The following equations, due to Kremser, give the fraction not absorbed, , or not stripped, , as a function of the effective absorption, , or stripping factor, :

,

,

where and are the liquid and vapor rate down and up the tower and is the equilibrium constant of the key component (for example in the feed gas that is to be absorbed). Both equations assume that the key component mole fraction in the absorbent and stripping agent is zero.

This Demonstration plots these functions and allows the user to (1) vary the number of equilibrium stages, ; and (2) get values of the fraction not absorbed or not stripped for an effective absorption or stripping factor by simply clicking on the blue curve. The coordinates of the selected point on the curve will appear in black.