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Latent Heat

Latent Heat. When raised to a sufficiently high temperature many solids can be converted into liquids. During the transition the temperature (which is styled the melting- or freezing-point) remains constant, provided the pressure is unaltered, but heat is absorbed by the body. This heat, which produces change of state, and not rise of temperature, is known as the latent heat of fusion, and is generally defined as the amount of heat required to change one gramme of the solid substance into its liquid form. A similar absorption of heat without rise of temperature takes place at the boiling-point, when a liquid is converted into its vapour. This is called the latent heat of vaporisation, and is defined in similar units. The latent heat of water is 79, and of steam is 536, that number of C.G.S. units of heat being required to convert one gramme of ice into water, or water into steam. This heat is given out again when the process is reversed - i.e. the vapour liquefied or the liquid frozen.