| Appearance | White Crystalline Powder with SO2 Odor |
| pH @ 25c (5% Solution | 4-5 |
| Assay as Na2S2O5 | 98%min. |
| Assay as SO2 | 66.0% Min. |
| Assay as Na2SO3 | 1.5% Max |
| Assay as Na2SO4 | 2.0% Max. |
| Bulk Density | 1.2-1.3gm/cm3 |
| Chloride | 50 ppm Max. |
| Water insoluble (10% Solution) | Clear Liquid |
| Iron as Fe | 5 ppm Max. |
| Heavy Meals as Pb | 5 ppm max. |