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and granularly foliated, it contains feveral fub-ftances imbedded in it, fuch as quartz, arrago-nite, boracite and fulphur, and moft of the faitfprings are found in this formation. Themolt recent gypfum refts upon the fecond fand-ftone formation, and alternates witli induratedclay and fandftone, and is frequently coveredwith fecondary floetz limeltone; fibrous gyp-fum is chiefly charadleriftic of this formation,and it contains as well as the preceding thebones of quadrupeds, but fcarcely any otherorganic remains.
Gypfum generally forms banks and hills oflittle elevation in plain countries, or at themouth of large vallies. It abounds in. the neigh-bourhood of Paris , at the foot of the Alps inSwitzerland, Italy, and Tyrol; in Bavaria ,Saxony, Thuringia, Poland and Spain y in
England, in Derbylhire, Yorkfhire, and Notting--hamlhire ; in Penr.fylvania in North America .
The ufes of gypfum are very extenlive ; whenit is fufiiciently compact it is employed by thearchitect for columns and other ornaments,being eafier to work than marble; it is alfo turnedby the lathe into cups, bafons, vafes, and otherfimilar articles. When expofed to a low red-heat it parts with its water of cryftallization,is converted to a fine powder called plafler ofParis , like meal, and this when beaten up withwater to the confidence of pafte, fliortly afterlets and becomes folid, hence it is largely ufedfor taking calls of various magnitude, from a.medal to a coloffal flatue, and enters into thecompofition of many cements. For furtherparticulars relative to the chemical propertiesof this fubftance, fee Sulphat of Lime.
H
HAEMATITE. See Iron , Ores of.
HAIR. The chemical compofition of hairappears by the experiments of Mr. Hatchett torefemble very clolely that of nail and horn.Boiling water extracts from hair a very fmallportion of gelatin, and the hair after drying isi'omewhat differ and more brittle than before.The chief conftituent of hair appears to beorganic, condenfed albumen. (See Horn.)
Hair may be dyed permanently in feveralways. A black or dark colour, which isgenerally defxred, is given by many metalliclolutions, particularly that, of filver much weak-ened, but thefe are liable to corrode its fub-ftance, if not carefully ufed. Pallas 3 relatesthat the women of Altracan dye their hair,while growing, of a fine gloffy black, in thefollowing way: twenty-five galls are firft boiledin oil, then dried and powdered: to this isadded, 3 drams of green vitriol, one dram ofcream of tartar, and one dram of indigo, andthe whole ftirred up with a quart, of water, towhich is added a handful of the dyeing herbhenne. The hair is anointed with this over night,care being taken not to blacken the Ikin, and iswaffled in the morning. This application givesa fhining black which lafts feveral months.
HALBOPAL. See Opal.
HARTSHORN, Salt, Spirit , Oil, & Earth of.
Salt of Hartjhorn is properly the carbonat ofammonia, prepared by the Ample diftillation ofbone, or flag's horn, purified by rectification.
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It'is a tolerably pure carbonat of ammonia, butretaining a ftrong fub-empyreumatic fcent of theanimal oil, which is intimately mixed with it,and is apt to render it yellow. The fpirit ofhartfhorn is this ammoniacal fait diffolved inalcohol, by the medium of diftillation, and is a-ftrong and powerful cordial and llimulant.
The Oil of Hartfjorn is commonly dark-coloured and fetid, but may be rendered limpidand fragrant by rectification. It is then called-Dippel’s Oil. The Earth of Hartjhorn is phof--phat of lime. (See the articles Horn and Bone.,)
HEAT. See Caloric.
HEAVY-SPAR. Barofelenite ICirw. Schiver-fpath, Wern. Spath Pefant , Broch. BaryteSulfatee , Hauy.
Of this mineral there are the followingfubfpecies.
1. Subfpecies. Foliated FIeavy-spar. Ge~rad-fchaaliger and Krumm/chaaUgcr SchiverfpathWern.
The principal colours of this fubftance aremilk-white, greyifh yellowifh and reddifh-white,yellowifh-grey, fmoak and pearl-grey, wineyellow, yellowifh-brown, flefh-red, blood andliver-red, alfo very rarely, greyifh-black; green-ilh-grey, olive and oil-green; bluifh-grey, fmaltand indigo-blue.
It occurs cryllallized, in mafs, reniform, andglobular.
Its primitive figure is a flrait rhomboidalprifm, the meafure of whofe angles is ioi° 30'and 78° 30ft and this is again diviiible by planesthe Taurida *