This question was already asked and this was the answer that was posted:
"So basically, before you start the experiment the vapors have already formed, meaning that thermodynamic equilibrium has been achieved. Then you start bubbling through dry gas, which then mixes with the vapor gas already in the bubbles. If you set the gas flow appropriately, you get a near-equilibrium situation (see the graphic below) and the gas that exits the bulb assemply has exactly the same amount of vapor in it as the vapor "layer" (which can not be thought of as a layer anymore because of the bubbling) above the liquid surface.
We do not have an equilibrium situation, which is why so much care has to be taken that we get as close as possible to the equilibrium situation. (Also, we do not have a closed system, so everything starts to get slightly problematic at this point. But to a first degree of approximation, this will hold up fine.)" (For more, visit: How does Ostwald-Walker method work? )
My questions are:
1) What is this 'near' equilibrium situation that is created?
2) If dry air gets saturated when it passes through the solution bulbs, then how is it able to absorb more solvent vapours when it is passed through the solvent bulbs?