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Carbon Dioxide (CO2) can solidify when cooled below -78 °C, in this state it is known as dry ice. When heated to atmospheric pressure, it passes directly to the gaseous state, without passing through the liquid (sublimation). For CO2 to become liquid, a pressure greater than 5 atmospheres is required. When warm air is blown over dry ice, a dense white cloud forms at ground level, an effect often used in theaters. Its sublimation temperature is 194.7 K (-78.5 °C; -109.2 °F) at Earth's atmospheric pressure. However, its use must be done with caution, as direct contact with the extremely cold solid can cause frostbite. While generally not toxic, if released indoors it can lead to hypercapnia (abnormally high levels of carbon dioxide in the blood).
