_a._ (Ph. D. 1826; Scheele's Process.) Equal parts of benzoin and hydrate
of lime, in fine powder, are intimately mixed together and boiled for
about an hour, with 40 parts of water; the liquor, after filtration, is
evaporated to 1/5th, and the lime saturated with hydrochloric acid; the
benzoic acid crystallised out as the liquor cools, and is then either
washed with very cold water, and dried by a gentle heat, or it is dried
and sublimed in the manner already explained. The product of the
sublimation is extremely white and pure.
_Obs._ An economical and productive process; but, to ensure success, a
perfect mixture of the dry ingredients must be first made; as otherwise
the benzoin runs into a solid mass in the boiling water, and the operation
fails. _Prod._ "1 lb. of (gum) benjamin yields 1 oz. 6 dr. 2 scr. of
flowers." (Gray.)[150]
[Footnote 150: A quantity which, in our own experiments, we were never
able to obtain.]
_b._ (Process of Stoltze.) The benzoin is dissolved in 3 times its weight
of alcohol, the solution introduced into a retort, and a solution of
carbonate of soda in weak spirit-and-water, is gradually added, until all
the free acid present is neutralised; water, equal to about twice the
weight of the benzoin employed, is next poured in, and the alcohol removed
by distillation. The floating resin is now skimmed off the residual liquid
and washed with a little water, and the washings added to the contents of
the retort, which will deposit crystals of benzoate of soda on cooling,
and more by subsequent evaporation. From this salt the benzoic acid is
obtained by saturating the alkali with an acid (as the hydrochloric), and
by subsequent sublimation of the crude precipitated crystals.