Sodium hypophosphates

When a solution of hypophosphoric acid is neutralized with sodium carbonate, methyl-orange being employed as indicator, the hexahydrate of disodium dihydrogen hypophosphate, Na₂H₂P₂O₆, is formed. The crystals dissolve in water, yielding a solution of slight acidity, the solubility in cold water being 2.2 per cent., and in hot water about 20 per cent. The refractivity of the solid and the electric conductivity of the solution have been investigated.

Excess of sodium carbonate converts this salt into the normal sodium hypophosphate, Na₄P₂O₆, which crystallizes as decahydrate, isomorphous with the corresponding pyrophosphate. It yields a slightly alkaline solution, its solubility being given by Salzer as about 2 per cent. With an equimolecular proportion of disodium dihydrogen hypophosphate it yields a trisodium hydrogen hypophosphate, Na₃HP₂O₆. This substance crystallizes as nonahydrate, its solubility at ordinary temperatures being given by Salzer as about 4.5 percent. The solution has an alkaline reaction.