It comprises two vertical cylinders a b, and a set of pipes a. The first vessel a is formed with an inlet d at its lower part, for admitting the compressed air, which passes upwards through a, then by a connecting passage c, to the top of b, in which it descends, and thence passes into the pipes c. At the top of a, is a pipe f for the intro duction of water of ordinary temperature (or colder when conveniently obtainable), such water being forced by a pump so as to overcome the internal pressure of the compressed air. This injection pipe is fitted with a 'rose-nozzle g, for spreading and distributing the water over the area of the vessel, it being important that the air and water should mingle intimately. To ensure complete contact and action between the water and air, so that the water may abstract as much as possible of the heat rendered sensible by the compression of the air, the vessel a is provided with a number of perforated metal diaphragms k, which aro fixed across the lower part of the vessel, but above the air-inlet, and are arranged with the holes in each opposite the solid metal of the nest above and below, in order that the subdivided currents of air may have their directions continually changed, and be made to impinge upon the wetted surfaces of the diaphragms. Similar diaphragms i are fitted in the second vessel b, for separating from the air any moisture it carries over from a into b. The jets of air, passing through the perforations in each plate in succession, impinge on the next plate, and deposit the suspended moisture. At the bottom of each vessel, is a casing j k, to receive the water ready for drawing off.
Assuming that the water employed is of the ordinary temperature, it cannot reduce the air below that temperature, and the air will atilt retain some moisture, both mechanically suspended and invisible, which will be precipitated, and possibly congealed, on the air being subsequently expanded, and becoming of considerably lower temperature. It is the purpose of the pipes c to cause the separation and deposition from the air, before it reaches the expansion-cylinders, of any moisture which would thus tend to congeal. Theae pipes are placed in an atmosphere below the ordinary temperature, and, being inclined up wards from b, the moisture deposited in them, in consequence of the additional cooling of the air in passing through them, drains back into b. The pipes are best placed in the chamber in which the meat is preserved, the tem perature there being always kept above the freezing-point. They should be of considerable length, the precise length in each case depending upon the tem perature intended to be maintained in the chamber, and other circum atances. Where several chambers are to be kept cool, e. g. a number of vans composing a, railway-train, or several separate compartments in a ship, the pipes may be arranged iu only one compartment. At their higher ends, the pipes communicate with a single pipe, which leads the air to the expan sion-cylinders ; after the air has been expanded, it is led to the chambers, where it is discharged in its expanded and cool state, being distributed by pipes fitted with valves, which can be adjusted so as to secure a temperature as uniform as possible throughout.
The air drawn into the compressing-cylinders e by the pipes a will generally be led from the chambers, so that the same air continually circulates through the entire apparatus, and has to be deprived only of the heat which it absorbs each time it passes through the chambers. The cooling action of the machinery depends on the power developed by the steam-cylinders, and the tempera ture in the chambers can consequently be regulated by suitably adjusting the steam throttle valve. (See Ice.) Knott's and Kent's.—In Knott's refrigerating-car, air is cooled by passage over a freezing-mixture, or ice alone, and a constant circulation of it is kept up, the temperature being best maintained at a little above the freezing-point, say at 33° F. The air is both dried and cooled. Kent's well-known refrigerator-safes are made upon much the same principle, the great feature being a downward draught. Importations of meat from America have been made by this system, the meat being sewn up in bags and suspended in a chamber, surrounded by a temperature of about 3° (37° F.), the draught being produced by a steam-fan worked over the ice-tanks.
Desiccation.—Animal matter, preserved by the absorption of its moisture, loses its flavour, and becomes tough and indigestible ; the fat becomes rancid, and, in damp weather, the meat absorbs moisture, and turns mouldy and sour. Theae tendencies are corrected by adding absorbent sub_ stances with fat food—as sugar and spice, to form "pemmican," and farina, to produce " meat biscuits." Altogether, the process seems ill-adapted for preserving meat in a fresh state, and two metboda only need be mentioned.
Tellier's.—The meat is placed in vessels, whose air is repeatedly exhausted, and replaced by carbonic acid gas, which latter is finally absorbed by a concentrated solution of potash. The meat loses 18-20 per cent. by weight, and ia kept in vacuo.
Sacc's.—Thia process has been described above, under Fruit. When applied to meat, the brine produced furnishes an extract of meat on evaporation, the acetate of soda crystallizing out. This extract ia added in the proportion of about 3 per cent. to the preserved meat. The latter, before use, requires to be steeped for 12-24 hours in water containing about 2 oz. sal ammoniac to the pint.
Antiseptics.—The use of chemical antiseptics has long been known, common salt being a very generally employed agent of this class. The difficulty seems to be to ensure the meat retaining its freshness, and to avoid its acquiring any unpleasant flavour. From among the very various processes devised, the following are selected as being most noteworthy, Ilerzon's.—The quarter-camases aro soaked for 24-36 hours in a solution composed of 3 parts borax, 2 parts boracle acid, 3 saltpetre. and 1 salt, in 100 parts water ; they are then packed with some of the same. Before use, they need 24 hours soaking in fresh water.