Another branch of the by-product industry is the recovery of oils of the aromatic series from the gases. Of the 10,000 cubic feet of gas produced from a ton of coal, 6,5Q0 cubic feet are required in the coking process. This gas contains on an average 0.75 per cent of benzene (benzol) and its homologues. The heat value of this gas is affected only slightly by the removal of the benzene. By washing gas with petroleum or coal tar oil, a benzolized oil containing 2 to 3 per cent of benzene is pro duced, and by distillation of crude benzene light oil is obtained.
Only slight quantities of impurities, carbon disulphide, hydrogen sulphide, thiophene and napthalene are found to be present, and purifi cation and redistillation furnish a benzene 100 per cent pure, and suitable for nitrifying and convening into aniline.
From the oil which is with the pitch (the result of the distillation of crude coal tar) is obtained anthracene, another important base of dyestuffs. From creosote oil are obtained napthalene, carbolic acid and other homologues. Carbolic acid is the base of picric acid, which is the main ingredient of the latest high ex plosives, as English Lyddite, French Melinite, the Japanese Shimose powder and our own Maximite.
The by-product ovens are the leading pro ducers of ammonia in the country, and this crude product forms the raw matenal for re fined ammonia products, and also furnishes a supply for the manufacture of soda try the am monia process. Ammonia is also being used for the manufacture of explosives and for the pro duction of the refined aqua ammonia which is largely consumed in refrigerator machines, either as aqua ammonia or anhydrous ammonia. As sulphate, ammonia is largely consumed in the manufacture of fertilizer. The consumption of fertilizer is increasing in this country, espe cially in the South, and sulphate of ammonia is regarded as a most valuable form of plant food. Commercially speaking, therefore, the by product oven cannot have a healthier growth than ib justified by the demand of the indus tries that consume its by-products.
The Beehive The type of this oven is as shown in illustration. It is 12 to 13 feet in diameter, with a 7 to 8 feet height of dome above floor level, lined with siliceous brick backed with concrete or masonry. The
charging hole is on top, and the oven door slightly higher than the level of the charge.
Vanous systems have been established to utilize the waste gases and heat of the coking operation, either by surrounding the furnace with ducts, or utilizing the heat in an adjoin ing plant. All these steps in the progress of development tend toward the by-product oven, but more particularly is it true when it is the aim to save the by-products.
At the close of 1905 practically 89 per cent of the coke in the United States was manufac tured in beehive ovens, due to the non-available market for the by-products. In 1915 the bee hive ovens made only 66 per cent of the whole. The cost of erecting a beehiVe oven is very small in comparison with that of a by-product oven, hence the commercial policy of replacing the beehive oven with a by-product oven only as fast as the market conditions demand the by-product& The By-product Coke Oven.—The by product coke ovens are of two types: the waste heat oven adopted where the gas produced is not in demand by local industries and the regenerative oven built in localities where the surplus gas can be sold. Coals not available in the beehive ovens can be coked in the by product ovens and specific grades of coke can be produced by skilful mixing of different kinds of coal. The yield of coke in a by-product oven is conunonly 75.3 per cent of the coal consumed as against 64,7 per cent in the beehive oven. If the larger yield had been obtained for the coal coked in the beehive ovens also, the coun try would have been the richer by 4,253,218 tons of coal, wholly wasted in the beehive process, to say nothing of the value of the by products recovered. The coal consumed in the by-product ovens is a mixture of high volatile or gas coal— from Kentucky, the Kanawha or Fairmont districts of West Virginia or from southwestern Pennsylvania — with the low vola tile or smokeless coal from the Pocahontas and New River fields of West Virginia, or from central Pennsylvania. It is not uncommon to find West Virginia coal at the coke ovens of Wisconsin and Minnesota. A representative plant of 100 ovens has been selected for de scription as applying the principles underlying by-product oven practice to-day in the United States.