Phosphomolybdotungstic Reagent

Lithium and sodium molybdotungstophosphate solution.

Folin Ciocalteau phenol reagent of commerce.

Dissolve 100 g of sodium tungstate and 25 g of sodium molybdate in 700 mL of water, add 100 mL of hydrochloric acid and 50 mL of orthophosphoric acid and heat the mixture under a reflux condenser for 10 hours. Add 150 g of lithium sulfate, 50 mL of water and 0.2 mL of bromine and boil to remove excess bromine (about 15 minutes), cool, dilute to 1000 mL with water and filter. The reagent should be yellow in colour. If it acquires a greenish tint, it is unsatisfactory for use but may be regenerated by boiling with 0.2 mL of bromine. Care must be taken to remove excess bromine by boiling.

Store at 2° to 8°.