produced by Catalytic Bodies. 203 



in the black oxide, but merely that the attraction became 

 stronger when one of the elements which divided it was 

 removed. If it be admitted that the attraction of a radical 

 for oxygen is equally divided between all the atoms of that 

 element associated with it, the action to ^^ hich we have al- 

 luded becomes comprehensible. In an oxide mc have the 

 attraction of affinity opposed by the elasticity of its oxygen 

 and by the cohesive force of the metal. If a be the attraction 

 of the central nucleus or radical, c the cohesive force of the 

 metal, and e the elasticity of the oxygen, then the molecular 



formula of a protoxide will be , of a sesquioxide — j 



and of a binoxide r— . Now if, as in oxide of silver, the a 



c + 2e 



and e are nearly equal, or the a only slightly preponderating, 

 and the c or cohesive force very powerful, we can readily con- 

 ceive that the added force of a second e may overcome the 

 small amount of preponderating force in favour of a. Thus, 

 when oxide of silver is placed in contact with peroxide of 

 hydrogen, its affinity for more oxygen is sufficient to draw 

 the second atom of oxygen beyond the sphere of attraction of 

 H, and deliver it over to its own elasticity. But in doing 

 this the attraction of silver for oxygen has been divided be- 

 tween its own oxygen and that of the peroxide of hydrogen. 

 Scarcely at any time capable of retaining its own oxygen, 

 this division of its attractive force has been fatal to the exist- 

 ence of its oxide, and the water in statu nascens at the same 

 time exerting an affinity for the oxygen just ready to escape ; 

 all these causes combined result in the reduction of the 

 silver*. 



When pyruvic acid is in contact with oxide of silver, it 

 unites and forms a salt; but when acting on carbonate of 

 silver, a certain quantity of oxygen also leaves the oxide 

 during the escape of carbonic acid, and metallic silver re- 

 mains-}-. As Liebig J suggests, motion may aid this result; 

 but were this the only explanation, we should expect that 



* During the passage of this paper tlirough tlie press, Mr. Brodie, in a 

 lecture at the Royal Institution, showed that peroxide of potassium reduces 

 chloride of silver, the two atoms of oxygen passing off in the gaseous state, 

 while chloride of i-utassium and metallic silver remain behind, a singular 

 decomposition, when the behaviour of potash is remembered. But the 

 action is strictly the same as that here described ; the atoms of oxygen, - 

 being liberated at the same time, are presented to the silver, which, dividing 

 its attractive force between them, is not able to overcome the influence of 

 elasticity of the oxygen and its own cohesion, and therefore remains in a 

 metallic state. 



f Berzelius, Lehrhuch der Chemie, fifth edit. vol. iv. p. 231. 



I Chemistry of Agriculture, 4th edit., page 283. 



