A System of Instruction in the Practical Use of the Blowpipe Part 15

in the reducing flame.

As with borax.

7. EXAMINATIONS WITH CARBONATE OF SODA.

The carbonate of soda is pulverized and then kneaded to a paste with water; the substance to be examined, in fine powder, is also mixed with it. A small portion of this paste is placed on the charcoal, and gradually heated until the moisture is expelled, when the heat is brought to the fusion of the bead, or as high as it can be raised.

Several phenomena will take place, which must be closely observed.

Notice whether the substance fuses with the bead, and if so, whether there is intumescence or not. Or, whether the substance undergoes reduction; or, whether neither of these reactions takes place, and, on the contrary, the soda sinks into the charcoal, leaving the substance intact upon its surface. If intumescence takes place, the presence of either tartaric acid, molybdic acid, silicic, or tungstic acid, is indicated. The silicic acid will fuse into a bead, which becomes clear when it is cold. t.i.tanic acid will fuse into the bead, but may be easily distinguished from the silicic acid by the bead remaining opaque when cold.

Strontia and baryta will flow into the charcoal, but lime will not.

The molybdic and tungstic acids combine with the soda, forming the respective salts. These salts are absorbed by the charcoal. If too great a quant.i.ty of soda is used, the bead will be quite likely to become opaque upon cooling, while, if too small a quant.i.ty of soda is used, a portion of the substance will remain undissolved. These can be equally avoided by either the addition of soda, or the substance experimented upon, as may be required.

As silica and t.i.tanic acid are the only two substances that produce a clear bead, the student, if he gets a clear bead, may almost conclude that he is experimenting with silica, t.i.tanic acid being a rare substance. When soda is heated with silica, a slight effervescence will be the first phenomenon noticed. This is the escape of the carbonic acid of the carbonate of soda, while the silicic acid takes its place, forming a gla.s.s with the soda. As t.i.tanic acid will not act in the same manner as silica, it can be easily distinguished by its bead not being perfectly pellucid. If the bead with which silica is fused should be tinted of a hyacinth or yellow color, this may be attributed to the presence of a small quant.i.ty of sulphur or a sulphate, and this sometimes happens from the fact of the flux containing sulphate of soda. The following metals, when exposed with carbonate of soda to the reducing flame, are wholly or partially reduced, viz. the oxides of all the n.o.ble metals, the oxides and acids of tungsten, molybdenum, a.r.s.enic, antimony, mercury, copper, tellurium, zinc, lead, bis.m.u.th, tin, cadmium, iron, nickel, and cobalt. Mercury and a.r.s.enic, as soon as they are reduced, are dissipated, while tellurium, bis.m.u.th, lead, antimony, cadmium, and zinc, are only partially volatilized, and, therefore, form sublimates on the charcoal. Those metals which are difficult of reduction should be fused with oxalate of pota.s.sa, instead of the carbonate of soda.

The carbonic oxide formed from the combustion of the acid of this salt is very efficient in the reduction of these metals. Carbonate of soda is very efficient for the detection of minute quant.i.ties of manganese.

The mixture of the carbonate of soda with a small addition of nitrate of pota.s.sa, and the mineral containing manganese, must be fused on platinum foil. The fused ma.s.s, when cooled, presents a fine blue color.

1. The following minerals, according to Griffin, produce beads with soda, but do not fuse when heated alone: quartz, agalmatolyte, dioptase, hisingerite, sideroschilosite, leucite, rutile, pyrophyllite, wolckonskoite.

2. The following minerals produce only slags with soda: allophane, cymophane, polymignite, aeschynite, oerstedt.i.te, t.i.taniferous iron, tantalite, oxides of iron, yttro-tantalite, oxides of manganese, peroxide of tin (is reduced), hydrate of alumina, hydrate of magnesia, spinel, gahnite, worthite, carbonate of zinc, pechuran, zircon, thorite, andalusite, staurolite, gehlenite, chlorite spar, chrome ochre, uwarowite, chromate of iron, carbonates of the earths, carbonates of the metallic oxides, basic phosphate of yttria, do. of alumina, do. of lime, persulphate of iron, sulphate of alumina, aluminite, alumstone, fluoride of cerium, yttrocerite, topaz, corundum, pleonaste, chondrodite.

3. The following minerals produce beads with a small quant.i.ty of soda, but produce slags if too much soda is added: phenakite, pierosmine, olivine, cerite, cyanite, talc, gadolinite, lithium-tourmaline.

1. The following minerals, when fused alone, produce beads. Of these minerals the following produce beads with soda: the zeolites, spodumene, soda-spodumene, labrador, scapolite, sodalite (Greenland), elaeolite, mica from primitive lime-stone, black talc, acmite, krokidolite, lievrite, cronstedt.i.te, garnet, cerine, helvine, gadolinite, boracic acid, hydroboracite, tincal, boracite, datholite, botryolite, axinite, lapis lazuli, eudialyte, pyrosmalite, cryolite.

2. The following minerals produce beads with a small quant.i.ty of soda, but if too much is added they produce slags: okenite, pectolite, red silicate of manganese, black hydro-silicate of manganese, idocrase, manganesian garnets, orthite, pyrorthite, sordawalite, sodalite, fluorspar.

3. The following minerals produce a slag with soda: brevicite, amphodelite, chlorite, fahlunite, pyrope, soap-stone (Cornish) red dichroite, pyrargillite, black potash tourmaline, wolfram, pharmacolite, scorodite, a.r.s.eniate of iron, tetraphyline, hetepozite, uranite, phosphate of iron, do. of strontia, do. of magnesia, polyhalite, hauyne.

4. The following metals are reduced by soda: tungstate of lead, molybdate of lead, vanadate of lead, chromate of lead, vauquelinite, cobalt bloom, nickel ochre, phosphate of copper, sulphate of lead, chloride of lead, and chloride of silver.

The following minerals fuse on the edges alone, when heated in the blowpipe flame:

1. The following produce beads with soda: steat.i.te, meerschaum, felspar, albite, petalite, nepheline, anorthite, emerald, euclase, turquois, sodalite (Vesuvius).

2. The following minerals produce beads with a small quant.i.ty of soda, but with the addition of more produce slags: tabular spar, diallage, hypersthene, epidote, zoisite.

3. The following minerals produce slags only with soda: stilpnosiderite, plombgomme, serpentine, silicate of manganese (from Piedmont), mica from granite, pimelite, pinite, blue dichroite, sphenc, karpholite, pyrochlore, tungstate of lime, green soda tourmaline, lazulite, heavy spar, gypsum.

The reactions of substances, when fused with soda in the flame of oxidation may be of use to the student. A few of them are therefore given. Silica gives a clear gla.s.s.

The oxide of tellurium and telluric acid gives a clear bead when it is hot, but white after it is cooled.

t.i.tanic acid gives a yellow bead when hot.

The oxide of chromium gives also a clear yellow gla.s.s when hot, but is opaque when cold.

Molybdic acid gives a clear bead when hot, but is turbid and white after cooling.

The oxides and acids of antimony give a clear and colorless bead while hot, and white after cooling.

Vanadic acid is absorbed by the charcoal, although it is not reduced.

Tungstic acid gives a dark yellow clear bead while hot, but is opaque and yellow when cold.

The oxides of manganese give to the soda bead a fine characteristic green color. This is the case with a very small quant.i.ty. This reaction is best exhibited on platinum foil.

Oxide of cobalt gives to the bead while hot a red color, which, upon being cooled, becomes grey.

The oxide of copper gives a clear green bead while hot.

The oxide of lead gives a clear colorless bead while hot, which becomes, upon cooling, of a dirty yellow color and opaque.

The following metals, when they are fused with soda on charcoal, in the flame of reduction, produce volatile oxides, and leave an incrustation around the a.s.say, viz. bis.m.u.th, zinc, lead, cadmium, antimony, selenium, tellurium, and a.r.s.enic.

_Bis.m.u.th_, under the reduction flame, yields small particles of metal, which are brittle and easily crushed. The incrustation is of a flesh color, or orange, when hot, but gets lighter as it cools. The sublimate may be driven about the charcoal from place to place, by either flame, but is finally dissipated. While antimony and tellurium, in the act of dissipation, give color to the flame, bis.m.u.th does not, and may thus be distinguished from them.

_Zinc_ deposits an incrustation about the a.s.say, which is yellow while hot, but fades to white when cold. The reduction flame dissipates this deposit, but not that of oxidation. All the zinc minerals deposit the oxide incrustation about the a.s.say, which, when moistened with a solution of cobalt and heated, changes to green.

_Lead_ is very easily reduced, in small particles, and may be easily distinguished by its flattening under the hammer, unlike bis.m.u.th. It leaves an incrustation around the a.s.say resembling that of bis.m.u.th, in the color of it, and in the peculiar manner in which it lies around the a.s.say.

_Cadmium_ deposits a dull reddish incrustation around the a.s.say.

Either of the flames dissipate the sublimate with the greatest readiness.

_Antimony_ reduces with readiness. At the same time it yields considerable vapor, and deposits an incrustation around the a.s.say.

This deposit can be driven about on the charcoal by either of the flames. The flame of reduction, however, produces the light blue color of the antimony.

_Selenium_ is deposited on the charcoal as a grey metallic-looking sublimate, but sometimes appearing purple or blue. If the reduction flame is directed on this deposit, it is dissipated with a blue light.

_Tellurium_ is deposited on the charcoal as a white sublimate, sometimes changing at the margin to an orange or red color. The oxidation flame drives the deposit over the charcoal, while the reduction-flame dissipates it with a greenish color.

_a.r.s.enic_ is vaporized rapidly, while there is deposited around the a.s.say a white incrustation of a.r.s.enious acid. This deposit will extend to some distance from the a.s.say, and is readily volatilized, the reducing flame producing the characteristic alliaceous color.

The following metals, or their compounds, are reduced when fused with soda on charcoal, in the flame of reduction. They are reduced to metallic particles, but give no incrustation, viz. nickel, cobalt, iron, tin, copper, gold, silver, platinum, tungsten, and molybdenum.