This reagent is available commercially in a form ready for use.
Alternatively it may be prepared as follows: dissolve 100 g of sodium
tungstate, Na2WO4.2H2O, and 25 g of sodium molybdate, Na2MoO4.2H2O, in
700 mL of distilled water. Add 50 mL phosphoric acid 85% (20 =
1.71 g/mL), and 100 mL of concentrated hydrochloric acid (20 = 1.19 g/mL).
Bring to the boil and reflux for 10 hours. Then add 150 g of lithium sulfate,
Li2SO4.H2O, and a few drops of bromine and boil for 15 minutes. Allow to
cool and make up to one liter with distilled water.