Refraction. Dia- 

 gram showing the 

 law of refraction. 

 See text 



REFRACTION 



the ground that it was not suffi- 

 ciently Protestant to meet their 

 views. They objected to the doc- 

 trines of the real presence, bap- 

 tismal regeneration, the eucharis- 

 tic sacrifice, the power of the 

 priesthood, and the necessity for 

 episcopal ordination. Cummins 

 consecrated other bishops, and a 

 few local churches were started. 

 The movement found some adher- 

 ents in England, where there is a 

 presiding bishop. At the present 

 day it is said to have about 10,000 

 adherents and about 100 ministers. 

 Refraction. In optics, a phe- 

 nomenon caused when waves of 

 light from one medium pass into 

 another me- 

 dium. Usually 

 when light 

 waves traverse 

 two media, the 

 waves have 

 their directions 

 changed or re- 

 fracted. The 

 phenomenon is 

 of importance, 

 for it is due 

 to refraction 

 that mirages 

 exist, that the 

 day appe ars 

 longer than it is, etc. A common ex- 

 ample of the effect of refraction is 

 seen when a walking-stick is partly 

 submerged in water. The stick ap- 

 pears to be broken at the surface 

 of the water, due to the different 

 indices of refraction of air and 

 water. In the figure A B is a ray 

 of light refracted at B along the line 

 B C. B D is the plane between the 

 two media, and E B F the perpen- 

 dicular at that plane. By the laws 

 of refraction the refracted ray 

 makes with the normal an angle 

 whose trigonometrical sine bears a 

 constant ratio, for any two par- 

 ticular media, to the sine of the 

 angle the incident ray makes with 

 the normal. Certain kinds of crys- 

 tals are remarkable for their power 

 of giving two refracted rays, i.e. 

 double refraction. See Crystallo- 

 graphy ; Light ; Optics. 



Refractometer. Instrument 

 which assumes various forms for 

 determining the refractive index 

 of solids, liquids, or gases. 



In a Pulfrich refractometer for 

 determining the refractive index 

 of liquids, of which only a small 

 quantity is available, the principle 

 of total reflection is used. The 

 figure shows diagrammatically the 

 principle of such a refractometer. 

 A is a Geissler tube and the source 

 of light, concentrated by lenses in 

 B on to a glass cylinder C, which 

 contains a liquid whose refractive 

 index is being tested. D is a prism, 

 a and b refracted ray, bed angle 



6533 



read by telescope E, mounted on 

 a graduated circular scale F ; e is 

 a shadow area to left of ray, / 

 bright area to right. Calculation 

 of angle bed gives refractive index. 

 In an interference refractometer, 

 the index is determined by the use 

 of interference fringes, and so 

 allows of the measurement of the 

 difference of path of two interfering 

 rays. The instrument may be em- 

 ployed in different forms to measure 

 very minute linear distances where 

 great accuracy is required. 



Refractory Materials. Mate 

 rials which strongly resist the 

 destructive or disintegrating action 

 of fire or high temperatures gener- 

 ally. In its broadest sense this 

 term thus covers a great variety 

 of substances, including metals 

 used for the manufacture of articles 

 which have to stand the action of 

 fire or great heat in other forms, as 

 pots and pans, kettles, boilers, 

 and so on. An ore which can be 

 smelted only with great difficulty, 

 and by the aid of very high tem- 

 peratures, is said to be highly 

 refractory. The term refractory 

 has, however, during recent years 

 been used in the technical sense as 

 a specific term for the earths, 

 clays, sands, stone, and other non- 

 metallic substances employed for 

 the manufacture of pottery, bricks, 

 crucibles, ovens, kilns, retorts, and 

 the linings of metallurgical and 

 other forms of furnaces. These sub- 

 stances have been of great indus- 

 trial importance from the very 

 earliest times. They are the raw 

 materials of the potter and of the 

 brickmaker. 



In metallurgy, with the great 

 advances which have been made in 

 recent years in the production and 



Refractometer. Dia- 

 gram of Pulfrich 

 instrument. See 

 text 



employment of high temperatures, 

 researches in refractory materials 

 have become of vital importance. 

 The results attainable in a metal- 

 lurgical operation may depend 

 absolutely on the character of the 

 refractory materials used in con- 

 structing the furnace or converter. 

 In preparing refractories for 

 metallurgical purposes three im- 

 portant conditions have to be 

 kept in mind ; the possible chemi- 

 cal reactions between the ores, 

 tiuxes, fuel, and metal, and the 



REFRIGERATION 



material of the furnace lining ; the 

 dead weights tending to crush the 

 refractory ; and the mechanical 

 actions of heavy masses of ore, fuel, 

 and flux moving over the surfaces 

 of the refractory. The great aim to 

 to be kept in view is to lengthen 

 the life of the refractory. In some 

 operations the life is represented by 

 only one or two heats, after which 

 the refractory material must be 

 renewed or repaired ; frequently 

 a crucible can only be used once ; 

 but the life of the lining of a great 

 blast furnace must extend to many 

 months for its profitable working. 



The natural substances mostly 

 used in the preparation of refrac- 

 tories comprise the clays common 

 clay, china clay or kaolin, and fire 

 clay ; many varieties of sands ; 

 Dinas rock, ganister, bauxite, gra- 

 phite (plumbago), lime, mag- 

 nesia, dolomite or magnesian lime- 

 stone, magnesite, chromite, stea- 

 tite, flints, and other forms of 

 quartz, marl, and asbestos. Some 

 of these may be used in their 

 natural condition, but mostly they 

 have to be subjected to treatment, 

 frequently of an elaborate char- 

 acter, comprising grinding, sieving, 

 washing, or chemical treatment, 

 subsiding, filter .pressing, drying, 

 and firing. Of artificial prepara- 

 tions the most important are car- 

 borundum and the forms Q com- 

 pressed carbon representea by the 

 electrodes of electric furnaces and 

 arc lamps. See Furnace. 



Refrigeration. Application of 

 cold for the preservation of food. 

 The principle of the preservation 

 of food by the abstraction of heat 

 is old. Cold caverns, cellars, and, 

 where available, snow, have always 

 been used for the purpose. The 

 freezing mixture of ice and salt was 

 known in the 17th century. In 

 1834 Jacob Perkins invented a 

 machine which included in simple 

 form the principles of the modern 

 refrigerator : the evaporator, the 

 compressor, the condenser, and the 

 refrigerator, and since that time 

 many types have been invented. 



The principal kinds are : (1) The 

 air machine, in which the cooling 

 process is accomplished by the 

 alternate compression and expan- 

 sion of air. 



(2) The absorption machine, 

 where the process is accomplished 

 by the alternate vaporisation and 

 condensation of some substance. 

 While the condensed vapour is re- 

 evaporating, it takes up heat from 

 the bodies round it, thus accom- 

 plishing refrigeration. The com- 

 monest type of absorption machine 

 is that in which ammonia dissolved 

 in water is the medium. 



(3) The vapour compression 

 machine is one which acts by the 



