TANNING MATERIALS 83 



duce bark of commercial importance in the tanning industry. Through- 

 out the tropical regions, coasts, and river swamps of South America and 

 Central America, the mangrove occurs in great abundance. All of 

 the above three species of mangrove are also found in the swamps of 

 southern Florida, but have not been developed on account of the excessive 

 cost of cutting, transporting and delivering the product to market. The 

 industry is being exploited especially in Colombia and Brazil, and to a 

 lesser extent in the Guianas, Venezuela, and Trinidad. 



The yield varies considerably with the various regions. Altogether 

 this variation is said to be from 5 to 45 per cent. The older the tree, 

 however, the greater is said to be the tannin content. The mangrove 

 cut and placed on the market in large commercial quantities usually 

 produces a yield of tannin of from 22 to 33 per cent. The leaves of the 

 mangrove also contain merchantable quantities of tannin and are fre- 

 quently used in the tanneries of southern Brazil, particularly in Santos 

 and Cartagena. 



The bark is exceedingly hard and heavy. When used locally the bark 

 is employed directly by the tannery, and not used for extraction pur- 

 poses. The methods for the extraction of tannin from mangrove bark 

 have not been perfected to the same extent as for quebracho. Up to 

 the present time, the process of extraction is somewhat similar to that 

 employed for quebracho, but it is more difficult, and it is likely that the 

 process will be still further developed in the future. It is said that 

 extract from the mangrove forests of Africa contains from 60 to 70 per 

 cent of tannin, whereas that produced in the Colombian factories con- 

 tains about 48 to 50 per cent of tannin. 



The use of mangrove bark began in Europe in 1804, and it has only 

 recently begun to enter this country on a large scale. It is generally 

 regarded by the tanneries as one of the cheapest forms of tannin and this 

 accounts largely for its general acceptance and its increasing use. Man- 

 grove tannin is seldom used alone as it has the reputation of imparting 

 an undesirable color to leather. In France, a mixture of one-third man- 

 grove bark, about two-fifths hemlock, and the remainder of oak or mimosa 

 bark, is commonly used. 



Owing to the various resources of mangrove forests found along the 

 tidal shores of the tropics in nearly all parts of the world, this material 

 constitutes a great asset for the future of the tanning industry. Its 

 habit of growth renders it somewhat difficult to cut and transport to 

 market, but improved methods are being constantly devised whereby it 

 can be successfully produced. Xo estimates have been made of the 



