BIRCH, LARCH AND WILLOW BARK. 661 



this ratio is as 1 to 8 or 12, averaging 1 to 10. In younger 

 wood the ratio is more in favour of the bark. 



SECTION YI. BIRCH -BARK. 



Birch-bark is more in use for tanning in the North of 

 Europe, especially in Kussia ; in Germany, hitherto, it has 

 been used only experimentally. It contains much less tannic 

 acid than oak-bark, and even than that of spruce, but in the 

 north repays harvesting owing to the absence of oak. In 

 Germany, it is not used for tanning, but for macerating sole- 

 leather, with the object of opening the pores of the leather 

 and preparing it to receive tannin. Leather tanned with 

 birch-bark is softer and less water-tight than that tanned with 

 oak-bark, but it has a lighter colour and a better appearance. 



Birch-bark is harvested in the same way as oak-bark, it can 

 be peeled only about a fortnight later than the latter, though 

 the birch shoots first. It is easier to peel old birch trees than 

 young stems and branches, but they are not nearly so easy to 

 peel as are oaks. The few data regarding birch-bark give 65 

 to 80 kilos of air-dried bark for a stacked cubic meter of peeled 

 birch billets, from trees 20 years old (say 2 cwt. of bark per 

 load of 50 cubic feet of wood). 



SECTION VII. LARCH-BARK. 



Larch-bark is harvested seldom in Germany, but is used 

 extensively in Russia, Hungary, and Austria for tanning. 

 Accordingly to Wessely, in the Carpathian Mountains and the 

 Alps, it is preferred to the bark of spruce and birch. Probably 

 it is unsuitable for tanning sole-leather, but deserves con- 

 sideration for tanning calf-skin and when added to other 

 tanning materials. Owing to the straightness and freedom 

 from branches of the larch, it is peeled more easily than oak. 



SECTION VIII. WILLOW-BARK, ETC. 



Willow-bark contains a considerable amount of tannic acid. 

 Besides Salix Caprea and 3. alba, the so-called osier-willows 

 are best in this respect. According to data furnished by the 



