Page:Collier's New Encyclopedia v. 07.djvu/564

LEFT BEFBIGEBATION 478 BEFUGE, CITIES OF that many substances ordinarily not double refracting become so when ex- posed to unequal stress, as by pressure, heat, or rapid cooling. Conical Refraction. — In certain cases light, passing as a single ray through a plate of a biaxial crystallized body, emer<Tes 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 extraordinary appearances were pre- dicted from the wave theory of light by Sir W. R. Hamilton, and experimentally realized by Lloyd. See Preston's "Theory of Light" (1890). BEFBIGEBATION. In refrigerating machines there is a transference of heat from the substance which is to be re- frigerated 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 If 80.025 pound- Centigrade units of heat be withdrawn from a pound of water at 0" C. it will become a pound of ice of the same tem- perature. If this heat be withdrawn from the water by an evaporating liquid there are two conditions which must be fulfilled; the evaporating liquid must evaporate very rapidly, and the latent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. €., the heat ab- sorbed 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that temperature its evaporation ought accordingly to be able, if the whole of the heat required for evaporation were withdrawn from water, to free 94 -4- 80.025 times its weight of water at 0° C, so that a ton of ice (2,240 pounds) would be produced by the evaporation at 0° C. of a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 evap- oration is as much as 294, the produc- tion of a ton of ice would thus only de- mand the evaporation of a minimum of 610 pounds of liquid ammonia. Ma- chines for using ether have been con- structed by Siebe, Duvallon, Lloyd, Miihl and others. The ether is caused to evap- orate 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 over again. Ammonia was first used by Carre 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 ves- sel is now cooled, and the liquid ammonia rapidly evaporates (its vapor being ab- sorbed), chilling its surroundings. An- hydrous liquid ammonia has been used by Reece and others. The Bell-Coleman apparatus, greatly employed for producing cold dry air for use in the refrigerating chambers of dead-meat-carrying steamers, the prin- ciple is that compressed and cooled air will, when allowed to expand against an external resistance, so that it does me- chanical 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 refrig- erating apparatus; the evaporation at the outer surface of the jar of the water passing through the porous earthenware taking latent heat from the water. BEFBIGEBATOB, that which refrig- erates, cools, or allays heat. Specifically applied to: Brewing: An apparatus consisting of a shallow vat traversed by a continuous pipe, through which a stream of cold water passes. Steam: (1) The casing with connecting tubes, through which feed-water passes on its way to the boiler, and is warmed by the current of hot brine passing in the other direction, on the outside of the tubes. The hot brine, at a temperature of say 218° F., is that which has been removed from the boiler by the brine pump. (2) A form of condenser, in which the injec- tion water (fresh) is cooled by a surface application of cold sea water.^ A chest or closet holding a supply of ice to cool provisions and keep them from spoiling in warm weather. BEFTJGE, that which shelters or pro- tects from danger, distress, or calamity; a sanctuary; a place to flee to in time of danger. Specifically, an institution for affording temporary shelter to the destitute or the homeless; a house of refuge. BEFTJGE, CITIES OF, in Jewish law and history, six Levitical cities divinely appointed as places of refuge to one who had committed manslaughter, and was pursued by the "Revenger" or "Aven- ger" of Blood. Three (Kedesh Naph- tali, Schechem, and Hebron) were W. of the Jordan, and three (Bezer in Reu- ben, Ramoth Gilead in Gad, and Golan in the half-tribe of Manasseh, were E. of that river.