For example, it is now known that three products—­gas, oil, and salt or brine—­lie within natural receptacles formed by the rock strata in the order of their weight.  This law, as has well been said, forms the foundation of all successful boring experiments, and the search for natural fuel, therefore, becomes as easy and as reliable a duty as that for artesian water or for coal.  The great oil fever of the West was attended at first, as Professor M’Gee tells us, with much waste of the product.  Wells were sunk everywhere, and the oil overflowed the land, tainting the rivers, poisoning the air, and often driving out the prospectors from the field of discovery.  In Baku accidents and catastrophes have, similarly, been of frequent occurrence.  We read of petroleum flowing from the ground in jets 200 feet high, and as thick as a man’s body; we learn how it swept away the huge cranes and other machinery, and how, as it flowed away from the orifices, its course was marked by the formation of rivers of oil many miles in length.

In America the pressure of rock gas has burst open stills weighing over a ton, and has rushed through huge iron tanks and split open the pipes wherewith it was sought to control 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.