ICE AND REFRIGERATION. Va rious methods of freezing water have been in use to a small extent for some hundredS of years, but the modern indus try of ice manufacture and refrigeration, now of considerable magnitude and great dates from about the year 1870. At that time there were four plants in operation in the United States as against nearly 2000 now engaged in the production of ice for general sale, in addi tion to the very large number of ice and refrigerating plants used in the meat, cold storage, brewery and other lines. Artifi cial ice was formerly soft and consequent ly of poor keeping qualities, but the present standard product is both hard and lasting. The great reduction in the cost of manufacture is attributable to the high efficiency of improved machinery.
The principal methods of modern use are the Compressor, Absorption, Vacuum and Cold Air. Nearly all American plants are operated either by the compressor or absorption system, the former being the more popular, and anhydrous ammonia is the gas most generally employed.
In the Compressor system, the gas is condensed by pressure and then reduced to a liquid by chilling in cooled "coils" or pipes. This liquid is released into another coil, known as the "expansion pipe," where it again becomes gas and in so doing absorbs heat from its surroundings—converting water into ice, or reducing the atmosphere in cooling rooms, refrigerator cars, etc. The expanded gas goes back to the compressor to be used over and over again in the same way.
By the Absorption method, liquid ammonia is employed as the fundamental agent, the gas being released by heating to about 200° to 210° Fahr. The course of the gas produced is similar to that in the Compressor method, being chilled into a gaseous liquid in a condensing coil and going then to the Expansion Pipes, where its action is identical. It is later sucked back into the mother-water tank and the cess repeated. In commercial operation, the process is practically continuous.
The action of the Expansion Pipes may be either Direct or Indirect. By the former, they come in close or complete contact with the water or atmosphere to , be frozen or chilled. By the latter, their direct action is on strong brine or on air coils, which are employed as the imme agents. The brine may be made
with common salt, but preferably with calcium chloride.
The principal forms of manufactured ice are Can, Plate and Block.
Can Ice is obtained by setting cans of water, previously distilled and filtered to remove both impurities and air bub bles, in brine freezing tanks. It is gen erally good in quality but has a tendency to be soft in the center.
Plate Ice is made in oblong tanks in which the water is. agitated by air-jets to remove the air particles and assist the freezing action to drive the impurities to the center, which remains uncongealed and is later run off. The sides of the tanks consist of iron plates in contact with Expansion Coils. The ice forms on these plates—hence its name. As re moved from the tanks, it is obtained in blocks, generally about sixteen feet long, eight feet wide and one foot thick, weighing three tons and upwards.
Block Ice is made in the same way as Plate Ice, except that it is formed in cells or plate-tanks which are frozen solid, or direct on the Expansion Pipes.
Ice should always be thoroughly washed before placing in the refrigerator, both for hygienic reasons and to avoid clogging the pipes.
Cheap ice, like most "bargains," is very wasteful. Clear, hard, non-porous ice lasts longer and is cheaper in the end.
For its economical use, good insulation in the construction of refrigerators and cooling rooms is essential (see REFRIG ERATORS) . The color of pure ice is deep blue, but this is only discernible when it is seem in large quantities, as in gla ciers See also article on COLD STORAGE.