• 2,010 g of P₂O₅
• 4,300 g of 85% H₃PO₄
• 10 mg CrO₃
• 3 ml H₂O₂

1. Slowly dissolve the 2,010g P₂O₅ in the 4,300 g 85% H₃PO₄ in a 4 liter beaker
2. Add 10 mg of CrO₃; cover the solution and heat at 200 °C for 7 hours
3. Add 3 ml of H₂O₂ and heat at 220 °C for an additional 4.5 hours.
4. Let it cool overnight.
5. Check to make sure the specific gravity is between 1.90 and 1.92. If not, either add water or more P₂O₅ and reheat.
6. Pour and store in brown glass bottles with caps containing conical plastic inserts for tight sealing. Coplen et al. (1983) recommend storing acid one month prior to using it.