ABSTRACT
Many varieties of coal produce a quantity of fine dust which settles in the roadways—on roof, and sides, and floor. Probably no industrial operation excites more widespread interest than the winning of coal, and that because of the dangers which attend it. The greatest advance in the economical use of coal is by converting it into gas. The production of gas by distilling coal in retorts is, of course, more than a century old. Petroleum occurs in certain porous layers of the earth’s crust just in the same way that water collects in porous sandstones. If a mixture like crude petroleum or rock-oil is heated, the constituents of lower boiling-point come off first, and if the receiver into which the liquids are distilled is changed from time to time, fractions boiling between certain limits of temperature are obtained. From the heavier samples come vaseline, which is closely allied to the lubricating oils, petroleum jelly, and other similar substances.
