atomic

weight 87.62

See also:

• atomic weight 87.62 STRONTIUM [Symbol Sr (0=16)]

STRONTIUM [

See also:

• SYMBOL (Gr. o-uµ(3oXov, a sign)

Symbol Sr (0=16)]  , a metallic chemical element belonging to the alkaline earth group . It is found in small quantities very widely distributed in various rocks and soils, and in mineral waters; its chief sources are the minerals strontianite, celestine and barytocelestine . The metal was detected in the mineral strontianite, found at Strontian in Argyllshire, by Cruikshank in 1787, and by Crawford in 1790; and the discovery was confirmed by Hope in 1792 and by Klaproth in 1793 . The metal was isolated in 1807 by Sir H . Davy by electrolysing the moist hydroxide or chloride, and has been obtained by A . Guntz and Roederer (Comptes rendus, 1906, 142, p . 400) by heating the hydride in a vacuum to I000° . By electrolysing an aqueous solution of the chloride with a mercury cathode, a liquid and a solid amalgam, SrHg11, are obtained; the latter on heating gives a mixture of Sr2Hgs and SrH$6, and on distillation an amalgam passes over, and not the metal . It is a silver-white ductile metal (of specific gravity 2.54) which melts at 800° . It oxidizes rapidly when exposed to air, and burns when heated in air, oxygen, chlorine, bromine or sulphur vapour . With dry ammonia at 6o° the metal forms strontium ammonium, which slowly decomposes in a vacuum at 2o° giving Sr(NH3)2 ; with carbon monoxide it gives Sr(CO)2; with oxygen it forms the monoxide and peroxide, and with nitric oxide it gives the hyponitrite (Roederer, Bull. sac. chim., 1906 [iii.], 35, P . 715)• The hydride, SrH2, was obtained by Guntz on heating strontium amalgam in a current of hydrogen .

It is a white solid, which readily decomposes

water in the cold and behaves as a strong reducing agent . It dissociates when heated to a high temperature and is not affected by oxygen . The monoxide or strontia, Sr(); is formed by strongly heating the nitrate, or commercially by heating the sulphide or carbonate in superheated steam (at about 500-60o° C.) . It is a white amorphous powder which resembles lime in its general character . By heating the amorphous form in the electric furnace H . Moissan succeeded in obtaining a crystalline variety . The amorphous form readily slakes with water, and the aqueous solution yields a crystalline hydrated hydroxide approximating in composition to Sr(OH)2.8H20 or Sr(OH)2.9H20, which on standing in vacuo loses some of its water of crystallization, leaving the monohydrated hydroxide, Sr(OH)2-H20 . The ordinary hydrated variety forms quadratic crystals and behaves as a strong base . It is used in the extraction of sugar from molasses, since it combines with the sugar to form a soluble saccharate, which is removed and then decomposed by carbon dioxide . A hydrated dioxide, approximating in composition to SrO2'8H20, is formed as a crystalline precipitate when hydrogen peroxide is added to an aqueous solution of strontium hydroxide . Strontium fluoride, SrF2, is obtained by the action of hydrofluoric acid on the carbonate, or by the addition of potassium fluoride to strontium chloride solution . It may be obtained crystalline by fusing the anhydrous chloride with a large excess of potassium hydrogen fluoride or by heating the amorphous variety to redness with an excess of an alkaline chloride .

Strontium chloride, SrCl2.6H20, is obtained by dissolving the carbonate in hydrochloric acid, or by fusing the carbonate with

calcium chloride and extracting the melt with water . It crystallizes in small colour-less needles and is easily soluble in water; the concentrated aqueous solution dissolves bromine and iodine readily . By concentrating the aqueous solution between 90-130° C., or by passing hydrochloric acid gas into a saturated aqueous solution, a second hydrated form of composition, SrC12.2H20, is obtained . The anhydrous chloride is formed by heating strontium or its monoxide in chlorine, or by heating the hydrated chloride in a current of hydrochloric acid gas . It is a white solid, which combines with gaseous ammonia to form SrCl2 8NH3, and when heated in superheated steam it decomposes with evolution of hydrochloric acid . Strontium sulphide, SrS, is formed when the carbonate is heated to redness in a stream of sulphuretted hydrogen . It phosphoresces very slightly when pure . Strontium sulphate, SrSO4, found in the mineral kingdom as celestine, is formed when sulphuric acid or a soluble sulphate is added to a solution of a strontium salt . It is a colourless, amorphous solid, which is almost insoluble in water, its solubility diminishing with increasing temperature; it' is appreciably soluble in concentrated sulphuric acid . When boiled with alkaline carbonates it is converted into strontium carbonate . Strontium nitride, Sr3N2, is formed when strontium amalgam is heated to redness in a stream of nitrogen or by igniting the oxide with magnesium (H . R .

Ellis, Chem . News, 1909, 99, p . 4) . It is readily decomposed by water, with liberation of ammonia . Strontium nitrate, Sr(NOa)2, is obtained by dissolving the carbonate in dilute nitric acid . It crystallizes from water (in which it is very soluble) in monoclinic prisms which approximate in composition to Sr(N0a)2-4H20 or Sr(NOa)2-5H20 . When heated it fuses in its own water of crystallization and becomes anhydrous at Ito° C . It is used in pyrotechny for the manufacture of red-fire . A strontium boride, SrB6, was obtained as a black crystalline powder by H . Moissan and P . Williams (Comptes rendus, 1897, 123, p . 633) by reducing the borate with aluminium in the electric furnace .

Strontium

carbide, SrC2, is obtained by heating strontium carbonate with carbon in the electric furnace . It resembles calcium carbide, decomposing rapidly with water, giving acetylene . Strontium carbonate, SrCO3, found in the mineral kingdom as sttontianite, is formed when a solution of a carbonate is added to one of a strontium salt . It is an amorphous solid, insoluble in water, but its solubility is increased in the presence of ammonium nitrate . It loses carbon dioxide when heated to high temperature . Strontium salts may be recognized by the characteristic crimson colour they impart to the flame of the Bunsen burner and by the precipitation of the insoluble sulphate . On the preparation ofpure strontium salts, see Adrian and Bougarel, Journ. pharm. chem., 1892 (5), p . 345; and S . P . L . Soerenoen, Zeit. anorg. chem., 1895, II, p . 305 .

Recent determinations of the atomic weight of strontium are due to "T . W . Richards (Zeit. anorg . Chem., 1905, 47, p . 145), who, by estimating the ratios of strontium bromide and chloride to silver, obtained the values 87.663 and 87.661 .