4 BULLETIN" 989, U. S. DEPARTMENT OF AGRICULTURE. 



in charge and on what he considers to be his most important product. 

 If it is charcoal, he will heat longer and at a higher temperature; if 

 it is wood turpentine, he will heat carefully at first ; and so on. 



The methods in use in the spring of 1919 were in general as fol- 

 lows : The lightwood is brought to the plant in cordwood lengths, or 

 shorter, and split to about the size of ordinary cordwood. The stump- 

 wood, of course, is very crooked and does not pack well, but is usually 

 richer in resinous material than the upper timber. This wood may 

 be packed in the retort by hand as received, or after being cut into two- 

 foot lengths, or it may be loaded on cars which are run into the re- 

 torts. The retorts are then sealed, steam run in to displace the air, 

 and firing is begun. At first a mixture of aqueous distillate and light 

 oils comes over. This contains most of the turpentine and pine oil, 

 and the heat is kept low until it is over. Then the receiver is changed 

 and the heat increased for the destructive part of the distillation. 

 A fairly large amount of gas is formed in this part of the operation 

 and is usually emploA^ed for firing. The heavy oils, which contain 

 most of the tar oils, are gathered in a tank. This material may or 

 may not be separated into two fractions. The tar ma}^ be distilled 

 from the retort or it may be allowed to run out from the bottom of 

 the retort through a water seal. When the distillation, which takes 

 from 18 to 48 hours, is finished, the retort is permitted to cool down so 

 that the charcoal will not take fire when it comes into contact with 

 the air. Some plants provide covers about the size of the retort into 

 which the cars containing the charcoal are drawn, and any fire is 

 smothered by shutting off the air. Thus, less time between charges 

 is lost, and the retorts are heated to some extent for the next distilla- 

 tion. In other plants it is necessary to cool the retorts sufficiently to 

 permit the removal of the charcoal by hand, or even to allow a man 

 to go inside to repack the retort. This usually causes a decided loss 

 of time in the distillation cycle. 



The oils are refined by fractional distillation in steam stills, re- 

 peated once or more according to the purity of the product desired, 

 and distilled once, at least, from over soda solution to remove the 

 creosote oils. The products are a wood naphtha, apparently quite 

 similar to rosin spirits, wood turpentine, pine oil, tar oil, tar, pitch, 

 and creosote. Owing to the heavy demand for flotation oils in the 

 past few years, however, a very large amount of the oil has been sold 

 unrefined for this purpose. 



The yields of oils vary with the amount of resinous material in 

 the wood and the methods employed in the distillation. Another 

 factor in the reported variations of yields is that results are usually 

 reported as so much a cord, while the wood charge is weighed rather 

 than measured, the weight called a cord varying from about 3,500 

 to 5,000 pounds. Yields of total crude oils claimed vary from 40 to 



