Step 1: Describe the test and its specificity.
The carbylamine reaction is a qualitative test specific to primary amines (both aliphatic and aromatic). Secondary and tertiary amines do not give this reaction, making it useful for distinguishing primary amines from others.
Step 2: State the reagents.
A primary amine is heated with chloroform ($CHCl_3$) and ethanolic potassium hydroxide ($KOH$).
Step 3: Explain the mechanism briefly.
The base generates dichlorocarbene ($:CCl_2$) from chloroform. The reactive carbene intermediate then adds to the primary amine nitrogen, and successive loss of two HCl molecules yields an isocyanide.
Step 4: State the product and observation.
The product is an isocyanide ($R$-$NC$), also called a carbylamine, which has an extremely foul, nauseating odour. The balanced equation is: $R$-$NH_2 + CHCl_3 + 3KOH \xrightarrow{\Delta} R$-$NC + 3KCl + 3H_2O$. The characteristic offensive smell confirms a primary amine.