CHR
CHR
( 287 )
. Chromat of Lime is prepared like the prece-ding: by adding the liquid acid to lime-water,an orange-yellow precipitate falls down, differ-ing from the chromat of barytes only in beinglefs foluble, and in a fomewhat different orderof affinities.
The carbonated alkalies are decompofed witheffervefcence by chromic acid, forming veryfoluble and cryftallizable falts of a lemon-yellowcolour. The chromat of ammonia is deftroyedby a red-heat, the alkaline bafe being decom-pofed, and deoxygenating the acid fo that onlya green oxyd of chrome remains behind. Thealkaline chromats are decompofable with ab-ftraction of their acid by barytes, lime, andftrontian, and with abftraCtion of their bafe bythe mineral acids: when added to any of thefoluble metallic falts a double decompofitiontakes place, and the chromated metal is precipi-tated in form of a coloured powder; mercurygives a vermillion-red precipitate, filver a car-mine-red, lead an orange-yellow, tin a green,See.
Chromic acid appears to be very eafily redu-cible to the Rate of oxyd, in which Rate it is ge-nerally of a green colour. Thus, when heated oncharcoal before the blow-pipe, it firfl boils, andwhen the moilture is evaporated, a green pulve-rulent infufible oxyd remains. By fufion withborax and glafs of phofphorus it affords vitreousglobules of a bright emerald green. Withtannin chromic acid forms an infoluble yellow-ifh-brown flocculent fediment, and with hvdro-fulphuret of potafli a brownifh-green one.
Muriatic and chromic acids when heated to-gether in a retort occafion a confiderable effervef-cence; part of the muriatic acid is convertedinto oxymuriatic acid which flies off, and thechromic acid is changed into the green oxyd.Ether or alcohol when heated for a few fecondswith this acid produce a fimilar effect; as doesalfo muriat of tin, the fame metal in the regu-line ftate, iron, zinc, and moll of the othermetallic fubftances. Even light will decompofechromic acid, for a paper wetted by it, andexpofed during a few days to the fun, affumes apermanent green colour.
In order to reduce chromic acid to a regulus;it is fufficient to heat it ftrongly in a cruciblelined with charcoal, the refult will be a brittle,brilliant, greyifh white metallic button amountingto about 67 per cent, of the acid employed. At ahigh temperature it affumes the form of featherycryftals. A fragment of this metal when ex-pofed to the blcw-pipe, firft tarnifhes, and then
* Emmerling. Brochant. Hauy,
acquires a thin coating of greenifh oxyd. Whenfinely pulverized, and treated with concentratedboiling nitric acid, it is oxydated with extremedifficulty, and gives the acid a light bluifh-greencolour; by repeated abftraCtions it is at lengthcompleatly acidified, and then exhibits exactlythe fame characters as the native acid.
Chrome on account of its fcarcity, and thefhort time that it has been known has not yetbeen applied to any ufe; it is probably howevercapable of furnifhing fome fine pigments to thepainter and enameller: in particular it willtinge glafs with a true emerald green; thecolouring matter of this beautiful gem havingbeen recently proved to be this very metallicoxyd.
CHRYSOBERYL a . Cymophane of Hauy.Oriental and opalefcent Chryfolite of fome natura-lifts.
The colour of this mineral is afparagus-green,palling into greenilh-white on one fide, and onthe other through olive green into yellowifh-grey, and fometimes reddiffi-brown. It gene-rally exhibits a bluifh milky light, undulatingwithin the cryftals. It is ufually met with infmall rounded pieces, but occafionally poffeffesa well marked cryftalline figure. Its primitiveform is that of a rectangular parallelopiped, andthe figures which it has hitherto been obfervedto affeCt are,
1. A fhort, regular hexahedral prifm or table..
2. The fame with a truncated hexahedralpyramid raifed upon each bafe.
The.furface of the rounded pieces is fomewhatrough, and generally reflects glittering varie-gated colours. The cryftals poffefs a doublerefraCtion, are externally fhining, and verybrilliant internally, fo that when polifhed it mayoften be confounded with the yellow diamond.The fraCture of ehryfobery] is perfectly con-choidal; its fragments are indeterminately an-gular, and fharp-edged; its hardnefs is fuperiorto that of quartz ; its fp. gr. is=r 3.7.
It is infufible per fe before the blow-pipe ; and-confifts, according to the analyfis of Klaproth 6 ,of Alumine . 71.5
Lime . . 6.
Oxyd of iron 1,5.
Silex . .. 18.
97.0Lofs 3.