Carius method for quantitative analysis of halogens Carius method: A known mass of an organic compound is heated with fuming nitric acid in the presence of silver nitrate contained in a hard glass tube known as Carius tube, (Fig.12.17) in a furnace


I want to know :


What is the significance of using $\ce{HNO3}$ ? Can we carry out oxidation with other acids like $\ce{H2SO4}$?
Why $\ce{AgNO3}$ is added to $\ce{HNO3}$ and not to the organic compound? Will it be wrong if I add $\ce{AgNO3}$ directly to the organic compound after it is subjected to fuming nitric acid?
Wouldn't precipitation of compounds other than that of halogens occur since we are carrying the reaction in a closed furnace?


Any help is greatly appreciated.
1) $\ce{HNO3}$ is a more oxidizing acid than $\ce{H2SO4}$.  

2) The silver nitrate would not dissolve well in the organic solution.

3) Sulfide is an example of something you might worry about interfering as it forms a very insoluble compound with silver. But silver sulfide and most anything else that might interfere will decompose in the fuming nitric acid.