206 ANALYTICAL CHEMISTRY. 



removed from the charcoal and washed with water in a small 

 mortar. 



A characteristic incrustation, due to the precipitation of some 

 metallic oxide around the heated spot on the charcoal, is formed 

 by some metals. 



If sulphur as such, or in any form of combination, be present 

 in the substance examined by this test, the fused mass contains 

 a sulphide of the alkali (hepar), which may be recognized by 

 placing it on a piece of bright silver (coin) moistened with a drop 

 of water, when the silver will be stained black in consequence 

 of the formation of silver sulphide. The presence of the alkaline 

 sulphide may also be demonstrated by the addition of a few 

 drops of hydrochloric acid to the fused mass, when hydrosul- 

 phuric acid is evolved and may be recognized by its odor. 



6. Flame tests. Many substances impart a characteristic color 

 to a non-luminous flame. The best mode of performing this 

 test is as follows: A platinum wire is cleaned by washing in 

 hydrochloric acid and water, and heated in the flame until the 

 latter is no longer colored. One end of the wire is fused in a 

 short piece of glass tubing (serving as handle), the other end is 

 bent so as to form a small loop, which is heated, dipped into the 

 substance to be examined, and again held in the lower part of 

 the flame, which then becomes colored. 



Some substances show the color-test after being moistened 

 with hydrochloric or sulphuric acid. 



A second method of showing flame reactions is to mix the 

 substance with alcohol in a small dish; the alcohol, upon being 

 ignited, shows a colored flame, especially in the dark. 



7. Colored borax beads. The compounds of some metals when 

 fused with glass, impart to it characteristic colors. For ana- 

 lytical purposes not the silica-glass, but borax-glass is generally 

 used. This latter is made by dipping the loop of a platinum 

 wire in powdered borax and heating it in the flame (directly, or 

 by means of the blowpipe) until all water has been expelled and 

 a colorless, transparent bead has been formed. To this color- 

 less bead a little of the finely powdered substance is added 

 and strongly heated. The metallic compound is chemically 

 acted upon by the boracic acid, a borate being formed which 



