are charred and
deposited by the action of strong sulphuric acid. By further distillation
a lighter oil is given off, often known as _artificial turpentine oil_,
which is used as a solvent for varnishes and lackers. This is very
familiar to the costermonger fraternity as the oil which is burned in the
flaring lamps which illuminate the New Cut or the Elephant and Castle on
Saturday and other market nights.

By distillation of the _heavy oils_, carbolic acid and commercial
_anthracene_ are produced, and by a treatment of the residue, a white and
crystalline substance known as _naphthalin_ (C_{10}H_{8}) is finally
obtained.

Thus, by the continued operation of the chemical process known as
fractional distillation of the immediate products of coal-tar, these
various series of useful oils are prepared.

The treatment is much the same which has resulted in the production of
paraffin oil, to which we have previously referred, and an account of the
production of coal-oils would be very far from satisfactory, which made
no mention of the production of similar commodities by the direct
distillation of shale. Oil-shales, or bituminous shales, exist in all
parts of the world, and may be regarded as mineral matter largely
impregnated by the products of decaying vegetation. They therefore
greatly resemble some coals, and really only differ therefrom in degree,
in the quantity of vegetable matter which they contain. Into the subject
of the various native petroleums which have been found--for these
rock-oils are better known as petroleums--in South America, in Burmah
(Rangoon Oil), at Baku, and the shores of the Caspian, or in the United
States of America, we need not enter, except to note that in all
probability the action of heat on underground bituminous strata of
enormous extent has been the cause of their production, just as on a
smaller scale the action of artificial heat has forced the reluctant
shale to give up its own burden of mineral oil. However, previous to
1847, although native mineral oil had been for some years a recognised
article of commerce, the causes which gave rise to the oil-wells, and the
source, probably a deep-seated one, of the supply of oil, does not appear
to have been well known, or at least was not enquired after. But in that
year Mr Young, a chemist at Manchester, discovered that by distilling
some petroleum, which he obtained from a spring at Riddings in
Derbyshire, he was able to procure a light oi