Copperplate

“ When lead is the only easily oxidisable metal present, the stained portion of cupel is yellow when cold. A greenish tint may be due to small quantities of copper or, perhaps, nickel, cobalt, or platinum. Larger quantities of copper give a greenish grey or almost black colour. A dark green and corroded cupel may be due to iron. Rings of pale-coloured scoria may be due to tin, zinc, antimony, or arsenic. When the cupel shows signs of the presence of these metals in objectionable quantity, it is well to repeat the assay and scorify so as to remove them before cupellation. ”

“ The metal obtained is run out into moulds of sand. It is covered with black blisters, like steel of cementation; whence it has got the name of blistered copper. In the interior of these pigs, the copper presents a porous texture, occasioned by the ebullition produced by the escape of the gases during the moulding. The copper being now almost entirely purged from the sulphur, iron, and the other substances with which it was combined, is in a fit state to be refined. ”

“ As the transfer from the plate can be readily made it is also better applicable to small editions than is photolithography. It is, however, not as convenient in the latter respect as plate printing, and it does not give a resulting impression equal in clearness or durability to the impression directly from the plate.
Etching on copper for chart publication has been recently developed in the Coast and Geodetic Survey. A finished tracing is made, the surface of a smooth copper plate is sensitized, and by exposure to the sun a print is made on the sensitized surface. ”

“ The alloys of copper and tin may be decomposed by dissolving them in an acid, the muriatic for instance, and immersing a sheet of iron, which will precipitate the copper. The tin may then be separated by immersing a plate of lead, or zinc, by either of which metals, it will be precipitated.
Bronze, being a mixed metal, in which the copper forms the principal ingredient, is sometimes used in fire-works, in lieu of copper or brass; for its effects are similar. By the combustion of bronze filings, we have an oxide of copper and an oxide of tin. ”

“ Now, we know that copper is found in the mines in a state of such comparative purity as to require very little smelting for the purpose of being brought into a state fit for use, while, on the other hand, iron in its rough state looks more like a stone than a metal, and, moreover, before it can be worked at all, must be subjected to a difficult process of smelting by means of a very powerful fire. If we look at the question only on this side, we are forced to conclude, that copper must have been found and employed before iron. ”

“ Next to gold, silver, and platinum, copper is the most malleable and ductile of metals; it may be drawn into wires as fine as hair, or beaten into leaves as thin as those of silver. The rust of copper is very poisonous. Copper, mixed with a certain quantity of tin, forms bell-metal. With a smaller proportion, it forms bronze, a substance used in sculpture for casting figures and statues. It is an abundant metal, and is found in various parts of the world. Native oxides of copper are found in Cornwall, Siberia, and in North and South America. ”

“ The excess of oxygen is removed by “poling”—that is, reduction, effected largely by charcoal, as well as by reducing gases—successive samples showing less and less of the characteristics of dry copper. The surface becomes level, the metal exceedingly tough, the fracture fine-grained to silky in texture, and a fine salmon-pink in colour. With satisfactory mechanical properties, the metal has now become tough pitch copper. ”

“ Copper may be separated, in a state of great purity, from ANTIMONY, ARSENIC, BISMUTH, LEAD, IRON, TIN, ZINC, &c., as it exists in bell-metal, brass, bronze, gun-metal, mosaic gold, and other commercial alloys, by fusing it in a crucible for about half an hour, along with copper scales (black oxide) and ground bottle-glass, or other like flux. The pure metal is found at the bottom of the crucible, whilst the impurities are either volatilised or dissolved in the flux. The proportions for refining commercial copper are, metal, 10 parts ”

“ The thin copper-plate, when removed from the wax mould, is just as minutely correct in the lines and points as was the wax mould, and the original page of type. But it is obvious that the copper sheet is no use to get a print from. You must have something as solid as the type itself before it can be reproduced on paper. So a basis of metal is affixed to the copper film, and this again is backed up with wood thick enough to make the whole type-high. ”

“ The very great variety of purposes for which the metal called copper is used, renders it one of the most valuable productions of this country, and several very important manufactures would be incomplete without it, since it is the principal material of which many large vessels are formed, and is also largely employed as an alloy for other metals. Although the metal is sometimes found in a pure or native state, its most abundant ore is that known as copper pyrites, of which there are many kinds. ”

“ Though copper is such a tough substance, and though tin is also tough, yet when melted together to make speculum metal, as this alloy is called, they produce an exceedingly hard and brittle material. When we remember that we could never break a copper penny piece by throwing it down on the flags, it may seem strange that the “speculum metal” should be so exceedingly brittle. A piece the size of a penny would be more brittle than a bit of glass of the same dimensions, and when the speculum is cast, unless it is cooled very carefully, it will fly into pieces. ”

“ To apply it on new plates use somewhat dilute nitric acid applied with a swab to free the surface of the copper from oxides or impurities, then rub the ball of amalgam over the surface, using some little force. It is always well when copper-plates are coated with silver or zinc by means of mercury to let them stand dry for a day or two before using, as the mercury oxidises and the coating metal more closely adheres.
Only the very best copper-plate procurable should be used for battery tables; bad copper will always give trouble, both in the first “curing,” and after treatment. ”

“ The roasted ore is then smelted to a mixture of copper and iron sulphides, known as copper “matte” or “coarse-metal,” which contains little or no arsenic, antimony or silica. The coarse-metal is now smelted, with coke and siliceous fluxes (in order to slag off the iron) , and the product, consisting of an impure copper sulphide, is variously known as “blue-metal,” when more or less iron is still present, “pimple-metal,” when free copper and more or less copper oxide is present, or “fine” or “white-metal,” which is a fairly pure copper sulphide, containing about 75% of the metal. ”

“ A white crystaline stone is also found to contain a great quantity of yellow copper. The lodes of copper ore generally lie deeper than those of tin, and its ores are mostly of the pyritous and sulphurated kinds, with more or less arsenic. “The lodes, both of tin and copper, appear most frequently to have granite for their country, and to make an angle from 60° to 76° with the horizon.” The matrices of copper ore are very numerous. Among the blue ores, there is one of an extremely fine blue earth. ”

“ If neither of these evils should arise, still the bur produced by the punching might be expected to interfere with the goodness of the impression produced by the copper-plate; and the plate itself, after having all but its edge covered with figures, might change its form, from the unequal condensation which it must suffer in this process, so as to render it very difficult to take impressions from it at all. It is impossible by any drawings to solve difficulties such as these, experiment alone can determine their effect. ”

“ When granulated by falling molten into water, it acquires a rough but exceedingly beautiful surface. Reduced from the chloride in the humid way, it appears as a gray, spongy powder. It crystallizes in cubes and octahedrons when allowed to cool from the molten condition or precipitated from solution for instance, by copper or zinc. Sometimes it is precipitated black by the galvanic current or by zinc. In hardness and strength it is superior to gold and inferior to copper; a slight alloy of copper hardens and strengthens it. In malleability and ductility it is inferior to gold only. (See Metal.) ”

“ 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. ”

“ In the reduction of the oxides of this group, no sublimate is visible upon the charcoal.
(a.) Copper (Cu) .—This metal occurs in the metallic state, also as the protoxide, and as oxides combined with acids in different salts (carbonate of copper as malachite, etc.) The sulphide of copper is the principal ore of copper occurring in nature. In the metallic state, copper is of a red color, has great lustre and tenacity, is ductile and malleable, and crystallizes in octahedrons and cubes. It melts at a bright red heat, is more difficult than silver to fuse, but fuses more readily than gold. ”

“ When the refining has been properly done, and neither too much nor too little oxygen is present, the copper is in the condition of “tough pitch,” and is in a fit state to be worked.
Copper is said to be “tough pitch” when it requires frequent bending to break it, and when, after it is broken, the color is pale red, the fracture has a silky luster, and is fibrous like a tuft of silk. On hammering a piece to a thin plate it should show no cracks at the edge. At tough pitch copper offers the highest degree of malleability and ductility of which a given specimen is capable. ”

“ After taking out a somewhat rumpled shirt, a suit of underclothes and a couple of pair of socks, Prawle said:
“Now, young gents, I’m going to show you some of the finest specimens of real virgin copper ever dug out of mother earth.”
“Oh!” exclaimed Charlie, a slight shade of disappointment in his voice, “I thought it was gold or silver quartz you had there. But copper——”
“Young man,” said Prawle, diving one hairy paw into his grip and fishing out a magnificent specimen of raw copper, “look at that and hold your breath. There is ninety per cent of copper in that hunk. Think of that! ”

“ Sulphuret of Copper; Kupferglanz. Of a steel gray metallic aspect; crystallizes in rhomboids; specific gravity 5·69; somewhat sectile, yet brittle; fusible with intumescence at the blowpipe, and yields a copper bead with soda; soluble in nitric acid; becomes blue with ammonia, but lets fall scarcely any oxide of iron. Its constituents are, sulphur 19; copper 79·5; iron 0·75; silica 1·00. It occurs in small quantities in Cornwall, &c.
The chemical preparations of copper which constitute distinct manufactures are, Blue or Roman vitriol; for which see Sulphate of Copper ”

“ Best Select Copper.—For the production of copper alloys, such as best brass, etc., it is essential that the copper should be pure. The impurities which are present in ordinary tough copper, and which may be valuable for imparting strength to the material, have a very harmful effect when present in alloys. In the older Welsh process of manufacturing copper, a special method was employed for obtaining metal free from these impurities, especially arsenic and antimony. ”

“ The tensile strength of pure cast copper is 8 to 9 tons per square inch. Mechanical work causes an increase in the value up to 14, or even 16 tons, cold work exerting a still more marked influence; whilst 33 tons and more per square inch has been recorded with cold-drawn fine wire. The elongation varies according to the mechanical work which the metal has undergone; the amount ranges from 35 to 40 per cent. ”

“ It is then, in his opinion, the solution of the metal—the wear of its surface, by keeping it smooth, which prevents the adhesion of foreign matter. Whenever the copper is unequally worn, deposits will, without doubt, rest in the rough parts, or depressions in the metal, and afford a soil or bed in which sea-weeds can fix their roots, and to which zoophytes and shell-fish can adhere; but there is another cause of foulness on the protected sheathing, arising from the deposit of earthy matter upon the copper, in consequence of its electro-negative condition. ”

“ Sometimes native copper, and carbonate of copper, are also present in the same specimen. In some instances, a partial decomposition has taken place, converting its green color into greenish-white, or perfect white, and rendering it so soft as to be cut with a knife. Sometimes the grains or masses of native copper are interspersed among the prehnite, and slender threads of this metal occasionally pass through the aggregated mass of greenstone, prehnite, &c., so that, on breaking it, the fragments are still held together by these metallic fibres. ”