Used as a photographic developer due to its strong reducing properties, especially in black-and-white film processing. Commonly employed in gas analysis to absorb oxygen in respirometers and oxygen-free environments. Acts as a reducing agent in analytical chemistry for detecting the presence of metal ions. Utilized in the preparation of certain dyes and in the synthesis of antioxidants. Also finds use in hair dyes and skin conditioning agents in cosmetics, though limited due to potential irritation. Historically used as a biological stain in microscopy to enhance contrast in tissue samples.