The Elements of Blowpipe Analysis Part 8

H = 6.0-6.5, G = 4.95-5.20.

Color, bra.s.s-yellow. l.u.s.tre, metallic. Occurs commonly in cubes. It often contains small quant.i.ties of Au, Ag, Cu, As, Co, and Mn. Heated in an ignition tube gives a sublimate of sulphur, the residue becoming magnetic. Before the Bp. on Ch. in O. F. sulphur is burned off and the red oxide remains. This residue may then be examined for iron, etc.

~Marcasite~ (White Iron Pyrites).--Having the same general composition as pyrite, but much lighter in color. Crystals, prismatic. Before the Bp.

on Ch. behaves like pyrite.

~Pyrrhot.i.te~, Fe_{7}S_{8}, Fe . 60.5, S . 39.5.--

H = 3.5-4.5, G = 4.58-4.64.

Color, bronze-yellow. Closely resembles pyrite, but may be distinguished from it by being feebly magnetic. Heated in an ignition tube yields no sublimate. Before the Bp. on Ch. fuses to a magnetic globule, which exhibits a yellowish crystalline structure when fractured.

~Mispickel~, Fea.s.s, Fe . 34, As . 46, S . 20.--H = 5.5-6.0, G = 6.0-6.2.

Color, silver-white. l.u.s.tre, metallic; very brittle. Often a.s.sociated with it we find small quant.i.ties of Co, Ag, and Au. Heated in an ignition tube it first yields a red sublimate of sulphide of a.r.s.enic, and then afterward a crystalline sublimate of metallic a.r.s.enic. Before the Bp. on Ch. emits dense fumes of a.r.s.enic and deposits a coating on the coal; it then fuses to a globule which behaves like pyrrhot.i.te.

~Siderite~, FeCO_{3}, FeO . 62, CO_{2} . 38.--H = 3.5-4.5, G = 3.7-3.9.

Color, grayish yellow to reddish brown. l.u.s.tre, pearly. Crystallizes in rhombohedrons with curved faces; these crystals are distinctly cleavable and ma.s.sive. Heated in an ignition tube it decrepitates with evolution of carbon dioxide. Before the Bp. on Ch. infusible. Before the Bp. on Ch. with Na_{2}CO_{3} it fuses to a magnetic ma.s.s. With borax bead it reacts for iron and sometimes for manganese.

ORES OF LEAD

~Galena~, PbS, Pb . 87, S . 13.--

H = 2.5, G = 7.4-7.6.

Color, bluish gray, slowly tarnishing. l.u.s.tre, 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 gla.s.s 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. l.u.s.tre, 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. l.u.s.tre, 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. l.u.s.tre, 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 quant.i.ties of Fe_{2}O_{3}, Al_{2}O_{3}, BaO, SiO_{2}, etc., a.s.sociated 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

~Native Mercury, Hg.~--G = 13.5-13.6. Color, silver-white. Is liquid at all ordinary temperatures. Heated in an ignition tube is volatilized, the vapors condensing in the upper end of tube to small metallic globules of Hg. Before the Bp. on Ch. it is volatilized. Frequently contains Ag.

~Cinnabar~, HgS_{2}, Hg . 86, S . 14.--

H = 2.0-2.5, G = 8.0-8.2.

Color, scarlet-red to brick-red. l.u.s.tre, non-metallic. When pulverized yields a powder of vermilion-red color. Heated in an ignition tube it volatilizes, yielding a black sublimate, which by friction becomes red.

Before the Bp. on Ch. it is wholly volatilized. Heated in an ignition tube with Na_{2}CO_{3} metallic mercury sublimes, condensing in the upper portion of the tube in minute globules.

ORES OF NICKEL

~Millerite~, NiS, Ni . 64.4, S . 35.6.--

H = 3.0-3.5, G = 5.2-5.6.

Color, bra.s.s-yellow. Brittle. Before the Bp. on Ch. it fuses to a magnetic, metallic globule. The roasted mineral gives in the borax bead the color reaction characteristic of nickel, and sometimes that of cobalt, which is often a.s.sociated with it.

~Niccolite~, NiAs, Ni . 44, As . 56.--

H = 5.0-5.5, G = 7.35-7.67.

Color, pale copper-red. l.u.s.tre, metallic. Very brittle. Heated in an ignition tube yields a copious sublimate of a.r.s.enious oxide, the residue falling to a greenish powder. Before the Bp. on Ch. fuses to a white brittle globule emitting a.r.s.enical fumes. In borax bead gives color characteristic of nickel. Frequently in this mineral a portion of the a.r.s.enic is replaced by antimony.

ORES OF SILVER

~Native Silver, Ag.~--

H = 2.5-3.0, G = 10.1-11.0.

Color, silver-white. l.u.s.tre, metallic. Ductile and malleable. Usually occurs a.s.sociated with Au, As, Sb, Cu, Fe, etc. Before the Bp. on Ch.

easily fuses to a globule which is surrounded with a dark red coating on the coal.

~Argent.i.te~, Ag_{2}S, Ag . 87.1, S . 12.9.--