418 VEGETABLE SUBSTANCES. 



should be at least twenty or thirty years. A hollow, 

 about three inches square and an inch deep, is then 

 cut into its trunk at half a foot from the ground, 

 and the bark is stripped off to a foot and a half 

 above, exposing the sappy wood. Some of the 

 trees are cut on two sides, leaving 1 only two longitu- 

 dinal strips of bark of about four inches in breadth 

 to convey the sap necessary for the support of the 

 tree. The turpentine flows from the trees sometimes 

 six or seven, but more usually only during four 

 years; every year the bark being cut away higher 

 and higher until the juice will flow no longer. 

 Some trees die in consequence, but others continue 

 to thrive, and do not appear to be much injured by 

 the exhaustion of their juice. It is considered a 

 good day's work for one man to box* sixty trees a 

 day. About once a week it is found necessary to 

 take off a thin piece of wood from the barked part, 

 as otherwise the resin dries, and forming a coating 

 prevents the free flowing of the juice ; this operation 

 is also performed after rain, which checks the running 

 of the turpentine. 



The hard concrete turpentine, which forms about 

 the incisions of fir-trees while exuding, is a brittle 

 and opaque resin called by the French brai-sec. 



Turpentine, as first obtained from the trees, is 

 loaded with impurities from which it is freed by two 

 distinct methods ; one consists in enclosing it in. a 

 cask perforated at bottom, when by exposure to a hot 

 sun it becomes so fluid as to filter through, which 

 gives the finest and most valued turpentine. The 

 other method is to heat it moderately in a large 

 copper until it is quite liquid, and then filter it 

 through a strainer, made of rows of straws laid close 



* For the meaning of this term, and also for farther particulars 

 concerning turpentine, we refer the reader to page 82, of the vo- 

 lume on Timber Trees in this series, 



