Nitre may be commodiously taken in the form of troches. The London college direct one part of the purified salt to be ground with three parts of fine sugar, and one and a half of gum tragacanth in powder, and the mixture made up with water. In this and all other solid forms it is accompanied, however, with one inconvenience; being liable, especially when the dose is considerable, to occasion a pain or un-eafinefs at the stomach, which can be prevented only by plentiful dilution. A liquid form is therefore, in general, the most eligible, and may be easily rendered grateful by a proper addition of sugar.

The chemists have thought to improve the virtue of nitre, by deflagration with a small portion of sulphur: they melt the nitre, in a crucible, and gradually sprinkle on it one twenty-fourth its weight of flowers of sulphur: when the deflagration is over, they pour out the melted salt into clean, dry, warm brass moulds, so as to form it into little cakes. In this process, a part of the acid of the nitre, and the inflammable principle of the sulphur, detonating together, are both destroyed; while that part of the alkali of the nitre, which is thus forsaken by its acid, unites with the acid of the sulphur, which is the same with that of vitriol, into a new neutral salt, the same with vitriolated tartar; and the preparation is found to be no other than a mixture of unchanged nitre with a small portion of this vitriolated salt. If the nitre and sulphur be taken in equal quantities, the mixture injected by a little at, a time into a red-hot crucible, and kept in till all detonation ceases, nearly the whole of the nitre will thus be changed; and the remaining salt, purified by solution in water, proves almost wholly the same with vitriolated tartar.

Trochifci e nitro Ph. Lond.

Sal prunellas.

Crystallus mineralis.

Sal polychreft. Ph. Ed.

The same salt is produced by pouring gradually on nitre the pure acid of vitriol or sul-phur: this acid, uniting with the alkali, disen-gages the acid of the nitre, which begins to exhale, immediately on mixture, in yellow or red fumes, and may be collected by distillation in a glass retort with a moderate fire. Two parts of nitre to one of vitriolic acid, is a proper proportion for disengaging all the acid of the nitre; the remaining salt is nearly a pure vitriolated tartar. If three parts of nitre be used to one of the vitriolic acid, a part of the nitre remains unchanged: on dissolving the whole residuum in hot water, and setting the filtered solution to cry-stallize, the vitriolated salt shoots first, greatest part of the nitre continuing dissolved.

The nitrous spirit is obtained also by distillation in a strong fire with vitriol in substance; the vitriol parting, when strongly heated, with its own acid, which then acts upon the nitre and extricates its acid in the same manner as when the pure vitriolic acid is used. The spirit thus distilled, called aqua fortis, is more phlegmatic than the preceding, in proportion as the vitriol employed contains more phlegm than the oil of vitriol: it is likewise liable to an admixture of the vitriolic acid, more or less of which is generally forced over. The proportion usually directed is three parts of nitre, three of green vitriol uncalcined, and one and a half of the same vitriol calcined. The ingredients are well mixed together, the distillation performed in an earthen retort or an iron pot fitted with an earthen head and a receiver, and continued so long as any red vapours arise. *The colleges of London and Edinburgh have now discarded this kind of preparation, and direct a weaker nitrous acid to be made by mixing equal parts of the strong acid and pure water.

Acidum ni-trofum vulgo spiritus nitri glauberi Ph. Ed.

Acidum ni-trofum Ph. Lond.

Aqua fortis.

The nitrous spirit, usually dislilled from rough nitre, contains often an admixture of the marine acid as well as of the vitriolic. The first is discovered, and separated, by dropping in a little solution of silver, the latter by a solu-tion of chalk or any other calcareous earth, made in the pure nitrous acid; the silver ab-sorbing the marine acid, and the chalk the vitriolic, and forming with those acids, respec-tively, indissoluble concretes, which immediately render the liquor milky, and on (landing settle to the bottom. The solutions are to be cautioufly and slowly dropt in, so long only as they continue to produce a milkinefs:: in case of an excess in their quantity, if the spirit is required perfectly pure, it is to be rectified by redistillation.

By the property on which the above method of purification depends, the nitrous spirit may be readily distinguished from the other two mineral acids. By the red or yellowish red colour of its fumes; by its forming with one fourth its weight of fal ammoniac, or with sea salt or its acid, a menstruum that perfectly dissolves gold; by its deflagrating on the contact of any inflammable matter, when heated to ignition, whatever other body it be previously combined with; it may with certainty be distinguished both from those and from every other known species of acid.

This acid has been sometimes given as a diuretic, from two or three to fifty drops, diluted largely with water; but its principal use is in combination with other bodies.

Acidum nitrofum tenue Ph. Ed. - dilutum Ph. Lond.

Combined with vegetable fixt alkalies, it reproduces common nitre. With the mineral fixt alkali, or soda, it composes a species of nitre in some respects different from the common, cryftallizing not into a prifmatic but a cubical figure; with volatile alkalies, a subtile pungent salt remarkable for its solubility in spirit of wine:*(a) of these two compounds, the medicinal qualities are little known, though they should seem to be well deserving of inquiry.