BARK OF BIRCH AND LARCH. 509 



per load of 50 cubic feet). It is also sold by the tree, by the 

 hundred rolls, by the volume of the barked wood, or by the 

 drying stack (Fig. 277) containing 12 to 15 pieces of bark. 

 Selling by the amount of peeled wood is the simplest method, 

 provided sufficiently accurate ratios between the wood and bark 

 have been ascertained ; for wood 80 — 100 years old, this ratio is 

 as 1 to 8 — 12, averaging 1 to 10. In younger wood the ratio is 

 more in favour of the bark. 



3. Birch- and Alder- Bark. 



Birch-bark is more in use for tanning in the north of Europe, 

 especially in Russia ; in Germany it has hitherto been used only 

 experimentally. It contains much less tannic acid than oak- 

 bark, and even than that of spruce, but sometimes repays 

 harvesting when the price of silver-bark is high. 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 although the 

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

 young ones, but they are not nearly so easy to bark as oaks. 

 The few data regarding birch-bark give 65 — 80 kilos of air- 

 dried bark for a stacked cubic meter of peeled birch billets 

 from trees 20 years old (say 2 cwt. per load of 50 cubic feet). 

 Alder-bark is occasionally used for tanning, but is of no more 

 importance than that of birch. Russian leather is tanned with 

 willow-bark, but its pleasant odour is the result of soaking it 

 during the tanning process wdth birch-oil, which is distilled 

 from the external white layer of birch-bark. 



4. L'lrch-Bark. 



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

 sively used in Russia, Hungary, and Austria for tanning. 

 According to Wessely, in the Carpathian Mountains and the 



