( -to ) 



cell (l)eutsc'lies TelegTuphenelenieiit), as iioniuil cell a WESTON-cell 

 wiiicli was always kept in a Ihermostat at 25°. 



Ill this tlieniiostat was also j)lacc(l a Ci-akk normal cell to allow 

 comparison between the Jioi-mal elements. 



The rheostats used [2 rheostats of I'J'Jll.ll olims each Hartmanx 

 and Bkaun) were carefully compared with a third rheostat stajidar- 

 dised l»y the "Physikalisch-Technische Reichsanstalt." 



y. The measurements took j)lace as follows: after a cell had been 

 tilled with the rcipui-ed solutiojis it was (without the copper electrode) 

 placed in the thermostat at 15^. After havin<!; reached that temperature 

 the copi)ei" electrode was taken from the copi)er[)lating bath and after 

 having been treated as directed it was introduced throuüh the tube 

 into the solution. The tap was m)w opejied and the measurement 

 carried out; this lasted 1 or 2 minutes. When the tap had been 

 closed, the cell was taken from the tliermostat. The sidution in A 

 was then tested for copper, but as already stated not the slightest 

 trace of copper was found iji this part of the ap|)aratus. 



JO. As the measui-ements of Aldkk WnKHrr, Ft-kmin(t and Loru 

 lvAYT,i';i(;n -), which were done with faii-ly coiu*enti-ated solutions of 

 zinc sulj)hate had })ro\ed that the reju'oductioji of these cells to less 

 than 1 millivolt is almost impossibh* and as our own experieiu'cs had 

 shown us that with more dilute ziiu* sulphate solutioJis we get still 

 greater deviations, we ojdy give our measiu-cments in millivolts 

 although the method of measuring employed i-emlered the deterujina- 

 tion (d" tenths of millivolts (and less) quite |)ossible. 



As Chaudikh only gives one series of measuremeids we can say 

 nothing as to the i-eproduceableness of his cells. According to our 

 e.\|)erience no im|)ortance lU'ed be attached to statemeids of teidhs 

 of millivolts. Whether it would be possible to attain a greater accuracy 

 Avhen working with solutions quite free from air is a matter which 

 wc cannot go into any fiii'tlier as our results are (pute accui'ate 

 enough to conq)letely answer the (piestion in dispute"^). 



11. Before |»i-oceeding to comnuuncate our ligures we would 

 point out that a cell constructed according to the scheme: 



„.I I copi)er sulphate solution 



Zmc water ^ ^ . . ^,-r. copper 



saturated at 15° '^ 



cannot practically be classed among the reversible cells. 



1) Transacliüiis of the Royal Society ot London. Vol. 76, SOO (1886). 



3) See Ebeling, Wied. Annalen, 30, 530 (1887) and G. Meyer, ibid, 33, 265(1888). 



