28 OZONE 



tion of rain-water, collected in various parts of the world, the reader 

 is referred to a paper by Miller. 1 



Ozone, the active form of oxygen, is present in air, but in very 

 varying and always excessively small amount. The measurement of 

 the absolute proportion of ozone in air is difficult, and the greater 

 number of observations recorded merely give the relative amounts 

 according to an arbitrary scale (Schonbein and Houzeau). Moreover 

 it is very probable that many of the results obtained are really due, 

 wholly or in part, to the presence of hydrogen peroxide. 



Houzeau, who estimated the relative amount of ozone present in 

 air by the colour imparted to strips of red litmus paper coated for half 

 their length with 1 per cent solution of potassium iodide and exposed 

 for a given time, concluded that the amount of ozone in country air 

 was, at the most, 1 in 450,000 by weight or 1 in 700 7 000 by volume. 

 He observed that the amount was greatest in May and June and least 

 in December and January, and that during rain and particularly dur- 

 ing violent thunder-storms and gales the amount was often greatly 

 increased. Over marshes or in towns no ozone can be detected. 



According to Schone - the indications usually ascribed to ozone are 

 really due to hydrogen peroxide. In 1874 and 1875 he made many 

 determinations (in Moscow) of the amount of hydrogen peroxide in 

 rain and snow, also, by artificially producing hoar-frost, in air. He 

 found the maximum amount occurred in air at 4 p.m. and the mini- 

 mum between midnight and 4 a.m., and that it was most abundant in 

 July and least abundant in December and January. 3 



It seems established as a fact that country and sea air contains a 

 powerful oxidising agent in small quantity, that this substance, 

 whether it be ozone or hydrogen peroxide, is destroyed by contact with 

 organic putrescible substances, and that the fact of its presence in any 

 particular sample of air is practically an indication of the purity of that 

 air. The popular belief in the health-giving character of " ozone- 

 laden " air is thus seen to possess a real foundation in fact, but not in 

 the way it is generally supposed. The ozone is not of itself important, 

 so far as is known, except as proof of the purity of the air from all 

 readily oxidisable ingredients, and probably from germs of micro- 

 organisms. It has been shown that ozonised air quickly destroys 

 germs in air. 4 



According to Bach ^ hydrogen peroxide is present in the leaves of a 

 large number of plants, being produced by the decomposition of car- 

 bon dioxide in presence of water by the chlorophyll of the plants. 

 Peyru 6 found that ozone (or hydrogen peroxide) was evolved from 

 growing plants. He found that more ozone was in nearly all cases to 

 be detected in the air over a field with a growing crop than over a 

 fallow field. He noticed that the amount of ozone was fairly con- 



1 Jour. Agric. Sci., 1905, i. 280. 



2 Ber., 1880 [13], 1503. 



s Jour. Chem. Soc., 1878, Abstracts, 552. 



4 Chappuis, Jour. Chem. Soc., 1881, Abstracts, 632. 



5 Jour. Chem. Soc., 1895, Abstracts, 26 and 239. 



6 Compt. Bend., 1894, 1206; Jour. Chem. Soc., 1895, Abstracts, ii. 240. 



