When it is desired to determine the action of fluorine upon a solid
substance, the following method of procedure is adopted. A preliminary
experiment is first made, in order to obtain some idea as to the
degree of energy of the reaction, by bringing a little of the solid,
placed upon the lid of a platinum crucible held in a pair of tongs,
near the mouth of the delivery tube of the preparation apparatus. If a
gaseous or liquid product results, and it is desirable to collect it
for examination, small fragments of the solid are placed in a platinum
tube connected to the delivery tube by flexible platinum tubing or by
a screw joint, and the resulting gas may be collected over water or
mercury, or the liquid condensed in a cooled cylinder of platinum. In
this manner the action of fluorine upon sulphur and iodine has been
studied. If the solid, phosphorus for instance, attacks platinum, or
the temperature of the reaction is sufficiently high to determine the
combination of platinum and fluorine (toward 500°), a tube of
fluorspar is substituted for the platinum tube. The fluorspar tubes
employed by M. Moissan for the study of the action of phosphorus were
about twelve to fourteen centimeters long, and were terminated by
platinum ends furnished with flanges and screw threads in order to be
able to connect them with the preparation apparatus. If it is required
to heat the fluorspar tubes, they are surrounded by a closely wound
copper spiral, which may be heated by a Bunsen flame.
In experimenting upon liquids, great care is necessary, as the
reaction frequently occurs with explosive violence. A preliminary
experiment is therefore always made, by allowing the fluorine delivery
tube to dip just beneath the surface of the liquid contained in a
small glass cylinder. When the liquid contains water, or when
hydrofluoric acid is a product of the reaction, cylinders of platinum
or of fluorspar are employed. If it is required to collect and examine
the product, the liquid is placed along the bottom of a horizontal
tube of platinum or fluorspar, as in case of solids, connected
directly with the preparation apparatus, and the product is collected
over water or mercury if a gas, or in a cooled platinum receiver if a
liquid.
During the examination of liquids a means has accidentally been
discovered by which a glass tube may be filled with fluorine gas. A
few liquids, one of which is carbon tetrachloride, react only very
slowly with fluorine at the ordinary temperature. By filling a glass
tube with such a liquid, and inverting it over a platinum capsule also
containing the liquid, it is possible to displace the liquid by
fluorine, which, as the walls are wet, does not attack the glass. Or
the glass tube may be filled with the liquid, and then the latter
poured out, leaving the walls wet; the tube may then be filled with
fluorine gas, which being slightly heavier than air, remains in the
tube for some time. In one experiment, in which a glass test tube had
been filled with fluorine over carbon tetrachloride, it was attempted
to transfer it to a graduated tube over mercury, but in inclining the
test tube for this purpose the mercury suddenly came in contact with
the fluorine, and absorbed it so instantaneously and with such a
violent detonation that both the test tube and the graduated tube were
shattered into fragments. Indeed, owing to the powerful affinity of
mercury for fluorine, it is a most dangerous experiment to transfer a
tube containing fluorine gas, filled according to either the first or
second method, to the mercury trough; the tube is always shattered if
the mercury comes in contact with the gas, and generally with a loud
detonation. Fluorine may, however, be preserved for some time in tubes
over mercury, provided a few drops of the non-reacting liquid are kept
above the mercury meniscus.
For studying the action of fluorine on gases, a special piece of
apparatus, shown in Fig. 3, has been constructed. It is composed of a
tube of platinum, fifteen centimeters long, closed by two plates of
clear, transparent, and colorless fluorspar, and carrying three
lateral narrower tubes also of platinum. Two of these tubes face each
other in the center of the apparatus, and serve one for the conveyance
of the fluorine and the other of the gas to be experimented upon. The
third, which is of somewhat greater diameter than the other two,
serves as exit tube for the product or products of the reaction, and
may be placed in connection with a trough containing either water or
mercury.
The apparatus is first filled with the gas to be experimented upon,
then the fluorine is allowed to enter, and an observation of what
occurs may be made through the fluorspar windows. One most important
precaution to take in collecting the gaseous products over mercury is
not to permit the platinum delivery tube to dip more than two or at
most three millimeters under the mercury, as otherwise the levels of
the liquid in the two limbs of the electrolysis U-tube become so
different, owing to the pressure, that the fluorine from one side
mixes with the hydrogen evolved upon the other, and there is a violent
explosion.
[Illustration: FIG. 3.]