STRONTIUM, a metallic chemical element (symbol Sr. atomic weight 87.63, atomic number 38), belonging to the alka line earth group. It is found in small quantities very widely dis tributed 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 179o; and the discovery was confirmed by Hope in 1792 and by Klaproth in 1793.
The metal was isolated (possibly not quite free from mercury) in 1808 by Sir H. Davy, who electrolysed a mixture of the moist hydroxide or chloride with mercuric oxide, using a mercury cathode. It has been obtained in a state of purity by A. Guntz and Roederer by heating the hydride in a vacuum to r,000° C. It may be obtained in the form of sticks by the "contact cathode" method, in which a cooled iron rod, acting as a cathode, just touches the surface of a fused mixture of potassium and strontium chlorides and is raised as the strontium collects on it. Few, if any, of the amalgams are chemical individuals ; the richest in strontium contains 52% and distils unchanged. Strontium is a sil ver-white ductile metal (of sp.gr. 2.54-2.63) 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 20° giving excess of ammonia gives a dark blue solution, and evaporation gives bronze crystals of With carbon monoxide the metal gives Sr(CO)2; with oxygen it forms the monoxide and peroxide.
The hydride, obtained by Guntz on heating strontium amalgam in a current of hydrogen, is a white solid, which readily decomposes water in the cold and behaves as a strong reducing agent. The monoxide or strontia, SrO, is formed by strongly heating the nitrate, or commercially from the hydroxide which is produced by heating the sulphide or carbonate in superheated steam (at about 500-600° 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. 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 peroxide, approximating in composition to is formed as a crystalline precipitate when alkali is added to an aqueous solution of a strontium salt containing hydro gen peroxide. If all the solutions are above so° and very concen
trated, the anhydrous peroxide results.
Strontium fluoride, is obtained by the action of hydro fluoric acid on the carbonate, or by the addition of potassium fluoride to strontium chloride solution. Strontium chloride, is obtained by dissolving the carbonate in hydrochloric acid, or, commercially, by fusing the carbonate with calcium chloride and extracting the melt with water. It crystallizes in small colourless needles and is easily soluble in water; the con centrated aqueous solution dissolves bromine and iodine readily. By concentrating the aqueous solution between 90-130° C, or by passing hydrogen chloride into a saturated aqueous solution, a sec ond hydrated form of composition, SrC1,211,0, corresponding with dihydrated barium and radium chlorides, is obtained. The anhydrous chloride is formed by heating the hydrated chloride in a current of hydrogen chloride.
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, found in the mineral kingdom as celestine, i> 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 appre ciably soluble in concentrated sulphuric acid. When boiled with alkaline carbonates it is converted into strontium carbonate.
Strontium nitride, is formed when strontium amalgam is heated to redness in a stream of nitrogen or by igniting the oxide with magnesium. It is readily decomposed by water, with libera tion of ammonia. Strontium nitrate, 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 It is used in pyro techny for the manufacture of red-fire.
Strontium salts may be recognized by the characteristic crim son colour they impart to the flame of the Bunsen burner and by the precipitation of the insoluble sulphate. Strontium salts are only very feebly toxic.