The above facts have, however, been disputed
by some observers, whilst others have refused to regard them as anything more than coincidences, and have indeed cited evidence of a totally opposite character; thus Grellois has stated that he found more ozone in a marsh than elsewhere.
Mr Kingzett has shown the incorrectness of Schönbein’s statement that, when oil of turpentine and other essential oils are oxidised by exposure to the air, ozone is formed. Schönbein was misled because from the oxidised oil and the air in its vicinity he obtained the ozone reaction with potassium iodide.
Mr Kingzett has demonstrated that the compound can be neither ozone nor hydrogen dioxide, because it is destroyed at the boiling point of oil of turpentine, viz. 160°, at which temperature ozone and hydrogen dioxide are permanent; besides which it resists to a certain extent the action of sodium thiosulphate, and its solution in water retains its properties after long-continued boiling. Mr Kingzett believes the active properties of the oxidised turpentine oil are due to the formation of monohydrated terpene oxide (C10H16O.H2O).
One of the most delicate tests for ozone is potassium iodide, either alone or mixed with starch. A brown colour in the former case, a blue in the latter, indicates the liberation of iodine. In the ozometer, strips of paper saturated with starch and potassium iodide are exposed to the action of a definite volume of air in a dark chamber. The comparative quantities of ozone in different samples of air are judged of by the intensity of the colour compared with a fixed scale on which 1 is the lightest and 10 generally the darkest shade. See Ozonometer.
Ozone acts as a reducing agent in certain curious cases. Thus, hydrogen peroxide and ozone reduce one another, water and oxygen being the sole products; and some substances, such as platinum black and manganese peroxide, convert it into oxygen without suffering change themselves, being probably oxidised and reduced alternately.
OZONOM′ETER. This name has been given to paper prepared with a mixed solution of starch and iodide of potassium. It is white, but is turned blue by ozonised air when exposed to it in a slightly moistened state.
The following are the proportions given by Schönbein for the preparation of the paper:—1 part of pure iodide of potassium, 10 parts of starch and 200 of water. Lowe gives 1 part of iodide to 5 of starch; Moffatt, 1 to 21⁄2. The best arrowroot must be used for the starch. It must be dissolved in warm water and filtered, so that a clear solution is obtained.
The iodide is dissolved in another portion of water, and gradually added. The paper, cut in slips and previously soaked in distilled water, is placed in the mixed iodide and starch for several hours; and lastly, slowly dried in a cool dark place, the slips being hung horizontally.
Schönbein’s papers require moistening with water after exposure before the trial is taken.