73 
1915-16.] The Origin of Oil-Shale. 
necessary. Even albertite, with 90 per cent, or more insoluble in carbon- 
disulphide, yields as much as 112 gallons of oil and 65 lbs. of ammonium 
sulphate per ton. 
IV. Properties and Analyses of Clays. 
If it be possible, then, that an oil-shale can be formed through the 
absorptive and adsorptive powers of clays for inspissated petroleums, it 
would be natural to expect that the mineral matter of an oil-shale should 
possess some characteristics, chemical or mechanical, which specially favour 
absorption and adsorption, characteristics which distinguish it from 
ordinary clay-shales. It was seen in the Scottish shale-fields that the 
gradation from a bituminous shale not rich enough to be mined and 
retorted with profit to an oil-shale is frequently almost insensible, and that 
the richness of a shale is subject to variations. Are these variations 
coincident with any variation in chemical composition or mechanical con- 
stitution ? It would require a great number of chemical analyses and much 
experimental work to prove this conclusively, but there is a certain amount 
of evidence upon the point which can be brought forward. 
In the first place, a comparison of specific gravities gives interesting 
results. 
The average specific gravity of Scottish oil-shales from 58 samples 
taken from more than 10 different mines is 2'054. This is distinctly a low 
figure; but as the average contents of hygroscopic moisture and volatile 
hydrocarbons plus fixed carbon are P58 and 29 ‘20 respectively, it is evident 
that to arrive at the specific gravity of the mineral contents we must increase 
the figure slightly. As we do not know in what chemical or mechanical 
combination the kerogen exists, it is impossible to make an accurate allow- 
ance ; but if we suppose that it has a specific gravity similar to that of an 
inspissated petroleum or a native bitumen, we can make a rough approxi- 
mate estimate. Such an estimate is of course open to many sources of 
error, but an estimate, however rough, will enable us to make some com- 
parison between the specific gravity of the mineral matter of oil-shales with 
other clays. Taking, then, the specific gravity of the kerogen at 1*0 to 1*1, 
which is certainly not erring on the low side, we find a value for the specific 
gravity of the mineral constituents of not more than 2 '3. 
Comparing this with a normal clay, we find that the average specific 
gravity of brick clays is approximately 2*3 to 2*5, and that for some reason 
the mineral contents of an oil-shale differ from normal clays by having a 
slightly lower specific gravity. The specific gravity of a clay, however, 
