THEIR CAUSE. 295 



drogen, 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 hydrogen, and, as a result of the decomposition, 

 water and metallic silver remain. When peroxide 

 of lead * is used for the same purpose, half its oxy- 

 gen escapes as a gas. Peroxide of manganese may 

 in the same manner be reduced to the protoxide, and 

 ogygen set at liberty, if an acid is at the same time 

 present, which will exercise an affinity for the pro- 

 toxide and convert it into a soluble salt. If, for ex- 

 ample, we add to peroxide of hydrogen sulphuric 

 acid, and then peroxide of manganese 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 oxygen has been evolved from the peroxide of 

 that metal. 



A similar phenomenon occurs, when carbonate of 

 silver is treated with several organic acids. Pyruvic 

 acid, for example, combines readily with pure oxide 

 of silver, and forms a salt of sparing solubility in 

 water. But when this acid is brought in contact 

 with carbonate of silver, the oxygen of part of the 

 oxide escapes with the carbonic acid, and metal- 

 lic silver remains in the state of a black powder. 

 (Berzelius.) 



Now no other explanation of these phenomena 

 can be given, than that a body in the act of com- 

 bination or decomposition enables another body, with 

 which it is in contact, to enter into the same state. 

 It is evident that the active state of the atoms of one 

 body has an influence upon the atoms of a body in 

 contact with it ; and if these atoms are capable of 

 the same change as the former, they likewise under- 



* A peroxide is one that contains the largest proportion of oxygen. 

 When several compounds of metals and oxygen occur, that which con- 

 tains the smallest proportion of oxygen is called the first or protoxide. 



