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

In the Carius method for the estimation of halogens in an organic compound, the compound is heated with fuming nitric acid in a sealed tube (Carius tube). The organic matter is oxidised and the halogen is converted to the corresponding halide ion (X$$^-$$).

Silver nitrate (AgNO$$_3$$) is added to the resulting solution. The halide ions react with $$Ag^+$$ to form an insoluble silver halide precipitate (AgCl, AgBr, or AgI), which is then filtered, washed, dried and weighed to determine the amount of halogen present.

Therefore, the Carius method uses fuming nitric acid in the presence of $$AgNO_3$$.