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This salt is composed of nearly equal proportions of the alkali and the acid.
447- When submitted to a red heat, it is decomposed in consequence of the destruction of its acid.
Illus. By distilling nitre in an iron retort or gun barrel, oxygen gas is obtained in abundance. It is not perfectly pure, but sufficientlv so for ordinary experiments.
448. This salt is rapidly decomposed by charcoal at a high temperature. It is also decomposed by sulphur.
Illus. Mix powdered nitre and sulphur, and throw the mixture, a little at a time into a red hot crucible. The sulphur will unite with the oxygen of the nitric acid, and form sulphuric acid. The potash being thus left free, there is formed a union between this and the new acid, and sulphate of potash remains in the crucible.
449. Nitre is the base of gun powder, fulminating powder, $c.
Illus. 1. A mixture of five parts powdered nitre, one part sulphur, and one of powdered charcoal composes gunpowder. The materials are first finely powdered separately, then mixed together, and beaten with a wooden pestle, a quantity of water being added to prevent an explosion. The mixture is afterwards granulated by passing it through sieves, and cautiously dried.
2. Fulminating powder is made by mixing three parts of powdered nitre, two of carbonate of potash, or common .salts of tartar and one of sulphur. These ingredients must be carefully mixed by grinding them together in a mortar.
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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