Desiccators are large jars with a shelf inside and a lid. Below the shelf, desiccators are kept. These are substances which absorb moisture and so remove humidity in an enclosed space. Such substances include silica gel, calcium sulphate and montmorillonite clay.
Substances which need to be dried should be placed on the shelf in open topped containers to allow all moisture to escape. The lid of the desiccator should be sealed tightly using vaseline or liquid paraffin which will ensure a near air-tight seal.
A piece of cobalt chloride paper should be kept inside the desiccator to alert you if either moisture gets in or if the desiccant reaches saturation point, in which case it should be removed and replaced with a fresh desiccant.
Vacuum pumps can be used with some newer desiccators to remove the air inside, these allow substances to dry much faster.