APPENDIX 



ON VARIOUS CHEMICAL STATES OF 

 OXYGEN 



ONE of the most important and interesting branches of 

 chemical investigation to which it would seem sufficient 

 attention has not been devoted is the influence exerted 

 on the affinity of a substance by the other substances 

 with which it is combined. In many cases the same 

 element in an isolated condition shows an essentially 

 different behaviour towards certain substances from that 

 which it exhibits when in combination. In this con- 

 nection oxygen of all simple bodies shows the most 

 remarkable behaviour ; for according as it is isolated, or 

 in this or that state of combination, it may show either a 

 very high degree of chemical activity or none at all, 



If I am not mistaken there is no single element with 

 which dry oxygen combines at ordinary temperatures; 

 but when it is united with certain substances its be- 

 haviour is wholly different. Contrary to what theoretical 

 considerations would lead us to expect, combined oxygen 

 shows such a degree of chemical activity that even at low 



