In Carius method, halogen containing organic compound is heated with fuming nitric acid in the presence of:

Organic compound is heated with fuming nitric acid in the presence of silver nitrate in carius method. Lunar caustic $\left({\mathrm{AgNO}}_3\right)$ is used as reagent hare to distinguish ${\mathrm{Cl}}^{-},\mathrm{Br}$ and ${\mathrm{I}}^{-}$ respectively as follows.

${\mathrm{Cl}}^{-}\left(\mathrm{aq}\right)\stackrel{{\mathrm{AgNO}}_3}{⟶}\mathrm{AgCl}{\downarrow }_{\mathrm{ppt}}$ white

${\mathrm{Br}}^{-}\left(\mathrm{aq}\right)\stackrel{{\mathrm{AgNO}}_3}{⟶}\mathrm{AgBr}{\downarrow }_{\mathrm{ppt}}$ pale yellow

${\mathrm{I}}^{-}\left(\mathrm{aq}\right)\stackrel{{\mathrm{AgNO}}_3}{⟶}\mathrm{AgI}{\downarrow }_{\mathrm{ppt}}$ Dark yellow