It is difficult to make a general statement concerning how often the molecular sieve should be replaced, because this is dependent on the humidity in the laboratory. Our experience has shown us that replacement every six weeks is appropriate in the presence of medium humidity. An increase in drift indicates that the leak-tightness of the cell should be inspected and that the molecular sieve should possibly be replaced.
Tip: Write the date on which you have last replaced the molecular sieve on the glass of the drying tube. In this way, you will always know when the next replacement is due.