Desiccator cabinets provide dry storage for critical low-humidity environment requirements. Even the brightly colored desiccator cabinets provide interior visibility for supervising sensitive samples without exposure. Stainless steel storage cabinets may come either fixed or adjustable in different quantities. Optimum air circulation is achieved with perforated shelving. Vacuum models may include hygrometers for continual moisture monitoring. Desiccator storage cabinets must be set up, so that appropriate nitrogen flows out all moisture- and contamination-laden air. Because nitrogen has lower specific gravity than air, it is introduced into the upper section of the desiccator; the inert gas is then purged out of the bottom. While capacities and dimensions vary, the compact designs of nonelectric and automatic desiccators are easy to stack and may fit in refrigerators.