CHEMICAL AFFINITY. 141 



intensity by these reduplications, is in itself a striking instance 

 of the mutual relations and dynamic analogies of different 

 forces. Let a plate of zinc or other metal possessing a strong 

 affinity for oxygen, and another of platinum or other metal 

 possessing little or no affinity for oxygen, be partially im- 

 mersed in a vessel, A, containing dilute nitric acid, but not in 

 contact with each other ; let platinum wires touching each 

 of these plates have their extremities immersed in another 

 vessel, B, containing also dilute nitric acid : as the acid in 

 vessel A is decomposed, by the chemical affinity of the zinc 

 for the oxygen of the acid, the acid in vessel B is also 

 decomposed, oxygen appearing at the extremity of the wire 

 which is connected with the platinum : the chemical power is 

 conveyed or transferred through the wires, and, abstracting 

 certain local effects, for every unit of oxygen which combines 

 with the zinc in the one vessel, a unit of oxygen is evolved 

 from the platinum wire in the other. The platinum wire is 

 thus thrown into a condition analogous to zinc, or has a 

 power given to it of determining the oxygen of the liquid to 

 its surface, though it cannot, as is the case with zinc, combine 

 with it under similar circumstances. If we now substitute for 

 the platinum wire, which was connected with the platinum 

 plate, a zinc wire, we have, in addition to the determining 

 tendency by which the platinum was affected, the chemical 

 affinity of the oxygen in vessel B for the zinc wire : thus we 

 have, added to the force which was originally produced by 

 the zinc of the combination in vessel A, a second force pro- 

 duced by the zinc in vessel B, co-operating with the first ; 

 two pairs of zinc and platinum thus connected produce, there- 

 fore, a more intense effect than one pair ; and if we go on 

 adding to these alternations of zinc, platinum, and liquid, we 

 obtain an indefinite exaltation of chemical power, just as in 

 mechanics we obtain accelerated motion by adding fresh 

 impulses to motion already generated. 



The same rule of proportion which holds good in chemical 

 combinations also obtains in electrical effects, when these are 

 produced by chemical actions. Dalton and others proved 

 that the constituents of a vast number of compound sub- 

 stances always bore a definite quantitative relation to each 



