Dark green crystals or powder; soluble in water (deep blue solution), alcohol, and chloroform; C₁₆H₁₈N₃SCl⋅3H₂O used in medicine; (C₁₆H₁₈N₃SCl)₂⋅ZnCl₂⋅H₂O used as a textile dye, biological stain, and indicator. Also known as methylthionine chloride.