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Carius tube

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 :

  1. What is the significance of using $\ce{HNO3}$ ? Can we carry out oxidation with other acids like $\ce{H2SO4}$?
  2. 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?
  3. 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.

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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.

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