= 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, 1s 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 employed 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 may 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, piteh, 
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 
