Used primarily in analytical chemistry for qualitative inorganic analysis, especially to precipitate metal sulfides from solution. Commonly applied in laboratory settings to separate and identify metal ions in mixtures, such as in the analysis of cations from different groups (e.g., HgS, PbS, CdS). Also employed in the production of certain dyes, pharmaceuticals, and photographic chemicals. In the leather tanning industry, it aids in depilation (hair removal) and softening hides. Occasionally used in engraving processes. Due to its strong odor (from H₂S and NH₃) and instability, it is typically prepared and used in situ or handled under controlled conditions, often as a freshly made solution.