GENERAL SUMMARY. 227 



stitution of the exciting fluid, whatever that may be. To avoid 

 complication, attention has hitherto been confined to the action 

 of the primary affinity of the exciting acid (that of its salt-radical) 

 upon the zinc, but the secondary affinities of the accessory 

 constituents of the exciting acid must also be supposed to act 

 upon the positive metal, although in a subsidiary manner to the 

 primary affinity. 



In the constitution of many compound bodies, a provision for 

 the formation of new compounds is observed, similar to what is 

 now supposed to exist in the zinc. In the crystallized sulphate 

 of zinc itself, there is a provision, in the single constitutional 

 atom of water of that salt, for the formation, by replacement, of 

 the double sulphate of zinc and potash, and in the water of cry- 

 stallization of the same salt, provision for the formation of 

 various subsalts containing excess of oxide of zinc or ammonia, 

 by similar replacements. The assumed molecular structure of 

 the metal, thus leads to a farther development of the extending 

 law of substitution. 



The peculiarities of iron, by which it is enabled to resist amal- 

 gamation, to assume magnetism, to exhibit an indifference to 

 nitric acid in certain circumstances, must depend upon the 

 molecular structure of that metal, and are subjects which the 

 chemist approaches with advantage when unfettered by the 

 electrical hypothesis. 



GENERAL SUMMARY. 



1. No chemical affinity has been observed to act inductively, 

 but that kind which has been described as operating in the 

 voltaic circle. The affinity between two salts, the affinity of one 

 metal for another, of one metal for a free non-metallic element, 

 &c., appear to be incapable of acting in this way; or it may be 

 that we have not the means of observing the inductive mode of 

 action of these affinities. The action of the circles which have 

 been formed of organic matters, such as slices of brain and beet- 

 root, or the combinations of acid, alkali, and salts, employed by 

 Becquerel, are too minute and obscure, to interfere with this 

 general conclusion. That arrangement also of pairs of thin 

 discs of positive and negative metals, with paper between each 

 pair, which is known as the dry pile, acts only, it is admitted, 

 when damp, and therefore when oxidation of the positive metal 

 may occur. 



Q 2 



