An important application of the ammoniacal liquor of the gas works is in its extraction of the sulphur from the gas, by the scrubbing process. As much as nine-tenths of the sulphur is said to be removed by this process, and the illuminating power of the gas itself is increased. Mr. Bowditch does not believe that the sulphur is removed by the ammonia liquor, but the experiments made a few years ago at Nottingham and Taunton, seem conclusively to prove that at least a very large proportion of the sulphur is removed. According to the same authority the ammeniacal liquor, diluted with at least three times its bulk of water, may be applied as manurial matter to land. This ought to be a useful hint to small gas companies who at present do not find it profitable to save the liquor.
Other methods have been proposed for reducing the bulk of the ammoniacal liquor from gas works, with the view of rendering its transport practicable in a financial sense. Mr. F. Braby, in a paper read before the British Association, in 1869, gives a very sirnple and interesting method for effecting this object. The cost of carriage is evidently v. matter of the first con sideration. Mr. Braby states that on the average one gallon of liquor contains only 2 oz. of real ammonia, so that if any plan could be devised by which a concentration could be made that one gallon should contain say 40 oz. of real ammonia, the cost of transit would be twenty times less, or in tho one ease the eost of carriage being 201. for a given bulk of liquid containing a certain quantity of ammonia ELS produced at the gas works, the cost of carriage would be reduced to 20s. for the same quantity of ammonia by removing simply the greater bulk of the water. At present to carry 1 ton of ammonia, it is necessary to take with it no less than 80 tone of water. The result of this dilution is, that a very great deal of this liqnor is thrown away, forming no doubt in most cases a great nuisance to many localities ; by concentrating, the nuisance would be removed a.nd converted into a source of profit.
The process is thus described :—" To the common ammoniacal liquor a certain quantity of slaked lime is added. The liquor thus treated is placed in a capacious boiler or still, capable of holding 5000 gallons. The whole is then heated and maintained at a temperature of from 38° to 94°, the liquor being slowly but constantly stirred by means of an internal agitator, the spindle of which passes through a stuffing box, in the end of the boiler. A powerful blast of air from a double action force-pump, actuated by a small steam engine or otherwise, is blown continuously through the liquor. The air enters by two long perforated pipes placed near the bottom of the boiler, and in its upward passage it is compelled to pass through a horizontal diaphragm drilled with numerous small holes. The result of this arrangement being, that the air in its ascent is sub
divided into innumerable small sheaves and bubbles, to which and all of which, in accordance with well-known and recognized laws, the ammonia attaches itself, and is carried away, with only a very small proportion of aqueous vapour. An exit pipe is fixed to the top of the boiler, so as to carry away the mixture of air and ammonia, and the extremity of this pipe dips into a supply of water contained in a cool and suitable receiver, where the ammonia is immediately absorbed, and the air, after thus affecting its removal in a separate state, escapes through the water and is permitted to pass off into the atmosphere. These receivers are almost three parts full of broken ice.
The following dimensions are given of a working plant which was erected at Deptford. A reservoir 35 ft. long, 7 ft. wide, and 6 ft. deep, was made to contain the liquor. The bottom was formed of 1 ft. of concrete, 2 courses of bricks, and 2 courses of red flat tiles; the sides were of 14 in. brickwork, 2 courses with tiles in conjunction with concrete. The wrought iron still is set in brickwork so that the flame may play more than half round its external surface ; it is 30 ft. long by 6 ft. in diameter. About 4000 gallons of liquor are pumped into it for each operation. Two cast iron 3-in. air pipes, which are attached to the ammonia generator, extend along its whole length, and are situated one on either side, and nearly at the bottom. They are perforated with holes increasing in size as they extend from the inlet. Into these pipes, and from them into the gas liquor, is driven atmospheric air by means of a pair of cast iron force-pumps. These are 20 in. in diameter, 1 ft. 8 in. stroke, with rods and slings, wrought-iron connecting rod and crank, and a cast-iron beam 6 ft. long. On the entry of the streams of air they are caught and agitated by the twelve iron fans of a stirrer, making about 80 revolutions per minute. The air together with the lime the various constituents of the gas liquor (viz. water, ammonia, carbonic dioxide, sul phuretted hydrogen, sulpho-cyanides, &c.,) are thus brought continuously into intimate contact. The air loaded with the volatile alkali, which has become eliminated from the solution, passes upwards into the steam chest and through a branch pipe into the purifier or washer. This is a small wooden vessel of the capacity of 350 gallons, containing lime and being about one-third full of water. It has a tight head and a stout perforated elm false bottom, the holes being con centric and increasing in number and dimension as they radiate from the inlet which is brought below the false bottom.