Salt is a chemical compound with a number of interesting properties:
- Crystals or white crystalline powder.
- Transparent and colourless in crystalline form – rather like ice.
- Crystallises in the isometric system, usually in the form of cubes.
- Soluble in water (35.6g/100g at 0°C and 39.2g/100g at 100°).
- Slightly soluble in alcohol, but insoluble in concentrated hydrochloric acid.
- Melts at 801°C and begins to vaporize at temperatures just slightly above this boiling point 1,413°C.
- Hardness of 2.5 on the MOH scale of hardness.
- Specific gravity of 2.165.
- Non-combustible – low toxicity.
- Hygroscopic – absorbs moisture from damp atmospheres above 75 per cent relative humidity – below this, it will dry out.
In its natural form, salt often includes traces of magnesium chloride, magnesium sulphate, magnesium bromide, and others. These impurities can tint the otherwise transparent crystals, yellow, red, blue or purple.