Spilltech ans5 acid neutralizing, sorb 5-gallon pail visible color change signifies complete neutralization of acids. Color indication initially indicates the strength (ph) of the acid: gold indicates a strong acid; yellow indicates a mild acid. When mixture turns purple a second time it has beenneutralized to a safe ph range which can then be cleaned up. Absorbs and solidifies liquids. Environmentally friendly. note: not for use with hydrofluoric acid.