DISOXIDATION EFFECTED BY THE ALKALINE PEEOXIDES. 857 
After the evolution of gas had ceased, the solution was titred. It required 9" 31 cub. 
centims. of permanganate solution. 
3 P. of peroxide had been added, and 2 P. decomposed. The manganese was in the 
form of protoxide, as at the commencement of the experiment. 
Exp. II. — ^To 1 P. of a solution of ferrocyanide of potassium, which required for its 
titration 5-96 cub. centims. of permanganate, was added 1 P. of an acid solution of per- 
oxide of hydrogen, which required for titration 3-681 cub. centims. of the same solution 
of permanganate. An equivalent portion of ferricyanide of potassium was formed. 
The solution was rendered alkaline, and to it was added 1 P. of an alkaline solution 
of peroxide of sodium, which required for its titration 3-33 cub. centims. of the same per- 
manganate solution. 
The solution, rendered acid and titred, required 5-66 cub. centims. of permanganate. 
Therefore a portion of peroxide equivalent to 7-15 of permanganate had disappeared. 
The total peroxide added required 7-01 parts of permanganate. 
In these experiments the final is the same as the initial condition of the chemical sub- 
stances, with the single exception that the peroxide of hydrogen is decomposed. If the 
oxidation and reduction which in the preceding examples are separately realized had 
taken place simultaneously and under the same general conditions, no result would 
have appeared but the decomposition of the alkaline peroxide, and the action would 
have been termed a contact action. Now, although in the case of the catalytic decom- 
position of the alkaline peroxide we are undoubtedly not able to specify in each case 
the precise reaction by which the final result is attained, we have yet in several instances 
indications that the decomposition proceeds by successive stages of this kind. 
When an alkaline solution of peroxide of sodium is added to a solution of proto- 
sulphate of manganese, a precipitate is formed of hydrated peroxide of manganese. If, 
however, a few drops of an excessively dilute solution of protosulphate of manganese be 
added to an excess of peroxide of sodium, there is no precipitate, but the solution 
remains clear, becomes brown in colour, and the peroxide undergoes the catalytic 
decomposition. If a great excess of a solution of the peroxide of sodium be added to a 
very small quantity of freshly precipitated hydrated peroxide of manganese, the peroxide 
of manganese dissolves, forming the same clear brown solution. It is thus seen that 
the peroxide of manganese can be further oxidized by the peroxide of sodium, and that 
the product of this oxidation decomposes in solution the peroxide of sodium. 
Again, if a solution of peroxide of sodium be added to an alkaline solution of per- 
manganate, the latter is first reduced to manganate, the solution becoming green : on 
farther addition of the peroxide of sodium, the solution becomes of the same clear brown 
colour as that produced by the oxidation of the protoxide. If, however, the peroxide be 
sparingly added, or if permanganate be added to this solution, a precipitation takes place 
of peroxide of manganese. It is the compound which forms this brown solution by the 
agency of which the peroxide of sodium is decomposed ; and it is only when the decom- 
position of the latter is complete, or close upon this point, that the peroxide of manga- 
