Spiro[3H-2,1-benzoxathiole-3,9'-[9H]xanthene]-3',4',5',6'-tetrol, 1,1-dioxide

UsesThe white powdery crystal was made by the superheating of gallic acid. Pyrogallic acid, popularly known as pyro, is one of the earliest developers and its use has spanned three centuries. It was first used in an acid state to physically develop wet collodion negatives. When silver bromide gelatin plates were adopted pyro was used again but in an alkaline state for chemical development. It was used throughout the 20th century and often chosen for the peculiar yellow stain it imparted to gelatin negatives.

UsesPyrogallol Red is a complexometric indicator for the metal elements molybdenum and copper. Dyes and metabolites.