106 FOREST UTILIZATION 



evenly and gradually from the cap down to the bottom. 

 The means of guidance are : 



(a) To check draft, increased earth cover. 



(b) To increase draft, holes of about i l / 2 inches diam- 



eter punctured through the cover with the pad- 

 dle reversed. 



If wind is strong, all holes are closed and earth 

 cover increased. 



Cracks forming in the cover must be closed at 

 once. ' x 



In dry weather the kiln is continuously sprinkled. 



The kiln may explode if cover is too heavy and 

 draft too strong. 



The color of the smoke escaping through the 

 punctures indicates the completion of the char- 

 ring process above the holes (transparent bluish 

 color). 



The holes are then closed, and another row of 

 punctures is made about two feet below the 

 closed holes. 



V. Refilling is required where dells are forming irregularly, 



while the kiln gradually collapses to half of its original 

 volume. 



For refilling, the cover over the dell is quickly removed, 

 all holes having been closed beforehand, and the dell 

 is rapidly filled with fresh wood. 



VI. When the bottom holes show the proper color of smoke, 



the charring process is completed. All holes are then 

 closed and the kiln is allowed to cool. 

 The duration of the charring process is from six days 

 to four weeks, according to size of kiln. The contents 

 vary between four and sixty cords. 



VII. The kiln is gradually, beginning at the leeward side, un- 



covered, and the crust of earth, after hoeing, is thrown 

 on again. The earth, trickling down, quenches the fire. 

 After another twelve to twenty-four hours, preferably 

 at night, the coal is taken out in patches. 

 Water must be ready at hand, since fire usually breaks 

 out when coal is drawn. 



E. Statistical notes. 



The loss of weight in the charring process is 75 %. 

 The loss of volume is 50%. 



In America charcoal is sold by the bushel, a bushel weighing about 

 25 Ibs. 



F. Appendix. 



In Norway, Sweden and Russia kilns of trapezium form are built 



of peeled logs 15 to 30 feet long. 

 The lighting channel runs lengthwise on the ground. 



