6/8 BOTANY AND PHARMACOGNOSY. 



•pyrocatechin (this distinguishing it from Juniper Tar), and is 

 colored brownish-red by an equal volume of calcium hydrate test- 

 solution. The petroleum ether extract is colored greenish by a 

 O.I per cent, solution of copper acetate. 



Constituents. — Tar consists of a resinous substance, with 

 which are admixed a small quantity of turpentine, acetic acid, 

 methyl alcohol and various volatile empyreumatic substances. 

 On distillation 4 distinct classes of products are obtained: (i) 

 An AQUEOUS DISTILLATE, from 10 to 20 per cent., consisting chiefly 

 of acetic acid, methyl alcohol and acetone. (2) A light oily 

 DISTILLATE, from lo to 1 5 per cent., coming over under 150° C, 

 and consisting of mesit, toluene, xylene, cumene, methene and 

 eupion, which products are used as solvents for varnishes 

 and similar substances. (3) A he.wy oily distillate, about 15 

 per cent., distilling over between 150° and 250" C, and consisting 

 of the creosote oils, viz. : phenol, cresol, creosote, paraffin, naph- 

 thalene, pyrene, chrysene, retene and some other substances. (4) 

 A black resinous mass, called pitch (50 to 65 per cent.) which 

 has the odor of tar and is still official in some pharmacopoeias. 



In the distillation of pine wood tar the distillate which is 

 lighter than water contains a volatile oil known as oil of tar 

 (Oleum Picis Liquidae). When recently prepared it is colorless, 

 but it gradually darkens, becoming finally dark reddish-brown, 

 there separating at the same time a blackish, resinous substance. 

 Oil of tar consists chiefly of oil of turpentine, with some of the 

 lighter hydrocarbons and phenol compounds, acetic and other 

 acids, and a number of empyreumatic products. 



Allied Products. — Beech wood tar is the product of the 

 destructive distillation of the wood of Fagtis sylvatica and F. 

 ferruginea (Fam. Fagaceae). It is distinguished from pine tar 

 by the petroleum ether extract not giving a green color with 

 copper acetate solution, and in the creosote oils containing a 

 considerable amount of guaiacol. The official creosote is a mix- 

 ture of guaiacol and creosol with some other phenol derivatives, 

 as xylenol, methyl creosol and. methyl guaiacol, obtained from 

 the heavy oily distillate of beach wood tar. Guaiacol is of inter- 

 est because on treatment with chemicals it may be converted into 

 vanillin. 



