Primary amines when heated with chloroform and alcoholic caustic potash give isocyanides (carbylamines) having very unpleasant smell which can be easily detected.
\(\underset{Ethyl\,amine}{C_2H_5NH_2}+CHCl_3+3KOH \longrightarrow \underset{Ethyl\,isocyanide}{C_2H_5NC}+3KCl+3H_2O\)
\(\underset{Aniline}{C_6H_5NH_2}+CHCl_3+3KOH \longrightarrow \underset {Phenyl\,isocyanide}{C_6H_5NC}+KCl +3H_2O\)