TAR. 



251 



essential oil has evaporated naturally. Thus, properly speak- 

 ings is the turpentine of AUes resince [Conifer a), but the 

 hardened American turpentine above mentioned is more 

 generally substituted for it. Mixed with perfumed gums, 

 it is burned as incense in the performance of Eoman Ca- 

 tholic ceremonials. 



Canada Balsam, a clear, transparent oleo-resin, which 

 exudes from Alieshalsamea {ConifercB) (Plate XIX. fig. 98) ; 

 it is about the thickness of sperm oil, but soon gets less 

 fluid ; it is used chiefly for preparing microscopic objects, 

 by rendering them transparent, and in making some var- 

 nishes. 



Tae is a product procured by a species of distillation 

 termed distillation per descensum, from the roots of various 

 Coniferous trees, particularly ~Pinus sylvestris (Plate XIX. 

 fig. 100). It was known to the ancients, and the mode of 

 preparation described by Theophrastus was nearly the same 

 as that now employed. A bank is chosen in the forests near 

 w^hich the timber is plentiful. In this bank a circular hole 

 is made, the sides of which are beaten very hard; at the 

 bottom a cast-iron pan, having a spout, is placed ; a tube 

 is fitted to the spout, and passes through the side of the 

 bank. The large hole is then filled with billets, nicely cu 



