Thiosulfate (S2O32−) is an oxyanion of sulfur prouced by the reaction of sulfite ions with elemental sulfur in boiling water. Thiosulfate occurs naturally in hot springs and geysers, and is produced by certain biochemical processes. It instantly dechlorinates water, and is notable for its use to halt bleaching in the paper-making industry. Thiosulfate is also useful in smelting silver ore, in producing leather goods, and to set dyes in textiles. Sodium thiosulfate was widely used to fix black and white photography negatives after the developing stage.