African Logwood or Hæmatoxylon Africanum.(CHAPTER IX. Dihydro-pyran 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.

H. africanum = H. dinteri

The genus hæmatoxylon has hitherto been represented by only one species, the H. campeachianum, and the recent discovery of a South African species is of particular interest. This, now termed the H. africanum, was found among the rocks at Holoog in Great Namaqualand by Dr. H. H. W. Pearson in February, 1909, during the Percy Sladen Memorial Expedition in South-West Africa, 1909. It consists of a shrub 1-1.5 metres tall, the flowers of which are yellow, and the leaves smaller than those of the H. campeachianum (Stephens, Trans. Roy. Soc. S. Africa, 1913, iii., 2, 255).

Stems of this plant sent to England for examination were covered with a thin brownish bark, and varied from ½-1¼ inches in diameter, and from 11-16 inches in length. Cut transversely they were seen to consist mainly of a reddish-brown core surrounded by an almost colourless layer of wood, and this core, as is the case with logwood itself, darkened somewhat on exposure to air and became of a richer colour. When ground, the ochre-coloured powder is of a much lighter tint than either ground logwood or Brazilwood.

The aqueous extract of the ground wood gives in comparison with those obtained from logwood and Brazil-wood the following colour tests:

	H. africanum	Brazil-wood.	Logwood.
NaOH	Pink.	Crimson.	Deep red-violet.
FeCl2	Brown.	Deep brown.	Purplish-black.
Pb(Ac)2	Pale pink, almost colourless precipitate.	Pink precipitate.	Deep blue precipitate.

The alkaline extract of the H. africanum on boiling deepens considerably in colour and possesses a faint greenish fluorescence, and this property is also exhibited by the corresponding extract of Brazilwood.

Dyeing trials with both the H. africanum (170 per cent.) and Brazilwood (40 per cent.) employing mordanted woollen cloth gave the following shades:

	Cr.	Al.	Cu.	Sn.	Fe.
H. africanum	Red-brown-violet.	Dull bluish-red.	Brown.	Very pale brown.	Dull purple.
Brazilwood.	Red-violet.	Bluish-red.	Claret-brown.	Red-brown very pale.	Blue-violet.

The H. africanum, therefore, differs from logwood in that the colouring principle it contains is not haematoxylin, but a substance which somewhat closely resembles brazilin in its general properties. It is a much poorer dyestuff than Brazilwood and on this account is of no technical importance, but should it eventually prove to contain brazilin, the matter is of special interest in view of the connection between this latter and haematoxylin which has been shown to exist by W. H. Perkin and his co-workers (loc. cit.). The slight difference in the properties of the H. africanum and Brazilwood may be due to certain impurities in the former dyestuff not possessed by the latter, but on the other hand a methyl ether of haematoxylin of the type [KUVA PUUTTUU] will without doubt dye shades of an almost identical character with those given by brazilin itself (Perkin, J. Soc. Dyers,1918, 34, 99).