Magnesium Hydrogen Sulphates

Magnesia dissolves more readily in sulphuric acid of density 1.7 than in more concentrated acid. By cooling the former solution or evaporating it at boiling-point, prismatic crystals of Mg(HSO₄)₂ separate. MgSO₄.3SO₄ crystallises in small shining tables from the latter solution on cooling. These latter crystals, on heating, melt with decomposition. Prismatic doubly refracting crystals of KMg(SO₄)₂.2H₂O are obtained by treating a solution of leonite, KSO₄.MgSO₄.4H₂O, with 85 per cent, nitric acid. Water converts them into schonite, KSO₄.MgSO₄.6H₂O.