ABSTRACT
In order to sell coal something must be known about its suitability for particular purposes. Coal is not homogeneous, and its properties differ from seam to seam and pit to pit. Whatever it is used for, the heat content (calorific value) of the coal is important, and the size of the coal must be suited to the consumers’ plant or appliances. For some users other factors assume great importance: coal for gas making must provide a high yield of gas, and coal suitable for coke-ovens must produce a good quality coke sufficiently hard to withstand the burden of the blast furnace charge. For steam raising, heat content alone is most important, but if the coal is needed in large-sized lumps its tendency to break up must be considered if it is to be transported long distances or shipped abroad. Trade usage has made familiar such terms as ‘coking’, ‘gas’, ‘household’ and ‘steam’ as general descriptions of different kinds of coal, and the name of the colliery, and even of the seam from which the coal has been produced, has indicated to the trade its particular qualities. Coal salesmen have considerable knowledge and experience of the properties of different coals, and they provide a useful service in giving advice to the consumer on the suitability of certain coals to his plant. The trade nomenclature, however, is lacking in precision, and does not bring under a common heading different coals which would serve the same purpose equally well; it has resulted in unnecessary complexity with about 6,000 named coals on the market; and it does not take account of the fact that the quality of coal varies even in the same seam.
