070> 7 E AND HYDROGEN PEROXIDE DALTON'S LAW 205 



much more easily. This was actually shown to be the case, in 1880, by 

 Chappuis and Hautefeuille in their researches on the physical properties 

 of oxygen. Its absolute boiling point is about 106, and consequently 

 compressed and refrigerated ozone when rapidly expanded gives drops, 

 is liquefied. Liquid and compressed u ozone is blue. In dissolving in 

 water ozone partly passes into oxygen. Ozone violently explodes when 

 suddenly compressed and heated, changing into ordinary oxygen, and 

 evolving, like all explosive substances, 12 that heat which distinguishes 

 it from oxygen. 



Thus, judging by what has been said above, ozone should be 

 formed in nature not only in the many processes of oxidation which 

 go on, but also by the condensation of atmospheric oxygen. The 

 significance of ozone in nature has often arrested the attention of 

 observers. There is a series of ozonometrical observations which show 

 the different amounts of ozone in the air at different localities, at 

 different times of the year, and under different circumstances for 

 instance, on the appearance of epidemics. But the observations made 

 in this direction cannot be considered as sufficiently exact, because the 

 methods in use for determining ozone were not quite accurate. It is 

 however indisputable 13 that the amount of ozone in the atmosphere is 

 subject to variation ; that the air of dwellings contains no ozone (it dis- 

 appears in oxidising organic matter) ; that the air of fields and forests 

 always contains ozone, or substances (peroxide of hydrogen) which act 

 like it ; that the amount of ozone increases after storms ; and that 

 miasms, c., are destroyed by ozonising the atmosphere. It may be 

 imagined that the influence exerted by ozone on animal life is due to 

 the fact that it easily oxidises organic substances, and miasms are 

 formed of organic substances and the germs of organisms, which are 

 easily changed and oxidised. Indeed, many miasms for instance, 



conditions, evidently be less capable of passing into a state of gaseous movement, should 

 sooner attain a liquid state, and have a greater cohesive force. 



11 The blue colour proper to ozone may be seen through a tube one metre long con- 

 taining oxygen 10 p.c. ozonised. The density of liquid ozone has not, as far as I am 

 aware, been determined. 



12 All explosive bodies and mixtures (gunpowder, detonating gas, &c.) evolve heat in 

 exploding (in giving a greater number of molecules from one molecule, and sometimes 

 several substances from one substance, as in the explosion of nitro-compounds ; see later) 

 that is, the reactions which accompany explosions are exothermal. In this manner 

 ozone in decomposing evolves latent heat, although generally heat is absorbed in 

 decomposition. This shows the meaning and cause of explosion. 



13 In Paris it has been found that the further from the centre of the town the greater 

 the amount of ozone in the air. The reason of this is evident : in a city there are many 

 conditions for the destruction of ozone. This is why we distinguish country air as being 

 fresh. In spring the air contains more ozone than in autumn ; the air of fields more than 

 the air of towns. 



