268 CHEMICAL TRANSFORMATIONS. 



CHAPTER II. 



On the Causes which effect Fermentation, Decay,* and Putrefaction. 



Attention has been only recently directed to the fact, that a 

 body in the act of combination or decomposition exercises an in- 

 fluence upon any other body with which it may be in contact. 

 Platinum, for example, does not decompose nitric acid ; it may 

 be boiled with this acid without being oxidized by it, even when 

 in a state of such fine division that it no longer reflects light 

 (black powder of platinum). But an alloy of silver and platinum 

 dissolves with great ease in nitric acid : the oxidation which the 

 silver suffers, causes the platinum to undergo the same change ; 

 or, in other words, the latter body, from its contact with the 

 oxidizing silver, acquires the property of decomposing nitric 

 acid. 



Copper does not decompose water, even when boiled in 

 dilute sulphuric acid ; but an alloy of copper, zinc, and nickel, 

 dissolves easily in this acid with evolution of hydrogen gas. 



Tin decomposes nitric acid with great facility, but water with 

 difficulty ; and yet, when tin is dissolved in nitric acid, hydro- 

 gen is evolved at the same time, from a decomposition of the 

 water contained in the acid, and ammonia is formed in addition 

 to oxide of tin. 



In the examples here given, the only combination or decompo- 

 sition which can be explained by chemical affinity s the last. In 

 the other cases, electrical action ought to have retarded or pre- 



* An essential distinction is drawn in the following part of the work, 

 between decay and putrefaction ( Verwesung und Faulniss), and they are 

 shown to depend on different causes ; but as the word decay is not gene- 

 rally applied to a distinct species of decomposition, and does not indicate 

 its true nature, I shall in future, at the suggestion of the author, employ 

 the term eremacausis (from ij/>t/ua by degrees, and itavtis burring). — Ed. 



