CHAPTER XXVI. OZONE.

127. Preparation.

Experiment 78.--Scrape off the oxide from the surface of a piece
of phosphorus 2 cm long, put it into a wide-mouthed bottle, half
cover the P with water, cover the bottle with a glass, and leave
it for half an hour or more.

128. Tests.

Experiment 79.--Remove the glass cover, smell the gas, and hold
in it some wet iodo-starch paper. Look for any blue color. Iodine
has been set free, according to the reaction, 2 KI + 03= K20 + O2
+ I2, and has imparted a blue color to the starch, and ordinary
oxygen has been formed. Why will not oxygen set iodine free from
KI?. What besides ozone will liberate it?

129. Ozone, oxidized oxygen, active oxygen, etc., is an
allotropic form of O. Its molecule is 03, while that of ordinary
oxygen is 02.

Three atoms of oxygen are condensed into the space of two atoms
of ozone, or three molecules of O are condensed into two
molecules of ozone, or three liters of O are condensed into two
liters of ozone. Ozone is thus formed by oxidizing ordinary
oxygen. 02 + O = 03. This takes place during thunder storms and
in artificial electrical discharges. The quantity of ozone
produced is small, five per cent being the maximum, and the usual
quantity is far less than that.

Ozone is a powerful oxidizing agent, and will change S, P, and As
into their ic acids. Cotton cloth was formerly bleached, and
linen is now bleached, by spreading it on the grass and leaving
it for weeks to be acted on by ozone, which is usually present in
the air in small quantities, especially in the country. Ozone is
a disinfectant, like other bleaching agents, and serves to clear
the air of noxious gases and germs of infectious diseases. So
much ozone is reduced in this way that the air of cities contains
less of it than country air. A third is consumed in uniting with
the substance which it oxidizes, while two-thirds are changed
into oxygen, as in Experiment 79.

It is unhealthful to breathe much ozone, but a little in the air
is desirable for disinfection.

Ozone will cause the inert N of the air to unite with H, to form
ammonia. No other agent capable of doing this is known, so that
all the NH3 in the air, in fact all ammonium compounds taken up
by plants from soils and fertilizers, may have been made
originally through the agency of ozone. At a low temperature
ozone has been liquefied. It is then distinctly blue.

Electrolysis of water is the best mode of preparing this
substance in quantity. When prepared from P it is mixed with
P2O3.