Select Plants for Industrial Culture and 



vshelter in treeless localities for raising forests where no severe 

 frosts occur. Its bark, rich in tannin, and its gum, not dissimilar 

 to gum arabic, render this tree highly important. The typical A. 

 decurrens with longer leaflets, rises seldom above 30 feet ; it has, 

 according to the Hon. Dr. J. Cox, a bark of less tannic strength 

 than A. mollissima, also is of quicker and taller growth ; its flower- 

 ing time is between that of A. dealbata and A. mollissima. The 

 English price of the bark ranges generally from 10 to 14. In 

 Melbourne it averages about 7 to 10 per ton. It varies, so far 

 as experiments made in my laboratory have shown, in its contents 

 of tannic principle from 30 to 40 per cent, in bark completely dried, 

 but this is not all pure tannic acid. In the mercantile bark the 

 percentage is somewhat less, according to the state of its dryness, 

 it retaining about 10 per cent, moisture. \\ Ibs. of Black Wattle- 

 bark give 1 Ib. of leather, whereas 5 Ibs. of English Oak-bark are 

 requisite for the same results ; but the tannic principle of both is 

 not absolutely identical. Melbourne tanners consider a ton of 

 Black Wattle-bark sufficient to tan 25 to 30 hides ; it is best 

 adapted for sole -leather and other so-called heavy goods. The 

 leather is fully as durable as that tanned Avith oak-bark, and nearly 

 as good in color. Bark, carefully stored for a season, improves in 

 tanning power considerably. From experiments made under the 

 author's direction it appears, that no appreciable difference exists 

 in the percentage of tannin in Wattle-bark^ whether obtained in 

 the dry or in the wet season. The tannin of this Acacia yields a 

 gray precipitate with ferric and a violet color with ferrous salts ; 

 it is completely precipitated from a strong aqueous solution by 

 means of concentrated sulphuric acid. The bark improves by age 

 and dessication, and yields about 40 per cent, of catechu, rather 

 more than half of which is tannic acid. Bichromate of potash, 

 added in a minute quantity to the boiling solution of mimosa- 

 tannin, produces a ruby -red liquid, fit for dye-purposes ; and this 

 solution gives with the salt of sub-oxide of iron black pigments, 

 and with the salts of the full oxide of iron red-brown dyes [F. v, 

 M. and Rummel]. As far back as 1823 a fluid extract of Wattle- 

 bark was shipped to London, fetching then an extraordinary price, 

 1 ton of bark yielding 4 cwt. of extract of tar-consistence [Sim- 

 monds], thus saving much freight and cartage. 



Tan-extract is best obtained from the bark by hydraulic pressure 

 and evaporation of the strong liquid thus obtained in wide pans 

 under steam-heat, or better still, to avoid any decomposition of the 

 tannic acid, by evaporation under a strong current of cold air. For 

 cutch or terra japonica the infusion is carefully evaporated by 

 gentle heat. The estimation of tannic acid in Acacia-barks is 

 effected most expeditiously by filtering the aqueous decoction of the 

 bark after cooling, evaporating the solution and then re-dissolving 

 the residue in alcohol and determining the weight of the tannic 

 principle obtained by evaporating the filtered alcohol -solution to 

 perfect dryness. 



