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CHAPTER IV 



OZONE AND HYDROGEN PEROXIDE. DALTON's LAW 



VAN-MARUM, during the last century, observed that oxygen in a glass 

 tube, when subjected to the action of a series of electric sparks, acquired 

 a peculiar smell and the property of combining with mercury at the 

 ordinary temperature. This was afterwards confirmed by a number of 

 fresh experiments. Even in the simple revolution of an electrical 

 machine, when electricity diffuses into the air or passes through it, the 

 peculiar and characteristic smell proper to ozone, proceeding from 

 the action of the electricity on the oxygen of the atmosphere, is 

 recognised. In 1840 Prof. Schonbein, of Basle, turned his attention 

 to this odoriferous substance, and showed that it is also formed, 

 with the oxygen evolved at the positive pole, in the decomposition of 

 water by the action of a galvanic current ; in the oxidation of phos- 

 phorus in damp air, and also in the oxidation of a number of 

 substances, in consequence of which it is found in the atmosphere, 

 although it is distinguished for its instability and capacity for oxidis- 

 ing other substances. The characteristic smell of this substance (which 

 is always mixed with unaltered oxygen) gave it its name, from the Greek 

 ow, ' to emit an odour.' Schonbein pointed out the characteristic pro- 

 perties of ozone, and especially its power of oxidising many substances, 

 even silver, acting like oxygen, but with this difference that there are 

 a number of substances on which oxygen does not act at the ordinary 

 temperature, whilst ozone does so very energetically. It will be 

 enough to point out, for instance, that it oxidises silver, mercury, 

 charcoal, and iron with great energy at the ordinary temperature. It 

 might be thought that ozone was some new substance, simple or com- 

 pound, as it was at first supposed to be ; but careful observations 

 made in this direction have long led to the conclusion that ozone is 

 nothing but oxygen altered in its properties. This is most strikingly 

 proved by the complete transformation of oxygen containing ozone into 

 ordinary oxygen when it is passed through a tube heated to 250. 

 Further, at a low temperature pure oxygen gives ozone when electric 



