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RUBIDIUM [symbol Rb, atomic weight 85...

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Originally appearing in Volume V23, Page 809 of the 1911 Encyclopedia Britannica.
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RUBIDIUM [See also:symbol Rb, atomic See also:weight 85.45 (0=16)] , a metallic See also:element belonging to the See also:group of the See also:alkali metals. It is found in the minerals See also:lepidolite, See also:petalite and in various specimens of See also:mica and of carnallite, and in some See also:mineral See also:waters. It also occurs in See also:tea, See also:cocoa, See also:coffee, See also:tobacco and in the ashes of beetroot. It was discovered by R. See also:Bunsen and See also:Kirchhoff (See also:Ann., 186o, 113, p. 337), in the spectroscopic examination of the residues obtained on evaporation of See also:water from a mineral See also:spring at See also:Durkheim, being characterized by two distinctive red lines. The best source of rubidium salts is the See also:residue See also:left after extracting See also:lithium salts from lepidolite, the method of separation being based on the different solubilities of the plating-chlorides of See also:potassium, rubidium and See also:caesium in water (R. Bunsen, Ann., 1862, 122, p. 351). A somewhat similar See also:process based on the varying solubilities of the corresponding alums has also been devised by Redtenbacher (Jour. prak. Chem., 1865, 95, P. 148).

The See also:

metal is prepared by distilling the carbonate with See also:carbon (an explosive See also:compound similar to that obtained from potassium and carbon monoxide is liable to be formed simultaneously); by reducing the hydroxide with See also:aluminium: 4RbOH+2AI=Rb2O Al203+ 2Rb + 2H2 (N. Beketoff, Ber., 1888, 21, p. 424 ref.); by reducing the carbonate (C. Winckler, Ber., 189o, 23, p. 51) or the hydroxide with See also:magnesium (H. See also:Erdmann and P. Kothner, Ann., 1899, 294, p. 55) ; and by See also:heating the fused chloride with See also:calcium in an exhausted See also:glass See also:tube at 400--500° C. (L. Hackspill, Comptes rendus, 1905, 141, p. 101). The metal was first obtained electrolytically in 1910 by electrolysing the fused hydroxide in a See also:nickel See also:vessel, with an See also:iron See also:wire See also:cathode and iron See also:cylinder anode; the product on cooling being opened under See also:pyridine cooled by a freezing mixture (G. von Hevesy, Zeit. anorg.

Chem., 1910, 67, p. 242). It is a silvery See also:

white metal which melts at 38.5° C. and has a specific gravity of 1.52. It oxidizes rapidly on exposure to See also:air, and decomposes See also:cold water very rapidly. It closely resembles caesium and potassium in its See also:general properties. The rubidium salts are generally colourless, mostly soluble in water and isomorphous with the corresponding potassium salts. Rubidium hydride, RbH, was obtained in the See also:form of colourless needles by H. See also:Moissan (Comptes rendus, 1903, 136, p. 587) from the See also:direct See also:combination of its constituent elements. It rapidly dissociates when heated in vacuo to 300° C. The existence of the See also:oxide Rb2O appears to be doubtful, the results of Erdmann and Kiithner (loc. cit.) pointing to the formation of RbO2 by the direct See also:union of the metal with dry See also:oxygen. E.

Rengade (Comptes rendus, 1907, 144, p. 920), by partially oxidizing the metal in a current of dry oxygen and removing excess of metal by See also:

distillation in vacuo, has obtained oxides of See also:composition Rb202 (yellowish white), Rb203 (See also:black) and Rb204 (yellow). Rubidium hydroxide, RbOH, is a colourless solid which is formed by the See also:action of rubidium on water, or by the addition of baryta water to a See also:solution of rubidium sulphate. It is readily soluble in water, the solution being very alkaline and See also:caustic. It melts at 301'. Evaporation of the aqueous solution at 15° C. deposits a crystalline hydrated hydroxide of composition RbOH•2H2O (R. de Forcrand, Comptes rendus, 1909, 149, p. 1341). Rubidium chloride, RbCI, is formed on burning rubidium in See also:chlorine, or on dissolving the hydroxide in aqueous hydrochloric See also:acid. It crystallizes in colourless cubes and volatilizes when heated very strongly. It is soluble in water and combines with many metallic chlorides to form See also:double salts. It combines also with See also:iodine chloride and bromide and with See also:bromine chloride and with bromine (H. L.

See also:

Wells and H. L. See also:Wheeler, Amer. Jour. Sci., 1891 (3), 43, P. 475)• Rubidium sulphate, Rb2SO4, is formed by the action of sulphuric acid on the carbonate or hydroxide of the metal, or by the action of See also:milk of See also:lime on rubidium See also:alum, the excess of lime being precipitated by rubidium carbonate and the solution neutralized by sulphuric acid. It forms large colourless hexagonal crystals. Several sulphides of the metal have been described by W. Biltz and E. Wilke-Di rfurt (Zeit. anorg. Chem., 1906, 48, p. 297).

The normal sulphide, Rb2S•4H2O, is colourless, and when heated in aqueous solution with the requisite amount of See also:

sulphur is transformed into the yellow tetrasulphide, Rb2S4.2H2O. A pentasulphide, Rb2S3, which crystallizes in red prisms melting at 223° C., 1s also obtained by the direct union of the normal sulphide with sulphur. When heated in a current of See also:hydrogen it is transformed into the colourless disulphide, whilst if the heating be carried out in a current of See also:nitrogen it yields the trisulphide, Rb2S,.See also:H2O. These sulphides are much less hygroscopic than the corresponding caesium compounds. Rubidium nitrate, RbNO3, obtained by the action of nitric acid on the carbonate, crystallizes in needles or prisms and when strongly heated is transformed into a mixture of nitrite and oxide. Rubidium ammonium, RbNH3, was prepared by H. Moissan (Comptes rendus, 1903, 136, p. 1177) by the action of liquid See also:ammonia on rubidium. The product combines with See also:acetylene to form rubidium acetylide acetylene, Rb2C2•C2H2, which on heating in vacuo loses acetylene and leaves a residue of rubidium See also:carbide Rb2C2 (ibid. p. 1217). Rubidium carbonate, Rb2CO3, formed by the addition of ammonium carbonate to rubidium hydroxide, is a crystalline See also:mass which melts in its water of See also:crystallization when heated. The atomic weight of rubidium was determined by R.

Bunsen (Pogg. Ann., 1861, 113, p. 339), See also:

Picard (Zeit. anal. Chem., 1862, 1, p 519) and Godeffroy (Ann., 1876, 181, p. 185), the methods being E. on the See also:conversion of rubidium halides into the corresponding See also:silver See also:salt, and the values obtained vary from 85.4o to 85.5o. Thedetermination of E. H. See also:Archibald (Jour. Chem. See also:Soc., 1904, 85, p. 776) from the See also:analysis of the chloride and bromide gives the mean value as 85.485 (0 =16).

End of Article: RUBIDIUM [symbol Rb, atomic weight 85.45 (0=16)]

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