Experiment 43. If to a solution of nitrate of copper pulverised lime be added, and the mixture shaken, a precipitate will be produced, which, when collected, washed and dried, will form a green pigment.

Rationale. The nitric acid of the nitrate of copper unites with the lime, forming nitrate of lime, whilst the copper is precipitated in the state of an oxyd.

Experiment 44. If the green precipitate of the last experiment be mixed on a slab with a little quicklime, it will acquire a lively blue colour, forming the blue verditer.

Remark. Sulphate of copper is generally used instead of the nitrate; but in that case, besides being contaminated with sulphate of lime, some oxyd of iron is always present. The combination of copper and arsenic acid, forming arseniate of copper, or Scheele's green, is effected in the following manner:

Experiment 45. Dissolve potash in water with heat; add white oxyd of arsenic or arsenic acid to the point of saturation, and filter the liquor. Then take a warm solution of sulphate of copper, and pour it into the arseniate of potash: a little only must be added at a time, and it must be continually stirred with a glass rod. Leave the mixture at rest till a precipitate is formed; then decant the liquor, and having washed the residuum repeatedly in warm water, filter it and leave it to dry. By this process a beautiful green colour is obtained.

As this colour is not alterable by air, it is employed in painting.

Experiment 46.

If prussiate of potash be added to a solution of sulphate of copper, a brown precipitate will be formed, which has been used as a paint under the name of Hume's pigment.

Rationale. The sulphuric acid of the sulphate of copper, unites with the potash, forming sulphate of potash, whilst the prussic acid of the prussiate of potash, combines with the copper, thus separated, in the state of prussiate of copper.

Experiment 47. If plates of copper be moistened with vinegar, they will be corroded, and form a green

oxyd or sub-acetate of copper, known by the name of verdigrise; or,

Experiment 48. If copper plates be stratified with the husks of grapes, yet under the vinous fermentation, which soon grow acid, they become corroded, forming verdigrise.

Copper is acted upon by the acids, forming peculiar salts. See Salts of Copper.

Copper is capable of combining with the most of the metals. With gold it combines in any preparation. If only a little copper be added, the ductility of gold is not much impaired, though its hardness is considerably increased. Gold coin, sterling or standard gold, consists of pure gold alloyed with th of some other metal.* The metal used is always either copper or silver, or a mixture of both. The mixture of gold with copper is called red carating, to distinguish it from the less usual one, made with silver, and which is termed white carating. To ascertain the quantity of fine gold contained in the alloy, the touchneedles, as they are called, are of service. needles are small bars composed of different proportions of copper.‡

These

With platinum, copper unites by fusion, forming a ductile alloy, which has been employed with advantage for composing the mirrors of reflecting teles

copes.

A method has lately been proposed for coating copper vessels with platinum instead of tin; it consists in rubbing an amalgam of platinum over the copper, and then exposing it to the proper heat. Silver is easily alloyed with copper by fusion; these two metals are combined to form solder. The compound is harder and more sonorous than silver. In the silver coin, copper always constitutes a part. In Great Britain, the standard silver is a compound of 231 silver

*Hatchet on the Alloys of Gold, p. 66.

† Gren, ii. 280.

Ibid. 281:

and one copper. Its specific gravity, after simple fusion, is about 10.200. The old French silver coin was composed of 261 parts of silver and 27 of copper, or one part of copper alloyed with 93 of silver. The Austrian silver coin contains of copper. The silver coin of the ancients was nearly pure. Dr. Thomson analyzed an East Indian rupee, and found it to contain part of copper. The Dr. also examined other coin; the result of his experiments are to be seen in his System of Chemistry, vol. i. p. 214. Silver is not only combined with copper for the purpose of coin, but it is always mixed with this metal before it is wrought into plate, trinkets and the like. The alloy of silver and copper is specifically denominated by the number of loths (half ounces) of pure silver contained in one mark of the silver. The touch needles for silver are made upon the same principles as those for gold; but they are required only for one kind of alloy, namely, with copper.* Besides the separation of silver from copper, by cupellation, and precipitation, Mr. Engenstrom has proposed the following method with liver of sulphur :

Experiment 49. If silver alloyed with copper be fused with sulphuret of potash, the silver will be separated.

Rationale. During the fusion, the copper unites with the sulphuret, forming a scoriæ, which floats on the silver.

Experiment 50. If melted copper be cautiously poured into mercury heated nearly to the boiling point, the two metals combine and form a soft white amalgam; or,

Experiment 51. According to Boyle: triturate together two parts of mercury, two and an half parts of

* For a particular account of the mode of separating silver, or gold, from its alloys, as effected by cupellation, &c. consult Schluter's and Cramer's Metallurgy.

verdigrease, and one part of common sat, with some acetous acid, and keep them for some time, over a moderate fire, stirring them constantly, and supplying acid as it evaporates; then wash the amalgam and pour it into a mould; it is at first nearly fluid, but in a few hours it crystallizes and becomes quite solid:* or, this amalgam may be formed in the following

manner :

Experiment 51. Put a plate of copper into a solution of mercury in nitric acid; the plate will soon become impregnated with mercury.

Remark. The amalgam of copper is of a white colour, and may be readily decomposed by heat; the mercury evaporates and leaves the copper. Lead and copper unite by fusion, but the compound is not lasting. With bismuth copper also combines, rendering the former paler.

Respecting the combinations of copper with palladium, rhodium, iridium, and osmium, all that is known on the subject is mentioned in the preceding section. The union of copper and zinc constitutes brass, which may be made in the following manner :

Experiment 52. Put into a crucible four parts of granulated copper and six or eight of zinc, and nearly fill the crucible with charcoal-powder, cover it and bring it briskly to a red heat; the copper will unite with the zinc, and form brass.

Experiment 53. If plates of copper be cemented with native oxyd of zinc reduced to powder, and mixt with charcoal also in powder; by bringing the mixture to a red heat in a covered crucible, the copper and zinc will unite, and likewise form brass.

Brass is made in the large way by a process similar to this. Similor or Manhein gold, is also formed of zinc and copper.

Experiment 55. If twelve parts of copper and three of zinc be melted together in a crucible, the mixed

* Shaw's Boyle, i. 343.

metal, called tombac will be formed. Arsenic is sometimes added.

Experiment 54. If copper be melted with one tenth part of tin, gun metal will be produced.

Experiment 55. If copper be alloyed by melting it with one sixth part of tin, the result is bell-metal. The proportion of the ingredients of this metal, varies according to the uses to which the bells are to be applied. A similar mixture constitutes bronze.

Copper and tin, it appears, formed the ancient metallic arms. Dr. Pearson examined some of them, and found them to contain these two metals, in the proportion of from six to twelve parts of copper to one of tin, according to the uses to which they were intended.

The union of copper with the other metals, not here enumerated, will be considered hereafter.

SECTION X.

OF IRON.

Experiment 1. If iron ore be roasted in a strong heat, afterwards reduced to small pieces, then mixed with charcoal, or coke, and exposed to an intense heat in a close furnace excited by bellows, iron will be obtained in its metallic state.

Rationale. The roasting dissipates the sulphur, carbonic acid, or other volatile matter if it be present, whilst the charcoal in the subsequent operation carries off the oxygen from the metal, which is generally present in the form of carbonic acid. The iron, therefore, appears in the state of metal.

Remark. In the reduction of some iron ores, different fluxes are sometimes used. The ores of iron very often occur in a matrix of argillaceous, or calcareous earth, and occasionally with silicious earth;

I