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 

 limit, equivalent to about a gallon a half hour in these experiments, 

 and the oil passing over no longer contains turpentine, as shown 

 when it is dry distilled. 



Along with the drop in speed of condenser discharge, 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 

 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 



