Sodium Thiosulfate (redirected from Hyposulfite of Soda)

sodium thiosulfate, Na₂S₂O₃, colorless crystalline compound that is more familiar as the pentahydrate, Na₂S₂O₃·5H₂O, an efflorescent, monoclinic crystalline substance also called sodium hyposulfite or "hypo." Sodium thiosulfate is readily soluble in water and is a mild reducing agent. Because it dissolves silver salts, its major use is in photography for developing film. It is also used in chrome-tanning leather and in chemical manufacture. Sodium thiosulfate is produced chiefly from liquid waste products of sodium sulfide or sulfur dye manufacture. It is also produced from sodium carbonate, sulfur dioxide, and sulfur by a process that involves several steps.

---

sodium thiosulfate [′sōd·ē·əm ‚thī·ə′səl‚fāt]

(inorganic chemistry)

Na₂S₂O₃·5H₂O White, translucent crystals or powder with a melting point of 48°C; soluble in water and oil of turpentine; used as a fixing agent in photography, for extracting silver from ore, in medicine, and as a sequestrant in food. Also known as sodium hyposulfite; sodium subsulfite.

---

Sodium Thiosulfate 

(also sodium hyposulfite, N₂S₂O₃), colorless crystals freely soluble in water (41.2 percent by weight at 20°C, 69.9 percent at 80°C). Sodium thiosulfate forms several crystal hydrates, of which only the pentahydrate Na₂S₂O₃·5H₂O is used in industry and in the laboratory.

Sodium thiosulfate is obtained by boiling a solution of sodium sulfite with sulfur in powder form: Na₂SO₃ + S = Na₂S₂O₃. It is used as a fixing agent in photography and for determinations of iodine in iodometry; it also finds use in the textile industry and in other fields. In medicine, sodium thiosulfate is used as a desensitizer, an antiphlogistic, and an antitoxic agent. The antitoxic effect is based on the ability of sodium thiosulfate to form nontoxic compounds, including sulfites with arsenic, thallium, mercury, and lead and rhodanides with hydrocyanic acid. Sodium thiosulfate is usually administered intravenously (as a 10–30 percent solution) to those suffering from arthritis, dermatosis, poisoning, and illnesses related to allergies.