OZONE
The great difference between the atmospheric conditions before and
after a thunderstorm must have been noticed by everybody. Before the
storm the air feels lifeless. It does not satisfy us as we draw it
into our lungs, and however deeply we breathe, we feel that something
is lacking. After the storm the air is delightful to inhale, and it
refreshes us with every breath. This remarkable transformation is
brought about to a very large extent by ozone produced by the lightning
discharges.
As far back as 1785 it was noticed that oxygen became changed in
some way when an electric spark was passed through it, and that it
acquired a peculiar odour. No particular attention was paid to the
matter however until about 1840, when Schönbein, a famous German
chemist, and the discoverer of gun-cotton and collodion, became
interested in it. He gave this strange smelling substance the name of
“ozone,” and he published the results of his experiments with it in
a treatise entitled, “On the Generation of Ozone.” Schönbein showed
that ozone could be produced by various methods, chemical as well as
electrical. For instance, if a piece of phosphorus is suspended in
a jar of air containing also a little water, in such a manner that
it is partly in the water and partly out of it, the air acquires
the characteristic smell of ozone, and it is found to have gained
increased chemical energy, so that it is a more powerful oxidizing
agent. For a long time the exact chemical nature of ozone could not be
determined, mainly because it was impossible to obtain the substance
in quantities sufficiently large for extensive experimental research,
but also on account of its extremely energetic properties, which made
it very troublesome to examine. These difficulties were so great that
investigators were in doubt as to whether ozone was an element or a
compound of two or more elements; but finally it was proved that it was
simply oxygen in a condensed or concentrated state.
Apparently ozone is formed by the contraction of oxygen, so that from
three volumes of oxygen two volumes of ozone are produced. In other
words, ozone has one and a half times the density of oxygen. Ozone has
far greater oxidizing power than oxygen itself; in fact it is probably
the most powerful of all oxidizing agents, and herein lies its great
value. It acts as nature’s disinfectant or sterilizer, and plays a very
important part in keeping the air pure, by destroying injurious organic
matter. Bacteria apparently have a most decided objection to dying; at
any rate they take an extraordinary amount of killing. Ozone is more
than a match for them however, and under its influence they have a
short life and probably not a merry one.
Ozone exists naturally in the atmosphere in the open country, and more
especially at the seaside. It is produced by lightning discharges, by
silent electrical discharges in the atmosphere, by the evaporation of
water, particularly salt water, by the action of sunlight, and also by
the action of certain vegetable products upon the air. The quantity
of ozone in the air is always small, and even pure country or sea air
contains only one volume of ozone in about 700,000 volumes of air. No
ozone can be detected in the air of large towns, or over unhealthy
swamps or marshes. The exhilarating effects of country and sea air,
and the depressing effects of town air, are due to a very large extent
to the presence or absence of ozone.
A great proportion of our common ailments are caused directly or
indirectly by a sort of slow poisoning, produced by the impure air in
which we live and work. It is popularly supposed that the tainting of
the air of rooms in which large numbers of people are crowded together
is due to an excessive amount of carbonic acid gas. This is a mistake,
for besides being tasteless and odourless, carbonic acid gas is
practically harmless, except in quantities far greater than ever exist
even in the worst ventilated rooms. The real source of the tainted
air is the great amount of animal matter thrown off as waste products
from the skin and lungs, and this tainting is further intensified
by the absence of motion in the air. Even in an over-crowded room
the conditions are made much more bearable if the air is kept in
motion, and in a close room ladies obtain relief by the use of their
fans. What we require, therefore, in order to maintain an agreeable
atmosphere under all conditions, is some means of keeping the air in
gentle motion, and at the same time destroying as much as possible of
the animal matter contained in it. Perhaps the most interesting and
at the same time the most scientific method of doing this is by ozone
ventilation.
In the well-known “Ozonair” system of ventilation, ozone is generated
by high-tension current. Low-tension current is taken from the public
mains or from accumulators, and raised to a very high voltage by
passing it through a step-up transformer. The secondary terminals
of the transformer are connected to a special form of condenser,
consisting of layers of fine metal gauze separated by an insulating
substance called “micanite.” The high tension between the gauze layers
produces a silent electrical discharge or glow. A small fan worked
by an electric motor draws the air over the condenser plates, and so
a certain proportion of the oxygen is ozonized, and is driven out of
the other side of the apparatus into the room. The amount of ozone
generated and the amount of air drawn over the condenser are regulated
carefully, so that the ozonized air contains rather less than one
volume of ozone in one million volumes of air, experiment having shown
that this is the most suitable strength for breathing. Ozone diluted to
this degree has a slight odour which is very refreshing, and besides
diminishing the number of organic germs in the air, it neutralizes
unpleasant smells, such as arise from cooking or stale tobacco smoke.
Ozone ventilation is now employed successfully in many hotels,
steamships, theatres and other places of entertainment, municipal and
public buildings, and factories.
[Illustration:
_By permission of_] [_Ozonair, Ltd._
FIG. 42.--Diagram of Ozonizing Plant, Central London Tube Electric
Railway.]
One of the most interesting examples of ozone ventilation is that of
the Central London tube electric railway. The installation consists of
a separate ozonizing plant at every station, except Shepherd’s Bush,
which is close to the open end of the tunnel. Fig. 42 is a diagram of
the general arrangement of one of these plants, and it shows how the
air is purified, ozonized, and sent into the tunnel. The generating
plant is seen at the top left-hand corner of the figure. Air is drawn
in as shown by the arrows, and by passing through the filter screen
F it is freed from dirt and smuts, and from most of the injurious
gases which always are present in town air. The filter screen is kept
moist by a continual flow of water from jets above it, the waste
water falling into the trough W. The ozone generator is shown at O.
Continuous current at about 500 volts, from the power station, is
passed through a rotary converter, which turns it into alternating
current at 380 volts. This current goes to the transformer T, from
which it emerges at a pressure of 5000 volts, and is supplied to the
ozone generator. From the generator the strongly ozonized air is
taken by way of the ozone pipe P, to the mixing chamber of the large
ventilating fan M, where it is mixed with the main air current and then
blown down the main air trunk. From this trunk it is distributed to
various conduits, and delivered at the air outlets marked A. Altogether
the various plants pump more than eighty million cubic feet of ozonized
air into the tunnels every working day.
In many industries pure air is very essential, especially during
certain processes. This is the case in brewing, in cold storage, and in
the manufacture and canning of food products; and in these industries
ozone is employed as an air purifier, with excellent results. Other
industries cannot be carried on without the production of very
unpleasant fumes and smells, which are a nuisance to the workers and
often also to the people living round about; and here again ozone is
used to destroy and remove the offending odours. It is employed also in
the purification of sewage and polluted water; in bleaching delicate
fabrics; in drying and seasoning timber; in maturing tobacco, wines and
spirits, and in many other processes too numerous to mention.