When using stock solutions from the refrigerator or any stock solution that has been standing for some time, be sure to thoroughly mix the stock solution before use. Storing stock solutions in the refrigerator can result in condensation forming on the inside upper portion of the bottle. If this condensation falls into the stock solution it will create a heterogeneous stock concentration which in turn could make reproducing the experiment difficult. Condensation can occur with any sealed container when there is a temperature change in the environment. So it is possible for this phenomena to occur with room temperature stored stocks if the temperature in the room changes significantly. To avoid such problems it is generally good technique to mix crystallization reagents prior to pipetting.