The second advance in manufacture was that of enclosing the mound in a furnace, thus utilizing to some extent the heat passing off from the coal. This form of manufacture was termed the °Bee Hive Oven,)) and finally re sulting in having a series of ovens, utilizing the heat on three sides of the oven and the heat of the escaping gases, to assist in coking. There was also a development in this form of oven which endeavored to throw down the solid con stituents of the escaping gas in the form of tar, but the methods were, comparatively speaking, very crude, and resulted in saving but little of the 40 per cent unaccounted for.
About 1881-82 two forms of ovens ap peared, which, since that date, have been de veloped to such an extent that but 10 to 15 per cent of the calorific efficiency of the coal is lost. In America to-day there are two standard types of ovens, the beehive and the by-product, both of which are described in a following paragraph.
Chemical and Physical These two qualities of the coke do not seem to hold much if any relation to each other —that is, the coke may have a fairly good analysis chem ically and yet, if its physical qualities are below the standard, it would be useless for the metal lurgist.
Several theories have been brought forward to explain the coking of coal, and that held by M. Lemoine is presented but the question is still undecided. Lemoine comes to the conclu sion that there is a substance, which he calls °Carbene,0 which determines the coking quality of coals. This substance he claims resembles a 'gat coal.° It is black, solid, friable, with a tendency toward crystallization, and is of the formula Csi.H.406.
Carbene, he says, has the property of ad hering to solid bodies and spreading itself over their surface to an extent which is unknown in any other body. When a large amount of coal is subjected to distillation, as in a coke oven, the carbene may be driven from one part of the heated coal to settle itself upon the cooler portion of the mass, and thus to increase the agglutination of this part. This process may continue throughout the entire thickness of the mass until the coke is formed.
M. Lemoine claims that laboratory experi ments laave shown the possibility of trans forrning a non-coking coal into a good coking coal by means of the addition of 2 per cent of carbene. In one coal tested, which had 10 per cent volatile, the yield was 93 per cent. In con
clusion, he claims we may therefore hope to produce good coke from coals which have hitherto been considered non-coking coals, and further experiments in this direction are being carried on.
The physical characteristics of a coke are of far greater economic importance than its chemical 'character. Hardness is exceedingly important, and porosity is an essential. Certain coals in the coking operation, in giving off their volatile ingredients, produce in the viscous mass a greater amount of cellular structure than others. According to Fulton, good coke has a hardness of body of 2 to 3 in the usual physics scale. Condensed coke does not mean great hardness, but, on the other hand, means softness.
An important point which goes to prove the extreme adaptability of coke in blast furnace and lime kiln practice is the fact that, due to its cellular condition or porosity, the heat can the more readily prepare it for combustion, and consequently after it has in its descent in the furnace reached the zone of combustion it is in the most perfect state possible for such action, and yet, due to its hardness, it has held its form and sustained the immense mass above it without being crushed, thereby allowing the highest per cent efficiency for blast.
Another consideration is that in equal cal °rifle quantities of anthracite coal and coke the volume of space occupied by coke is much greater than that of coal; hence, it can dis tribute its heat to a greater mass of burden than the coal and avoid concentration of an ex cessive heat at one point as when using anthra cite coal.
Economical and Commercial Considera ticm of Coke Manufacture.—These features of the industry should not be considered inde pendently. As stated previously, the waste from the beehive method of producing coke to-day is enormous; not alone is part of the coal consumed in the coking operation, but all the gases and volatile matters escaping from the furnace contain material of great value.
The by-product oven of to-day requires in its management a large amount of chemical and metallurgical slcill.
The distillate from tar has many new uses besides the well-known one of creosoting rail road ties. The expansion of the American dyestuff industry, due to the failure of the European supply, and-the immense increase in munition manufacture has made a new market for tar distillates.