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gold upon silver wire is capable of considerable extension, so much so that it would measure, according to Lewis, more than 1300 miles in length, We are told, that 16 ounces of gold will completely gild a silver wire sufficiently long to encircle the globe. As to the tenacity of this metal, although not so considerable as some of the other metals, yet from the experiments of Sickingen it appears, that a gold wire 0.078 inch in diameter is capable of supporting a weight of 150.071bs. avoirdupois, without breaking. Gold melts at 320 of Wedgwood's pyrömeter.
It requires a violent heat for volatilization; it is therefore exceedingly faced. A number of experiments have been made on this subject by different chemists, both in the heat excited by the common furnaces, as well as that produced by powerful burning glasses. After fusion, gold is susceptible of assuming a crystalline form. It has been obtained in short quadrangular pyramidal crystals.
In the arts, &c. gold is used for jewellery, for plate, and for current coin, but for these purposes it is geacrally alloyed. It is also employed to be spread over other metals, to preserve them fiom tarnishing or rusting. Paie gold, as it is called, is alloyed with sil. vel, Gold, when pure, is considered twenty four cara's fine. If twenty-two parts of gold, and two parts of copper be fused together, the gold is said to be i wenty-Fo carats line, or gold of twenty-two carats.
Experiment 4. If a narrow strip of gold leaf be put, with both ends hanging out between two glass plates tied together, and a strong electrical explosion passed through it, the good leaf will appear to be consumed, and to have tinged the glass of a purple colour.
Karibale. The gold is oxydized by the agency of electricity, and the oxyd imparts colour to the glass, which is partly fused.
Remark. Dr. Franklin was the first who made this experiment, which was afterwards repeated in 1773 by Camus. It was doubted whether gold in this manner is oxydized, but it was discovered, that gold wir'e, by
a powerful electrical battery, burns with a green coloured flame, and is completely dissipated in fumes in the state of the purple oxyd.
Experiment 5. If gold leaf be exposed to the action of the galvanic battery, it will be immediately consumed.
Rationale. In this experiment also the metal is burnt, the purple oxyd of gold being produced.
Remark. Dr. Thomson observes, that he has succeeded in co::suming gold by exposing a wire of that metal to the action of a stream of oxygen and hydrogen gas mixed together and burning.
Experiment 6. If sulphuric acid be poured on gold, and even digested with the assistance of heat, the gold will remain unaltered; or,
Experiment 7. If muriatic acid be used in the same manner, no effect will take place; or,
Experiment 8. If nitric acid be employed, no solution will be formed ; but,
Experiment 9. If a piece of gold, or gold leaf, be introduced into oxygenized muriatic acid, a solution will immediately be formed; or,
Experiment. 10. If a thin sheet of gold be dropt into oxymuriatic acid gas, it will inflame, and muriate of gold will be formed. See the Properties of Oxymuriatic Acid Gas.
Rationale. The oxygen of the oxy-muriatic acid oxydizes the gold, which then combines with the remaining acid, forming the muriate of gold.
Experiment 11. If gold be introduced into nitromuriatic acid, it will be dissolved.
Rationale. The action of nitro-muriatic is analogous to the oxy-muriatic acid gas; it first imparts oxygen to the metal, and then dissolves the oxyd. The effect of a mixture of the nitric and muriatic acid is apparent in the following experiment.
Experiment 12. Pour a little 'purified nitric acid into one wine glass, and muriatic acid in another, and dropa little gold leaf in each of them: neither of the acids will act; but mix the contents of both glasses, and the gold will be dissolved.
Ralionaie. The thcory of the formation of nitromuriatic acid, by the the production of which the solution is effected, will be shewn when we treat of that acid; but in the mixture, the oxygen of the nitric acid is partly transferred to the muriatic acid, and is taken from that acid by the metal, forming an oxyd, which is afterwards dissolved.
Remark. A saturated solution of gold in the nitromuriatic or oxygenized muriatic acid, affords, by evaporation, crystals of muriate of gold, which will be afterwards noticed.
Experiment 13. To a solution of gold in nitro-muriatic acid, add a solution of potash, and a yellowish brown oxyd of gold will be precipitated.
Rationale. The potash unites with the acid, and the gold, being disengaged from the muriatic acid, is precipitated in the state of an oxyd.
Remark. Gold, thus precipitated, forms the per oxyd of that metal, which is composed of 91 parts of gold, and 9 parts of oxygen.
Experiment 14. Expose the oxyd formed in the ast experiment to a moderate heat, and it will be changed into the purple oxyd of gold; but,
Experiment 15. If the same oxyd be exposed to a stronger heat, the oxygen will altogether be disengaged, and the metal revived.
Experiment 16. If gold be subjected to combustion, or to the action of electricity, the purple, or prot-oxyd of gold will be produced; or,
Experiment 17. If the per-oxyd of gold be placed in the direct rays of the sun, it will be changed into the prot-oxyd.
Remark. The oxyds of gold are but imperfectly known. Proust has lately endeavoured to shew, that the purple oxyd of gold is nothing more than gold in a metallic state.
Experiment 18. If a piece of tin be immersed in a solution of gold, the gold will be precipitated of a purple colour, forming the purple powder, or precipitate of Cassius; or,
Experiment 19. If tin be dissolved in nitro-muria
tic acid, composed of two parts of nitric acid, and one of muriatic acid, and to this solution another of gold diJuted in eighty times its weight of distilled water be added, the purple precipitate will be formed as in the last experiment.
Rationale. As the purple precipitate is a compound of the oxyds of gold and tin, it follows, that a decomposition of the solution of gold as well as that of the tin takes place. In order to produce the effect, it is necessary that the tin should be oxydized to the minimum ; for the tin robs the oxyd of gold, held in solution, of a part of its oxygen, and is therefore render. ed insoluble, at the same time it is precipitated along with a portion of the oxyd of tin in the form of a purple powder.
Experiment 20. If a silp of zinc be immersed in a similar solution of gold, the latter will be precipitated in a metallic state.
Rationale. The zinc takes the oxygen from the oxyd of gold, and the gold, being thus rendered insoluble, precipitates in a metallic state, whilst a portion of the zinc is dissolved in its place.
Experiment 21. Dissolve a few crystals of nitro. muriate of gold in about eight times their weight of pure water; place a thin slip of charcoal in the solution, and heat the whole by means of a sand-bath. When the solution has acquired nearly a boiling heat, the gold will precipitate itself on the charcoal, in its metallic splendour, forming a singular and beautiful appearance.
Experimeut 22. Proceed as in the last experiment, and submit the vessel with its contents to the rays of the sun. Here the metal will be reduced, and the charcoal effectually gilt as before.*
Rationale. In the first experiment the action of charcoal, assisted by the heat of a sand bath, separates the oxygen from the oxyd of gold; the metal is there
fore precipitated in a metallic state. In the latter the same decomposition ensues, assisied by the sun's rays. In the first experiment, particularly, we are presented with the fact, that metals become insoluble the moment they part their oxygen to foreign bodies. The latter is illustrative of the deoxydizing power of the sun's rays.
Experiment 23. If to a solution of gold in nitromuriatic acid, highly rectified ether be added, the gold will be precipitated, and the precipitate afterwards dissolved, forming the etherial solution of gold.
Rationale. The ether would appear to abstract a portion of oxygen from the oxyd of gold, which, in consequence of a part of the oxygen necessary for the solution of the metal being removed, is precipitated, which is then redissolved by another part of the ether, forming the etherial solution. It is asserted, however, that the etherial solution, if evaporated, will afford gold in a state of absolute purity.
Remark. It was this preparation of gold, that received the name of potable gold, and was kept in the shops of the apothecaries. It was estimated an universal medicine.
Experiment 24. If any polished steel instrument or utensil be dipped in the etherial solution of gold, and instantly plunged into water, the surface will have acquired a coat of pure gold.
Remark. This appears to be a very elegant and economical mode of preserving steel from rust.
Experiment 25. If an essential oil be substituted for ether, a solution of gold will be formed similar to the etherial solution.
Experiment 26. If a white sattin ribbon be moist, ened with a diluted solution of gold in nitro-muriatic acid, and then exposed, while moist, to a current of hydrogen gas, the gold will be reduced and the ribbon become gilt with the metal.
Remark. If the silk be dry no effect takes place. By means of a camel hair pencil the gold may
be so applied as to exhibit regular ornaments, or figures, when reduced.