Barium Bromide, BaBr₂

Barium Bromide, BaBr₂, may be formed by the action of hydro-bromic acid on barium carbonate, by the precipitation of ferrous bromide with barium hydroxide or carbonate, by the action of a solution of bromine on barium sulphide, by the action of bromine on barium hydroxide and extraction by alcohol of the bromide from admixture with bromate, or, finally, by calcination of barium bromate. To obtain the anhydrous salt the solution formed by most of these methods is evaporated to dryness and heated to a little above 130° C. It is a white deliquescent substance of density 4.79 at 24° C. It melts at 880° C., and sublimes at 820° C. The heat of formation is 179.82 Cal., and the heat of solution 4.98 Cal.

The following values have been found for the solubility at different temperatures: -

Temperature, °C	-20	-9	7	16	19	40	71	76	77	104	145	160	175
Grams BaBr2 per 100 grams solution.	45.7	46.5	48.5	48.8	49.3	50.9	55.1	55.5	55.6	56.6	60.5	59.4	60.3

Milikan determined the concentration of solutions in contact with ice at different temperatures.

Temperature, °C	-3.9	-14.1	–21.1
Grams BaBr2 per 100 grams solution	17.8	38.2	44.6

The cryohydric temperature is – 22.6° C., the concentration of the solution being 46.6 per cent, of barium bromide.

The solubility is diminished by the presence of the barium or bromine ion. The effect of barium iodide has been studied by Etard.

The properties of barium bromide solutions have been investigated from the point of view of density, vapour pressure, electrical conductivity, freezing-point, and refractive index.

An aqueous solution of barium bromide is decomposed by carbon dioxide with the formation of bromine and barium carbonate.

Barium bromide is soluble in both ethyl and methyl alcohol, but more so in the latter than the former.

From saturated solutions at ordinary temperatures the dihydrate separates out in rhombic or monoclinic crystals, which are rather hygroscopic, but do not liquefy under ordinary atmospheric conditions, and which have a density of 3.852 at 24° C. At red heat the hydrated salt is slightly decomposed with loss of bromine. It is isomorphous with barium chloride dihydrate. The solubility in methyl alcohol, which is considerable, decreases with the addition of water, reaching a minimum at about 50 per cent, of alcohol.

The heat of solution of the dihydrate is –4.130 Cal., and, therefore, since the heat of solution of the anhydrous salt is 4.98 Cal., the heat of hydration is 9.11 Cal.

The dihydrate is in equilibrium with the monohydrate, BaBr₂.H₂O, at about 70° C. In dry air the dihydrate may be reduced to the monohydrate at ordinary temperatures. By heating to 100°-130° C. the anhydrous salt is obtained.

By the action of pure dry ammonia on dry barium bromide the compound BaBr₂.8NH₃ is formed. Its dissociation pressure is 760 mm. at 35-4° C. An addition compound with glycine is also formed, of composition BaBr₂.2NH₃CH₂COOH.H₂O.

The following double salts have been mentioned: BaRhBr₅, BaBr₂.HgBr₂, BaBr₂.2Hg(CN)₂.6H₂O or 7H₂O, and BaBr₂.2KBr.