Phosphoric Acid: Red Phosphorus Dissolved in Concentrated Nitric Acid (Watson)

Orthophosphoric acid, H3PO4, from amorphous phosphorus and nitric acid (Watson, 1892), as Thorpe's Dictionary (1913) gives it: heated with concentrated nitric acid the phosphorus slowly dissolves with red fumes. The solution is evaporated with repeated additions of nitric acid until no more red fumes come off, so that no phosphorous acid is left. The red fumes are poisonous: fume hood, respirator. The picture: our diagram.