrated maker of carmine, the statement that the effective precipitating agents are potassium nitrate and potassium binoxalate, is difficult to understand.

Chinese carmine is said to be prepared by extracting cochineal with a boiling solution of alum, heating the filtered decoction with the addition of a solution of tin in nitric and hydrochloric acid (aqua regia), and finally leaving the liquid to stand till the carmine separates.

Cochineal-carmine is insoluble in water, but soluble in alcohol. In ammonia solution it dissolves readily with a purplish-crimson colour; from this solution tartaric acid precipitates the original carmine, for although when dried the precipitate has a brownish-red colour, it becomes bright red when powdered. The following analysis of cochineal-carmine is given by C. Liebermann (Ber., 18, 1969):

Moisture........ 17 per cent
Nitrogenous matter ........ 20 "
Ash........ 7 "
Colouring matter........ 56 "
Wax........ traces

The ash consists of SnO₂ 0,67 per cent., A1₂O₃ 43,09, CaO 44,85, MgO 1,02, Na₂O 3,23, K2O 3,56, P₂O₅ 3,20. From these analyses Liebermann considers cochineal-carmine to be a peculiar aluminium calcium protein compound of the carmine colouring matter, somewhat analogous to the Turkey-red lake, in which alizarin is combined with aluminium and calcium. According to the experiments of the late J. Bedford of Leeds, cochineal-carmine can only be prepared if a calcareous water is employed, or if calcium salts are added during the reaction. Cochineal-carmine can, indeed, be readily produced by adding to a cold extract of the dye prepared with a hard water potassium carbonate, alum, and subsequently cream of tartar (or potassium binoxolate) in definite proportion. The carmine precipitate separates very gradually during some days, and has an extremely brilliant character. If a small quantity of stannic chloride is also added to the mixture the precipitation is hastened and the product possesses a more scarlet tint (Perkin, private communication).