Applicable to products having a normal composition for which the molar ratio NaF/AlF3 is equal to about 3. Dissolution of a test portion in concentrated suphuric acid and elimination of hydrogen fluoride. Treatment with hydrochloric acid and water. Atomization of the solution into an acetylene measurement of the absorption of the 309.3 nm line emitted by an aluminium hollow cathode lamp. Has also been approved by the IUPAC.