while the violet-colored
vapor of the iodine can be easily discerned. The nitrate of silver is
the best test for iodine, the yellow color of the iodide of silver
being not easily mistaken, while its almost insolubility in ammonia
will confirm its identity. The chloride of silver, on the contrary,
dissolves in ammonia with the greatest facility.

The reactions of iodine are similar to those of bromine with
concentrated sulphuric acid and binoxide of manganese, and with nitric
acid: The iodine is released and, if the quantity be not too great,
colors the liquid brown. If there be a considerable quantity of iodine
present, it is precipitated as a dark colored powder. Either of these,
when heated, gives out the violet-color of the iodine.

With starch paste free iodine combines, producing a deep blue
compound. If, however, the iodine be in very minute quantity, the
color, instead of being blue, will be light violet or rose color.

If to a solution of the sulphate of copper, to which a small portion
of sulphurous acid has been added, a liquid containing iodine and
bromine is poured in, a dirty, white precipitate of the subiodide of
copper is produced, and the bromine remains in the solution. The
latter may then be tested for the bromine by strong sulphuric acid.

(11.) _Fluorine_ (Fl).--This element exists combined with sodium,
calcium, lithium, aluminium, magnesium, yttrium, and cerium. Fluorine
also exists in the enamel of the teeth, and in the bones of some
animals. This element has a strong affinity for hydrogen, and,
therefore, we find it frequently in the form of hydrofluoric acid.
Brazil-wood paper is the most delicate test for hydrofluoric acid,
which it tinges of a light yellow color. Phosphoric acid likewise
colors Brazil paper yellow, but as this acid is not volatile at a heat
sufficient to examine hydrofluoric acid, there can be no mistake. If
the substance is supposed to contain this acid, it should be placed on
a slip of glass, and moistened with hydrochloric acid, when the test
paper may be applied, and the characteristic yellow color will
indicate the presence of the fluorine.

As hydrofluoric acid acts upon glass, this property may be used for
its detection. The substance may be put into a glass tube, and
sulphuric acid poured upon it in sufficient quantity to moisten it; a
slight heat applied to the tube will develop the acid, which will act
upon the glass of the tube. If the acid is retained in the