362 



GALVANISM. 



tive ; but in a Voltaic combination of zinc water and dilute nitric acid, the side 

 of the zinc exposed to the acid is negative. The chemical action of the acid 

 on the zinc being in both cases the feame, it is argued that if the electric cur- 

 rents originated at the common surface of the zinc and acid, which they would 

 do if chemical change were their primary source, the direction of the currents 

 would be the same, instead of being contrary in the two cases. 



As a further argument against the chemical theory of the pile, Davy main- 

 tained that in mere cases of chemical change, electricity is never exhibited; 

 and endeavored to support this position by the examples of iron burned in oxy- 

 gen, the deflagration of nitre and charcoal, the combination of solid potash and 

 sulphuric, acid, and other chemical actions. Subsequent investigation, how- 

 ever, has shown that this principle is not tenable, and that chemical change is 

 attended with the evolution of electricity. 



With Davy, as with Franklin, application ever trod closely on the heels of 

 discovery. The same memoir which disclosed the brilliant series of discov- 

 eries of which we have here attempted to give a brief analysis, also indicated 

 the vast applications of which they were susceptible, in the further investiga- 

 tions of the laws of nature, and in arts conducive to the economy of life. The 

 detection of acid and alkaline matter in mineral, animal, and vegetable sub- 

 stances, and their separation from them, was sufficiently obvious. A piece of 

 muscular fibre, through which the electric current was transmitted for five days, 

 was rendered dry and hard. Potash, soda, ammonia, lime, and oxide of iron, 

 were carried from it by the negative current ; and the three mineral acids, with 

 phosphoric acid, passed off with the positive current. From a laurel leaf the 

 negative current carried green coloring matter, resin, alkali, and lime, and the 

 positive current took vegetable prussic acid. Mint gave potash and lime with 

 the negative, and an acid matter with the positive current. The flesh of the 

 living hand, carefully washed in pure water, gave a mixture of muriatic, sul- 

 phuric, and phosphoric acids with the positive current, and fixed alkaline mat- 

 ter with the negative current. This fact accounts for the acid and alkaline 

 tastes first observed by Sulzer given by metals in contact. 



By converting the processes, the Voltaic currents may be made the means 

 of introducing acids and alkaline or metallic principles, into the animal and 

 vegetable system. This idea has since been realized in medical practice by 

 some physicians. 



In the experiments hitherto made, the acids and alkalies themselves were 

 not decomposed. The history of scientific discovery affords no more remark- 

 able example of that instinctive foresight which enables the philosopher to 

 suspect the direction in which truth lies, and prompts him in the selection of 

 subjects of inquiry, than is apparent in comparing Davy's present guesses with 

 the result of his subsequent researches. " These facts," says he, " induce us 

 to hope that this new mode of analysis may lead to the discovery of the true 

 elements of bodies, if the materials acted on be employed in a certain state of 

 concentration, and the electricity be sufficiently exalted. For if chemical 

 union be of the nature which I have ventured to suppose, however strong the 

 natural electrical energies of the elements of bodies may be, there is yet every 

 probability of a limit to their strength : whereas the powers of our artificial 

 instruments seem capable of indefinite increase." 



How soon he led the way toward the realization of this magnificent conjec- 

 ture will presently appear. 



Sudden and violent derangements of the electrical equilibrium of the ele- 

 ments of our system are manifested in other cases besides the glaring intt 

 offered by atmospheric phenomena. The electrical appearances which pre- 

 cede and attend earthquakes and volcanic eruptions admit of easy explanation 



