Potassium silicates

Potash water-glass is prepared similarly to the corresponding sodium product. When the calculated proportion of potassium hydroxide and silicic acid is employed, addition of alcohol to the solution precipitates potassium metasilicate, K₂SiO₃. When kept for a prolonged period over sulphuric acid, the syrup-like potash water-glass deposits hygroscopic plates, probably K₄SiO₄,2KOH,8H₂O.

Niggli has demonstrated that on fusion of potassium carbonate and silica an equilibrium between the disilicate (see below) formed and the carbonate is attained:

K₂CO₃ + K₂Si₂O₅ ⇔ 2K₂SiO₃ + CO₂.

With rise of temperature the proportion of metasilicate increases.

By heating mixtures of water and finely powdered glasses at high temperatures, Morey and Fenner have prepared potassium hydrogen disilicate, KHSi₂O₅, in the form of orthorhombic crystals which do not lose water even at 350° C.; and potassium disilicate, K₂Si₂O₅, a hygroscopic salt readily acted upon by water, and melting at 1015°±10° C.