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Characteristics Of Gold

Characteristics Of Gold image
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Pure iroiil is so soft that it woulrl BOOB be worn away by use, and it is alvvays alloj'ed with a varying proportion of copper or silver, usually about onetenth. Pure gold is said to be twentyfour karats. Thus eighteen karat gold contaiu.s eighteen parts of pi;re metal in twenty-four, or is fchree-quarters pure. Many cheap alloys oí base metáis can be made whichvery stronly resemble gold ín color and luster; but, in the absence f a complete chemical test, the highly specific gravity of old is the tes1 for Lts pturity, thoogb this has been imitated by covc-ring the Leavier but eheaper metal piutinum with gold. Iron pyrites and other yellowish minerals ure constantly being mistaken for fold by inexperienced persons, much to their disappointment, but a very simple test wül show whether a doubtful specimen is really the true metal. Gold is very sectile - that is, it can be cut and shaved witli a knife like a piece of wood or horn, while pyrites and wortliless minerals will crumble under the knife blade like a lump of suar. If any reader of this article ever finds a yellowish mineral which can be cut without crumbling, it is worth a more thorough test; otherwise he may save himself unnecessary trouble and disappointment. Very few Chemicals have any effect on gold. Scienic acid will dissolve it, but few chemists have ever seen this very rare substance. A mixture of nitric and hydrochloric acids will dissolve it. forming a chlorine gas in water. In both of these liquida a peculiar active form of chlorine known as nasceni chlorine is present, which probably unites directly with the metal. Gold, like all the noble metáis, is unehanged by heating in the air. lts oxides can be obtained by chemieal reactions, but they are very unstable and easily reduced back to the metal. The chloride above referred to is the only salt of any practical importance and is used to produce the beautiful purple of Cassius, a compound of tin an gold of uncertain composition, but yielding a mnjrnificent ruby color whcn melted luto glass. A hundredth of a grain of gold will deeply color a cubic inch of glass. The most extensivo use of the chloride is, however, in photography. iviiere it is used to '"tone'' or color prints on silvered paper, This darkening oí the prints is due to the decomposition of the salt. and the ! position in the picture of f i n ■ 1 divided metallic gold, which not only givee it t'ne desired color, but renders the image very permanent, liy beating out bétween pieces of membrane, grold may be formed into I caves of snch thinness that 282,000 of them will only make a pile one inch i A siiig-le ounce of g-old may thus be spread over 100 square feet. In th iture of gold thread for embroidery, :i cylinder of silver is ed with .1 afterwarda drawn out intó wire. In this way six s ol gold have been ■ ield over 2 f gilt wire. Even at this ie tenuity the co; -rfect and does not rust or


Old News
Ann Arbor Courier