of silica.  If the substances treated with this salt consist of sulphides or arsenides, the bead must be heated on charcoal.  But if the substance experimented upon consists of earthly ingredients or metallic oxides, the platinum wire is the best.  If the latter is used a few additional turns should be given to the wire in consequence of the greater fluidity of the bead over that of borax.  The microcosmic salt bead possesses the advantage over that of borax, that the colors of many substances are better discerned in it, and that it separates the acids, the more volatile ones being dissipated, while the fixed ones combine with a portion of the base equally with the phosphoric acid, or else do not combine at all, but float about in the bead, as is the case particularly with silicic acid.  Many of the silicates give with borax a clear bead, while they form with microcosmic salt an opalescent one.

It frequently happens, that if a metallic oxide will not give its peculiar color in one of the flames, that it will in the other, as the difference in degree with which the metal is oxidized often determines the color.  If the bead is heated in the reducing flame, it is well that it should be cooled rapidly to prevent a reoxidation.  Reduction is much facilitated by the employment of metallic tin, whereby the protoxide or the reduced metal may be obtained in a comparatively brief time.

The following tables, taken from Plattner and Sherer, will present the reactions of the metallic oxides, and some of the metallic acids, in such a clear light, that the student cannot very easily be led astray, if he gives the least attention to them.  It frequently happens that a tabular statement of reactions will impress facts upon the memory when long detailed descriptions will fail to do so.  It is for this purpose that we subjoin the following excellent tables.

* * * * *

TABLE I.

  A. BORAX.
    1.  Oxydizing flame.
    2.  Reducing "

  B. MICROCOSMIC SALT.
    1.  Oxydizing flame.
    2.  Reducing "

A. BORAX

1.  Oxydizing flame

-------------------------------------------------------

-------------------
Color of Bead.
--+---------------------------------------------------------

--------------
|               Substances which produce this color
+--------------------------------------+--------------------

------------
|    in the hot bead.                  |      in the cold bead.
--+--------------------------------------+------------------

--------------
Colorless
-----------------------------------------+------------------

--------------
| Silica            \                  | Silica
| Alumina            \                 | Alumina        _
| Oxide of Tin       |                 | Oxide of Tin    \
| Telluric Acid      |                 | Telluric Acid    \
| Baryta             |                 | Baryta            \