Indian Yellow (Euxanthone).(CHAPTER IV. The Xanthone Group.)(Osa artikkelista)

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.

Indian yellow, Piuri, Purree, or Pioury, is a pigment mainly used in India for colouring walls, doors, and lattice-work, and by artists for water-colour work. On account of its disagreeable smell it is but rarely employed as a dyestuff. It is, or was, made almost exclusively at Monghyr in Bengal, and is obtained from the urine of cows which have been fed upon mango leaves. On heating the urine, usually in an earthen pot, the colouring matter separates out; this is pressed into a ball and dried partly over a charcoal fire and finally in the sun. It sold on the spot at about 1 rupee per lb. and is, or was, mainly sent to Calcutta and Patna. One cow produces, on the average, 3.4 litres of urine per diem, yielding 2 oz. (56 grams) of piuri. The yearly production is stated to have been from 100 to 150 cwts., which was probably over-estimated (v. Journ. Soc. Arts, 1883, (v.), 32, 16, and Annalen, 254, 268).

Piuri occurs in commerce in the form of round balls, which internally are of a brilliant yellow colour, whereas the outer layers are either brown or of a dirty green colour. The substance has a characteristic urinous smell. The undecomposed part consists only of euxanthic acid (C₁₉H₁₈O₁₁) in the form of a magnesium or calcium salt; the outer and decomposed portion contains in addition euxanthone, both free and combined. The composition of piuri seems to be variable; a fine sample, according to Graebe, contained
Euxanthic acid … 51.0
Silicic acid and alumina … 1.5
Magnesium … 4.2
Calcium … 3.4
Water and volatile matter … 39.0
[total] 99.1

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Euxanthone possesses only feeble tinctorial properties; the respective shades obtained with woollen cloth mordanted with chromium, aluminium, and tin being dull brown-yellow, pale bright yellow, and very pale bright yellow (Perkin and Hummel, Chem. Soc. Trans., 1896, 69, 1290).