Praseodymium sulphate, Pr₂(SO₄)₃

At 0°, 23.6 parts, and at 20°, 17.7 parts of the anhydrous Praseodymium sulphate, Pr₂(SO₄)₃, can be dissolved in 100 of water.

The monoclinic octahydrate, Pr₂(SO₄)₃.8H₂O, is the only hydrate stable in contact with the solution from 0°-75° its solubility, in grams of anhydrous salt per 100 grams of water, is as follows: -

Temp. °C.	0°	18°	35°	55°	75°
Grams of Pr2(SO4)3	19.80	14.05	10.40	7.02	4.20

The monoclinic pentahydrate, Pr₂(SO₄)₃.5H₂O, separates from the aqueous solution at 90°-100°. Its solubility, in grams of anhydrous sulphate per 100 grams of water, is as follows (Muthmann and Rolig): -

Temp. °C	85°	90°	95°
Grams of Pr2(SO4)3	1.60	1.35	1.00

The transition-point (from octa- to penta-hydrate) is about 75°. Two labile hydrates, Pr₂(SO₄)₃.15½H₂O and Pr₂(SO₄)₃.12H₂O, have been isolated at low temperatures by von Scheele and by Muthmann and Rolig respectively; Brauner mentions a hexahydrate.

For acid and basic sulphates, Pr(HSO₄)₃ and Pr₂O₃.SO₃ respectively.

The following double sulphates have been described: -

Pr₂(SO₄)₃.Cs₂SO₄.2H₂O and Pr₂(SO₄)₃.Cs₂SO₄.4H₂O; Pr₂(SO₄)₃.K₂SO₄.4H₂O; Pr₂(SO₄)₃.3K₂SO₄.H₂O; density 3.29 Pr₂(SO₄)₃.(NH₄)₂SO₄.8H₂O; density 2.53