TAR. 251 



essential oil has evaporated naturally. Thus, properly speak- 

 ing, is the turpentine of Abies resina (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 horn. Abies halsamea (Coniferce) (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. 



Tab, is a product procured by a species of distillation 

 termed distillation per descensum, from the roots of various 

 Coniferous trees, particularly Finns 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 

 which 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 



