200 HISTORY OF CHEMISTRY. [LECTURE XI. 



The formation of nitrogen by heating ammonium nitrite is 

 also explained in the same way : 



NO 4 H 4 N = 4 HO + NN. 



This mode of regarding the matter is very specially suitable 

 for explaining the reductions by means of hydrogen peroxide, 

 which were at that time partially known and had been chiefly 

 studied by Brodie himself. 8 He regards the formation of 

 oxygen as a consequence of the different polarities which this 

 element possesses in the two oxides. We have, for example : 



HOO + Ag, AgjO = HO 4- OO + Ag. 



The reduction of potassium permanganate and of potassium 

 bichromate is supposed to proceed in a similar manner. Two 

 atoms are always set at liberty simultaneously, and these, in 

 consequence of their chemical difference, then unite with each 

 other. 9 



Further, the discovery of ozone by Schonbein ; 10 the 

 recognition of its nature as an isomeric modification of 

 oxygen ; n and in particular the proof that it is condensed 

 oxygen (a fact which was first stated by Andrews and Tait 12 

 on the strength of some highly interesting experiments, but was 

 especially demonstrated by Soret 13 ) only find an explanation in 

 the hypothesis of the divisibility of the elementary molecules. If 

 ozone, as appears from Soret's experiments, possesses a relative 

 density, one and a half times as great as that of oxygen, then 

 the smallest particles of this latter gas must contain at least two 

 atoms, whilst those of ozone consist of three atoms. But if this 

 assumption is admitted in the case of oxygen, it cannot easily 



8 Phil. Trans. 1850, 759. 9 Compare also the explanation which 

 Wurtz gives of the fact that the combination of nitrogen and oxygen takes 

 place much more easily in presence of hydrogen (Wurtz, Le9ons. 65). 

 10 Pogg. Ann. 50, 616 ; 59, 240 ; 63, 520 ; 65, 69, 161, 190, etc. ; compare 

 "Ueber das Ozon," Basel 1844. n Archives des sciences phys. et natur., 

 Geneve 12, 315 ; 17, 61 ; 18, 153. 12 Annalen. 104, 128 ; 112, 185 ; Ann. 

 Chim. [3] 52, 333, and 62, 101. 1S Annalen. 138, 45 ; Supplementband 



