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Acidum Boricum (U. S. P.)—Boric Acid.

Botanical name:

Other tomes: Petersen

FORMULA: H3BO3. MOLECULAR WEIGHT: 61.78
SYNONYMS: Boracic acid, Orthoboric acid, Acidum boracicum.

Source, History, and Preparation.—This acid is found in nature in several species of plants, in the waters of the sea, and such mineral springs as Vichy, Wiesbaden, and Aix-la-Chapelle, as well as in several of the hot springs of America. It is found in nature in minerals, and especially in the niter regions of Chili and Peru, where it occurs as borocalcite. As a constituent of natural borax it has been discovered in enormous quantities in Borax Lake, California, and it also occurs in the same natural combination as tincal in the dried-up, saline lagoons or lake-beds of Thibet. Owing to the recent development of the borax industry along the Pacific coast, the major part of the boric acid consumed in the United States is now derived from the California deposits, while the greater part of the world is supplied from the extensive natural products from the volcanic rocks of Tuscany and the isle of Volcano, of the Lipari group, north of Sicily, where free boric acid occurs naturally under the name of sassoline.

On the volcanic mountain-sides of Tuscany are to be seen innumerable fissures which throw out jets of steam, called suffioni, charged with various gases and boric acid. Surrounding one or more of these crevices (also called suffioni or soffioni) may be seen either a natural basin or lagoon, or one constructed of masonry. Several of these circular lagoons are arranged on the mountain-side and made to connect with each other by a series of canals. Cold water from a mountain spring is then allowed to fill these basins, and receives the steamy vapors which either condense and flow into them, or else shoot up into them from the bottom. These jets constantly breaking into the water heat it and yield to it boric acid. This acid solution is then allowed to pass down the declivity into another lagoon and so on until, by receiving an added amount from each basin, it becomes saturated, when it is conducted into leaden pans, where it is evaporated to such an extent that when drawn off into wooden vats and cooled, it will deposit crystals of crude boric acid. This acid is then shipped to various countries where it is converted into borax either by boiling it with a soda solution, or fusing it with calcined carbonate of sodium. The latter method is usually employed. The medicinal boric acid is then made from the borax so produced. Boric acid was first made by Homberg (1702), after whom it was known as the "sedative salt of Homberg" (sal sedativum Hombergi). The medicinal acid maybe prepared as follows: Take borax 10 parts, boiling water 24 parts. Dissolve the borax in the water and filter while hot. Mix with the filtrate 6 parts of chlorhydric acid and allow the mixture to stand in a cool place for 24 hours. Collect the resultant crystals upon a strainer or in a funnel, wash them with cold water, and dissolve them again in 5 parts (by weight) of boiling distilled water, and allow the solution to stand for a few days. Re-collect the crystals, wash with cold water to free them from traces of foreign matter, and dry them in a moderately warm situation.

Description.—Boric acid occurs, according to the Pharmacopoeia, in "transparent, colorless scales, of a somewhat pearly lustre, or, when in perfect crystals, six-sided, triclinic plates, slightly unctuous to the touch, odorless, having a faintly bitterish taste, and permanent in the air. Soluble at 15° C. (59° F.), in 25.6 parts of water, and in 15 parts of alcohol; also soluble in 10 parts of glycerin. Addition of hydrochloric acid increases its solubility in water. When heated to 100° C. (212° F.), boric acid loses water, forming metaboric acid (HBO2), which slowly volatilizes at that temperature. Heated to 160° C. (320° F.), it fuses to a glassy mass of tetraboric (or pyroboric) acid (H2B4O7); at a higher temperature the fused mass swells up, loses all of its water, and becomes boron trioxide (B2O3), which fuses into a transparent, non-volatile mass. From a boiling solution, boric acid readily volatilizes. The solution in alcohol or glycerin burns with a flame enveloped with a green-colored mantle"—(U. S. P.).

Boric acid has feeble acid properties. It dissolves in the essential oils. "An aqueous solution (1 in 50) of boric acid colors blue litmus paper red, but yellow turmeric paper brownish-red after drying, even when the solution had been acidulated with hydrochloric acid; this brownish-red color is changed to bluish-black by ammonia water. A 2 per cent aqueous solution of the acid should not be precipitated by barium chloride T.S. (absence of sulphate); silver nitrate T.S. with nitric acid (absence of chloride); ammonium sulphide T.S. (lead, copper, iron, etc.); ammonium oxalate T.S. (calcium); or sodium phosphate T.S. and ammonia water (magnesium). No odor of ammonia should be evolved by heating the acid with potassium or sodium hydrate T.S. In a solution of 1 Gm. of boric acid in a mixture of 1 Cc. of hydrochloric acid and 49 Cc. of water, 0.5 Cc. of potassium ferrocyanide T.S. should not at once produce a blue color (limit of iron). A fragment heated on a platinum wire (thoroughly cleansed by washing and heating until it no longer colors the flame), should not impart to the non-luminous flame a persistent yellow color (absence of sodium)"—(U. S. P.).

Action, Medical Uses, and Dosage.—Though used for the destruction of roaches and other insects, boric acid is generally without any marked action on the higher animals. When absorbed, however, from local applications to raw surfaces, or when injected into the pleural sac of man (5 per cent solution) death has resulted preceded by vomiting, singultus, and collapse, some cases exhibiting general erythema of the skin and diarrhoea, followed by bloody vomiting and increased activity of the kidneys, finally ending in complete renal inaction and death.

Applied to the cutaneous surface boric acid is wholly unirritating, and when an antiseptic and antipyic dressing for wounds is demanded it may be used with advantage. It is of value as a dressing for burns and scalds, a petrolatum ointment being the preferred form. Cloths dipped in a saturated solution may be continuously applied to dog bites. Certain aphthous conditions are benefited by its local application, and Prof. Locke directs for badly ulcerated diphtheria: Rx Boric acid 1 part; glycerin 30 parts. Mix. Sig. Apply locally. Ozena and other forms of nasal catarrh, as well as pharyngitis, are benefited by it.

Owing to the property of correcting fetor possessed by this drug, it has yielded efficient results in modifying the fetid eructation accompanying fermentative stomach disorders, and by its chemical action it corrects excessive alkalinity of the renal secretions resulting in ammoniacal urine and its consequent cystic irritation. Mucopurulent secretions, such as accompany gonorrhoea, vaginitis, cystitis, nasal catarrh, etc., are in a measure controlled by a solution of this acid. It is also one of the most efficient remedies for fetid perspiration, particularly of the axilla and feet. Its main use, however, outside of its application to wounds, has been in ophthalmic and aural practice. Though often an abused drug, if properly used in well selected cases it gives admirable results. It is signally useful in irritable eyes with redness and itching, and for the various forms of conjunctivitis, with much secretion, it gives excellent results. Where the conjunctival surfaces are thickened and velvety and the secretions copious and watery, the acid in impalpable powder may be dusted upon the parts, though the practice should not be long continued lest unpleasant dryness of the membranes should result (Foltz). Phlyctenular conjunctivitis and corneal ulceration are well treated in the same manner. For ciliary blepharitis, an ointment of from 5 to 10 grains of boric acid to 2 drachms of petrolatum forms a soothing and effectual application. The ointment has also been successfully applied in certain skin affections. The acid is combined with Lloyd's ergot by Foltz (Dynamical Therapeutics) in all conjunctival disorders as follows: From 10 to 30 drops of the ergot are added to a solution of 6 grains of boric acid in 1 fl℥ of water; of this 2 drops are instilled in the eye every 2 or 3 hours. In ear diseases this acid has proved of great service. In purulent inflammation of the middle ear with turgid membranes and slight discharge, apply it with ergot; if the membranes be pallid combine it with iodoform; if a moderately profuse, thin, acrid pus be discharged, calendula and boric acid give the best results. For polypoid growths and granulations it may be combined with salicylic acid and dusted upon the parts. In otorrhoea the powder should be frequently dusted upon the parts, and excellent results have attended this procedure. The internal dose of boric acid is from 1 to 15 grains; for external use from a 1 per cent to a saturated solution, according to the parts to which it is to be applied.

Specific Indications and Uses.Locally: Wounds; conjunctival disorders with velvety, thickened membranes and profuse secretion; otorrhoea; fetid perspiration. Internally: Fetid eructations, ammoniacal urine.

Related Product.—GLACIALIN. This is said to be a mixture of boric acid (6), biborate of sodium, and sugar of each (3) and glycerin (2) parts, and is employed to preserve foods and is used as an antiseptic.


King's American Dispensatory, 1898, was written by Harvey Wickes Felter, M.D., and John Uri Lloyd, Phr. M., Ph. D.



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