Desiccants are chemicals that absorb moisture. Anhydrous calcium chloride is a common one that can also be reactivated and then reused. The water absorbed by the desiccant can be removed by heating it to a high temperature until the water evaporates, leaving just calcium chloride behind.
Heat the oven to 300 degrees centigrade.
Place the wet desiccant in the glass dish.
Put on gloves and place the desiccant in the oven.
Allow the desiccant to cook for at least six hours. Some calcium chloride is laced with a dye, causing it to turn red when wet and blue when dry. Once the desiccant turns blue, it can be removed, even if it hasn't been in for six hours. Also, if it hasn't turned blue in six hours, allow more time.
Using the gloves, remove the hot desiccant and pour it into the desiccator. Put the top on and occasionally flush it with nitrogen as the desiccant cools.