Ores of Lead
Galena, PbS, Pb . 87, S . 13.—
H = 2.5, G = 7.4-7.6.
Color, bluish gray, slowly tarnishing. Lustre, metallic. Crystals in the form of cubes. Heated in an ignition tube it sometimes decrepitates and yields a sublimate of sulphur. Before the Bp. on Ch. easily reduced to the metallic state, the Ch. becoming coated with sulphate and oxide of lead. The metallic globule usually contains a little silver. To separate this, the process known as "cupellation" is employed. A hole is bored into the Ch. about 1 cm. in diameter and about 6 mm. deep. Into this hole is placed a stiff paste made by mixing finely pulverized bone-ash with a little soda and water. This paste is pressed in hard, and then the surface is smoothed off, and the centre is slightly depressed with the rounded end of a glass rod. The charcoal so prepared is set in a warm place to allow the paste to dry. When the paste is quite dry the small globule of lead is placed in the depression in the centre of the bone-ash "cupel," and is there exposed to the O. F. from the Bp. The lead is oxidized and is absorbed by the bone-ash, while any silver present will remain in the central depression as a bright shining bead.
Cerusite, PbCO3, PbO . 84, CO2 . 16.—H = 3.0-3.5, G = 6.46-6.57. Color, white, gray, or yellow. Lustre, adamantine. Crystallizes in prismatic needles. When heated in an ignition tube carbon dioxide is evolved and the residue turns yellow. Before the Bp. on Ch. readily reduced to metallic lead.
Anglesite, PbSO4, PbO . 74, SO3 . 26.—H = 2.0-3.0, G = 6.12-6.39. Color, yellow, gray, and brown. Lustre, adamantine, resinous. Heated in an ignition tube decrepitates, and sometimes yields a little water. Before the Bp. on Ch. fuses to a clear bead, which on cooling becomes opaque. Before the Bp. on Ch. with Na2CO3 is reduced to the metal giving a yellow coating. The Na2CO3 absorbed by the coal reacts for S.
Ores of Manganese
Pyrolusite, MnO2, Mn . 63.2, O . 36.8.—H = 2.0-2.5, G = 4.82. Color, iron-black to steel-gray. Lustre, non-metallic. Heated in an ignition tube yields generally a little water, and if the temperature be high enough, oxygen is evolved. Before the Bp. on Ch. infusible. In borax bead gives characteristic color.
Psilomelane, Mn2O3 + H2O.—
H = 5.5-6.0, G = 3.7-4.7.