234 



VEGETABLE SUBSTANCES. 



because the inner part is then destroyed by putrefac- 

 tion, while the external white bark remains uncor- 

 rupted for ages. Proofs of this indestructibility were 

 found in some old burial places, and in the vaults of 

 the very ancient castle at Moscow which had been 

 covered with birch bark. 



Birch oil is obtained by distillation in the following 

 manner. Pits made in the form of inverted cones 

 are prepared in a clay soil ; these have a hole, like 

 that of a funnel, at bottom, and a large wooden 



Birch Bctula albi. 



