302 TANNINS 



employed for this purpose ; large quantities of leather are, 

 however, nowadays manufactured with the use of chemicals 

 such as chromium salts, etc. Many of the tannins, such as 

 gambler cutch, quebracho, etc., are employed for tanning, 

 calico printing, and dyeing, etc. 



COMPOSITION OF CERTAIN DYE WOODS AND BARKS AND 



THEIR EXTRACTS. 



The wood of a great number of tropical trees yield extracts 

 containing mixtures of substances, some of which have tinc- 

 torial properties and others are tannins or allied substances. 

 The substances possessing tinctorial properties are flavones or 

 flavonols and are mostly sparingly coloured substances which 

 only produce dyes, more or less deeply coloured, with salts of 

 metals such as aluminium, iron, tin, etc., acting as mordants. 

 In illustration a few examples, selected from a very large 

 number, are given below: — 



Old Fustic. 



Old fustic, the wood of Chlorophora tinctoria (formerly 

 known as Morns tinctoria), a native of Cuba, Jamaica, and 

 Brazil, contains the fiavonol morin which, though forming 

 colourless crystals, is soluble in alkali to give a yellow solution, 

 and with chromium copper, iron, tin, or aluminium mordants, 

 gives various shades of olive-brown or yellow. 



Besides the above, old fustic also contains maclurin, at one 

 time called moritannic acid, which is a penta-hydroxybenzo- 

 phenone (for formula, see p. 280) ; this substance precipitates 

 gelatine from solution and thus has tanning properties, and 

 with iron salts it gives a green-black colour. 



Jack Wood. 



Perkin * found that the Indian dyestuff, jack wood [Arto- 

 carpus integrifolia) contained in addition to the colouring matter 

 morin (i.), CisHjoOT^isomeric with quercetin (see p. 296)— 

 a substance, cyanomaclurin (11.), C^rJrl^^O^; this substance is 

 colourless and has no dyeing properties but gives a violet colour 



* Perkin : " J. Chem. Soc," 1895, 67, 939, and 1905, 87, 715. 



