236 MICHAEL FARADAY — HIS LIFE AND WORKS. 



generated hy the chemical action which produces the direct decomposition of an 

 equal quantity of the same, or of a cliemically equivalent quantity of some other 

 body. He is thus led to pay attention to the theory of the pile, and to recog- 

 nize that the power of this apparatus originates in chemical action, and not in 

 the contact of two heterogeneous metals — a contact which is not necessary 

 either to produce a spark or to cause a chemical decomposition. 



He establishes, in the first place, that, either to effect a decomposition or to 

 produce a spark, a plate of zinc immersed in acidulated water is sufficient with- 

 out its being necessary to bring the zinc into contact with any other metal. He 

 shows that in every pile the presence of an electrolyte (that is to say, a liquid 

 susceptible of being decomposed) is indispensable for the evolution of elec- 

 tricity. Then, distinguishing in the electricity generated the intensity (or the 

 tension) and the quantity, he studies the circuuistances, de ending eitlier'on the 

 nature of the chemical action or the number of voltaic pairs associated, which 

 exert an influence on these two characters of the cuixent. In a word, he estab- 

 lishes such a correlation between that which occurs in the interior of a pile, and 

 that which takes place in the electrolyte interposed between the poles of this 

 pile, that it is impossible not to admit (with him) that electrolytic decomposi- 

 tion is nothing but a form of chemical aflinity transferred from the pile into the 

 electrolyte deconq^osed. 



Wishing to ol)tain an idea of the quantity of electricity which is associated 

 with the particles of_ which matter is composed, he endeavors to estimate that 

 which is necessary for the decomposition of a grain of water, regarding it, as he 

 is justified in doing, as equivalent to that produced by the direct chemical 

 action (of the acidulated water upon the zinc) which decomposes this grain of 

 water. He arrives at this incredible result, namely : tlMit this quantity of elec- 

 tricity, appreciated by the heat evolved by it in traversing a fine platinum wire, 

 is supeiior to that manifested in 800,000 discharges of a battery of Leydcn jars, 

 charged l)y thirty turns of a powerful plate-machine, and consequently equiva- 

 lent to that constituting a violent flash of lightning. 



The researches of which I have been speaking were made in 1833, 1834, 

 and 1835. I had previousl}^ paid attention to the same questions, and had 

 arrived l)y somewhat different methods at the same conclusion with Faraday, 

 namely: that it is in chemical action that resides the origin of the evolution of 

 electricity in the voltaic pile. Faraday frequently alludes to my investigations 

 in a very kind manner ; and subsequently (in 1840) he wrote me a letter in 

 which he said that, being a thorough adherent of the chemical theory, he had 

 just attacked the question directly, as I had already done, by demonstrating that 

 contact alone, if not accompanied by chemical action, is not a source of elec- 

 tricity. The memoir in which he probes this question to the bottom is the last 

 which he devoted to this department of electricity. In it, by means of a multi- 

 tude of ingenious experiments, he demonstrates that the presence of an electro- 

 lyte (that is to say, of a liquid which is at once a compound and a conductor of 

 electricity) is indispensable for the production of electricity in a voltaic couple; 

 he varies his experiments in a thousand ways, sometimes b}^ exhausting the 

 number of chemical compoimds employed as electrolytes, son;ietimes by the inter- 

 vention of temperatm-e or of other agents ; and he concludes by showing by 

 general considerations the improbability of the existence of a force of contact. 



We may say that this last work, a ]n-ecious supplement to the preceding ones, 

 has rendered perfectly evident the truth of the chemical theory. This theory, 

 foreseen by Wollastou and Fabroni, but opposed by most of the physicists of 

 the earh' part of the present centmy, had found a powerful argument in its favor 

 in the beautiful experiments of the elder Becquerel upon the electricity developed 

 by chemical actions. It was then (from 1825 to 1835) that, profiting by these 

 experiments, and seeking, on my own part, to make others of the same kind 

 although in a slightly different direction, I published several memou's to support 



