SCIENCE. 



183 



electro-magnetic problem. The present development of 

 science, however, shows, as I think, a state of things very 

 favorable to the hope that Faraday's fundamental con- 

 ceptions may in the immediate future receive general as- 

 sent. His theory, indeed, is the only existing one which 

 is at the same time in perfect harmony with the facts ob- 

 served, and which at least does not lead into any contra- 

 diction against the general axioms of dynamics. 



It is not at all necessary to accept any definite opinion 

 about the ultimate nature of the agent which we call 

 electricity. 



Faraday himself avoided as much as he could giving 

 any affirmative assertion regarding this problem, although 

 he did not conceal his disinclination to believe in the ex- 

 istence of two opposite electric fluids. 



For our own discussion of the electro-chemical phe- 

 nomena, to which we shall turn now, I beg permission 

 to use the language of the old dualistic theory, because 

 we shall have to speak principally on relations of 

 quantity. 



I now turn to the second fundamental problem aimed 

 at by Faraday, the connection between electric and 

 chemical force. Already, before Faraday went to work, 

 an elaborate electro-chemical theory had been established 

 by the renowned Swedish chemist, Berzelius, which 

 formed the connecting-link of the great work of his life, 

 the systematisation of the chemical knowledge of his 

 time. His starting point was the series into which Volta 

 had arranged the metals according to the electric tension 

 which they exhibit after contact with each other, a 

 fundamental point which Faraday's experiment contra- 

 dicted with the supposition that the quantity of elec- 

 tricity collected in each atom was dependent on their 

 mutual electro-chemical differences, which he considered 

 as the cause of their apparently greater chemical affinity. 

 But although the fundamental conceptions of Berzelius's 

 theory have been forsaken, chemists have not ceased to 

 speak of positive and negative constituents of a com- 

 pound body. N'dbody can overlook that such a contrast 

 of qualities, as was expressed in Berzelius's theory, really 

 exists, well developed at the extremities, less evident in 

 the middle terms of the series, playing an important part 

 in all chemical actions, although often subordinated to 

 other influences. 



When Faraday began to study the phenomena of de- 

 composition by the galvanic current, which of course 

 were considered by Berzelius as one of the firmest sup- 

 ports of his theory, he put a very simple question ; the 

 first question, indeed, which every chemist speculating 

 about electrolysis ought to have answered. He asked, 

 What is the quantity of electrolytic decomposition if the 

 same quantity of electricity is sent through several elec- 

 trolytic cells ? By this investigation he discovered 

 that most important law, generally known under his 

 name, but called by him the law of definite electrolytic 

 action. 



Faraday concluded from his experiments that a defi- 

 nite quantity of electricity cannot pass a voltametric cell 

 containing acidulated water between electrodes of plati- 

 num without setting free at the negative electrode a 

 corresponding definite amount of hydrogen, and at the 

 positive electrode the equivalent quantity of oxygen, one 

 atom of oxygen for every pair of atoms of hydrogen. If 

 instead of hydrogen any other element capable of sub- 

 stituting hydiogen is separated from the electrolyte, this 

 is done also in a quantity exactly equivalent to the quan- 

 tity of hydrogen which would have been evolved by the 

 same electric current. 



Since that time our experimental methods and our 

 knowledge of the laws of electrical phenomena have 

 made enormous progress, and a great many obstacles 

 have now been removed which entangled every one of 

 Faraday's steps, and obliged him to fight with the con- 

 fused ideas and ill-applied theoretical conceptions of 

 some of his contemporaries. We need not hesitate to 



say that the more experimental methods were refined, 

 the more the exactness and generality of Faraday's law 

 was confirmed. 



In the beginning Berzelius and the adherents of Volta's 

 original theory of galvanism, based on the effects of 

 metallic contact, raised many objections against Faraday's 

 law. By the combination of Nobili's astatic pairs of 

 magnetic needles with Schweigger's multiplicator, a coil 

 of copper wire with numerous circumvolutions, galvano- 

 meters became so delicate that the electro-chemical 

 equivalent of the smaller currents they indicated was 

 imperceptible for all chemical methods. With the 

 newest galvanometers you can very well observe currents 

 which would want to last a century before decomposing 

 one milligram of water, the smallest quantity which is 

 usually weighed on chemical balances. You see that if 

 such a current lasts only some seconds or some minutes, 

 there is not the slightest hope to discover its products of 

 decomposition by chemical analysis. And even if it 

 should last a longtime the feeble quantities of hydrogen 

 collected at the negative electrode can vanish, because 

 they combine with the traces of atmospheric oxygen 

 absorbed by the liquid. Under such conditions a feeble 

 current may continue as long as you like without pro- 

 ducing any visible trace of electrolysis, even not of 

 galvanic polarisation, the appearance of which can be 

 used as an indication of previous electrolysis. Galvanic 

 polarisation, as ycu know, is an altered state of the 

 metallic plates which have been used as electrodes during 

 the decomposition of an electrolyte. Polarised electrodes, 

 when connected by a galvanometer, give a current which 

 they did not give before being polarised. By this current 

 the plates are discharged again and returned to their 

 original state of equality. 



This depolarising current is indeed a most delicate 

 means of discovering previous decomposition. I have 

 really ascertained that under favorable conditions one 

 can observe the polarisation produced during some sec- 

 onds by a current which decomposes one milligram of 

 water in a century. 



Products of decomposition cannot appear at the elec- 

 trodes without motions of the constituent molecules of 

 the electrolyte throughout the whole length of the liquid. 

 This subject has been studied very carefully, and for a 

 great number of liquids, by Prof. Hittorff, of Miinster, 

 and Prof. G. Wiedemann, of Leipsic. 



Prof. F. Kohlrauseh, of Wiirzburg, has brought to light 

 the very important fact that in diluted solutions of salts, 

 including hydrates of acids and hydrates of caustic alka- 

 lies, every atom under the influence of currents of the 

 same density moves on with its own peculiar velocity, in- 

 dependently of other atoms moving at the same time in 

 the same or in opposite directions. The total amount of 

 chemical motion in every section of the fluid is repre- 

 sented by the sum of the equivalents of the cation gone 

 forwards and of the anion gone backwards, in the same 

 way as in the dualistic theory of electricity, and the total 

 amount of electricity flowing through a section of the 

 conductor corresponds to the sum of positive electricity 

 going forwards and negative electricity going backwards. 



This established, Faraday's law tells us that through 

 each section of an electrolytic conductor we have always 

 equivalent electrical and chemical motion. The same 

 definite quantity of either positive or negative electricity 

 moves always with each uni' alent ion, or with every unit 

 of affinity of a multivalent ion, and accompanies it during 

 all its motions through the interior of the electrolytic 

 fluid. This we may call the electric charge of the atom. 



Now the most startling result, perhaps, of Faraday's 

 law is this : If we accept the hypothesis that the elemen- 

 tary substances are composed of atoms we cannot avoid 

 concluding that electricity also, positive as well as nega- 

 tive, is divided into definite elementary portions, which 

 behave like atoms of electricity. As long as it moves 

 about on the electrolytic liquid each atom remains united 



