CHEMICAL AFFINITY. 157 



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

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

 er given to it of determining the oxygen of the liquid to its 

 surface, though it cannot, as is the case with zinc, com- 

 bine with it under similar circumstances. If we now substi- 

 tute for the platinum wire which was connected with the 

 platinum plate, a zinc wire, we have in addition to the deter- 

 mining 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 pro- 

 duced by the zinc of the combination in vessel A, a second 

 force, produced by the zinc in vessel B, co-operating with the 

 first ; two pairs of zinc and platinum thus connected produce, 

 therefore, 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 chemi- 

 cal 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 substances 

 always bore a definite quantitative relation to each other : 

 thus, water, which consists of one part by weight of hydro- 

 gen united to eight parts of oxygen, cannot be formed by the 

 same elements in any other than these proportions ; you can 

 neither add to nor subtract from the normal ratio of the 

 elements, without entirely altering the nature of the com- 

 pound. Further, if any element be selected as unity, the 

 combining ratios of other elements will bear an invariable 

 quantitative relation to that and to each other : thus if hydro- 

 gen be chosen as 1, oxygen will be 8, chlorine will be 36 ; 

 that is, oxygen will unite with hydrogen in the proportion of 

 8 parts by weight to 1, while chlorine will unite with hydro- 

 gen in the proportion of 36 to 1, or with oxygen in the pro- 



