28 WATTLES AND WATTLE-BARKS. 



results up to the present. Nothing is easier than to decolorise extract, but 

 the difficulty is not to destroy the tannic acid at the same time. 



The following notes relating to the making of extract of hemlock bark are 

 taken from Proctor's " Text-book of Tanning," and may be suggestive : 



" The bark, in pieces J-lin. thick and several inches long, is soaked for 

 about fifteen minutes in water at 200 deg. F. (93 deg. C.) ; it is then fed 

 into a hopper, which conducts it to a 3-roller machine, something like a 

 sugar-cane mill, through which it passes, coming out lacerated and com- 

 pressed ; it next falls into a vat of hot water, where it is agitated by a 

 wheel that the tannin from the crushed cells may be dissolved in the water ; 

 hence it is raised by a series of buckets on an endless chain, somewhat in 

 the manner of a grain elevator to another hopper, whence it is fed to 

 another 3-roller mill ; here it receives its final compression, and comes out 

 in flakes or sheets, like coarse paper, and almost free from tannin. The 

 buckets are made of coarse wire that the water may drip through during 

 elevation. In order to avoid the blackening action of iron, whenever this 

 metal will come into contact with the solutions it is thickly coated with zinc. 

 The solution is evaporated to a solid consistency, generally by vacuum-pans. 

 About 2 tons of bark are represented by 1 barrel (of less than 500 Ib.) of 

 extract." 



And, again, " It is one of the great attractions of extracts that they 

 avoid almost all the expense and labour inseparable from the exhaustion of 

 other tanning materials. It is usually necessary to dissolve the fluid 

 extracts in water or liquor of as high a temperature as has been employed 

 in their preparation, as otherwise, from some unexplained chemical change, 

 a large portion of the tannin is precipitated, probably as an anhydride of 

 tannin." 



A South Coast correspondent informs me that he has obtained 1 ton of 

 extract, 40 per cent., from 4 tons of hickory or black-wattle bark (Acacia 

 penninervis, var.) There is now a good market in Europe for well prepared 

 wattle bark extract, but the demand has only sprung up again within the 

 last few years. 



The following notes on extracts from the Moruya district examined by 

 me may be interesting : 



1. Hickory extract (Acacia penninervis), of the consistency of thin 

 treacle, contains only 20'25 per cent, of tannic acid, 61*15 percent, 

 of water, and S'2 per cent, of gum precipitated by alcohol after 

 twenty-four hours. The phlobaphenes and other organic sub- 

 stances were not estimated. Damaged by over-heating and over- 

 concentration. 



