687 



For this purpose besides a Ni-electrode, also a Pt-electrode 

 covered with Pt-black was placed in the same Ni-nitrate-solution, 

 and then after addition of lir-water the jtotential of the Ni' and of 

 the Bromine-electrode was determined. 



Then the following was found : 



Ni and Pt-electrodes immerged in 100 cin3 N. Ni (N03)2-solution. 



Observations 



Potential of the Ni-elec- 

 trode with respect to 

 VioN. Calomel electrode 



Potential of theBr-elec- 

 trode with respect to 

 '/lo N. Calomel electrode 



4 



1 „ „Na-thiosulphate 



+ 0,41 „ 

 - 0.43 „ 



> 0,05 „ 



> - 0,84 „ 



+ 0,75 „ 

 - 0,04 „ 



> - 0,04 „ 

 >-0,79 „ 



Of an unassailable metal which behaves as bromine electrode it 

 may be expected according to the formula : 



V, 



met. 



V,,:, =/\ = L, -f 0,058 /o^' 



Cb,-' 



that the addition of the first small quantity of bromine will give 

 rise to a considerable increase of the potential difference, while a 

 subsequent increase of the bromine concentration must exercise a 

 much smaller influence. Our bromine electrode very clearly exhibited 

 this behaviour ; the first 10 drops of brominewater made the potential 

 rise 0,85 Volt, whereas the subsequent addition of 1 cm'' resp. 3 cm' 

 of bromine water no longer practically changed the potential. 

 Increase of the Br'-ion-concentration must lower the potential differ- 

 ence of the bromine electrodes again, and this too was observed. 

 By the addition of 1 cm' of N. KBr-solution the potential fell 0.04 

 Volt. That this lowering is not greater is owing to this that during 

 the action of Bromine on nickel l)romine ions had already been 

 formed. 



In conclusion we I'emoved all the bromine by addition of Na- 



1) This negative value must be altiibutcd to tlie catalytic influence exerleJ by 

 KBr in the preceding experiment. 



