This purifying vessel is furnished with a small agitator having two blades, one revolving above and the other below the false bottom. There are two trial or test taps at appropriate heights, to test for gas or for water, and there is also a pipe sealed at one end, rather less than half way from the bottom, for the purpose of leading away any excess of liquid that may accumulate, owing to the condensation of aqueous vapour, which may pass over with the volatile alkali. There is a long straight tube or safety pipe from the washer, and the bent pipe from the ammonia generator is also provided with a safety valve and a vacuum valve. In the washer the ammonia is deprived of any remaining hydrosulphuric acid or other impurity that may have escaped being fixed in the generator. About half a bushel of finely sifted slaked chalk lime is found to be a suitable charge for the washer, and, when this becomes saturated or impure, it is renewed by means of a pipe and tap placed at the bottom of the vessel. The washer being a close vessel soon becomes full of air and gas, which are forced by the pressure through a pipe opening into the top, and leading to a coil or worm placed in a cold water cistern, and terminating in a deep close vessel about one-third full of pure cold water, which has been condensed from the waste steam from the engine. A portion of the ammonia becomes absorbed by the water, but the residue together with all the air, after bubbling up through the liquid, is conducted by a bent pipe to nearly the bottom of a second similar receiver, and thence in the same to a third, but which is open at the top.
The air, having fulfilled its function, is now permitted to escape into the atmosphere, the whole of the ammonia having, however, been arrested. This last receiver, instead of water, contains a strong solution of chloride of iron, which being denser and possessing a higher specific gravity than water offers a greater pressure and resistance to the passage of the gas. The iron salt is, of course, decomposed, with the formation of muriate of ammonia in solution, with deposition of a green mud containing sesquioxide of iron, which, after having been calcined, is found to constitute an excellent pigment for rough iron or wood-work.
After the whole of the ammonia has been extracted from the gas liquor, the contents of the still are mu off into a draining pit, from which the clear solution finds its way into the sewers, and the solid inrtlorous limo compounds may be carted away. This draining pit is constructed of 14-in. dead boards together with sand and brickwork. It is 4 ft. 9 in. wide, 5 ft. 4 in. deep, and 10 ft. long. There are fillets on which are resting three perforated shelves or platforms. The bottom is formed of perforated deals with 6 in. of sand, also with gravel and cement. There are channels and small drain pipes leading into a large central earthenware pipe, and from thence into the sewer. The sharp sand, &c., under the perforated hoards can be removed at will, and be replaced by fresh materials whenever required. Care must be taken that the large pipe from the boiler to the washer be sufficiently high to guard against any back pressure. The vacuum valve opens and
admits air, when tle• fire of the still is withdrawn and the steam becomes condensed.
In order to ascertain the exact state of the contents of the boiler at any required height, and to avoid tapping tho upper portion of the boiler at too many places, the following simple contrivance is adopted :—There is one tap at the lower end, to which is attached a short pipe inside the still, working easily on an elbow. To this is connected a copper wire having its outlet just above the external surface of the boiler, and by which wire the short pipe may have its orifice presented at any required height, to ascertain the state of the contents of the vessel. For instance, supposing the fire to be withdrawn and the agitators to be at rest, if the end of the tube were pulled up by the wire and the tap opened, a clear liquid would issue, which could be tested in order to ascertain whether the whole of the ammeniaeal gas had been removed. On the other hand, if the short tube were allowed to lay along the bottom of the still the opened cock would allow the sulpho-cal careens mud to escape.
There are many gasworks where ammoniacal salts are now manufactured, but it is suggested that in now works, or at these whore the gas-liquor is not at present utilized, it would la preferable, in the event of the adoption of the principle herein advocated, that the ammonia, after concen tration, should be sent to the sulphuric or muriatic acid works, rather than that the acids should be sent to the gas-works. In metallurgy, it is found more advantageous to transport the calcined or partly-prepared ores to the coal districts for smelting, rather than to take the fuel to the mines. Barges fitted with tanks ordinarily employed in the conveyance of gas-liquor, contain from 3000 to 8000 gallons. A land journey of 12 miles, with two horses for a load of 500 gallons in a tank-van, now costs 11. By rail the cost of freight is Id. per ton per mile.
The advantages of the above-described system may be summed up as affecting a considerable economy in labour, time, and occupation of plant, together with the facility of extracting the whole of the ammonia from the gas liquor iu a pure condition. A manufactory, previously consuming 10,000 gallons of gas liquor per week, may now utilize 24,000 gallons, and at about half the expense of fuel of that furmerly incurred.
According to Sir Robert Kane, the yield of ammonia from pent as sulphate was 24•8 lb. per ton. Dr. Hodges, of Belfast, obtained 22'75 lb. per ton. These results were obtained from the working of Irish peat, presumably on an experimental scale ; for in Mr. Sullivan's report to the Directors of the Irish Pent Company, in 18.15, the working results showed only 3 cwt. per 100 tons of peat = 3.36 lb. per ton. The production of ammonia from the putts occurring in the Highlands of Scotland is stated to be more satisfactory; and if peat can be profitably worked for the production of oils and paraffin, there can be no reason why it should not become an important source of ammonia. Bituminous schist, when distilled, yields ammonia, though generally in small quantities.