24 BULLETIN 314, U. S. DEPARTMENT OF AGRICULTURE. 
When solid matter deposits upon the sides of the condenser, it may be 
melted by syphoning hot water through the condenser, and collected in 
the fraction to which it belongs. The last fraction is collected up to 
300°C., after which the flask and graduates are cooled to room tempera- 
ture, and their contents determined by volume and weight. The 
volume of pitch remaining in the retort is found by deducting the 
total volume of the distillates from the origmal 100 cubic e-nti- 
meters taken. Note should be made of the approximate volume of 
solids which precipitate from the distillates upon cooling to 25° C. | 
The results obtained are calculated in percentages by volumes and 
weights to tenths of 1 per cent and reported as follows: 
Per cent, | Per cent, 
2S AES | by volume. | by weight. 
! 
Wiateronammoniacal HQHOr). 922022235. ase oh sealer | 
irs Hehe oils to lies Cees A ee Pate fey ae ace Spee 
Second light oils 110° C_t0.1470° C_...-. 2 -3.5-5--252-5< | ee Me plete Bes! 
Heavy oils 170°C. te 20°C) = Bro. Veh ob ee cee ae 8 [Sec ) geen 
Heavy ols 2/027 C.\to 300°C eo te a ee eee ne 
PILCH TeESICUG. 52552228 oe ee a ee ee 
Soup tie eve Ne te 
| | 
The above is applicable only to tars which contain no water. In 
distilling crude tars or tars which are contaminated with water, it is 
necessary to dehydrate them before submitting them to the regular 
distillation. A cylindrical copper still with circular burner, as 
shown in figure 13, is convenient for this purpose. Two hundred and 
fifty cubic centimeters of the tar to be dehydrated is weighed in the 
retort and the apparatus is set up as shown. A low flame is applied 
to the upper part of the retort and the heating slowly and carefully 
continued until the volume of water in the separatory funnel shows 
no further increase. The volume of water collected is noted and 
calculated. The water is then drained from the separatory funnel - 
and the supernatant layer of oil is run into and thoroughly mixed 
with the contents of the retort, which should first be cooled below 
100° C. A 100 cubic centimeter sample of the dehydrated tar is 
then submitted to the regular distillation test as above described 
USE OF THE DISTILLATION TEST. 
The distillation test is made upon tars and tar products but seldom 
upon other materials unless the presence of tar is suspected, or where 
a determination of water is required. In making the water deter- 
mination on viscous or semisolid bituminous materials, it is usually 
advisable to render the samples fluid by the addition of kerosene or 
benzo] before attempting the distillation. 
