(Ie siilfjile (Ie ciiixrc duns ruiili-c. ('e (lis|)(isitif ma paiMi (loimer (ies 

 i-êsiiltals plus ('oiislaiils (jiio les aiitros." 



It .seciiis lo MS strange tliat llie E. M. F. should he liiveii to ^ ,\^, 

 millivolt. All authors who up to the pi'oseiit luivo made a study 

 of the I)AMKiJ,-eell have ))oiiited out h(»\v dilKicidt it is to ohtaiii 

 ('oiistaul values with sueli eelis. For iiistaiiee, the E. M. F. is in a 

 high degree dependent oji the nature of the eop])er or ziju* electrode. 

 For particulars in tliis direction we refer to the i-esearches of Aj.deu 

 Wright ^). 



Ill coiniection \vitli the measurements under cojisideration tlie 

 following taille of Fi,KMiN(i's will he fouml interesting: 



K. M . F. of (I ct'iitt/ii Damkm.wvV/. 



Copper, pcrleclly pure, iiiioxidised 1.072 Volt 



„ slightly oxidised, hrowii s|K>ts l.()7<) ,/ 



„ more oxidised 1.082 ,/ 



;/ co\ei-('d with dai'k hrown oxide lilm 1.089 tr 



II cleaned. replate<l with fresh piiddsh electro-surface 1.072 // 



4. In re|>eating ('iiArniKK's measui-ements it is of the greatest 

 importance to have the determinations mutually comparable; eiTors 

 caused l»y an unlike nature of the electrodes ha<l to be carefully 

 excluded. 



As negative electrodes we used pure zinc amalgam (Ipart of zinc 

 to 1) parts of mei-ciiry) as used in the ('i.akk standard-cell. The zijic 

 was a very |)nre specimen frimi AIkkck of Darmstadt in which ii-on 

 was not even delectable. The mei-cury was lirst shaken with nitric 

 acid and then distilled twice in vacuum acc(n'ding to Hulett's ^) 

 method. As we know, the potential dilference between this amalgam 

 and pure zinc is very small. Previous experiments by one of us") 

 iiave shown that this dilference is only 0.00048 volt, at 0'^ and 

 0.000570 volt, at 25°. 



As positive electrode we used at lirst a thick wii*e of j)ui*e coj>|»er. 



The copper sul|)hate solution in the diflerent cells was jirepared 



') Pliilosophical magazine (5), 13, :>0r) (18S:>); Fleming, ibid. (.")\ 20, 12(5 (18S5). 

 St. Lindeck, Zeit.'^dif. fiif Instruinentfiikniulc 12, 17 (IS'.»i2). (loinp. also Cauiiart, 

 Primary Batteries (Huston 1S".I'.)). l/ilteratnre up to ISUli in: Wieuemann, die Lehre 

 von der Elektrieiliit. (Brannseliweig 1SÏK}). pag, 798. 



2) Zeitscln-. fur pliys. Chemie 33, GU (1900). 



3) Cohen, Zeitschr. fur phys. Chemie 34, 619 (1900). 



