Preparation

Benzoic acid is by both Pharmacopoeias directed to be procured by sublimation. it is the odorous product obtained in this way that is intended, and not the chemically pure benzoic acid, which is inodorous, or that procured from the urine of animals, which, as found in the shops, has an odour, but very unlike that of the officinal acid. The true officinal 'substance is procured by sublimation from benzoin. For the method of conducting the process, the reader is referred to the U. S. Dispensatory.

Properties and Composition. As officinally prepared, benzoic acid is in beautifully white, soft, feathery, shining crystals, having a highly fragrant odour, arising from a portion of volatile oil that is given over along with it, and a warm, somewhat pungent, acidulous taste. it is fusible by heat, and readily vaporized, sending forth pungent, suffocating fumes. it is also inflammable. Boiling water dissolves a small proportion, which is deposited upon cooling; it is wholly dissolved by alcohol, the fixed oils, and alkaline solutions. The crystallized acid consists of one equivalent of a compound radical called benzyle, one of oxygen, and one of water.

Medical Effects and Uses

Benzoic acid is locally irritant, stimulant to the system, and perhaps expectorant. it is upon this acid probably, or the analogous cinnamic acid, that the balsams depend mainly for their virtues, and especially for the effects they produce by fumigation. But it will be remembered that it is the officinal acid which we are now considering. it is, however, very seldom used internally except as an ingredient of the camphorated tincture of opium, or paregoric, of which it is a constituent.

I have occasionally employed the acid in cases of phosphatic lithia-sis, with the object of dissolving the phosphates deposited by the urine, and, in some cases, with striking results, so far as the object aimed at was concerned. Though it is not impossible that the impregnation of the urine, resulting from the use of the acid, may sometimes prove serviceable by a stimulant or alterative influence upon the diseased surfaces, yet it was not with that object that I have prescribed it, as there are other medicines more efficacious. From the experiments of Dr. Garrod and Mr. Keller, it appears that, when benzoic acid is taken internally, the urine becomes impregnated with the soluble hippuric acid, into which it is probable that the benzoic acid is converted. The urine may thus be kept in an acid state whenever desired, and consequently made to hold the phosphates in solution. The acid has also been given for nocturnal incontinence. The dose is from ten to thirty grains, which may be conveniently administered with two parts of borax, or four of phosphate of soda, by which it is rendered soluble in water.

Two of the benzoates have of late years been introduced into medical use, and appear to merit a brief notice.

Benzoate of Ammonia (Ammoniae Bbnzoas, Br.) is an officinal of the British Pharmacopoeia, which directs it to be prepared by dissolving two avoirdupois ounces of benzoic acid, in three fluidounces of solution of ammonia, previously mixed with eight fluidounces of distilled water, evaporating the solution at a gentle heat, and setting aside to crystallize. Thus prepared, the salt is in minute, white, glistening, very thin, four-sided plates, with a feeble odour of benzoic acid, a bitter, saline, and somewhat balsamic taste. it sublimes without residue, is soluble in water and alcohol, and deliquescent in the air. it is the neutral benzoate, consisting of one eq. of ammonia, one of benzoic acid, and two of water. When heated, it is converted into the acid benzoate.

In its effects on the system benzoate of ammonia is a slightly stimulant diuretic, operating especially by the benzoic acid it contains, as its ammonia is quickly neutralized by the gastric acids. The benzoic acid is changed in the system into hippuric acid, in which form it is eliminated by the kidneys. it has been used internally for the removal of the gouty deposits of urate of soda about the joints, which it is supposed to effect by the great solubility of the salt which its acid forms with soda. it may also be used as a gentle diuretic, and as a solvent of phosphatic deposits by means of the hippuric acid, into which the benzoic is changed. it is probably through the same agency that it sometimes seems to act advantageously in chronic inflammation of the urinary passages. The dose is from 10 to 30 grains, which, if thought desirable, may be much increased, as the salt has not been found poisonous in any quantity hitherto given.

Benzoate of Soda (Sodae Benzoas), though not yet recognized by the officinal standards, has been remedially employed. it may be made by saturating a solution of benzoic acid by carbonate of soda, evaporating, and crystallizing. it crystallizes in needles, has a sweetish, pungent taste, is efflorescent, and is very soluble in water, but only slightly soluble in alcohol, even though boiling hot {Berzelius). it has the same remedial properties as the benzoate of ammonia, and may be used in the same diseases, and the same doses.