286
ELEMENTS OP MATERIA MEDICA.
History. — This salt, also called hydrobromate of potash, was firstdescribed by Balard in 1826 (Ann. de Chim. xxxii.)
Natural History. —(See Iodide of Potassium).
Preparation.- —The modes of preparing bromide of potassium areanalogous to those of the iodide.
In the Pharmacopoeia the bromide is directed to be made by addingfirst an ounce of iron filings and afterwards two ounces of bromine to apint and a half of distilled water. Set them by for half an hour,frequently stirring with a spatula^, Apply a gentle heat, and when agreenish colour is produced, pour in^tfie carbonate of potash dissolved ina pint and a half of water, Strain and wash wh at remains in two pints ofboiling distilled water, and again strain. Let the mixed liquors beevaporated so that crystals may be formed.
In this process bromide of iron is first formed, and afterwards decom-posed by carbonate of potash, by which protocarbonate of iron andbromide of potassium are produced.
REAGENTS. RESULTS.
leq.BromMronlOG ^ “ ne 1 “l- Br0md '- P ° taSS "'- 118
V * —--' *■ ~
1 eq.Carb.Pot h . 70 <1 eq. Oxygen 8 . lei/. Pretax. Jron'ACi
C 1 eq. Carb.A d . 22-----A. 1 eq. Carbonate Iron. 58
Another mode of procuring this salt is to mix bromine with a solution )
of caustic potash, by which bromide of potassium and bromate of potash
are formed (see diagram, p. 123). The bromate of potash may be con-verted into bromide of potassium by heat or hydrosulphuric acid.
Properties. —This salt crystallizes in whitish transparent cubes, orrectangular prisms. It is inodorous: its taste is pungent, saline, andsimilar to common salt, but more acrid. It is permanent in the air.When heated it decrepitates, and at a red heat fuses without sufferingdecomposition. It is very soluble in both cold and hot water, and slightlyso in alcohol.
Characteristics. —That this salt is a bromide is known by thecharacters before mentioned (see the characteristics of the bromides,at p. 124) That its base is potassium is shewn by the charactersof this metal mentioned when noticing iodide of potassium (see p. 281.)
Composition.-— This salt consists of bromine and potassium in thefollowing proportions:—
Per Cent.. 66-1 .. 33-9 .
Liebig.
Eq.
Eq.Wt.. 78 .
. 40 .
Balard.
65-56
34-44
Bromine .Potassium
67-42
32-58
1
1
Bromide Potassium ....I.118
100-00
100 00
1000
The crystals contain water lodged mechanically between their plates,but no combined water (water of crystallization).
Purity. —The purity and goodness of this salt may be known by thefollowing characters:—The form of the crystals, their freedom from colour,