A common procedure for increasing the moisture content of air is to bubble it through a column of water. Assume the air bubbles to be spheres of radius \(r_{o}=\) \(1 \mathrm{~mm}\) and to be in thermal equilibrium with the water at \(25^{\circ} \mathrm{C}\). How long should the bubbles remain in the water to achieve a vapor concentration at the center that is \(90 \%\) of the maximum possible (saturated) concentration? The air is dry when it enters the water.