The temperature at which a liquid changes to a gas (vapor) at normal atmospheric pressure. A more specific definition of boiling point is the temperature at which the vapor pressure of a liquid is equal to the external pressure. The normal boiling point is the temperature at which the liquid boils when the external pressure is one atmosphere (760 torr = 760 mm Hg = 1 atm = 101.3 kPa = 14.7 psi). Additional Info: How can one determine the temperature at which water boils? After all, bubbles start to appear in water well below the known boiling point of 100 degrees C (212°F). The answer lies in monitoring the temperature of the material with time. When the boiling point is reached, the temperature will not rise again until all of the liquid has evaporated. This is due to the high heat capacity of water (it takes much more energy to convert water from liquid to gas than it does to raise the temperature of liquid water). Of course, if water is heated under pressure this may raise the boiling point above its normal boiling point of 100 degrees C. Likewise, the addition of a solute may also raise the boiling point, a phenomenon called boiling point elevation (See Further Reading below for more information). MSDS Relevance: Knowing the boiling point of a substance is an important consideration for storage. For example, storing a chemical with a boiling point of 50 oC (122 oF) in direct sunlight or next to a boiler could cause the material to completely vaporize and/or result in a fire or explosion. Items with a low boiling point generally have a high vapor pressure. Containers of such material can build up signicant pressure even when they are below their boiling point. Likewise, low-boiling materials easily produce large amounts of vapor which can be flammable or even explosive. See also: Evaporation Rate, Freezing Point, Vapor Pressure