44 BULLETIN 1003, U. S. DEPARTMENT OF AGRICULTURE. 



ing t<> the desired capacity. An oven 52 feet long, G feet 3 inches 

 wide, and 8 feet 4 inches high holds 10 cords of wood. 



The charge of wood, of regular con 1 wood size, is loaded onto 

 steel tramcurs of special construction and hauled into the retort or 

 oven, which is, of course, tightly closed during the distillation. At 

 the end of this operation, the train of cars bearing the still hot 

 charcoal is hauled out into the cooling shed of sheet iron, where the 

 charcoal cools down without loss of fire. Simultaneously, another 

 trainload of wood enters the oven, and the new distillation proceeds 

 with a minimum heat loss. 



In addition to the ovens, coolers, cars, and necessary brickwork or 

 the setting of the ovens, condensers, which should be of ample ca- 

 pacity to handle the distillate under the most unfavorable operating 

 conditions, will be required, as well as stills, steel tanks to hold the 

 product, wooden tanks, pumps, generators, steam boilers and engine, 

 yard tracks, piping, etc., and the necessary buildings for housing the 

 plant. 



A conservative estimate of the cost of such a plant is between 

 $4,000 and $5,000 a cord capacity. Before the war these plants could 

 be built for from $1,500 to $3,000 a cord capacity, or at a total cost, 

 including working capital, of approximately $20,000 for a 10-cord 

 .plant. The cost of construction and of operation and the design and 

 character of the equipment "will vary, and quite widely, with the pro- 

 posed location of the plant and the work it is to do, and with the 

 experience and practice of the designing and constructing engineers. 

 For these reasons, no details of equipment or specifications are given. 

 This information can best be secured from wood-distillation engi- 

 neers and from builders of the equipment, whose advertisements ap- 

 pear in the various industrial journals. The Bureau of Chemistry 

 can furnish a list of engineers and builders of wood-distilling plants. 



CONTROLLED TEMPERATURE PROCESS. 



The controlled temperature or circulating oil process and retort 

 have been fully described in the preceding pages. Even on a com- 

 mercial scale a prerequisite of this process is that the pieces of wood 

 be relatively smaller in diameter than those used in the ordinary de- 

 structive process, to insure rapid distillation. When properly car- 

 ried out, better separation of the several products of distillation is 

 obtained, with the result that the turpentine ordinarily obtained com- 

 mands a slightly higher price (3 to 5 cents a gallon) for paint or 

 varnish purposes than the turpentine produced by the regular de- 

 strnctive process, in which the temperature is not definitely con- 

 trolled. While tliis process yields a better grade of wood turpentine, 

 the equipment and upkeep are more expensive, and greater skill and 



