202 — TRANSACTIONS OF THE 
breaking the vacuum. Distillation progresses, as before, 
under a pressure of 40 mm. absolute. The reduced pres- 
sure, of course, lowers the boiling temperatures of the oils 
in the still and makes possible their distillation without 
danger of decomposition. 
The first fraction taken off under vacuum is that 
boiling up to 200°C at this reduced pressure, then the 
tube in the container is shifted by an external connection 
and successive separate fractions taken for every 25°C 
rise in temperature up to 300°C. As the distillation pro- 
gresses the water in the condenser is heated; otherwise 
the solid paraffin that distills from many shale-oils at 
high temperatures would congeal in and clog the con- 
denser tube. 
The still and residual oil are then cooled and the 
volume of residue is determined from its weight and 
specific gravity. The character of the residuum is noted 
—whether it is of an asphaltic or paraffin nature—; its 
setting point taken as an indication of wax remaining in 
it; and a test made to determine the carbon deposited 
when it is burned under ‘a definite set of conditions—the 
Conradson carbon test. This test serves to indicate the 
suitability of the heavy residues for making. certain 
heavy lubricating oils. 
All the separate fractions are then examined. Vol- 
ume and specific gravities of the air distillation fractions 
are determined for the purpose of calculating percentages 
distilled and to give an indication of the chemical nature 
of the oil. Afterwards all the fractions distilled up to 
200°C are combined, as are those distilling between 
200°C and 275°C, and a test made to determine the 
percentage of ‘‘unsaturated hydrocarbons”, or more 
correctly speaking, the percentage soluble in an excess of 
concentrated sulphuric acid under certain definite con- 
ditions? in each combined fraction. 
The vacuum fractions are examined; volume and 
specific gravity of each cut determined, as are also the 
setting point and viscosity of each, the latter two tests 
3Unsaturation test is described by E. W. Dean and H. H. Hill, 
The Determination of Unsaturated Hydrocarbons in Gasoline: Bureau 
of Mines Tech. Paper 181; 1917, 25pp. 
