Sodium thiosulfate

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White, translucent, odorless crystals. Sodium hyposulfite, or hypo, is primarily used as a fixing agent in photographic developing baths to dissolve unchanged silver halides. It is also used as an antichlor to remove excess chloride ions from bleached papers and textiles. Sodium thiosulfate is used in the chrome tanning of leathers.

Synonyms and Related Terms

hypo; sodium hyposulfite; disodium thiosulfate; hyposulfite of soda; sodium subsulfite; Blankit; Sodothiol; antichlor; sodium thiosulphate (Br.)

Chemical structure

Sodium thiosulfate.jpg


  • May cause irritation by inhalation or contact.
  • Ingestion may cause diarrhea.
  • Used as an antidote for cyanide poisoning.
  • ThermoFisher: SDS

Physical and Chemical Properties

Soluble in water and ammonia solutions.

Composition Na2S2O3 - 5H2O
CAS 7772-98-7
Melting Point 48 C
Density 1.685 g/ml
Molecular Weight mol. wt. = 158.11
Boiling Point (dec)

Resources and Citations

  • G.S.Brady, Materials Handbook, McGraw-Hill Book Co., New York, 1971 Comment: p. 786
  • Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
  • Hermann Kuhn, Conservation and Restoration of Works of Art and Antiquities, Butterworths, London, 1986
  • Michael McCann, Artist Beware, Watson-Guptill Publications, New York City, 1979
  • Matt Roberts, Don Etherington, Bookbinding and the Conservation of Books: a Dictionary of Descriptive Terminology, U.S. Government Printing Office, Washington DC, 1982
  • Book and Paper Group, Paper Conservation Catalog, AIC, 1984, 1989
  • Marie Svoboda, Conservation Survey Index, unpublished, 1997
  • The Dictionary of Paper, American Paper Institute, New York, Fourth Edition, 1980
  • Van Nostrand's Scientific Encyclopedia, Douglas M. Considine (ed.), Van Nostrand Reinhold, New York, 1976
  • Random House, Webster's Encyclopedic Unabridged Dictionary of the English Language, Grammercy Book, New York, 1997
  • The Merck Index, Martha Windholz (ed.), Merck Research Labs, Rahway NJ, 10th edition, 1983 Comment: entry 8844
  • The American Heritage Dictionary or Encarta, via Microsoft Bookshelf 98, Microsoft Corp., 1998
  • Photographic chemicals at
  • Thomas B. Brill, Light Its Interaction with Art and Antiquities, Plenum Press, New York City, 1980