Prep. Certain soils in India contain nitrates of lime and potash; these, by being treated with wood ashes (carbonate of potash), yield nitrate of potash and carbonate of lime; the former is dissolved out and crystallized, and purified by re-solution and crystallization.
Prop. & Comp. Nitrate of potash forms six-sided prisms, transparent, striated, with a peculiarly cooling taste, soluble in water, not precipitated by chloride of barium or nitrate of silver; it fuses, but does not lose weight unless the heat is intense, when it gives off oxygen, and is converted into nitrite of potash, which last yields nitrous vapours when treated with sulphuric acid; deflagrates with heated charcoal, and forms carbonate of potash; when treated with sulphuric acid, it yields 85 per cent. of sulphate of potash; warmed in a test tube with sulphuric acid and copper filings, it evolves ruddy fumes (peroxide of nitrogen). Nitric acid can also be shown to be present by dissolving the salt in a little water, adding an equal bulk of sulphuric acid, and afterwards, when the mixture has cooled, a few drops of a solution of protosulphate of iron; a dark olive colour is produced, which is very characteristic. The solution acidulated with hydrochloric acid, gives a yellow precipitate with bichloride of platinum.
Therapeutics. Nitre is refrigerant and diuretic, it also produces some alteration in the condition of the blood, and a powerful sedative action upon the heart and vascular system. It is used in small doses as a refrigerant and diuretic in febrile affections, and to allay irritation of the mucous membrane of the stomach in inflammatory forms of dyspepsia; in large doses, as a vascular sedative in febrile affections, and especially in acute rheumatism. In dropsical affections, its action on the kidneys has sometimes proved useful.
Dose. 5 gr. to 20 gr. as a refrigerant and diuretic; 20 gr. to 30 gr. as a vascular sedative.
Adulteration. It may contain traces of sulphate or chloride; detected by chloride of barium and nitrate of silver: lime, if present, would yield a precipitate with oxalate of ammonia.