48 WILLIAMS. 



standpoint. The natural resources are sufficient for a profitable in- 

 d\istry, the swamps being fully as valuable, hectare for hectare, as many 

 now being worked in the East Indies. 



It has further been observed that, in general, the tannin content of 

 the bark increases with the size of the tree. It is probable that the age 

 rather than the size of the tree is the true coefficient of the tannin content, 

 but since these trees show no seasonal rings of growth it is almost im- 

 possible more than roughly to approximate the age. Such variations 

 from the general rule as will be observed in the tables given below, 

 where the approximate diameters are noted, are easily accounted for by 

 differences in the conditions of growth of the individual trees. However, 

 further work must be done to establish the fact. 



Like many other barks, these deteriorate when allowed to dry slowly 

 in the air. Molds may grow on the fresh bark and rapidly destroy the 

 tannin. Exposure to the air and light in any case causes oxidation, 

 resulting in loss of tannin and production of red coloring matter. All 

 samples, the analyses of which are given below, were dried over quick 

 lime and placed in dark, air-tight bottles until analyzed. The analyses 

 in all eases were made within sixty days after collection. Samples col- 

 lected near Manila, dried and preserved in this manner, at the end of 

 two months showed no losses of tannin exceeding 0.5 per cent. The 

 analyses were made by the method of the Association of Official Agricul- 

 tural Chemists, substantially as published in Bulletin No. 107 of the 

 United States Bureau of Chemistry. Somewhat larger quantities of 

 hide powder than those recommended were found necessary completely 

 to detannize the solutions. 



Data, both analytical and general, regarding the principal trees of 

 the swamps are given below. Botanical descriptions ® have not been 

 included. 



Rhizophora mucronata Lam. Bacauan (Tagalog). 



This tree is found in stands of even development, usually on the 

 water side of the swamp. It makes up two-fifths to one-half of the 

 total timber producing commercially valuable bark. Its maximum 

 diameter is 50 centimeters; the average 25 to 30 centimeters, excluding 

 young trees below 20 centimeters in diameter. It attains a height of 

 15 to 25 meters. Three average-sized trees were found to yield 140 

 kilograms each of fresh bark. The bark bears a thin, hard, outer scale 

 easily removed from the inner bark, which is orange colored, nonfibrous 

 and somewhat pulpy, and contains 50 to 60 per cent of moisture. The 

 wood is hard and heavy (specific gravity about 1.1 when dry), and is 

 reddish in color. It is an excellent firewood and well adapted for 



' Foxworthy, F. W., hoc. cit. Also Hooker, Flora of British India, and Schim- 

 per, Indo-Malayische Strand-flora. 



