LEAD. 



411 



We proceed now to speak of the ores of this metal, 

 and the method of their reduction. 



1. There exists but a single ore of lead which ever 

 :>rcurs in sufficient quantity by itself to justify its 

 exploration ; that ore is the Sulphuret. (See Gale- 

 na.) It not unfrequently happens, however, that 

 the veins and beds of this species embrace a variety 

 of other ores of lead dispersed through them, which, 

 being mingled with the sulphuret, materially augment 

 the yield of that ore, and which, therefore, require 

 to be noticed, not merely as objects of natural history, 

 but as of value to the miner, who, from their often 

 unpromising aspect, is liable to overlook them among 

 the refuse matters of the mine. In addition to what 

 has already been said of the sulphuret under the arti- 

 cle Galena, we give here a simple mode of assaying 

 a small portion of this ore. Separate fifty grammes 

 of it as perfectly as possible from the engaging rock, 

 or srangue ; pulverize it, and, mingling it with 12 '5 

 grammes of iron in small pieces (small tacks, for 

 example), introduce the mixture into a Hessian 

 crucible, which, being placed within a second one, is 

 to be exposed to the heat of a wind-furnace, or of an 

 ordinary forge, during fifteen minutes ; it is then 

 removed, suffered to cool, and broken : a button of 

 lead occupies the bottom of the crucible, which on 

 being weighed, makes known the richness of the 

 ore. 



2. Carbonate of Lead, or White Lead Ore, so 

 called from its prevailing colour, like all the salts of 

 lead, is perfectly unmetallic in its appearance, and is 

 not unfrequently rejected from among common lead 

 ore, as an earthy mineral. It is both crystallized and 

 Tiassive. The crystals are very oblique four-sided 

 prisms, six-sided prisms variously terminated, acute, 

 double six-sided pyramids, tabular crystals, and twin 

 and macle crystals. They cleave parallel to the sides 

 of a right rjiombic prism of 117" and 63, which is 

 the primitive form of the species. Lustre adaman- 

 tine ; hardness equal to that of calcareous spar ; 

 brittle ; specific gravity, 6 - 26. It dissolves with 

 effervescence in muriatic and nitric acids, yields a 

 metallic globule on charcoal before the blow-pipe, 

 and is composed of oxide of lead 82, carbonic acid 

 16, and water 2. This species often occurs massive, 

 and intermingled with earth and metallic oxides, and 

 is sometimes tarnished and blackened, so as to be 

 with difficulty recognised. It occurs in veins in 

 primitive and secondary countries, accompanying 

 galena and other ores of lead. It is pretty abundant 

 in European countries but has been found very spar- 

 ingly in the United States. 



,'j. Sulphate of Lead. Its principal crystallizations 

 are an oblique four-sided prism, variously bevelled or 

 truncated, and a broad, rectangular, four-sided pyra- 

 mid. It admits of cleavage parallel to the planes of a 

 right rhombic prism of 103 42' and 76 18', its 

 primitive form ; lustre shining, adamantine ; fracture 

 conchoidal ; translucent ; hardness that of calcareous 

 spar ; streak white ; brittle ; specific gravity, 6-3. It 

 decrepitates before the blow-pipe, then melts, and is 

 soon reduced to the metallic state. Its constituents 

 are. oxide of lead 70-5, sulphuric acid 25'75, water 

 2'25. It occurs not very plentifully, in life Hartz, 

 Spain, England, and Scotland. 



4. Mr Brooke has described within the few last 

 years, three oilier varieties of lead ore ; one of which 

 consists of 46 9 of carbonate and 53-1 of sulphate of 

 lead ; another of 55-8 of sulphate, 32 8 of carbonate 

 of lead, and 11 4 of carbonate of copper ; the remain- 

 ing one of 71 '4 sulphate of lead, 18 oxide of copper, 

 m-d 4-7 of water. These will, doubtless, constitute 

 distinct species. 



5. Chromate of Lead is of a deep orange- ml colour ; 

 when pulverized, orange-yellow. It occurs crystal- 



lized and massive ; cleaves parallel to all the planes 

 of an oblique rhombic prism of about 93 30' and 86 

 30'. The cross fracture is uneven, passing into con- 

 choidal, with a splendent lustre. It is sometimes 

 translucent ; brittle ; specific gravity, 6. When 

 exposed to the blow-pipe, it crackles and melts into 

 a grayish slag. It consists of oxide of lead 63-93, 

 chromic acid 36-40. It has hitherto been found only 

 in Siberia, where it occurs in a vein traversing gneiss 

 and mica slate in the gold mine of Beresof, and in a 

 sand-stone near the same place. 



6. Molybdate of Lead occurs crystallized in obtuse 

 octahedrons, variously modified, and in tabular crys- 

 tals. It cleaves parallel to the sides of a right square 

 prism, its primary form ; colour wax or honey-yellow; 

 lustre resinous ; translucent ; hardness below that of 

 calcareous spar ; brittle ; fracture uneven, passing 

 into conchoidal ; specific gravity, 5-09. Before the 

 blow-pipe, it decrepitates ; on charcoal, it fuses into 

 a dark-gray mass, in which globules of reduced lead 

 are visible. It consists of 58'4 oxide of lead 38 

 molybdic acid, and 2-08 oxide of iron. It occurs 

 principally at Bleiberg in Carinthia, with other ores 

 of lead. 



7. Phosphate of Lead occurs crystallized in the form 

 of a six-sided prism, generally modified on the edges ; 

 and, as it cleaves parallel to the sides of the hexagonal 

 prism, that figure is regarded as its primary form ; 

 colour, shades of green and yellow ; translucent ; 

 lustre resinous ; fracture imperfect, conchoidal, un- 

 even ; brittle ; hardness equal to that of calcareous 

 spar. Besides occurring in distinct crystals, it 

 assumes globular, renifonn, botryoidal and fruticose 

 shapes. Before the blow-pipe, it melts by itself upon 

 charcoal, and the bead exhibits, in cooling, crystalline 

 facets. It consists of oxide of lead 78-58, phosphoric 

 acid 19-73. In some varieties of this species, arsenic 

 acid is substituted for phosphoric acid. Phosphate of 

 lead is found accompanying the common ores of lead, 

 though rarely in any considerable quantity. Finely 

 crystallized varieties are found at Przibram in Bohe- 

 mia, atHuelgoet in Brittany, at Lead-hills in Scotland, 

 and at Cornwall in England. In America it occurs 

 at the lead mine near Freyberg in Maine. 



Such are the ores of lead, all of which, with the 

 exception of the chromate, are more or less employed 

 in furnishing the lead of commerce ; but the salts, as 

 has been remarked above, in very limited quantity, 

 compared with the sulphuret. As the principal thing 

 in the metallurgic treatment of these ores, is to expel 

 the sulphur, after picking and pulverization, they are 

 roasted either in the open air, or in reverberatory fur- 

 naces. During this operation, the sulphur volatilizes, 

 and the lead, reduced to the metallic state, or tc that 

 of an oxide, runs into the basin, or crucible of the fur- 

 nace, where it is deoxidized by being maintained 

 in contact with ignited charcoal, Thus, by this me- 

 thod, which is that generally adopted, the sulphuret 

 passes at first to the state of an oxide in the rever- 

 beratory furnace, afterwards is converted principally 

 into the metallic state, and the remainder is passed 

 into other furnaces, where a renewed heating with 

 charcoal compels it to give up its oxygen, and to 

 assume the condition of perfectly metallic lead. 

 There is another mode of treatment practised in 

 Germany and France to a considerable extent. It 

 consists in presenting to the sulphur of the ore a 

 substance with which it has a more powerful affinity 

 than with the lead ; this substance is iron. The 

 workmen commence by melting the ore in a rever- 

 beratory furnace of small size, and when the bath is 

 full, they throw in twenty-eight per cent, of old iron. 

 In a little time, the sulphur passes from the lead to 

 the iron, leaving the former metal free, which occu- 

 pies the bottom of the basin. By this means, the 



