Modern Gasworks Practice

388 MODERN GASWORKS PRACTICE the coke, and he found in the case of coke-oven coke (which is essen.tially subjected to this type of heating) that the nitrogen percentage was only 0-384. It would appear that in all cases the figures given for the nitrogen distributed as cyanogen are considerably below those prevailing in modern practice. At the present time there are many cyanogen plants at work recovering on an average from 4 to 5 Ib. of ammonium sulphocyanide per ton of coal, tliese quantities of sulphocyanide representing from 0-75 to 1 Ib. of nitrogen, or nearly 3 per cent, of the total nitrogen. As nitrogen, however, is drawn in from the atmosphere and furnace it is possible that a portion of the nitrogen combined in the cyanogen is obtained from such external sources. The nitrogen, combined in tar is chiefly present in the form of nitrogenens bases such as pyridine. It will be realized that if it were possible to recover the whole of the original nitrogen in coal as sulphate of ammonia the yield of sulphate would approximate to 180 Ib. per ton of coal carbonized. A good deal of uncertainty exists as to the type of coal which is likely to prove the most eflicient producer of ammonia. Schilling, for instance, says that the amount of ammonia yielded rises and falls according to the quantity of nitrogen in the coal. Knublauch is of the opinion that the coals which give very high yields of gas and. tar have a tendency not to form ammonia, the hydrogen uniting with the carbon, whilst the coals which account for high ammonia yields show an inklination to leave the nitrogen in the coke and not to form free nitrogen in the gas. More important considerations, however, do not permit of a coal beiug purchased on its -nitrogen-yielding proclivities alone. With regard to the formation of ammonia, there is now little doubt that it is the direct result of two distinct reactions, and that whereas the chief of these takes place at lower temperatures, the second is probably most in evidence at higher heats. Accordingly, ammonia resulting from distillation may be formed :— (a) By direct evolution from an ammonia-yielding body contained in the coal. (b) Synthetically, by the combination of hydrogen and nitrogen. Little is known as to the actual mode of existence of the nitrogen compounds in coal, but there is evidence to show that the element is combined in two or more ways. Lewes is of the opinion that the humus bodies are most likely to be those carrying the nitrogen. So far as the coke is concerned, Harger says the only con-clusion he could arrive at, atter careful consideration of all the facts, was that some of the nitrogen in the coke is present as one or more stable organic nitrogen ring compounds. Under the influence of distillation ammonia is one of the first compounds to be expelled, the evolution commencing at temperatures between 300° and 400° C., and contimiing up to about 540° C., when the whole of the primary portion appears to be evolved. Little or none is given ofi as the temperature rises from 54-0 C. to 870° C., but beyond the higher temperature further appreciable quantities are discernible. Accordingly, the maximum yield of ammonia is obtained only when the distillation temperature has reached 870° C. or slightly over. The possibility of an easily decomposible compound being able to exist at this temperature is