THEIR CAUSE. 2G9 



vented the oxidation of the platinum or copper while they were 

 in contact with silver or zinc, but, as experience shows, the in- 

 fluence of the opposite electrical conditions is more than counter- 

 balanced by chemical action. 



The same phenomena are seen in a less dubious form in com- 

 pounds, the elements of which are held together by a feeble 

 affinity. It is well known that there are chemical compounds, 

 of so unstable a nature, that changes in temperature and elec- 

 trical condition, or even simple mechanical friction, or contact 

 with bodies apparently totally indifferent, cause such a disturb- 

 ance in the attraction of their constituents, that the latter enter 

 into new forms, without any of them combining with the acting 

 body. These compounds appear to stand but just within the 

 limits of chemical combination, and agents exercise a powerful in- 

 fluence on them, which are completely devoid of action on com- 

 pounds of a stronger affinity. Thus, by a slight increase of tem- 

 perature, the elements of hypoclriorous acid separate from one 

 another with evolution of heat and light ; chloride of nitrogen 

 explodes by contact with many bodies, which combine neither 

 with chlorine nor nitrogen at common temperatures ; and the 

 contact of any solid substance is sufficient to cause the explosion 

 of iodide of nitrogen, or of fulminating silver. 



It has never been supposed that the causes of the decomposition 

 of these bodies should be ascribed to a peculiar power, different 

 from that which regulates chemical affinity, — a power which 

 mere contact with the down of a feather is sufficient to set in 

 activity, and which, once in action, gives rise to the decom- 

 position. The substances have always been viewed as chemical 

 compounds of a very unstable nature, in which the component 

 parts are in a state of such tension, that the least disturbance 

 overcomes their chemical affinity. They exist only by the vis 

 inertia, and any shock or movement is sufficient to destroy the 

 attraction of their component parts, and consequently their ex- 

 istence as definite compounds. 



Peroxide of hydrogen belongs to this class of bodies ; it is 

 decomposed by all substances capable of attracting oxygen from 

 it, and even by contact with many bodies, such as platinum or 

 silver, which do not enter nto combination with any of its con 



