Explanation:
Double salt:
A double salt is a type of salt that is formed by the combination of two different salts. These salts are formed when two different salts crystallize out of a solution together, forming a single crystal structure. Double salts have a unique crystal structure and are different from their constituent salts.

KCl.MgCl2.6H2O:
KCl.MgCl2.6H2O is a double salt. It is formed by the combination of two different salts, potassium chloride (KCl) and magnesium chloride (MgCl2), along with six water molecules (6H2O). The formula of this double salt indicates that it contains one molecule of KCl and one molecule of MgCl2, along with six molecules of water.

Properties of KCl.MgCl2.6H2O:
KCl.MgCl2.6H2O is a white crystalline solid that is soluble in water. It has a molar mass of 234.06 g/mol and a density of 1.88 g/cm3. This double salt has a melting point of 708°C and a boiling point of 1412°C.

Uses of KCl.MgCl2.6H2O:
KCl.MgCl2.6H2O is used in the production of magnesium metal. It is also used in the manufacture of fireproof materials, as a flux in metallurgy, and as a de-icing agent for roads and runways.

Conclusion:
In conclusion, KCl.MgCl2.6H2O is a double salt that is formed by the combination of potassium chloride and magnesium chloride along with six water molecules. It has various industrial applications and is an important compound in the field of metallurgy.