VEGETABLE TANNAGE 41 



Mangrove Extract is made from the bark of Rhizophona 

 Mangle and other species of mangrove which grow freely 

 in the tropical swamps of West Africa, Borneo, etc. Much 

 solid and liquid extract has been made from this material, 

 but is not very popular on account of its harsh tannage and 

 dark red colour. 



Pine Bark Extract (Larch extract) is made in Sweden 

 from the Norway spruce (Pinus abies). It is slightly 

 sulphited and gives a good colour. It is a liquid extract 

 of about 30 per cent, strength, and is sometimes used as a 

 chestnut substitute. It should not be confused with the 

 so-called " spruce " or " pine wood " extract, which is a 

 paper trade bye-product and contains ligneous matters 

 rather than tannin. 



American Chestnut Extract, made from the chestnut 

 oak, is either a liquid or a solid extract in powder form. It 

 gives a wretched brown-black colour, which is quite unsuited 

 to the usual British needs. 



THEORY OF VEGETABLE TANNAGE. 



Vegetable tannage is a phenomenon of colloid chemistry. 

 The old arguments as to whether tanning was a chemical or 

 a physical process have been rendered obsolete by the advent 

 of a new set of explanations, which, though shedding light on 

 many obscure points, have enormously increased the com- 

 plexity of the problem. In vegetable tannage an emulsoid 

 gel (pelt) is immersed in a complex emulsoid sol (tan liquor), 

 which immersion results, not in simple reaction or change, 

 but in a series of changes. 



One of these changes is adsorption. Pelt is a gel which 

 possesses a great development of surface. It not only 

 exhibits like gelatine the phenomenon of imbibition and 

 dehydration to a very marked extent, but also possesses 

 a very fine fibrous structure due to its organic origin ; thus 

 pelt possesses an enormous specific surface, further intensified 

 by the preparation processes previously discussed, which 

 split up the hide fibres into smaller bundles and into much 



