purpose of determining that point.

_Selenium_ will likewise sublime by heat as does sulphur. This is the
case if selenides are present. Selenium gives off the smell of decayed
horse-radish.

When the persalts are heated they are reduced to protosalts, with the
elimination of a part of their acid. This will be indicated by the
blue litmus paper.

If some of the neutral salts containing a volatile acid be present,
they will become decomposed. For instance, the red nitrous acid water
of the nitrates will indicate the decomposition of the salt,
especially if it be the nitrate of a metallic oxide.

If there is an odor of sulphur, then it is quite probable, if no free
sulphur be present, that a hyposulphite is decomposed.

If an oxalate be present, it is decomposed with the evolution of
carbonic oxide, which may be inflamed at the mouth of the tube; but
there are oxalates that give off carbonic acid gas, which, of course,
will not burn. A cyanide will become decomposed and eliminate nitrogen
gas, while the residue is charred. Some cyanides are, however, not
thus decomposed, as the dry cyanides of the earths and alkalies.

There are several oxides of metals which will sublime, and may be thus
examined in the tube. _Arsenious acid_ sublimes with great ease in
minute octohedral crystals. The oxides of tellurium and antimony will
sublime, the latter in minute glittering needles.