White, monoclinic crystal or powder. To the eye, the skin, the mucous membrane has the stimulation function, may pollute the water source. Decomposition by high heat produces toxic sulfide fumes. In industry, it is mainly used in the production of cellulose sulfite esters, sodium thiosulfate, organic chemicals, bleaching fabrics, etc. . It is also used as reducing agent, preservative, dechlorination agent, etc. .