COL

COP

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©re) and the white flocculent matter weighedabout 155 grains. This laft being obvioufly apeculiar fubftance was examined feparately,and was found to have the following properties,which (collectively taken) diftinguifh it fromany other known fubftance, and at prefent maybe conlidered as pure columbium, or rather asthe fuppofed oxyd. (but as yet irreducible) of ametal to which the name of columbium hasbeen given.

This fubftance is white and not very heavy.It has no tafte, and is fcarcely foluble in water,but, laid on litmus-paper, it turns it red, andhence it may be inferred to be fliglatly acid.

Under the blow-pipe it is not fufible per fe tnor with borax, but readily, and with efl'ervef-cence with the carbonats of foda and potafli.Phofphat of ammonia, or phoi'phoric acid dif-folve it alfo in this way, and produce a purplifliblue globule.

Nitric acid has no aCtion whatever upon it.

Boiling fulphuric acid is the belt of the acidmenftrua for this fubftance, and diffolves iteafily, but the greater part of the l'olution isdecompofed by dilution with water, and aheavy infoluble fulphat of columbium fubfidesas a white powder. It requires fome minutesfor this effeCt to take place.

Pruffiat of potafh, added to the fulphuricfolution produces immediately a copious beauti-ful olive precipitate.

TinCture of galls gives an orange-colouredprecipitate.

All the alkalies decompofe the fulphuric folu-tion, but when in excefs do not rediflolve theprecipitate unlefs heated.

Boiling muriatic acid diffolves the white pre-cipitate from the folution of columbium, inpotafh, by an acid, if taken wet and recentlyfeparated.

A muriat of columbium is thus producedwhich is not cryftallizable. A piece of zincimmerfed in this folution gives a white floccu-lent precipitate, but nothing in a metallic ftate.

The fixed alkalies diffolve columbium in themoift way as well as by fufion. The folutionin potafh, when evaporated, gives a white

From its reddening litmus it appears to be inthe ftate of an acid.

COMBUSTION is the rapid decompofitionof any body attended with the production ofLight and Caloric. In all the great pro-cefles of combuftion that are conftantly goingon, the prefence of Oxygen in one form orother is effentially requifite, which appears to bethe great agent of this decompofition; as theproduSls of combuftion confift principally of thecombuftible materials united with the oxygenemployed. As the evolution of light and heatare included in the popular idea of combuftion,it feems proper to retain thele phenomena inthe definition, and thereby to diftinguifh it fromoxygenation in which they are wanting. It muflbe acknowledged however that the produfts ofcombuftion, in many inftances, do not fenfiblydiffer from thofe of Ample oxygenation, andhence Lavoifier was led to ufe the term Jlowcombujiion , to exprefs oxygenation without thefenfible evolution of light and heat. This hasled to fome probable opinions on the nature ofoxygen, which will be mentioned under thatarticle.

CONGELATION. See Freezing.

COPAL . This Angular kind of refin i&brought principally from South America,,and partly from the Eaft Indies, and is a naturalexfudation from a large tree which hardens onexpofure to air. Copal is one of the hardeft ofthe refins, and eafily reducible to a very finepowder. It is beautifully tranfparent, andchiefly of a light-lemon colour, fometimesinclining to orange, but the colour of the fineftfort is fo faint that when fpread thinly over anyfurface as a varnifh it is not perceptible, andonly gives a fine hard fmooth tranfparentglazing. It is this union of hardnefs withcolourlefs tranfparency that makes copal foeminently valuable as a varnifh for pictures,white-wood works, and a variety of other pur-pofes.

The common refins are characterized bybeing infoluble in water, foluble in alcohol,eflential oils, and ether, and highly combuftible.Copal agrees with the refins in combuftibility

glittering fcaly fait refembling boracic acid in and all external charadters, but it cannot be

appearance, and of an acrid alkaline flavour.

Columbium is inferred to be of a metallicnature, by forming coloured precipitates withpruffiat of potafli and galls, by being feparablefrom its folution by zinc, and by colouringphofphoric acid melted with it, but the attempts

difl'olved in the above menftrua without parti-cular pains, and requires them to be in a ftateof extreme purity. In thefe qualities thereforeit appears to hold an intermediate ftate betweenthe true refins and amber, refembling the for-mer by being foluble in oily fubftances which

to reduce it to the reguline ftate by fufion with do not touch amber, and the latter by greatlycharcoal, have not fucceeded. refilling the action of alcohol.

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