In the Air Machines, this gas is compressed in a cylinder against a piston, which is driven by a steam engine. The compressed air is cooled by water jets sprayed in the compression cylinder, and also in a cooling tank which has a water bath passed over it at the same time.
The condensed moisture is deposited in the cooling tank and in drying tubes, which are exposed to the spent air which has done refrigeration duty, and is still cool enough to further lower the temperature of the compressed air. After being dried, the air is expanded, producing an intense cold. This air can be circulated in tubes, or used for cooling brine, as in the methods already mentioned, or the air can be expanded directly into the storage rooms or ice tanks.
A Large Plant for the Storage of Fruit is situated at Waldo, Fla., and is controlled by the American ice and cold storage company. It is illustrated in [Fig. 88]. A perfectly dry, cool atmosphere is maintained, and a temperature so uniform as to demand only one degree of variation. The temperature at which the rooms have to be kept varies from 33° to 45° F., depending on the character of the fruit which is to be stored. The higher temperatures are preferable, if sufficiently low to preserve the fruit. Retarding houses for keeping oranges or the more delicate fruits, can usually be more successfully managed by the use of refrigerating machinery, as it is not always possible to maintain a sufficiently even and low temperature by means of ice.
FIG. 88. A FRUIT RETARDING HOUSE IN FLORIDA, WHICH USES REFRIGERATING MACHINERY.
The Latest Inventions.—All these ice-making and cold air machines are more or less expensive and complicated. It is natural, therefore, that inventors should be constantly seeking some plan, idea or method, for securing a low temperature at less cost for the plant involved. The expense of the existing systems also prevents their use, except on a large scale; hence inventors are striving to find not only a method of producing cold at low cost, but one that can be adapted for use in houses, offices, stores, shops, cars, etc., on a more or less limited scale. Several devices for this purpose have already been patented. Some of them promise good results, though at this writing none seem to be thoroughly perfected. One of these devices employs a gas jet, or lamp light, the heat from which, acting on a kettle filled with chemical compound, produces a low temperature for a small house refrigerator, while the same principle is claimed to be applicable on a larger scale.
The Uses of Artificial Refrigeration are numerous. For cooling and ventilating buildings, aiding in some lines of manufactures, and in chemical works, it has proved its usefulness. In all hot climates it is extensively employed for making ice. In breweries it is applied very extensively, and is practically indispensable.
The handling of fresh meat, in the modern method, is directly dependent upon artificial refrigeration, and in no other direction are its benefits more marked or widespread. The cattle on our Western plains have become the daily food of those living at the antipodes. In ten years, from 1880 to 1891, the imports of fresh beef and mutton into Great Britain increased from 400 to nearly 3,300,000 carcasses. During the same period the exports of beef alone from the United States advanced from 50,500 tons to 101,500 tons.
Not only are meats carried in refrigerator vessels from America and the antipodes to England, but within a year Australian milk has been shipped in frozen blocks in such quantities as to be retailed in the streets of London for four cents per quart. Butter, cheese, eggs, fruits and other perishable products, are likewise transported enormous distances by rail or water, without injury to the quality, and at a low cost for freight.
It is also worthy of mention that refrigeration is now employed by the engineer, in substructure work in soils abounding in quicksands. A solid wall of earth is frozen and maintained in such soils, within which excavating and construction can proceed with ease and safety.