Domestic Encyclopædia (1802)/Copper
COPPER, one of the finest imperfect metals, is found in the bowels of the earth, in the following states.
I. Native or pure copper, which possesses the red colour, the malleability, and all the other properties of this metal, and is discovered in various parts of England and Wales, but more particularly in the county of Cornwall. It is formed into threads or branches, and lies in veins of considerable thickness, contained in blackish serpentine stone, mixed with a brownish red, and covered externally with a greenish nephrites.
II. Mineralized by fixed air; of which there are several varieties: 1. Red copper, or hepatic ore of copper, which is known by its dusky colour. It is generally mixed with native copper and mountain green. 2. Earthy copper, or mountain green, which is mostly found in a loose friable state, and frequently blended with calcareous earth, iron, and sometimes with arsenic.
III. Mineralized by sulphur, with a small proportion of iron. This is of a deep violet grey, or liver colour, melts with a gentle heat, is ponderous, flexible, and yields to the knife. When broken, it appears of a bright golden colour, and is the richest of all the copper ores, affording from 80 to 90 per cent. of copper, 10 or 12 of sulphur, and a small proportion of iron.
IV. Mineralized by sulphur, with a large proportion of iron, or azure copper ore; it varies from the preceding sort only in the quantity of iron it contains, which sometimes amounts to 50 per cent. It yields 50 or 60 pounds of copper per cwt. the rest being sulphur.
The principal parts of Great Britain, which afford copper, are the counties of Cardigan, Chester, Cornwall, Cumberland, Derby, Devon, Northumberland, Lancaster, Salop, Somerset, Stafford, York, Warwick, Westmoreland; in the Islands of Mann and Anglesey; and also in Scotland.
Copper is less difficult to be purified than iron; and, when exposed to the air, calcines, being converted into a green rust or calx, which is soluble in water, and imparts an astringent taste, as well as pernicious qualities.
When taken into the human body, copper acts as a violent emetic, and is generally considered as poisonous: and, though it has occasionally been prescribed by physicians, it is always an unsafe and hazardous remedy. Hence, the greatest precaution is necessary in using this metal, of which so many kitchen utensils are manufactured. Beside the most scrupulous attention to cleanliness, it is extremely improper to leave any liquid to cool in a copper vessel; for this metal is more easily decomposed by liquids, when cold, than in a heated state.
In order to prevent the deleterious effects of copper, the vessels made of it are usually covered with tin, on the inside. It is nevertheless justly complained, that the tinning of copper vessels is not sufficient to defend them from the action of the air, moisture, and saline substances; because, even when strongly coated, they are liable to rust. This may be remedied by a thicker covering of tin; and a manufacture of this kind was established a few years since at Edinburgh; in which the following method is adopted: The surface of the copper is made very rough, by means of a machine contrived for that purpose; then a thick coat of tin is laid on, and the copper hammered smooth as before. To prevent the tin from being melted, and the surface of the copper from being left uncovered, in consequence of a degree of heat superior to that of boiling water, the tin is alloyed with iron, silver, or platina, in order to diminish its fusibility, and render it capable of being applied in thicker layers on the copper.
A patent was also granted, in August 1770, to Mr. Maurice Crawford, of Edinburgh, for his new method of tinning copper, which would last ten times longer than that by any former process. This patent is now expired; we shall therefore communicate the following particulars: The copper must be wrought in the common way, till it is ready for the first pickling, which should be performed in the usual mode. It is next frozen on the inside, on rough stakes, or by any other method of freezing, which opens the pores of the copper, and causes the tinning to penetrate. It is then to be pickled a second time, and scoured clean on both sides, when it should be coated with sal ammoniac and grain tin; after which the copper should be well lined with a metal, consisting of one pound of grain-tin, and one pound and a half of zinc, spelter, or other metal of equal wholesomeness and durability: when this operation is performed, the outside should be scoured clean, and rough-planished on a bright stake. The inside is also to be rubbed with chalk and water, till the tin become clean, when it is to be polished, and smoothed hard to give it a gloss. Ladles, skimmers, and all such culinary utensils, as require to be tinned on both sides, are to be frozen on a cut stake, in the manner already mentioned, and dipped in the melted metal. By this process, the vessel will be much more beautiful and regular, better calculated to resist the effects of heat, and at the same time prevent fatal accidents.
Copper is likewise applied to various other purposes: when combined with tin and zinc, it is employed in enamel painting, dyeing, &c. If it be mixed with a considerable proportion of tin, it produces what is called bell-metal; if in a smaller quantity, Bronze (see voi. i. p. 362), With zinc it forms Brass (ibid. p. 326-7), Pinchbeck, &c. according to the proportions used.
By the 2d and 3d Edward VI. c. 37, and also by the 5th and 6th William and Mary, c. 17, no copper, brass, latten, bell-metal, pan-metal, gun-metal, or shruff-metal, whether clean or mixed (except tin and lead, and also except copper and mundic-metal made of British ore and foreign copper in bars), may be exported, on forfeiture of double the value, and of 10l. for every thousand weight. But, by an order of Council, dated July 3, 1799, no sheet copper, copper in bolt-staves, bars, rings, and nails, or copper in such a state that can be easily converted into naval stores, shall be exported without leave of the Privy Council, on penalty of forfeiture, besides treble the value thereof, and the ship; 33 George III. c. 2.
With respect to the poisonous qualities of copper, when introduced into the stomach, it is less dangerous than arsenic; as the former is more easily dissolved.—And though the editors of the Encyclopædia Britannica have declared that they have not met with any well authenticated instance of a person who has died in consequence of having swallowed even verdigrease itself, yet so many examples have lately occurred, that there is not the least doubt of the deleterious properties of copper. Of the many cases that might be adduced, we shall select one, which is authenticated by Dr. Percival, of Manchester. A young lady had eaten about 3 or 4 ounces of pickled samphire, strongly impregnated with copper, and had drunk afterwards the 5th part of a pint of vinegar, on an empty stomach. She had not applied for medical aid, for two days, and in the course of ten she died. Dr. Percival is of opinion, that an emetic, if it had been administered in an early stage, might probably have saved her life. Persons apprehensive of the pernicious effects of copper, have been successfully relieved by castor oil, or clysters; and, if any suspicion arise of metallic salts having been swallowed, the same physician judiciously recommends calcined magnesia, as it will not only decompose them, but at the same time gently contribute to carry off the noxious matter.