(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.
D. YELLOW.
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.
E. RED.
(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.