Waterbury evening Democrat., 1890-11-17
FAoTs AsoOT GOLD.

single Ounce May Be Spread Over One
 Hundred Square Feet.
 Pure gold Is so soft that it would soon be worn away by use and it is always alloyed with a varying proportion of copper or silver, usually about one tenth. Pure gold is said to be 24 carats. Thus 1s-carat gold contains IS parts of the pure metal in 24, or, is three-uuar- ters pure. Many cheap alloys of base metals can be made which very strongly, resemble gold in color and luster: but. in the absence of complete chemical test the high specific gravity of gold (19.8) is the best test of It's purity, though this has been ingeniously irni- tated by covering the heavy but cheaper metal, platinum, with layer of gold. Iron pyrites and other yellowish miner als are constantly being mistaken for gold, by inexperienced persons, much to their disappointment,b but very sim pie test will show whether doubtful specimen is really the true metal Gold is very sectGIe-that is, it can be cut and shaved with a knife, like 8 piece of wood or horn; while pyrites and other. worthless minerals will crumble under the knife-blade like lump of sugar. If any reader of this article ever finds 8 yellowish mineral which can be cut without crumbling, it is worth more thorough test; otherwise he may as we'll. save himself unnecessary trouble and disappointment Very few chemicals have any effect on gold. Selenic acid will dissolve it. but few chemists have ever seen this very rare substance. A mixture of nitric and hydrochloric acids (GQuG regIG) will also dissolve 1t, form ing a chloride of gold; and so will solu- tion of chlorine gas in water. In both these liquids a peculiarly active form; Of chlorine, known as nGsceRt ch lorine, is present, which probably unites directly with the metal Gold, like all the noble metals, is unchanged by heat ng in the air. Its oxides can be obtained by chemical 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 im- portance, and is used to produce the beautiful Purple of Cassius, a compound of tin and gold of uncertain compost tion, but yielding a magnificent ruby color when melted into glass. A hun- dredth of 8 grain of gold will deeply color cubic inch of glass. The most extensive use of the chloride is, how ever, III pno0ogfephy, where 1t IS used to 'tone" or color prints on silvered pa- per. This darkening of the prints is due to the decomposition of the salt and the deposition in the picture of f1nely-dividsd metallic gold, which not only gives 1t the desired color, but rem ders the image very permanent By beating out between pieces of mem- brane. gold may be formed into leaves of such thinness that 292, 900 of them will only make pile one inch in height A single ounce of gold may thus be spread over one hundred square feet. In the manufacture of gold thread for embroidery, cylinder of silver is covered with gold and after wards drawn out into wire. In this way six ounces of gold have been made to yield over two hundred miles of gilt wire. Even at this extreme tenuity the coating is perfect, and does not rust or tarnish. Science News. .,,