A Grade	B Grade
Main Content (based on H3PO3 ) (%)	≥ 99.0	≥ 98.5
Iron Content (based on Fe) (%)	≤ 0.001	≤ 0.003
Chloride Content (based on CL) (%)	≤ 0.01	≤ 0.02
Sulfate Content (based on SO4) (%)	≤ 0.008	≤ 0.01
Phosphate Content (based on PO4) (%)	≤ 0.2	≤ 0.6
Appearance	Pure white crystal	White crystal
70% Aqueous Solution Test	Colorless transparent	Colorless transparent, without impurities
Liquid Phosphorous Acid (%)	≥ 70-80	Colorless, transparent

Properties
Phosphorous acid is a colorless crystal. It can be slowly oxidized to phosphoric acid in the air. When heated to 180 °C, it can be decomposed into phosphoric acid and phosphine (highly toxic). As a dibasic acid, it has slightly ber acidity than phosphoric acid. Phosphorous acid has b reducibility and can easily reduce Ag+ to metal silver. It can also reduce sulfuric acid to sulfur dioxide. It is corrosive and has b hygroscopicity.
Relative Density: 1.651 (21.1 °C)
Melting Point: 73.6 °C
Boiling Point: 200 °C (Decomposes)
Solubility: Easily soluble in water and alcohol.

Applications
Phosphorous acid is mainly used in the production of phosphates, synthetic fibers and organophosphorus pesticides, etc.. It is also used in producing high performance water treating agent ATMP.