The melting point is the temp. At which a substance changes from a solid into a liquid.  The melting points of different substances vary greatly- the higher the point, the highter the temp. Needed; for example Tungsten melts at 3410 degrees Celsius.  The melting point of a material depends partly on whether the material is a pure substance or a mixture.  A pure substance is either a pure element, such as iron, or a simple compound, such as water.  A mixture consists of two or more substances that are not chemically combined- the Tungsten mentioned above.  Note: Some solids do not melt when heated- instead they change directly from a solid to a gas.  Such substances as arsenic, dry ice, and iodine go through this process, which is called sublimation.
