to the Theory of Electro capillarity. 



479 



solution of potassium chloride are immersed alloys of the 

 elements potassium and chlorine with substances that are 

 insoluble in water. The ionic solution pressures of the 

 alloys are equal to the osmotic pressure of the potassium 



and chlorine ions in the solution. The alloys are in elec- 

 trical contact with the mercury, and electromotive forces 

 can be inserted in the circuits thus formed at B and C. 

 The potential difference between the solution and the mer- 

 cury can be increased by removing from the solution small 

 amounts of ionic mercury and chlorine by means of the 

 circuit C. 



With this engine we perform the following reversible cycle 

 of operations, keeping the concentration of the potassium 

 chloride constant. 



I. We start with a negligible amount of mercury surface 

 in contact with the solution, the osmotic pressure of the 

 mercury ions being equal to the solution pressure of the 

 mercury. Mercurous chloride is withdrawn from the solu- 

 tion until the difference of potential between the solution 

 and the mercury has risen to V. The work performed in 

 this operation is in any case negligibly small, and is, more- 

 over, almost completely recovered in a subsequent operation. 

 After this operation there will be a negative charge on the 

 metal and a positive charge in the solution. 



II. The mercury surface is increased by unity. Now the 

 positive charge in the solution close to the surface of the 

 metal exists by reason of there being in that region a large 

 excess of potassium ions, a large deficiency of chlorine ions, 

 and a small excess of mercury ions. Therefore, if the con- 

 centration of the solution is kept constant as the surface 

 increases, potassium and mercury ions must be introduced 

 into the solution, and chlorine ions removed with the assistance 

 of the circuits B and G. As the potassium ions with their 

 positive charges enter the solution an equal amount of 

 negative electricity passes from K to A. Let the quantity 



