Sodium Thiosulfate: Soda and Sulphur Fusion (Thorpe, 1913)

A small batch of 'hypo' (photographic fixer) from soda and sulphur: dry sodium carbonate is fused with a third of its weight of flowers of sulphur in an open porcelain basin, stirred so air reaches every part, then dissolved, boiled with more sulphur and crystallised. The sodium sulphide formed first takes up oxygen from the air and turns, with a faint glow, into thiosulphate. Source: T. E. Thorpe, Dictionary of Applied Chemistry vol. V (1913), p. 29. Picture: the book's text.