Chemical elements
    Physical Properties
    Chemical Properties
      Barium Hydride
      Barium Subfluoride
      Barium Fluoride
      Acid Barium Fluoride
      Barium Subchloride
      Barium Chloride
      Barium Bromide
      Barium Perbromides
      Barium Iodide
      Barium Periodides
      Barium Mixed Halides
      Barium Mixed Perhalides
      Barium Oxychloride
      Barium Hypochlorite
      Barium Chlorite
      Barium Chlorate
      Barium Perchlorate
      Barium Oxybromide
      Barium Hypobromite
      Barium Bromate
      Barium Perbromate
      Barium Oxyiodide
      Barium Iodate
      Barium Periodate
      Barium Manganites
      Barium Manganate
      Barium Permanganate
      Barium Suboxide
      Barium Oxide
      Barium Hydroxide
      Barium Peroxide
      Barium Peroxyhydrate
      Barium Tetroxide
      Barium Sulphide
      Barium Hydrosulphide
      Barium Polysulphides
      Barium Hydroxyhydrosulphide
      Barium Oxysulphides
      Barium Sulphite
      Barium Thiosulphate
      Barium Dithionate
      Barium Trithionate
      Barium Tetrathionate
      Barium Pentathionate
      Barium Sulphate
      Acid Barium Sulphates
      Barium Pyrosulphate
      Barium Persulphate
      Barium Selenide
      Barium Selenite
      Barium Selenate
      Acid Barium Selenate
      Barium Telluride
      Barium Tellurite
      Barium Tellurate
      Barium Chromite
      Barium Chromate
      Barium Dichromate
      Barium Potassium Trichromate
      Barium Chlorochromate
      Barium Perchromate
      Barium Molybdate
      Barium Permolybdate
      Barium Tungstate
      Barium Uranate
      Barium Diuranate
      Barium Peruranate
      Barium Nitride
      Barium Azide
      Barium Hexammoniate
      Barium Ammonium
      Barium Amide
      Barium Amidosulphonate
      Barium Imide
      Barium Imidosulphonate
      Barium Hyponitrite
      Barium Nitroxysulphite
      Barium Nitrososulphate
      Barium Nitrohydroxylaminate
      Barium Nitrite
      Barium Nitrate
      Barium Phosphide
      Barium Dihydrohypophosphite
      Barium Hydrophosphite
      Barium Hypophosphate
      Barium Orthophosphates
      Barium Pyrophosphate
      Barium Metaphosphate
      Basic Barium Phosphates
      Barium Thiophosphites
      Barium Thiophosphates
      Barium Selenophosphates
      Barium Azophosphates
      Barium Phosphimates
      Barium Arsenide
      Barium Orthoarsenite
      Barium Pyroarsenite
      Barium Orthoarsenates
      Barium Pyroarsenate
      Barium Thioarsenites
      Barium Thioarsenates
      Barium Sodium Selenoxyarsenate
      Barium Metantimonate
      Barium Thioantimonites
      Barium Chloroantimonite
      Barium Orthothioantimonate
      Barium Hypovanadate
      Barium Vanadates
      Barium Metapervanadate
      Barium Niobate
      Barium Tantalate
      Barium Pertantalate
      Barium Carbide
      Barium Carbonyl
      Barium Formate
      Barium Acetate
      Barium Oxalate
      Barium Carbonate
      Barium Thiocarbonate
      Barium Percarbonate
      Barium Cyanide
      Barium Cyanamide
      Barium Cyanate
      Barium Cyanurate
      Barium Thiocyanate
      Barium Selenocyanate
      Barium Silicide
      Barium Silicates
      Barium Fluosilicate
      Barium Stannate
      Barium Orthoplumbate
      Barium Titanate
      Barium Peroxide Pertitanate
      Barium Pertitanate
      Barium Fluoroxytitanate
      Barium Zirconate
      Barium Boride
      Barium Borates
      Barium Fluorborate
      Barium Perborate
      Barium Aluminates
      Barium Ferrite
      Barium Ferrate
      Barium Gobaltite
      Barium Dinickelite
      Barium Platinate
    Detection of Barrium
    PDB 1djh-3iqp
    PDB 3iqr-4e7y

Barium Sulphate, BaSO4

Barium Sulphate, BaSO4, occurs naturally as the mineral barytes or heavy spar. It was the first known of the compounds of barium- It crystallises in the rhombic system and is usually white and opaque, but it sometimes forms transparent crystals which are colourless, or have brownish, greenish, or bluish shades. The finest specimens come from the Auvergne, Hungary, Bohemia, and Cumberland. A monoclinic form of the naturally occurring compound found in Quebec has been described. The mineral barytocelestine is an isomorphous mixture of barium and strontium sulphates. The water of a chalk well in Harrow has been found to contain barium sulphate.

Barium sulphate may be prepared by the precipitation of a soluble barium salt with a soluble sulphate or sulphuric acid. There is no action if pure sulphuric acid be placed in contact with anhydrous barium oxide, a little water being necessary. Spring obtained it by compressing a mixture of sodium sulphate and barium carbonate under 6000 atmospheres.

The precipitated sulphate is amorphous, or composed of crystals of microscopic dimensions. Larger crystals may, however, be obtained by very slow precipitation in very dilute solutions; by heating the precipitate in a sealed tube with hydrochloric acid or sodium bicarbonate at 250° C.; by fusion of potassium sulphate with barium chloride, of barium fluoride with calcium sulphate in presence of potassium chloride and sodium chloride, or of barium sulphate with barium chloride at 1150 ° C., or with sodium sulphate at 1130° C., which is simply crystallisation from a solvent; and, finally, by evaporation of a sulphuric acid solution of barium sulphate at, or a little below, the boiling-point. Manross found the density of the crystallised product to be 4.179. According to von Weimarn, a substance usually precipitated in the crystalline state may be obtained in the colloidal form under conditions which diminish the solubility and thus increase the number of centres of precipitation. Barium sulphate may, therefore, be prepared in a colloidal form by precipitation from solutions containing methyl or ethyl alcohol, glycerol, amyl alcohol, or an alkaline solution of casein. In the latter case crystallisation is probably prevented by the coating of the particles of barium sulphate with casein. Colloidal barium sulphate is also obtained by precipitating a very concentrated solution of barium acetate with aluminium sulphate, or with magnesium or sodium sulphate.

The melting-point of barium sulphate is 1580° C., at which temperature partial decomposition also takes place. The specific heat increases linearly from 0.1137 at 150° C. to 0.1486 at 1050° C.

There is apparently a transition point from β-BaSO4 to α-BaSO4 on heating above 1149° C. Strontium and barium sulphates are completely miscible in all proportions in both α- and β-forms; barium and calcium sulphates are isodimorphous, but the miscibility is at most 5 gram-molecules per cent, of calcium sulphate in barium sulphate.

Barium sulphate alone does not fluoresce under the influence of the cathode rays, but will do so if a little bismuth be present.

The effect of reducing agents on barium sulphate has already been described. By fusion with alkali carbonates, or boiling with solutions of the latter, it is transformed into the carbonate. This reaction was Guldberg and Waage's classic example in their deduction of the law of mass action. When heated with ammonium chloride, barium chloride is formed.

The solubility of barium sulphate in water is exceedingly small. From electrical conductivity determinations Kohlrausch found for precipitated barium sulphate 0.0197 milli-equivalents, or 2.30 mgm. per litre at 18° C., and 0-0226 milli-equivalents for the natural barytes. The higher value for the latter may be due to impurities in the mineral. Melcher obtained the following values at different temperatures: -

Temperature, °C.182550100
Milli-equivalents per litre 0.01900.02120.02880.0334

By calculation from the change of solubility with temperature the heat of solution is -6.0 Cal. Thomsen, from precipitation data, deduced the value -5.580 Cal.

Higher values for the solubility have been obtained owing to super- saturation. According to Hulett, the solubility depends on the size of the solid particles in equilibrium with the solution. By grinding so finely that the diameter of a particle is less than 0.001 mm., the solubility may reach 4.15 mgm., or 0.0355 milli-equivalents per litre at 25° C., or with barytes 6.18 mgm.

The solubility is reduced by salts with a common ion, including sulphuric acid if dilute. Other salts and acids increase it.

The solubility is increased in 40 per cent, hydrobromic and hydriodic acids, and in metaphosphoric acid solutions. Barium sulphate is very soluble in concentrated sulphuric acid, and also to a considerable extent in hydrogen peroxide. The latter fact has a bearing on the preparation of hydrogen peroxide.

Owing to its insolubility barium sulphate is used in quantitative analysis for the estimation of barium or sulphate, and the conditions necessary for satisfactory precipitation have been studied by numerous investigators. The chief sources of error are naturally the increased solubility of the precipitate due to the presence of other substances in solution, and the adsorption of foreign substances by the precipitated sulphate.

Barium sulphate has the power of precipitating colloidal solutions, for example colloidal gold or arsenious sulphide. The action is mechanical.

Barium sulphate alone, on account of its slight solubility, does not go through the same setting and hardening process as calcium sulphate, but hardening may be effected by mixing finely divided barytes with a 10 per cent, solution of aluminium, iron, or magnesium chloride, which acts by increasing the solubility.

According to Tingle there are three hydrates of barium sulphate: 10BaSO4.H2O, separating from a hot neutral solution; 10BaSO4.2H2O, from a hot acid solution; and 10BaSO4.4H2O, from a cold acid solution.

Barium sulphate is used in the production of permanent white and lithopone, and also for glazing and weighting paper.

Several double salts are known, for example BaSO4.SbSO4.6H2O, 2BaSO4.3TiSO4, and BaSO4.Sn(SO4)2.3H2O. The freezing-point curve of mixtures of barium and sodium sulphates apparently indicates the existence of the compound BaSO4.6Na2SO4, but it has not been isolated, and, from the form of the curve, it is very easily dissociated.

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