APPARATUS. 



Iron or steel retorts are used, varying in capacity from 1 to 4 cords. 

 They are either vertical or horizontal. The vertical retorts have 

 their long axis upright, and are set singly in brickwork with suitable 

 flues, usually with the openings for charging and discharging at the 

 top and bottom. The firebox below is at one side, so that the heat 

 goes around the outside of the retort itself. Few of these retorts 

 are now in use. 



The horizontal retorts are similar to those used in hardwood distilla- 

 tion. Though they differ as to form, all are cylindrical steel vessels 

 set in batteries in brickwork and are charged and discharged through 

 doors at one or both ends. The gases escape through pipes to copper 

 condensers. The firebox is sometimes constructed to fire two retorts 

 at a time, though usually but one. 



PRODUCTS. 



Though there are a number of methods which differ somewhat in 

 results, the five products usually obtained are: (1) Charcoal; (2) a 

 noncondensible gas; (3) light oils, which are often taken in two 

 fractions, one of which is a crude turpentine; (4) tar, and (5) pyro- 

 ligneous acid. At some plants the light oil vapor, which volatilizes 

 easily, is led off into condensers with the gas and pyroligneous acid, 

 while the tar, which is heavier, is drawn off at the bottom; at others, 

 the entire volatile product is driven off through a pipe at the top 

 and, after passing through the condenser, is separated into the crude 

 turpentine and tar fractions. 



There is no more uniformity in heating methods than in the form 

 of the retorts. The run is thirty-six or forty-eight hours, or longer. 



Charcoal which is to be sold is cooled in the retort, and that which 

 is to be used for fuel is drawn hot and sprayed with water to prevent 

 fire. The gas is allowed to run to waste or is burned under the 

 retorts and boilers. 



The pyroligneous acid from hardwoods contains the most valuable 

 products, but that from pine, which has a strong odor and a reddish- 

 brown color, is of such different composition that very little is done 

 w T ith it. The yield from a cord of pine wood is, according to the 

 most widely accepted figures, not more than 3 gallons of 82 per cent 

 wood alcohol and about 70 pounds of brown acetate of lime. The 

 extraction of wood alcohol from pine wood is not at present on 

 a. commercial basis, and at the majority of plants the pyroligneous 

 acid runs to waste. 



The crude turpentine is a dark red oil with the bad odor associated 

 with products of destructive distillation. After proper fractional 

 distillation, it yields for market a nearly colorless turpentine, which 

 has a distinctive odor. 



The tar is sometimes refined far enough to produce a good quality 

 of retort tar and to yield oils which, with the heavy distillates from 

 the crude turpentine, make disinfectants, wood creosote, and a num- 

 ber of market articles. 



The refining processes, which are largely secret, are not the same 

 at .all plants, while the products sold are far from uniform. 



[Cir. 114] 



