# How rate of absorption remains same throughout the process?

While reading surface chemistry, I got

Rate of adsorption is high at begining and then decreases till equilibrium is attained . On the other hand , rate of absorption remains same throughout the process .

Regarding adsorption I have no doubts as logically after some time there will be no surface area for upcoming molecules. But how the rate can be same in case of absorption ? Just if we take an example of cotton ball , it absorbs water and after some time being fully wet by water how further the rate of absorbing be same ? Please help if I am lacking somewhere in the concept ...

• Obtain some agar gel, phenolphthalein indicator, dilute $$\ce{HCl}$$ and dilute $$\ce{NaOH}$$ solution.
• Dissolve the agar in warm water, mixed with a little phenolphthalein indicator and a drop of $$\ce{HCl}$$, and pour into a vertical test-tube, leaving a few cm empty at top. Wait for the gel to cool to room temperature.
• Add a few ml of $$\ce{NaOH}$$ solution at the top.