238 VEGETABLE SUBSTANCES. 



Another method pursued is to place the tar-wood 

 in a receptacle enclosed by an arch and walls, a 

 small opening only being left near the bottom for 

 the egress of the tar : a fire is then made round the 

 arch in such a manner that the heat may communi- 

 cate to the inside, and cause the tar to be distilled 

 from the wood in the same way as if retorts had been 

 used. This plan is perhaps more expensive than 

 the first, and therefore less generally practised ; the 

 operation is, however, performed in much less 

 time, and the quantity of tar produced from a 

 given quantity of wood is greater than that obtained 

 by the other method, while a very superior kind of 

 charcoal is at the same time afforded from the wood 

 thus carbonized. In the common way a cube of six 

 feet of tar-wood yields from two to three, and some- 

 times four tuns of tar : burnt by this last described 

 method, the same bulk of wood produces, in half the 

 time, five or six tuns. An equal quantity of common 

 fir-wood yields only about one tun, or one tun and 

 a half. 



In Norway, and other countries bordering on the 

 Baltic sea, where the vast extent of their pine forests 

 induces the natives to be less economical in the use 

 of the wood, stacks of it are built on the slope of 

 a hill, and covered with moss and turf : fires are 

 then kindled in different parts ; and the tar which 

 oozes out flows through channels or spouts into 

 barrels placed for the purpose at the bottom of the 

 hill. 



A more economical process for making tar is pur- 

 sued in France and Switzerland, by which the wood 

 is charred more equably, and the product is of a 

 much more uniform, and probably also of a better 

 quality. In the Valais the pines are felled the pre- 

 ceding year, that the wood may be sufficiently dry 

 for use ; and the outer bark and twigs being stripped 



