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Experiment 16. If a mixture of oxyd of copper, and charcoal, or oil, be exposed in a crucible to heat, metallic copper will be obtained.

Rationale. The oxyd is decomposed ; if charcoal be used, carbonic acid is disengaged ; if oil, carbonic acid and water; the metal being revived; or,

Experiment 17. If the oxyd be mixed with zinc filings, and exposed to heat, the copper will be obtained in a metallic state.

Rationale. The oxygen having a greater affinity for the zinc, unites with it, forming an oxyd of zinc, whilst the copper is revived.

Experiment 18. If equal parts of sulphur and copper, are stratified alternately in a crucible, they melt and combine in a red heat.

Remark. Sulphuret of copper, thus obtained, is of a black, or of the colour of icon, and composed, according to Proust, of 78 parts copper and 22 of sulphur ; or,

Experiment 19. If copper filings and sulphur be mixed, and formed into a paste with water, and allowed to remain for some short time, a compound of sulphur and copper will be formed; and,

Experiment 20. If this be exposed a longer time, and in contact with air, and afterwards lixivated, sulphate of copper may be obtained by evaporation and crystallization.

Rationale. The sulphur unites with the copper into a sulphuret : in the second case, the sulphuret is decomposed, oxygen is absorbed, and sulphate of copper formed.

Experiment 21. If a mixture of three parts of copper filings and one of sulphur, be melted in a glass tube, at the moment of combination, a brilliant inflammation ensues, and a sulphuret of copper is formed.

Remark. This experiment was first made by the associated Dutch chemists, Dieman, Troostwyk, Nieuwland, Bendt, and Laurenburg, in 1793. This experiment has excited much attention, as it appears to contradict the Lavoiserian theory of the necessity of oxygen in every instange of combustion.

The cofiper-matt, as the workmen call it, seems to contain sulphuret of copper.

Experiment 22. If a polished plate of copper be immersed into water containing sulphuretted hydrogen, or into an alkaline hydrosulphuret, it will become tarnished, and covered with a blackish brown crust.

Remark. Hence this metal may be used as a test for hepatic water. See Hydrosulphurets.

Experiment 23. If the sulphuret of copper, formed as before mentioned, be melted with sulphur; a compound will be formed, called super sulphuret of copper.

Remark. The ore known by the name of copper pyrites, is a super-sulphuret of this metal.

Experiment 24. If 16 parts of copper, the same quantity of phosphoric glass, and one part of charcoal be fused in a crucible, the phosphuret of copper will. be formed.

Rationale. The charcoal decomposes the phosphoric acid ; carbonic acid is disengaged; and the phosphorus at the instant unites with the copper into a phosphuret; or,

Experiment 25. According to Margraf, if phosphorus and oxyd of copper be distilled, the same com: pound will result; or,

Experiment 26. If phosphorus be projected into red hot copper, a union will ensue, and the same proan duct will be formed.

Remark. According to Pelletier, the phosphuret of copper is composed of 26 parts of phosphorus, and 80 of copper. Several experiments have been made on this compound.

Experiment 27. If to a diluted solution of sulphateof copper, caustic ammonia be added, the copper will be precipitated in the state of an oxyd ; it more ammonia be now added, the precipitate will become dissolved, forming an ammoniaret of copper, or aqua Gelesiis.

Rationale. The ammonia at first unites with the sulphuric acid of the sulphate of copper, forming sulphate of ammonia, which remains in solution, whilst the oxyd of copper is precipitated; another portion

of the ammonia then dissolves the oxyd, forming a beautiful blue liquid, or ammoniaret of copper.

Experiment 29. If eight ounces of lime water, two scruples of sal ammoniac, and four grains of verdigrise be mixed and digested for a short time, the aqua sappiharina, or liquor of ammoniated copper of the Dublin Dispensatory will be formed; or,

Experiment 3C. If one dram of sal ammoniac and one pint of lime water be suffered to stand together in a copper vessel, the same preparation will be produced.

Rationale. The lime water decomposes the muriate of ammonia ; muriate of lime is formed, and ammonia is disengaged, which dissolves the oxyd of copper in the verdigrise. In the latter process, the copper is oxydized, and the oxyd of copper afterwards dissolved. The quantity of lime is not sufficient to decompose all the muriate of ammonia, hence it is, that this preparation contains muriate of ammonia, muriate of lime, and ammoniaret of copper. The cufirum ammoniacum of the shops, is prepared in the following manner :

Experiment 31. Take of sulphate of copper, two parts; and carbonate of ammonia, three parts. Rub ihem carefully together in a glass mortar, until after the effervescence has entirely ceased, they unite into a violet coloured mass, which must be wrapt up in blotting paper, and first dried on a chalk stone, and alterwards by a gentle heat.

Rationale. As soon as the ingredients begin to act upon each other, a quantity of water is set at liberty, which renders the mass soft ; during the action, the sulphuric acid of the sulphate of copper passes to the ammonia, whilst the ammonia of the carbonate of ammonia combines with oxyd of copper into an ammoniaret of copper. Prepared according to the above formula, cuprum ammoniacum evidently contains oxyd of copper, ammonia, and sulphuric acid. The following process has been recommended in preference.

Experiment 32. Decompose a solution of sulphate of copper by ammonia as before stated ; concentrate

the solution of copper in the ammonia by evaporation, and mix it with about an equal quantity of alcohol, and the whole of the salt will be precipitated in silky blue crystals, which are to be collected by filtration, dried, and kept in a vial, with a ground glass stopper.

Rationale. The theory of the formation of cuprum ammoniacum has already been noticed. When alcohol is added, the water of the solution is abstracted, and the whole of the saline matter is precipitated.

Experiment S3. If copper filings be put into a vial with ammonia, and the air excluded, no solution will take place; but,

Experiment 34. If air be admitted into the same vial, the liquor will gradually become blue.

Rationale. Metallic copper is not solubie in ammonia; but when air is admitted, the metal is oxydized, and the oxyd is taken up by the ammonia.

Experiment 35. If cuprum ammoniacum be exposed to the air, it will change from a blue to a green colour.

Rationale. The ammonia, on exposure, is disengaged from the oxyd of copper, and the latter, by absorbing carbonic acid, becomes green, forming the carbonate of copper.

Experiment 36. If copper filings be boiled with a solution of sal ammoniac, a solution will be formed, which, when evaporated, produces the Brunswick green.

Remark. This preparation appears to be a triple compound; and, according to Goetling, is the Brunswick green. This pigment, however, is considered by some as a triple tartrate of potash and copper. See Salts of Copper.

Experiment 37. If a small quantity of copper, or its oxyd, be mingled by triturating it with muriate of ammonia, and sublimed, some ammonia is at first disengaged, but after it the remaining muriate of ammonia rises, tinged of a greenish yellow by the muriate of copper, which also sublimes. This last product has been called cupreous flowers of sal ammoniac (ens veneris). See Salts of Copper.

Experiment 38. Prepare two glasses of very diluted nitrate of copper; into one drop a little ammonia, and into the other some diluted arseniate of potass. The addition of these two colourless solutions will produce very different effects, for the one glass will have an abundant precipitate of a beautiful grass green, and the other precipitate of a brilliant sapphire blue.

Rationale. With the arseniate of potash, an arseniate of copper is formed, which is of a green colour; with ammonia, ammoniaret of copper is produced.

Experiment 39. If paper be written on with a diluted solution of muriate of copper, the writing will not be visible, but on being warmed before the fire, it will become of a beautiful yellow, forming a sympathetic inka

Experiment 40. Write with a solution of sulphate of copper, wash the paper with prussiate of potass, and the writing will be revived of a reddish brown colour. In this experiment the sulphate is converted to a true prussiate of copper.

Experiment 41. If a piece of bright silver be dipped in a solution of sulphate of copper. it will come out unchanged: but if the blade of a clean penknife, or any piece of polished iron, be dipped in the same solution, the iron will instantly put on the appearance of copper.

Experiment 42. Take the piece of silver employed in the last experiment, hold it so that the silver and the polished steel may be in contact ; then in this situation plunge them into the same solution, and in a moment Both will be covered with copper.*

Rationale. Silver will not precipitate copper from its solution ; but iron has this property. The copper, thus precipitated by iron, is called copper of cementation. But when silver and polished steel are immersed together in contact, the property which they both possess in this state of precipitating copper from its solution, appears to depend on the galvanic influence.

+ Parke's Rudiments.

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