its progress. The roar of
this great stream of natural gas was heard for miles around as it
escaped from the outlet, and when it was ignited the pillar of flame
illumined the surrounding country over a radius extending in some
cases to forty miles. It is clear that man having tapped the earth's
stores of natural fuel, stood in danger of having unloosed a monster
whose power he seemed unable to control. Yet, as the sequel will show,
science has been able to tackle with success the problems of mastering
the force and of utilizing the energy which are thus locked up within
the crust of the globe.

As regards the chemistry of rock gas, we may remark in the first place
that this natural product ranks usually as light carbureted hydrogen
gas. In this respect it is not unlike the marsh gas with which
everyone is familiar, which is found bubbling up from swamps and
morasses, and which constitutes the "will o' the wisp" of romance. In
rock gas, marsh gas itself is actually found in the proportion of
about 93 per cent. The composition of marsh gas is very simple. It
consists of the two elements carbon and hydrogen united in certain
proportions, indicated chemically by the symbol CH4. We find, in fact,
that rock gas possesses a close relationship, chemically speaking,
with many familiar carbon compounds, and of these latter, petroleum
itself, asphaltum, coal, jet, graphite or plumbago, and even the
diamond itself--which is only crystallized carbon after all--are
excellent examples.

The differences between these substances really consist in the degree
of fixing of the carbon or solid portion of the product, as it were,
which exists. Thus in coal and jet the carbon is of stable character,
such as we might expect to result from the slow decomposition of
vegetable matter, and the products of this action are not volatile or
liable to be suddenly dissociated or broken up. On the other hand,
when we deal with the _hydrocarbons_ as they are called, in the shape
of rock gas, naphtha, petroleum, tar, asphaltum, and similar
substances, we see how the carbon has become subordinated to the
hydrogen part of the compounds, with the result of rendering them more
or less unstable in their character. As Professor M'Gee has shown us,
there is in truth a graduated series leading us from the marsh gas and
rock gas as the lightest members of this class of compounds onward
through the semi-gaseous naphtha to the fluid petroleum, the
semi-fluid tar,