SELENIUM is not difficult of fusion, and gives off brown fumes in either the oxidation or reduction flame.  The deposit upon the charcoal is of a steel-grey color, with a slightly metallic lustre.  The deposit however that fuses outside of this steel-grey one is of a dull violet color, shading off to a light brown.  Under the flame of oxidation this deposit is easily driven from one portion of the charcoal to another, while the application of the reducing flame volatilizes it with the evolution of a beautiful blue light.  The characteristic odor of decayed horse-radish distinguishes the volatilization of this metal.

TELLURIUM.—­This metal fuses with the greatest readiness, and is reduced to vapor under both flames with fumes, and coats the charcoal with a deposit of tellurous acid.  This deposit is white near the centre, and is of a dark yellow near the edges.  It may be driven from place to place by the flame of oxidation, while that of reduction volatilizes it with a green flame.  If there be a mixture of selenium present, then the color of the flame is bluish-green.

ARSENIC.—­This metal is volatilized without fusing, and covers the charcoal both in the oxidizing and reducing flames with a deposit of arsenious acid.  This coating is white in the centre, and grey towards the edges, and is found some distance from the assay.  By the most gentle application of the flame, it is immediately volatilized, and if touched for a moment with the reducing flame, it disappears, tinging the flame pale blue.  During volatilization a strong garlic odor is distinctly perceptible, very characteristic of arsenic, and by which its presence in any compound may be immediately recognized.

ANTIMONY.—­This metal fuses readily, and coats the charcoal under both flames with antimonious acid.  This incrustation is of a white color where thick, but of a bluish tint where it is thin, and is found nearer to the assay than that of arsenic.  When greatly heated by the flame of oxidation, it is driven from place to place without coloring the flame, but when volatilized by the flame of reduction, it tinges the flame blue.  As antimonious acid is not so volatile as arsenious acid, they may thus be easily distinguished from one another.

When metallic antimony is fused upon charcoal, and the metallic bead raised to a red heat, if the blast be suspended, the fluid bead remains for some time at this temperature, giving off opaque white fumes, which are at first deposited on the surrounding charcoal, and then upon the bead itself, covering it with white, pearly crystals.  The phenomenon is dependent upon the fact, that the heated button of antimony, in absorbing oxygen from the air, developes sufficient heat to maintain the metal in a fluid state, until it becomes entirely covered with crystals of antimonious acid so formed.