Coefficient of Expansion

The coefficient of linear expansion is the increase per unit length of a body when its temperature is raised from 0° to 1o C. If Lt be the length at temperature to and Lo that at temperature 0°, then Lt=Lo (1+ at ) in which a is the coefficient of expansion. In this expre ion 1+ at is called the "expansion factor." can be worked together in places subject to wide range of temperature. Few substances have negative expansion coefficients, notably the iodides of lead and silver, and water from 0° to 4o C. In crystals the expansion is usually different along the different crystalline axes. All gases have approximately the same coefficient of expansion (viz., 0.003665 or), so that if the pre ure be kept constant the volume of a ma of gas at to is given by the expre ion V-Vo (1+0.003665 t) in which Vo is its volume at 0°. Expansion of liquids may be said to be of two kinds, apparent or real. The former is the apparent increase of volume in a ve el which expands also, though to a le extent, than the contained fluid. By real expansion is meant the true expansion of the fluid without reference to the containing ve el. For wrought iron and steel its value ranges from 0.0000065 to 0.000075. In continuous bridges and fixed metallic arches the stre es due to changes of temperature are often large and must be carefully provided for.