r 



GALVANISM. 359 



In all cases in which bodies combine chemically, they are found to have 

 contrary electrical energies. Examples are numerous. "The bodies in the 

 first of the following columns are all negative with respect to those which are 

 opposite to them in the second : 



Oxygen Zinc. 



Oxygen Silver. 



Copper Zinc. 



Gold Mercury. 



Metals Sulphur. 



Acids Alkalies. 



The constituent particles of each of these substances when brought into 

 contact, being naturally in opposite states of electricity, will, according to thn 

 common laws of electricity, attract each other. If they be solid bodies, the 

 force of aggregation of these particles, which constitutes the character of their 

 solidity, will resist their separation ; but if the constituent particles be free to 

 move and intermingle among each other, then the attraction due to their proper 

 electricity will take effect, combination will ensue, the conditions of equilibri- 

 um of the electrical forces will be satisfied, and all signs of free electricity 

 will cease. 



In support of this hypothesis it is argued, that when, by artificial means, the 

 elements of any compound are invested with electricity contrary to that which 

 naturally belongs to them, such electricity exerting a force contrary to that 

 which produces or maintains, or tends to produce or maintain their combina- 

 tion, that combination, if it exist, is dissolved, and if it tend to be effected, is 

 prevented. 



Thus zinc is one of the metals which have the strongest natural tendency to 

 combine with oxygen. Let it be charged with negative electricity, and its ox- 

 ydation becomes impossible, because, according to Davy's hypothesis, the pos- 

 itive electricity naturally belonging to its molecules is neutralized by the nega- 

 tive electricity artificially imparted to it. Again, silver is one of the metals 

 which have the least tendency to unite with oxygen ; but let silver be charged 

 with positive electricity, and it oxydates easily. The positive electricity sup- 

 plied artificially gives increased power to that which the particles possess, so 

 as to augment their attraction for the negative particles of the oxygen. 



The cases of bodies which have contrary electrical energies, either in rela- 

 tion to a third body or in relation to each other, are therefore simple, and easily 

 apprehended. But two bodies may have electrical energies with respect to a 

 third, the same in kind, but unequal in degree. Thus all acids are negative in 

 relation to metals, but any two of them will be unequally so ; and in like man- 

 ner all alkalies are positive, but unequally positive in relation to metals. Sul- 

 phuric acid is more negative than muriatic acid in relation to lead, and potash is 

 mure positive than soda in relation to tin. Such bodies compared with each 

 other may have the same or contrary electrical energies, or they may be neu- 

 tral. Sulphur and the alkalies are positive in relation to the metals, but their 

 electrical energies with respect to each other are contrary. 



The evolution of heat and light, which commonly attends the restoration of 

 electrical equilibrium between two bodies strongly charged with electricity by 

 artificial means, is brought by Davy in further support of his theory. It is well 

 known that heat and light also result from intense chemical action. When the 

 electric current passes through bodies, the electricity being then incomparably 

 more feeble in intensity than that which proceeds from the common machine, 

 heat is evolved without light, and the degree of this heat is, catcris paribns, 

 augmented as the intensity of the electricity is increased. In the same man- 

 ner in slow chemical combinations there is an increase of temperature without ! 

 luminous appearance. 



Heat, by producing fusion, and liberating the constituent particles of bodies 

 from their natural aggregation, has been regarded as being conducive to their < 



