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Ozone

Aiton's Encyclopedia (1910)

a colorless gas with the odor and chemical activity of air. It is, in fact, condensed oxygen. It is highly destructive, of offensive odor, and is, in general, an active purifier. In nature, the air of high altitudes and cool, wind-swept prairies is supposed to contain more or less ozone. It is highly favorable to active, energetic animal life. Ordinarily two atoms of oxygen unite to form one molecule, but three atoms of oxygen unite to form a molecule of ozone. Three volumes of oxygen form two volumes of ozone. Ozone is formed by nature during thunderstorms. An electrical discharge is accompanied by the making of ozone. When an electrical machine is operated rapidly, the pungent, offensive odor that arises is due to ozone. On the principle that two are good company and three are none at all, the third atom of the ozone molecule is dissatisfied-eager for other company. When ozone and bacteria--germs--come together, the third atom seizes the hydrogen of the bacteria. The result is oxygen and dead bacteria. For this reason ozone is the natural foe of the germs of tuberculosis; and for this reason consumptives find relief in sleeping in the open air, where ozone is most abundant. The same eagerness of the third atom to enter into another combination makes ozone a valuable gas for many purposes. It is manufactured by the use of electrical discharges and is used in many of the arts. It is used to refine oils; to whiten wax, ivory, and bone; to bleach feathers and cotton goods; to harden the wood used in musical instruments, and for many other purposes. In Paris, ozone is used to purify the linen from hospitals. The liking of ozone for the lives of bacteria has been put to good account by the citizens of Philadelphia. A municipal plant manufactures ozone and uses it in the purification of drinking water. Samples of water known to contain as high as 720,000 bacteria were treated with ozone. The average number of living bacteria was reduced, it is believed, to twenty-five per sample. Ozone tarnishes silver, it bleaches indigo, corrodes cork, hardens India rubber and turns moist litmus paper blue. See Oxygen ; Bacterium ; Tuberculosis

What Has Changed in the Last Century

When Aiton's wrote this in 1910, ozone was thought a tonic "highly favorable to active, energetic animal life" and a natural cure-aid for consumptives sleeping outdoors. That reputation collapsed: ground-level ozone is now classed as a harmful pollutant that inflames the lungs, and the US EPA's health standard, tightened to 70 parts per billion in 2015, treats smog-season ozone as something to warn people away from rather than breathe deeply. The entry also predates the great discovery about ozone high in the atmosphere " the shield against ultraviolet light whose Antarctic "hole" was reported in 1985 and which led to the 1987 Montreal Protocol banning CFCs; Crutzen, Molina and Rowland shared the 1995 Nobel Prize in chemistry for working out the destruction. The one part that still stands is the chemistry: three atoms to a molecule, made by electrical discharge, and still used to disinfect drinking water in cities worldwide.

Written for this edition, 2026.