Three parts of nitre, one of sulphur, and one of fine saw-dust, well mixed, constitute what is called the powder of fusion. If a bit of base copper be fold ed up and covered with this powder in a walnut shell, and the powder be set on fire with a lighted paper, it will deto nate rapidly, and fuse the metal into a globule of sulphuret, without burning the shell.
If nitrate of potash b.e heated in a re tort, with half its weight of solid phospho ric or boracic acid, as soon as this acid begins to enter into fusion, it combines with the potash, and the nitric acid is ex pelled, accompanied with a small portion of oxygen gas and nitric oxide.
Silex, alumine, and barytes, decompose this salt in a high temperature by uniting with its base, as was observed when speaking of aqua fortis. The alumine will effect this even after it has been made into pottery.
The uses of nitre are various. Beside those already indicated, it enters into the composition of fluxes, and is extensively employed in metallurgy : it serves to pro mote the combustion of sulphur in fabri cating its acid ; it is used in the art of dy ing; it is added to common salt for pre serving meat, to which it gives a red hue ; it is an ingredient in some frigorific mix tures; and it is prescribed in medicine, as cooling, febrifuge, and diuretic, and some have recommended it mixed with vinegar as a very powerful remedy for the sea scurvy.
Nitrate of soda, formerly 'called cubic or quadrangular nitre, approaches in its properties the nitrate of potash ; but dif fers from it in being somewhat more so luble in cold water, though less in hot, which takes up little more.than its own weight ; in being inclined to attract mois ture from the atmosphere ; and in crys tallizing in rhombs, or rhomboidal prisms. It may be prepared by saturating soda with the nitric acid, by precipitating nitric solu tions of the metals, or oldie earths, except barytes, by soda : by lixiviating and crys tallizing the residuum of common salt distilled with three-fourths its weight of nitric acid ; or by saturating the mo ther waters of nitre with soda instead of potash.
This salt has been considered as useless; but professor Proust says, that five parts of it, with one of charcoal and one of sulphur, will burn times as long as common powder, so as to form an ceconomical composition for fire works.
Nitrate of strontian may be obtained in the same manner as that of barytes, with which it agrees in the shape of its crys tals, and most of its properties. It is much more soluble, however, requiring but four or five parts of water according to Vauquelin, and only an equal weight according to Mr. Henry. Boiling water dissolves nearly twice as much as cold. Applied to the wick of a candle, or add ed to burning alcohol, it gives a deep red colour to the flame. On this account it might he useful, perhaps, in the art of pyrotechny.
Nitrate of lime, the calcareous nitre of older writers, abounds in the mortar of old buildings, particularly those that have been much exposed to animal effluvia, or processes in which azote is set free. Hence it abounds in nitre beds, as was observed when treating of the nitrate of potash. It may also be prepared artifi cially, by pouring dilute nitric acid on carbonate of lime. If the solution br boiled down to a syrupy consistence, and exposed in a cool place, it crystallizes in long prisms, resembling bundles of nee dles diverging from a centre. These are soluble, according to Henry, in an equal weight of boiling water, and twice their weight of cold ; soon deliquesce on ex posure to the air ; and are decomposed at a red heat. Foureroy says, that cold water dissolves four times its weight, and that its own water of crystallization is suf ficient to dissolve it at a boiling heat. It is likewise soluble in less than its weight of alcohol. By evaporating the aqueous so lution to dryness, continuing.the heat till the nitrate fuses, keeping it in this state five or ten minutes, and then pouring it into an iron pot previously heated, we obtain Baldwin's phosphorus. This, which is, perhaps, more properly nitrite of lime, being broken to pieces, and kept in a phial closely stopped, will emit a beauti ful white light in the dark, after having been exposed some time to the rays of the sun. At present no use is made of this salt, except for drying some of the gases by attracting their moisture ; but it might be employed instead of the nitrate of potash for manufacturing aqua fords.