ELECTUOMOTIVE l-'OUCES IN THE VOLTAIC CELL. 



475 



atcr or 

 itiou of 

 plates 

 . on tlic 

 tcs ; for 

 ,ed coii- 



aud and 

 .M.F. of 



divided 



Ha effect 

 jpresents 

 , ; at tlio 

 ,f can be 

 1 olectro- 

 le electric 

 called the 



lents, gold 

 Dcvs being 



N AUt.' 



Vi.lts 



With surfiue 

 strongly 

 scratcli''! 

 bv ruoMii',; 

 with I'liu'iy. 



or ill !'>'""■ "' 

 the last <a><s 

 with<'l"ti>"r 

 tiltiT i>!n"''' 



•H7 

 •2- 



+ •or. 

 + •07 



.:-•() 1 



t in tho i'PPi'- 



■ f„r in yi'f""'- 

 attl.eSwan^e;. 



, which rt'lat.-^ 

 upk^tc couipc''- 

 sm-omenls vvcvo 

 :neutwithtl.o|^' 

 01 with vfMi ' 



Ld until rciW' 



4. Meanwhile some experimenters, starting with a belief in the chemi- 

 cal origin of the Yolta effect, hud made experiments suji'iosed to support 

 this view. Mr. J. Brown, of Belfast, in 1878,' repeated Tliomson's divided 

 ring experiment, as well as Kohlransch's condenser experiment, in other 

 gases than air ; and found a very decided difference, and even a reversal 

 of sign, when sulphuretted hydrogen was substituted for air. The metals 

 Ihown used Avere copper and iruu, and he obtaiued a one centimetre 

 • lellection in the direction indicating iron + in air, while in S llj ho 

 obtaiued a o centimetre defection indicating that iron was — . On 

 leadmitting air the deilection again reversed, and so on, until the cojiper 

 coated itself with a blue film of sulphide, when the dctlection became 

 undecided, owing, as Brown supposes, to ' the cessation of chemical 

 action. ' 



!'iu. 8.— Mr. .T. linnvn's Arrangement for observiuf; the Volta Et?ect in difTcront 

 fin MS by sir William Thomson's ilL'tliod of a bimetallic ring with an oleetritied 

 needle hangini,' over it. 



In IftSl he observed a time change (decrease) of the Volta effect at a 

 eojiper-zinc junction, and reckoned that at the first instant after cleaning 

 the potential difference would be as high as '0 Daniell, ' which,' he says, 

 'ngrecs with J. Thomscn's determination of the difference of the heats of 

 <'onibustion of zinc and copper and oxygen.' He here gives a hint of holding 



i'apcr liad appeared in the Journal dc P/n/Kir/vr, ^lay 1 880. Fig. 1 sufliiuently exhibits 

 ^ii' WillianiV arrangement. In a post.-<eri])t art' described a few additional experi- 

 'ii'iits (it tliu same kind as tliose j)ublished in 1881 b\- (Schultze-Iiergc, in which a 

 I'latinui:! plate is .soaked for a certain time in dry liydrogen or oxygen, and then 

 "^('ilin the Volta condenser. The observation is made that merely soaking a plate in 

 -as is tuore etl'eetive than electroplating it with the same gas with an K.II.F. of 

 nvfilt. 



' J. Brown : P/iil. Mag., August 1878, Feb. 18711, and JIarch 1881 ; see also Brit. 

 •V.SSOC., Tnins. of Sects., 1881, and Electrician, vol. vii. p. 105. 



