Chromotropic acid disodium salt dihydrate is widely used as a reagent in analytical chemistry for the detection and quantification of formaldehyde. It reacts with formaldehyde in acidic conditions to form a purple-colored complex, which can be measured spectrophotometrically, making it a key component in environmental and industrial monitoring to assess formaldehyde levels in air, water, and other samples. Additionally, it is employed in histological staining techniques to identify specific tissue components, aiding in medical and biological research. Its stability and sensitivity make it a valuable tool in both qualitative and quantitative analyses.