405 



(fig. 4) shows us, tliat sucli pofenlial is rendered less negative by 

 increasing mercur)» content. 



no 



2% 



N0I3HG 



X 



Fig. 4. 



Ho 



Finally we must consider a remarkable phenoitienDu to which 

 brief reference has already been made. 



If we add a little HgCl, in an aqueous solution of MgSO, or of 

 MgCl, in which there is a magnesium electrode, there is an im- 

 modiate fine deposit of metallic mercury on the electrode whose 

 potential becomes less negative. 



As follows from the formula 



Mg,:;lMgV + 2ö.s 



it it It 



MgL:;!: MgL + 2(9l and 2 (9l + HgL'-^ HgL 



Tiie precipitations of mercury proves tiiat mercury ions penetrate 

 the surrounding liquid layer and that these on arrival combine with 

 electrons, thereby disturbing the heterogenous equilibrium with the 

 result that electrons and magnesium ions enter the solution. 



It must also be observed that in consequence of the hydrolysis 

 in the magnesium salt solution to which no acid has been added 

 the magnesium electrode will contain dissolved Mg(OH), and will 

 conseqiienty behave inertly, so that by sending ions and electrons 

 into solution, the potential of magnesium will be altered in the 

 directio)! of that of the noble metals. 



The experiment mentioned liere is very important; it shows in 

 the first place that the magnesium electrode notwithstanding its non 



