Nitre, or Salt - petre, is a species of salt, which, in Persia and the East Indies, is extracted from certain native earths. It is likewise artificially produced in several parts of Germany, Hungary, and especially in France; either from the rubbish of old clay-walls and ceilings, or from animal and vegetable matters suffered to undergo putrefaction, which is promoted by the addition of ashes and of lime ; when the whole is exposed for a considerable time to the access of the air, in a direction from north to south.

Nitre is of a sharp, bitterish, penetrating taste, followed by a sensation of coldness. When pure, it dissolves in about six times its weight of water, and, on evaporating the latter, concretes into transparent crystals. It easily melts in the fire ; where it deflagrates with a bright flame, accompanied with a crackling noise, and afterwards deposits a large portion of alkaline earth.

Salt-petre is of great utility both in the arts and in medicine. Its spirit, known under the name of AQUA - FORTIS, is extensively employed both in dyeing, and in refining, as well as for other purposes, the principal of which we have- already stated.

Purified nitre is prescribed with advantage in numerous disorders : it is usually given in doses of from two or three grains to a scruple ; being a very cooling and resolvent medicine, which, by relaxing the spasmodic rigidity of the vessels, promotes not only the secretion of urine, but at the same time insensible perspiration, in febrile disorders ; while it allays thirst, and abates heat ; though in malignant cases, in which the pulse is low, and the patient's strength exhausted, it produces contrary effects.

When combined with the Peruvian bark, nitre affords an useful corrective to that drug in the cure of spreading gangrenes ; as it prevents the additional heat which the bark frequently occasions : so that the efficacy of the latter is increased by the antiseptic quality of the former. But this cooling salt should never be administered in cases where the violence of the fever depends on bilious or putrid impurities in the abdomen; and where the patient is subject to hemorrhages or fluxes of blood, arising from a vitiated state of the fluids. On the contrary, salt-petre will be most beneficially used in acute rheumatisms, inflammatory fevers, and even in those hemorrhages arising from congestions of the blood in general, or from a plethoric state.

With respect to the antiseptic properties of nitre, in domestic economy, we refer to the articles Beef; Butter (vol. i. p. 405) ; Pickling; and Pork.