A System of Instruction in the Practical Use of the Blowpipe Part 20

_Sesquioxide of Antimony_ (Sb^{2}O^{3}).--In the pure state this oxide is a white powder, is fusible at a dull red heat to a yellow liquid, which, after cooling, is greyish-white and crystalline. If it is heated excluded from the air, it can be volatilized completely; it sublimes in bright crystals having the form of needles. It occurs sometimes in nature as white and very bright crystals. It takes fire when heated in the open air, and burns with a white vapor to antimonious acid. It fuses with the ter-sulphide of antimony to a red bead. It is distinguished from the other oxides of antimony by the readiness with which it is reduced to the metallic state upon charcoal, and by its easy fusibility and volatility.

The sesquioxide is the base of some salts--for instance, the tartar emetic. It is not soluble in nitric acid, but is soluble in hydrochloric acid. This solution becomes milky by the addition of water. A part of the salts of the sesquioxide of antimony are decomposed by ignition. The haloid salts are easily volatilized, without decomposition. Its soluble neutral salts change blue litmus paper to red, and are converted, by admixture of water, into insoluble basic and soluble acid salts.

Antimonious acid (antimoniate of sesquioxide of antimony, Sb^{2}O^{3} + Sb^{2}O^{5}) is of a white color, but, when heated, of a light yellow color, but changes to white again when cold. It is infusible and unaltered by heat. It forms a white hydrate, and both are insoluble in water and nitric acid. It is partly soluble in hydrochloric acid, with the application of heat. The addition of water causes a precipitate in this solution.

_Antimonic Acid _(Sb^{2}O^{5}).--In the pure state this acid is a light yellow-colored powder. Its hydrate is white, and is insoluble in water and nitric acid. It is sparingly soluble in hot concentrated hydrochloric acid. It forms salts with every base, some of which are insoluble, and others sparingly so. Notwithstanding that antimonic acid is insoluble in water, it expels the carbonic acid from the solutions of the carbonates of the alkalies. Antimonic acid and its hydrate changes moistened blue litmus paper to red.

_Behavior of Antimony and its Oxides before the Blowpipe._

_Metallic Antimony_ fuses easily upon charcoal. When heated to glowing, and then removed from the flame, it continues to glow for awhile, and produces a thick white smoke. The vapor crystallizes gradually, and coats the a.s.say with small crystals which iridesce like mother of pearl (sesquioxide of antimony). It is not volatile at the temperature of melted gla.s.s. Ignited in an open gla.s.s tube, it burns slowly with a white vapor, which condenses upon the cool part of the tube, and exhibits some indications of crystallization. This vapor consists of the sesquioxide, and can be driven by heat from one place to another, without leaving a residue. If the metallic antimony contains sulphide of antimony, there is a corresponding portion of antimonious acid produced, which remains as a white sublimate after the sesquioxide is removed.

_Sesquioxide of antimony_ melts easily, and sublimes as a white vapor.

It may be prepared by precipitating and drying. When heated, it takes fire previous to melting, glows like tinder, and is converted into antimonious acid, which is now infusible. When heated upon charcoal in the flame of reduction, it is reduced to the metallic state, and partly volatilized. A white vapor sublimates upon the charcoal, while the external flame exhibits a greenish-blue color. Antimonious acid is infusible, produces a strong light, and is diminished in volume when heated in the external flame, during which time a dense white vapor sublimes upon the charcoal. It is not, however, in this manner reduced to the metallic state like the sesquioxide.

_Antimonic acid_, when first heated, becomes white, and is converted into antimonious acid. Hydrated antimonic acid, which is originally white, appears at first yellow while giving off water, and then becomes white again, while oxygen is expelled, and it is converted into antimonious acid.

The oxides of antimony produce, with blowpipe reagents, the following reactions: borax dissolves oxides of antimony in the oxidation flame in considerable quant.i.ty to a clear bead, which is yellow while hot, but colorless when cold. If the bead is saturated, a part of the oxide is volatilized as a white vapor. Upon charcoal, in the oxidation flame, it is completely volatilized, and the charcoal is covered with a white sublimate. Heated upon charcoal in the reducing flame, the bead is of a greyish color, and partially, if not wholly opaque, from the presence of reduced metallic particles. A continued heat will volatilize them, and the bead becomes clear. The addition of tin promotes the reduction.

Microcosmic salt dissolves the compounds of antimony in the flame of oxidation with intumescence, to a clear light-yellow colored bead, which when cold is colorless. Heated upon charcoal in the reduction flame, the bead is first turbid, but soon becomes transparent. The addition of tin renders the bead greyish while cooling, but a continued blast renders it transparent. Soda dissolves the compounds of antimony upon platinum wire in the oxidation flame, to a clear colorless bead, which is white when cold.

Upon charcoal, both in the oxidation and reduction flames, the antimony compounds are readily reduced to the metal, which is immediately volatilized, and produces a white incrustation of oxide of antimony upon the charcoal. If the antimony compounds are heated upon charcoal in the flame of reduction, with a mixture of carbonate of soda and cyanide of pota.s.sium (KCy), there are produced small globules of metallic antimony. At the same time, a part of the reduced metal is volatilized (this continues after the a.s.say is removed from the flame) and re-oxidized. A white incrustation appears upon the charcoal, and the metallic globules are covered with small white crystals. If this white sublimate upon the charcoal is moistened with a solution of cobalt-oxide, and exposed to the reduction flame, a part of it is volatilized, while the other part pa.s.ses into higher oxidation, and remains, after cooling, of a dirty dark-green color.

(_d._) _Tellurium_ (Te).--This is one of the rare metals. It occurs very seldom in the metallic state, but often with bis.m.u.th, lead, silver, and gold. Tellurium, in the pure state, is silver-white, very bright, of a foliated or lamellar structure, brittle, and easily triturated. It is inclined to crystallize. It is soluble in concentrated sulphuric acid without oxidation. The solution is of a fine purple color, and gives a precipitate with the addition of water.

_Tellurium in the Metallic form._--By the aid of heat it is oxidized in sulphuric acid, a portion of the oxygen of the acid oxidizing the metal, while sulphurous acid gas escapes. This solution is colorless, and is tellurous acid, dissolved in sulphuric acid. It melts at a low red heat, and volatilizes at a higher temperature. If tellurium is heated with free access of air, it takes fire, and burns with a blue color, the flame being greenish at the edges, while a thick white vapor escapes, which has a feeble acidulous odor.

_Tellurous Acid_ (TeO^{2}) is of a fine, granulous, crystalline or white earthy ma.s.s, which is partly soluble in water. The solution has a strong metallic taste, and an acid reaction upon litmus paper.

Heated in a tube closed at one end until it begins to glow, it fuses to a yellow liquid which is colorless, crystalline, and opaque when cold. Beads of it remain usually transparent like gla.s.s. Heated upon platinum wire in the flame of oxidation, it melts, and is volatilized as a white vapor. When heated upon charcoal in the oxidation flame, it melts, and is reduced to the metallic state, but volatilizes and a sublimate of white tellurous acid is formed upon the charcoal. The edge of this deposit is usually red or dark-yellow.

Heated upon charcoal in the flame of reduction, it is rapidly reduced, the external flame exhibiting a bluish-green color.

Borax dissolves it in the oxidation flame upon platinum wire to a clear colorless bead which turns grey when heated upon charcoal, through the presence of reduced metallic particles. Upon charcoal, in the reduction flame, the bead is grey, caused by the reduced metal.

After a continued blast, tellurium is completely volatilized, and the bead appears clear again, while a white sublimate is deposited upon the charcoal.

With microcosmic salt, the same reactions are produced.

With carbonate of soda, tellurous acid fuses upon platinum wire to a clear colorless bead, which is white when cold. Upon charcoal it is reduced, and forms _tellur-sodium_, which is absorbed by the charcoal, and metallic tellurium, which is volatilized, and deposits upon the charcoal a white incrustation (tellurous acid).

If tellurous acid, finely powdered charcoal, and carbonate of soda are mixed together, and the mixture be well ignited in a closed tube, until fusion is effected, and a few drops of boiled water are brought into the tube, they are colored purple, indicating the presence of _tellur-sodium._

_Telluric Acid _(TeO^{3}) forms six-sided prismatic crystals. It has not an acid, but rather a metallic taste. It changes blue litmus paper to red; is slowly soluble in water, and rather sparingly. Exposed to a high temperature, but not until glowing, the crystalline acid loses its water, and acquires an orange color, but still it preserves its crystalline form, although no longer soluble in water, and is in fact so much changed in its properties as to present the instance of an isomeric modification.

If telluric acid is heated gently in a closed tube, it loses water and turns yellow. Heated still more strongly, it becomes milk-white, oxygen is expelled, and it is converted into tellurous acid. The presence of oxygen can be recognized by the more lively combustion which an ignited splinter of wood undergoes when held in it. Telluric acid produces the same reactions with the blowpipe reagents as tellurous acid.

SEVENTH GROUP.--LEAD, BIs.m.u.tH, TIN.

The oxides of these metals are also reduced to the metallic state by fusion with soda upon charcoal in the flame of reduction, but they are volatilized only after a continued blast, and a sublimate is thrown upon the charcoal.

(_a._) _Lead_ (Pb).--This metal occurs in considerable quant.i.ty in nature, chiefly as galena or lead-glance (sulphide of lead). Likewise, but more rarely, as a carbonate; also as a sulphate, and sometimes combined with other acids and metals.

In the metallic state, lead is of a bluish-grey color, high l.u.s.tre, and sp. gr. 11.4. It is soft, and communicates a stain to paper. It is malleable, ductile, but has very little tenacity. It melts at about 612. Exposed to the air it soon tarnishes, being covered with a grey matter, which some regard as a suboxide (Pb^{2}O), and others as simply a mixture of lead and protoxide. At a glowing heat it is oxidized to a protoxide, and at a white heat it is volatilized. It is insoluble in most acids. It is, however, soluble in nitric acid, but without decomposing water.

(_L._) _Protoxide of Lead_ (PbO).--It is an orange-colored powder, which melts at a glowing temperature, and forms a lamellar ma.s.s after cooling. Protoxide of lead absorbs oxygen from the atmosphere while melting, which is given off again by cooling. Being exposed for a longer while to the air, it absorbs carbonic acid and water, and becomes white on the surface. It is soluble in nitric acid and caustic alkalies. It forms with most acids insoluble salts. It is slightly soluble in pure water, but not in water which contains alkaline salts.

This hydrate is white.

([beta].) _Red Oxide of Lead_ (PbO^{2}, PbO).--It forms a puce-colored powder. It is insoluble in caustic alkalies. Hydrochloric acid dissolves it and forms a yellow liquid, which is soon decomposed into chloride of lead and chlorine. It is reduced by ignition to the protoxide.

([gamma].) _Peroxide of Lead _(PbO^{2}).--It is a dark-brown powder.

It yields with hydrochloric acid the chloride of lead and chlorine gas. When heated it liberates oxygen, and is reduced to the protoxide.

Lead combinations give the following reactions before the blowpipe: Metallic lead tarnishes when heated in the oxidation flame, and is instantly covered with a grey matter, consisting of the protoxide and the metal. It fuses quickly, and is then covered with a yellowish-brown protoxide until all the lead is converted into the protoxide, which melts to a yellow liquid. In the reduction flame and upon charcoal, it is volatilized, while the charcoal becomes covered with a yellow sublimate of oxide. A little distance from the a.s.say, this sublimate appears white (carbonate of lead). Protoxide of lead melts in the flame of oxidation to a beautiful dark yellow bead. In the flame of reduction, and upon charcoal, it is reduced with intumescence to metallic lead, which is volatilized by a continued blast, and sublimates on charcoal, as mentioned above.

Red oxide of lead turns black when heated in the gla.s.s tube closed at one end, and liberates oxygen, which is easily detected by the introduction of an ignited splinter, when a more lively combustion of the wood proves the presence of uncombined oxygen. The red oxide in this case is reduced to the protoxide. Heated upon platinum foil, it first turns black, is reduced to the protoxide, and melts into a dark yellow liquid. In the reduction flame, upon charcoal, it is reduced to the metal with intumescence. After a continued blast, a yellow sublimate of protoxide is produced upon the charcoal, and at a little distance off, around this sublimate, a white one of carbonate of lead is produced. This sublimate disappears when touched by the flame of reduction, while it communicates an azure blue-tinge to the external flame. This is likewise the case with the peroxide of lead.

The different oxides of lead produce with the blowpipe reagents the same reactions.

_Borax_ dissolves lead compounds with the greatest readiness upon platinum wire in the oxidation flame to a transparent bead, which is yellow when hot, but colorless after being cooled. With the addition of more of the lead oxide, it becomes opalescent. When heated by the intermittent flame, and with still more of the oxide, it acquires a yellow enamel after cooling. Heated upon charcoal, in the flame of reduction, the bead spreads and becomes opaque. After a continued blast, all the oxide is reduced with effervescence to metallic lead, which melts and runs towards the edges of the bead, while the bead again becomes transparent.

_Microcosmic Salt_ dissolves oxides of lead upon platinum wire in the flame of oxidation easily to a clear, colorless bead, which appears, when highly saturated, yellow while hot. A saturated bead becomes enamel-like after cooling. The bead appears in the flame of reduction, and upon charcoal, of a greyish color and dull. By the addition of more oxide, a yellow sublimate of protoxide is produced upon the charcoal. By the addition of tin, the bead appears of a darker grey, but it is never quite opaque.

_Carbonate of Soda_ dissolves oxide of lead in the flame of oxidation upon platinum wire quite readily to a transparent bead, which becomes yellow when cooling, and is opaque. Upon charcoal in the flame of reduction, it is rapidly reduced to metallic lead, which yields, after a continued blast, a yellow sublimate of oxide upon the charcoal.

(_b._) _Bis.m.u.th_ (Bi).--This metal occurs mostly in the metallic state, and less frequently as the sulphide. In the pure metallic state, it is of a reddish-white color and great l.u.s.tre. It crystallizes in cubes. It is brittle, and may be readily pulverized.

It melts at 476, and is volatilized at a white heat. It is soluble in nitric acid, and forms the nitrate of bis.m.u.th.

([alpha].) _Oxide of Bis.m.u.th _(Bi^{2}O^{3}).--This oxide is a light yellow powder, fusible at a red heat, insoluble in caustic potash and ammonia. It is the base of the salts of bis.m.u.th. Its hydrate is white, and easily soluble in acids. The addition of water causes these solutions to become milky, because they are decomposed into a soluble acidulous and an insoluble basic salt of bis.m.u.th.

([beta].) _Peroxide of Bis.m.u.th_ (BiO^{2}) is a dark-colored powder, completely soluble in boiling nitric acid, and yielding oxygen; produces, with hydrochloric acid, chlorine gas. It can be heated up to the temperature of 620 without being decomposed; but, exposed to a temperature of 630 it yields oxygen. Mixed with combustible substances, it glows with brightness.

([gamma].) _Bis.m.u.thic Acid _(Bi^{2}O^{5}) is a brown powder similar to the peroxide, but is converted by boiling nitric acid into a green, scarcely soluble substance (Bi^{2}O^{3}, Bi^{2}O^{5}). Its hydrate is of a red color.

BLOWPIPE REACTIONS.--Metallic bis.m.u.th is converted, when exposed upon platinum wire to the flame of oxidation, into a dark brown oxide, which turns light yellow while cooling. It is slowly volatilized when heated, and a yellow sublimate of oxide is produced upon the charcoal.

Oxide of bis.m.u.th melts upon platinum foil in the flame of oxidation very easily into a dark-brown liquid, which changes to a light yellow while cooling. By too strong a heat, it is reduced and penetrates the platinum foil.

Upon charcoal, in the flame of oxidation and of reduction, it is reduced to metallic bis.m.u.th, which melts into one or more globules.

By a continued blast they are slowly volatilized, and produce a yellow sublimate of oxide upon the charcoal, beyond which a white sublimate of carbonate of bis.m.u.th is visible. These sublimates disappear in the flame of reduction, but without communicating any color to it.

_Borax_ dissolves oxide of bis.m.u.th upon platinum wire, in the flame of oxidation, easily to a clear yellow bead, which appears colorless after cooling. By the addition of more oxide, the hot bead becomes orange. It turns more yellow while cooling, and when cool is opalescent. Upon charcoal in the flame of reduction, the bead becomes turbid and greyish colored. The oxide is reduced with intumescence to the metallic state, and the bead becomes clear again. The addition of tin promotes the reduction.

_Microcosmic Salt_ dissolves oxide of bis.m.u.th upon platinum wire, in the flame of oxidation, to a yellow bead, which becomes colorless after cooling. By the addition of more oxide, the bead is yellowish-brown while hot, and colorless after cooling, but not quite transparent. This bead becomes enamelled when heated by the intermittent flame; also, by the addition of still more of the oxide, after it is cooled.

Upon charcoal, in the flame of reduction, and particularly with the addition of tin, the bead is colorless and transparent while hot, but while cooling becomes of a dark-gray color and opaque.

Oxide of bis.m.u.th is reduced, by fusion with carbonate of soda, as well in the oxidating as in the reducing flame, instantly to metallic bis.m.u.th.

As the above mentioned higher oxides of bis.m.u.th are converted by ignition into oxide of the metal and free oxygen, they have the same behavior before the blowpipe.