COL

COL

( 314 )

'V In fhort hexahedral prifms.

Its luftre is gliftening or ihining: its fractureis imperfectly foliated: it is femi-tranfparent,rarely traufparent. In hardnefs and frangibilityit refembles the preceding variety. Sp. gr.—3.5.

It has been analyfed by Vauquelin, and foundto contain 54 Strontian

46 Sulphuric acid

xoo

It occurs in the neighbourhood of Briftol inloofe nodules, and very finely cryftallized inSicily.

3. Compact cceleftine. Dichte celejlin.

Its colour is bluifh or yellowifh-grey. Itoccurs in mafs and in flattened fpheroidal andkidney-fhaped pieces. Its fracture is fine-fplintery, palling into foliated. It is opake,and fometimes tranflucent on the edges. It isfoft and eafily frangible. Sp. gr.zzt3.59. Ithas been analyfed by Yauquelin, and confifts of91.42 Sulphat of Strontian8.33 Carbonat of lime0.25 Oxyd of iron

100.00

It occurs imbedded in clay in the gypfumquarries of Mont Martre, near Paris .

COHOBATION is the repeated expofure ofone fubftance to the chemical action of anotherfubltance, either by returning the latter whendriven off by diftillation, or by fupplying a frefhquantity after the action of the fall has beenexhaulted.

COLCOTHAR is the red oxyd of ironwhich remains after the diftillation of aqua-fortis in the large way, when the fulphat ofiron is the fait ufed for the decompofition ofthe nitre. Colcothar is iron in its higheft ftateof oxygenation, and when wafhed, and properlyfifted and levigated, it is much ufed in polifhingiron and other hard bodies.

COLD. The opinions relative to the natureof cold are mentioned under the article Caloric.For the different means of producing artificialcold, fee alfo Freezing.

COLOPHONY is a hard black refin, artifi-cially prepared from Turpentine , (which fee).

COLOURING Matter . For the nature ofcolouring matter fee the article Dyeing. Someof the mod important of thefe, fuch as cochineal ,indigo, madder, &c. have been analyzed by clie-nt ills, and are feparately noticed.

COLUMBIUM is the name given by thedifcoverer, Mr. Hatchett, 3 to a fubltance hither-to undefcribed, and apparently metallic, foundin a certain fpecimen in the Britilh Mufeum,fent from fome part of North America , pro-bably Mafiachufets.

The fpecimen is a dark brownifh grey ore,imperfectly lamellated in its longitudinal frac-ture, of a vitreous luftre, moderately hard andbrittle, not magnetical, its fpecific gravity is5.918.

The following analylis fhews it to confift ofiron and a peculiar unknown fubftance in theproportions of about one of the former to 3 ofthe latter.

The ore was fucceffively boiled with muri-atic, nitric, and fulphuric acids. Of thefe, thefulphuric added the moll powerfully, and themuriatic the next, but neither of them produceda full folution of the ore but appealed only toa£t on a portion of the iron which it contained.

It was therefore necefiary to purfue the ad-mirable method of previoufly breaking thecohefion of its parts by fufion with alkali, foadvantageoufly employed by Klaproth and othermodern analyfts in the examination of refrac-tory minerals.

The ore was accordingly powdered andheated in a filver crucible with five times itsweight of carbonat of potafli. When the alkalibegan to melt, an effervefcence took place,owing to the union of the ore with the potafh,after which the whole fubfided into a mafs,greyilh-brown when cold. Boiling water dif-folved a portion, making a clear alkaline folu-tion. The infoluble refidue was digefted inmuriatic acid, which diffolved another portion,but ftill leaving a refidue. This laft was againfufed with carbonat of potalh, and gave asbefore a portion foluble in water, another onmuriatic acid, and a refidue. This laft entirelydifappeared by continuing the fame plan, andthus the whole was refolved into feveral fimilarportions of an alkaline folution, and an equalnumber of muriatic folutions. The alkalinefolutions fuperfaturated with nitric acid gave awhite flocculent precipitate, not foluble in anexcefs of the fame acid. The muriatic folutionswere mixed, faturated with ammonia, and gavean ochery precipitate, the iron of which was dif-folved in nitric acid, and the remainder wasnow white, and refembled the precipitate fromthe alkaline folutions.

The nitrat of iron gave by ammonia 42grains of oxyd of this metal (from 200 of the

• Phil. Trans.for i8oi.