210 [June 19, 



connect the double function of this class of peroxides with the 

 peculiar catalytic decompositions which they undergo. It is shown 

 that the catalytic decomposition may be regarded as a combination 

 of these two actions, an oxidation and a reduction simultaneously 

 occurring. Thus in an alkaline solution of the peroxide of hydrogen, 

 protoxide of manganese is oxidized to peroxide. In the acid solution 

 the peroxide of manganese is reduced to protoxide, the results being 

 expressed in the following equations : 



while the result of the catalytic decomposition effected by the peroxide 

 of manganese is given in the equation derived from the above by 



elimination, 



2H 2 2 =2H 2 + 2 , 



the result being the same as though the peroxide of manganese were 

 alternately reduced and oxidized by the alkaline peroxide. We are 

 thus enabled to analyse the catalytic action into its constituent de- 

 compositions. 



That in numerous cases the catalytic change is brought about by 

 the intervention of intermediate compounds, which are alternately 

 formed and destroyed during the action, is shown in various examples. 

 For instance, the addition of a solution of peroxide of sodium to an 

 excess of a solution of a protosalt of copper causes the formation of 

 a precipitate of a yellow peroxide of copper. If, on the other hand, 

 a few drops of the salt of copper be added to an excess of the alkaline 

 peroxide, the same yellow body is formed, but the whole of the 

 peroxide is ultimately decomposed ; after the decomposition hydrated 

 protoxide of copper remains. Similar phenomena occur with an 

 ammoniacal solution of the copper-salt. If a few drops of this 

 solution be added to an ammoniacal solution of the peroxide of 

 hydrogen, the solution becomes of a yellow colour, and the cata- 

 lytic action is set up. This action may continue, in dilute solutions, 

 for several hours ; during the whole of this time the yellow colour is 

 permanent ; but ultimately, when the peroxide is entirely decom- 

 posed, the blue colour of the ammoniacal solution of the protoxide 

 reappears. The ammoniacal solution of the protoxide of copper 

 decomposes the peroxide of hydrogen into water and oxygen, precisely 

 as sulphuric acid decomposes alcohol into ether and water. But in 

 this case the colour of the solution gives actual evidence of the 



