722 COMMERCIAL COPPER-ITS PROPERTIES. longest known to man before the art of working iron was understood, it was in extensive use, either alone or alloyed with tin, for many of the purposes to which iron is now applied. It is of a well-known red colour, and has a peculiar, disagreeable odour and taste when moistened and rubbed. It is rather a hard metal, very tenacious, ductile, and malleable; after it had been melted beneath a layer of common salt, to exclude atmospheric air, pure copper was found by Scheerer and Marchand to have a sp. gr. of 8921: the density was increased by hammering, and when drawn into fine wire it was obtained as high as 8952: Daniell estimated its fusing-point at 1996° F. When heated to a temperature approaching its melting-point it becomes so brittle that it may be reduced to powder, and an ingot may be broken by a blow from a hammer. If exposed to a very intense heat, copper is capable of volatilization, but it is usually considered to be fixed in the fire. By slow voltaic action it may be obtained crystallized in cubes and octohedra, and is sometimes found native in these forms. It ranks amongst the best conductors of heat and electricity. If heated to redness in the open air, copper combines with oxygen rapidly, a layer of oxide is formed upon the surface, and as the oxide contracts more slowly than the metal beneath, it scales off if suddenly cooled, leaving a bright, clean, metallic surface. Copper is not oxidized when heated to redness in a current of steam. Exposure to a moist air at ordinary temperatures has no effect upon copper; neither has pure water; but in sea water, or in solutions of the chlorides, it is gradually corroded with the formation of an oxychloride of copper. Finely divided copper becomes ignited when touched with a glowing coal, and burns like tinder, being converted into the black oxide. Chlorine attacks the metal, which when in the form of leaf takes fire in the gas spontaneously. Nitric acid oxidizes and dissolves the metal with rapidity. Oil of vitriol does not act upon it in the cold, but if heated with it, the acid is decomposed, sulphurous anhydride being evolved and oxide of copper formed, which reacts upon the excess of acid to form the sulphate (410). Hydrochloric acid with access of air dissolves it but if air be excluded, it has no such effect at ordinary temperatures; though if boiled upon the finely-divided metal, it dissolves it very slowly, and hydrogen is evolved (Odling). Copper also decomposes hydrochloric acid gas when heated in it to redness, cupreous chloride being formed and hydrogen separated. The fixed alkalies have little action on copper, but ammonia gradually dissolves the metal if the air has access to it, slow oxidation taking place. Before the USES OF COPPER-BRASS. 723 oxyhydrogen blowpipe it burns with a green flame, and if introduced into a flame of gas or of alcohol it communicates to it a green colour. Uses.-The applications of copper in the arts are very numerous. Independently of its use in coinage, vast quantities of it are annually consumed in the sheathing of ships* and in the manufacture of boilers, and of various utensils for domestic purposes. It also forms the basis of a number of valuable alloys in extensive use with zinc it furnishes the different varieties of brass; and with different proportions of tin, it forms bronze, bellmetal, gun-metal, and speculum-metal (812); whilst its oxides and salts are largely employed as pigments, and yield articles of some importance in the materia medica. An alloy of copper and silicon containing 12 per cent. of the latter may be obtained by fusing together 3 parts of silicofluoride of potassium, I part of sodium and I of copper turnings: it is hard, brittle, and white, like bismuth. Another alloy may be obtained by prolonged heating of a mixture of sand, charcoal, and copper: when it contains 4.8 per cent. of silicon it is of a fine bronze colour. It is as fusible as bronze, very ductile, and yields a wire a little softer than iron, but quite as tenacious: it may be worked well at the lathe. (874) Brass.-The combination of zinc with copper has a well-known yellow colour, the tint of which becomes paler in proportion as the quantity of zinc is increased. A curious observation upon this point was made by Mr. D. Forbes, who found that a brittle crystalline alloy of a silver-white colour may be formed, containing 53'49 per cent. of zinc, and consisting of 7 equivalents of copper and 8 of zinc; but if the quantity of zinc were either increased or diminished, the alloy had the usual yellow colour of brass. The specific gravity of brass is greater than the mean of that of the metals which form it. Ordinary brass has a sp. gr. of 8.29; it contains about 64 per cent. of copper, being nearly Єu,Zn. Brass which contains 25 per cent. of zinc melts at 1750° (Daniell), and a larger proportion of zinc increases its fusibility. By exposure to a long-sustained high temperature in closed vessels, the whole of the zinc may be expelled, and it is not possible to fuse the alloy without losing a portion of the zinc. The alloys of zinc and copper are malleable when cold, but are generally brittle when hot. An alloy largely used under *Percy's experiments appear to show that the presence of a small quantity of phosphorus in the copper has some effect in protecting the metal from the corrosive action of sea water.. 724 ALLOYS OF COPPER-OXIDES OF COPPER. the name of Muntz metal, or yellow metal, for the sheathing of ships, may be rolled whilst hot: it contains 2 equivalents of zinc to 3 of copper, or 60 per cent. of copper. The addition of about 2 per cent. of lead to brass improves its quality if it is to be used at the lathe; it diminishes its toughness, and prevents it from hanging to the tool and clogging the file; but if intended for wire, the presence of lead must be avoided. A very small proportion of tin, even if it does not amount to 1 part in 200, greatly increases the hardness of the alloy. The ordinary hard solder for brass is an alloy consisting of 2 parts of brass and 1 of zinc. Brass is usually made by melting granulated copper in crucibles with rather more than half its weight of zinc formerly a mixture of calamine and charcoal was substituted wholly or partially for metallic zinc. At Swansea, the Muntz metal is prepared by melting the two metals in a reverberatory furnace, which enables a large quantity of the alloy to be prepared with rapidity but the process is attended with a considerable waste of zinc. Gedge's and Aich's alloys consist of a mixture of copper, zinc, and iron, which can be forged, cast, rolled, or drawn into wire; 100 parts of the best description of Gedge's alloy contain-copper 60 parts, zinc 382, and iron 18 parts. It is very hard, and appears to be well adapted to the sheathing of ships. It acquires great stiffness and elasticity if worked cold, but may be softened by annealing. Another alloy of a similar kind, termed sterrometal, consists of copper 5504, zinc 42:36, iron 177, and tin 0.83 parts. (875) OXIDES OF COPPER.-There are two salifiable oxides of copper, both of which are found in the native state; viz., the red oxide or suboxide (Eu,), and the black oxide (Eu✪), which is the basis of the ordinary salts of the metal. Rose has lately pointed out the existence of a still lower oxide, which he terms a quadrantoxide (Eu,,xH2O), which is only known as a green hydrate of extreme oxidability, obtained by digesting a salt of copper in closed vessels for 24 hours with an excess of stannous chloride dissolved in a large excess of caustic potash. Some indications have been obtained of the existence of a still higher oxide than Єue, probably Єues. Suboxide of Copper, or Cupreous Oxide (Eu,0=143, or Cu2O =715; Sp. Gr. 5'75; Comp. in 100 parts, Eu 88·8; → 11·2).— This compound occurs native, crystallized either in the octohedron, or in some of its derived forms, or else in capillary crystals or in lamellar masses. There are various ways of obtaining this oxide artificially; one of the best consists in boiling the dibasic acetate of copper with sugar; the oxide of copper contained in the salt is thus deprived of half its oxygen, and the red oxide is deposited in small octohedra. It may also be procured by igniting 5 parts of powdered black oxide of copper with 4 parts of copper filings, in a covered crucible. The red oxide fuses at a full red heat. By decomposing cupreous chloride with hydrate of potash it is obtained as an orange-yellow hydrate (4 Eu,, H2O; Mitscherlich). In this condition it is readily attacked by acids. A cupreous sulphate as well as carbonate and acetate appear to exist. The cupreous salts are unstable, and absorb oxygen readily. Some of its double salts are more stable: a sulphite of copper and potassium (Єu,§Ð ̧, 2 K2SO,; Muspratt) may be obtained as a yellow insoluble precipitate, by mixing solutions of normal or of acidsulphite of potassium with cupric sulphate; in this case, the cupric salt is reduced to the state of cupreous salt by the sulphite. 3 Red oxide of copper is soluble to some extent in metallic copper, which it renders, in technical terms, dry, or brittle. Abcl found as much as 46 of the suboxide in a specimen of very dry copper which he examined.* The anhydrous suboxide is resolved by most of the stronger acids into a cupric salt, and into metallic copper. Nitric acid converts it into cupric nitrate: hydrochloric acid converts it into the cupreous chloride, which is soluble in the excess of the acid. Hydrated cupreous oxide is soluble in a solution of ammonia, forming with it a colourless liquid. This solution is an extremely delicate test of the presence of oxygen in a gaseous mixture; a mere trace of oxygen causes it to assume a blue tint from the formation of the black oxide of copper, which when dissolved in a solution of ammonia has an intense blue colour. The principal * Abel has contrived a method of determining the amount of oxide in the metal, founded upon the fact that suboxide of copper decomposes the neutral nitrate of silver, furnishing an insoluble basic nitrate of copper, Eu‚Ð + 2 AgNO3=2 Ag+Єu 2 NO,,ue. This basic salt is soluble in dilute sulphuric acid; Eu 2 Ne,,u✪ + 2 H2SO,= 2 HNO3 + H2O + 2 use. The plan consists in digesting 500 or 600 grains of the copper for trial in a solution of 400 grains of neutral nitrate of silver in the cold, for three or four hours. The undissolved portion of copper is removed, washed into the solution of silver, dried, and weighed. The mixture of precipitated silver and insoluble basic nitrate of copper is separated by decantation from the solution, then washed, and digested for half-an-hour with a known quantity of standard sulphuric acid, being frequently agitated with it. It is filtered, and the washings neutralized by carbonate of soda. The proportion of acid neutralized by the basic nitrate of copper furnishes the means of estimating the quantity of suboxide of copper; 80 grains of SO, being equivalent to 16 grains of oxygen in the sample, or to 143 of suboxide of copper. 726 BLACK OXIDE OF COPPER. employment of suboxide of copper is in the manufacture of stained glass, to which it imparts a beautiful ruby or purple colour. (876) Cupric oxide, or black oxide of copper (Єu✪=79'5 or, CuO=397); Sp. Gr. 6·5: Comp. in 100 parts, Eu 79.85; →, 2015. This oxide is a compound of considerable importance to the chemist. It is employed largely as a means of furnishing oxygen to organic substances in the regulated combustion by means of which their composition is determined. The best process for obtaining the black oxide of copper consists in dissolving copper in pure nitric acid, and decomposing the resulting nitrate in an earthen crucible, by the application of a red heat: the water and the nitric acid are thus expelled, and the black oxide remains in a state of purity: the heat should be long continued, but not too violent; otherwise the oxide sinters together and concretes into hard masses, which are pulverized with difficulty. A very pure oxide is also furnished by the decomposition of the carbonate by heat; or still more simply by heating a plate of copper to reduess in a brisk current of air, and suddenly quenching it in water, in which case the oxide separates in black scales. It may be obtained as a hydrate of a light blue colour (Eu‚H ̧Ð), from any of its salts, by the addition of a slight excess of hydrate of potash, washing quickly with cold water, and drying at ordinary temperatures: when boiled with water it becomes black and anhydrous. This hydrate is soluble in an excess of a solution of ammonia, forming a liquid with a splendid blue colour: if slips of metallic copper be introduced into a bottle which is filled with this liquid, and closed so as completely to exclude the air, a portion of the metal equal to that already in solution is dissolved, the metal deriving oxygen from the oxide already in solution, both portions being thus reduced to the state of cupreous oxide Єu+Єue=Єu,; the colour gradually disappears, since cupreous oxide produces a colourless solution with ammonia; but the moment that air is admitted, the blue colour is reproduced. Black oxide of copper is soluble in oils and fats, so that greasy matters boiled in a copper saucepan which is not kept bright are liable to become impregnated with the metal. Oxide of copper The combines with glass, and gives it a beautiful green colour. oxide is hygroscopic, particularly if in a finely divided state, and it absorbs water rapidly from the air. Its oxygen cannot be expelled from it by mere exposure to heat, but if the oxide be plunged into an atmosphere of hydrogen while warm, it is decomposed with evolution of light and heat, while water is formed. Black oxide of copper is soluble in most of the acids, and com ; |