Potassium antimonyl tartrate trihydrate, also known as tartar emetic, is a specialty chemical reagent used in analytical chemistry, particularly as a component in the molybdenum blue method for the determination of phosphorus in water and environmental samples. It facilitates color development in the presence of ammonium molybdate and a reducing agent. Additionally, it is employed as a mordant in the textile industry to enhance dye adhesion and fixation on fabrics. It also serves as a catalyst in certain oxidation reactions and in the synthesis of other antimony compounds. Historically, it was used in medicine as an emetic to induce vomiting and for treating parasitic infections such as schistosomiasis, but these applications have been largely discontinued due to its high toxicity and the availability of safer alternatives.