Logwood

Logwood, the dark red heart-wood of Hæmatoxylon campechianum, a tree of the natural order Leguminosæ. This tree, which is a native of Mexico and Central America, and has been naturalised in some of the West India Islands, grows to a height of 20 to 50 feet. The tree is generally felled when about ten years old, and the sapwood being worthless is hewed off with the bark. The heart-wood is slightly heavier than water, hard, and close-grained. It has a slight smell resembling that of violets, is astringent, and has a sweetish taste. The source of the colouring properties of logwood is a crystalline substance called hæmatoxylin, $C\_\{16\}H\_\{14\}O\_6$, itself colourless when pure, but in an alkaline solution in the presence of oxygen (air) it becomes converted into hæmatein, $C\_\{16\}H\_\{12\}O\_6$, which is of a purple-red colour. For dyers' use ground or rasped logwood is moistened and made up into heaps or layers in a moderately warm place, where, turned over at intervals, it undergoes fermentation, ammonia being one of the products of the process. The result is that hæmatoxylin is first formed and afterwards hæmatein, crystals of which, of a reddish-brown colour and greenish lustre, coat the particles of wood. The hæmatein or colouring matter is easily dissolved by placing the rasped wood, so treated, in hot water. Extracts of logwood also are made for dyeing purposes. Logwood, although itself dark red, does not produce red colours either alone or with any of the ordinary mordants in use for it. Shades of purple, blue, lavender, drab, and gray are obtained from it with suitable mordants, but none of these are permanent. Its most important application is for dyeing black colours (see DYEING). It is also used in the manufacture of writing Ink (q.v.). As a medicine logwood is sometimes given in cases of chronic diarrhoea. The introduction of coal-tar colours has not as yet materially diminished the use of logwood as a dyeing substance, as the quantity sent to Great Britain in 1888 (62,306 tons, valued at £366,131) rather exceeded the annual average imports twenty years earlier.