ACIDUM BENZOICUM. L.E.D.
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.