POTASSIUM BROMATE AND POTASSIUM BROMIDE 245Procedure: Dissolve the potassium hydroxide in 100 cc. of water
in a 300-cc. Erlenmeyer flask. At the hood obtain the liquid
bromine in a measuring cylinder and perform all the operations
with bromine under the hood. Cool the KOH solution to room
temperature and pour the bromine into it, about 1 cc. at a time,
rotating the contents of the flask until the bromine has dissolved
after each addition. When all the bromine is added, it should be
in slight excess, which is shown by a distinct reddish tint in the
solution, not merely a yellow color.
Now heat the contents of the flask to boiling and boil until the
excess of bromine has been expelled. Then cool to 15° or lower.
Collect the crystals on a suction filter. Preserve the nitrate to
obtain the by-product, potassium bromide.
Dissolve the crystals in four times their weight of hot water. Un-
less the solution is perfectly clear, filter it hot, and without suction,
to remove dirt, rinsing the filter with about 5 cc. of boiling water.
Cool the nitrate to below 15° as before, and collect the crystals.
Add the mother liquor to that reserve for obtaining the by-product.
Dissolve 0.05 gram of the crystals in 2 cc. of hot water; add 1
drop of AgNO 3 solution. A precipitate while the solution is at the
boiling temperature is silver bromide and shows that the product
has not been purified from bromide. Repeat the recrystallization
as many times as necessary to obtain a pure product.
Potassium Bromide. Combine all the mother liquors, evaporate
in a porcelain dish until a pasty mass is obtained, mix this thor-
oughly with 5 grams of powdered charcoal, and dry the friass
completely. Pulverize the dry mixture in a mortar and heat
it to redness, for 20 minutes, in an iron crucible surrounded by an
asbestos mantle. Extract the product with 60 cc. of hot water,
filter, wash the residue and filter with an additional 15 cc. of hot
water, and evaporate the solution to dryness to obtain potassium
bromide. The solution of potassium bromide " creeps." If it has
to be set away over night the vessel containing it should be placed
in a clean large dish to catch any of the salt that creeps over the
edge of the smaller vessel.
Test the product for absence of bromate by dissolving some in a
little water and acidifying with sulphuric acid. If no bromate
is present, no free bromine will be produced, i.e., the solution will
remain colorless and odorless.
Put up the two products in separate cork-stoppered bottles.