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Chemistry. — ''On the introduction of the conception of the solu- 

 hility of metal ions /rith electromotive equilibrium." By Dr. 

 A. Smits. (Communicated bv Prof. H. W. Bakhuis Roozeboom). 



(Communicated in the meeting of April 27, 1906.) . 



If a bar of NaCl is placed in pure water or in a dilute solution, 

 the NaCl-molecules will pass into the surrounding liquid, till an 

 equilibrium has been established ; then the moleiadar thermodynamic 

 potential of the Na CI in the bar has become equal to that of the 

 Ka CI in the solution. 



As known, this equilibrium of saturation, represented by the equation : 



ftNaCI = ftNaCl 



is characterized by the fact that per second an equal number of 

 molecules pass from the bar into the solution, as from the solution 

 into the bar. 



We shall call this equilibrium a purely chemical equilibrium. It 

 is true that in solution the Na Cl-molecules split up partially into 

 particles charged either with positive or negative electricity, which 

 are in equilibrium with the unsplit molecules, but for the hetero- 

 geneous equilibrium solid-liquid under consideration this is not of 

 direct importance. 



If, however, we immerge a metal e. g. Zn into a solution of a 

 salt of this metal, e. g. ZnSO^, we observe a phenomenon strongly 

 deviating from the one just discussed, which according to our present 

 ideas may be accounted for by the fact that a metal does not send 

 out into the solution electrically neutral molecules as a salt, but 

 exclusively ions with a positive charge. 



If the particles emitted by the bar of zinc were electrically 7ieutral, 

 then the zinc would continue to be dissolved till the molecuhir 

 thermodynamic potential of. the zinc in the bar of zinc had become 

 equal to that of the zinc in the solution, in which case the equation : 



^zn — f* zn 



would hold. 



This, however, not being the case, and the emitted Z/i-particles 

 being electro-positive, an equilibrium is reached lorn/ before the 

 thermodynamic potential of the zinc-particles with the positive electric 

 charge in the solution has become equal to that of the zinc in 

 the bar of zinc with the negative electric charge. That in spite of 

 this an equilibrium is possible, is due to the fact that an electrical 

 phenomenon acts in conjunction with the chemical phenomenon. 



