Cuprous oxide

“ 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. ”

“ It is easily fusible, and even volatile. Under the action of oxidising agents, it passes into the cupric salt, and it absorbs oxygen from moist air, forming cupric oxychloride, Cu2Cl2O. Aqueous ammonia easily dissolves cuprous chloride as well as cuprous oxide; the solution also turns blue on exposure to the air. Thus an ammoniacal solution of cuprous chloride serves as an excellent absorbent for oxygen; but this solution absorbs not only oxygen, but also certain other gases—for example, carbonic oxide and acetylene. ”

“ When gently heated it disengages hydrogen; it gives cuprous oxide when exposed to the air, burns in a stream of chlorine, and liberates hydrogen with hydrochloric acid: CuH + HCl = CuCl + H2. Zinc, silver, mercury, lead, and many other heavy metals do not form such a compound with hydrogen, neither under these circumstances nor under the action of hydrogen at the moment of the decomposition of salts by a galvanic current. The greatest resemblance is seen between cuprous hydride and the hydrogen compounds of potassium, sodium, Pd, Ca, and Ba. ”

“ The presence of lead seems to be an obstacle to its [33] formation. This dark green patina consists of variable proportions of basic copper hydrate and copper carbonate. The green layer frequently rests upon one of a red colour, a circumstance which proves that the dark green patina is almost always the result of two successive reactions: cuprous oxide is first formed and subsequently takes up water and carbonic acid. Tin is present as copper stannate. The cuprous oxide, which is generally regarded as unaffected by air, is perhaps drawn into further reaction through the agency of ammonia. ”

“ When the reactions given above have resulted in the formation of a certain amount of copper oxychloride, it is to be supposed that a small quantity of sodium chloride comes into simultaneous contact with the oxychloride and with the metallic copper. A slow reaction takes place and a double compound of cuprous chloride and sodium [30] chloride is formed. The remaining portion of copper is converted into cuprous oxide:
3CuO, CuCl2, 4H2O + 4Cu + 2NaCl = Cu2Cl2, 2NaCl + 3Cu2O + 4H2O.
The solution of the double salt is also in turn oxidized by the air which penetrates the whole mass. ”

“ 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. ”

“ It is a bright red substance and can easily be prepared by heating copper to a high temperature in a limited supply of air. It is used for imparting a ruby color to glass.
By treating cuprous oxide with different acids a number of cuprous salts can be made. Many of these are insoluble in water, the chloride (CuCl) being the best known. When suspended in dilute hydrochloric acid it is changed into cupric chloride, the oxygen taking part in the reaction being absorbed from the air:
2CuCl + 2HCl + O = 2CuCl2 + H2O.
Cupric compounds. ”

“ 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. ”

“ The black oxide, which is formed by the combustion of iron, and by other processes, contains 56 iron + 16 oxygen. The common rust of iron is the peroxide of this metal, combined with carbonic acid. It may be formed by exposing the protosulphate of iron, or green vitriol, in solution, to the atmosphere, and then adding an alkali. This oxide contains more oxygen than the preceding; it consisting of 56 iron + 24 oxygen.
The tempering of cutting instruments, an operation which requires great delicacy and exactness, after that of hardening, is intended to obtain a fine and durable edge ”

“ 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. ”

“ Cupric oxide fuses at a strong heat, and on cooling forms a heavy crystalline mass, which is black, opaque, and somewhat tenacious. It is a feebly energetic base, so that not only do the oxides of the metals of the alkalis and alkaline earths displace it from its compounds, but even such oxides as those of lead and silver precipitate it from solutions, which is partially due to these oxides being soluble, although but slightly so, in water. ”

“ Thus, when copper is heated to redness in a furnace it increases in weight and absorbs oxygen, until for 63 parts of copper there is absorbed not more than 8 parts of oxygen by weight, forming a red mass, which is suboxide of copper; but if the roasting be prolonged, and the draught of air increased, 63 parts of copper absorb 16 parts of oxygen, and form black oxide of copper. Sometimes to distinguish between the degrees of oxidation a change of suffix is made in the oxidised element, -ic oxide denoting the higher degree of oxidation, and -ous oxide the lower degree. ”

“ Thus, for instance, copper combines with oxygen in at least two proportions, forming the oxides found in nature, and called the suboxide and the oxide of copper, Cu2O and CuO; the oxide contains twice as much oxygen as the suboxide. Lead also presents two degrees of oxidation, the oxide and peroxide, and in the latter there is twice as much oxygen as in the former, PbO and PbO2. When a base and an acid are capable of forming several kinds of salts, normal, acid, basic, and anhydro-, it is found that they also clearly exemplify the law of multiple proportions. ”

“ 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. ”

“ 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. ”

“ These ornaments, when the paint is removed, have the natural colour of polished steel. When steel is heated in hydrogen gas, no appearance of the kind takes place, a fact which shows, that it is owing to the oxidizement of the metal.
Iron is soluble in the acids. By the assistance of water, it is acted upon by sulphuric acid; the metal being oxidized, and the oxide dissolved, while hydrogen gas is evolved. The salt, formed in this case, is the sulphate of iron, green vitriol, or copperas. With muriatic, nitric, acetic and other acids, it forms various salts ”

“ At the same time, a part of the reduced metal is volatilized (this continues after the assay is removed from the flame) and re-oxidized. A white incrustation appears upon the charcoal, and the metallic globules are covered with small white crystals. If this white sublimate upon the charcoal is moistened with a solution of cobalt-oxide, and exposed to the reduction flame, a part of it is volatilized, while the other part passes into higher oxidation, and remains, after cooling, of a dirty dark-green color. ”

“ Microcosmic Salt dissolves oxides of lead upon platinum wire in the flame of oxidation easily to a clear, colorless bead, which appears, when highly saturated, yellow while hot. A saturated bead becomes enamel-like after cooling. The bead appears in the flame of reduction, and upon charcoal, of a greyish color and dull. By the addition of more oxide, a yellow sublimate of protoxide is produced upon the charcoal. ”

“ When oxygen is present in quantities above the eutectic proportion, the first constituent to solidify from the molten over-oxygenated copper is brittle copper oxide, and the presence of such brittle material disseminated through the metal explains why “dry copper” cannot be worked. ”

“ It is said, that by employing more charcoal than is necessary to decompose the nitric acid of the nitre, the excess passes off, not as carbonic acid, but carbonic oxide, or gaseous oxide of carbon, which is necessarily inflamed, and finally forms carbonic acid, as one of the products with the carbonic acid originally formed. But the carbonic oxide, to be changed into carbonic acid, requires in fact the oxygen of the atmosphere. ”

“ This oxide is black; it contains 25 oxygen on 100 copper: the black oxide is obtained by dissolving copper in nitric or sulphuric acid, then precipitating by lime water or an alkali, and heating the dried precipitate red hot. It may also be obtained by exposing copper to a red heat for some time in common air or oxygen gas, removing the scales and exposing them in like manner, till at length the black oxide is formed. ”

“ Metallic iron itself is capable of reducing carbonic anhydride to carbonic oxide, just as it liberates the hydrogen from water. Copper, which does not decompose water, does not decompose carbonic oxide. If a platinum wire heated to 300°, or spongy platinum at the ordinary temperature, be plunged into a mixture of carbonic oxide and oxygen, or of hydrogen and oxygen, the mixture explodes. ”

“ 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. ”

“ If the filings of steel, brass, zinc, or copper, enter into the composition, besides the products above-mentioned, there would be either an oxide of iron, an oxide of zinc, or, an oxide of copper, according as one or other of these metals are employed.
Copper, in fire-works, has the effect of communicating a green colour to the flame. M. Homberg, (Collection Acad.) observes, that the green colour in such cases is owing to the dissolution of the metal, which in fact is nothing more than the effect of its oxidizement. ”

“ Oxides.—Lead combines with oxygen to form five oxides, viz. Pb2O, PbO, PbO2, Pb2O3 and Pb3O4. The suboxide, Pb2O, is the first product of the oxidation of lead, and is also obtained as a black powder by heating lead oxalate to 300° out of contact with air. It ignites when heated in air with the formation of the monoxide; dilute acids convert it into metallic lead and lead monoxide, the latter dissolving in the acid. The monoxide, PbO, occurs in nature as the mineral lead ochre. This oxide is produced by heating lead in contact with air and removing the film of oxide as formed. ”

“ Third, by calcining iron or repeatedly exposing iron filings to a red heat, and trituration. Fourth, by treating a solution of the sulphate or other salt of the protoxide with oxymuriatic acid, or oxymuriate of lime till oxymuriatic acid is evolved; then precipitating the oxide which is thus converted [Pg 30] into the red. Fifth, by agitating water containing the green oxide recently precipitated, with oxygen gas. The red oxide is not sensibly magnetic. ”

“ Thus, when copper filings are heated in the air, it is evident that the material of the copper has united with that portion of the air we call oxygen to form the black product we call oxide of copper; and again, when oxide of silver is heated, it is evident that the resulting silver and oxygen gas were formerly portions of the material of the oxide. So, when water is decomposed by electricity, the conditions of the experiment show that the resulting oxygen and hydrogen gases must have come from the material of the water, and could have come from nothing else. ”