Ammonium sulfide, with the chemical formula (NH4)2S, is a chemical compound composed of ammonium ions (NH4+) and sulfide ions (S^2-). It is a white to yellowish solid that is highly soluble in water, producing a colorless to yellow solution.

Ammonium sulfide is not a stable compound and is mainly used as an aqueous solution rather than a solid. It is a reagent commonly used in laboratory settings and certain industrial processes. Some key properties and uses of ammonium sulfide include:

1. Analytical Chemistry: Ammonium sulfide is used as a reagent in analytical chemistry, particularly in qualitative analysis. It is used to detect and identify certain metal ions, such as copper, nickel, and silver, by forming characteristic precipitates or color changes.
2. Photography: Historically, ammonium sulfide was used in photography as a photographic fixer to remove unexposed silver halide from photographic films or papers.
3. Leather Tanning: Ammonium sulfide is sometimes used in leather tanning processes as a reducing agent to remove hair and other unwanted materials from animal hides.
4. Laboratory Reducing Agent: It is used as a reducing agent in various chemical reactions in the laboratory.

Ammonium sulfide is considered a hazardous chemical due to the release of toxic hydrogen sulfide gas (H2S) when it reacts with acids or acidic substances. Hydrogen sulfide is highly toxic and can be harmful upon inhalation or skin contact. Therefore, proper safety measures, such as good ventilation and the use of personal protective equipment, should be followed when working with ammonium sulfide or its solutions in the laboratory or industrial settings.