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When a small quantity of this powder is gently heated nearly to redness on a shovel, or by other meanj, it explodes with violence, giving a loud and stunning report. , Only 15, or 20 grains ought to be exploded at a time, within doors.
450. Nitrate of ammonia. This salt is prepared by saturating dilute nitric acid with carbonate of ammonia.
Exp. Dilute some aqua-fortis with three, or four parts of water. Put this into a porcelain or earthern dish, and set it in a sand bath, or in hot ashes; then throw in pieces of carbonate of ammonia until it ceases to effervesce. Continue the evaporation until about two thirds of the solution is exhausted, or until a drop readilv shoots into crystals on being placed on a piece of glass. Then set the dish aside until the crystals are formed.
Remark. If the solution is evaporated slowly, and with a jrentle heat, and the vessel in which it crvstalizes has a broad flat bottom, the crystals are very beautiful, long, shining, (tinted, prisms. If the solution is exhausted nearly to the point of crystalization while it remains hot. and this is done with a higher heat, it either shoots into small fibrous crystals, or concretes into a shapelei-s mass.
Obs. The most important property of this salt is its yielding, when decomposed by heat, thenitrous oxide.
MURIATES.
451. The muriates have a saltish taste, more or less pure. They emit white fumes when mixed with sulphuric acid. With nitric acid they emit oxymtiriatic acid gas. They are all soluble in water, and difficultly decomposed by heat.
452. Muriate of Soda. Common salt. Sea salt. Of all the saline substances this is the most common and abundant in nature. It is frequently found in extensive solid masses in the earth, or dissolved in springs and lakes far inland. The ocean, is however, the great depository of this salt, about a thirtieth of its weight being muriate of soda. Illus. In Cheshire, England, there is a mine of this salt, . whose beds are alternate with those of clay. The first bed of salt commences about 90 feet below the surface, and varies from 60 to 00 feet-in thickness. Below this there is another bed whose thickness is not known, though it has already been penetrated to a great depth. The salt fro.-a this mine is carried to Liverpool where it is purified by solution in sea water, and by subsequent crystallization. Many thousand tons are annually shipped from that place, and hence it has acquired the name of Liverpool salt.
453. In Spain are many salt springs ; and in Catalo- . nia there is a mountain of rock salt, whose height is estimated at 500 feet, and it is about three miles in circumference.

 

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The remainder of the sulphur unites to the potash of the alum and forms sulphuret of potash. Thus the powder consists of sulphuret of potash, alumine and carbon. When this is exposed to the air the sulphuret absorbs the oxygen, not only from the air itself, but also from the water which it contains with such avidity, as to occasion a degree of heat which sets fire to charcoal and sulphur.
The nitrates by the action of fire, furnish oxygen gas Most of them scintillate when thrown on burning charcoal. >
Obs. This last effect is in consequence of their increasing the combustion by imparting oxygen gas. Hence most of the nitrates uro capsb1 <<fsupporting combustii n.
444. Nitrate of Potash. Nitre. Saltpetre. This well known substance is found native in all countries, where circumstances are favorable to its production. It however seldom occurs in large masses, but is generally found either in the form of a whitish efflorescence on the soil, or in small masses, or incrustations in limestone caverns. Its particles are also diffused through particular kinds of soi:, but never to any considerable depth.
Obs. 1 The mode of obtaining nitr e is by lixiviation, that is by passing water through, the earth which contains it. The water dissolves the nitre, which is then crystalized by-ja,a-po ration. .|F V
2". The calcareous caverns which abound in Kttmucky furnish largt quantities of ibis,salt. One of these situated in Ma;lison county, is upwards of 600 x ai ds in length and about 40 feet wide. It extends through a hill, and affords a passage for horses and waggons to bring out the earth to be lixiviated. One bushel of this earth yields from one, to two pounds of nitre.
3. The earth taken from under old and. decayed buildings, which have been inhabited, always contains a quantity of this salt, and is sometimes lixiviated for this purpose. During our revolutionary struggle, considerable quantities of nitre were manufactured in this war.
445. The formation of nitre depends on circumstances which are easily imitated by art. Hence a considerable proportion of what is used in the arts, is produced by what are called artificial nitre beds. These consist of certain materials thrown together in heaps, with attention to the circumstances which are known to favour its production.

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