BUSHONG.| Chemical Composition of Petroleum. 309 
of distillation in refining petroleum, because of the fact that 
the quantity of distillates corresponding in gravity to gaso- 
line and kerosene is thereby increased. It has been found, 
however, that the cracked oils have a very disagreeable odor, 
become colored after standing for a short time, especially on 
exposure to air and light, and burn with a smoky flame. 
Furthermore, they require the use of too large quantities of 
sulfuric acid to refine them sufficiently to make them market- 
able. The yield of gasoline and of kerosene reported in the 
tables to follow do not include cracked products, and hence are 
not so large as the maximum amounts that might be obtained. 
Cracking began in the two oils examined when the temperature 
of the oil in the flask reached 350° C., and proceeded very rap- 
idly at 400° C. Finally the thermometers were removed and 
distillation was carried on until the glass flask began to melt. 
During the latter part of the distillation the gravity of the 
products increased rapidly and the final distillate was yellow 
wax, of which about one or two per cent. was obtained. A 
residue of about 6 per cent of brittle coke was left in the flask. 
Fresh samples of these oils were then distilled as before up 
to the point where the temperature of the vapors passing over 
reached 300° C. The condenser was then connected to a Briihl 
receiver and the pressure was reduced by means of a Chapman 
pump. Vacuum distillation is simply a process which enables 
us to distil substances about 100° or more below their boiling- 
points under ordinary atmospheric pressure. The oil began to 
distil over in the vacuum at 160°-170° C. The density of the 
fractions and the percentages of distillate increased propor- 
tionately to the rise in temperature until the oil in the flask 
reached about 350° C., when cracking began. By means of 
vacuum distillation, then, it is possible to distil without de- 
composition those constituents of the oil which range in den- 
sity from 0.83 to 0.90. While distillation under ordinary at- 
mospheric pressure yields only 33 per cent. of undecomposed 
products, vacuum distillation increases that yield to a total of 
about 65 per cent. The densities of the fractions and total 
percentages of distillate are shown in the curves, the points of 
separation between fractions being marked by small crosses. 
Vacuum distillation is sometimes employed in the refining of 
lubricating oils. 
