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~, PbCO_{3}, PbO . 84, CO_{2} . 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~, PbSO_{4}, PbO . 74, SO_{3} . 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 Na_{2}CO_{3} is reduced to the metal giving a yellow coating. The Na_{2}CO_{3} absorbed by the coal reacts for S. ORES OF MANGANESE ~Pyrolusite~, MnO_{2}, 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~, Mn_{2}O_{3} + H_{2}O.-- H = 5.5-6.0, G = 3.7-4.7. Color, iron-black to steel-gray. Generally resembles pyrolusite, but is distinguished from it by its superior hardness. It frequently contains BaO and Li_{2}O. It behaves before the Bp. like pyrolusite. ~Wad~ (Bog Manganese).--This mineral is essentially MnO_{2}, MnO, and H_{2}O, with small quantities of Fe_{2}O_{3}, Al_{2}O_{3}, BaO, SiO_{2}, etc., associated with it. H = 0.5-6.0, G = 3.0-4.2. Color, dull black. Heated in an ignition tube yields water in abundance, otherwise it behaves like pyrolusite. ORES OF MERCURY