Ozone is produced naturally in the
atmosphere whenever an electric current, or a
natural electric discharge takes place. This
constitutes atmospheric ozone. Chemical
ozone is produced in our laboratories under
conditions that are known and well–determined.
Sticks of phosphorus, a little less
than half an inch thick, plunged half in. air
and half in water, are the materials at
present employed to obtain artificial ozone. In
this operation, the vapour of the phosphorus
combines with a portion of the atmospheric
oxygen, and so forms hypophosphoric acid,
which is immediately dissolved in the water
in the flask; this chemical combination gives
rise to a disengagement of electricity, which
acts on the rest of the oxygen remaining in
the air, and the production of ozone is the
consequence. The properties acquired by
electrisation appear to belong to oxygen only,
and not to other gases, such as hydrogen or
azote. If such shall prove to be the fact,
these properties may perhaps be derived from
the luminous fluid contained by this gas, and
which may in some sort be combined with it
by electrisation. Oxygen is the only gas
which exhibits luminosity under compression
in a glass tube. Carbonic acid gives some
trace of light, by the oxygen which it
contains; hydrogen, azote, and other gases,
made to undergo compression, give no trace
of light at all.

Monsieur Schoœbein contrived to demonstrate
the presence of ozone in the air, by
means of a delicate reagent, namely paper
impregnated with iodide of potassium and
starch. The prepared paper is cut into
slips five inches long, and an inch and a half
broad, and is kept in a close box, or in a
bottle, in the dark, till it is required to be
used as an ozonoscopic test. More than that,
he has contrived to measure the quantity of
ozone contained in the atmosphere at any
given time, by comparing the coloration of
the prepared paper with coloured patterns
carefully studied, and placed so as to form a,
graduated scale. The ozonometer given in
Monsieur Scoutteten's book consists of a
chromatic scale of eleven degrees of different
shades, hues, or tints of violet. Zero, or 0, is
white or undiscoloured paper, when no ozone
is discoverable in the air. Number one is
lightest shade, number ten is the most intense;
the intermediate degrees are shades which
vary in depth according as they approach or
recede from the intensest tint. To find the
degree in the ozonometric scale attained by the
atmosphere at any time, a, slip of prepared
paper is suspended in a spot sheltered from
the direct rays of the sun, and to which the
open air has free access, but removed as far
as possible from any cesspool, offensive drain,
or other source of gas which destroys ozone.
The slip is thus exposed for twelve hours,
after which it is dipped in water. The
coloration assumed by the wetted paper is
compared with the scale, and the result registered
accordingly. Two observations are made
every four–and–twenty hours, one for the day
and one for the night. The first from six in
the morning till six in the evening; the
second, from six in the evening till six in the
morning. By these imperfect tests it has
been already ascertained that ozone is formed
more abundantly in the upper regions of the
atmosphere than in the lower strata; and
that ozone diminishes in quantity, when the
atmospherical conditions favour the escape
of the electric fluid. The first of these facts
helps us to explain some of the peculiar
effects of mountain air.

But, according to Monsieur S. Clolz, iodised
starched paper, can no longer be trusted, as
has hitherto been believed, as a certain
reagent of ozone; because the said paper, in
the open air, is coloured by the azotic acid
and other vapours existing in the atmosphere;
it is also tinged by the essential oils which
evergreen trees and aromatic plants are
continually exhaling. In order, therefore,
to judge of the sanitary condition of a place, as
affected by the presence of ozone, it is requisite
to be cognisant of the precise and actual
cause of the coloration of the iodised paper,
as well as of the accessory circumstances
which are likely to modify the sanitary state.
This alone is sufficient to prove that the study
of ozone has scarcely advanced beyond its
rudiments, and that great caution is
indispensable before any certain physiological
conclusions can be arrived at.

Of the ozonometric papers prepared on the
Continent, the two best are those of Monsieur
Schoœbein and of Monsieur Jame, chemist
and druggist (pharmacien) of Versailles.
Monsieur Schœnbein's paper, compared with
itself, does not give identical results; it is
almost always full of large veins, like
marblepaper, owing to the interior quality of
the paper itself, and the hygrometric influence of
the air. These veins increase the difficulty
of the observer's ascertaining the place which
the paper, after being tinged by ozone,
occupies in the chromatic scale. Different
observers might make a mistake of several
degrees in the determination of this position;
and, consequently, it is far from easy to
make a comparison of the results obtained by
means of Schoœbein's paper. Monsieur
Jame's paper is free from this objection; it
is more sensitive; compared with itself, it is
uniform in its indications; its tint is very
equal and even. Notwithstanding which,
the determination of the quantity of ozone in
the atmosphere by a scale of hues or tints is
a regrettable source of error. In this
particular, ozonometry is still in its infancy,
and can never arrive at its adult state until its
data are obtainable independently of the
observer's visual delicacy. The very same
person who has fixed the position of a shade
in the scale of colour during a moment of
fatigue, will raise or depress it a degree or
two if he looks at it again after a few hours.