A Manual of Mineralogy Author:Thomas Hogg Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. Excerpt from book: Section 3 METALLIC MINERALS, * I. PLATINUM. textit{Platinum.—'ll was first brought to England from South America, in 1741. It is of a light steel grey colour; in small flat grains, shinin... more »g and of a metallic lustre. In this state it is ex* ceedingly impure, containing either in combination, or mechanically mixed, several other metals. It is one of the most infusible of all the metals. It is reduced in conjunction with arsenic. Refined platinum is the heaviest body in nature. Welding, or- adhesion by hammering, in a white heat, is peculiar to irqn and platinum. It is soluble in nitro-muriatic atrid. Of all metals it expands the least by heat, and resists most agents; hence, it is used for pendulums, pyrometers, watch-wheels, chemical vessels, and speculums for telescopes, ia ;' ' ' which, from its density, it augments the reflecting power. II. GOLD. textit{Gold.—The original form of its crystals is a cube. It does not combine with mineralizing substances. It has no attraction tor sulphur, and very little for arsenic. It remains unalterable in the hotest furnace. Aqua regia, (or nitro-muriatic acid,) is its. usual solvent. It has been lound in some of the stream- works Oi' Cornwall, and no where else in the county. It most commonly occurs in grains. A quantity of stream tin-ore was found at Treworda, K iiiwyn, a good deal of which textit{is Still preserved, contaiuug very many grains. To these vales tt.ere is reason to believe that the gold was Drought down from mountains, with the tin, by long continued floods. The higher up the country they are found, the grains generally are rougher; those farthest down are evidently smoothed by attrition. These rolled tin pebbles and gold are the relics of mountains which have been deposited on mountains which are ^washed away; and are proofs of the ...« less