Copper oxide

“ Cuprous oxide is black when in the massive form, and has a red hematite colour when powdered. It is readily formed by the oxidation of copper, and melts at a red heat without decomposition; further heating in the presence of air produces the cupric oxide which is less fusible. As has been already indicated, cuprous oxide dissolves in the molten metal. It is easily reduced to metallic copper by heating with carbon, the metal being also obtained if the oxide be heated in the presence of reducing gases; it combines readily with silica when heated, yielding fusible silicates. ”

“ The copper, by successive heating and lamination, gets covered with a coat of oxide, which is removed by steeping the sheets for a few days in a pit filled with urine; they are then put upon the sole of the heating furnace. Ammonia is formed, which acts on the copper oxide, and lays bare the metallic surface. The sheets are next rubbed with a piece of wood, then plunged, while still hot, into water, to make the oxide scale off; and lastly, they are passed cold through the rolling press to smooth them. ”

“ The presence of excess of copper oxide in the metal is particularly dangerous when copper is to undergo annealing in a reducing atmosphere, since the reducing gases acting upon the oxides at the crystal boundaries destroy them, thus tending to produce that rottenness in the material which is so often encountered under such circumstances. ”

“ The impurities contained in coarse-copper are mainly iron, lead, zinc, cobalt, nickel, bismuth, arsenic, antimony, sulphur, selenium and tellurium. These can be eliminated by an oxidizing fusion, and slagging or volatilizing the products resulting from this operation, or by electrolysis (see below) . In the process of oxidation, a certain amount of cuprous oxide is always formed, which melts in with the copper and diminishes its softness and tenacity. It is, therefore, necessary to reconvert the oxide into the metal. ”

“ This metal, by the facility with which it scorifies, acts as a purifier, aiding the oxidation of the iron and other metals that may be present in the copper. The lead ought to be added immediately after removing the door to skim the surface. The copper should be constantly stirred up, to expose the greatest possible surface to the action of the air, and to produce the complete oxidation of the lead; for the smallest quantity of this metal alloyed in copper, is difficult to clear up in the lamination; that is to say, the scale of oxide does not come cleanly from the surface of the sheets. ”

“ Cuprous oxide is reduced by hydrogen, carbon monoxide, charcoal, or iron, to the metal; it dissolves in hydrochloric acid forming cuprous chloride, and in other mineral acids to form cupric salts, with the separation of copper. It dissolves in ammonia, forming a colourless solution which rapidly oxidizes and turns blue. A hydrated cuprous oxide, (4Cu2O, H2O) , is obtained as a bright yellow powder, when cuprous chloride is treated with potash or soda. It rapidly absorbs oxygen, assuming a blue colour. ”

“ The silver oxide thus formed is added, little by little, till the blue or greenish colour has entirely disappeared. This will precipitate the copper oxide from the copper nitrate, setting free the nitric acid, which, in its turn, will combine with the silver oxide. The copper will fall as a black powder mixed with any excess of silver oxide there may be. Take one or two drops of the solution in a measure, and add a drachm of water, and then add ammonia to it till the precipitate first formed is re-dissolved. ”

“ Copper Hydroxide.—By precipitating carefully a solution of a copper salt with caustic soda, a blue precipitate of copper hydroxide is obtained, which, though not distinguished by any particular beauty, is adapted for use as a distemper colour and for similar purposes. The operation is conducted at ordinary temperatures; on account of its voluminous nature the pale blue precipitate requires a long time for washing. Hot solutions must not be used; at a temperature near the boiling point of water copper hydroxide is completely decomposed into black copper oxide. ”

“ When ignited with charcoal, they easily give up their oxygen to it, and yield metallic copper; hydrogen also easily takes up the oxygen from copper oxide when heated. Copper occurs in a native state, sometimes in association with other ores, in many parts of the Urals and in Sweden, and in considerable masses in America, especially in the neighbourhood of the great American lakes; and also in Chili, Japan, and China. The oxygen compounds of copper are also of somewhat common occurrence in certain localities; in this respect certain deposits of the Urals are especially famous. ”

“ Protoxide of Copper, or red oxide of Copper: its colour is a deep red, sometimes very lively, especially when bruised. It is friable, difficult of fusion at the blowpipe, reducible on burning charcoal, soluble with effervescence in nitric acid, forming a green liquid. Its constitution when pure, is 88·9 copper + 11·1 oxygen = 100.
6. Black oxide of Copper, is of a velvet black, inclining sometimes to brown or blue; and it acquires the metallic lustre on being rubbed. It is infusible at the blowpipe. Its composition is, copper 80 + oxygen 20; being a true peroxide. ”

“ If the poling—that is, the reduction of the oxidised constituents of the tough pitch copper—be carried too far, the metal becomes brittle again, being known as over-poled copper. The fracture then tends to become coarse and fibrous, the colour lighter, and the upper surface of the ingot exhibits a ridge. The reasons for these effects have not yet been quite fully explained, but there is no doubt that they arise from the removal of oxygen from the oxygenated constituents, and the withdrawal from the metal of the protecting influence of the cuprous oxide. ”

“ Although, of course, if the cupel is very coarse-grained the metal may sink into the hollows.
Copper, antimony, tin, and most other metals, form powdery oxides, which are not of themselves easily fusible, and it is necessary when these are present to add some solvent or flux to render the oxide sufficiently fluid. Fortunately, oxide of lead is sufficient for the purpose; hence, mixed oxides of copper and lead, provided the lead is present in proper proportion, form a fluid slag. ”

“ Burnt copper is nothing more or less than copper in the overpoled condition. This is brought about by the action of reducing gases in the muffle. By this means the small amount of oxygen necessary to give the copper its tough pitch is removed. This oxygen is combined with impurities in the copper, and thus renders them inert. For example, the oxide of arsenic or antimony is incapable of combining more than mechanically with the copper, but when its oxygen is removed the arsenic or antimony is left free to combine with the copper. ”

“ When heated in air, a black scale, consisting of cuprous oxide, Cu2O, is obtained, which is readily detached by quenching and hammering. Water at ordinary temperatures is without effect upon copper; concentrated sulphuric and nitric acids have little action upon it in the cold, but attack it on heating. The best solvent for the metal is dilute nitric acid, which dissolves it very readily. Copper is liable to corrosion when subjected, whilst hot, to the action of chlorine or hydrochloric acid gas ”

“ The precipitate becomes lighter-hued the more it is washed, and consists of hydrated oxide of copper with a little carbonic acid; it does not turn brown even when heated in presence of excess of potash or soda. Moreover the presence of ammonia renders the hydrated oxide of copper much more permanent. The composition of this pigment is given by Gentele as 331⁄2 per cent. copper oxide, 231⁄2 sulphuric acid, 16 lime, and the remainder water, &c. ”

“ When a little oxide of antimony and oxide of copper are combined with copper, they occasion the appearance of micaceous scales in the fractured faces. Such metal is hard, brittle, yellowish within, and can be neither laminated nor wire-drawn. These defects are not owing to arsenic, as was formerly imagined; but, most probably, to antimony in the lead, which is sometimes used in refining copper. They are more easily prevented than remedied. ”

“ In modern practice, losses of copper as silicate and oxide, for reasons such as those detailed above, occur to a marked extent in those operations where the sulphur is present in small proportions only, and particularly where the reactions are intensely oxidising, as in the furnace-refining operations and the later stages in the converter process. ”

“ The oxide ores of copper would be deoxidized by the savage’s wood fire even more easily than those of iron, and the resulting copper would be recognized more easily than iron, because it would be likely to melt and run together into a mass conspicuous by its bright colour and its very great malleableness. ”

“ Crystals of oxide of arsenic sublime, and oxide of copper remains, which, on being dissolved in nitric acid, yields a fine violet-blue solution with ammonia.
The mineral-green of the shops, however, is seldom arsenite of copper. The substance sold in Edinburgh under that name, although believed by colourmen to be a preparation of arsenic, is not the arsenite of copper, but a mixture of hydrated oxide of copper and carbonate of lime ”

“ Copper is generally WEIGHED under the form of black oxide, but sometimes as pure metal:—By throwing it down from its solution by pure potassa, after which it must be carefully collected, washed, dried, ignited in a platinum crucible, and weighed therein as soon as it is cold. ”

“ A copper deposit oxidises very easily when exposed to the air. Consequently if the surface be required free from oxide, as, for instance, when it is to be silvered or gilt, it must be quickly washed when withdrawn from the coppering bath, scratch-brushed, and transferred immediately to the silvering or gilding bath. ”

“ Oxygen.—Mercury and copper and some other metals are capable of dissolving their own oxides. Mercury, by doing so, becomes viscid and unfit for its ordinary applications. Copper, when pure to start with, suffers considerable deterioration in plasticity. But the presence of moderate proportions of cuprous oxide has been found to correct the evil influence of small contaminations by arsenic, antimony, lead and other foreign metals. ”

“ In order to facilitate the oxidation of the copper by the atmospheric oxygen, a current of air may be aspirated through the apparatus. The solution of the oxide prepared in this way is more effective in its action on cellulose than that obtained by dissolving the precipitated hydrate in ammonia. Cellulosic tissues in contact with this reagent are seen to undergo a disaggregation of their fibres, which swell up, become gelatinous, and disappear in solution. ”

“ Copper has a brilliant yellowish-red colour, a nauseous, styptic taste, and emits a disagreeable odour when rubbed; is very malleable and ductile; unchanged in dry air; in damp air it soon becomes covered with a greenish rust (carbonate of copper) ; slightly soluble in dilute sulphuric and hydrochloric acid; freely soluble in boiling oil of vitriol (sulphurous anhydride being evolved) ; dilute nitric acid dissolves it readily with copious evolution of nitric oxide; heated to redness in the air, it rapidly becomes covered with a black scale (oxide) ; it fuses at a full red heat ”

“ Much of the metal sold contains as much as one per cent. of foreign substances, of which arsenic is the most important. The other elements to be looked for are bismuth, lead, antimony, silver, gold, iron, nickel, cobalt, sulphur, and oxygen. In "blister copper" (which is the unrefined metal) , aluminium, silicon, and phosphorus may be met with.
Oxygen.—All commercial copper carries oxygen; most of it is present as cuprous oxide, which is dissolved by molten copper. The estimation of oxygen is often made "by difference." ”

“ The impurities which commercial copperas most frequently contains are more or less sulphate of sesquioxide, together with a little sesquichloride of iron, and more rarely, traces of the sulphate of copperas, manganese, alumina and lime. A small addition of oxide of silver to the solution will precipitate all chlorine present, and subsequent digestion for a few minutes with carbonate of baryta will remove every trace of sulphate of sesquioxide of iron, and of alumina. Copper may, of course, be removed by immersion of metallic iron. ”

“ Cobalt pyrites (linnæite) .
Nickel ores are used for extraction of the metal, which is used as a substitute for silver. The name is derived from the German, kupfernickel, or false copper. It was discovered in 1751.
Copper, again, forms a number of minerals, and the chief is the red oxide of the metal, called cuprite. It crystallizes in the cubic system. Its colour is red, and tinges a flame green. Cuprite yields excellent copper, and is found in Cornwall, and in many places on the continent. The black oxide is rarely found. ”