A System of Instruction in the Practical Use of the Blowpipe Part 22

Upon charcoal, the oxide is reduced to the metal, and the bead appears colorless after cooling. With the addition of some tin, the bead becomes brownish-red and opaque after cooling.

_Microcosmic Salt_ dissolves oxide of copper in the flame of oxidation to a green bead, not so intensely colored as the borax bead. In the reduction flame the bead, if pretty well saturated, becomes dark-green while hot, and brownish-red when cool, opaque and enamel-like. If the oxide is so little that no reaction is visible, by the addition of some tin, the bead appears colorless while hot, and dark brownish-red and opaque when cold.

_Carbonate of Soda_ dissolves oxide of copper in the oxidation flame upon platinum wire, to a clear, green bead, which loses its color when cooling, and becomes opaque.

Upon charcoal, it is reduced to the metal, the soda is absorbed by the charcoal, and the metallic particles melt with sufficient heat to a grain.

(_b._) _Silver_ (Ag).--This metal occurs in nature in the metallic state, and in combination with other metals, particularly with lead.

It also occurs as the sulphide in several mines. It crystallizes in cubes and octahedrons; is of a pure white color, great l.u.s.tre, is very malleable and ductile, and is softer than copper, but harder than gold. It is not oxidizable, neither at common temperatures nor at those which are considerably higher. It is soluble in dilute nitric acid, and in boiling concentrated sulphuric acid.

([chi].) _Protoxide of Silver_ (Ag^{2}O).--It is a black powder. It is converted by acids and ammonia into oxide and metal.

([beta].) _Oxide of Silver_ (AgO).--It is a greyish-brown or black powder, and is the base of the silver salts. With aqua ammonia, it is converted into the black, fulminating silver.

([gamma].) _Superoxide or Binoxide of Silver_ (AgO^{2}).--This oxide occurs in black needles or octahedral crystals of great metallic l.u.s.tre. It is dissolved by the oxygen acids with the disengagement of oxygen gas.

_Behavior before the Blowpipe._--When exposed to the flames of oxidation and reduction, the oxides of silver are instantly reduced to the metallic state.

_Borax_ dissolves silver-oxides upon platinum wire in the oxidation flame but partially, while the other portion is reduced, the bead appearing opalescent after cooling, in correspondence to the degree of saturation. The bead becomes grey in the flame of reduction, the reduced silver melting to a grain, and the bead is rendered clear and colorless again.

_Microcosmic Salt_ dissolves oxides of silver in the flame of oxidation upon platinum wire to a transparent yellowish bead, which presents, when much of the oxide is present, an opalescent appearance.

In the flame of reduction, the reaction is a.n.a.logous to that of borax.

By fusion with carbonate of soda in the oxidation and reduction flames, the silver oxides are instantly reduced to metallic silver, which fuses into one or more grains.

(_c._) _Gold_ (Au).--This metal occurs mostly in the metallic state, but frequently mixed with ores, and with other metals. Gold crystallizes in cubes and octahedrons, is of a beautiful yellow color, great l.u.s.tre, and is the most malleable and ductile of all the metals.

It melts at a higher temperature than copper, gives a green colored light when fused, and contracts greatly when cooling. It does not oxidize at ordinary temperatures, nor when heated much above them. It is soluble in nitro-hydrochloric acid (_aqua regia_).

([chi].) _Protoxide of Gold_ (Au^{2}O).--This oxide is a dark violet colored powder which is converted by a temperature of 540 into metallic gold and oxygen. It is only soluble in aqua regia. Treated with hydrochloric acid, it yields the chloride of gold and the metal.

With aqua ammonia, it yields the fulminating gold, which is a blue ma.s.s and very explosive.

([chi].) _Peroxide of Gold_ (Au^{2}O^{3}).--This oxide is an olive-green or dark brown powder, containing variable quant.i.ties of water. Decomposed at 530, it yields metallic gold and oxygen.

_Reactions before the Blowpipe._--Oxides of gold are reduced, in both the oxidation and reduction flames, to the metal, which fuses to grains.

_Borax_ does not dissolve it, but it is reduced to the metallic state in this flux in either flame. The reduced metal fuses upon charcoal to a grain.

_Microcosmic Salt_ presents the same reactions as borax.

When fused with soda, upon charcoal, the soda is absorbed, and the gold remains as a metallic grain.

TENTH GROUP.--MOLYBDENUM, OSMIUM.

These metals are not volatile, and are infusible before the blowpipe; but some of their oxides are volatile, and can be reduced to an infusible metallic powder.

(_a._) _Molybdenum_ (Mo) occurs in the metallic state; also combined with sulphur, or as molybdic acid combined with lead. It is a white, brittle metal, and is unaltered by exposure to the air. When heated until it begins to glow, it is converted into a brown oxide. Heated at a continued dull red heat, it turns blue. At a higher temperature, it is oxidized to molybdic acid, when it glimmers and smokes, and is converted into crystallized molybdic acid upon the surface.

([chi].) _Protoxide of Molybdenum_ (MoO).--This oxide is a black powder.

([chi].) _Deutoxide of Molybdenum_ (MoO^{2}).--This oxide is a dark copper-colored crystalline powder.

_Reactions before the Blowpipe._--Metallic molybdenum, its protoxide and binoxide, are converted in the oxidation flame into molybdic acid.

This acid fuses in the flame of oxidation to a brown liquid, which spreads, volatilizes, and sublimes upon the charcoal as a yellow powder, which appears crystalline in the vicinity of the a.s.say. This sublimate becomes white after cooling. Beyond this sublimate there is visible a thin and not volatile ore of binoxide, after cooling; this is of a dark copper-red color, and presenting a metallic l.u.s.tre.

Heated in a gla.s.s tube, closed at one end, it melts to a brown ma.s.s, vaporizes and sublimates to a white powder upon a cool portion of the tube. Immediately above the a.s.say, yellow crystals are visible; these crystals are colorless after cooling, and the fused ma.s.s becomes light yellow-colored and crystalline.

Upon platinum foil, in the flame of oxidation, it melts and vaporizes, and becomes light yellow and crystalline after cooling. In the reduction flame it becomes blue, and brown-colored if the heat is increased.

Upon charcoal, in the reduction flame, it is absorbed by the charcoal; and, with an increase of the temperature, it is reduced to the metal, which remains as a grey powder after washing off the particles of charcoal.

_Borax_ dissolves it, in the oxidation flame, upon platinum wire easily, and in great quant.i.ty, to a clear yellow, which becomes colorless while cooling. By the addition of more of the molybdenic acid the bead is dark yellow, or red while hot, and opalescent when cold. In the reduction flame, the color of the bead is changed to brown and transparent. By the addition of more of the acid, it becomes opaque.

_Microcosmic Salt_ dissolves it in the oxidation flame, upon platinum wire, to a clear, yellowish-green bead, which becomes colorless after cooling. In the reduction flame the bead is very dark and opaque, but becomes of a bright green after cooling. This is the case likewise upon charcoal.

_Carbonate of Soda_ dissolves it upon platinum wire in the oxidation flame with intumescence, to a clear bead, which appears milk-white after cooling. Upon charcoal the soda and the molybdic acid are absorbed, the latter is reduced to the metallic state, the metal remaining as a grey powder after washing off the particles of charcoal. When molybdic acid, or any other oxide of this metal, is exposed upon platinum wire, or with platinum tongs, to the point of the blue flame, a yellowish-green color is communicated to the external flame. If also any of the compounds of molybdenum are mixed in the form of a powder with concentrated sulphuric acid and alcohol, and the latter inflamed, the flame of the alcohol appears colored green.

(_c._) _Osmium_ (Os).--This metal occurs a.s.sociated with platinum. It is of a bluish-grey color, and is very brittle. Ignited in the open air, it is oxidized to volatile osmic acid, which is possessed of a pungent smell, and affects the eyes. It communicates a bright white color to the flame of alcohol. Osmium oxide (OsO^{2}) is converted in the oxidation flame to osmic acid, which is volatilized with a peculiar smell, leaving a sublimate.

In the reduction flame it is reduced to a dark-brown infusible metallic powder. It produces no reactions with fluxes. Carbonate of soda reduces it upon charcoal to an infusible metallic powder, which appears, after washing off the particles of charcoal, of a dark-brown color.

ELEVENTH GROUP.--PLATINUM, PALLADIUM, IRIDIUM, RHODIUM, RUTHENIUM.

These metals are infusible before the blowpipe. They are not volatile, nor are they oxidizable. Their oxides are, in both flames, reduced to a metallic and infusible powder. They give no reactions with fluxes, but are separated in the metallic form. These metals are generally found a.s.sociated together in the native platinum, also with traces of copper, lead, and iron.

The metal palladium is found native, a.s.sociated with iridium and platinum. This metal generally occurs in greatest quant.i.ty in Brazil.

The metal rhodium is found along with platinum, but in very small quant.i.ties.

Iridium occurs in nature a.s.sociated with osmium, gold, and platinum, in the mines of Russia. Its great hardness has rendered it desirable for the points of gold pens. In South America this metal is found native, a.s.sociated with platinum and osmium. The latter metal, a.s.sociated with platinum and iridium, has been found in South America.

As these metals will not oxidize or dissolve, they cannot be separated from each other by the blowpipe with the reagents peculiar to that species of a.n.a.lysis. It is true that colors may be discerned in the beads, but these tints proceed from the presence of small traces of copper, iron, etc.

The ore of osmium and iridium can be decomposed, and the former recognized by its fetid odor. This metal, strongly ignited in a gla.s.s tube with nitrate of potash, is converted to the oxide of osmium, which gives an odor not unlike the chloride of sulphur.

As the metals of this group are very rare ones, especially the last four ones, we shall not devote an especial division to each of them.

For a more detailed statement of their reactions, the student is referred to the large works upon blowpipe a.n.a.lysis.

CLa.s.s III.

NON-METALLIC SUBSTANCES.

1. _Water_--2. _Nitric Acid_--3. _Carbon_--4. _Phosphorus_ --5. _Sulphur_--6. _Boron_--7. _Silicon_--8. _Chlorine_ --9. _Bromine_--10. _Iodine_--11. _Fluorine_--12. _Cyanogen_ --13. _Selenium_.