Nitrum Pharm. Lond. & Edinb. Nitre, or Saltpetre: a neutral salt, formed by the coalition of the common vegetable fixt alkaline salt with a peculiar acid: of a sharp penetrating cooling taste: soluble in eight times its weight of very cold water, in less than thrice its weight of water temperately warm, and, as is said, in one third its weight of boiling water: concreting from its saturated solutions, on evaporation of a part of the fluid or a gradual diminution of the heat that kept it disslved, into colourless transparent crystals, which in figure are hexagonal prisms terminated by pyramids of the same number of sides: melting thin as water in a moderate heat: when heated to ignition, deflagrating, on the contact of any inflammable sub-stance, with a bright flame and a considerable hissing noise; and leaving, after the detonation, its fixed alkaline salt, the acid being destroyed in the act of accension.

The origin of nitre, or rather of the acid which makes the characteristic part of nitre, is unknown. Thus much only is known with certainty, that common waters, both atmo-spherical and subterraneous, often contain a little of this acid in combination with earthy or other bodies, so as to yield, by crystallization, on supplying the vegetable fixt alkali, a perfect nitre: and that when animal and vegetable sub-stances, mixed with porous absorbent earths, have lain exposed to the air till they are thoroughly rotted, they are found in like manner to contain a small portion of nitre or of nitrous acid, so as to give out a little nitre to water, either without addition, or on being supplied with the proper alkaline basis. On this foundation, some nitre is prepared in different parts of Europe: but the greatest quantities are the produce of the East Indies; the means by which it is there so plentifully obtained, or whether it is a natural or artificial production, have not yet, so far as I can learn, been revealed.

Nitrum Fixum

Nitre, as brought into the shops, has generally a greater or less admixture of sea salt; from which it is purified, by dissolving it in boiling water, and, after duly evaporating the filtered solution, setting it in a cold place to crystallize. The more impure brown nitre requires repeated dissolution and crystallization: to promote the purification, it is commonly disslved in lime-water, or the solution suffered to percolate through quicklime or a mixture of quicklime and wood ashes. It is observable that nitrous solutions differ from those of most other salts in contracting no pellicle in evaporation: if a solution of rough nitre, containing sea salt, be boiled down till a pellicle appears, or till a part of the salt begins to concrete and fall to the bottom, all that thus separates is said to be sea salt, boiling water keeping far less of this salt dissolved than it does of nitre: but if the liquor be now poured off, though it should still retain a quantity of the sea salt, only the nitre will crystallize in cooling, sea salt continuing dissolved in nearly as little water when cold, as was sufficient to keep it dissolved when boiling.

Nitrum purificatum

Ph. Lond

This salt is one of the principal medicines of the antiphlogistic class; of general use in disor-ders accompanied with inflammatory symptoms whether chronical or acute, and as a corrector of the inflammation or irritation produced by stimulating drugs. Hoffman thinks it has an advantage above the refrigerants of the acid kind, in not being liable to coagulate the animal juices; solutions of it mingling with or dissblving recent thick blood, and in some degree preserv-ing it from coagulation as well as corruption; at the same time changing its colour, when dark or blackish, to a crimson, an effect which it produces also, in a less degree, upon the fleshy parts of dead animals (a). It retards likewise the coagulation of milk, but seems, from Stahl's account, to increase the consistence of thin serous humours; for he observes, that when used in gargarifms for inflammations of the fauces in acute fevers, it thickens the salival fluid into a mucus, which keeps the parts moist for a considerable time, whereas, when nitre is not added, a dryness of the mouth presently enfuesf (b).

This medicine generally promotes urine, and often gives relief in stranguries and heat of urine whether simple or proceeding from a venereal taint. It sometimes loosens the belly, particularly in hot dispositions: in cold phlegmatic temperaments it rarely has this effect, though given in very large doses: the diarrhoeas of acute diseases, and fluxes in other circumstances from an acrimony of the bile or inflammation of the intestines, have been frequently restrained by it. In high fevers, it often promotes a dia-phorefis or sweat; in malignant fevers, where the pulse is low and the strength greatly de-pressed, it impedes that salutary excretion and the eruption of the exanthemata; in consequence of its general power of diminishing inflammation and heat. It seems to be prejudicial in disor-ders of the lungs, though some (a) have ventured to prescribe it in haemoptyses.

(a) Hoffman, Defolium mediorum virtute, § 16. De medicament is felectioribus, § 13. De praeftantiffima nitri virtute, § 5. - We cannot, however, conclude much, from these kinds of experiments, in regard to the medical powers of nitre, or its effects on the animal fluids, whilst under the laws of the vital oeconomy.

(b) De ufu nitri medico, Menfis martius, Opufc. p. 569.

The usual dose of nitre, among us, is from two or three grains to a scruple; though in many cases it may be given with great safety, and to better advantage, in larger quantities. It has been said, that nitre loses, in being melted, half its weight of watery moisture, and recovers this weight again on being dissolved and crystal-lized (b) from whence it would follow, that one part of melted nitre is equivalent to two of the crystals: but there was probably some mis-take in this experiment, for I have repeated it with different parcels of nitre, and never found the loss to be so much as one twentieth of its weight.

(a) Riverius, Cent. i. obf. 83. Stahl, ubi fupra, & Obferv. chym. phyf. med. curios. p. 464. Tralles, Virium terreis afcriptorum examen, p. 246. Dickson, Lond. med. obf. iv. 106. This last writer ventures to assert, that he can depend upon an electuary of conserve of roses and nitre in the cure of an haemoptoe almost equally with bark in an intermittent.

(b) Geoffroy, Memoires de l'acad. des scienc. de Paris, pour I'ann. 1717.