of destructive distillation, it is nevertheless true that " steam dis- 

 tillation," as the term is technically used, signifies the separation of 

 volatile products from wood with, at most, but little decomposition of 

 the wood fiber. 



With both these processes the vaporized compounds after leaving 

 the retort pass through water-cooled tubes, where they are condensed 

 into the crude liquors which after refining yield marketable products. 



Different woods give different marketable products after distilla- 

 tion. Thus, the hardwoods beech, birch, and maple yield acetate 

 of lime, wood alcohol, and charcoal, and longleaf pine yields turpen- 

 tine, tar, pine oils, and charcoal. This difference in the products is 

 due to the fact that pine woods are resinous, while hardwoods are 

 nonresinous. From the point of view of products, therefore, it is 

 necessary to distinguish between the kinds of wood used, as well as 

 between the distillation processes. 



DESTRUCTIVE DISTILLATION OF HARDWOOD. 



Hardwood distillation has been an established industry in the 

 United States for a number of years. The products already men- 

 tioned are wood alcohol, charcoal, and acetate of lime, each of which 

 has important uses. The plants are located in the northern part of 

 the United States, where, except for the Appalachian hardwood belt, 

 the hardwoods are most common. 



The woods used are largely beech, birch, and maple, with the last 

 preferred. The wood is cut into cord wood lengths and allowed to 

 season for a year. According to the best information, the amount of 

 the products obtained from green wood and from ordinary dry wood 

 is not different, cord for cord, but the higher water content of green 

 wood dilutes the distillate and necessitates more fuel for the carboni- 

 zation. Excessive seasoning .will doubtless reduce the yield of valu- 

 able constituents. Body wood is better than slab wood. Very small 

 wood, such as thin edgings, carbonizes so rapidly that it must be 

 mixed with larger pieces. The problem of the destructive distilla- 

 tion of sawdust has not yet been satisfactorily solved. 



APPARATUS. 



Wood is heated or carbonized in three forms of apparatus: (a) In 

 brick kilns, (6) in retorts, (c) in ovens. 



The charring of wood is a process as old as civilization. In the 

 early days the wood .was charred under sod in the old charcoal kiln, 

 which has been a familiar sight over a good part of the world. The 

 modern charcoal kiln is so made that valuable vapors are condensed 

 from the smoke, which in the old-fashioned kiln escaped into the 

 air and were wasted. Kilns are now mainly used to produce char- 

 coal for blast furnaces for pig iron. They are made of brick, with 

 a circular base, and divided approximately into two semicircular sec- 

 tions. They hold each about 50 cords, and are charged and dis- 

 charged by hand. The vapors are carried off into condensers, where 

 the condensable ones are liquefied. 



The name " retort" is given to a small form of cylindrical vessel 

 holding about three-fourths, of a cord. The retorts are set horizon- 

 tally in brickwork, in pairs, each pair forming a "battery," and 

 heated from beneath. They are filled and discharged from a single 



[Cir. 114] 



