228 WOODS 



reddish brown ; they are hard and heavy, but easily split. The 

 transverse section exhibits under the lens very narrow and closely 

 approximated medullary rays and narrow concentric dark zones 

 alternating with paler ones, a difference due to the colouring matter 

 secreted in the former. The freshly felled trunk wood is pale in colour ; 

 the gradual darkening is due to oxidation of the haematoxylin to 

 haematein. 



The odour of the chips is faint but pleasant, recalling that of violets ; 

 the taste is sweetish and astringent. It imparts a violet colour to 

 dilute aqueous solutions of caustic alkalies. 



Logwood is cut by suitable machinery into chips or turnings of 

 a reddish brown colour, and these are usually subjected to a process 

 of fermentation ( ' ageing ' ). They are well moistened, heaped together, 

 and exposed to the air for a period of from four to six weeks, the heaps 

 being frequently turned over ; they are then dried. By this process 

 the chips darken in colour and exhibit patches of a dark beetle-green 

 lustre. The unfermented chips are alone official. Fermentation of 

 logwood is not much practised, as it has been found that the oxidation 

 of the haematoxylin to haematein that is necessary in the dyeing process 

 can be effected by using an oxidising mordant (potassium dichromate). 



The student should observe 



(a) The reddish brown colour of the chips, 



(b) The violet colour they produce in contact with alkaline solutions. 



Constituents. The principal constituent of unfermented logwood is 

 haematoxylin, C 16 H 14 6 ,3H 2 O, of which it contains about 10 per cent. 

 This, when pure, forms colourless crystals which acquire a reddish 

 colour on exposure to the air. It is sparingly soluble in water, but 

 dissolves readily with purple coloration in solutions of the caustic or 

 carbonated alkalies and ammonia. The latter solution absorbs oxygen 

 from the air, forming haematein-ammonia, from which acids separate 

 haematein, C 10 H 12 O 6 , a dark violet crystalline body with green metallic 

 lustre. This change takes place during the fermentation of logwood, 

 the hsematoxylin being partially converted into hsematein. Haemato- 

 xylin is hydroxybrasilin (see below) and haematein hydroxybrasilein. 



Logwood contains, further, tannin, resin, quercetin, and a trace 

 of volatile oil. The sweetish taste is produced by the haematoxylin, 

 the astringency by the tannin. 



Varieties. Several commercial varieties of the wood are recog- 

 nised, that from Yucatan (Campeachy) being considered the best, 

 while British Honduras and San Domingo also furnish wood of good 

 quality ; Jamaica logwood is less esteemed as it is inferior in colouring 

 power. Bastard logwood is the name given to a variety of the wood 

 of paler colour and much less colouring power than the genuine ; 

 it appears to be derived from a variety of H. campechianum. 



