Ammonium Magnesium Sulphate, (NH₄)₂SO₄.MgSO₄

Ammonium Magnesium Sulphate, (NH₄)₂SO₄.MgSO₄.6H₂O,

occurs as cerbolite in the fumaroles of Mount Cerboli in Tuscany, and is a by-product of the Tuscan boric acid industry. It is also known as boussingaultite. Yellowish-white transparent masses of this salt were formed at the Riga gasworks because the lime used for purifying contained much magnesia.

It crystallises from the mixed solutions of its constituent salts in transparent monoclinic prisms with a density of 1.723 at 20°/4° C. Its solubility in parts per 100 of solution has been represented by

10.55+0.2215t+0.000668t²

from 0°-100° C., within 1 per cent., though there are discrepancies among the various determinations. No transition-point was found between 0° C. and 100° C.

The crystals can apparently be dehydrated by heating without losing their form.