The chlorides of these substances exhibit these flame reactions best, and hence before applying the flame tests we dip the wire which serves as a support into hydrochloric acid and then into the substance. When the substance has been taken up on the wire, it is placed in the edge of the long colorless flame of the Bunsen burner near the apex, when instantly the flame becomes tinged with the characteristic color of the substance. _Illustrations._ Sodium compounds color the flame yellow, and a crystal of potassium dichromate appears colorless in the sodium light. This sodium reaction is extremely delicate, it being possible to detect with ease a quantity of a sodium salt less than 1/3000000 of a milligram in weight. Potassium colors the flame purplish-violet. Barium colors the flame apple-green. Strontium colors the flame crimson. Calcium colors the flame orange-red, distinguished from strontium, by appearing gray when seen through blue glass. Boracic acid colors the flame green when the substance has been moistened with glycerine. ~Examination in Borax Bead.~--Borax, Na_{2}B_{4}O_{7}, and microcosmic salt, NaNH_{4}H . PO_{4}, possess the property of dissolving many of the metallic oxides at the temperature of the Bunsen flame. For example, with oxide of cobalt, the following reactions take place with the two fluxes:-- CoO + Na_{2}B_{4}O_{7} = Co(BO_{2})_{2} + 2 NaBO_{2}. On heating, NaNH_{4}H. PO_{4}, it is decomposed into the metaphosphate of sodium, NaPO_{3}, CoO + NaPO_{3} = CoNaPO_{4}. 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.