Excessive moisture buildup within a waveguide can cause arcing inside the waveguide itself, damaging the power amplifier feeding it. Silica gel may also be used to keep the relative humidity inside a high-frequency radio or satellite transmission system waveguide as low as possible. By adding sachets of silica gel, these items can be preserved longer. Condensation may also damage other items like electronics and may speed the decomposition of chemicals, such as those in vitamin pills. In many items, from leather to pepperoni, moisture encourages the growth of mold and spoilage. Some types of silica gel will "pop" when exposed to enough water. Once saturated with water, the gel can be regenerated by heating to 150 ☌ (300 ☏) for 1.5 hours per liter of gel. Silica gel's high surface area (around 800 m²/g) allows it to adsorb water readily, making it useful as a desiccant. 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. The substance was known to exist as early as the 1640s as a scientific curiosity.
Prior to that, it was used in World War I for the absorption of vapors and gases in gas mask canisters. Patrick at Johns Hopkins University, Baltimore, Maryland in 1919. Silica gel was patented by chemistry professor Walter A. The food-grade desiccant, however, should not include any poisons that could cause long-term harm if consumed in the quantities normally included with the items of food. Given that silica gel strongly adsorbs moisture and may contain poisonous additives (such as color indicators, fungicides, or pesticides), packets of silica gel usually bear warnings for the user not to eat the contents but to throw the packets away.