BOR

( 157 )

BON

of chalk with one of fedative fait, give by fufionin an earthen crucible a very hard yellow glafswhich ftrikes fire plentifully with fteel: if theproportions are inverted, the refult is a fome-what fofter glafs which often runs through thecrucible. Three parts of earth of bones withone of fedative fait, gives a white porcellanousmafs of extreme hardnefs. h

Borat of Magnesia.

Magnefia by long digeftion with boracic acidis flowly diffolved, and the liquor by coolingdepofits cryftalline grains of borat of magnefia,.which are exceedingly difficult of folution inwater. Paper dipped in a folution of this faitand afterwards dried, burns with a yellowifli-green flame. Alcohol in a great meafure de-compofes it, taking up the acid and leaving theearth behind. According to Achard ‘ one partof fedative fait fufcd with two parts of car-bonated magnefia affords a yellow porous vitref-cent mafs, which corrodes the crucible andgives fire with fteel.

Borat of Alumine.

If newly precipitated undried earth of alumjs digefted with boracic acid, and the clear folu-tion then evaporated, there will be depofitedminute cryftals mixed with a gummy fubftanceof a remarkably ftyptic tafte. This gummymatter appears to be chiefly borat of alumine.It is decompofed in the moift way by magnefia,lime and the alkalies, and by a melting heatruns into a glafs. One part of dried earth ofalum mixed with four parts of fedative fait, byexpofure to a ftrong heat underwent little or noalteration, except that the infide of the cruciblewas ftudded with fmall white very brilliantcryftals. k

BORAX. (See the preceding article.)

BORACITE. 1 Borazit, Wurfelflem, Mag -nefte boratee of Hauy.

The colour of this mineral is yellowifh, fmoakor alh-grey, paffing into greyilh or greenifh-white. It occurs in fmall cubic cryftals trun-cated on the angles- The cryftals are for themod part opake, fome are femitranfparent, anda few of the fmalleft are entirely tranfparent.Their luftre internally is confiderable and of thevitreous kind. The fracture is fmall and flat con-ehoidal, paffing into uneven and fplintery. Thecryftals are often more or lefs corroded, andthen are eafily pulverizable, but when perfeftthey are hard enough to give brilk and livelyfparks with fteel.. Sp. gr. 2.56.

Boracite, when expofed to a full red heat, be-comes opake and lofes about per cent, of its

weight, but undergoes no other change. Whenintenfely heated in a clay crucible, it runs into ayellowifh glafs. It is entirely though with diffi-culty foluble in muriatic acid by long digeftion.According to the analyfis of Weftrumb it con-fifts of

68 boracic acid,

13.5 magnefia,

11. lime,

1. alumine

0.75 oxyd of iron,.

2. filex

96.25

Some later experiments however of Vauquelii*make the proportion of lime to be much fmaller rand it appears probable that the only eflentiafingredients of this mineral are magnefia andboracic acid.

Boracite is found near I.uneburg in the duchyof Brunfwick, lining the fides of a vein in ahill of gypfum. The cryftals from their fliapewere known in the neighbourhood by the nameof wurfelfpath or cubic fpar, and were fup-pofed by fome mineralogifts to be a variety ofquartz. The prefence of boracic acid in themwas not fufpebted till their analyfis byWeftrumb-

BONE. This important fubftance is foundto compofe a necefl'ary part of the organizedftrufture of all the mammalia, of birds, of thegreater number of fifties, fome of the reptiles,and the oviparous quadrupeds. In all, its ufeis to give firmnefs and fupport to the body*and to fupply an unyielding fulcrum for theorigin and ijifertion, of moft o£ the mufcles fub-fervient to locomotion. The fame fubftance, a.little modified in the proportion of its con-ftituent parts, alfo furniffies many of the naturalweapons of defence, as the teeth, tufles of allkinds, and the folid horns, fuch as the antlersof the ftag or elk. On the whole, fo great afimilarity of compofition is found in all thefervarieties of bone that a general defeription mayfirft be given, and the bone of any quadruped(of the ox for inftance) may be taken as anexample of the whole genus..

It may be premifed that there are at Ieaft twoother great claffes of organs ferving for aflaultor defence, deferibed in their proper places,one, the cuticular organs, nails, claws, andhoofs, which clofely partake of the chemicalnature of the fofter and lighter Horns j, and theother, the vaft variety of cruftaceous and tef—taceous coverings or calcareous habitations of

« wjjatvc rtitu luica duuui 2 j- ,w * wyumg'J v* *,***w~--— - -*

Achard, Mem, del'Acad.de Berlin, 1799. P' 26 , ’Ditto, ‘‘Ditto. > Emmerling. Hauy. An.deChim