26 BULLETIN 1003, U. S. DEPARTMENT OF AGRICULTURE. 
the distillation can be distinguished by an experienced person within 
fairly close limits by means of the changes indicated. 
Contamination with decomposition products and the proportion of 
_ heavier oils, that subsequently must be removed, increase rapidly be- 
yond this point. This comparatively pure fraction, therefore, is not 
allowed to mingle with that coming over beyond this point, but is 
collected separately as “ first crude turpentine,” while the remainder 
constitutes “second crude turpentine.” The aqueous distillate com- 
ing over with the first crude turpentine, being practically free from 
alcohol and acid, is discarded, but that from the second turpentine is 
collected and saved with the pyroligneous acid obtained throughout 
the remainder of the run. The temperature being held fairly con- 
stant, the second turpentine fraction is continued to the point where 
the flow of distillate from the condenser drops below a practical 
hmit, equivalent to about a gallon a half hour in these experiments, 
and ile oil passing over no longer contains unpenpine, as shown 
when it is dry distilled. 
Along with the drop in speed of Adin ones the distillate 
suddenly takes on a true consistency and undergoes such a char- 
acteristic change of odor that there is no mistaking the point at 
which all turpentine has passed over. By the time combustible 
gases that burn with a pale blue flame begin to escape from the 
vent pipe. The bottom coil is then opened and the temperature 
of the jacket oil run up to approximately 345° C., where it is main- 
tained until the end of the distillation. The oil becomes heavier as 
the temperature rises, until presently it separates from the aqueous 
portion of the distillate only after standing for some time. This 
marks the end of the “light-oil” period. The greater viscosity of 
the heavy oil and its characteristic odor are further relied on in 
cutting the light and heavy oil fractions. The discharge of non- 
condensable gases now reaches a maximum, and these suddenly burn 
with a bright luminous flame in place of the one hitherto blue. 
RESULT OF DISTILLATION. 
The products obtained by this method of destructive distillation 
are, therefore, seven in number: Crude first turpentine, crude second 
turpentine, light oil, heavy oil, pyroligneous acid, pitch, and char- 
coal. The temperatures and the volumes of oil and acid distillate — f 
collected were entered every half hour in a log kept of each charge 
(Table 13). The distillates were collected in large graduated cylin- 
ders and the oil removed from the aqueous layer in separatory fun- 
nels. The sum of the half-hour oil readings tends to be a little high 
because of the imperfect separation of the water and the volume 
of the oil accumulated by the end of the period a little low because 
