Tans and Dyes 



OF THE 



UW 'VE RS ITY 



351 



which contains from twenty -six to thirty per cent, of tannin. This is principally made in 

 Hungary and Italy. 



Galls. These are excrescences produced on the gall oak (Quercus tinctoria) as the result of 

 punctures made by the " gall insect." They contain forty to fifty per cent, of tannin, and are 

 used principally in the manufacture of ink. 



Valonia. This consists of the acorn cups of the valonia oak {Quercus aegilops), which occurs 

 widely distributed in Asia Minor and the Balkan Peninsula. The cups are picked by hand 

 after the acorns have fallen and are simply dried in the sun. 



Valonia contains from twenty -five to thirty per cent, of tannin, and is used for the 

 production of sole leather, for which purpose it has largely replaced oak bark in the 

 United Kingdom. 



Tanning Materials obtained from Coniferous Trees 



A considerable number of coniferous trees yield barks suitable for use in tanning. In 

 Scotland the bark of the larch (Larix Europaea) is employed ; it contains about nine per cent, 

 of tannin, and is valued particularly for light leathers. Throughout Austria the bark of the 

 Norwegian spruce is commonly made use of ; it contains about eleven per cent, of tannin, and 

 yields a plump, nicely coloured, but rather poorly filled leather. Considerable quantities of 

 tanning extract are now made from spruce bark in Austria for export. The same spruce grows 

 commonly in the United Kingdom and in Scandinavia, but, curiously enough, in spite of the 

 large supplies of the bark which must be available in Norway and Sweden, it is but little used 

 in those countries. 



" Hemlock Bark.'''' This is obtained from the " hemlock " fir (Abies canadensis), a tree 

 widely distributed in Canada and throughout the northern part of the United States, in which 

 countries it forms the staple tanning material. The bark contains from seven to ten per 

 cent, of tannin, and yields a plump, rather reddish leather. Hemlock bark is a bye-product 

 of the timber industry, and as disafforestation is rapidly proceeding in the United States, the 

 bark is becoming scarce. There are, however, large forests of hemlock fir in Canada, and there 

 the bark is used in the local tanneries, but probably a much larger quantity is converted 

 into " hemlock extract," which is imported into European countries and the United States. 

 The Canadian extract contains from twenty-eight to thirty per cent, of tannin. 



Birch Barks 



These are also products 

 which are fairly extensively 

 used in several countries, but 

 are too poor in tannin to be 

 worth export. White birch 

 bark (Betula alba) is collected 

 and used to a small extent in 

 Scotland and is employed on 

 a considerable scale in Russia. 

 The bark contains about ten 

 per cent, of tannin and in 

 addition a small quantity of 

 a pleasant-smelling volatile 

 oil, which is absorbed by 

 hide. It is to the presence 

 of this oil that the charac- 

 teristic fragrant odour of 

 " Russia " leather is due. oak apple galls 



