[Snip3r]

We have 2 samples of some unknown white crystalline substance. Substances are dissolved in water.

To first sample we add 0.1 M HCl, but we do not see any change.
Then we add H2S and we acidified solution. However, we do not see any change.
Then we neutralize solution with ammonia.
To solution we add ammonium sulfide - on the begining white precipitate formed, but in excess of the reagent, the precipitate dissolves.

To second sample we add BaCl2 instead of HCl, but nothing happens.
We acidified solution with 0.1 M diluted nitric acid - there is no change.
Then we add AgNO3 and we get a white precipitate.
FeCl3 do not show up any change.

What is the test substance?

[Arkcon]

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