CHR
C H R
( 235 )
degree flexible. It is tranflucent on the edges,is foft and eafy frangible. It contains accordingto Lampadius,
35. Silex29.9 Magnefi*
18. Alumine
9.7 Oxyd of iron
2.7 Water
95-3
It occurs in the Duchy of Salzburg, and MontSt. Gothard, in Switzerland , accompanied byprifmatic cryftals of titanium; it has alfo beenfound in the Ifland of Jura in the Hebrides . Itfeems to be confidered by Hauy as a variety ofMica.
CHROME.
Chrome is a metallic fubftance of a greyifhwhite colour, extremely brittle, acidifiable withdifficulty by nitric acid, and then capable ofcombining into a lemon-yellow fait with caufticpotalh. This fait being added in folutionto nitrat of lead occafions a deep orange-redprecipitate of chromated lead.
Chrome has hitherto been only found in theacid ftate combined with lead and with iron. a
Sp. I. Chromat of Lead; Red Lead-fpar ,
Kirw. Rothes Bleyerz, Werner. Plomb rouge ,Broch. Plomb Chromate , Hauy.
The colour of this mineral is aurora-redpalling into hyacinth-red: it occurs very rarelyin mafs, fometimes diffeminated, but molt com-monly cryltallized. Its primitive cryllallineform is that of a rectangular prifm divifiblealong the diagonals of its bafe into trihedralprifms: it is alfo found with two of the lateraledges of the prifms- truncated, thus forming afix-fided prifm, two of the faces of which aremuch wider than the reft; fometimes all thelateral edges are truncated, whence refults aneight-ftded prifm. The cryftals are of moderatefize, adhering laterally to each other, and gene-rally very imperfect and ill-deftned : the lateralfaces are flightly ftriated longitudinally, andhave a brilliant external luftre. The fraiture isfine-grained uneven, paffing into conehoidal,and irregularly lamellar. It breaks into blunt-edged indeterminate fragments. It is tranflucid,paffing into femitranfparent, is brittle, eafilyfrangible, and, when feraped, gives a yellowifhorange coloured powder. Sp. gr. 6.02.
Chromat of lead when expofed to the blow-pipe crackles a little, and melts into a blackilhflag: with borax it is in part reduced to the
* Hauy,
metallic ftate, and communicates a green colourto the flux. The refults of its analyfis by Vau-quelin were 63.96 Oxyd of lead36.40 Chromic acid,
100.36
The only fubftances liable to be confoundedwith this mineral are realgar and red-filver; thefirft of thefe however differs from the chromatof lead in its inferior fpecific gravity, its volati-lity before the blow-pipe, and its arfenical odourwhen heated; the fecond is diftingaiffied by itscolour which is a pure red without any mixtureof orange, and by its fuperior metallic luftre.
Chromat of lead has hitherto been found onlyin the gold mine of Berezof, to the north ofEkaterinenburg, on the eaftern fide of theUralian mountains : it is thinly difperfed in avein paffing through gneifs and micaceousfchiftus, accompanied by quartz, galena, andauriferous pyrites. None of the cryftallizedvarieties have been found for fome years, inconfequence of which they are now fold at amoft enormous price, being valued at theirweight in gold. The only ufe to which thisfubftance has been applied is as a pigment: itis in high efteem among the Ruffian paintersboth on account of the unalterability and beautyof its colour.
Sp. 2. Chromat of iron. Per Chromate ,Hauy and Broch.
The colour of this mineral is greyilh or black-ilh-brown ; it occurs in mafs; it poffeffes aflight degree of metallic luftre; its frafture iscompact, uneven; fometimes imperfectly la-mellar ; when pulverized it is of an afh-colouredgrey.. It is fulficiently hard to fcratch glafs, isdifficult to break, is opake, and gives an argilla-ceous odour when breathed on. Sp. gr. 4.03.
It is infulible before the blow-pipe without:addition, but with borax it melts into a beauti-ful green-coloured glafs. It contains accordingto the analyfis of Vauquelin,
43 Chromic acid35 Oxyd of iron20 Alumine2 Silex
100