G20 CONIFERi^:. 



w 



History — Theoplirastus gives a circumstantial description of the 

 preparation of tar, which applies with considerable accuracy to the 

 processes still practised in those districts where no improved methods 

 of manufacture have yet been introduced. 



Production — The great bulk of the vegetable tar used in Europe, 

 and known in commerce as Archangel or Stockholm Tar, is prepared in 

 Finland, Central and Northern Russia, and Sweden. 



The process is conducted in the following manner : — vast stacks of 

 pine wood consisting chiefly of the roots and lower portions of the 

 trunks (the more valuable parts of the trees being used as timber), and 

 containing as much as 30,000 to 70,000 cubic feet, are carefully packed 

 together, and then covered with a thick layer of turf, moss, and earth, 

 beaten down with heavy stampers. The whole stack of billets is 

 constructed over a conical or fuimel-like cavity made in the ground, if 

 possible on the side of a hill, this arrangement being adopted for the 

 purpose of carrying on a downward distillation. Fire being apphcd 

 ■the combustion of the mass of wood has to be carried on very slowly 

 and without flame in order to obtain the due amount of tar and a 

 charcoal of good quality. During its progress the products, chiefly tar, 

 collect in the funnel-like cavity, from which they are discharged by a 

 tube into a cast-iron pan placed beneath the stack, or simply into 

 hollow tree trunks. The time required for combustion varies from 

 one to four weeks, according to the size of the stack. 



During the last few years this rude process has been improved and 

 accelerated by the introduction of rationally constructed wrought-iron 

 stills, furnished with refrigerating condensers, as proposed in Russia by 

 Hessel in 1861, By this mode of manufacture the yield in tar of pine 

 wood is about 14 per cent, from stems, dried by exposure to the open 

 air; and 16 to 20 per cent, from roots. Large quantities of pyroligneonj 

 acid and oil of turpentine are at the same time secured. The wood oi 

 the beech and of other non-coniferous trees appears not to afford more 

 than 10 per cent, of tar, while turf yields only from 3 to 9 per cent. 



Description — The numerous empyreumatic products which resiii^ 

 from the destructive distillation of pine wood, and which we call W, 

 constitute a dark brown or blackish semi-liquid substance, of peculiar 

 odour and sharp taste. When deprived of water and seen in thin 

 layers, tar is perfectly transparent. The magnifying glass shows som^ 

 of the varieties to contain colourless crystals of Fyrocatcchhh scattere^ 

 throughout the dark viscid substance, and to these tar owes its ^^J^^^^J" 

 ally granular, honey-like consistence.^ A gentle heat causes them 

 melt and mix with the other constituents. , ... j^ 



True vegetable tar has always a decidedly acid reaction. ^^ ' 

 readily miscible with alcohol, glacial acetic acid, ether, fixed and volatile 

 oils, chloroform, benzol, amylic alcohol or acetone. It iJ^ **^ . | o^he 

 caustic alkaline sohitions, but not in pure water or watery liquids. 



(Hessel) 



somewhat elevated temperature, it becomes lighter than warm ''l^^f,^ 

 Water agitated with tar acquires a light yellowish tint, and the ta 



and odour of tar, as well as an acid reaction. On evaporation 



1 The crystals are a pretty object for the microscope, when examined hy V^ 

 hght. 



larize^ 



