An",umie from Phis Liquor.—The ammoniacal fluid collected in the manufacture of gas from coal contains both free and fixed ammonia. Its value as a source of ammonia is generally regulated by its specific gravity. A liquid having asp. gr. of 1.023 should yield about 1200 grains per gallon of ammonia by boiling alone, and on the addition of caustic lime should yield about 200 grains per gallon. Converted into sulphate, the total ammonia should amount to about 80 lb. per 100 gallons of the liquid.
The quantity of ammonia contained in gas liquor is subject to great variation, due partly to the coal itself and to the quantity of water which is produced during the distillation. All the nitrogen contained in coal is not converted into ammonia ; cyanogen compounds are also produced, which are condensed as well. Probably the temperature of the retorts when the coal is thrown in, or the rapidity of the heating, may influence the changes which take place.
When coal is distilled a quantity of impure hydrocarbons are formed ; these, together with the water and other volatile matters, pass from the retorts, and are separated from the gas as it leaves the hydraulic main, the gas being received in the holders, whilst the matters separated from it flow into large wells or underground tanks. On standing, a separation takes place, the watery portion which contains the ammonia and its salts falling to the bottom, and the hydrocarbons floating on the top. The watery portion is known as " gas liquor," and the black oily portion is called " gas tar." Ono ton of good cannel coal will yield about 8 gallons of gas liquor. The gas liquor is pumped up from these tanke as required into suitable reservoirs for removal, such as boilers or tanks, whieli are fixed on railway trucks or waggons, for conveyance by rail or road, or barges where water transit is available. The latter is the most convenient and economical, the bargee are of large capacity, and fitted with tanks capable of holding from 80 to 100 tons of liquor. The liquor, at its destina tion, is pumped into large tanks, usually constructed of masonry and wood, from which it is sup plied either to the boilers or stills as required, or mixed with acid at once for the production of salts, the gases which are liberated in this latter case being conveyed to the furnace and burnt.
As a large quantity of sulphur compounds are disengaged, it has been proposed to utilize the gases for the production of sulphuric acid.
The treatment of the crude liquor with acid does not appear to be so extensively practised as it was a few years ago, it seems more usual at present to bring the liquor into some more easily manageable bulk, which is effected by distilling with milk of lime when all the ammonia is to ho recovered, or by driving off the free ammonia, by heat alone, when circumstances render the recovery of the combined ammonia unremunerative.
The best method for treating the gas liquor is evidently a matter to be determined by local conditions; for instance, the erection of a large plant in London, to work on the principle of saturating the liquor at once, could scarcely be so profitable an undertaking as the same arrange ment carried out where land is so much cheaper. There are some localities where the lime refuse used in liberating the combined ammonia would either accumulate to become a serious nuisance, or would have to be carted away, and land purchased to discharge it upon. Such a thing could not he thought of in a city like our own metropolis. Where large quantities of acid and liquor can be easily and cheaply obtained, it is evidently more economical, especially where land is dear, to avoid the accumulation of useless refuse, and to work up the liquor in the quiokest possible way ; this at present necessitates the throwing away of a large quantity of the combined ammonia. The advan tages of this latter method are the compact form which the plant may be made to take, and, the conditions of the raw supply being favourable, the rate at which the salts of ammonia may be obtained ready for the market.
Ammonia from Tar.—When the tar from gas works is distilled, a quantity of ammonia passes over at the commencement of the operation which is condensed in lead chambers with sulphuric acid ; the sulphate thus obtained is supplied principally for agricultural manures. It is generally contaminated with all the impurities found in commercial sulphuric acid.
Frequently the tar as received from the gas works is run off into large tanks, and the ammonia liquid drawn off by decantation, neutralized with sulphuric acid and evaporated in iron pans.