This standard specifies the method for the determination of free sulfur content by the potentiometric Titrimetric method, which is suitable for the determination of free sulfur content in raw rubber, mixed rubber and vulcanized rubber. A series of standard documents are quoted, including the preparation of standard titration solutions for chemical reagents and the determination of rubber solvent extracts. The principle of determination is to treat free sulfur extracted from rubber with acetone into potassium thiocyanate, and then perform Potentiometric titration, poten-tiometry. Reagents and materials required include acetone, 95% ethanol, potassium cyanide solution and gelatin solution.