Dye Stuffs and 



38 



cut down for timber, and the bark was wasted until its value as a tanning agent 

 was discovered. In the German protectorate the bark is now stripped from the 

 stems and branches of the living trees, conveyed to convenient centres, broken up, 

 and dried in the sun (or by artificial heat produced usually by the combustion of 

 mangrove timber), and exported. 



The industry is under the control of the Forest Department, which insists 

 on the bark being carefully stripped, so that the trees are not destroyed (stripped 

 trees are said to renew their bark in from four to six months), and the authorities 

 also prohibit the export of bark containing less than 45 per cent, of tannin. 



In M. Baillaud's experiments much the same plan was followed, and it was 

 found that natives working piece-work could collect about 200 lb. of bark per day, 

 and it was estimated that to place a ton of the bark in Europe would cost fr. 124 

 c. 50, which seems to be an unnecessarily high figure. It was noticed that if the 

 bark is exposed to the rain after collection, a considerable loss of tannin occurs, 

 so that it is desirable that the drying be conducted under cover when wet weather 

 prevails. In the East Indies the bark is stripped, then dried, and roughly ground 

 and packed in small bales, sometimes under pressure. In this way the cost of 

 transport to Europe is reduced somewhat. Allusion has also been made to the fact 

 that the authorities in German East Africa prohibit the export of bark containing 

 less than 45 per cent of tannin, and where such regulations are not officially in force, 

 it would be well for exporters to adhere to this rule, since tanning materials are now 

 almost universally bought on their actual content of tannin, and mangrove bark 

 containing less than 45 per cent, of tannin is scarcely saleable, and the inclusion of 

 such material with good bark might lead to losses. 



But little attention has as yet been paid to the utilisation of mangrove 

 timber. M. Baillaud states that it is, as would be expected, peculiarly resistent to 

 the action of water, and is therefore suitable for the construction of piles, railway 

 sleepers, and similar articles where hardness and great resistence to the action of 

 water are of importance. It has also been used for street paving in Paris, but 

 apparently the price obtainable for it for this purpose did not prove remunerative. 



MANUFACTURE OF MANGROVE EXTRACT. 



In the countries where mangrove bark is principally produced at the present 

 time, skilled labour is not usually available, and consequently the manufacture of 

 mangrove extract from the bark is difficult if not impossible. There can be no doubt, 

 however, that if the extract could be made in these countries much of the poorer 

 bark at present discarded could be utilised, and as the export of extract would mean 

 that only the really useful portion of the bark would be sent to Europe, a great 

 saving in the cost of transpox^t would be effected. It may be worth while, 

 therefore, to give here a short account of the modern process of preparing tanning 

 extracts from mangrove bark and similar products. 



The bark, after being thoroughly air-dried, is ground in a bark mill or 

 disintegrator so as to form a powder, through which water will percolate slowly. 

 This is then packed into " leaches " or extractors, which usually consist of round 

 pine-wood tubs, strengthened by iron hoops and provided with perforated false 

 bottoms, below which the extracting liquor may collect. A series of these 

 " leaches " is employed, a connection by means of a copper or leaden pipe running 

 from the chamber below the false bottom of each to the mouth of the next. 

 Each is also provided with a pipe, whereby steam can be introduced, so that 

 the extracting liquid may be heated to any desired temperature. Water is allowed 

 to flow into the first extractor of the series, which is then heated by means of its 

 steam jet. The warm water percolating dowmvards through the ground bark, 

 extracts the tannin and other soluble matters, and the liquor so produced gradually 



