In tho manufacture of liquor ammonia, where the use of ordinary ice is inadmissible, and it is nocossary to employ distilled water, the gas may be conveniently cooled by being passed through a long si s of tubes surrounded with cold water, or a freezing mixture, before being conducted into the water.
In 1867, Air. Reece obtained a patent fur producing c,old by the evaporation of liquid ammonia in a special form of apparatus, the same arrangement is claimed of nearly anhydrous ammonia. It consists essentially of a boiler, an analyzer, which, with slight modifications, resembles Coffey's ammonia still, a rectifier and a condenser. The other portions of the apparatus belong to its refrigerating functions and the collection of the volatilized ammonia. From the condenser the ammonia may be passed into water c,ontained in Woulfe's bottles, or any suitable receiver. Mr. Reece works his apparatus for refrigerating to a pressure of eight atmospheree, but for producing liquor ammonia there is obviously no occasion to work beyond the ordinary pressure.
The boiler may be supplied with gas liquor, or an ammoniacal salt dissolved in water, to which milk of lime or a caustic alkaline solution may be added. On heating the c,ontents of the boiler, the ammonia and steam together pass into the analyzer, thence into the rectifier, which is kept well cooled ; the rectifier, which consists of a series of straight tubes, open at both ends, and, fitting into chambere, allows the condensed steam to fall back into the analyzer, from which it flows into the boiler again ; the gas finally passes into the condenser almost free from water. The operation is continued until all the ammonia ie expelled from the boiler and analyzer.
The ammonia accumulating in the condenser may be liquefied provided the pressure be suffi ciently high, and the analyzer eupplied with a eolution of ammonia. The liquefied ammonia is allowed to flow into a suitable vessel containing tubes or coils through which the liquid to be cooled is made to traverse. By the abstraction of heat the ammonia beeornes gaseous, and is led back again to the analyzer or rectifier.
For freezing purposes liquids of a non-oongealable character are passed through the tubes until the temperature is eufficiently low; for this purpoee a solution of chloride of calcium is preferred.
There are seveml methods in use for expelling ammonia from the raw gas liquor, or the mixture of the liquor and milk of lime, viz. by heating in large boilers fixed in masonry, so that the direct aotion of tho furnace fire may be employed; by the injection of high pressure steam into the heated liquor, or the circulation of steam through tubes traversing the vessel containing the liquid, or by blowing a current of air through the liquid.
The method whieh has lately been most strongly advocated for expelling the ammonia, especially for the production of eulphats, is that known as the "steaming process," and which consists in injecting into the liquor high proseure steam through numerous small orifices, in a tube or series of tubes circulating through the liquor. To the manufacturer it is a matter of great importance not only to know that he is obtaining the maximum amount of ammonia, attainable by the process he adopts, but to get off the ammonia with the least possible consumption of fuel. In any case it is advisable to heat the liquor before passing into the stills or boilers ; this is generally done by the waste steam from the evaporating pane or heat from the flues ; preference however is given to the steam, which should circulate through tho liquor, so as to avoid further dilution.
The injection of the steam as jets into the liquor does certainly not appcar so economical a process as the testing with circular coils, for the waste steam and water from the coils may be made to heat the ovaporatore, or may be turned to account in other ways, or returned to the boilers themselves; on the other hand, the waste liquor itself may be utilized fur some of these purposes, so long es there is no fear of fouling or stopping up the pipes, &c. From an economical point of view, as regards fuel, the expulsion of the ammonia by steam circulating in pipes may be the beet, but if tho injected steam facilitate the escape of the ammonia, even with an extra consumption of fuel, there may bo cfrournstanees under which it may be a more desirable process to adopt.