Sodium Pyrophosphate: Disodium Phosphate Heated to 300 °C

Sodium pyrophosphate is a white salt that dissolves to an alkaline solution. Thorpe's Dictionary (1913) makes it in two easy stages: neutralise phosphoric acid with soda until alkaline and crystallise disodium phosphate, then heat the dried salt to 300 °C, when it gives off water and turns into the pyrophosphate. The picture: our diagram.