into a bead, after which the
silica must be added, and then the bead submitted to the flame of
oxidation.

The silicates dissolve in soda but partially, and then with
effervescence. If the oxygen of the acid be twice that of the base, a
clear bead will be obtained that will retain its transparency when
cold. If the soda be added in small quantity, the bead will then be
opaque. In the first instance, a part of the base which separates is
re-dissolved, and, therefore, the transparency of the glass; but, if
too large a quantity of the soda is added, the separation of the base
is sufficient to render the assay infusible.

(8.) _Chlorine_ (Cl).--Chlorine exists in nature always in
combination, as the chlorides of sodium, potassium, calcium, ammonium,
magnesia, silver, mercury, lead, copper, etc.

The chlorine existing in metallic chlorides may be detected as
follows: the wet way may be accomplished in the following manner. If
the substance is insoluble, it must be melted with soda to render it
soluble; if it be already soluble it must be dissolved in pure water,
and nitrate of silver added, when the one ten-thousandth part of
chlorine will manifest its presence by imparting a milky hue to the
fluid.

By the blowpipe, chlorine may be detected in the following manner:
Oxide of copper is dissolved in microcosmic salt on the platinum wire
in the flame of oxidation, and a clear bead is obtained. The substance
containing the chlorine is now added, and heat is applied. The assay
will soon be enveloped by a blue or purplish flame. As none of the
acids that occur in the mineral kingdom give this reaction, chlorine
cannot be confounded with them, for those which impart a color to the
flame, when mixed with a copper salt, will not do so when tested in
the microcosmic salt bead as above indicated.

If the assay is soluble in water, the following method may be
followed: a small quantity of sulphate of copper or iron is dissolved;
a few drops of the solution is placed upon a bright surface of silver,
and the metallic chloride added; when, if chlorine is present, the
silver is blackened. If the chloride is insoluble in water, it must be
rendered soluble by fusion upon a platinum wire with soda, and then
treated as above.[2]

[2] Plattner.

(9.) _Bromine_ (Br).--The bromide of magnesium and sodium exists in
many salt springs, and it is from these that the bromine of commerce
is obtained. The metallic bromides give the same