The dissociation of the crystallo-hydrate of baryta is given in Chapter I., Note 112. 100 parts of water dissolve 0° 20° 40° 60° 80° BaO 1·5 3·5 7·4 18·8 90·8 SrO 0·3 0·7 1·4 3 9 Supersaturated solutions are easily formed. The anhydrous oxide BaO fuses in the oxyhydrogen flame. When ignited in the vapour of potassium, the latter takes up the oxygen; whilst in chlorine, oxygen is separated and barium chloride formed.
Brugellmann, by heating BaH2O2 in a graphite or clay crucible, obtained BaO in needles, sp. gr. 5·32, and by heating in a platinum crucible—in crystals belonging to the cubical system, sp. gr. 5·74. SrO is obtained in the latter form from the nitrate. The following are the specific gravities of the oxides from different sources:— MgO CaO SrO from RN2O6 3·38 3·25 4·75 „ RCO3 3·48 3·26 4·45 „ RH2O2 3·41 3·25 4·57
The property of barium oxide of absorbing oxygen when heated, and giving the peroxide, BaO2, is very characteristic for this oxide (see Chapter III., Note 187). It only belongs to the anhydrous oxide. The hydroxide does not absorb oxygen. Peroxides of calcium and strontium may be obtained by means of hydrogen peroxide. Barium peroxide is insoluble in water, but is able to form a hydrate with it, and also to combine with hydrogen peroxide, forming a very unstable compound having the composition BaH2O4 (obtained by Professor Schöne), which in course of time evolves oxygen (Chapter IV., Note 266).
Even in solutions a gradual progression in the increase of the specific gravity shows itself, not only for equivalent solutions (for instance, RCl2 + 200H2O), but even with an equal percentage composition, as is seen from the curves giving the specific gravity (water 4° = 10,000) at 15° (for barium chloride, according to Bourdiakoff's determinations): BeCl2: S = 9,992 + 67·21p + 0·111p2 CaCl2: S = 9,992 + 80·24p + 0·476p2 SrCl2: S = 9,992 + 85·57p + 0·733p2 BaCl2: S = 9,992 + 86·56p + 0·813p2