MUR

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MUR

white denfe Vapour, which however is not de-compofed.

This fait is fomewhat deliquefccnt in a moiftair. If a little fulphuric acid is poured on it themuriatic acid is expelled in the form of whitefumes. The nitric acid decompofes it partiallyand caufes the evolution of nitro-muriatic acid.The phofphoric acid alfo expells the muriatic ata high heat.

This fait is compofed according to Kirwan,of 64 of potafh and 36 of acid when dried at oo°of which however about 8 are mere water ofcryftallization ; and 100 parts of the fait whendecompofed by nitrat of filver give 217.65 ofdry luna cornea.

Muriat of potafh is not ufed. It is rarelyproduced in the large way in chemical proceiTesexcept when the comparative prices of potafhand foda make it worth while to procure fodafrom fea fait by means of potaih, as will bementioned in the next article.

Muriatic acid may be procured from muriatof potafh in the fame way as from muriat offhda, but the bitter tarte and rather greater deli-quefeence of the former, render it probablyfearoely lit for any of the culinary ufes of com-mon fait.

Muriat of Soda. Sea Salt. CommonSalt .

This fait exills abundantly native either as afolid foflil or diffolved in water. In the formercafe it ranks as a peculiar mineral fpecies, andwill be dcfcribed accordingly.

Rock Salt, or Fossil Salt, or Sal Gem.•—Steinjalz. Wern. Sel gemme. Broch.

Of this fpecies there are the two followingvarieties.

Var. 1. Foliated Rock Salt.

Its colour is ufually greyifh, yellowifli, ormilk-white, or aih-gvey, fmoke and pearl-grey.It alfo though rarely occurs flefh, blood or brickred, and ftill more rarely violet or fky-blue orgreen. It is found in ma-fs, dilfeminated, inlarge columnar or fpherical diftindt concretions,or cryftallized in cubes. The recent fradlureis brightly finning with a luftre between vitre-ous and refinous. Its fra&ure is ftrait foliatedin three rediangular directions ; hence the formof its fragments is cubical, but this is the cafeonly when it is cryftallized, the maffive varietiesare thick foliated approaching to flaty, andbreak into blunt-edged irregularly wedge-lhapedfragments. It is femi-tranfparent, palling onone hand into tranflucent and on the other intotramgareut. It i s moderately hard and not

very brittle. To the touch it is fmooth andalmoft greafy. Sp. gr. 2.14* It is t0taite, it is deliqueicent in a moift atmofphere,is readily foluble in water, decrepitates ftrongiywhen laid on hot coals, and is fufible at a lowred heat.

Var. 2. Fibrous rock fait.

Its colour is greyifh-white, yellowifli or pearl-grey, lavender or violet-blue, or flefh-red. Itsinternal luftre is pearly varying from fhining togliftening. Its fnufture is fibrous, either parallel,with fine and curved fibres, or divergent, withcoarfe and ftrait ones. Its fragments are wedge-fhaped or fplintery. It varies from tranflucentto femi-tranfparent: it is tender and brittle : inether refpedfs it agrees with the preceding va-riety.

Rock fait'forms a peculiar fpecies of rock,the proper geological fnuation of which is be-tween the oldeft iecondary gypfum and fecon-dary fandftone: it forms continuous beds ofgreat thicknefs, and often occurs in large foli-tary blocks: it is always accompanied by femi-indurated clay, for the rnoft part ftrongiy im-pregnated with fait; and alternates with bedsof fwineftone, gypfum, limeftone, and fandftone.The beds of fait are moftly below the furface ofthe ground, but fometimes it rifes into hills ofconfidcrable elevation. At Cordova in Spain ,according to Bowles, there is a hill betweenfour and five hundred feet high, compofed en-tirely of this mineral.

F-ock fait, though not of very frequent occur-rence, is however by no means rare; the mo ftcelebrated mines are thofe of Wieficza inGallicia, of Halle in the Tirol, of Poland , ofCaftille in Spain , and Chefhire in England.In the province of Lahor in Hindoftan, is a hillof rock fait of equal magnitude with that nearCordova. The mines of Iletfki in Ruftia, yieldvaft quantities of this fubftance; it is fo plenti-ful in the defart of Caramania, and the air is fodry, that it is there ufed as a material for build--ing: it forms the furface of a large part of theNorthern defart of Lybia, according to Horne-man ; it is alfo found in abundance in the defarts -of Peru .

Muriat of foda has a pure faline tafte without:any mixture of bitternei's. It cryftallizes in cubes -when obtained by flow evaporation from its iolu-tion, but when procured by a boiling heat (as is-the cafe with mod of the fait ufed for culinary,-purpofes) the form is that of a hollow inverted,pyramid, refembling a hopper, and is made fcya fuccelfive aggregation of cubes round a centralone, whilft floating on the furface of the brine,,