COAL AND COAL-OIL.
The common varieties of mineral coal are divided into several classes, according to their density and the volatile or bituminous matter they contain. Hard anthracite is the most dense and contains the most carbon. On the Lehigh and through a great por tion of the eastern end of the First and Middle coal-fields the density of anthracite is about 1500, water being 1000, and its constituents are—carbon about 90 parts, water and volatile matter from 5 to 6 parts, and earthy impurities from 4 to 5 parts.
The density of the Wyoming coals is rather less than the above, while the volatile matter is a little more. In the western end of the First and Middle coal-fields the density of the coal, which is a semi-anthracite, is about 1400, and its constituents, carbon 85 to 88, volatile matter 8 to 12, and earthy impurities 5 to 8.
The semi-bituminous coals of Broad Top and Cumberland have a density of 1300 to 1400, and their constituents are—carbon 75 to 85, volatile matter 10 to 20, and earthy impurities from 5 to 7. The rich bituminous coals of the West have a density of 1200 to 1300 ; their constituent parts are—carbon 50 to 60, volatile matter 35 to 48, and ashes from 2 to 6. Cannel coals are usually a little lighter than the common bituminous, and Contain more volatile matter, frequently as high as 50 and even 60 per cent.
Coal-oil and illuminating gas are made only from the two last-named coals,—the rich bituminous or the richer cannel,—not because it is impossible to turn the former back into oil or gas, but because under present development it has not been considered prac tical, and because the richer bituminous coals can be made to give up their volatile matter with more economy. We presume our coal-oil manufacturers will scarcely realize that nearly the whole mass of the coal can be reduced to oil; but such is the fact. The present mode of destructive distillation is extremely wasteful and expensive. We have shown that all valuable coal is composed of from 90 to 98 per cent, of carbon and volatile matter,—principally hydrogen; but when the volatile matter is very great, per haps oxygen and nitrogen may form small portions of the volatile constituents of coal. It has been demonstrated that the solid body of coal was produced from gas or gases, first condensed in the form of oil, and subsequently solidified by the evaporation of the most volatile parts. Coal, therefore, is a solidified gas, which may be again resolved
into its original condition by heat, and again condensed to oil and solidified as coal by the natural process. That loss will take place in the practical treatment is evident, since much of the rarefied vapor would escape; but the process which produces only 40 gallons of oil from a coal containing 50 per cent. of bituminous matter, which should produce over 100 gallons, is certainly far from perfection. When we consider, however, that the entire mass of coal, excepting the earthy impurities, may be reduced to gas, and again condensed into oil, we find how very far we are from the perfect chemical processes of Nature. Yet we think they may be imitated with success and economy. The cost of obtaining 100 gallons of oil from a ton of cannel coal should not be greater than that now sustained in the production of 40 gallons ; and perhaps we may be safe in stating that double the quantity of oil specified, or 200 gallons of oil, may be pro duced from a ton of rich cannel coal, and proportionate amounts from coal of a less variety.
Oil may be produced from anthracite and semi-bituminous coals; but it is a question whether any process which could be adopted would pay as a practical operation.
Our view of the matter may be stated in a few words. Nature has produced and stored away for man a vast amount of carbon in various forms,—as gas, as oil, as bitumen, and as coal. It seems contrary to the rules of chemistry and the laws of reason that we should let the gas from which she produced oil and coal go to waste, while we convert the coal back into gas and then into oil. Would it not be more prac tical and economical to convert the waste gases into oil, rather than the coal into gas, and this coal-gas into oil? The question may be asked, Can it be done? We think it can, and we hope to demonstrate the fact. But it cannot be done here and now, since patents are pending on the processes, and neither our space nor time would permit their discussion in this connection.