Part 6 A System of Instruction in the Practical Use of the Blowpipe

Part 6

(_d._) _Lime._--The color of the flame of lime does not greatly differ from that of strontia, with the exception that it is not so decided.

Arragonite and calcareous spar, moistened with hydrochloric acid, and tried as directed for strontia, produce a red light, not unlike that of strontia. The chloride of calcium gives a red tinge, but not nearly so decided as the chloride of strontium. The carbonate of lime will produce a yellowish flame for a while, until the carbonic acid is driven off, when the red color of the lime may be discerned.

If the borate or phosphate of lime be used, the green color of the acids predominates over the red of the lime. Baryta also destroys the red color of the lime, by mixing its green color with it. There is but one silicate of lime which colors the flame red, it is the variety termed tabular spar.

5. EXAMINATIONS IN THE BORAX BEAD.

In order to examine a substance in borax, the loop of the platinum wire should, after being thoroughly cleaned, and heated to redness, be quickly dipped into the powdered borax, and then quickly transferred to the flame of oxidation, and there fused. If the bead is not large enough to fill the loop of the wire, it must be subjected again to the same process. By examining the bead, both when hot and cold, by holding it up against the light, it can be soon ascertained whether it is free from dirt by the transparency, or the want of it, of the bead.

In order to make the examination of a substance, the bead should be melted and pressed against it, when enough will adhere to answer the purpose. This powder should then be fused in the oxidation flame until it mixes with, and is thoroughly dissolved by the borax bead.

The princ.i.p.al objects to be determined now are: the color of the borax bead, both when heated and when cooled; also the rapidity with which the substance dissolves in the bead, and if any gas is eliminated.

If the color of the bead is the object desired, the quant.i.ty of the substance employed must be very small, else the bead will be so deeply colored, as in some cases to appear almost opaque, as, for instance, in that of cobalt. Should this be the case, then, while the bead is still red hot, it should be pressed flat with the forceps; or it may, while soft, be pulled out to a thin thread, whereby the color can be distinctly discovered.

Some bodies, when heated in the borax bead, present a clear bead both while hot and cold; but if the bead be heated with the intermittent flame, or in the flame of reduction, it becomes opalescent, opaque or milk-white. The alkaline earths are instances of this kind of reaction, also glucina oxide of cerium, tantalic and t.i.tanic acids, yttria and zirconia. But if a small portion of silica should be present, then the bead becomes clear. This is likewise the case with some silicates, provided there be not too large a quant.i.ty present, that is: over the quant.i.ty necessary to saturate the borax, for, in that case, the bead will be opaque when cool.

If the bead be heated on charcoal, a small tube or cavity must be scooped out of the charcoal, the bead placed in it, and the flame of reduction played upon it. When the bead is perfectly fused, it is taken up between the platinum forceps and pressed flat, so that the color may be the more readily discerned. This quick cooling also prevents the protoxides, if there be any present, from pa.s.sing into a higher degree of oxidation.

The bead should first be submitted to the oxidation flame, and any reaction carefully observed. Then the bead should be submitted to the flame of reduction. It must be observed that the platinum forceps should not be used when there is danger of a metallic oxide being reduced, as in this case the metal would alloy with the platinum and spoil the forceps. In this case charcoal should be used for the support. If, however, there be oxides present which are not reduced by the borax, then the platinum loop may be used. Tin is frequently used for the purpose of enabling the bead to acquire a color for an oxide in the reducing flame, by its affinity for oxygen. The oxide, thus being reduced to a lower degree of oxidation, imparts its peculiar tinge to the bead as it cools.

The a.r.s.enides and sulphides, before being examined, should be roasted, and then heated with the borax bead. The a.r.s.enic of the former, it should be observed, will act on the gla.s.s tube in which the sublimation is proceeding, if the gla.s.s should contain lead.

It should be recollected that earths, metallic oxides, and metallic acids are soluble in borax, except those of the easily reducible metals, such as platinum or gold, or of mercury, which too readily vaporize. Also the metallic sulphides, after the sulphur has been driven off. Also the salts of metals, after their acids are driven off by heat. Also the nitrates and carbonates, after their acids are driven off during the fusion. Also the salts of the halogens, such as the chlorides, iodides, bromides, etc., of the metals. Also the silicates, but with great tardiness. Also the phosphates and borates that fuse in the bead without suffering decomposition. The metallic sulphides are insoluble in borax, and many of the metals in the pure state.

There are many substances which give clear beads with borax both while hot and cold, but which, upon being heated with the intermittent oxidation flame, become enamelled and opaque. The intermittent flame may be readily attained, not by varying the force of the air from the mouth, but by raising and depressing the bead before the point of the steady oxidating flame. The addition of a little nitrate of potash will often greatly facilitate the production of a color, as it oxidizes the metal. The hot bead should be pressed upon a small crystal of the nitrate, when the bead swells, intumesces, and the color is manifested in the surface of the bead,

6. EXAMINATIONS IN MICROCOSMIC SALT.

Microcosmic salt is a better flux for many metallic oxides than borax, as the colors are exhibited in it with more strength and character.

Microcosmic salt is the phosphate of soda and ammonia. When it is ignited it pa.s.ses into the biphosphate of soda, the ammonia being driven off. This biphosphate of soda possesses an excess of phosphoric acid, and thus has the property of dissolving a great number of substances, in fact almost any one, with the exception of silica. If the substances treated with this salt consist of sulphides or a.r.s.enides, the bead must be heated on charcoal. But if the substance experimented upon consists of earthly ingredients or metallic oxides, the platinum wire is the best. If the latter is used a few additional turns should be given to the wire in consequence of the greater fluidity of the bead over that of borax. The microcosmic salt bead possesses the advantage over that of borax, that the colors of many substances are better discerned in it, and that it separates the acids, the more volatile ones being dissipated, while the fixed ones combine with a portion of the base equally with the phosphoric acid, or else do not combine at all, but float about in the bead, as is the case particularly with silicic acid. Many of the silicates give with borax a clear bead, while they form with microcosmic salt an opalescent one.

It frequently happens, that if a metallic oxide will not give its peculiar color in one of the flames, that it will in the other, as the difference in degree with which the metal is oxidized often determines the color. If the bead is heated in the reducing flame, it is well that it should be cooled rapidly to prevent a reoxidation. Reduction is much facilitated by the employment of metallic tin, whereby the protoxide or the reduced metal may be obtained in a comparatively brief time.

The following tables, taken from Plattner and Sherer, will present the reactions of the metallic oxides, and some of the metallic acids, in such a clear light, that the student cannot very easily be led astray, if he gives the least attention to them. It frequently happens that a tabular statement of reactions will impress facts upon the memory when long detailed descriptions will fail to do so. It is for this purpose that we subjoin the following excellent tables.

TABLE I.

A. BORAX.

1. Oxydizing flame.

2. Reducing "

B. MICROCOSMIC SALT.

1. Oxydizing flame.

2. Reducing "

A. BORAX

1. Oxydizing flame

-------------------------------------------------------------------------- Color of Bead.

--+-----------------------------------------------------------------------

Substances which produce this color +--------------------------------------+--------------------------------

in the hot bead.

in the cold bead.

--+--------------------------------------+-------------------------------- Colorless -----------------------------------------+--------------------------------

Silica

Alumina

Alumina _

Oxide of Tin

Telluric Acid

Baryta

Strontia

Lime

Magnesia

Glucina

In all

Glucina

Yttria } proportions.

Yttria

Zirconia

Thoria

With

Oxide of Lanthanum

intermittent

" " Silver }flame

Tantalic Acid

opaque

Niobic "

white.

Pelopic " /

Pelopic "

t.i.tanic " _/

t.i.tanic "

Tungstic " In small

Tungstic "

Molybdic " quant.i.ty

Molybdic "

Oxide of Zinc

only.

Oxide of Zinc /

" " Cadmium }

" " Cadmium_/

" " Lead

In large

" " Lead

" " Bis.m.u.th / quant.i.ty

" " Bis.m.u.th

" " Antimony / yellow.

" " Antimony --+-----------+--------------------------+-------------------------------- Yellow, orange-red and reddish-brown.

--+-----------+--------------------------+--------------------------------

t.i.tanic Acid, yellow

Tungstic Acid, yellow

Molybdic Acid, dark yellow

when in

Oxide of Zinc, pale-yellow

large

Oxide of Cadmium, }quant.i.ty.

pale-yellow

Otherwise

Oxide of Lead, yellow

colorless.

Oxide of Bis.m.u.th, orange /

Oxide of Antimony, yellow/

Oxide of Cerium, red

Oxide of Cerium with interm.

Oxide of Iron, dark red

flame opaque white.

Oxide of Uranium, red

Oxide of Iron, yellow

Oxide of Silver

Oxide of Uranium with interm.

flame opaque yellow.

Oxide of Silver in large

proportion, with interm.

flame yellow.

Vanadic Acid, yellow

Vanadic Acid, yellow.

Oxide of Chromium, dark-red

Oxide of Nickel,

reddish-brown.

Oxide of Manganese, red to

violet.

--+--------------------------------------+-------------------------------- Violet or Amethyst.

--+--------------------------------------+--------------------------------

Oxide of Nickel

" " Manganese

Oxide of Didymium.

" " Didymium

--+--------------------------------------+-------------------------------- Blue.

--+--------------------------------------+--------------------------------

Oxide of Cobalt

Oxide of Cobalt.

" Copper, blue to

greenish-blue.

--+--------------------------------------+-------------------------------- Green.

--+--------------------------------------+--------------------------------

Oxide of Copper

Oxide of Chromium, with

yellowish tinge.

A. BORAX

2. Reducing flame

--+--------------------------------------+-------------------------------- Color of Bead.

--+-----------------------------------------------------------------------

Substances which produce this color +--------------------------------------+--------------------------------

in the hot bead.

in the cold bead.

--+--------------------------------------+-------------------------------- Colorless --+--------------------------------------+--------------------------------

Silica

Alumina

Oxide of Tin

Oxide of Tin _

Baryta

Strontia

Lime

Magnesia

With

Glucina

intermittent

Yttria

Yttria }flame

Zirconia

opaque-white.

Thoria

Thoria only when

saturated

Oxide of Lanthanum

" " Cerium

" " Cerium /

Tantalic Acid

Tantalic Acid _/

Oxide of Didymium

" " Manganese

Niobic Acid In small

Pelopic " } proportions.

Oxide of Silver

Oxide of Silver After

" " Zinc After long

" " Zinc long

" " Cadmium

continued

" " Cadmium

continued

" " Lead } blowing.

" " Bis.m.u.th

Otherwise

" " Bis.m.u.th

Otherwise

" " Antimony

grey.

" " Antimony

grey.

" " Nickel /

Telluric Acid _/

Telluric Acid _/ --+--------------------------------------+-------------------------------- Yellow to brown.

--+--------------------------------------+--------------------------------

t.i.tanic Acid

t.i.tanic Acid.

Tungstic "

Molybdic "

Vanadic "

--+--------------------------------------+-------------------------------- Blue.

--+--------------------------------------+--------------------------------

Oxide of Cobalt.

t.i.tanic Acid with intermittent

flame opaque-blue.

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