In pyrotechny, it is necessary to have the nitre in powder. Pulverizing it in a mortar is a tedious method, if a large quantity is required for use. There is an advantage, likewise, in the mode we will describe; because the saltpetre, besides being extremely fine, is made perfectly dry. Put into a copper kettle, whose bottom must be spherical, fourteen pounds of refined saltpetre, with two quarts or five pints of water. Put the kettle on a slow fire, and if any impurities rise and form a scum, remove them; keep constantly stirring with two large spatulas, till the water evaporates, and the nitre is reduced to a powder. This will be perfectly white, and almost impalpable. If it should boil too fast, remove the kettle, and set it on wet sand, which will also prevent the nitre from adhering to the pot. It should be kept in a dry place. This process of powdering saltpetre is performed on a large scale for the manufacture of gunpowder. _Sec. II. Of Nitrate of Soda._ This salt has been recommended in lieu of nitre, for preparing certain fire-works; but we confess, we can see no particular advantage in using it. It has the property of attracting humidity from the air, and on that account is rendered unfit for the manufacture of gunpowder. This salt is composed of nitric acid and soda. It was formerly called _cubic nitre_. It may be formed, very readily, by saturating nitric acid with soda, and evaporating the solution. It crystallizes in rhomboidal prisms. It may be formed more economically, by mixing together the solutions of nitrate of lime and sulphate of soda, filtering the mixture, and evaporating the filtered liquor. It will be sufficient to observe, that it deliquesces, or absorbs moisture, and in the fire, that its phenomena are the same as those of nitre. It does not melt so readily. Used in the same proportion as nitre, it will form a gunpowder, which soon, however, spoils by exposure. It will, like nitre, communicate a yellow colour to the flame of alcohol. Experiments were made with this salt, with the view to the fabrication of gunpowder, by MM. Bottée and Riffault. Their conclusions, as we have stated, may be seen in their work on _gunpowder_. Professor Proust says, that five parts of nitrate of soda, with one of charcoal, and one of sulphur, will burn three times as long as common powder, so as to form an economical composition for fire-works. The _cubic nitre_, and the _nitrum flammans_ were known, and so called, by the older chemists. The former we have seen, is the nitrate of soda, and the latter, is a combination of nitric acid and ammonia. Nitrate of soda, consists of 6.75 acid + 3.95 soda. Nitrate of ammonia possesses the property of exploding; and, when exposed to a temperature of about six hundred degrees, is decomposed, furnishing the nitrous oxide, called also the protoxide of azote, and exhilarating gas, besides water. Nitrate of ammonia is composed of 6.75 acid + 2.13 ammonia + 1.125 water.