Saltpeter

Saltpeter, white, translucent, lustrous mineral composed of potassium nitrate, KNO₃. It crystallizes in the orthorhombic system in prismatic crystals, which have a hardness of 2 and a specific gravity of 2.1, and these crystals exhibit perfect domal cleavage. The mineral, which is also called niter, forms delicate crusts on the surfaces of rocks and stone walls, and occurs as a component of surface soil in Spain, Iran, Egypt, and India. In the U.S. it occurs in loose soil of the limestone caves of Kentucky, Tennessee, and the Mississippi Valley. Saltpeter is of commercial importance as a fertilizer, in the manufacture of glass, as a food preservative, and in some medicines as a diuretic. Saltpeter was once used in gunpowder and is now found in explosives, fireworks, and matches. In addition, this substance is employed in fluxes used in metallurgy. It is important as a source of nitrogen in the manufacture of nitrogen-containing compounds, particularly nitric acid, and as an oxidizing agent in many industrial chemical processes.

Chile saltpeter, or soda niter, is composed of sodium nitrate, NaNO₃. It occurs over vast areas in South America, particularly in Chile, in beds which vary in thickness from 15 cm to 3.6 m (6 in to 12 ft). The beds, called caliche, are interspersed with deposits of gypsum, sodium chloride and other salts, and sand. The caliche is quarried and purified in Chile before the Chile saltpeter is exported. In the U.S. small deposits are found in Nevada and California. Pure Chile saltpeter crystallizes in the rhombohedral system, forming white, semitransparent, lustrous crystals that are crystallographically similar to calcite. It has a hardness ranging from 1.5 to 2 and a specific gravity of 2.24 to 2.29, and exhibits perfect rhombohedral cleavage. Chile saltpeter deliquesces; that is, it absorbs water from the atmosphere, becomes moist, and gradually dissolves. It is used extensively as a fertilizer and in the manufacture of nitric acid. It is not used in the manufacture of gunpowder because of its deliquescence, but it is used in making the less abundant saltpeter.