APPENDIX 107 



temperatures it forms chemical compounds with a series 

 of bodies, on which free oxygen under conditions other- 

 wise the same has no action whatever. Among the 

 substances which by their union with oxygen raise its 

 chemical activity are several oxides of the general formula 

 RO, such as HO, PbO and MnO. When one of these 

 oxides combines with a further atom of oxygen bodies are 

 formed which have a remarkable power of oxidation ; for 

 example, they expel iodine from potassium iodide, convert 

 the yellow prussiate of potash into the red, turn guaiacum 

 solution blue, and destroy indigo solution. These com- 

 pounds also resemble one another in their voltaic be- 

 haviour; they possess a remarkable degree of electro- 

 motive power, i.e., they are eminently electro-negative. 

 The peroxides owe all these properties to their second 

 atom of oxygen. "We must therefore assume that this 

 second atom is in an essentially different condition from 

 the first. It seems to me that it would be desirable for 

 science to possess a term to distinguish the chemically 

 active oxygen in such a compound ; perhaps we might use 

 the expression " oxylized," by which I understand oxygen 

 which has a tendency to leave the substance with which 

 it is united in order to attach itself to some other oxidiz- 

 able body. Perhaps it would also be convenient to use 

 a special symbol such as to denote the oxylized atom of 

 oxygen in a compound. The peroxides of hydrogen, lead 

 and manganese would accordingly receive the formulae 

 HO, PbO Mn6. 



As is well known, nitric oxide (N0 2 ) exerts a very 

 peculiar influence on the two atoms of oxygen which 

 combine with it to form nitrous acid. The condition of 

 the two oxygen atoms combined with N0 2 is not the 

 same as that of the second atom of oxygen in the per- 



