_Benzoic Acid._ Vulgo, Flowers of Benzoin, or _Benjamin_.
QUALITIES. _Form_, small feathery crystals of a brilliant white colour,
which are not brittle, but possess a kind of ductility and elasticity,
and, on being rubbed in a mortar, assume the consistence of paste.
_Odour._ As generally met with, it possesses a peculiar aromatic smell,
but this depends upon the oily matter which adheres to it, for Mr. Guise
informs us, that on dissolving the benzoic acid in as little alcohol as
possible, filtering the solution, and precipitating by water, the acid
will be obtained pure, and void of smell, the odorous oil remaining
dissolved in the spirit. _Taste_, rather acrid and sour; _Specific
Gravity_, ·667. It is not altered by exposure to air. SOLUBILITY. Four
hundred parts of cold water dissolve but one, although the same quantity
of boiling water dissolves twenty parts, nineteen of which separate on
cooling; in alcohol it is soluble in a much greater proportion.
MEDICINAL USES. It is said to be stimulant and expectorant; in certain
cases of tracheal irritation, a pill, composed of two grains of Benzoic
acid, and three of Extract of Poppy, has been found serviceable.
OFFICINAL PREPARATIONS. _Tinctura Camphoræ Composita_, L.D. _Tinct: Opii
Ammoniat:_ E. IMPURITIES. The crystals ought not to be discoloured; they
should dissolve without residuum in alcohol, and when subjected to heat,
ought to be entirely volatilized.
Although this acid is commonly procured from the resinous substance
called Benzoin, yet it exists extensively in other vegetable, and in
some animal substances. In the Tonca bean (_Dipterix odorata_) it is
frequently to be seen beautifully crystallized on its surface. It exists
also in vanello; cinnamon; cloves; ambergris; in the urine of children,
and sometimes in that of adults, and always in that of quadrupeds living
on grass and hay.
ACIDUM CITRICUM. (_Crystalli_) Citric Acid.
_Concrete Acid of Lemons._
QUALITIES. _Form_, crystals which are right rhombic prisms, white,
semi-transparent, and persistent. _Taste_, extremely acid, almost
caustic. SOLUBILITY, f℥j of cold water dissolves ʒx, but of boiling,
℥ij. ʒx of the crystals dissolved in a pint of water, are about
equivalent to one pint of lemon juice, the solution however if kept is
liable to spontaneous decomposition. The following table of equivalents
may be found of practical use; the author is aware that they do not
exactly agree with the proportions of Dr. Haygarth, but they are the
results of careful and repeated experiments, and as such they are
submitted with confidence.
EQUIVALENT PROPORTIONS OF CONCRETE CITRIC ACID AND LEMON JUICE,
NECESSARY FOR THE NEUTRALIZATION OF ALKALINE SALTS.
┌──────────────────────┬──────────────────────┬───────────────────────┐
│ Citric Acid. │ Lemon Juice. │A Scruple of Alkalies. │
├──────────────────────┼──────────────────────┼───────────────────────┤
│ grs. x. │ fʒiij │ Carbonate of Potass. │
├──────────────────────┼──────────────────────┼───────────────────────┤
│ grs. xv. │ fʒiiij │ Sub-Carbonate of │
│ │ │ Potass. │
├──────────────────────┼──────────────────────┼───────────────────────┤
│ grs. xxv. │ fʒvij │ Sub-Carbonate of │
│ │ │ Ammonia. │
└──────────────────────┴──────────────────────┴───────────────────────┘
These alkaline citrates are decomposed by the _oxalic_, _tartaric_, and
the stronger _mineral acids_, and by the solutions of _lime_ and
_barytes_. _Form. 107, 123, 137, 168._
Citric acid decomposes the following salts, _viz._ _The Alkaline,
Earthy, and Metallic Carbonates_; _the Alkaline and Metallic Acetates_;
_the Sulphurets of Earths and Alkalies, and Alkaline Soaps_. It is also
incompatible with _Tartrate of Potass_, which it converts into citrate
and super-tartrate of potass. It curdles the milk of most animals, but
it does not produce that effect on human milk, whether applied hot or
cold. ADULTERATIONS. _Tartaric Acid_, with which it is sometimes mixed,
may be detected by adding to the solution an excess _of Potass_, which
will instantly form with it an insoluble super-tartrate, and precipitate
in granular crystals, or, if a little of the suspected acid be saturated
with potass, and then boiled with a dilute solution of muriate of
Platinum, if tartaric acid be present, a black protoxide of Platinum
will be precipitated. If we add the tartrate of potass for this purpose,
we may be deceived, for the citric acid, by neutralizing a portion of
its base, will convert the remainder into super-tartrate. See _Potassæ
Tartras_. _Sulphuric Acid_ is known by the acetate of lead producing a
precipitate, insoluble in nitric acid. _Muriatic Acid_ may be discovered
in the same manner, substituting only an acidulous solution of nitrate
of silver for the acetate of lead. The presence of _Oxalic Acid_ may be
inferred, if the solution, when added to that of sulphate of lime,
produce a precipitate. Malic acid has the power of precipitating silver,
mercury, and lead, from their solutions in nitric acid, but no doubt or
difficulty can arise from this circumstance, for the fact of its forming
a soluble salt with lime will prevent every chance of accidental
intrusion, and its price at once secures us against its fraudulent
introduction; it might moreover be easily detected by throwing the
suspected precipitate upon burning coals, when it would be decomposed.
Where the presence of _lime_ is suspected, it may be known by dissolving
some of the crystals in water, saturating the solution with ammonia, and
then treating it with the oxalate of that alkali, which, if lime be
present, will immediately separate it in a palpable form. The juices of
many other fruits besides the lemon and lime, will furnish the citric
acid in abundance, and may be obtained from them by a similar process;
e. g. VACCINIUM OXYCOCCUS, the _Cranberry_; PRUNUS PADUS, the _Bird’s
Cherry_; DULCAMARA SOLANUM, the berry of the _Nightshade_; CYNOSBATUS,
vel ROSA CANINA, the hep or fruit of the _Wild Briar_. There are many
plants whose juices contain combinations of the _Citric_ and _Malic_
acids in considerable abundance, such as FRAGARIA VESCA, the _Wood
Strawberry_, and the common _Raspberry_; RIBES RUBRUM the _Red
Gooseberry_; VACCINIUM MYRTILLUS, the _Bilberry_; CRATÆGUS ARIA, the
_Hawthorn_; PRUNUS CERASUS, the _Black Cherry_, &c. This fact is
interesting, since the juices of such fruits have been long known to
possess the property of dissolving the _tartareous_ incrustations on the
teeth.