Silica gel

Silica gel is a granular, porous form of silica made synthetically from sodium silicate. It was invented at the Johns Hopkins University, Baltimore, Maryland in the 1920s. Its high porosity, around 800 m²/g, allows it to adsorb water readily, making it useful as a desiccant (drying agent). It can reduce the relative humidity in a closed space to around 40%. Once saturated with water, the gel can be regenerated (dried) by heating it to 150°C (300°F). The gel is non-toxic, non-flammable and chemically highly inert. It is sometimes supplied mixed with a moisture indicator, which is a chemical that changes colour when damp.