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Refuge (CITIES OF over again Ammonia)

CITIES OF over again. Ammonia was first used by Carré in 1860; ammonia gas driven off by heat from its solution in water is condensed in a cooled vessel under its own pressure; the original ammonia vessel is now cooled, and the liquid ammonia rapidly evaporates (its vapor being absorbed), chilling its surroundings. Anhydrous liquid ammonia has been used by Reece and others.

Conical Refraction. In certain cases light, passing as a single ray through a plate of a biaxial crystallized body, emerges as a hollow cone of rays; and in others a single ray, falling on the plate, becomes a cone inside the crystal, and emerges as a hollow cylinder. These The Bell-Coleman apparatus, greatly extraordinary appearances were pre-employed for producing cold dry air for dicted from the wave theory of light by use in the refrigerating chambers of Sir W. R. Hamilton, and experimentally dead-meat-carrying steamers, the prinrealized by Lloyd. See Preston's "Theory of Light" (1890).

REFRIGERATION. In refrigerating machines there is a transference of heat from the substance which is to be refrigerated to the cooling agent, which is evaporating fluid, expanding gas, or a material which promotes evaporation of the liquid to be cooled. If 80.025 pound Centigrade units of heat be withdrawn from a pound of water at 0° C. it will become a pound of ice of the same temperature. If this heat be withdrawn from the water by an evaporating liquid there are two conditions which must be fulfilled; the evaporating liquid must evaporate very rapidly, and the latent heat of evaporation (i. e., the heat absorbed from outside during evaporation) must be as great as possible. Ether boils at 35.5° C. (95.9° F.), and has at 0° C. (32° F.) a vapor-pressure of 18.4 cm. (7.36 inches) of mercury; at 0° C. it requires 94-pound-Centigrade units of heat to evaporate a pound of it; and at that temperature its evaporation ought accordingly to be able, if the whole of the heat required for evaporation were withdrawn from water, to free 94 80.025 times its weight of water at 0° C., so that a ton of ice (2,240 pounds) would be produced by the evaporation at 0° C. of a minimum of 1,907 pounds of ether. Liquid ammonia boils at -35°C.(-31° F.), and has at 0° C. a vapor-pressure of 318 cm. (127.2 inches), or more than four atmospheres; it is thus extremely rapidly volatilized at 0° C.; and, as its latent heat of evaporation is as much as 294, the production of a ton of ice would thus only demand the evaporation of a minimum of 610 pounds of liquid ammonia. Machines for using ether have been constructed by Siebe, Duvallon, Lloyd, Mühl and others. The ether is caused to evaporate rapidly by an air pump or pumps worked by steam; it cools brine or a solution of calcium chloride, and this cools the water to be frozen or the air to be refrigerated; the ether vapor is condensed by pressure and cold and used unds ciple is that compressed and cooled air will, when allowed to expand against an external resistance, so that it does mechanical work during expansion, lose heat equivalent to the energy which it has expended.

Porous jars, used to keep water cool, are among the simplest kinds of refrigerating apparatus; the evaporation at the outer surface of the jar of the water passing through the porous earthenware taking latent heat from the water. a