BENZOIC ACID. — Benzoic acid is a peculiar principle and is had from many different sources. It is made by oxida tion of toluene with nitric acid, which is the most common form. It is derived, also, from the different benzoins, Asiatic and American; from urine, etc. The best, however, is that made from Siamese benzoin, technically known as pheni formic acid, and presents white, pearly plates or needles, though with age and exposure to light it sometimes acquires a slight-yellowish tinge. It possesses an agreeable aromatic odor and taste, and is soluble in the proportions of 1 to 500 in cold and 1 to 15 in boiling water; 1 to 2 in alcohol; 1 to 3 in ether; 1 to 7 in chloroform; 1 to 10 in glycerin. Borax or sodium phosphate increases its solubility in water. With different bases it forms very soluble salts.
Preparations and Doses. — Benzoic acid, 10 to 30 grains.
Benzoate of ammonium, 10 to 30 grains.
Benzoate of bismuth, 10 to 20 grains. Benzoate of calcium, 5 to 15 grains. Benzoate of iron, 2 to 6 grains. Benzoate of lithium, 15 to 30 grains. Benzoate of mercury, for external use only.
Benzoate of potassium, 5 to 20 grains. Benzoate of sodium, 30 to 120 grains. Benzoate of zinc, for external use only. Physiological Action. — Externally benzoic acid and, in less degree, its salts are irritant, and the vapors when inhaled tend to bronchial irritation and catarrhal inflammation. Internally administered in ordinary therapeutic doses it exerts no untoward effects except, perhaps, to provoke a moderate amount of gastric irritation with resultant nausea and vom iting. Sometimes there is acceleration of the heart's action and of respiration.
Schreiber took in two days about `I, ounce of the acid, and experienced only a feeling of abdominal warmth, spread ing over the whole body, and accom panied by an increase of the pulse-rate amounting to 30 beats per minute; also increased reaction and excretion of phlegm, with slight disturbances of di gestion. H. C. Wood ("Principles and Practice of Therapeutics," ninth ed.).
Benzoic acid and the benzoates are eliminated mainly by the kidneys, partly as benzoic acid, but chiefly as hippuric acid. The exact method by which the latter acid is produced constitutes one of the great problems of physiological chemistry, though the change is gener ally presumed to take place in the kid neys; certainly it does not happen in the intestines or in the blood.
The benzoates generally, yet in less degree, evince much the same action as the acid. The ammonium salt borrows from its base a neutralizing action upon acids and increases the activity of the kidneys. Benzoate of bismuth resembles other salts of the same base. Calcium benzoate, as might be expected, com bines in a measure the action of both base and acid. As it is unofficial, and in little use or repute, it demands no further mention. The same remarks practically apply also to the iron salt. The lithia salt is supposed to possess a special affinity for uric acid and urea, dissolving the one and eliminating the other, but the claims made in this direc tion are by no means substantiated. It is eliminated by the kidneys the same as benzoic acid, but more frequently yields succinic instead of hippuric acid: a phenomenon that is most puzzling. Potassium benzoate presents nothing from a physiological stand-point that does not accrue to other salts, except it is more difficult of elimination than the sodium salt; the latter most closely re sembles the acid in its action, but is more readily absorbed and more con tinuous in its effects.
Therapeutics. — Benzoic acid exter nally employed is an antiseptic of con siderable value, and both benzoate of bismuth and benzoate of zinc have been lauded and exploited in connection with surgical dressings. All are practically unobjectionable and devoid of unpleas ant odor; hence may be made available when more acrid and unpleasant agents are inhibited. Indeed, there is little doubt, in antiseptic surgery benzoic acid might in a majority of instances be sub stituted for carbolic or salicylic acid with benefit. Friar's balsam—balsa mum trau maticum of the old pharmacopceias was formerly in great repute as a vul nerary, and the experiences of Mr. Bryant, of London, evidences its value: He, when confronted with a compound fracture or other severe wound, dresses with lint thoroughly saturated with this compound tincture of benzoin and main tains absolute quiet with non-removal of dressing for several days; and his results challenge those obtained by the most complicated antiseptic dressing. It is, perhaps, needless to remark that the value of the tincture, or "balsam," lies in its contained benzoic acid.