294 



INDUSTRIAL PLANTS 



logwood of itself docs not make a jjermanent dye. It requires 

 the use of a mordant, that is to saj', some substance such as 

 a salt of iron which fixes the dye upon the fabric. Thus used 

 it makes one of the best blacks for wool or cotton. In com- 

 bination witli iron, etc., it is used also widely in the manu- 

 facture of writing inks. 



Lampblack is the finely divided carbon deposited from 

 the smoke of rosin or oil burned with slight access of air in 



Fig. 276. — Logwood-treo {Hwmatoxylon campcchcanum. Pulse Family, 

 Legumi}ioii(F). A, flowering branch. B, flower. C, same, cut verti- 

 cally. D, pod. (Taubert.) — Tree about S m. tall; leaves smooth; 

 flowers yellow, fragrant; fruit drj-. Native home, Tropical .A.merica. 



a special chamber. It is used extensively in the making of 

 printing-ink, and forms the basis of india-ink and of various 

 black pigments used in painting, leather-finishing, and the 

 like. Lampblack is one of the mo.st important of coloring 

 matters. 



Tan-hark is obtained from many tr(>es, including hem- 

 lock (Fig. 26.3), oak (Fig. 243), willow (Fig. 22S), chestnut 

 (Fig. 24), larch (Fig. 25it), anil spruce (Fig. 260), which are 

 rich in tannins. These sul)stances, as already explained in 

 sections f)? and 60, are astringents which are present in 



