with excess of acid, improperly called _cream of tartar_, which in our
new nomenclature is named _acidulous tartarite of potash_; by a second
or equal degree of saturation a perfectly neutral salt is formed,
formerly called _vegetable salt_, which we name _tartarite of potash_.
With soda this acid forms tartarite of soda, formerly called _sal de
Seignette_, or _sal polychrest of Rochell_.
SECT. XXVII.--_Observations upon Malic Acid, and its Combinations with
the Salifiable Bases[45]._
The malic acid exists ready formed in the sour juice of ripe and unripe
apples, and many other fruits, and is obtained as follows: Saturate the
juice of apples with potash or soda, and add a proper proportion of
acetite of lead dissolved in water; a double decomposition takes place,
the malic acid combines with the oxyd of lead and precipitates, being
almost insoluble, and the acetite of potash or soda remains in the
liquor. The malat of lead being separated by decantation, is washed with
cold water, and some dilute sulphuric acid is added; this unites with
the lead into an insoluble sulphat, and the malic acid remains free in
the liquor.
This acid, which is found mixed with citric and tartarous acid in a
great number of fruits, is a kind of medium between oxalic and acetous
acids being more oxygenated than the former, and less so than the
latter. From this circumstance, Mr Hermbstadt calls it _imperfect
vinegar_; but it differs likewise from acetous acid, by having rather
more charcoal, and less hydrogen, in the composition of its radical.
When an acid much diluted has been used in the foregoing process, the
liquor contains oxalic as well as malic acid, and probably a little
tartarous, these are separated by mixing lime-water with the acids,
oxalat, tartarite, and malat of lime are produced; the two former, being
insoluble, are precipitated, and the malat of lime remains dissolved;
from this the pure malic acid is separated by the acetite of lead, and
afterwards by sulphuric acid, as directed above.
TABLE _of the Combinations of Citric Acid, with the Salifiable Bases, in
the Order of Affinity(A)._
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