6 BULLETIN 989, U. S. DEPARTMENT OF AGRICULTURE. 
Probably the first wood turpentine sufficiently refined to compete 
with gum turpentine was put out by these plants. They are also to 
be credited with early refining of pine oil. By 1908 they were selling 
it in tank-car lots (20). Most of the steam distillation plants, how- 
ever, were unable to exist on the low turpentine market of 1911-12, 
so that by 1913 no plants were operating, except one or two on saw- 
mill waste. In the spring of 1919 none were known to be in oper- . 
ation other than in connection with sawmills. | 
The methods used on sawmill waste are somewhat different from 
those used on hghtwood. The wood is “hogged” and run into the 
extractors. Steam is turned on and extraction begun. The period 
of steaming is much shorter than in the case of lightwood, because 
there is usually a large amount of waste wood to work on, and 
since the distilling plant is never large enough to treat all of the ~ 
waste by complete extraction, it pays better to distill the part of 
the oil that comes off easily and then discard the chips than com- 
pletely to extract a smaller amount of wood. As a rule, the saw- 
mil] refuse is partly selected so that the distillation plant gets the 
most resinous part of the waste, including box facings and rich 
butts. Still, the yields are very low. The oils are separated from 
the aqueous distillate and fractionally steam distilled in steam- 
heated stills to give wood turpentine and pine oil, which are the only 
products obtained by this method of manufacture. 
STEAM-AND-SOLVENT PROCKESS. 
As the rosin is left in the waste wood by the steam process the 
problem of recovering it arises. The wood, being already shredded, 
is in good condition for extraction, and so the process of extraction 
with a volatile solvent is added to the steam process. As carried 
out at present, the lightwood is first “ hogged,” then shredded, and 
put into large extractors. Steam is turned on and steam distillation 
continued as long as an appreciable amount of oils comes over. ‘Then 
the steam is turned off, a light petroleum distillate turned in, and 
extraction with this continued for some time with heating. When 
practically all the rosin is extracted the solvent-rosin mixture is run 
into a storage tank, and the chips are steamed to recover residual 
solvent, after which they are used for fuel. The oil from the aqueous 
layer is fractionally distilled into wood turpentine and pine oil. 
The solvent-rosin mixture is fractionated into solvent, pine cil, and 
rosin. The pine oil obtained from this process contains small 
amounts of the solvent, and for most commercial purposes it is sold 
mixed with the pine oil obtained from the steam part of the process. 
A diagrammatic scheme of the process is as follows: 
