Mar. 5, 1874] 



NATURE 



347 



OZONE'^ 

 I. 

 •yOWARDS the end of the last century, Van Manim, while 

 "'■ experimenting with his powerful electrical machine, ob- 

 served that oxygen gas through which electrical sparks had been 

 passed acquired a peculiar odour and the property of attacking 

 mercury. This subject attracted no further attention for up- 

 wards of half a century after the publication of Van Marum's 

 observations. 



The discovery of ozone was announced by Schonbein in a 

 memoir which he presented in 1S40 to the Academy of Munich. 

 In this important communication he states that in the electro- 

 lysis of water, an odorous substance accompanies the oxygen 

 evolved at the positive pole, that this substance may be preserved 

 foi a long time in well-closed vessels, and that its production is 

 influenced by the'nature of the metal which serves as the pole, 

 by the chemical properties of the electrolytic' fluid, and by the 

 temperature of that fluid, as well as of the electrode. The same 

 body he found to be produced by holding a strip of platinum or 

 gold near the knob of the prime conductor of an electrical 

 machine in good order. With great sagacity he recognised the 

 identity of the peculiar odour which accompanies a flash of 

 lightning with that of the new substance. In this memoir 

 Schonbein supposes the odorous body, for which, in a note at 



FIC-.Z. 



the end, he proposes the name of ozone, to be a new electro- 

 negati\e element belonging to the same class as chlorine and 

 bromine ; but in a paper published a little later he_ hints that 

 ozone may be one of the constituents of nitrogen. 



Schonbein soon afterwards discovered that ozone is formed when 

 phosphorus oxidises slowly in moist air or oxygen. 



In the following year, he returned to the consideration of the 

 subject, and partly from his own observations, partly from 

 experiments communicated to him by De la Rive and Marignac, 

 he abandoned his former view of the nature of ozone, and con- 

 cluded that it is an oxide of hydrogen different from the peroxide 

 of hydrogen of Thenard. 



Many of the properties of ozone described by Schonbein were 

 soon afterwards verified by Marignac, who found, as Schonbein 

 had already stated, that it is only in the presence of moisture that 

 air or oxygen when passed over phosphorus produces ozone, 

 and that no ozone can be formed from air, even if moist, which 

 has been deprived of its oxygen. He also confirmed the obser- 

 vations of Schonbein that the peculiar properties of ozone dis- 

 appear when it is heated to a temperature between 300° C. and 

 400° C, and that it is not absorbed by water or sulphuric acid. 



• An Addicss delivered before tlic Royal Society of Edinburgfl on 

 December 22, 1873, by Dr. Andrews, Ll^.D., F.R.S., Honorary Fellow of 

 the Royal Society of Edinburgh. 



In a subsequent investigation (1S45) which Marignac con- 

 ducted with De la Rive, the important fact was established that 

 ozone is formed by the passage of electrical sparks through pure 

 and dry oxygen gas. Fremy and Becquerel also showed that 

 pure oxygen contained in a tube inverted over a solution of iodide 

 of potassium is entirely absorbed by that liquid, if electrical 

 sparks are passed for a sufficiently long time through the gas. 



The last hypothesis of Schonbein, according to which ozone 

 is an oxide of hydrogen, was manifestly inconsistent with the 

 production of that body by the passage of electrical sparks 

 through pure and dry oxygen. On the other hand, it received 

 support from som - experimental inquiries which appeared about 

 this time, and particularly from an elaborate investigation which 

 was conducted by Baumeit in the laboratory of the University of 

 Heidelberg, and published in Poggendorff' s Anncilen for 1S53. 

 Baumert maintained that water is always formed when dry ozone, 

 prepared by electrolysis, is destroyed or decomposed by heat, 

 and further endeavoured to establish its composition by deter- 

 mining the increase of weight of a solution of iodide of potassium 

 when it is decomposed by ozone. He inferred, as the result of 

 his researches, that two distinct bodies had been confounded 



under the name of ozone ; (1) allotropic oxygen, formed by the 

 passage of the electrical spark through oxygen ; and (2) a 

 teroxide of hydrogen, produced in the electrolysis of water. The 

 experiments and conclusions of Baumert attracted a great deal 

 of attention at the time they were published, and received very 

 general assent. 



Having repeated, soon after it was announced, the experiment 

 of Baumert, in which ozone prepared by electrolysis was de- 

 stroyed by heat, and having failed to obtain the slightest trace of 

 water in numerous trials, I deemed it important to undertake a 

 careful investigation of the subject, the results of which were com- 

 municated in 1S53 to the Royal Society of London. By em- 

 ploying an acidulated solution of iodide of potassium, I found 

 that its increase of weight, when decomposed by ozone, exactly 

 agreed with the weight of the ozone calculated as allotropic 

 oxygen from the iodine set free. The numbers deduced from 

 five careful experiments were o'liyg grammes for the increase in 

 weight of the solution, an 1 O'liyS grammes for the calculated 

 weight of the oxygen. .\3 regards the supposed formation of 

 water in the destruction of ozone by heat, it may be sufficient to 

 mention the results of two experiments performed with great 

 care, in one of which 6"8 litres of electrolytic oxygen containing 



