What is Carbylamine reaction ? How is it used to distinguish primary amines from secondary and tertiary amines ?

Explanation

This reaction is given only by `1^(@)` amines (both aliphatic and aromatic)

If the given amine is a `1^(@)` amine, very bad smelling isocyanide or carbylamine is produced. This reaction is not given by `2^(@) and 3^(@)` amine.
Therefore, this reaction is used to distinguish `1^(@)` amines from `2^(@) and 3^(@)` amines.