CoO + Na2B4O7 = Co(BO2)2 + 2 NaBO2.
On heating, NaNH4H. PO4, it is decomposed into the metaphosphate of sodium, NaPO3,
CoO + NaPO3 = CoNaPO4.
Now in such cases of solution the metallic oxides impart a characteristic color to the flux.
The platinum wire is the best support,—it is heated to incandescence in the Bunsen flame, and then is quickly dipped into the borax, when a small globule will adhere,—this is removed to the flame again when the borax melts to a clear glassy bead. While the bead is still melted, touch it to the finely pulverized substance and replace in the flame. In a few seconds the small particles of the substance will have dissolved, and the bead will be seen to have assumed the color characteristic of the substance. Note the color when hot and then when cold; often there is a wide difference. Then, too, the test should be made in both O. F. and R. F.
Some analysts prefer to make a small loop in the end of the wire before taking up the borax to make the bead. Care should be taken to see that the bead is colorless before bringing it in contact with the substance.
As the depth of color produced is largely dependent upon the amount of substance taken, some little caution should be exercised to insure taking up about the same quantity each time.
Illustrations. Make several beads, and note the colors characteristic of the following oxides: cobalt, nickel, iron, manganese, chromium, and copper.
The microcosmic salt bead dissolves almost every oxide except silica, SiO2, and this is seen to float about in the melted mass. This is used as a test for silica.
Examination with Co(NO3)2.—If after examination on the Ch. per se, a white infusible residue remains, it is moistened with a drop of cobalt nitrate Co(NO3)2 and re-ignited before the Bp., when a change of color will be observed. This change in color is owing to the fact that the heat of the Bp. flame decomposes the cobalt nitrate, nitric acid being driven off, and the remaining CoO forming with the oxide of the residue a colored mass.