Planck's Other Quanta: Corpuscular Electrodiffusion
  When B\"acklund transformations are applied repeatedly to any solution of the nonlinear equations describing electrodiffusion through a liquid junction separating two infinite well-stirred layers, they give rise to quantized ionic fluxes across the junction. A particular exact solution is shown to imply that these fluxes consist of quanta of electric charge. 
L. Bass and A.J. Bracken
math-ph math.MP nlin.SI