Sodium pyrosulfate is an inorganic compound with the chemical formula Na₂S₂O₇. It is a white, crystalline solid that is highly hygroscopic and soluble in water, where it hydrolyzes to form sodium bisulfate (NaHSO₄). It is often prepared by the dehydration of sodium bisulfate. Its primary application is as a strong acidic flux in analytical chemistry, particularly for the fusion (decomposition) of refractory minerals, ores, and insoluble oxides (e.g., iron, aluminum, titanium oxides) prior to elemental analysis. It acts as a high-temperature sulfating agent, converting metal oxides into soluble sulfates. Industrially, it serves as a catalyst or acidic reagent in various chemical processes, including organic synthesis (e.g., sulfonation, condensation reactions) and as a component in metal surface treatment and cleaning formulations. As a strong acid and oxidant, it requires careful handling with appropriate personal protective equipment to avoid skin and eye irritation or respiratory issues upon dust inhalation. It should be stored in a cool, dry place in tightly sealed containers to prevent moisture absorption.