Just why some coals will coke while others of apparently the same composition as shown by the chemist’s analyses, will not, but instead of the hard brittle mass will leave a heap of brown or black powder, is not as yet definitely known. It is easy enough for chemists to determine with accuracy the amounts of hydrogen, nitrogen, oxygen, carbon, sulphur, and other elements; but it is a difficult and perhaps an impossible matter to determine just how these elements are “hitched up” in the very complex mineral, coal,—one of the most complex substances which we know. Various theories have been advanced in the attempt to explain the coking quality. A bulletin of the United States Geological Survey claims that the relative percentages of hydrogen and oxygen in the coal determines it; others have held that it depends upon the compounds of a tarry or asphaltic nature present. The fact remains that some coals coke without trouble, while others do not coke at all. As yet the only real way to tell whether a new variety of coal will or will not coke is to try it. Since 1713, when Abraham Darby in England succeeded in introducing it as a substitute for the fast disappearing charcoal for use in blast furnaces, coke has become the standard fuel. It is very strong and will bear up under the great weight of iron ore and limestone with which the furnace is charged. So furnaces for use with coke may be built much larger than those in which charcoal is to be the fuel. The porous nature of coke allows it to burn rapidly with intense heat, so that the output of an iron works is greatly increased through its use—a very desirable thing in these days of big things. It has its disadvantages, of course, mainly high sulphur, a deleterious substance for which molten iron, unfortunately, has a voracious appetite, and a rather high percentage of ash which must be fluxed out. But all in all, it is a very desirable fuel for blast furnace and other metallurgical purposes, as is shown by the fact that it is used in the production of about ninety-nine per cent of all iron and steel now made. [Illustration: DRAWING THE COKE ] What is known as the Appalachian coal region produces coal for more than seventy-five per cent of the coke made in the United States. This region includes the strip of territory extending from Western Pennsylvania and Ohio down to Tennessee, Georgia, and Alabama. The famous Connellsville district is a part of this region. Illinois and Indiana have a great deal of coal, which, however, has rather indifferent coking qualities. Almost constant experimentation has been carried on in the attempt to induce these semi-coking coals to coke. The best that has so far developed is the use of a considerable percentage of them in admixture with coals of good coking qualities. Such mixtures yield quite satisfactory coke. The Beehive Oven Process [Illustration: LARGE PIECES OF COKE ]