ASSAYING GOLD AND SILVER ORES. Gold and silver are generally associated together in ores, and such ores are universally determined by fire assay. The fire-assay consists essentially in the collection of the gold and silver in a button of metallic lead, either by scorification or by fu sion. The lead button is then freed from the adhering slag by hammering on an and is finally hammered into the form of a cube, when it is ready for cupellation. Both scot-Hien tion and fusion consist in melting the ore with lead and certain fluxes; the fluxes used, the size of the ore sample, and the Size and shape of the crucible differing in the two eases. The cube of lead. gold. and silver resulting from the seoritication or fusion process is SIlbjeCtCd v111)(211:I 0011 as follows: The cube is placed in a cupel, a small basin-shaped vessel, made of bone ash, and the cupel is placed in a small furnace of special construct ion. ea lled a muffle fur nace, VVII kb, as used in the United States assay offices, is heated by gas, hilt WI! iull May be con structed for use with either coal or coke. Ow
ing to the beat, the lead in the cube is oxidized, part being absorbed by the cupel and part run ning off in fumes. Just before the last traces of the lead are removed, the melted button exhibits a play of colors, when the heat is increased to dispel the last of the lead, this being indicated by the 'brightening' or 'winking' of the button. The button is then cleared of adhering dirt, and carefully weighed. It now consists of silver and gold mixed. To determine the amount of each, the button is submitted to the process of parting. In order that the button will part it must contain at least 2 times as much silver as gold. and should this not be the ease sufficient silver is added and fused with the button to secure the proper proportions. The button is now hammered into a flat ribbon or strip and boiled in nitric acid, which removes all the silver and leaves the gold, which is fused and weighed.