History
The synthetic route for producing silica gel was patented by chemistry professor Walter A. Patrick at Johns Hopkins University, Baltimore, Maryland in 1919. It was used in World War I for the absorption of vapors and gases in gas mask canisters, as part of his patent. The substance was in existence as early as the 1640s as a scientific curiosity.[1]
In World War II, silica gel was indispensable in the war effort for keeping penicillin dry, protecting military equipment from moisture damage, as a fluid cracking catalyst for the production of high octane gasoline, and as a catalyst support for the manufacture of butadiene from ethanol, feedstock for the synthetic rubber program.

Silica gel's high surface area (around 800 m²/g) allows it to absorb water readily, making it useful as a desiccant (drying agent). Once saturated with water, the gel can be regenerated by heating it to 120 °C (250 °F) for two hours. Some types of silica gel will "pop" when exposed to enough water.