The argentiferous galena has in general all the external characters of pure galena. The proportions of silver vary from one fifth part of the whole, as at Tarnowitz, in Silesia, to three parts in ten thousand, as in the ore called by the German miners Weisgultigerz ; but it must be observed, that whenever this lead ore contains above 5 per cent. of silver, several other metals are associated with it. The mean pro portion of silver in galena, or that which makes it be considered practically as an argentiferous ore, because the silver may be profitably extracted, is about two parts in the thousand. (See SILVER.) The above rich silver ores were first observed in the Freeberg mines, called Himrnels furst and Beschertgluck, combined with sulphuret of antimony ; but they have been noticed since in the Hartz, in Mex ico, and several other places. It is the most abundant lead era in the United States, occupying an immense tract of country on the Missouri River.
The antimonial galena (Bournondte) exhales at the blowpipe the odor peculiar to antimony, and coats the charcoal with a powder partly white and partly red. It usually contains some arsenic.
2. The Sekniuret of lead resembles galena, but its tint is bluer. At the blow pipe it exhales a very perceptible smell of putrid radishes. Nitnc acid liberates the selenium. When heated in a tube, oxide of selenium of a carmine red rises along with selenic acid, white and deliquescent. The specific gravity of this ore varies from 6.8 to 7.69.
3. Native minium or red lead has an earthy aspect, of a lively and nearly pure red color, but sometimes inclining to orange. It occurs pulverulent, and also compact, with a fracture somewhat la mellar. When heated at the blowpipe upon charcoal, it is readily reduced to metallic lead. Its specific gravity varies from 4.6 to 8.9. Tills ore is rare.
4. Tilite lead, carbonate of lead.—This ore, in its purest state, is colorless and trimsparent like glass, with an adaman tine lustre. It may be recognized by the following characters :— Its specific gravity is from G to 61; it dissolves with more or less ease, and with effervescence, in nitric acid; be comes immediately black by the action of sulphureted hydrogen, and melts on charcoal before the blowpipe into a button of lead. According to lilaproth, the car bonate of Leadhills contains 82 parts of oxide of lead, and 16 of carbonic acid, in 98 parts. This mineral is tender, scarcely scratches calc-spar, and breaks easily with a waved conchoidal fracture. It possesses the double refracting property in a very high degree ; the double image being very visible on looking through the flat faces of the prismatic crystals.
Its crystalline forms are very numerous, and are referrible to the octahedron, and the pyramidal prism. This ore has been found very sparingly in the United States.
5. Vitreous lead, or sulphate of lead.— This mineral closely resembles carbonate of lead ; so that the external characters are inadequate to distinguish the two. But the following are sufficient. When pure, it has the same transparency and lustre. It does not effervesce with nitric acid ; it is but feebly blackened by sul phureted hydrogen ; it first decrepitates and then melts before the blowpipe into a transparent glass, which becomes milky as it cools. By the combined action of heat and charcoal, it passes first into a red pulverulent oxide, and then into metallic lead. It consists, according to Klaproth, of 71 oxide of lead, 25 sulphuric acid, 2 water, and 1 iron. That specimen was from Anglesea; the Wanlockhead mineral is free from iron. The prevailing form of crystallization is the rectangular octahedron, whose angles and edges are variously modified. The sulphato-car bonate, and sulphato-tricarbonate of lead, now called Leadhillite, are rare min erals which belong to this head.
6. Phosphate of lead.—This, like all the combinations of lead with an acid, ex hibits no metallic lustre, but a variety of colors. Before the blowpipe upon char coal, it melts into a globule externally crystalline, which, by a continuance of the heat, with the addition of iron and boracic acid, affords metallic lead. Its constituents are 80 oxide of lead, 13 phosphoric acid, and 1.6 muriatic acid, according to Klaproth's analysis of the mineral from Wanlockhead. The con stant presence of mnriatic acid in the various specimens examined is a remark able circumstance. The crystalline forms are derived from an obtuse rhomboid. Phosphate of lead is a little harder than white lead ; it is easily scratched, and its powder is always gray. Its specific gra vity is 6.9. It has a vitreous lustre, some what adamantine. Its lamellar texture is not very distinct ; its fracture is wavy, and it is easily frangible. The phos phoric and arsenic acids being, according to M. Mitscherlich, isomorphous bodies, may replace each other in chemical com binations in every proportion, so that the phosphate of lead may include any pro portion, from the smallest fraction of arsenic acid to the smallest fraction of phosphoric acid, thus graduating inde finitely into arseniate of lead. The yel lowish variety indicates, for the most part, the presence of arsenic acid. This ore occurs at the lead mine near Frey burg, in Maine. It is also found in Tennessee.