COP

COP

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nitric folution fhould be evaporated to drynefs,rediffolved in muriatic acid, and again driedand moderately heated for fome time, wherebythe nitrous acid is expelled, and a metallicmuriat remains for further treatment.

Inftead of iron, tin or efpecially zinc maybe ufed as the precipitant of the copper from itsfolution: thefe adt more fpeedily and with equalcertainty. With either of thefe two, as theirxnuriat is colourlefs, the total abfence of thecopper (provided iron or nickel is not at thefame time prefent) is feen by the folution be-coming entirely void of colour.

Mr. Chenevix has alfo remarked d a lingularcircumftance in thefe precipitations, which is,that if the acid, (particularly the muriatic) be inexcefs, a quantity of hydrogen is difengaged,as occurs in the common folutions of thefemetals, and the whole of the copper is feparatedin a very Ihort time. With muriat of copper,zinc, and an excefs of muriatic acid, the fe-paration is furprifingly rapid, and much advan-tage may be made of this fadt in the analyfis ofcopper ores.

It is to be obferved, however, that zinc willprecipitate iron as well as copper from itsfolutions, but fcarcely any of the iron will fe-parate till all the copper is precipitated. Thusif zinc is added to a mixed folution of fulphator muriat of iron and copper, the firft precipi-tate is obvioufly copper and little elfe, but at thetime when the folution begins fcarcely to turnblue with ammonia, a black powdery oxyd ofiron mixes with the copper. Even if no iron becontained in the cupreous folution, if there isan excefs of acid, and common zinc (which al-ways contains iron) be ufed, fome of it will ftillappear in the precipitate; the excefs of acid ap-pearing firft to difTolve both the zinc and iron,and the latter being again feparated by the zincthat remains. On this account, perhaps, ironis a more accurate reagent than zinc in thefeanalyfes. As the muriat of copper feems toyield its metal with more eafe than the fulphat,it might perhaps be of ufe previoufly to convertthe fulphat into a muriat by the addition ofcommon fait. The colour immediately changesto green, which is a proof of this change ofthe cupreous fait.

The report of the afiay will probably be ftillmore accurate, if the precipitated copper, afterbeing walhed and dried, inftead of being im-mediately weighed, is put into a fmall crucible,moiftened with a drop or two of oil, covered

with borax, and ftrongly heated for a few mi-nutes whereby it becomes a folid button ofgood malleable copper.

The fecond ftate is that of the green carbonat.If carbonated potalli or foda be added to a fo-lution of copper, a green precipitate is formed,which, when walhed and dried at the heat ofboiling water, gives an uniform green powder.Its exaft nature will be mentioned when de-ferring the carbonat of copper, but it may behere added, that 180 parts of this carbonat areequivalent to ioo of metallic copper, and maybe reckoned as fuch in all analyfes. But as thepure fixed alkalies give a precipitate which mayoccafionally be confounded with this carbonat,this method of eftimation is not quite fo goodas the following.

The third ftate in which copper may be efti-mated is that of the black oxyd. If the greencarbonat laft mentioned .(and it need not bewalhed with particular care nor dried) be boiledfor a few moments in cauftic potalh, it at oncelhrinks confiderablyand becomes a deep brownilhblack fine powder, which is a pure oxyd of cop-per in its higheft ftate of oxygenation. Onehundred parts of this oxyd, well walhed anddried in a low red heat for a minute or two,invariably contain eighty parts of pure metalliccopper. The ammoniated copper gives the fameoxyd when boiled with potalh.

It is alfo produced at once by adding potalhor foda to the acid folutions of copper, andboiling for a minute or two (which laft is an ef-fential circumftance) and this is a better methodof proceeding in analyfis, fince an excefs of car-bonated alkali will redifiolve a part of the greencarbonat, and vitiate the analyfis, whereas nofuch effeft is to be feared from an excefs of thepure fixed alkalies at a boiling heat.

The leading fteps of the a£tual analyfes offome of the principal copper ores by the moltaccurate chemifts may now be given in a fewwords, as a fpecimen of the mode of proceedingin different cafes.

Of the ores compofed chiefly of copper, iron, andfulphur.

The vitreous copper ore was thus analyfed'by Klaproth . e

To 200 grains of the powdered ore muriaticacid was added in a boiling heat, which had noimmediate efFeft, but on dropping in a little,nitrous acid, folution began with violent difen-gagement of nitrous gas. When every thing folu-ble was taken up, the folution confided of a clear

f Effays, vol. i.

, Pljil. Tranf.for l8oi,p. an.