| OCR Text |
Show 42 , green stone, as in Hungary, Trr.nsylvania, and in Trachyte, a rock of comparatively recent origin, which is unknown in the United States proper. The latter rock contains the most powerful loads of gold, hitherto observed in place. In this rock are the workings of Krenigsberg and Pelkabanya, in Hungary, and the best mines in South America. Our geological knowledge of California is not very exact, but we have reason to believe that it is from the trachyte the golden sands are derived. The gold usual1y occurs in veins of quartz, often re· sembling honey-comb, sulphate of barytes, or calcspar it is, however, from the sands derived from these 'rocks that most of the gold is obtained. CHEMICAL TEsTs. BY THE BLoW .. PIPE.-Gold and silver have a feeble affinity for oxygen, whilst th~ metals with which they are associated, such as copper, iron and lead, oxydise rapidly, and sink into a cupel of bone-ash; when exposed to strong heat, the gold and silver remains on the surface. A skilfull operator, therefore, with a Elow-pipe, a lamp, a piece). of charcoal, with a little bone-ash bedded in it, will in a few minutes determine whether gold or silver occurs with any of the above oxydable metals. · When copper exists with gold, about 16 parts are necessary to sweat out the former~ One half of this amount is all that is needed to effect the separation of silver. BY Ac1ns.-Gold is unaffected by nitric, muriatic or sulphuric, but is dissolved by a mixture of nitric and muriatic acids,-the aqua regia of the old alchemist. If the acids are strong, they have no effect whatever. Col· - orless aqua fortis, and ordinary muriatic mixed to get her, become yellow, and acquire the power of dissolving this · metal as well as platina. Silver is readily soluble in. nitric acid, and hence this acid is used to effect its sepa .. ',. j ~ 43 ration from gold. This s~paration of platina from silver is effected by sulphuric acid, which dissolves the sil\'er and leaves the platina pure. Bv MERCURY OR QuicKSILVER.-Where the exist .. ence of gold is suspected in a strong Gangue, it should be roasted or burned, then pulverised and triturated with quicksilver, when it instantly seizes and amalgamates with the gold, however minute the particles. The gold is afterwards separated by distilling off the mercury.Such are some of the ordinary and available tests by which the pre5ence of gold may be detected. The ex-plorer can procure a tin box and place the principal tests-lamp, blow-pipe, &c., in it, and strap it to his back; thus he will have a portable furnace, with which he can instantly accomplish an a~say, or determine the nature of any mineral. Such an apparatus is worth all the books on geology and mineralogy that erer have been written. I |
