202 PRINCIPLES OF CHEMISTRY 



from it in stability, and by the fact that it oxidises a number of sub- 

 stances very energetically at the ordinary temperature. In this 

 respect ozone resembles the oxygen of certain unstable compounds, or 

 oxygen at the moment of its liberation. 



In ordinary oxygen and ozone we see an example of one and the 

 same substance, in this case an element, appearing in two states. This 

 indicates that the properties of a substance, and even of an element, 

 may vary without its composition varying. Very many such cases 

 are known. Such cases of a chemical transformation which determines 

 a difference in the properties of one and the same element are termed 

 isomerism. The cause of isomerism evidently lies deep within the 

 essence of the nature of a substance, and its investigation has already 

 led to a number of results of unexpected importance and of immense 

 scientific significance. It is easy to understand the difference between 

 substances containing different elements or the same elements in 

 different proportions. That a difference should exist in the latter 

 case necessarily follows, if, as our knowledge compels us, we admit 

 that there is a radical difference in the simple bodies or elements. 

 But when the quality and quantity of the elements (the composition) 

 in a substance are the same and yet its properties are different, 

 then it becomes clear that the conceptions of the elements and of the 

 composition of compounds, alone, are insufficient for the expression of 

 all the diversity of the properties of the matter of nature. Something 

 else, still more profound and internal than the composition of sub- 

 stances, must, judging from isomerism, determine the properties and 

 transformation of substances. 



On what is the isomerism of ozone with oxygen, and the peculiarities 

 of ozone, dependent ? In what, besides the store of energy, which in its 

 way expresses the peculiarities of ozone, resides the causes of its difference 

 from oxygen 1 These questions for long occupied the minds of investi- 

 gators, and were the motive for the most varied, exact, and accurate 

 researches, which were chiefly directed to the study of the volumetric 

 relations exhibited by ozone. In order to acquaint the reader with the 

 previous researches of this kind, I cite the following from a memoir by 

 Soret,in the * Transactions of the French Academy of Sciences ' for 1866 : 



4 Our present knowledge of the volumetric relations of ozone may be 

 expressed at the present time in the following manner : 



'1. " Ordinary oxygen in changing into ozone under the action of 

 electricity shows a diminution in volume." This was discovered by 

 Andrews and Tait. 



' 2. " In acting on ozonised oxygen with potassium iodide and other 

 substances capable of being oxidised, we destroy the ozone, but the 



