LOGWOOD.

343

is produced by the a&ion of the atmospheric oxygen upon the wood, and it isto that alteration that the aqueous decodtion owes its darkish tint. It is quiteclear that this alteration may be more or less advanced, and, as a consequencethereof, common salt causes in concentrated liquid extra&s (unless they havebeen made in vacuum) a precipitate of an almost black-coloured resinoussubstance, while in the freshly-made aqueous deco&ion the precipitate is of abright brick-red. The colouring power of the wood is largely increased if itis suffered to ferment, after having been rendered moist, by being placed inheaps, on a well-made wooden floor, the height of the heaps attaining fromi to i*5 metres : the wood thus heaped up should be frequently turned over, soas to renew the currents of air, and to prevent also a too great elevation oftemperature. If “ heating,” as it is technically called, once sets in, it is noteasily checked, and the colouring matter is soon entirely destroyed. Thisfermentation has the effedt of partly eliminating and greatly modifying thosesubstances which accompany haematoxylin : as a proof thereof we may statethe fadt that the so-fermented powder causes less soiling of the white portionsof the cloth in the dyeing process. The increase of colouring power observedunder these conditions is, in all likelihood, due to a saponification of thecolouring glucosides.

Haematoxylin in a crystalline state was first obtained by Chevreul, by ex-hausting with alcohol the dry residue left on cautiously evaporating theaqueous extradl of logwood. Prof. Erdmann prepared this substance bytreating either the aqueous extradf or the finely-pulverised wood, after previousadmixture with pulverised quartz, with ether. The solution so obtained isevaporated to the consistence of a thick syrup, mixed with water, and, onbeing left standing by itself, the crystallised haematoxylin is deposited aftersome days. It now and then happens that, at the bottom of the casks orvessels wherein liquid extradl of logwood is kept, brilliant crystalline tufts ofhematoxylin are found in the shape of prismatic crystals, externally of abrownish metallic hue, but bright yellow within. The following are theproperties of haematoxylin :—Bright yellow transparent crystals, yieldinga yellowish-white powder, and belonging to the tetragonal system; in tastevery like liquorice root; sparingly soluble in cold water, but far more readilyso in alcohol, ether, and boiling water. The prismatic crystals contain 15-1per cent of water. When a hot saturated solution of haematoxylin is left tocool in a stoppered bottle it deposits, after some time, granular irregular crys-tals, containing 5-6 per cent of water. Both these crystalline forms correspondto two different states of hydration.

According to Erdmann’s analysis the formula of haematoxylin is C^H^Oq ;the prismatic crystals contain 3 atoms of water, and the granular crystalsonly x atom. A portion of the water is expelled at ioo°, but the last tracescan only be volatilised at a higher temperature. When hematoxylin is heatedit first fuses in its water of crystallisation ; by continued and increased heat!t is decomposed, leaving behind an abundant carbonaceous residue.

Hematoxylin is not volatile, and when quite pure atts as a weak acid,yielding with bases colourless compounds, which exhibit, however, a verygreat tendency to absorb oxygen and become coloured : we obtain, for instance,a precipitate which is at first white, but becomes rapidly bluish when exposedt° air, and finally assumes a reddish-brown tinge. It is extremely difficult to