224 CHEMICAL TRANSFORMATIONS. 



attracted much attention, because it differs from 

 ordinary chemical phenomena. This is the reduc- 

 tion which certain oxides suffer by contact with this 

 substance, on the instant at which the oxygen sepa- 

 rates from the water. The oxides thus easily re- 

 duced, are those of which the whole, or part at 

 least, of their oxygen is retained merely by a feeble 

 affinity, such as the oxides of silver and of gold, 

 and peroxide of lead. 



Now, other oxides which are very stable in com- 

 position, effect the decomposition of peroxide of 

 hydrogen, without experiencing the smallest change ; 

 but when oxide of silver is employed to effect the 

 decomposition, all the oxygen of the silver is carried 

 away with that evolved from the peroxide of hydro- 

 gen, and as a result of the decomposition, water 

 and metallic silver remain. When peroxide of 

 lead is used for the same purpose, half its oxygen 

 escapes as a gas. Peroxide of manganese may in 

 the same manner be reduced to the protoxide, and 

 oxygen set at liberty, if an acid is at the same 

 time present, which will exercise an affinity for 

 the protoxide and convert it into a soluble salt. 

 If, for example, we add to peroxide of hydro- 

 gen sulphuric acid, and then peroxide of man- 

 ganese in the state of fine powder, much more 

 oxygen is evolved than the compound of oxygen 

 and hydrogen could yield; and if we examine 

 the solution which remains, we find a salt of 

 the protoxide of manganese, so that half of the 



