Nitrate of potassium of commerce, purified, if necessary, by crystallisation from solution in distilled water.

Characters. - In white crystalline masses or fragments of striated six-sided prisms, colourless, of a peculiar cool saline taste.

Reactions. - Thrown on the fire it deflagrates; warmed in a test-tube with sulphuric acid and copper wire it evolves ruddy fumes (nitrate). Its solution gives the reactions of potassium (p. 603).

Impurities. - Sulphates and chlorides, which are detected by the usual tests (v. p. 594).

Dose. - 10 to 30 grains.

Preparations.

B.P. Argenti et Potassii Nitras. U.S.P. Argenti Nitras Dilutus.

U.S.P. Charta Potassii Nitratis. Nitrate of Potassium Paper. Unsized paper dipped in a 20 per cent. solution of nitrate of potassium and dried.

Action. - In large doses, nitrate of potassium will produce death by gastro-enteritis, with vomiting, weakness, and arrest of the circulation, due partly to the reflex action of the drug, and partly to its direct action on the heart after absorption. When injected into the blood, it slows the pulse by lessening the irritability of the cardiac ganglia, lowers the temperature, and causes dyspnoea and death with convulsions. The convulsions are due to arrest of the heart, and consequent irritation of the brain by venous blood.

Uses. - Nitrate of potassium gives up its oxygen readily, and paper dipped in a strong solution of it (Charta potassii nitratis, U.S.P.) and then dried, may be burnt in a plate, and the fumes inhaled, in asthma. It has been suggested that among the products of combustion the nitrite of potassium is the most efficacious. A ball of nitre, kept in the mouth and allowed to melt slowly away, gives relief in cases of relaxed sore-throat. It has been used internally in acute bronchitis, spasmodic asthma (either internally or by inhaling its fumes), and in dyspepsia with congestion of the mucous membranes. Generally it is avoided in inflammation of the stomach, intestine, kidneys, and bladder, on account of its local irritant action. On account of its action on the heart it has been given in haemoptysis and other haemorrhages. On account of its supposed action on the blood it was, and is, used in inflammation, fevers, and exanthemata. As an alterative it is used in scurvy, purpura, rheumatism, and gout. Twenty grains of nitre with thirty of potassium bicarbonate taken in the morning in a large soda-water tumbler full of water will sometimes prevent the onset of a gouty paroxysm, and will also remove the headache consequent upon a debauch. Nitrate of potassium is also used as a diuretic in cases of dropsy and gonorrhoea, and as a stimulant to the bladder in cases of incontinence of urine.