with Formula: for ascertaining its poxver. 255 



same cause; (e) is very small. The result of such a state of 

 things necessarily causes a vast intensity of action, and an ex- 

 plosion is the result. 



Good specimens of contrasts in the magnitude in the se- 

 veral parts of the circuit are to be seen in the relative power 

 of (F), as obtained by zinc and silver; in the relative resist- 

 ance of (a) in the solubility of sulphate of lead and sulphate 

 of zinc ; in the resistance of (r) in the conducting power of 

 pure water and muriatic acid; of the resistance of (c) in a 

 leaden wire a hundred miles long, and a short silver one; in 

 the resistance of (e) in the evolution of hydrogen from smooth 

 platinum, and its removal by nitric acid. 



The relative degrees of action evinced by zinc, tin, iron, 

 and lead upon sulphate of copper are easily explained; (F) 

 differs from being larger, (a) in being smaller when zinc is 

 employed, whilst (c), (r), (e) in each case remain nearly the 

 same ; (a) indeed is so large when lead is employed as soon 

 to put a stop to the action. 



How intelligible is the want of action of dilute sulphuric acid 

 on amalgamated zinc, if examined by our equation for (c) ! the 

 adhesion of the second element, hydrogen, being increased 

 enormously, counterbalances (F), the affinity of zinc for the 

 first element, or oxygen, and no action takes place. Amalga- 

 mated zinc is rapidly dissolved if placed in a solution of salts 

 of copper or silver, for (e) in that case is depressed, the hy- 

 drogen rapidly reducing the copper. Nitric acid in the same 

 way does not respect the amalgamation of the zinc, for (e) in 

 that case is also diminished by the removal of hydrogen from 

 the decomposition of the acid. As the adhesion of hydrogen 

 to plumbago is very great, it occurred to me that the simple 

 application of black-lead to zinc would, by preventing the 

 evolution of hydrogen, increase (e), and therefore stop the 

 local action ; but although the experiment fully succeeded, 

 the plumbago so quickly came off, that I have not at present 

 made any practical application of the experiment. 



The above cases, with all their analogies, are not the only 

 ones to which the equation applies, for it will account per- 

 fectly for the action of bodies on each other. 



In cases of single elective affinity, as the action of sulphuric 

 acid on nitrate of barytes, a compound is decomposed, one 

 element enters into another combination, the other is set free ; 

 a voltaic circuit is therefore produced, the parts of which are 

 thus made: (c) Sulphuric acidl(F) 



o)/ Bar >' tes . j ( a ) 



v ' \Nitric acid (e) 

 In cases of double elective affinity, as the action of sulphate 



