An acid prepared from nitrate of potassium or nitrate of sodium by distillation with sulphuric acid and water, and containing 70 per cent. B.P., or 69.4 U.S.P., by weight of nitric acid, HNO3, corresponding to 60 per cent. of anhydrous nitric acid, N2O5.

Characters. - A colourless liquid, having a specific gravity of 1.42. Boiling-point, 250° F. When exposed to the air it emits an acrid, corrosive vapour.

Reactions. - If it be poured over copper-filings, dense, red vapours are immediately formed; but if the acid be mixed with an equal volume of water, and then added to the copper, it gives off a colourless gas, which acquires an orange-red colour as it mixes with the air, and which, if it be introduced into a solution of sulphate of iron, communicates to it a dark purple or brown colour, due either to solution of N2O2 in the sulphate or combination with it. If submitted to distillation the product continues uniform throughout the process.

Impurities. - Weaker or stronger acid, sulphuric or hydrochloric acids, fixed impurities.

Tests. - It leaves no residue when evaporated to dryness (no fixed impurities, as iron, lead, etc.). Diluted with six times its volume of distilled water it gives no precipitate with chloride of barium or nitrate of silver (absence of sulphuric or hydrochloric acids).

Preparations Containing Free Nitric Acids

B.P.

Dose.

Acidum Nitricum Dilutum

(acid 1, with about 4 of water by measure)............................

10-30 m.

Acidum Nitro-hydrochloricum

Dilutum..................................

Liquor Ferri Pernitratis....................

,, Hydrargyri Nitratis Acidus

Unguentum Hydrargyri Nitratis

U.S.P

Acidum Nitricum Dilutum (acid 1, water 6 by weight; 11/2, and 12 1/2 by measure).

Acidum Nitrohydrochloricum.

„ „ „ Dilutum.

Action. - It is an exceedingly powerful caustic, and destroys the tissues, but, unlike sulphuric acid, it forms, to some extent, a barrier to its own action by coagulating the albumin with which it meets. When swallowed, it may not only produce the symptoms of irritant poisoning already described (p. 395), but the vapour, getting into the larynx, may cause spasm of the glottis, and death from suffocation, or may produce intense bronchitis.

Uses. - Nitric acid is applied externally to destroy chancres, warty growths, and haemorrhoids; to the surface of phagedenic ulcers; and to bites of snakes or rabid dogs, in order to destroy the virus and prevent its absorption. Internally the dilute acid is used to quench thirst in febrile conditions, like other dilute acids, and it is useful in cases of dyspepsia. It is supposed to have an action upon the liver, and certainly appears to be of use in cases of so-called biliousness. When absorbed it has an astringent action, and is exceedingly serviceable in diminishing the secretion from the lungs in bronchitis and in the sub-acute exacerbations of phthisis. It is also employed in cases of syphilis occurring in debilitated subjects, where mercurials are not well borne. It diminishes the phosphatic deposits in the urine, and, in a dilute condition, has been injected into the bladder in order to dissolve calculi already formed.