34 Coller/e of Forestry 



doors the temperature attiiiiis an average of aljout 450 degrees 

 Fahrenheit. It is then maintained between 450 and 600 

 degrees Fahrenheit. Temperatures of over 600 degrees 

 Fahrenheit are considered undesirable. After about six 

 hours of heating the pvroligneous acid begins to flow, and the 

 best average is maintained up to about the eighteenth hour. 

 An operator can determine from the color of the pvroligneous 

 acid whether there is too much heat maintained, and if the 

 wood fibers have broken down sufficiently. At the end of the 

 heating process, the distillate forms tar to a large extent. 

 After about the eighteenth hour the latent heat in the oven 

 settings is sufficient to complete the process to the end, but 

 the heat is gradually decreased until the charcoal is with- 

 drawn. 



As the gases and vapors pass out through the nozzle of 

 the oven, they are condensed into a yellowish green, ill-smell- 

 ing liquor called pvroligneous acid. A copper run takes this 

 condensate to the raw liquor " sump,'' a tank in the ground, 

 and so placed that the liquor will run into it by gravity. 

 Meanwhile, the " fixed " or noncondensible gas is trapped 

 and taken oft" at the outlet of the condenser and used for fuel 

 underneath the boilers or ovens or perhaps both. A simple 

 goose neck is used to trap oft" the gas. 



The pyroligneous acid is next pumped from the " sump " 

 in the ground to a series of wooden settling tubs of which 

 there should be at least five in number. These tubs are usu- 

 ally from five to eight feet in diameter and six to eight feet 

 in height. The purpose of these tubs is to settle the tar and 

 heavy oils. The heavy tar is taken to a wooden tar still 

 equipped with a copper condenser. This tar still is of 

 wooden construction because the tar would eat up the copper 

 in about a year. The residue remaining in the tar still is 

 utilized together with residue from primarv stills as boiler 

 fuel. 



