(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.
C. THE GREEN COLOR.
(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.