Anchusa tinctoria, Alkanet(CHAPTER I. The Anthraquinone Group.)

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.

The Arabic name Al-henneh, modified to alkanna or al-kenna, was originally applied to the lythraceous shrub Lawsonia alba (Lam.), the root of which was described as Radix Alkanna vera, in contradistinction to the root of our alkanna, which is Anchusa tinctoria (Lam.), and which became known as Radix Alkanna spuria tinctoria. The latter, or False alkanet, is also known as Orcanette, Fr.; Orkanet, Ger.; Languedoc bugloss or dyers' bugloss, Radix Alkanna spuria. A rough plant with downy spear-shaped leaves, and clusters of purplish or reddish flowers; belongs to the Boraginaceæ. Found in Asia Minor, Greece, Hungary, etc. The roots, which have an astringent taste, occur in commerce, varying from the thickness of a quill to that of a finger.

Alkanet is one of the more ancient dyestuffs, having been employed by the Romans, but, on the other hand, it does not appear at any time to have attained such importance as madder, indigo, or even turmeric. The colouring matter of alkanet, known as anchusin or alkannin, has been examined by several chemists, but it is doubtful whether this compound has as yet been obtained in a chemically pure condition. Its composition is variously given as C₁₇H₁₀O₄ (Pelletier, Annalen, 6, 27), C₃₅H₂₀O₈ (Bolley and Wydlers, Annalen, 62, 41), C₁₅H₁₄O₄ (Carnelutti and Nasini, Ber., 13, 1514), and C₁₅H₁₄O₄ or C₁₅H₁₂O₄ (Liebermann and Romer, Ber., 20, 2428).

Alkannin forms a dark red amorphous powder possessing a beetlegreen iridescence, is readily soluble in most of the usual solvents, and its alkaline solution is deep blue coloured. On distillation with zincdust it gives, according to Liebermann and Romer, both methyl anthracene and anthracene.

Diacetylalkannin, C₁₅H₁₂O₄(C₂H₃O)₂, forms a dull yellow microcrystalline powder (C. and N.).

According to Eriksson (Ber. Deut. pharm. Ges., 1910, 20, 202), alkannin consists of two red pigments, the one being coloured green and the other blue by the action of alkalis. Red crystals have been observed by Tschirch in spaces in the cortex of old specimens of alkanet root. As alkannin is insoluble in water, in dyeing with alkanet an alcoholic extract is usually employed; and with aluminium and iron mordanted fabrics, violet and grey shades are respectively produced. These colours, however, are not fast to light, and are somewhat readily affected by weak alkalis or acids.

Haussmann of Mulhouse introduced alkanet into calico-printing, and for a short time it appears to have played a quite important part, but it is now little if at all employed in Europe for ordinary dyeing purposes. It is still used for colouring artificial wines, pomades, hair-oils, sweets, etc., and for these purposes it is well adapted on account of its ready solubility and harmless nature.

Bättger (J. f. prakt. Chem., 107, 146) and Eng (Jahres., 70, 935) recommend the use of papers stained by alkanet as indicators in alkalimetry.

According to Jolin (Chem. Schriften liber Alkanna, iv., 84), Thomson (Pharm. J., [3], 16, 860), and Eriksson (loc. cit.), alkanet root contains from 5-6 per cent, of anchusin.