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.
Carmine-lake is simply an ordinary aluminium or tin lake of the colouring matter of cochineal, produced by adding sodium carbonate to a cochineal decoction containing alum or stannous chloride, or both.
Florentine-lake is, or was, merely a special quality of carmine-lake, containing usually an excess of alumina, and sold in the form of "drops"; and the. so-called Venetian-lake, Hamburg-, Chinese-, Roman-, and Scarlet lakes were all varieties of Florentine-lake.
Brazil Indian-lake or Lac-lake, a dark purplish-red lake analogous to carmine-lake, can be prepared in a similar manner from the Indian product lac dye.
Brazilwood-lake was prepared by extracting Brazilwood or peachwood with boiling water, adding alum and tin solution to the filtered decoction, and finally precipitating with sodium carbonate, avoiding excess. Another method was to add precipitated and washed aluminium hydroxide to a filtered decoction of Brazilwood. Freshly prepared decoctions are never suitable for the manufacture of these lakes; they should always be oxidised, by exposure to air or otherwise, in order to change the principle brazilin into the necessary colouring matter brazilein.
Vienna-lake was a species of Brazilwood-lake, prepared in the following manner: A mixture of ground starch (30 kilos.), chalk (10 kilos.), and a little gypsum, is stirred up with a decoction of Brazilwood; then ground alum (1 kilo.) is added and the whole is well stirred for twelve hours and finally allowed to settle. After decanting the clear liquor, Brazilwood decoction is again added to the residual precipitate, together with a further quantity of alum (1 kilo.), and the stirring is continued as before. This process is repeated until the precipitate has taken up sufficient colouring matter and acquired the character of a lake. The decanted liquors are agitated with fresh starch, chalk, etc., in order to yield further quantities of lake.
In the foregoing process the alum is decomposed by the chalk, and the alumina precipitate thus produced combines with the colouring matter. At first the lakes appear violet through the presence of excess of chalk, but with the continued addition of alum they gradually acquire a crimson colour.
Fine dark carmine-red lakes can be obtained by adding stannous chloride and cream of tartar to a concentrated old decoction of Brazilwood.
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