200 FOREST PRODUCTS 



Brick Kilns. 



The brick kilns supplanted the old charcoal pit as a means of manu- 

 facturing charcoal when the iron industry in this country assumed large 

 proportions. Brick was substituted for the open-air or clay-covered pit 

 because manufacture was simplified, the loss of carbonization was mini- 

 mized and burning, therefore, could be carried on with greater safety. 

 However, a good portion of the vapors are lost with the brick kilns, as 

 they are with the old open-air pit, since the yield is only about 40 per 

 cent to 50 per cent of the yield from the oven process. These brick 

 kilns are made with a circular base, with holes in the base for drafts of 

 air regulated by special doors and the vapors are drawn off by exhausters 

 through wooden ducts. This practice was followed especially in Penn- 

 sylvania and in Wisconsin, where an abundant supply of the desirable 

 hardwoods was found in a location near blast furnaces where pig iron was 

 produced. Pig iron, manufactured by the use of charcoal, is considered 

 far superior to that made by coke. The pig iron made with charcoal 

 commonly brings about $5.00 a ton more than that manufactured with 

 coke. The brick kilns were usually built to hold 50 to 90 cords each and 

 were charged and discharged by hand. The complete manufacture of 

 charcoal by the brick kilns, including charging and discharging, required 

 from fifteen to twenty-five days. The heating necessary to distill the 

 wood is supplied by the combustion of part of the charge within the appa- 

 ratus, in the same way that charcoal is made in the open-aij pit; The 

 yield of charcoal by this method is somewhat below that manufactured 

 in the retorts or ovens and is generally considered inferior in grade. 

 The brick kiln is desirable only when the chief product is charcoal and 

 transportation facilities are not available or the market is too distant for 

 the other products of wood distillation, such as wood alcohol and acetate 

 of lime. Where other forms of fuel, such as natural gas and coal, are 

 out of the question and the manufacture of charcoal is desired, it is also 

 commonly used. 



Most of the brick kilns were in operation in Michigan and Wisconsin, 

 where charcoal was in great demand in connection with iron furnaces. 



Iron Retorts. 



The iron retort followed the brick kiln and was the first device in- 

 vented whereby the vapors from the carbonization of wood are collected 

 on an efficient basis and distilled in the form of pyroUgneous acid and 

 later refined into wood alcohol, acetate of lime, etc. The yields, how- 

 ever, are much lower on account of slow firing. These retorts were small 



