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

In halide anion analysis $AgN{O}_3$ added in Carius method to detect halide anion.

$$\begin{gathered} {\mathrm{AgNO}}_3(\mathrm{aq}.)+{\mathrm{Cl}}^{-}\to \underset{\mathrm{White}}{\mathrm{AgCl}\left(\mathrm{s}\right)} \\ {\mathrm{AgNO}}_3(\mathrm{aq}.)+{\mathrm{Br}}^{-}\to \underset{\mathrm{pale} \mathrm{yellow}}{\mathrm{AgBr}\left(\mathrm{s}\right)} \\ {\mathrm{AgNO}}_3(\mathrm{aq}.)+{\mathrm{l}}^{-}\to \underset{\mathrm{yellow}}{\mathrm{Agl}\left(\mathrm{s}\right)} \end{gathered}$$