1902 Encyclopedia > Copper

Copper




COPPER is a metal which has been known to and used by the human race from the most remote periods. Its alloy with tin (bronze) was the first metallic compound in common use by mankind, and so extensive and characteristic was its employment at an early stage in pre-historic times that the epoch is known in archaeological chronology as the Bronze Age. Metallic relics of that age in the form of arms, ornaments, and domestic implements are still very abundant. By the Greeks and Romans both the metal and its alloys were indifferently known as ^OAKÓS and oss. As, according to Pliny, the Roman supply was chiefly drawn from Cyprus, it came to be termed ces cyprium, which was gradually shortened to cyprium, and corrupted into cuprum, whence comes our copper, the French cuivre, and the German hupfer.
Copper (chemically, Cuprum, Cu) is a brilliant metal of a peculiar red colour, in which respect it differs from all others excepting, perhaps, titanium, The atomic weight of copper is 63 3, and its specific gravity varies between 8'91 and 8'95, according to the treatment to which it may have been subjected. It takes a brilliant polish, is in a high degree malleable and ductile, and in tenacity it only falls short of iron, exceeding in that quality both silver and gold. By different authorities its melting point is stated at from 1000° C. to 1398° C. In electric conduc-tivity it stands next to silver ; the conducting power of silver being equal to 100, that of perfectly pure copper is given by Matthiessen as 96-4 at 13° C. On solidifying from its molten condition it expands. Copper is not affected by exposure in dry air, but in a moist atmosphere it becomes coated with green carbonate. When heated or rubbed it emits a peculiar disagreeable odour.
Copper, according to Walchner, is as widely distributed in nature as iron, and occurs in all soils, and ferruginous mineral waters and ores. It has been discovered in sea-weed ; in the blood of certain Cephalopoda and Ascidia, and of a species of Limulus; in straw, hay, eggs, cheese, meat, and other food-stuffs ; in the liver and kidneys, and, in traces, in the blood of man and other animals ; it has also been shown by Church to exist to the extent of 5 -9 per cent, in turacin, the colouring-matter of the wing-feathers of the Turaco. The ores containing copper in suffi-cient proportion to render its extraction economically practicable are numerous. It occurs not unfrequently native, sometimes in very great masses, as on the south shores of Lake Superior, where pieces of 150 tons weight have sometimes been obtained. Native copper most frequently occurs in masses of irregular form in rocky fissures, and often crystallized. The principal ores of copper are Cuprite, Melaconite, Malachite, Cloessylite, Atacamite, Ckrysocolla, Chalcocite, Chalcopyriie, Erubescite, and Tetrahedrite. Cuprite, or red oxide of copper, Cu20, is a mineral which crystallizes in the cubic system, and con-tains 88-78 of metal. It occurs in most cupriferous mines, but never by itself in large quantities. Melaconite, or black oxide of copper, CuO, contains, when pure, 79-85 of the metal. It was formerly largely worked in the Lake Superior region, and is abundant in some of the mines of Tennessee and the Mississippi valley. Malachite, or green carbonate of copper, CuC03, Cu(HO)2, is a beautiful and valuable ore containing about 56 per cent, of the metal; it is obtained in very large quantities from South Australia, Siberia, and other localities. Frequently intermixed with the green carbonate is the blue carbonate of copper, chessy-lite or azurite, 2CuCOs, Cu(HO)2, an ore containing when pure 55-16 per cent, of the metal. It was formerly char-acteristic of Chessy, near Lyons. Atacamite is a hydrated oxychloride of copper, occurring chiefly in Chili and Peru ; it crystallizes in the rhombic system. Chrysocolla is a hydrated silicate of copper, CuSi03, 2HsO, containing in the pure state 30 per cent, of the metal ; it is an abundant ore in Chili, Wisconsin, and Missouri. The sulphur compounds of copper are, however, the most valuable in an economical point of view. Chalcocite, redruthite, copper-glance, or vitreous copper, is a sulphide, Cu2S, containing very nearly 80 per cent, of copper. Copper pyrites, or chalcopyrite, a sulphide of copper and iron, CuFeS2, crystallizes in the pyramidal system and contains 34-6 per cent, of copper when pure; but many of the ores, such as those worked specially by wet processes on account of the presence of a large pro-portion of sulphide of iron, contain less than 5 per cent, of copper. Cornish ores are almost entirely pyritous ; and indeed it is from such ores that by far the largest pro-portion of copper is extracted throughout the world. In Cornwall copper lodes usually run east and west. They occur both in the Icillas or clay-slate, and in the growan or granite. Erubescite, bornite, or horseflesh ore is a sulphide of copper andiron much richer in copper than the ordinary pyrites, and containing 56 or 57 or, according to the for-mula FeCu2S3, 62-5 per cent, of copper. Tetrahedrite, fahlerz, or grey copper, a sulphide crystallizing in the cubical system, contains from 30 to 48 per cent, of copper, with arsenic, antimony, iron, and sometimes zinc, silver, or mercury. The numerous other compounds of copper have more interest from a mineralogical than from a metal-lurgical point of view.
Copper is obtained from its ores by two principal methods, which may be denominated—(1) the pyro-metal-lurgical or dry method, and (2) the hydro-metallurgical or wet method ; and a small proportion of metallic copper is procured by (3) the electro-metallurgical method.
The methods of working vary according to the nature of the ores treated and local circumstances. The dry method, or ordinary smelting, cannot be profitably practised with ores containing less than 4 per cent, of copper, for which and for still poorer ores the wet process is preferred.
SMELTING.—In Great Britain ordinary copper smelting is almost entirely centred at Swansea in Wales, although it is also practised in Lancashire. The processes there employed for extracting copper are technically known as the " English method, " in contradistinction to numerous other modified processes adopted at Continental and other foreign smelting centres. The following is an outline of the English method as conducted at Swansea.
The ores are divided by the smelter into two general classes—those containing sulphur, and those having little or no sulphur. The former are subdivided according as they contain much silica, iron pyrites, tin, arsenic, &c, or a larger or smaller quantity of copper. The object of this classification of ores in the yard is to enable the operative smelter to make up a constant working mixture, having the following characters :—
1. The copper present is not under 9 nor above 14 per cent.; if under the former it would be unprofitably poor ; if over the latter, the slags would have a tendency to retain copper, creating a loss.
2. After being calcined for an ordinary length of time, it will fuse easily without the necessity of adding flux, giving a clean and easily fused slag.
3. The mat or coarse metal obtained from fusion contains as nearly as possible 30 per cent of copper.
4. The mixture does not contain ores having impurities cal-culated to make the copper of too low a quality.
There is no definite or fixed rule to guide the smelter in these classifications, except a practised eye in distinguish-ing the character of ores, and the report of the assayer.
I. Calcination of the Ores.—The mixture of ores being selected according to these rules, it is carried to hoppers on the top of a large reverberatory furnace, termed the calcining furnace, and is then let down into the hearth, where, after drying a little, it is spread equally over the bottom, and covered to a depth of from 6 to 8 inches. The quantity of ore put in varies, according to the size of the furnace, from 3 tons to 4 tons. The fire of the furnace is kept low at first; after two or three hours the ore on the sur-face becomes visibly red, and the heat is gradually increased to a yellow red ; but this heat penetrates to the depth of only about 2 inches, consequently the ore has to be stirred and turned over by means of long iron paddles every hour, so as to expose a new surface to the action of the air and fire. The calcination lasts generally from twelve to twenty-four hours, the length of time being dependent on the proportions of silica and sulphide of iron in the charge. Calcining furnaces are now very commonly provided with Siemens regenerators and heated, with gas. The following changes take place :—the sulphur is partly burned off, form-ing sulphurous and sulphuric acids, and partly volatilized in the free state; arsenic is volatilized and oxidized ; and part of the copper and iron lose sulphur and combine with oxygen, forming oxides.
Before Calcination.
Copper 12'3
Iron 327
Sulphur 31-0
Silica 24-0
When the ore is sufficiently calcined, it is let down into the cubs or vaults beneath, by openings in the floor. Water is added to the hot ore in the cubs to prevent dust and assist further oxidation; the ore is then removed to a yard, and there stored up, ready for the fusing furnace. The following analysis of ore, before and after calcining, will give an idea of the changes that have taken place :—
After Calcination.
Copper 12-2
Iron 22-7
Oxide of Iron 18'5
Sulphur 16-2
Silica 30-4
100-0
100-0
II. Fusion of Calcined Ore.—The next operation is the fusing of the calcined ore, which is done in a reverberatory furnace, termed an ore-fusing furnace, fitted also with a hopper on the top for charging it. The charge consists of From 25 to 30 cwt. of calcined ore ;
From 7 to 9 cwt. of sharp or metal slag from operation IV.; From 2 to I cwt. cobbing.
When the charge islet down into the furnace it is spread equally over the bottom, the doors are all closed, every air-hole is stopped with clay, and the heat of the furnace increased as rapidly as possible.
After about five hours' firing, when the furnace has reached a white heat, the door-plate is removed, and a long iron rake passed through the contents to make sure that the whole is perfectly fused. This being the case, the workman begins the operation of skimming, that is, drawing off the slag, which floats on the surface of the mat, and removing it at the front door. When the surface is skimmed, the common practice is to let down a second charge of ore, and to fuse and skim in the same manner, before tapping the furnace to let out the metal or mat, which is generally tapped into large pits of water, and so granulated. These pits are from 6 to 8 feet deep, and from 4 to 5 feet square, and into them a perforated box is lowered, which receives the charge of metal, and is raised by a crane or pulley. The metal is then removed to a yard for the next operation. This mat is termed granulated coarse metal. In many cases the coarse metal is first run into moulds and subsequently crushed for the next operation.
The average composition of good coarse metal is given by Le Play as
Copper 38-7
Sulphur 29-2
Iron 33 6
Foreign metals 2-0
Slag, mechanically mixed I'l
99-6
That of the slag or scoriae is
Silica, mixed and combined 60-5
Protoxide of iron 28-5
Alumina, Lime, &c 11-0
100-0
III. Calcination of Coarse Metal.—This operation is performed in the same manner as the calcination of the ore. The charge of metal, which is about 4 tons, covers the bottom of the hearth to the depth of 4 inches or so. It is put in through the hoppers fitted upon the top of the fur-nace, as described for the ore. The coarse metal being easily fused, great care is required not to raise the heat of the furnace too high, otherwise the metal will cake, and by adhering to the bricks will prove prejudicial both to the calcination and to the furnace. When the charge is let into the furnace, it is slowly brought to a visible red, which during the next fourteen hours is gradually increased to a bright red heat. This temperature is continued until the charge has been altogether twenty-four hours in the furnace, when it is let down through the bottom into the cubs, and water is thrown upon it.
Metal after Calcination.
Copper 33
Iron 38
Sulphur 13
Oxygen, &c 16
The following analyses give an average result of the changes effected in this operation :—
Metal put into Calciner.
Copper 32
Iron 39
Sulphur 25
Other matters and loss, 4
100
100
IV. Fusion of Calcined Coarse Metal.— In this operation the charge for an ordinary-sized furnace of 8 feet by 13 feet is—
25 cwt. of calcined metal, 5 to 7 cwt. slags from the roaster and refinery furnaces; 2 to 3 cwt. of cobbing
In this mixture the oxide of iron is in excess in relation to the silica, and it is therefore much more easily fused than the ore ; but the reactions which take place are similar : the silica and oxide of iron combine to form slag, which floats upon the surface of the mat and has to be skimmed off, after which the mat is tapped out into sand-moulds. Two charges are generally fused before the metal is tapped out. This mat is termed blue metal from its being of a slate-blue colour; the scoria is termed sharp slag, from its containing an excess of oxide of iron, and being consequently used as a flux for fusing the ore in operation II.
Sharp Slag.
Oxide of iron 53
Oxide of copper 2
Silica, &c 45
100
The following is the composition of good blue metal and sharp slag :—_
Blue Metal.
Copper 53-8
Sulphur 20-5
Iron 12-6
Insoluble 4'2
Oxygen and loss 8'9
100
Should there be no ores such as carbonates or oxides on hand to smelt, the blue metal, instead of being tapped into sand-beds as described, is run into pits of water in the same manner as coarse metal, and subjected to another cal-cination and fusion.
When oxides and carbonates, such as the Australian ores, are on hand, they are generally fused with the calcined coarse metal, by which means a double advantage is obtained ; the excess of oxide of iron in the calcined metal fluxes the silica of the ore which has little iron, and the copper in the ore is converted into cupric sulphide, a con-dition necessary for reduction by the present method of smelting. The produce of this fusion is a mat termed pimpled or white metal, from its having small rough granules on the surface of the ingots. The average com-position of this metal is—_
Copper 78
Sulphur 18
Iron 2
Silica 2
100
The composition of the slag from this operation is very variable; it always contains copper, and has to be remelted.
V. Roasting.—This operation has been often identified with calcining, from which, however, it is distinct. The roasting differs from the fusing furnace by having a large opening in the side for putting in the charge, and it is fur-nished with more air-holes in the bridge. The charge for an ordinary-sized furnace is 3 tons. When the metal is brought to fusion, the air-holes of the furnace are all opened, and a free current is allowed to pass over the surface of the fused mass : the heat of the fire is then regulated so as to keep the charge in a sort of semi-fluid state. This is con-tinued for about twenty-four hours, during which a great portion of the sulphur is driven off, and the iron, by unit-ing with silica and other matters, forms scoria, which is from time to time skimmed off. When all the impurities are removed, and the mat or regulus acquires the composi-tion of sulphide of copper, Cu2S, then (except when the regulus has been very rich) begins another operation termed the second roasting, or roasting proper, requiring other twenty-four hours. In this last roasting, when the air-holes are opened, a brisk effervescence ensues over the surface of the fluid mass.
The chemical reactions which give rise to this effer-vescence may be explained thus. The oxygen of the air combines in the first place with a portion of the sulphur.
forming sulphurous acid. A portion of the copper is also oxidized, to form the sub-oxide, and instantly reacts upon another portion of the sulphide, reducing the metal. The reactions are chemically represented thus :—
2Cu20 + Cu2S = 6Cu + S02.
The process is a very beautiful one, and exhibits a nice adaptation of principles to practice. The sponge regulus has a specific gravity of 5, the reduced copper of about 8 ; so that the copper sinks to the bottom, where it is protected, and a new surface of regulus becomes exposed to the action of the air.
If the ore be pure, or if no select copper be required, the operation of roasting is continued until the whole of* the copper is reduced; when it is tapped out into sand-moulds, forming coarse copper, bed copper, pimpled copper, or blistered copper, according to quality. The term coarse copper is applied occasionally to all these kinds except the blistered. If the ingot sets with contraction and exhibits a smooth, hollow surface, it is termed bed, and generally indicates the presence of other metals, as tin. When the surface of the ingot is covered with pimples, it is termed pimpled copper, and indicates the presence of sulphur. When covered with large scales of oxide of copper, it is termed blistered ; but this is only when the copper is good and ready for refining. The following analysis of blister copper is given by Le Play :—
Copper 98-4
Iron '7
.Nickel, Cobalt, and Manganese "3
Tin and Arsenic -4
Sulphur.. "2
100-0
To make select copper, the roasting is carried on until about one-fourth of the copper in the regulus is reduced ; the furnace is then tapped, and the reduced metal is obtained at the bottom of the first and second ingots, or pigs, as copper bottoms, which contain most of the metallic impurities. The regulus is collected and again roasted, which produces the purest metal the ordinary process of smelting can give ; it is termed best selected.
VI. Refining.—In this operation, the remainder of the sulphur and foreign metals present in the copper is removed, and the metal is brought into a condition fit for the market. The refining furnace is similar in general form to a roasting furnace, except that the bottom inclines gradually down from all sides towards a deep part, or well, which is near the end door. It has also a large door on one side, but neither opening in the roof nor side tap-hole. Siemens's regenerative furnace has been very generally intro-duced for refinery purposes. When the copper is to be finally ladled out of the furnace the deep part, or well, allows of the ladle being dipped into the metal till the last portions are quite baled out. From 6 to 8 tons of copper from the roasting furnace are put into the refining furnace, the doors and air-holes of which are closed, and the heat is raised until the metal is in fusion, when the air-holes are opened. A short roasting is generally required, which is done in the manner above described, and the scoria which collects is carefully skimmed off. The separation of impurities is facilitated by occasionally stirring the metal with a rake. Some refiners throw pieces of green wood upon the surface, under the impression that it assists the escape of sulphur. The roasting is continued until a ladleful of the metal taken out sets with contraction. If the metal be very coarse, it will set with a surface having a frothy appearance ; if finer, it sets with expansion, first round the edge, then swelling towards the centre, forming a little mound or cone, and occasionally boiling over and throwing up jets of metal, forming a miniature volcano. When the setting of the metal in the ladle is favourable, the charge is ready for the operation of poling. A quantity of charcoal or anthracite coal is first thrown upon the metal to prevent oxidation by the air, and then the end of a large pole of green wood, generally of birch or oak, is inserted into the melted copper, and kept pressed down to the bottom of the metal, which spurts and boils violently. This operation, it will be at once apparent, consists in the reduction of an oxide or suboxide. Since oxide of copper dissolves in metallic copper, as a salt dissolves in water, and makes it brittle, to put pieces of wood or charcoal upon the surface would not remove the oxygen; hence the necessity of poling, in order to bring the carbonaceous matters into contact with the dissolved oxide. As the poling proceeds the refiner takes from time to time small samples called assays, which he hammers and breaks for examination. When the copper reaches the proper " pitch " the assay bends without break-ing, and if cut and broken the fracture is fibrous, and pre-sents a silky lustre. When this pitch is attained the pole is withdrawn, and a quantity of charcoal thrown upon the surface ; and, if the copper is for rolling or hammering, a little lead is added to the charges to insure toughness.
In making what is termed best selected copper, the refining is performed in the manner described, but no lead is added. This quality of copper is used for the manufacture of fine alloys, such as the best brass, or Muntz's yellow metal. Copper a little over-poled is generally preferred for these purposes.
When the copper is brought to the proper pitch by the refining operation it is ladled out into moulds. The follow-ing are the forms in which British smelted copper is usually cast:—
Cake, 19 x \1\ x If inches, weight 1 cwt. 1 qr.
Tile, 19xl2ix | „ ,,1 qr. 3 lb.
Ingot, 11 x 3ixH ,, „ U to 16 lb.
During the ladling out the refiner takes an assay at short intervals, as the metal is liable to get out of pitch, or be-come dry, as under-poled copper is termed, in which case poling has to be resumed. So much depends upon refining, that the best copper by a defect in this operation will be rendered unmarketable.
A great variety of improvements in copper-smelting have been proposed and patented, one or two of which have been usefully applied. Several modifications of the various processes are also adopted, to suit the quality of the ores and the kind of copper to be produced. These are all suggested by the experience of the smelters in dealing with the materials at their disposal.
WET PROCESSES.—Several methods of extracting copper by the wet way have been more or less in practice at various periods ; but it is only of recent years that one of these has been established on a scale of great commercial extent and importance. From a very early time it has been known that the water which drained from mines containing pyritous copper ores, and which from the oxidation of the sulphide of copper contained some proportion of cupric sul-phate, yielded metallic copper by precipitation in the presence of malleable or cast iron. The copper obtained in this way is known as cementation copper, and from the Spanish and Portuguese pyrites mines a considerable amount of metallic copper has long been so precipitated. The process now very extensively adopted for treating Spanish and Portuguese pyrites, and some ores of similar composition from other countries is that patented by Mr William Henderson in 1859. Mr Henderson's process is in several essential particulars the same as one patented in 1842 by Mr William Longmaid, which, however, was chiefly designed for the production of sulphate of soda, copper being only a by-product. There can be no doubt that Mr Henderson is the practical originator of the wet process,
PER
which in Great Britain now occupies a most important position among metallurgical industries.
The orestreated by the Henderson process are remarkably constant in character, and the following may be taken as representing their average composition :—
Sulphur 49-00
Iron 43 '55
Copper 3-20
Lead 0-93
Arsenic 0-47
Zinc 0-35
Lime, with traces of silver, gold, &c 2-50
100-00
The pyrites is first employed by alkali manufacturers and other consumers of sulphuric acid as a source of that sub-stance, in burning for which the ore loses about 30 per cent, of its weight. It is this burnt pyrites which forms the raw material of the process. The various stages it undergoes are briefly as under.
I. Grinding.-—The burnt ore, as received from the acid
burners, is first mixed with about 15 per cent, of common
salt, and ground to a fine powder by jjassing it between a
pair of heavy cast-iron rolls. As the amount of sulphur
left in the burnt ore is apt to vary, it is necessary
to ascertain its proportion in each parcel of burnt pyrites.
When the sulphur falls short of the proportion necessary
for effecting the decomposition which follows, a sufficient
quantity of " green " or unburned pyrites, is added to pro-
duce a proper balance. If, on the other hand, the sulphur
has been insufficiently extracted, " dead" roasted ore is
added.
II. Calcination.—This operation is accomplished in
several kinds of furnaces, that used by the Tharsis Sulphur
and Copper Company being a large muffle or close furnace.
By others a patent furnace with a revolving hearth and
mechanical stirring arrangement has been adopted with
good results ; and some use open reverberatory furnaces
heated by gas from Siemens's generators. During the
roasting the mixture is frequently stirred, and, in the case
of hand-worked furnaces, turned with long rabbles, and the
completion of the operation is ascertained by test assays,
When the copper has been brought into a soluble condition,
the charge is raked out of the furnace and permitted to cool
under a screen at its mouth. By the calcination the
sulphur in the compound is first oxidized, sulphate of
sodium is formed, and at the same time the chlorine from
the sodium chloride unites with the copper to form cupric
chloride. A small proportion of cuprous chloride is also
formed, and special precautions have to be taken to prevent
the extensive formation of this compound, which is dissolved
only with difficulty. The hydrochloric acid and other
gaseous products evolved during the calcination are con-
densed as " tower liquor" in ordinary condensing towers,
and the product is used in the subsequent process of
lixiviation.
III. Lixiviation.—The calcined ore is conveyed to tightly-caulked wooden tanks, in which it receives repeated wash-ings with hot water, tower liquor, and dilute hydrochloric acid, till all the soluble copper is thereby extracted. The product of the later washings is pumped or drawn up by a modification of Giffard's injector, to serve as a first liquor for subsequent charges of the lixiviating tanks, and no solution under a definite strength is permitted to pass on to the next stage in the process. The insoluble residue in the tanks consists of "purple ore," an almost pure ferric oxide, largely used in " fettling" blast furnaces, and for smelting purposes; besides which it is available as jewel-ler's rouge.
Precipitation.—The precipitation of metallic copper from the solution of its chloride is accomplished in large tanks by means of metallic iron in the same way that cementation copper is obtained from solutions of the sulphate. The solution is run into the tanks, in which there are miscellaneous heaps of old malleable iron; the chlorine combined with the copper unites with the iron, and metallic copper in a state of fine division is throwzi down. The completion of the precipitation is ascertained by dipping a bright steel knife into the solution in the tank, and when no deposit of copper covers the steel the liquor is run off and a new charge conveyed into the tank. The tanks are drained periodically for removing the precipitate, which is first roughly separated from small pieces of iron, after which it is more thoroughly freed from iron, &c, by washing in water in a rocking sieve apparatus. The precipitate so obtained should contain 80 per cent, of metallic copper, which is either smelted directly for blister copper, or may be fused with the white metal of the ordinary smelting process, and subsequently roasted.
It has been found possible to extract in this process with profit the small proportions of lead, silver, and gold which Spanish pyrites is known to contain. Two processes are in operation for this purposes—one devised by Mr F. Claudet and the other by Mr W. Henderson, the original patentee of the wet process. The liquors from the first three washings contain practically all these metals, and they alone are treated. Mr Claudet precipitates them from the solution by means of iodide of potassium. Mr Henderson dilutes his solutions to from 20° to 25° Tvvaddell, and adds a very weak solution of a lead salt, such as the acetate, by which he obtains a cream-coloured precipitate containing about 53 per cent, of lead, 5 or 6 per cent, of silver, and 3 oz. of gold to each ton of the precipitate.
The importance of the wet process may be estimated from the fact that although it originated only in 18G0, already 14,000 tons of copper are annually produced by it in Great Britain alone, out of an annual production for the whole world estimated at from 126,000 to 130,000 tons.
ALLOYS OF COPPEE.—Copper unites with facility with almost all other metals, and a large number of its com-pounds are of the highest importance in the arts. Indeed copper is much more important and valuable as a con-stituent element in numerous alloys than it is as pure metal. The principal alloys in which it forms a leading ingredient are—1st, brass; 2d, bronze ; and 3d, German or nickel silver; and under these several heads their respective applications and qualities will be found. These alloys are each much diversified as regards the relative proportions of the various metals which enter into their constitution, and these differences similarly modify the appearance and physical properties of the compounds. In this way for practical purposes they may be regarded as a great number of separate metals, each possessed of distinct qualities which fit it for special industrial uses. The following tables, compiled from various authorities, represent the analysis of typical examples of the several alloys: —
TABLE A.—Composition of Brass or Copper and Zinc Alloys.

Copper. Zinc. Tin. Iron. Lend.
Roman coin—Titus
Tombac or Talmi gold
Statue of Minerva in Paris
English brass
Aich metal
Rosthorn's sterro-metal
Ship-nails, bad 96-06 86-40 83 00 70-29 60-20 54-00 52-73 62-62 2-71 12-20 14-00 29-26 38-10 40-50 41-18 24-64 1-10 2-00 ( -17
2-64 0-85 0-30
l'éo
5-50 l'-'oo
0-28
4-72 8-69
Muntz's metal, or yellow sheathing, consists of 60 parts of copper and 40 of zinc, but the copper may vary from 50 to 63 per cent, and the zinc from 50 down to 37.
Aluminium bronzes are composed of pure copper with from 2J? up to 10 per cent, of aluminium. Phosphor bronze, according to the purposes for which it is intended, contains from 3 to 15 per cent, of tin and from \ to 2J,- per cent, of phosphorus. Small proportions of other metals, among which are silver, nickel, cobalt, antimony, and bismuth, with sulphur, frequently enter into the composi-tion of bronzes.
TABLE C.—Composition of Nickel Silver.

a
p.
o O Nickel. S «
e Sj d Cadmium.
Chinese Packfong.. ...... . 40-40 69-80
63-34
62-63 31-60 19-80
19-17
10-85 2-60
trace trace 25-40 5-50
17-01
26-05
4-7
Parisian metal for spoons, forks, &c. ,.
English nickel silver for
plating
English nickel silver for plating (another kind)






SALTS OF COPPER.—Several salts of copper possess con-siderable industrial value, chiefly for the formation of bluo and green pigments, in dyeing and calico-printing, and for the deposition of metallic copper by electro-metallurgy, <fec. The principal salts of copper are the acetate, the carbonate, and the sulphate.
Acetate of Copper or Verdigris.—This salt is found in commerce in the two forms of basic and neutral acetate. The principal seat of the manufacture of the basic acetate is Montpellier in France, where the marc and other refuse of grapes, after the expression of the juice for wine-making, is employed as a source of the acetic acid necessary. Sheets of copper are placed among this refuse, and these soon become coated with a deposit of verdigris, which has only to be scraped off, kneaded up with water, and pressed into cakes. The neutral salt is prepared from basic acetate by dissolving it in pyroligneous acid (wood vinegar) and evaporating the solution to the crystallizing point. It is also formed by the double decomposition of the acetates of lead and calcium with sulphate of copper. Verdigris is much used as a pigment both in oil and water-colour paint-ing and in dyeing, and as a basis of compound pigments.
Carbonate of Copper in an impure condition forms a valuable series of pigments called verditer, Bremen blue, or Bremen green, possessing various shades of mingled green and blue according to the nature of the compounds with which the carbonate is mixed. The basis of these pigments is prepared by an elaborate and tedious process from the oxychloride of copper.
Sulphate of Copper, CuS04, 5H20, called also blue stone, or Roman vitriol, is, on the large scale, prepared direct from the cementation water from pyrites mines by evaporation to the crystallizing point. It is also prepared by the oxidation of sulphide of copper in a furnace at a compara-tively low heat, and by the direct action of sulphuric acid on metallic copper, as well as by various other processes. The sulphate of copper is very largely used as a basis for the preparation of other copper compounds, in electrome-tallurgy, in calico-printing, and in the American amalgama-tion method of extracting silver from its ores. In medicine it is employed as an emetic. On its use in the manufacture of chlorine, see vol. v. pp. 491 and 679.
Of pigments other than those above-mentioned having a
copper basis, there may be enumerated the native carbonate,
mountain or mineral green; Brunswick green, an oxy chloride
obtained by moistening copper foil exposed to the atmo-
sphere with hydrochloric acid or solution of ammonium
chloride ; Scheele's green (Cu2As205), an arsenite of copper;
and Schweinfurt green, an aceto-arsenite of copper.
Casselmann's green, a pigment discovered in 1865, is a
compound of cupric sulphate with potassium or sodium
acetate. While it almost rivals Schweinfurt green in
brilliancy, it possesses the advantage of being entirely free
from arsenic, which renders the latter pigment and Scheele's
green so virulently poisonous. At the same time it must
be remembered that all copper compounds are poisonous,
although the preparations that do not contain arsenic are
not so deleterious in their manufacture and applications as
are the others. (J. PA.)
COPPER ASSAYING.—In the Cornish method of assaying there are five operations,—the fusion for regulus, the roasting of the regulus, fusion for coarse copper, refining, and the cleaning of the slags. (1) The sample of ore is first inspected to ascertain its quality, and is then reduced to powder. If too much sulphur is present it may be expelled by roasting the ore, or by using nitre in the fusion ; in some cases it may be requisite to add sulphur in order to obtain a good regulus. A flux is employed consisting usually of lime, borax, fluor-spar, and glass, which form a slag with the excess of iron in the ore. The button of regulus obtained must be such that it separates easily from the slag without breaking. (2) The regulus ground to a fine powder is next roasted for from 20 to 30 minutes, the heat applied being raised towards the end of the operation ; the sulphides of iron and copper are thus converted into oxides. (3) In the fusion for coarse copper a flux of sodium bicarbonate with tartar or borax and nitre is employed ; a button of metallic copper is obtained which breaks with a fine-grained and greyish or orauge-coloured fracture. (4) Refining consists first in the fusion of the button of coarse copper and the oxidation by the air of sulphur and foreign metals present in it; secondly, in the addition of refining flux, with the production of dry copper, or copper at tough pitch. Commonly a flux of three parts by measure of tartar, two of nitre, and a little salt is melted in the crucible employed for the previous operation, and into it the button of coarse copper is dropped ; the surface of the fused copper having become clear of oxides, a little refining flux is now added, and in about a couple of minutes the contents of the crucible are transferred to the mould. (5) The slags from the two last operations are mixed with tartar or charcoal and fused; and the weight of the small prills or shots of copper obtained is ascertained. Assaying by the wet way is usually conducted by treating a weighed sample of the ore with nitric acid, neutralizing with ammonia, and adding standard solution of potassium cyanide till the blue colour of the liquid is discharged, copper-ammonium-cyanide, free ammonium cyanide, ammonium formate, and urea being produced. Silver, nickel, cobalt, and zinc may interefere with the estimation of the copper by this method ; the first may be removed by adding a little hydrochloric acid; from the three other metals the copper can be freed by precipitating it as sulphide by means of sodium thiosulphate, the sulphide obtained being decomposed by nitric acid, and the copper estimated by ammonia and potassium cyanide in the usual manner. Before analysis by the wet way it is often advisable to roast the copper ore in order to expel sulphur. Steinbeck's process for determining the amount of copper in poor ores and schists consists in the treatment of the pulverized rock with hydrochloric acid, digestion in the cold, subsequent boil-ing with nitric acid, precipitation of the copper from the re-sulting solution by zinc in presence of platinum, and finally the titration of a solution of the precipitated copper. Dr Haen's method of estimation is based upon the formation of free iodine when excess of potassium iodide is mixed with solution of a copper salt,—the sulphate, for example. Copper is estimated gravimetrically in the metallic state, as in Luckow's electrolytical process; as cuprous sulphide, Cu2S, which may be obtained by heating cupric sulphide, CuS, in a current of hydrogen, or a mixture of cuprous sulphocyanate, Cu2(CNS)2, with sulphur; and as cupric oxide, prepared by igniting the precipitate of hydrate, Cu(OH)2, formed when potash or soda is added to solu-tions of cupric salts. Before the blowpipe, copper com-pounds give with microcosmic salt or borax a green bead, which becomes blue on cooling ; when ignited on charcoal in the inner flame with sodium carbonate and cyanide, they afford scales of metallic copper; most of them, also, when heated in the inner, impart to the outer flame a brilliant green coloration.
For further details as to the chemistry of copper see CHEMISTRY, vol. v. pp. 528-30.









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