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RUSTLESS STEEL

A chromiumiron alloy, containing from 12 to 15 per cent, chromium, ard not more than 045 per cent, of carbon, now largely used tor the manufacture of cutlery, turbine blades, acid pumps, and exhaust valves for aircraft engines. It is not dissolved by strong or weak nitric acid, nor attacked by ammonia, but sulphuric and hydrochloric acids attack it readily.

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RESINS

A class of uncrystallizable vegetable products which are insoluble in water as distinct from gums. They soften, as a rule, upon heating and are more or less soluble in alcohol, ether, benzine, turpentine, and other solvents. Many of them are exudations from living trees and some of these are supposed to result from oxidation of the volatile or essential oils which are secreted by them. These exudations are sometimes artificially facilitated by incisions made in the trees as in the case of crude turpentine. Others are of fossil origin but have been probably produced by similar natural processes, while many others are extracted from plants by the use of solvents such as alcohol, benzene, or volatile oils. They are mostly yellow or brown in colour; some are hard and fracture easily; others are soft; and some become electric when rubbed. Descriptions of some of the following will be found under their several names 01 under the heading of Balsams: Amber, Ammoniacum, Anime, AsaCrtida, Benzoin, Burgundy, Capsicum, Copaiba, Copal, Dammar, Dragon

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RACEMIC COMPOUNDS

are mixtures of equal parts of the dextro and lsevo modifications of compounds, and are, in consequence, optically inactiveracemic. acid, for example.

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RESORCINE or RESORCINOL

2 isawhite crystalline phenolic bodyof antiseptic character, which can be prepared from many resins, such as galbanum and asaCetida, by fusion with caustic potash. It melts at r io degrees C., is soluble in water, alcohol, and ether, exhibits a therapeutical action mildly resembling that of carbolic acid, and is the bais of a number of dyes. Nitrous acid, for instance, transforms it into the socalled azodyes.

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REFRACTORIES

are substances difficult to fuse, and implies materials employed in the construction of furnaces, ovens, kilns, retort settings, furnace hearths, stoves, crucibles, etc., on account of their resistance to heat, abrasion, strain, and the action of gases and the chemical compounds to which tney are exposed in such use Clays, fireclays, and silica in the forms of flint, quartz, sandstone, and ganister, are described as acid refractories, containing as they do silicic acid alone or in combination with alumina while chromite, graphite, and plumbago, are neutral in character, and bauxite, lime, magnesia, and zirconia are examples of socalled basic refractories. Fireclay, being acidic in character, is destroyed when heated with bases such as lime; and magnesia, being basic, is destroyed when heated with an acid refractory such as clay. Mica, talc, alumina, and carborundum are further instances of refractories. The mineral chromite is largely used in the manufacture of bricks for lining steel and copper smelting furnaces. They usually contain about 33 per cent, chromic oxide, with less than 6 per cent, of silica, the bricks being compounded by mixing the powdered ore with water and a binding material such as tar, into paste form, moulding, drying, and burning up to 1,460 degrees C. in kilns. Refractory mortars and cements employed for joining, patching, or binding, and as washes over surfaces, are sometimes made of corresponding materials, but slightly more fusible than those to be treated, so that a vitrified bond is formed upon the application of strong heat. Zirkiie cement consists wholly of zirconia, finely ground and made into a paste with water, while silica bricks are generally used in the construction of electric furnaces. The clays used in the making of porcelain and earthenware, lose their chemically associated water when heated to from 480 degrees to 6oo degrees C., and the temperature used in making nonabsorbent or vitreous porceiain varies from 1,250 degrees to 1,550 degrees C., while that employed for poious or nonvitreous ware ranges from 1,150 degrees to 1,250 degrees C. In his work on “Refractories,” by A. B. Searle, it is stated that fire bricks heated in a darkened chamber exhibit the appearance s noted below, at various given temperatures: and that they begin to lose their shape when the temperature reaches to from 1,600 degrees to i,8oo degrees C. A German method of preparing ordinary bricks, so as to have a refractory character, consists in coating them with a mixture of 75 per cent, carborundum and 25 per cent, sodium silicate, and after drying, slowly heating, and burning in the mixture.

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ROCHELLE SALT

A double tartrate of potassium and sodum, being a colourless crystalline compound, soluble in water, used in the preparation of certain bakingpowders.

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REDUCING AGENTS

Substances are said to act as reducing agents, when, for example, oxygen is removed in some degree from an oxide by combination with hydrogen or carbon. Redlead is thus reduced to metallic lead by strongly heating it upon a piece of charcoal. Reduction can be effected by the addition of hydrogen to an organic compound by the action of sodium amalgam. The manufacture of aniline is carried out by a reducing action.

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RADIO ACTIVITY

is a phenomenon which appears to depend upon the expulsion of certain electrons from substances, thus explaining the apparent conversion of one kind of matter into another as referred to under the heading of Atoms and this is done without materially disturbing the general character and properties of the residual substance in its relation to the groupings of the periodic law. In other words, elements may exist generally identical in chemical and physical properties, but having different atomic weights. Crookes originally found that when an electric current was passed through a glass tube previously exhausted of air to a great extent, certain rays looking like light, pass from the cathode to the anode, although the anode is the pole at which the current enters. These rays, called “radiant matter,” are able to drive a little vane placed in their paththat is, to exercise some small mechanical pressure. These emanations are now regarded as electrons, and will pass, as afterwards ascertained, through thin sheets of metal. The cathode rays may be made to converge by the use of an aluminium cup, thus producing a green phosphorescent spot on the glass. They travel in straight lines, and cast a strong shadow from any intervening object placed in their path; they also develop great heat, which may rise to the meltingpoint of platinum. The socalled X rays are a form of light lying beyond the visible end of the spectrum, and Eecquerel, in his search for the possible emission of Rontgen rays by fluorescent substances, encountered rays which are considered to be corpuscular. For example, a double salt of uranium and potassium, w ithout exposure to liht, was found to emit rays which affected a photographic plate, and this was the first ascertained instance of socalled radioactivity. This discovery was followed bj that of Curie and his wife, to the effect that the activity of the uranium compounds is due to the presence in them of some other very active substanceviz., radium, which proved to be a million times more active than uranium. Then it was found that radium itself emits three different types of radiation: one known as the alpha rays, which are unable to pass through a few sheets of paper; another, the beta rays which can be cut oft by a thick sheet of lead, and the gamma rays, of more intensely penetrating character. The alpha rays are regarded as atoms of helium, the beta rays as identical with Crookes

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RUM

An alcoholic drink of characteristic odour, distilled from fermented molasses in the West Indies, and ordinarily containing about 48 per cent, alcohol.

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RACEMIC ACID

e2ll20A transparent crystalline form of tartaric acid obtained from tartar motherliquor devoid of the power of turning the plane of polarized light, and therefore termed “inactive.” It is soluble ir> water, melts at 205 degrees C., and admits of division into two modifications: the one known as dextrotartaiic acid, which turns the polarized light plane to the right; and the other as Ijevotartaric, which affects it to the left.

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