Characters. - A golden yellow, fuming, and very corrosive liquid, having a strong odour of chlorine and a strongly acid reaction. By heat it is wholly volatilised. It readily dissolves gold leaf, and a drop added to a test solution of iodide of potassium liberates iodine abundantly.

Preparation. - By mixing nitric acid (4) with hydrochloric acid (15 parts), and, when effervescence has ceased, preserving it in glass-stoppered bottles, which should not be more than half-filled and kept in a cool place.

Acidum Nitrohydrochloricum Dilutum, B. and U.S.P.

Dilute Nitrohydrochloric Acid. - It contains free chlorine, hydrochloric, nitric, and nitrous acids and other compounds, dissolved in water.

Preparation. - By mixing nitric acid 3, hydrochloric 4, water 25, by measure, and allowing it to stand for 14 days before it is used, B.P. By diluting nitrohydrochloric acid (1) with water (26 parts by weight, U.S.P.). The proportions of the components U.S.P. are, by measure, nitric acid 3, hydrochloric acid 13 1/2, water 80.

Dose. - 5 to 20 minims.

Use. - This, like nitric acid, is supposed to have a special action upon the liver. It is sometimes used, in the form of baths or compresses, in hepatic disorders, and is frequently given in cases of dyspepsia, biliousness, and jaundice. When given before meals it seems to check acidity in the stomach, and it is very useful in removing headache situated in the forehead, just above the eyebrows, and unaccompanied by constipation (Fig. 165). If the ordinary diluted acid fails, a few drops of the strong acid diluted with water at the time it is taken may succeed, and if this fails a mixture evolving oxides of nitrogen and oxides of chlorine may prove successful.1

Fig. 165.   Showing the position of the frontal headaches relieved by acids and alkalis in the absence of constipation. The lower is relieved by acids, the upper by alkalis before meals.

Fig. 165. - Showing the position of the frontal headaches relieved by acids and alkalis in the absence of constipation. The lower is relieved by acids, the upper by alkalis before meals. The lower one also indicates the occasional position of headache caused by straining the eyes.