ORES, in mineralogy. An ore is a me tal in the state in which it exists in the earth. It may be either native, that is pure, and uncombined with any other substance, or alloyed with another me tal ; or in a state of an oxide, or a sulphu ret, or a carburet, or of a metallic salt. It is also mixed in most instances with various earthy minerals. The ores of metals may be analyzed in two modes, in the humid and the dry way. The first is elected with the aid of acids, and of other liquid agents, and may often be ac complished by very simple means, and without the aid of a bulky and expensive apparatus. If sulphur be present, it im pedes the action of acids, and should be separated by roasting the ore on a muffle, or by projecting it mixed with twice its weight of nitre into a red-hot crucible, washing off the alkali afterwards with hot water. No solvent will act upon all the metals. Thus nitric acid does not act on gold and platina ; and the nitro-muriatic acid, which dissolves these metals, has no solvent action on silver. Hence the necessity of varying the solvent accord ing to the nature of the ore under exa mination. We shall give a few instances, by which the reader will understand the theory, and may be enabled to verify the facts by practice.
For " ores of gold and platina," the ni tro-muriatic acid is the most proper sol vent. A given weight of the ore may be digested with this acid, as long as it ex tracts any thing. The solution is to be evaporated to dryness, in order to expel the excess of acid, and dissolved in wa ter. The addition of a solution of tin and muria.tic acid will shew the presence of gold by a purple precipitate ; and platina will be indicated by a precipitate, on adding a solution of muriate of ammonia. When gold and platina are both contain ed in the same solution, they may be se parated from each other by the last men tioned solution, which throws down the platina, but not the gold, In this way platina may be detached also from other metals.
For extracting " silver" from.its ores, the nitric acid is the most proper solvent.
The silver may be precipitated from ni tric acid by muriate of soda. Every hun dred part of the precipitate contains se venty-five of silver. But, as lead may be present in the solution, and this metal is also precipitated by muriate of soda, it may be proper to immerse in the solu tion a polished plate of copper. This will precipitate the silver, if present, in a metallic form. The muriate of silver is also soluble in liquid ammonia, which that of lead is not.
"Copper ores" may be analyzed by boiling them with five times their weight of concentrated sulphuric acid, till a dry mass is obtained, from which water will extract the sulphate of copper. This salt is to be decomposed by a polished plate of iron, immersed in a dilute solu tion of it. The copper will be precipi tated in a metallic state, and may be scraped off and weighed. If silver be suspected with copper, nitrous acid must be employed as the solvent ; and a plate of polished copper will detect the silver.
" Iron ores" may he dissolved in dilute muriatic acid, or, if the metal be too highly oxydized to be dissolved by this acid, they must be previously mixed with one-eighth of their weight of powdered charcoal, and calcined in a crucible for an hour. The iron is thus rendered solu ble. The solution must then be diluted with ten or twelve times its quantity of water, previously well boiled, to expel the air, and must be preserved in a well stopped glass bottle for six or eight days. The phosphate of iron will within that time be precipitated, if any be present, and the liquor must be decanted off. The solution may contain the oxides of iron, manganese, and zinc. It may be preci pitated by carbonate of soda, which will separate them all. The oxide of zinc will be taken up by a solution of pure ammonia ; distilled vinegar will take up the manganese, and will leave the oxide of iron. From the weight of this, after ignition, during a quarter of an hour, twenty-eight per cent. may be deduct ed.