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1915-16.] The Origin of Oil-Shale. 
And lastly, why can a commercial yield of ammonium sulphate be obtained 
from an oil-shale and not from an oil-rock ? 
To attempt to answer these questions we must have recourse to experi- 
mental work, and fortunately we find that there is no lack of experimental 
and laboratory researches bearing upon the subject. 
Allusion has already been made to the natural filtration of oils : 
experiments in artificial filtration will furnish us with a clue to more 
than one of our difficulties. 
Mr Clifford Richardson, the acknowledged authority upon asphalt, and 
the author of The Modern Asphalt Pavement, found that solutions of the 
bituminous matter in natural asphalt could be filtered and decolorised by 
continued filtration through clays, the heavier and darker-coloured con- 
stituents of the solution remaining in the clay, while the more volatile 
constituents passed through in solution. The material he experimented 
with was the bituminous content of Trinidad asphalt from the asphalt lake. 
On treating the clay used for filtering with petroleum spirit it was 
found that the greater part of the bituminous matter could be recovered, 
but not all. A proportion remained in the clay which could not be ex- 
tracted by solution, but which could be recovered by distillation. For this 
property of clay Mr Clifford Richardson proposed the term “ adsorption,” 
to distinguish it from the absorptive property. Thus in any clay saturated 
or in contact with petroleum a portion is adsorbed and can only be re- 
covered by distillation. It must be left to the chemist to prove in what 
this adsorption consists — whether it be due to the formation of insoluble 
compounds with bases, or some other chemical action. The proportions 
absorbed and adsorbed vary, naturally, with different clays, but it is only 
the heavier molecules, the products of inspissation, that are thus removed 
from solution. This confirms what has been learnt about the natural 
filtration of petroleum. It is apparently chiefly the unsaturated hydro- 
carbons that are thus fixed in the argillaceous rock. 
The asphalt lake of Trinidad is formed on the outcrop of the La Brea 
oil-sand, and may be considered as a highly inspissated petroleum. Its 
average composition is given by Mr Clifford Richardson as : — 
Water .... 
Bitumen .... 
Organic matter not bitumen 
Inorganic matter 
. 29 per cent. 
33 
33 
33 
It is a very uniform mixture or emulsion. 
The percentage of “ organic matter not bitumen,” i.e. not soluble in 
carbon-disulphide, is remarkable. In every inspissated oil or asphalt, in 
every intrusive or native bitumen, and in every specimen of oil-rock taken 
