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92 Bull. Hist, Chem. 11 9 ll t Ch 11 (1991 tn t nd rnt" School Sci. Rev,, 84, 66, -5 3 frn 1 pp -91 2. A lt "On Eltrt Extd b th Mr Cntt f 33. Ibid., pp 1-13 Cndtn Sbtn f ffrnt Knd" Phil. Trans. Roy. Soc,, 34. Ibid., pp 1-15 800, 90, 3-31 35 C Sddn "rd Exprnt n Eltrhtr" 3 W hln nd A Crll "Ant f th Eltr- School Sci, Rev., 64, 46, 68 - 7 l r Glvn Apprt f S Alx lt nd Exprnt 3 frn 1 p 17 rfrd th Same", Nicholson' s J,, 800, 4, 179-17 37 S. hnl lltn "Iprvd l fr th 4. . St nd M Orn d Electrochemistry, Past and rd" J. Chem. Educ., 60, 37 5 Present, ACS Whntn C 199 5 Williams, Michael Faraday, Yr 195 p 9 John T. Stock is Professor Emeritus of Chemistry at the 6. C d Grtth "Mrnr r l ddptn d l University of Connecticut, Storrs, CT 06269. He is interested t d rp ll tnt n dltn ld d lltrt in the history of electrochemistry and chemical instrumenta- lvn" Ann, Chim., 80b, 58, 5-7 tion and is coeditor, along with M. V. Orna, of "Electrochem- 7 v n v d TheCollectedWorks ofSir Humphry istry, Past and Present", Davy, Bart, Sth Eldr C ndn 1 p 1 8. Ibid,, p 19 9. Ibid,, p 10. Ibid., p9 FROM ELECTROCHEMICAL 11 A l v "Mr r l-n d phnn EQUIVALENCY TO A MOLE OF prnt lltrt vlt dn p trvr l ELECTRONS: THE EVOLUTION ndtr ld" Ann. Chim. Phys., 82, 28, 19-1 OF THE FARADAY 1 A l v "Anl d rntn dtrnnt l n t l ntnt d rnt ltr dn n lnt vltl" Marcy Hamby Towns and Derek A. Davenport, Purdue Ann. Chim. Phys,, 828, 37, 5 -286. University 13 A l v "hrh r l d lltrt vltl" Mem. Soc. Phys. Géneve, 828, 4, 5 In the 1988 edition of Quantities, Units and Symbols in 1 M rd Experimental Researches in Electricity, J. M Physical Chemistry, (1) we find the following recommended nt ndn 191 p (h lt dtn f th thr-vl values for the Avogadro constant (L or NA), the elementary t pblhd b Qrth ndn 139-155 charge (e), and the Faraday constant (F): 15. Ibid., p. 15 16. Ibid., p 17 = 137(3 x 13 l 17. Ibid., p 9 = 117733(9 x 1-9 C 1 St nd hn The Development of Instruments = 9539(9 x 1 C to Measure Electric Current, Sn M ndn 193 19 W th "On th Eltt f hrd f Gl th S Simple multiplication of the first two of these yields, with f th Mt Ufl Appltn f th rprt t rn ln" suitably arcane adjustments of limits of error, the third, i,e, Phil. Trans. Roy. Soc., 80, 120, 15 - 222, 20. St "Sr Chrl rnn Grdn f th NAe = F Flame", Bull. Sci. Instr. Soc., 8, 3 - 6. 1 frn 1 p 31 Further examination reveals that the recommended values for 22. A "Mhl rd rt f Eltr- both NA and e are independent of any electrochemical meas- htr" n rfrn Chp 3 urement (2), It would seem that the long and fruitful marriage 3 frn 1 p 9 of electrochemistry and the Faraday has come to an amicable 24. Ibid., p35 parting of the ways, a parting endorsed by the units of C 25. Ibid., p5 mol-', A brief history of the "Faraday" will be given in terms 26. Ibid., p of a concept (however named), a value (however measured) 27. Ibid,, p 5 and a name (by whomever dubbed). 28. Ibid., p 53 Faraday's establishment of the law(s) of electrolysis - 29. Ibid,, p "electrochemical equivalents coincide, and are the same with 30. Ibid,, p ordinary chemical equivalents" - has been widely studied (3- 31 S Arrhn "Obr d tn dr n Wr ldtn 8). What has seldom been remarked is the sparsity of examples Stff" Phys. Chem., 88, I, 31- and the semiquantitative nature of much of the data upon which ll t Ch 11 (1991 93 his great quantitative generalization was based. In Faraday's table of relative electrochemical equivalents of some 60 anions and cations (including "quinia", "cinchona" and "morphia"!) less than ten were substantiated by direct electrochemical means; the remainder are "chemical results of other philoso- phers in whom I could repose more confidence, as to these points, than in myself' (9). He adds: I b lld t xpr hp tht th ndvr ll l b t t tbl f ea, nd nt yoeica, ltrhl vlnt; fr hll l vrrn th ft nd l ll ht nd nn f th nld ln drtl n r pth In the prefiguring of this passage in the Diary we find the more admonitory: "I must keep my researches really Experimental and not let them deserve any where the character of hypotheti- cal imaginations" (10), As to precision, the Diary gives the values 59.805, 56,833, 57,9 and 59,57 for the relative electrochemical equivalent of tin (11), (Faraday was charmingly cavalier when it came to significant figures.) In the published paper he states (12): hn rdr nll (lft nd Mhl rd (rht r 13 It nt ftn I hv btnd n rdn n nbr [th th ptd hl vlnt] nr tht I hv jt td h tn f rdnr ttr r thrd nd f pr r nt t vr f th fr xprnt v 553 th ltrhl thr n nt f ft hh jtf n blvn tht th vlnt f tn t f ttr r n ndd r td th ltrl pr t hh th thr t trn lt nd nt Similarly for lead one finds such varied values as 105,11, th thr tl hl ffnt 97.26, 101.29, 93.17 and 80,51 (13), Admittedly the experi- mental difficulties of working with molten salts were large but However, Faraday, like many of his contemporaries, was at as a later worker in the field somewhat ruefully remarked (14): best a reluctant atomist, a view he passionately believed to be fraught with hypothetical, if not quite horrible, imaginings, h xprnt pn hh h bd h l f ltrl r n One wonders what he would make of recent work on "electro- ntrtn lltrtn f th n nht hh ld rd t chemistry at single-molecule sites" (16). A later passage finds nnt nrl l pn ht td t b vr r nd him turning aside atomistic temptation (17): nrt dt h hrn hh th thr f th dfnt vltn nd th "On the Absolute Quantity of Electricity Associated with vlnt dfnt tn f ltrt ntrd nt th td the Particles or Atoms of Matter- - so runs the heading for the thr f dfnt prprtn nd ltr-hl ffnt vr concluding section of Faraday's magisterial Seventh Series of rt Ardn t t th vlnt ht f bd r pl Experimental Researches in Electricity. The opening para- th ntt f th hh ntn l ntt f ltrt graph might seem to raise our Whiggish hopes (15): r hv ntrll l ltr pr; t bn th EECICIY hh eemies th vlnt nbr ecause t dtrn th h thr f dfnt ltrltl r ltrhl tn ppr bnn fr Or f dpt th t thr r phrl t t th dtl pn th asoue quaiy f ltrt thn th t f bd hh r vlnt t h thr n thr r ltr pr blnn t dffrnt bd It pbl rdnr hl tn hv l ntt f ltrt ntrll prhp t p n th pnt tht ttn nlf bnd td th th t I t nf I jl f th tr ht prnt ft ll tn nd t t ll pbl nd aom fr thh t vr t tl f t t vr dfflt t prhp ld b plt nt t rn pn th bjt Althh fr lr d f thr ntr pll hn pnd bd r n nthn f ht n t t nnt rt frn ndr ndrtn d f ll prtl hh rprnt t t th nd; nd thh r n l f nt rtr nrn f ltrt Faraday's electrochemical researches, with their accompa- t b nbl t hthr t prtlr ttr r ttr r r nying nomenclature, quickly found their way into some of the 9 ll t Ch 11 (1991 more adventurous textbooks of the time (18, 19) but for over th vr rn tht n th prnt prftl frd tt f r 30 years no one probed much more deeply into their ultimate d bt ltrt th thr f ltrl r nt- significance than had Faraday himself. ftr The closest, and incomparably the most rewarding, reading of Faraday's Experimental Researches in Electricity was that Maxwell makes the characteristic point that: of James Clerk Maxwell. As befits one of the founding fathers of kinetic molecular theory Maxwell was reasonably comfort- th rdnr hl vlnt hvr r th mere nr- able with the concept of a molecule while remaining something l rt n hh th btn bn hr th ltrh- of an agnostic on the reality of Daltonian atoms. In 1873 (the l vlnt r ntt f ttr f dtrnt ntd year that saw the publication of his A Treatise on Electricity dpndn n th dfntn f th nt f ltrt and Magnetism) Maxwell gave a lecture on "Molecules" at the Bradford meeting of the British Association for the Advance- Ah, the physicist's "mere"! He continues: ment of Science (20), After paying tribute to his predecessors - "The lecture in which Democritus explained the atomic It thrfr xtrl ntrl t pp tht th rrnt f th n theory to his fellow citizens of Abdera realized, not in golden r nvtn rrnt f ltrt nd n prtlr tht vr opinions only, but in golden talents, a sum hardly equalled even ll f th tn hrd th rtn fxd ntt f in America" - Maxwell goes on to propound the conventional ptv ltrt hh th fr th ll f ll tn wisdom of physicists of his time (20): nd tht vr ll f th nn hrd th n l ntt f ntv ltrt Evr btn pl r pnd h t n ll If th ll b dvdd t prt r ll f dffrnt btn Maxwell, still an adherent of the "two fluid" theory, then issues r btn fr tht f hh th hl ll An t the caution (21): f thr h thn t b ll f n lntr btn Sn thrfr vr ll nt n t bt vr t t f n nd tht th ll f th n thn th ll I hll th rd ll th r nrl tr ltrlt r tll hrd th rtn dfnt ntt f ltrt ptv nd ntv tht th ltrlt rrnt Later in the lecture he turns to electrolysis but does not pursue pl rrnt f nvtn fnd tht th tptn hpth the question of a molecular charge (20): ld nt vr dfflt rnd If ntd f nl ll ndr n bl f ll ntttn n ltr- W hv n t t d r thn ntn tht t ndrfl hl vlnt f th n thn th ttl hr f ll th llr tn hh lld ltrl r n ltr ll hv n n nt f ltrt ptv r rrnt pn thrh dltd tr nd n xn t ntv ppr t n ltrd nd hdrn t th thr In th p W d nt t n h n ll thr r n n btn th tr prftl l nd t t ppt rrnt f ltrhl vlnt f n btn bt th llr thr xn nd f hdrn t b pn thrh t Eltrl f htr hh rrbrtd b n phl ndrtn thrfr nd f dffn td b ltrtv fr pp tht th nbr f ll n n ltrhl v- lnt th fr ll btn W thrfr n llr The reasons are not far to seek (20): pltn tht th nbr f ll n n ltr- hl vlnt nbr nnn t prnt bt hh hr nthr t f ntt hh t pl n th thrd hrftr fnd n t dtrn rn b r nld f th nthr pr n th frt Eh ll thrfr n bn lbrtd fr th tt f rn nr pprxt n th nd bt nl t f th ntr bntn prt th hr h ntd 1/ nd f prbbl njtr h r th blt f ll ptv fr th tn nd ntv fr th nn h dfnt t blt dtr nd th nbr f ll n b ntt f ltrt hll ll th llr hr If t r nttr nn t ld b th t ntrl nt f ltrt In the Treatise Maxwell addresses the question of molecular Maxwell's speculations are leading us close to macroscopic/ charge directly in the short chapter on "Electrolysis" (21): microscopic concept of the Faraday, G.
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