170 



MATHEMATICAL AND PHYSICAL SCIENCE. 



[Diss. VI. 



(763.) 



Electro- 

 chemical 

 theory 

 Berzelius, 

 Hisinger 

 Davy's 

 first Bake- 

 rian lec- 

 ture. 



(764.) 

 Davy's sa- 

 gacious 

 Induction? 

 respecting 

 polar 

 forces. 



Electro-chemical Theory Decomposition of the 

 Alcalies. In 1804 Berzelius had published, in con- 

 junction with Hisinger, a paper on Electro-chemical 

 Decompositions, in which he insisted on the general 

 fact, that alcalies, earths, and combustible bodies seem 

 to be attracted to the negative pole, and oxygen and 

 acids to the positive. He also showed that the sub- 

 division of bodies thus obtained was only a relative 

 not an absolute one; for the same body may act 

 as a base to a second, and as an acid to a third. 

 But we must observe that results almost similar 

 were contained in the early papers of Davy, and 

 that Berzelius did not carry out his own principle 

 so far as to lead to any striking discovery between 

 1803 (when his experiments were made) and 1806 

 (the date of Davy's first Bakerian lecture), during 

 which time the science of Galvanism or Voltaism 

 made little real progress. The numerous experi- 

 menters engaged with it were baffled by the anoma- 

 lous chemical results obtained, and by the appearance 

 of decompositions under circumstances wholly unex- 

 pected, such as appeared to threaten the existence of 

 some of the best established chemical truths. The 

 chemical theory of the pile, at first so plausible, pre- 

 sented new difficulties, and Berzelius having for a 

 while defended it, returned to the simple contact 

 theory of Volta. It was then that Davy seriously 

 addressed himself to the subject, resolved to trace 

 to their source every chemical anomaly ; and this 

 he effected in a masterly manner in his Bakerian lec- 

 ture read before the Royal Society in 1806. In it he 

 traces the unaccountable results of his predecessors to 

 impurities in the materials used by them, or to those of 

 the vessels in which the decompositions were made ; 

 and he brings into a far distincter light than his pre- 

 decessors had done, the power of the galvanic circuit 

 to suspend or reverse the action of even powerful 

 chemical affinity ; " different bodies naturally pos- 

 sessed of chemical affinities appearing incapable of 

 combining or of remaining in combination when placed 

 in a state of electricity different from their natural 

 order." We here see the fundamental doctrine of 

 the electro- chemical theory, that all bodies possess 

 a place in the great scale of natural electrical rela- 

 tions to one another ; that chemical reactions are 

 intimately connected with this electric state, and are 

 suspended or reversed by its alteration. 



In the interpretation of those striking experi- 

 ments, in which he caused acids to pass to the posi- 

 tive pole of the battery through the midst of alcaline 

 solutions, and the converse, we find so close an ap- 

 proach to the theory of polar decomposition as enfor- 

 ced by the discoveries and reasoning of Mr Faraday, 

 that it seems impossible to deny to Davy the merit 

 of having first perceived these curious relations. 

 " It is very natural," he says, " to suppose that the 

 repellant and attractive energies are communicated 



from one particle to another particle of the same kind 

 so as to establish a conducting chain in the fluid, 

 and that the locomotion takes place in consequence ;" 

 and presently adds, " there may possibly be a succes- 

 sion of decompositions and recompositions through- 

 out the fluid" (p. 29). 1 He likewise shows (p. 21) 

 that the decomposing power does not reside in the 

 wire or pole, but may be extended indefinitively 

 through a fluid medium capable of conducting elec- 

 tricity. Mr Faraday's experiments, which led him to 

 discard the term pole, lead to the same conclusion, 

 and are of the same character. A few pages further 

 on in this same Bakerian lecture, Davy observes (p. 

 42), that " allowing that combination depends on a 

 balance of the natural electrical energies of bodies, 

 it is easy to conceive that a measure may be found 

 of the artificial energies as to intensity and quantity 

 capable of destroying this equilibrium ; and such a 

 measure would enable us to make a scale of electrical 

 powers corresponding to degrees of affinity." Here 

 we see the acute presentiment of the beautiful disco- 

 very of the definiteness of electrical decompositions ; 

 as in the concluding portion of the same remarkable 

 paper we find a clear anticipation* of natural elec- 

 trical currents to be discovered in mineral, and espe- 

 cially metalliferous deposits, since established by 

 Mr R. W. Fox, and of the agency of feeble electric 

 energies, long continued, in effecting geological chan- 

 ges, and in producing insoluble combinations of earths 

 and metals, so ingeniously confirmed by the beautiful 

 and direct experiments of Becquerel. 



The sequel to this remarkable paper, read to the (765.) 

 Royal Society in November 18 07, contained the splen- Second Ba 

 did application of the principle and methods which it j^e de- C ' 

 described, to the decomposition of the alcalies and to C0 mposi- 

 the disco very of their singular bases, substances po- tion of the 

 sessing the lustre and malleability of metals, yet so alcahei 

 light as to float upon water, and having the extraordi- 

 nary property of becoming inflamed in contact with 

 ice. Potassium was discovered in the Laboratory of 

 the Royal Institution on the 6th October 1807, and 

 sodium a few days later. The battery used con- 

 tained 250 pairs of plates of 6 and 4 inches square. 

 Such success was fitted to charm a disposition like 

 that of Davy, and more than reward him for all his 

 toils. To have discovered two new bodies, and 

 opened an entirely new field of wide chemical re- 

 search, would itself have been enough. But the 

 extraordinary properties of the new bases were such 

 as seemed to correspond to the lively imagination 

 of the Chemist who produced them, and to transport 

 him to an Aladdin's palace more brilliant than even 

 his fertile imagination had ever conceived. Yet it is 

 pleasing to remember that these popular discoveries Receives i 

 followed, at the interval of a year, the patient and ^insd" 

 able researches which led him to them, and which tute of 

 had already been rewarded, at a period of the bitter- France, 



1 Of the Bakerian Lecture, in his collected Works. 



