When coal is converted into coke it gives off combustible gases. The idea of saving these gases and using them for illuminating purposes was first practically applied in the latter part of the eighteenth century. “Coal-gas” is made by heating coal in a closed vessel, called a “retort.” It is a mixture of hydrogen and methane (a compound of hydrogen and carbon), with small amounts of several other gases. Most of the carbon in the coal remains in the retort as coke, which is, therefore, a by-product in the process of making coal-gas. After the gas is given off from the coal it passes through a series of vessels, where, by chemical and other methods, it is freed from ingredients which would impair its value as an illuminant, but which are saved and used for other purposes; the most important of these are “coal-tar” and “ammoniacal liquor.” The purified coal-gas is finally conveyed to a gas-holder or “gasometer,” from which it is distributed to the consumers.
In recent times other methods of gas-making have come into use. In one of these nearly all the carbon in the fuel is turned into a combustible gas by passing air through the hot coal. The product is known as “producer-gas,” and is very valuable for use as fuel and as a motive power in gas-engines, but it is not an illuminant. A modification of this process, in which steam is passed over the heated fuel, gives a mixture of hydrogen and carbon monoxide, known as “water-gas.” This is also a valuable source of heat and power; but for use as an illuminant it must be mixed with a gas made from oil. It is then known as “carburetted water-gas,” and is very extensively used for lighting purposes; either by itself or mixed with ordinary coal-gas.
Of the by-products of gas-making, ammoniacal liquor was, until recently, the only commercial source of ammonia. Coal-tar, formerly thrown away as worthless, is today the source of innumerable substances of immense value to science and the industries. From coal-tar are obtained benzine, toluene, xylene, phenol (carbolic acid), naphthalene, anthracene, etc., and these more direct products are combined with one another or with other chemicals to produce coloring matters, explosives, perfumes, flavoring materials, sweetening substances, disinfectants, medicines, photographic developers—in short, a little of everything. The total number of coal-tar products runs into the thousands, and is constantly being increased by fresh discoveries.
In Germany, just before the war, the industries engaged in making these products (no longer by-products, but far more important than coke and gas) were capitalized at $750,000,000. One firm made no less than 1,800 coal-tar dyes, besides 120 pharmaceutical and photographic preparations.
PREPARED BY THE EDITORIAL STAFF OF THE MENTOR ASSOCIATION
ILLUSTRATION FOR THE MENTOR. VOL. 6, No. 6, SERIAL No. 154
COPYRIGHT, 1918. BY THE MENTOR ASSOCIATION, INC.
SMOKE PROBLEM—SCENE IN PITTSBURGH BEFORE AND AFTER THE SMOKE CURE
THE STORY OF COAL
The Smoke Problem
FIVE