melting point

Melting point is the specific temperature at which a solid turns into a liquid — and, like a fingerprint, it's a fixed, characteristic value for any given pure substance at normal atmospheric pressure.

• Because it's so consistent, scientists use melting point to help identify an unknown solid or check how pure a sample is — an impure substance usually melts over a range of temperatures instead of sharply at one point.
• Melting points vary enormously depending on how strongly a substance's particles attract each other — ice melts at a chilly 0°C, while tungsten, used in old light bulb filaments, holds its shape until over 3400°C.
• Not every solid has one clean melting point — materials like glass and wax soften gradually over a range of temperatures instead of melting sharply, because their particles aren't arranged as neatly as in substances like ice or iron.

Choosing the right material for a job — from a candle to a jet engine part — often comes down to knowing exactly where its melting point sits.