Answer is: Na₂SO₄ (sodium sulfate).
The solubility of sodium sulfate increases up to 32.38°C and than decreases at higher temperatures, the solubility becomes almost independent of temperature.
At 32.38°C it releases of crystal water and melting of the hydrated salt.
Sodium sulfate is the white, inorganic compound.
Sodium sulfate is highly soluble in water.