Lithium bromide, LiBr

The anhydrous bromide is obtained by dissolving the carbonate in aqueous hydrobromic acid, and evaporating the solution to dryness in a current of gaseous hydrogen bromide. Bogorodsky has isolated three hydrates from the aqueous solution, each forming very deliquescent crystals. At very low temperatures the trihydrate, LiBr,3H₂O, is deposited; at 4° C. it is changed to the dihydrate, LiBr,2H₂O; at 44° C. this substance yields the monohydrate, LiBr,H₂O; above 159° C. the anhydrous salt is deposited. A crystalline form is also described containing 1-1½H₂O. For the melting-point of anhydrous lithium bromide Carnelley gives 547° C., and Wartenberg and Schulz give 549° C.; but Ramsay and Eumorfopoulos found the much lower value 442° C. At its melting-point it evolves bromine freely. The boiling-point is 1310° C., and the vapour-pressure in atmospheres corresponds with the expression

log p = -35600/4.57T+5.109.

The values obtained by Kremers for the solubility in water are given in the table:

Temperature, °C	0	10	20	30	40	50	60	80	100
Grams LiBr in 100 g. H2O	143	161	177	190	202	214	224	245	266

Other investigations of the properties of aqueous solutions have been made by various experimenters. Bonnefoi has prepared complex compounds of lithium bromide and ammonia analogous to those formed by the chloride.

Although the heat of formation of lithium bromide in aqueous solution has not been determined, analogy with the corresponding sodium compounds indicates that it should be similar to that of lithium chloride -

LiOH,Aq.+HBr,Aq. =LiBr,Aq. +13.85 Cal.

By combining this value with the heat of solution of lithium in water (53.2 Cal.) and with the heat of formation of hydrobromic acid in dilute solution (28.38 Cal.), there results the equation

[Li]+Br+Aq.=LiBr,Aq.+95.43 Cal.

Subtraction of the heat of solution of the anhydrous bromide (11.35 Cal.) gives the heat of formation of the salt from its elements in accordance with the equation

[Li]+Br=[LiBr]+84.l Cal.

Like the chloride, lithium bromide yields double compounds with alcohols.

Lithium bromide forms double salts with other metallic bromides, such as those of copper and tin.