| A. VIOLET. | ||
|---|---|---|
| Potash, and all its compounds, with the exception of the phosphate and the borate, tinge the color of the flame violet. | ||
| B. BLUE. | ||
| Chloride of copper, | Intense blue. | |
| Lead, | Pale clear blue. | |
| Bromide of copper, | Bluish green. | |
| Antimony, | Bluish green. | |
| Selenium, | Blue. | |
| Arsenic, | English green. | |
| C. GREEN. | ||
| Ammonia, | Dark green. | |
| Boracic acid, | Dark green. | |
| Copper, | Dark green. | |
| Tellurium, | Dark green. | |
| Zinc, | Light green. | |
| Baryta | Apple green. | |
| Phosphoric acid, | Pale green. | |
| Molybdic acid, | Apple green. | |
| Telluric acid, | Light green. | |
| D. YELLOW. | ||
| Soda, | Intense yellow. | |
| Water, | Feeble yellow. | |
| E. RED. | ||
| Strontia, | Intense crimson. | |
| Lithia, | Purplish red. | |
| Potash, | Violet red. | |
| Lime, | Purplish red. | |
The student may often be deceived in regard to the colors: for instance, if a small splinter of almost any mineral be held at the point of the flame of oxidation, it will impart a very slight yellow to the flame. This is caused, doubtless, by the water contained in the mineral. If the piece of platinum wire is used, and it should be wet with the saliva, as is frequently done by the student, then the small quantity of soda existing in that fluid will color the flame of a light yellow hue.
The salts of potash, with the exception of the borate and the phosphate, color the flame of a rich violet hue. This color is best discovered in the outer flame of the blowpipe, as is the case with all the other colors. The flame should be a small one, with a lamp having a small wick, while the orifice of the blowpipe must be quite small. These experiments should likewise be made in a dark room, so that the colors may be discerned with the greatest ease. In investigating with potash for the discernment of color, it should be borne in mind that the least quantity of soda will entirely destroy the violet color of the potash, by the substitution of its own strong yellow color. If there be not more than the two hundredth part of soda, the violet reaction of the potash will be destroyed. This is likewise the case with the presence of lithia, for its peculiar red color will destroy the violet of the potash. Therefore in making investigations with the silicates which contain potash, the violet color of the latter can only be discerned when they are free from soda and lithia.
(a.) The Chloride of Copper.—Any of the chlorides produce a blue color in the blowpipe flame, or any salt which contains chlorine will show the blue tint, as the color in this case is referable to the chlorine itself. There are, however, some chlorides which, in consequence of the peculiar reactions of their bases, will not produce the blue color, although in these cases the blue of the chlorine will be very likely to blend itself with the color produced by the base. The chloride of copper communicates an intense blue to the flame, when fused on the platinum wire. If the heat be continued until the chlorine is driven off, then the greenish hue of the oxide of copper will be discerned.
(b.) Lead.—Metallic lead communicates to the flame a pale blue color. The oxide reacts in the same manner. The lead-salts, whose acids do not interfere with the color, impart also a fine blue to the flame, either in the platina forceps, or the crooked wire.
(c.) Bromide of Copper.—This salt colors the flame of a bluish-green color, but when the bromine is driven off, then we have the green of the oxide of copper.
(d.) Antimony.—This metal imparts a blue color to the blowpipe flame, but if the metal is in too small a quantity, then the color is a brilliant white. If antimony is fused on charcoal, the fused metal gives a blue color. The white sublimate which surrounds the fused metal, being subjected to the flame of oxidation, disappears from the charcoal with a bluish-green color.
(e.) Selenium.—If fused in the flame of oxidation, it imparts to the flame a deep blue color. The incrustation upon charcoal gives to the flame the same rich color.
(f.) Arsenic.—The arseniates and metallic arsenic itself impart to the blowpipe flame a fine blue color, provided that there is no other body present which may have a tendency to color the flame with its characteristic hue. The sublimate of arsenious acid which surrounds the assay, will give the same blue flame, when dissipated by the oxidation flame. The platinum forceps will answer for the exhibition of the color of arsenic, even though the salts be arseniates, whose bases possess the property of imparting their peculiar color to the flame, such as the arseniate of lime.
(a.) Ammonia.—The salts of ammonia, when heated before the blowpipe, and just upon the point of disappearing, impart to the flame a feeble though dark green color. This color, however, can only be discerned in a dark room.
(b.) Boracic Acid.—If any one of the borates is mixed with two parts of a flux composed of one part of pulverized fluorspar, and four and a half parts of bisulphate of potash, and after being melted, is put upon the coil of a platinum wire, and held at the point of the blue flame, soon after fusion takes place a dark green color is discerned, but it is not of long duration. The above process is that recommended by Dr. Turner. The green color of the borates may be readily seen by dipping them, previously moistened with sulphuric acid, into the upper part of the blue flame, when the color can be readily discerned. If soda be present, then the rich green of the boracic acid is marred by the yellow of the soda. Borax, or the biborate of soda (NaO, 2BO3) may be used for this latter reaction, but if it be moistened with sulphuric acid, the green of the boracic acid can then be seen. If the borates, or minerals which contain boracic acid, are fused on charcoal with carbonate of potash, then moistened with sulphuric acid and alcohol, then the bright green of the boracic acid is produced, even if the mineral contains but a minute portion of the boracic acid.
(c.) Copper. Nearly all the ores of copper and its salts, give a bright green color to the blowpipe flame. Metallic copper likewise colors the flame green, being first oxidized. If iodine, chlorine, and bromine are present, the flame is considerably modified, but the former at least intensifies the color. Many ores containing copper also color the flame green, but the internal portion is of a bright blue color if the compound contains lead, the latter color being due to the lead. The native sulphide and carbonate of copper should be moistened with sulphuric acid, while the former should be previously roasted. If hydrochloric acid is used for moistening the salts, then the rich green given by that moistened with the sulphuric acid is changed to a blue, being thus modified by the chlorine of the acid. Silicates containing copper, if heated in the flame in the platinum forceps, impart a rich green color to the outer flame. In fact, if any substance containing copper be submitted to the blowpipe flame, it will tinge it green, provided there be no other substance present to impart its own color to the flame, and thus modify or mar that of the copper.
(d.) Tellurium.—If the flame of reduction is directed upon the oxide of tellurium placed upon charcoal, a green color is imparted to it. If the telluric acid be placed upon platinum wire in the reduction flame, the oxidation flame is colored green. Or if the sublimate be dissipated by the flame of oxidation, it gives a green color. If selenium be present, the green color is changed to a blue.
(e.) Zinc.—The oxide of zinc, when strongly heated, gives a blue flame. This is especially the case in the reducing flame. The flame is a small one, however, and not very characteristic, as with certain preparations of zinc the blue color is changed to a bright white. The soluble salts of zinc give no blue color.
(f.) Baryta.—The soluble salts of baryta, moistened, and then submitted to the reduction flame, produce a green color. The salt should be moistened, when the color will be strongly marked in the outer flame. The insoluble salts do not produce so vivid a color as the soluble salts, and they are brighter when they have previously been moistened. The carbonate does not give a strong color, but the acetate does, so long as it is not allowed to turn to a carbonate. The chloride, when fused on the platinum wire, in the point of the reduction flame, imparts a fine green color to the oxidation flame. This tint changes finally to a faint dirty green color. The sulphate of baryta colors the flame green when heated at the point of the reduction flame. But neither the sulphate, carbonate, nor, in fact, any other salt of baryta, gives such a fine green color as the chloride. The presence of lime does interfere with the reaction of baryta, but still does not destroy its color.
(g.) Phosphoric Acid.—The phosphates give a green color to the oxidation flame, especially when they are moistened with sulphuric acid. This is best shown with the platinum forceps. The green of phosphoric, or the phosphates, is much less intense than that of the borates or boracic acid, but yet the reaction is a certain one, and is susceptible of considerable delicacy, either with the forceps, or still better upon platinum wire. Sulphuric acid is a great aid to the development of the color, especially if other salts be present which would be liable to hide the color of the phosphoric acid. In this reaction with phosphates, the water should be expelled from them previous to melting them with sulphuric acid. They should likewise be pulverized. Should soda be present it will only exhibit its peculiar color after the phosphoric acid shall have been expelled; therefore, the green color of the phosphoric acid should be looked for immediately upon submitting the phosphate to heat.
(h.) Molybdic Acid.—If this acid or the oxide of molybdenum be exposed upon a platinum wire to the point of the reduction flame, a bright green color is communicated to the flame of oxidation. Take a small piece of the native sulphide of molybdenum, and expose it in the platinum tongs to the flame referred to above, when the green color characteristic of this metal will be exhibited.
(i.) Telluric Acid.—If the flame of reduction is directed upon a small piece of the oxide of tellurium placed upon charcoal, a bright green color is produced. Or if telluric acid be submitted to the reduction flame upon the loop of a platinum wire, it communicates to the outer flame the bright green of tellurium. If the sublimate found upon the charcoal in the first experiment be submitted to the blowpipe flame, the green color of tellurium is produced while the sublimate is volatilized. If selenium be present the green color is changed to a deep blue one.
The salts of soda all give a bright yellow color when heated in the platinum loop in the reduction flame. This color is very persistent, and will destroy the color of almost any other substance. Every mineral of which soda is a constituent, give this bright orange-yellow reaction. Even the silicate of soda itself imparts to the flame of oxidation the characteristic yellow of soda.
(a.) Strontia.—Moisten a small piece of the chloride of strontium, put it in the platinum forceps and submit it to the flame of reduction, when the outer flame will become colored of an intense red. If the salt of strontia should be a soluble one, the reaction is of a deeper color than if an insoluble salt is used, while the color is of a deeper crimson if the salt is moistened. If the salt be a soluble one, it should be moistened and dipped into the flame, while if it be an insoluble salt, it should be kept dry and exposed beyond the point of the flame. The carbonate of strontia should be moistened with hydrochloric acid instead of water, by which its color similates that of the chloride of strontium when moistened with water. In consequence of the decided red color which strontia communicates to flame, it is used by pyrotechnists for the purpose of making their "crimson fire."
(b.) Lithia.—The color of the flame of lithia is slightly inclined to purple. The chloride, when placed in the platinum loop, gives to the outer flame a bright red color, sometimes with a slight tinge of purple. Potash does not prevent this reaction, although it may modify it to violet; but the decided color of soda changes the red of lithia to an orange color. If much soda be present, the color of the lithia is lost entirely. The color of the chloride of lithium may be distinctly produced before the point of the blue flame, and its durability may be the means of determining it from that of lithium, as the latter, under the same conditions, is quite evanescent. The minerals which contain lithia, frequently contain soda, and thus the latter destroys the color of the former.
(c.) Potash.—The salts of potash, if the acid does not interfere, give a purplish-red color before the blowpipe; but as the color is more discernibly a purple, we have classed it under that color.
(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.
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 principal 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 quantity 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 titanic 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 quantity present, that is: over the quantity 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 passing 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 arsenides and sulphides, before being examined, should be roasted, and then heated with the borax bead. The arsenic of the former, it should be observed, will act on the glass tube in which the sublimation is proceeding, if the glass 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,
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 passes 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 arsenides, 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.
A. BORAX.
1. Oxydizing flame.
2. Reducing flame.
B. MICROCOSMIC SALT.
1. Oxydizing flame.
2. Reducing flame.
| Color of Bead. | ||||
|---|---|---|---|---|
| Substances which produce this color | ||||
| in the hot bead. | in the cold bead. | |||
| Colorless. | ||||
| Silica | In all proportions. | Silica | ||
| Alumina | Alumina | |||
| Oxide of Tin | Oxide of Tin | With intermittent flame opaque white. | ||
| Telluric Acid | Telluric Acid | |||
| Baryta | Baryta | |||
| Strontia | Strontia | |||
| Lime | Lime | |||
| Magnesia | Magnesia | |||
| Glucina | Glucina | |||
| Yttria | Yttria | |||
| Zirconia | Zirconia | |||
| Thoria | Thoria | |||
| Oxide of Lanthanum | Oxide of Lanthanum | |||
| Oxide of Silver | ||||
| Tantalic Acid | Tantalic Acid | |||
| Niobic Acid | Niobic Acid | |||
| Pelopic Acid | Pelopic Acid | |||
| Titanic Acid | Titanic Acid | |||
| Tungstic Acid | In small quantity only. In large quantity yellow. | Tungstic Acid | ||
| Molybdic Acid | Molybdic Acid | |||
| Oxide of Zinc | Oxide of Zinc | |||
| Oxide of Cadmium | Oxide of Cadmium | |||
| Oxide of Lead | Oxide of Lead | |||
| Oxide of Bismuth | Oxide of Bismuth | |||
| Oxide of Antimony | Oxide of Antimony | |||
| Yellow, orange-red and reddish-brown. | ||||
| Titanic Acid, yellow | When in large quantity. Otherwise colorless. | |||
| Tungstic Acid, yellow | ||||
| Molybdic Acid, dark yellow | ||||
| Oxide of Zinc, pale-yellow | ||||
| Oxide of Cadmium, pale-yellow | ||||
| Oxide of Lead, yellow | ||||
| Oxide of Bismuth, orange | ||||
| Oxide of Antimony, yellow | ||||
| Oxide of Cerium, red | Oxide of Cerium | with interm. flame opaque white. | ||
| Oxide of Iron, dark red | Oxide of Iron, | yellow. | ||
| Oxide of Uranium, red | Oxide of Uranium | with interm. flame opaque yellow. | ||
| Oxide of Silver | 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 | ||||
| Oxide of Manganese | ||||
| Oxide of Didymium | Oxide of Didymium. | |||
| Blue. | ||||
| Oxide of Cobalt | Oxide of Cobalt. | |||
| Oxide of Copper, | blue to greenish-blue. | |||
| Green. | ||||
| Oxide of Copper | Oxide of Chromium, | with yellowish tinge. | ||
| Color of Bead. | ||||
|---|---|---|---|---|
| Substances which produce this color | ||||
| in the hot bead. | in the cold bead. | |||
| Colorless | ||||
| Silica | Silica | |||
| Alumina | Alumina | |||
| Oxide of Tin | Oxide of Tin | |||
| Baryta | Baryta | |||
| Strontia | Strontia | |||
| Lime | Lime | |||
| Magnesia | Magnesia | With intermittent flame opaque-white. | ||
| Glucina | Glucina | |||
| Yttria | Yttria | |||
| Zirconia | Zirconia | |||
| Thoria | Thoria only when saturated | |||
| Oxide of Lanthanum | Oxide of Lanthanum | |||
| Oxide of Cerium | Oxide of Cerium | |||
| Tantalic Acid | Tantalic Acid | |||
| Oxide of Didymium | Oxide of Didymium | |||
| Oxide of Manganese | Oxide of Manganese | |||
| Niobic Acid | In small proportions. | Niobic Acid | In small proportions. | |
| Pelopic Acid | Pelopic Acid | |||
| Oxide of Silver | After long continued blowing. Otherwise grey. | Oxide of Silver | After long continued blowing. Otherwise grey. | |
| Oxide of Zinc | Oxide of Zinc | |||
| Oxide of Cadmium | Oxide of Cadmium xx | |||
| Oxide of Lead | Oxide of Lead | |||
| Oxide of Bismuth | Oxide of Bismuth | |||
| Oxide of Antimony | Oxide of Antimony | |||
| Oxide of Nickel | Oxide of Nickel | |||
| Telluric Acid | Telluric Acid | |||
| Yellow to brown. | ||||
| Titanic Acid | Titanic Acid. | |||
| Tungstic Acid | Tungstic Acid | |||
| Molybdic Acid | Molybdic Acid | |||
| Vanadic Acid | ||||
| Blue. | ||||
| Oxide of Cobalt. | Oxide of Cobalt. | |||
| Titanic Acid | with intermittent flame opaque-blue. | |||
| Green. | ||||
| Oxide of Iron | Oxide of Iron, | bottle-green. | ||
| Oxide of Uranium | Oxide of Uranium, | bottle-green. | ||
| Oxide of Chromium | Oxide of Chromium, | emerald-green. | ||
| Vanadic Acid, emerald-green. | ||||
| Opaque-grey. (The opacity generally becomes distinct during cooling.) | ||||
| Oxide of Silver | After short blowing. Otherwise colorless. | Oxide of Silver. | ||
| Oxide of Zinc | Oxide of Zinc | After short blowing. Otherwise colorless. | ||
| Oxide of Cadmium | Oxide of Cadmium | |||
| Oxide of Lead | Oxide of Lead | |||
| Oxide of Bismuth | Oxide of Bismuth | |||
| Oxide of Antimony | Oxide of Antimony | |||
| Oxide of Nickel | Oxide of Nickel | |||
| Telluric Acid | Telluric Acid | |||
| Niobic Acid | After long continued blowing and in considerable proportion. | Niobic Acid | After long continued blowing and in considerable proportion. | |
| Pelopic Acid | Pelopic Acid | |||
| Opaque red and reddish-brown. | ||||
| Oxide of Copper | Oxide of Copper. | |||
| Color of Bead. | ||||
|---|---|---|---|---|
| Substances which produce this color | ||||
| in the hot bead. | in the cold bead. | |||
| Colorless | ||||
| Silica (only slightly soluble) | In all proportions. | Silica | ||
| Alumina | Alumina | |||
| Oxide of Tin | Oxide of Tin | |||
| Telluric Acid | Telluric Acid | With intermittent flame opaque white. | ||
| Baryta | Baryta | |||
| Strontia | Strontia | |||
| Lime | Lime | |||
| Magnesia | Magnesia | |||
| Glucina | Glucina | |||
| Yttria | Yttria | |||
| Zirconia | Zirconia | |||
| Thoria | Thoria | |||
| Oxide of Lanthanum | Oxide of Lanthanum | |||
| Oxide of Cerium | ||||
| Niobic Acid | Niobic Acid | |||
| Pelopic Acid | Pelopic Acid | |||
| Tantalic Acid | Tantalic Acid | |||
| Titanic Acid | Titanic Acid | |||
| Tungstic Acid | Tungstic Acid | |||
| Oxide of Zinc | In small quantity only. In large quantity yellow. | Oxide of Zinc | ||
| Oxide of Cadmium | Oxide of Cadmium | |||
| Oxide of Lead | Oxide of Lead | |||
| Oxide of Bismuth | Oxide of Bismuth | |||
| Oxide of Antimony | Oxide of Antimony | |||
| Yellow, orange, red and brown. | ||||
| Tantalic Acid | ||||
| Titanic Acid | In large quantity. | |||
| Tunstic Acid | ||||
| Oxide of Zinc | ||||
| Oxide of Cadmium | ||||
| Oxide of Lead | ||||
| Oxide of Bismuth | ||||
| Oxide of Antimony | ||||
| Oxide of Silver | Oxide of Silver. | |||
| Oxide of Cerium | ||||
| Oxide of Iron | Oxide of Iron. | |||
| Oxide of Nickel | Oxide of Nickel. | |||
| Oxide of Uranium | Oxide of Uranium, | yellowish-green. | ||
| Vanadic Acid | Vanadic Acid. | |||
| Oxide of Chromium | ||||
| Violet or Amethyst. | ||||
| Oxide of Manganese | Oxide of Manganese. | |||
| Oxide of Didymium | Oxide of Didymium. | |||
| Blue. | ||||
| Oxide of Cobalt | Oxide of Cobalt | |||
| Oxide of Copper, | to greenish-blue. | |||
| Green. | ||||
| Molybdic Acid, | yellowish-green | Molybdic Acid, | yellowish-green. | |
| Oxide of Copper | Oxide of Uranium, | yellowish-green. | ||
| Oxide of Chromium, | emerald-green. | |||
| Color of Bead. | ||||
|---|---|---|---|---|
| Substances which produce this color | ||||
| in the hot bead. | in the cold bead. | |||
| Colorless | ||||
| Silica (only slightly soluble) | Silica (only slightly soluble). | |||
| Alumina | Alumina. | |||
| Oxide of Tin | Oxide of Tin. | |||
| Baryta | Baryta | With an intermittent flame opaque-white. | ||
| Strontia | Strontia | |||
| Lime | Lime | |||
| Magnesia | Magnesia | |||
| Glucina | Glucina | |||
| Yttria | Yttria | |||
| Zirconia | Zirconia | |||
| Thoria | Thoria only when saturated | |||
| Oxide of Lanthanum | Oxide of Lanthanum | |||
| Oxide of Cerium | Oxide of Cerium. | |||
| Oxide of Didymium | Oxide of Didymium. | |||
| Oxide of Manganese | Oxide of Manganese. | |||
| Tantalic Acid | Tantalic Acid. | |||
| Oxide of Silver | After long continued blowing. Otherwise grey. | Oxide of Silver | ||
| Oxide of Zinc | Oxide of Zinc | After long continued blowing. Otherwise grey. | ||
| Oxide of Cadmium | Oxide of Cadmium | |||
| Oxide of Lead | Oxide of Lead | |||
| Oxide of Bismuth | Oxide of Bismuth | |||
| Oxide of Antimony | Oxide of Antimony | |||
| Oxide of Nickel | Oxide of Nickel | |||
| Telluric Acid | Telluric Acid | |||
| Yellow, red, and brown. | ||||
| Oxide of Iron, | red | Oxide of Iron. | ||
| Titanic Acid, | yellow | |||
| Pelopic Acid, | brown | Pelopic Acid. | ||
| Ferruginous Titanic Acid, | blood red | Ferruginous Titanic Acid. | ||
| Ferruginous Niobic Acid, | blood red | Ferruginous Niobic Acid. | ||
| Ferruginous Pelopic Acid, | blood red | Ferruginous Pelopic Acid. | ||
| Ferruginous Tungstic Acid, | blood red | Ferruginous Tungstic Acid. | ||
| Vanadic Acid | brownish | |||
| Oxide of Chromium, | reddish | |||
| Violet or Amethyst. | ||||
| Niobic Acid | in large proportion | Niobic Acid | in large proportion. | |
| Titanic Acid. | ||||
| Blue. | ||||
| Oxide of Cobalt | Oxide of Cobalt. | |||
| Tungstic Acid | Tungstic Acid. | |||
| Niobic Acid | in very large proportion. | Niobic Acid | in very large proportion. | |
| Green. | ||||
| Oxide of Uranium | Oxide of Uranium. | |||
| Molybdic Acid | Molybdic Acid. | |||
| Vanadic Acid | ||||
| Oxide of Chromium. | ||||
| Opaque-grey. (The opacity generally becomes distinct during cooling.) | ||||
| Oxide of Silver | Oxide of Silver. | |||
| Oxide of Zinc | Oxide of Zinc. | |||
| Oxide of Cadmium | Oxide of Cadmium. | |||
| Oxide of Lead | Oxide of Lead. | |||
| Oxide of Bismuth | Oxide of Bismuth. | |||
| Oxide of Antimony | Oxide of Antimony. | |||
| Oxide of Nickel | Oxide of Nickel. | |||
| Telluric Acid | Telluric Acid. | |||
| Opaque-red and reddish brown. | ||||
| Oxide of Copper | Oxide of Copper. | |||
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. Titanic 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 quantity of soda is used, the bead will be quite likely to become opaque upon cooling, while, if too small a quantity 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 titanic 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, titanic 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 glass with the soda. As titanic 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 quantity 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 noble metals, the oxides and acids of tungsten, molybdenum, arsenic, antimony, mercury, copper, tellurium, zinc, lead, bismuth, tin, cadmium, iron, nickel, and cobalt. Mercury and arsenic, as soon as they are reduced, are dissipated, while tellurium, bismuth, 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 potassa, 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 quantities of manganese. The mixture of the carbonate of soda with a small addition of nitrate of potassa, and the mineral containing manganese, must be fused on platinum foil. The fused mass, 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, æschynite, œrstedtite, titaniferous 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 quantity 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), elæolite, mica from primitive lime-stone, black talc, acmite, krokidolite, lievrite, cronstedtite, 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 quantity 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, arseniate 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: steatite, meerschaum, felspar, albite, petalite, nepheline, anorthite, emerald, euclase, turquois, sodalite (Vesuvius).
2. The following minerals produce beads with a small quantity 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 glass.
The oxide of tellurium and telluric acid gives a clear bead when it is hot, but white after it is cooled.
Titanic acid gives a yellow bead when hot.
The oxide of chromium gives also a clear yellow glass 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 quantity. 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 assay, viz. bismuth, zinc, lead, cadmium, antimony, selenium, tellurium, and arsenic.
Bismuth, 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, bismuth does not, and may thus be distinguished from them.
Zinc deposits an incrustation about the assay, 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 assay, 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 bismuth. It leaves an incrustation around the assay resembling that of bismuth, in the color of it, and in the peculiar manner in which it lies around the assay.
Cadmium deposits a dull reddish incrustation around the assay. 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 assay. 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.