November, 190S.] 



425 



Dyes and Tans. 



Russia, Austria, and Belgium all take 

 a fair amount of wattle bark, Russia 

 especially using Natal bark. In 1906, 1)1-4 

 tons were exported to Russia, and as 

 trade improves, it is hoped that more 

 will be taken. 



At present the United States takes 

 very little wattle bark, and none is 

 produced there. There are signs, how- 

 ever, that the United States is willing 

 to directly interest itself in the ques- 

 tion, although it is probable that few 

 parts of the country, except those in 

 the extreme south, are sufficiently free 

 from forest to make the culture of 

 wattle trees profitable. (U. £>. Dept. 

 Agri. Bull. No. 51, Part IV). it is 

 worth noting, however, that an experi- 

 mental plantation has been in existence 

 for a number of years in the Hawaiian 

 Islands. 



To be saleable in the United Kingdom, 

 wattle bark must be in good condition 

 and well harvested. The best prices are 

 only obtainable for barks which arrive 

 undamaged by weather or by wet pack- 

 ing. It is stated that the proportion 

 of damaged bark shipped from Natal 

 has been unusually large of late, and 

 allowances up to several pounds per 

 ton have had to be made. 



In Germany, most of the imported 

 bark is made into extract, and does not 

 go direct into the tanning pit. As a 

 result, weathered and damaged bark 

 is more readily saleable there than in 

 the United Kingdom. 



Wattle Bark Extract. 



Of late years the use of bark ex- 

 tracts has largely taken the place of 

 ground barks for tanning purposes. 

 Extracts are preferred by tanners, 

 since they are quicker and more regular 

 in their action, and there is practically 

 no waste in their use- Quebracho, valo- 

 nia, oak bark, sumac, and mangrove are 

 all largely utilised in the form of liquid 

 and solid extracts, and their application 

 in this form is being greatly extended 

 year to year. 



Besides these advantages to the tan- 

 ner, it is clear that advantage also 

 accrues to the producer, since he is 

 able by this means to utilise materials 

 deficient in tannin, and is aole to com- 

 pete in distant markets otherwise closed 

 to him by reason of high freights. 



These considerations have been of 

 late the subject of much discussion in 



the wattle-producing countries, and 

 notablv in Natal. The Union already 

 referred to appears to have decided 

 that the best chance for the expansion 

 of the industry lies in the direction of 

 manufacturing extract in the centre of 

 production of the bark. 



Manufacture of Wattle Bark 



Extracts. 



Tanning extract can be placed on the 

 market in either the liquid or solid 

 form. Where it is possible to concen- 

 trate the extract sufficiently without 

 decomposition, it is more advantageous 

 to prepare the solid extract, since this 

 is cheaper to pack and to transport. 

 The process of making extracts resolves 

 itself into several sections which may 

 be considered seriatim. 



Leaching.— This is the technical term 

 describing the process of dissolving 

 the tannin out of the bark. For this 

 purpose the latter is ground to a fine 

 powder to facilitate extraction. The 

 system of " leaches " or extractors now 

 considered the best admits of continu- 

 ous working. Pits, or tubs sunk in 

 the ground, and built in series of " bat- 

 teries " of six to eight, are packed with 

 the ground bark, and the liquor obtain- 

 ed by percolation with water in one pit 

 is used to extract the bark in the next 

 leach, and so on until a strong liquor, 

 is obtained. Continuity of action is ob r 

 tained by keeping a high head of wate 

 or spent liquor in the end vat by means 

 of a series of vertical pipes. The spare 

 vat may be heated by steam if re- 

 quired. 



Wattle hark is best extracted at a 

 temperature of about 60, beginning cold 

 and raising the temperature gradually. 

 The following table, taken from Proctor's 

 Principle* of Leather Manufacture, 

 shows the percentage of tanning matter 

 and the amount of colour (as measured 

 by Lovibond's tintometer) obtained by 

 extracting Natal wattle bark so long as 

 any colour or tannin could be ob- 

 tained. 



The object of the extract manufacturer 

 should be to remove the maximum 

 amount of tannin and the minimum 

 amount of colour in the minimum of 

 time and with the least possible quan- 

 tity of water, since the water will later 

 on have to be evaporated. The results 

 recorded in the following table clearly 

 indicate waterat about 60 C. as giving 

 the best results when all these re- 

 quirements are taken into consider- 

 ation. 



51 



