ECONOMIC POSSIBILITIES OF MANGROVE SWAMPS. 57 



colored bodies. The soluble coloring matter, like the tannin, is absorbed by 

 the hide to form true leather. The insolubles play a useful part in the latter 

 stages of tanning by mechanically inpregnating the surface of the hide and thus 

 rendering it heavier and more impervious to water. More often than other- 

 wise they are present in excess of the needed quantity and in that case are 

 a nuisance to the tanner. If present in the more dilute liquors in which the 

 hides are first immersed, they deposit in the pores or on the surface of the 

 goods and prevent the proper diffusion v of the soluble materials into the in- 

 terior of the hide. 



The r5le of the nontans is quite a different one. Such glucosidal matters 

 as are present ferment to form acids, chiefly lactic and acetic, which are neces- 

 sary to keep the hide open and promote the diffusion of the tannin. If not 

 present in sufficient amount, either acid or acid-forming material must be 

 added. Pyrocatechol tannins are frequently deficient in this particular, the 

 nontans being composed largely of salts. The" latter play no considerable 

 part in tanning except tliat the presence of large quantities may be deleterious 

 to the color and " grain. 



Therefore, in the manufacture of an extract it is desirable to reduce 

 the coloring matters, the "insolubles," and the metallic salts to a minimum 

 and to obtain the maximum concentration with the minimum loss of 

 tannin. The methods in use in Borneo are regarded as trade secrets 

 by the manufacturers ; however, they are known ^' in a general way, and 

 the process presents no great difficulties. 



Other things being equal, fine grinding promotes thorough extrac- 

 tion, especially if it be carried out at a low temperature ; but for various 

 reasons, fresh bark must be used and fine grinding of this material would 

 be difBcutt. On this account I believe a preliminary kiln drying of 

 the bark would be advisable, as it could be done cheaply and would make 

 possible the use of much cheaper mills. 



Extraction can best be done in wooden vats, using fresh water for the 

 nearly exhausted barks and liquors of higher concentration for the less 

 completely extracted material. With coarse bark the temperature would 

 necessarily be high in order to break up the cells and give a thorough 

 extraction. For finely ground material 50° to 60° is preferable. Parker 

 and Procter ^^ have shown that water at this temperature extracts more 

 tannin and less coloring matter from most materials, and among them 

 mangrove bark, than at higher temperatures. These comparisons were of 

 infusions made by exliaustive extractions at various temperatures. 



It was thought by me that most of the tannin might more readily be 

 extracted at some other temperature. Experiments were made with 

 Bhizopliora mucronata and Bruguiera eriopetala. 



Five grams of finely ground bark were treated two and one-half hours with 

 100 cubic centimeters of distilled water, the whole thrown on a sand filter and 



"Parker, Journ. 8oc. Chem. Ind. (1900), 19, 313-315. 



"Jeaw, Rev. Chim. Ind. (1896), 7, 269-271. 



" U. S. €Oth Cong. House Doc. 1505, 1, 221-228. 



"Parker, J. G., and Procter, H. R., Journ. Soc. Chem. Ind. (1895), 14, 635. 



