COP

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glafs. At a heat fomewhat above melting, ablue-green flame hovers on the oxidated furfaceof the metal, which is ftill more vifible whenthe oxyd is thrown on the naked coals, and ismod intenfely bright and beautiful when copperwire is burned by a ftrong galvanic pile.

The fame colour, with fome variation offliade, is alfo produced by all the falts of copperwhen in contact with any burning combuftible,thus they tinge the flame of alcohol very beau-tifully. The nitrat or muriat {hews this to thebelt advantage. The flame of burning copperdepofits, though fcantily, a fine greenifh-greyoxyd, and hence it gradually collects as a kindof foot in the chimneys of copper-fmeltinghoufes.

Copper foon rufts in a damp air, and becomesCovered with a fine green cruft, which alfo con-tains carbonic acid. But this fuperficial coatinglong preferves the reft of the metal beneath, andhence it is tire work of a great length of time, andof circumftances very unfavourable to preferva-tion, to corrode entirely a thick plate of thismetal. Water projected on white-hot copperdoes not oxydate it, as it does iron, and no hy-drogen is produced thereby.

Except in one or two rare combinations, cop-per appears to unite very uniformly with thelame dofe of oxygen, forming (when free fromwater and every other fubftance) a brownifli-black oxyd, of which 20 per cent, or one-fifth,is oxygen, and the remainder is metal. Thisoxyd, as already mentioned in the analyfis of theores, is invariably produced by boiling for a veryfhovt time in potafh any of the precipitates fromthe cupreous falts by any alkali, pure or carbo-nated, or the ammoniated folution of copper.The fub-oxyd will be defcribed with the muriat.

Copper or its oxyd is foluble in almoft everyacid with more or lefs eafe. Many of thefefalts are of confiderabie importance.

Sulphuric acid a&s upon copper only whenconcentrated and with the affiftance of heat.For this purpofe take copper-filings or clippingsof thin fheet popper, put them into a glafs vefielwith about twice their weight of fulphurieacid, and heat the mixture. As foon as folutionbegins, much fulphureous acid gas is given out(which is a very convenient way of procuringthis gas), and at laft the whole is difl'olved intoa dark coloured liquor, except a fmall quantityof black refidue, which is the fulphuret containedmore or lefs in all common copper. By dilutionwith water the liquor becomes of a fine blue.

This folution, by due evaporation and cooling,furnifties cryftals alfo of the fame colour, and

when regular (which they very feldom are) of arhomboidal fhape, forming the fulphat of cop-per, or blue or Ro7nan Vitriol of the {hops.

Blue vitriol is alfo found native in abundance,partly cryftallized, but generally difl'olved in thewater of copper mines. Here it is produced bythe decompofition of the native copper pyritesin the fame maner that the native fulphat ofiron arifes from decompofed iron pyrites.

Sulphuric acid diffolves the oxyds of copperwith eafe even in the cold, and when diluted.The green carbonated oxyd is the moft folublein this acid.

Sulphat of copper has a very ftrong ftyptic,fomewhat acid, and naufeous tafte. It is folublein about four times its weight of water. Whendried at a moderate heat, not exceeding thatof boiling water, this fait lofes, according toProuft, about 36 per cent, which is mere water,after which, the refidue, which is a whitepowdery mafs, is equally again foluble andcryftallizable. But if it is calcined with a ftrongheat the acid itfelf is at laft expelled, but withoutdecompofition, (being wholly fulphurie and notin part fulphureous acid, as in the calcination offulphat of iron) and a further lofs of 3 3 on the 100of thecryftallized fait takes place. The remainderafter being kept fome time in a low red heat toexpel all the acid, is the perfect black oxyd ofcopper weighing 32 parts, one-fifth of which isoxygen and the remainder copper. Hence 100parts of this fait, according to Prouft, confift ofCopper 25.6'! forming 'lOxygen 6.4 j Black Oxyd f 3 2,0Sulphuric Acid . . 32.

Water .... 3 6.

100.0

Bergman alfo reckons 2 6 per cent of copperin this fait, but only 28 of water and 46 of acid.

Prouft alfo defcribes a fub-fulphat of copper, orwith a lefs quantity of acid. To procure it, addpotafh to a folution of the common fulphat, butnot enough to precipitate the whole of the metal-lic oxyd. A green precipitate then appears, whichis the fub-fulphat in queftion. If faturatedwith the alkali the precipitate is blue , and is ofa different nature, confifting of a fingular com-pound of oxyd of copper with water, called bythe fame eminent chemift hydrat of coppery whichwill be prefently mentioned.

The fub-fulphat lofes by diftillation only 14per cent, of water. The refidue boiled withcauftic potalh gives 68 of the black oxyd,whence its component parts are