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, the solid asphaltum, and the rigid and brittle substance known as albertite, with other and allied products. Having said so much regarding the chemistry of the fuels of the future, we may now pass to consider their geological record. A somewhat curious distribution awaits the man of science in this latter respect. Most readers are aware that the geologists are accustomed to classify rocks, according to their relative age, into three great groups, known respectively as the primary, secondary, and tertiary periods. In the secondary period we do not appear to meet with the fuels of the future, but as far back as the Devonian or old Red Sandstone period, and in the still older Silurian rocks, stores of gas and petroleum abound. In the latest or tertiary period, again, we come upon nearly all the forms of fuels we have already specified.
The meaning of this geological distribution of the fuels is entirely fortuitous. Dr. M'Gee tells us that as their formation depended on local conditions (such as plant growth), and as we have no means of judging why such local conditions occurred within any given area, so must we regard the existence of fuel products in particular regions as beyond explanation. Of one point, however, we are well assured, namely that the volume of the fuels of the future is developed in an inverse proportion to their geological age. The proportionate volume, as it has been expressed, diminishes progressively as the geological scale is descended. Again, the weight of the fuels varies directly with their age; for it is in the older formation of any series that we come upon the oils and tars and asphaltum, while the marsh gas exists in later and more recently formed deposits. Further geological research shows us that the American gas fields exist each as an inverted trough or dome, a conformation due, of course, to the bending and twisting of the rocks by the great underground heat forces of the world. The porous part of the dome may be sandstone or limestone, and above this portion lie shales, which are the opposite of porous in texture. The dome, further, contains gas above, naphtha in the middle, and petroleum below, while last of all comes water, which is usually very salt. In the Indiana field, however, we are told that the oils lie near the springing or foundation of the arch of the dome, and at its crown gas exists, and overlies brine.
A very important inquiry, in relation to the statement that upon the products whose composition and history have just been described the fuel supply of the future will depend, consists in the question of the extent and duration of these natural gas and oil reservoirs. If we are beginning to look forward to a time when our coal supply will have been worked out, it behooves us to ask whether or not the supply of natural gas and oil is practically illimitable. The geologist will be able to give the coming man some degree of comfort on this point, by informing him that there seems to be no limit to the formation of the fuel of the future.
Natural gas is being manufactured to-day by nature on a big scale. Wherever plant material has been entombed in the rock formations, and wherever its decomposition proceeds, as proceed it must, there natural gas is being made. So that with the prospect of coal becoming as rare as the dodo itself, the world, we are told by scientists, may still regard with complacency the failure of our ordinary carbon supply. The natural gases and oils of the world will provide the human race with combustible material for untold ages—such at least is the opinion of those who are best informed on the subject. For one thing, we are reminded that gas is found to be the most convenient and most economical of fuels. Rock gas is being utilized abroad even now in manufacturing processes. Dr. M'Gee says that even if the natural supply of rock gas were exhausted to-morrow, manufacturers of glass, certain grades of iron, and other products would substitute an artificial gas for the natural product rather than return to coal. He adds that "enormous waste would thereby be prevented, the gas by which the air of whole counties in coke-burning regions is contaminated would be utilized, and the carbon of the dense smoke clouds by which manufacturing cities are overshadowed would be turned to good account." So that, as regards the latter point, even Mr. Ruskin with his horror of the black smoke of to-day and of the disfigurement of sky and air might become a warm ally of the fuel of the future. The chemist in his laudation of rock gas and allied products is only re-echoing, when all is said and done, the modern eulogy pronounced on ordinary coal gas as a cooking and heating medium.
We are within the mark when we say that the past five years alone have witnessed a wonderful extension in the use of gas in the kitchen and elsewhere. It would be singular, indeed, if we should happen to be already anticipating the fuel of the future by such a practice. Whether or not this is the case, it is at least satisfactory for mankind to know that the mother earth will not fail him when he comes to demand a substitute for coal. I may be too early even to think of the day of extinction; but we may regard that evil day with complacency in face of the stores of fuel husbanded for us within the rock foundations of our planet.—Glasgow Herald.
PORTABLE ELECTRIC LIGHT.
The famous house of MM. Sautter, Lemonnier & Co. takes a conspicuous part in the Paris exhibition, and from the wide range of its specialties exhibits largely in three important branches of industry: mechanics, electricity, and the optics of lighthouses and projectors. In these three branches MM. Sautter, Lemonnier & Co. occupy a leading position in all parts of the world.
The invention of the aplanetic projector, due to Col. Mangin, was a clever means of overcoming difficulties, practically insurmountable, that were inseparable from the construction of parabolic mirrors; this contributed chiefly to the success of MM. Sautter, Lemonnier & Co. in this direction. The firm has produced more than 1,500 of these apparatus, representing a value of nearly £500,000, for the French and other governments.