CHAPTER XII
THE HIGH TEMPERATURE CARBONIZATION OF COAL
The nature of the primary and secondary reactions associated with tlie carboniza-tion of coal in closed retorts has occupied the attention of the scientist and investi-gator for nearly a Century ; yet, although, to-day, we are in a position to understand several of the more perceptible developments accompanying this phenomenon, there still remain many anomalies 011 which light has yet to be shed. The results of carbonization, and the final mode of existence of the innumerable products yielded, are materiålly influenced by considerations otter than that of the temperature at which distillation occurs, so tliat it is impossible to form an opinion as to ultimate effects until the exact conditions under which the process is carried out are known.
The distillation of coal is usually characterized as “ destructive,” but the term is in reality a misnomer, owing to the faet that it implies finality; this only being the case so. far as the original structure and substance of the raw material are con-cerned. The distillation of coal differs from that of a complex liquid in that the treatment of the latter is carried out in a number of stages, depending upon the -original nature of the substance and the character of the products required. With the liquid, “ fractionation ” essentially occurs, whereas coal is dealt with. in a single stage, innumerable products being simultaneously evolved and no attempt being made, in the first instance, to separate out the various substances. A further faet of interest is that with coal, once distillation has occurred, there is no possibility of reproducing the original substance by collecting the products and causing tliem to recombine. In the case of a complex liquid, however, the various fractions may be Temixed, when a substance more or less in accordan.ee with the original substance will result.
The four fundamental bases of which the coal conglomerate is considered by some investigators to exist are fully discussed in the previous chapter, and it is there pointed out that when. subjected to distillation each of these bases gives rise to its own particular degradation products. Lewes found eviden.ee that the primary decomposition of the coal substance accounts for the various constituents in the following manuer:—
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