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BROMINE (symbol Br, atomic weight 79-96)
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See also:BROMINE (See also:symbol Br, atomic See also:weight 79-96) , a chemical See also:element of the halogen See also:group, which takes its name from its pungent unpleasant See also:smell Wows, a stench). It was first isolated by A. J. See also:Balard in 1826 from the salts in the See also:waters of the Mediterranean. He established its elementary See also:character, and his researches were amplified by K. J. Lowig (1803—1890) in Das Brom and See also:seine chemischen Verhaltnisse (1829). Bromine does not occur in nature in the uncombined See also:condition, but in See also:combination with various metals is very widely but sparingly distributed. See also:Potassium, See also:sodium and See also:magnesium bromides are found in See also:mineral waters, in See also:river and See also:sea-See also:water, and occasionally in marine See also:plants and animals. Its See also:chief commercial See also:sources are the See also:salt deposits at See also:Stassfurt in Prussian See also:Saxony, in which magnesium bromide is found associated with various chlorides, and the brines of See also:Michigan, See also:Ohio, See also:Pennsylvania and See also:West See also:Virginia, U.S.A.; small quantities are obtained from the See also:mother liquors of See also:Chile See also:saltpetre and See also:kelp. In combination with See also:silver it is found as the mineral bromargyrite (bromite). Manufacture.—The chief centres of the bromine See also:industry are Stassfurt , and the central See also:district of Michigan. It is manufactured from the magnesium bromide contained in " See also:bittern (the mother liquor of the salt industry), by two processes, the continuous and the periodic. The continuous See also:process depends upon the de-See also:composition of the bromide by See also:chlorine, which is generated in See also:special stills. A See also:regular current of chlorine mixed with See also:steam is led in at the bottom of a tall See also:tower filled with broken bricks, and there meets a descending stream of hot bittern: bromine is liberated and is swept out of the tower together with some chlorine, by the current of steam, and then condensed in a See also:worm. Any uncondensed bromine vapour is absorbed by moist See also:iron borings, and the resulting iron bromide is used for the manufacture of potassium bromide. The periodic process depends on the interaction between See also:manganese dioxide (pyrolusite), sulphuric See also:acid, and a bromide, and the operation is carried out in See also:sandstone stills heated to 6o° C., the product being condensed as in the continuous process. The substitution of potassium chlorate for pyrolusite is recommended when See also:calcium chloride is See also:present in the bittern. The crude bromine is purified by repeated shaking with potassium, sodium or ferrous bromide and subsequent redistillation. Commercial bromine is rarely pure, the chief impurities present in it being chlorine, hydrobromic acid, and bromoform (M. See also:Hermann, Annalen, 1855, 95, p. 211). E. See also:Gessner (Berichte, 1876, 9, p. 1507) removes chlorine by repeated shaking with water, followed by See also:distillation over sulphuric acid; hydrobromic acid is removed by distillation with pure manganese dioxide, or mercuric See also:oxide, and the product dried over sulphuric acid. J. S. See also:Stas, in his stoichiometric researches, prepared chemically pure bromine from potassium bromide, by converting it into the bromate which was purified by repeated See also:crystallization. By See also:heating the bromate it was partially converted into the bromide, and the resulting mixture was distilled with sulphuric acid. The distillate was further purified by digestion with See also:milk of See also:lime, precipitation with water, and further digestion with calcium bromide and See also:barium oxide, and was finally redistilled. Characters.—Bromine at See also:ordinary temperatures is a See also:mobile liquid of See also:fine red See also:colour, which appears almost See also:black in thick layers. It boils at 59° C. According to See also:Sir W. See also:Ramsay and S. See also:Young, bromine, when dried over sulphuric acid, boils at 57.65° C., and when dried over See also:phosphorus pentoxide, boils at 58.85° C. (under a pressure of 755.8 mm.), forming a deep red vapour, which exerts an irritating and directly poisonous See also:action on the See also:respiratory See also:organs. It solidifies at -21° C. (Quincke) to a dark See also: It does not combine directly with oxygen, See also:nitrogen or See also:carbon. With the other elements it unites to See also:form bromides, often with explosive violence; phosphorus detonates in liquid bromine and inflames in the vapour; iron is occasionally used to absorb bromine vapour, potassium reacts energetically, but sodium requires to be heated to 200° C. The chief use of bromine in See also:analytical See also:chemistry is based upon the oxidizing action of bromine water. Bromine and bromine water both bleach organic colouring matters. The use of bromine in the extraction of See also:gold (q.v.) was proposed by -R. See also:Wagner (Dingier's Journa,218, p. a53) and others, but its cost has restricted its general application. Bromine is used extensively in organic chemistry as a substituting and oxidizing agent and also for the preparation of addition compounds. Reactions in which it is used in the liquid See also:forum, in. vapour, in solution, and in the presence of the so-called " bromine See also:carriers," have been studied. Sunlight affects the action of bromine vapour on organic compounds in various ways, sometimes retarding or accelerating the reaction, while in some cases the products are different (J. Schramm, Monatshefte See also:fur Chemie, 1887, 8, p. ioi).. Some reactions, which are only possible by the aid of nascent bromine, are carried out by using solutions of sodium bromide and bromate, with the amount of sulphuric acid calculated according to the See also:equation 5NaBr+NaBrOa+6H2SO4 6NaHSO4+3H20+GBr. (See also:German Patent, 26642.) The diluents in which bromine is employed are usually ether, chloroform, acetic acid, hydrochloric acid, carbon bisulphide and water, and, less commonly, alcohol, potassium bromide and hydrobromic acid; the excess of bromine being removed by heating, by sulphurous acid or by shaking with See also:mercury. The choice of solvent is important, for the velocity of the reaction and the nature of the product may vary according to the solvent used, thus A. See also:Baeyer and F. Blom found that on brominating orthoacetamid'o-See also:acetophenone in presence of water or acetic acid, the bromine goes into the See also:benzene See also:nucleus, whilst in chloroform or sulphuric acid or by use of bromine vapour it goes into the See also:side See also:chain as well. The action of bromine is sometimes accelerated by the use of compounds which behave catalytically, the more important of these substances being iodine, iron, ferric chloride, ferric bromide, See also:aluminium bromide and phosphorus. For oxidizing purposes bromine is.generally employed in aqueous and in alkaline solutions, one of its most important applications being by Emil See also:Fischer (Berichte, 1889, 22, p. 362) in his researches on the sugars. The atomic weight of bromine has been determined by J. S. Stas and C. See also:Marignac from the See also:analysis of potassium bromide, and of silver bromide. G. P. See also:Baxter (Zeit. anorg. Chem. 1906, 50, p. 389) determined the ratios Ag: AgBr, and AgCI: Ag Br.
Hydrobromic Acid.—This acid, HBr, the only See also:compound of hydrogen and bromine, is in many respects similar to hydrochloric acid, but is rather less See also:stable. It may be prepared by passing hydrogen See also:gas and bromine vapour through a See also:tube containing a heated See also:platinum See also:spiral. It cannot be prepared with any degree of purity by the action of concentrated sulphuric acid on bromides, since secondary reactions take See also:place, leading to the liberation of See also:free bromine and formation of See also:sulphur dioxide. The usual method employed for the preparation of the gas consists in dropping bromine on to a mixture of amorphous phosphorus and water, when a violent reaction takes place and the gas is rapidly liberated. It can be obtained also, although in a somewhat impure condition, by the See also:direct action of bromine on various saturated See also:hydrocarbons (e.g. See also:paraffin-See also:wax), while an aqueous solution may be obtained by passing sulphuretted hydrogen through bromine water. See also: At ordinary temperatures hydrobromic acid is a colourless gas which fumes strongly in moist air, and has an acid See also:taste and reaction. It can be condensed to a liquid, which boils at -64.9°C. (under a pressure of 738.2 mm.), and, by still further cooling, gives colourless crystals which melt at -88.5° C. It is readily soluble in water, forming the aqueous acid, which when saturated at 0° C. has a specific gravity of 1.78. When boiled, the aqueous acid loses either acid or water until n solution of constant boiling point is obtained, containing 48% of the acid and boiling at 126° C. under atmospheric pressure; should the pressure, however, vary, the strength of the solution boiling at a constant temperature varies also. Hydrobromic acid is one of the " strong " acids, being ionized to a very large extent even in concentrated solution, as shown by the molecular conductivity increasing by only a small amount over a wide range of lilution. Bromides.—Hydrobromic acid reacts with metallic oxides, hydroxides and See also:carbonates to form bromides, which can in many cases be obtained also by the direct union of the metals with bromine. As a class, the metallic bromides are solids at ordinary temperatures, which fuse readily and volatilize on heating. The See also:majority are soluble in water, the chief exceptions being silver bromide, mercurous bromide, palladious bromide and See also:lead bromide; the last is, however, soluble in hot water. They are decomposed by chlorine, with liberation of ,bromine and formation of metallic chlorides; concentrated sulphuric acid also decomposes them, with formation of a metallic sulphate and liberation of bromine and sulphur dioxide. The non-metallic bromides are usually liquids, which are readily decomposed by water. Hydrobromic acid and its salts can be readily detected by the addition of chlorine water to their aqueous solutions, when bromine is liberated; or by warming with concentrated sulphuric acid and manganese dioxide, the same result being obtained. Silver nitrate in the presence of nitric acid gives with bromides a pale yellow precipitate of silver bromide, AgBr, which is sparingly soluble in See also:ammonia. For their quantitativedetermination they are precipitated in nitric acid solution by means of silver nitrate, and the silver bromide well washed, dried and weighed. No oxides of bromine have as yet been isolated, but three oxy-acids are known, namely hypobromous acid, HBrO, bromous acid, HBrO2, and bromic acid, HBrO3. Hypobromous acid is obtained by shaking together bromine water and precipitated mercuric oxide, followed by distillation of the dilute solution in vacuo at See also:low temperature (about 4o°C.). It is a very unstable compound, breaking up, on heating, into bromine and oxygen. The aqueous solution is light yellow in colour, and possesses strong See also:bleaching properties. Bromous acid is formed by adding bromine to a saturated solution of silver nitrate (A. H. See also:Richards, J. Soc. Chem. Ind., 1906, 25, p. 4). Bromic acid is obtained by the addition of the calculated amount of sulphuric acid (previously diluted with water) to the barium salt; by the action of bromine on the silver salt, ipthe presence of water, 5AgBrO2+3Br2+3H2O
5AgBr+6HBr,O3, or bypassing chlorine through a solution of bromine in water. The acid is only known in the form of its aqueous solution; this is, however, very unstable, decomposing on being heated to too°C. into water, oxygen and bromine. By reducing agents such, for example, as sulphuretted hydrogen and sulphur-dioxide; it is rapidly converted into hydrobromic acid. Hydrobromic acid de-composes it according to the equation HBrO3+5H'Br=3H2O+3Br2. Its salts are known as bromates, and are as a general See also:rule difficultly soluble in water, and decomposed by heat, with See also:evolution of oxygen.
Applications.—The salts of bromine are widely used in See also:photography, especially bromide of silver. For antiseptic purposes it has been prepared as " bromum solidificatum," which consists of kieselguhr or similar substance impregnated with about 75 % of its weight of bromine. In See also:medicine it is largely employed in the form of bromides of potassium, sodium and ammonium, as well as in combination with alkaloids and other substances.
Medicinal Use.—Bromide of potassium is the safest and most generally applicable sedative of the See also:nervous See also:system. Whilst very weak, its action is perfectly balanced throughout all nervous See also:tissue, so much so that Sir See also: Its most striking success is in See also:epilepsy, for which it is the specific remedy. It may be given in doses of from ten to fifty grains or more, and may be continued without See also:ill effect for See also:long periods in See also:grave cases of epilepsy (See also:grand mal). Of the three bromides in common use the potassium salt is the most rapid and certain in its action, but may depress the See also:heart in morbid states of that See also:organ; in such cases the sodium salt—of which the See also:base is inert—may be employed. In whooping-cough, when a sedative is required but a stimulant is also indicated, ammonium bromide is often invaluable. The conditions in which bromides are most frequently used are See also:insomnia, epilepsy, whooping-cough, See also:delirium tremens, See also:asthma, migraine, laryngismus stridulus, the symptoms often attendant upon the See also:climacteric in See also:women, See also:hysteria, See also:neuralgia, certain nervous disorders of the See also:hearts See also:strychnine poisoning, nymphomania and spermatorrhoea. `Hydro-bromic acid is often used to relieve or prevent the headache and singing in the ears that may follow the See also:administration of See also:quinine and of salicylic acid or salicylates. Additional information and CommentsThere are no comments yet for this article.
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