« PoprzedniaDalej »
Experiment 3. If copper ore be boiled in five times its weight of concentrated sulphuric acid, till a dry mass is obtained, and if to this mass water be added, and afterwards a polished plate of iron immersed, the copper will be precipitated in its metallic state. It may be scraped off and weighed. If silver should occur with the copper, the following process may be employed :
Experiment 4. Add to the ore nitric acid, as long as it continues to extract any metal; and, should silver be present, it may be detected and separated by a plate of copper.*
Remark. Copper is of a fine red colours and possesses considerable brilliancy. Its taste is nauseous and styptic. Its hardness is 7.5, and its specific gravity varies according to its purity. According to Lewis it is 8.830. Its malleability is so great, that it may be hammered out into leaves of extreme thinness. In this state it is known by the name of Dutch metal. It possesses considerable ductility and tenacity. A wire 0.078 inch in diameter is capable of supporting 302.26lbs. avoirdupois without breaking At 270 Wedgwood, or, according to Mortimer, at 14509 Fahrenheit, copper melts ; and if the heat be continued, it may be dissipated in visible fumes. If allow ed to cool slowly, it exhibits a kind of crystallization. The abbe Mongez obtained it in crystals of quadrangular pyramids.
Except gold and silver, copper seems to have been known at an earlier period than any other metal. Be. fore the working of iron was known, it was employed as a principal ingredient in all domestic utensils and instruments of war. In mixture with tin, it formed the bronze for the armour worn by the Trojans, as related by Homer.
* On the analysis of copper ores see Klaproth's Essays, vol. i. 54. 541. &c. Chenevix on the analysis of arseniates of copper and iron. Phil. Trans. 1801, &c.
The word copper, it is said, is derived from the island of Cyprus, where it was first discovered, or wrought, by the Greeks. Professor Kidd, however, is of opinion, that the word copper, cuprum, is derived from the name of an artificial alloy of this metal, called as cyprium ; which was a compound of copper and tin. In the early natural historians æs, when used simply, very often signifies copper.
Besides the ores of this metal enumerated in the general classification, copper in its native state has been known from time immemorial.
Native copper, which is as easily recognized as most substances by its external characters, is met with in many parts of the world : sometimes distinctly crystallized ; more frequently ramifying in various forms through the substance containing it.
Some of the most beautiful specimens of native copper are met with in Siberia, in the eastern extremity of the Qural mountains, in about the sixtieth degree of latitude: the matrix of copper is a granular white carbonate of lime.
Native copper is also met with in quartz, through which it often penetrates in the form of irregularly prismatic bars ; in serpentine ; in varieties of basalt and porphyry; and in granite.
According to Mr. Jameson it is frequently found in great masses dispersed over the surface of the earth, in uncultivated countries ; hence Werner conjectures that it was the first metal worked by man. From its obvious metallie characters the opinion may be considered as very probable, especially when supported by the account which is given of some of the savage tribes in the north western parts of America ; who though little civilized in most respects, have applied to domestic purposes the native copper with which their country abounds; and, from one of the uses to which they have applied it, are commonly denominated copper-knived Indians.
Lucretius alludes to the early use of copper in these words:
Prior æris erat, quam ferri cognitus usus. When native copper is met with in the body of primitive limestone, and other rocks which appear to have undergone a state of fusion, it is presumed that it originally crystallized in the situation where it is now found. In particular situations it appears to be the result of a secondary formation ; and is conjectured by some to have been derived from the saline form of this metal, called blue vitriol; which is a combination of copper and sulphuric acid. In these instances it is supposed that some substance, having a st nger attraction for sulphuric acid than copper, has decomposed the salt; and that the copper has been precipitated in consequence. Thus into the water of some mines, holding blue ritriol in solution, it is customary to throw pieces of iron in order to decompose that metallic salt : and the copper is precipitated on the iron in proportion as the decomposition proceeds. This method of separating copper was first practised at Herengrund, near Neusol, in Hungary. The copper so obtained is called copper of cementation, or cement copper: but Mr. Price, in his « Mincralogia Cornubiensis,” says, that the word cement is a corruption of « Ziment,” which is the name of a place liear Herengrund. From observing what bappens in this artificial process, and comparing the effect with the occasional stalagmitic appearance of native copper, somit mineralogists are inclined to attribute this apperance to a similar origin.*
Mr. Jameson mentions a mass of native copper, on the authority of Professor Vandilli, weighing 260) Portuguese pounds. It is said to have been found in a valley near Cachoeira, in Brasil.
Native copper has been discovered, sometines in farge quantities in many places in the United States,
† Kidd ii. 100. H
* Lib. V.
Experiment 5. If copper filings be put into water, and excluded from the air, the metal will remuin unaltered; or,
Experiment 6. If the vapour of water be passed through an ignited copper tube, the water will pass unchanged; but,
Experiment 7. If copper filings be exposed, when moistened with water, to the free access of air, they will corrode, and assume a green colour.
Remark. Copper exposed to the air gradually absorbs oxygen, more especially if moistened with water, - becoming tarnished, then brown, and at last green.
The latter consists of oxyd of copper and carbonic acid. The oxydizement of copper is facilitated, if,
Experiment 8. The metal be heated red hot, and plunged alternately after each heating into water : the scales thus produced fall to the bottom of the vessel. The gradual oxydizement of copper is shewn in the following manner :
Experiment 9. Expose a piece of copper to a low red heat, its surface will gradually assume various shades of orange, yellow, and blue. Childrens toys are ornamented with thin plates of copper, thus tinged of different colours.
Experiment 10. If copper be exposed to a violent heat, it will take fire and burn with great brilliancy ; or',
Experiment 11. If it be treated with a stream of hydrogen and oxygen gas, in the state of inflammation, the same effect will take place, and the product will be, in both cases, an oxyd of copper.
Experiment 12. If 57.5 parts of black oxyd of copper and 50 parts of metallic copper, obtained by precipitating it from its solution by a plate of iron, be mixed together, and dissolved in muriatic acid; and the solution decomposed by the addition of potash, the prot-oxyd of copper will be precipitated of an orange colour; or,
Experiment 13. If copper be dissolved in muriatic acid, and pieces of metallic, copper afterwards immersed into this solution, and potash then added, the prot-oxyd will be precipitated as before.
Rationale. When the black oxyd and metallic copper are dissolved together in muriatic acid, the whole being oxydized to the minimum, is dissolved ; and the muriate of copper then decomposed by the vegetable alkali, the muriatic acid unites with the latter, and the prot-oxyd of copper is precipitated. But when copperis dissolved in muriatic acid, and the solution exposed to plates of metallic copper, the latter abstracts oxygen to a certain degree from the oxyd of copper held in solution, so that on the addition of potash, the prot-oxyd of that metal is precipitated.
Remark. Mr. Chenevix, to whom we are indebted for the most accurate information respecting this oxyd, although it was first observed by Mr. Proust, says, that it is composed of 88.5 parts of copper and 11.5 oxygen.* It absorbs oxygen when moist with avidity, changing to a blueish green.
Experiment 14. If the scales of copper, obtained by immersing red hot copper into water, be exposed to a red heat in an open vessel, they become black, forming the per-oxyd of copper.
Rationale, The copper is further oxydized by exposure to air, assisted by an increased temperature ; hence it becomes oxydized to the maximum, forming.. the per-oxyd ; or,
Experiment 15. If the sulphate or nitrate of copper be decomposed by means of potash ; and the precipitate afterwards heated to drive off any moisture which it may retain, the per-oxyd of copper will be produced.
Rationale. The copper in the sulphate or nitrate is oxydized to the maximum ; hence on the addition of potash, a sulphate or nitrate of potash is formed, andi the per-oxyd of copper is precipitated.
Remark. The per-oxyd contains 20 per cent. of oxygen. The oxyds of copper may be reduced in several ways; as,
* Chenevix, Phil. Trans, 180,