Cerous sulphate, Ce_{2}(SO_{4})_{3}
In 100 parts of icecold water 40 parts of cerous sulphate can be dissolved. The specific heat (0°to 100°) of the anhydrous sulphate is 0.1168.
Cerous sulphate forms numerous hydrates. The existence of hydrates with 4H_{2}O, 5H_{2}O, 8H_{2}O, 9H_{2}O, and 12H_{2}O is definitely established, but the existence of the hydrate with 6H_{2}O is very doubtful.
 Solubility of the hydrates of cerous sulphate in water  The various hydrates may be obtained as follows:  The dodecahydrate, Ce_{2}(SO_{4})_{3}.12H_{2}O, separates from a concentrated solution of cerous sulphate over sulphuric acid at 0°C. in the form of tiny needles. The enneahydrate, Ce_{2}(SO_{4})_{3}.9H_{2}O, is prepared by evaporating the aqueous solution at 40°45°, and forms hexagonal prisms. The octahydrate, Ce_{2}(SO_{4})_{3}.8H_{2}O, is best prepared by warming to 45°50° a solution of the sulphate that was saturated at 0° C. The pentahydrate, Ce_{2}(SO_{4})_{3}.5H_{2}O, is obtained by preparing a cold saturated solution and heating it to 70°100°, and forms monoclinic prisms. The tetrahydrate, Ce_{3}(SO_{4})_{3}.4H_{2}O, is conveniently prepared by agitating the enneahydrate with a little water at 70° for 48 hours, and drying the mass at the same temperature.
The octahydrate has been generally regarded as crystallising in the orthorhombic system; but according to Wyrouboff, whose view is adopted by Groth, the crystals are triclinic and devoid of all elements of symmetry (a:b:c = 1.0650:1:1.1144, α = 90°52', β = 90°40', γ = 91°45'). Kammelsberg has described a monoclinic octahydrate, isomorphous with the octahydrates of the other metals.
The solubilities of the various hydrates, in grams of anhydrous sulphate per 100 grams of water, are given in the accompanying table (Koppel) and represented graphically in fig., from which the stable hydrate at any temperature is readily seen. It will be noticed that solubilities have been determined even where the hydrates are metastable in contact with the solution.
The acid sulphate, Ce(HSO_{4})_{3}, is known.
The following double salts with alkali sulphates have been described:  Ce_{2}(SO_{4})_{3}.K_{2}SO_{4}.2H_{2}O; 2Ce_{2}(SO_{4})_{3}.3K_{2}SO_{4}, and with 8H_{2}O; Ce_{2}(SO_{4})_{3}.2K_{2}SO_{4}.2H_{2}O; Ce_{2}(SO_{4})_{3}.3K_{2}SO_{4}; Ce_{2}(SO_{4})_{3}.5K_{2}SO_{4}. Ce_{2}(SO_{4})_{3}.Na_{2}SO_{4}.2H_{2}O; Ce_{2}(SO_{4})_{3}.(NH_{4})_{2}SO_{4}.8H_{2}O, and anhydrous; Ce_{2}(SO_{4})_{3}.5(NH_{4})_{2}SO_{4}.
They are sparingly soluble in water and practically insoluble in saturated solutions of the corresponding alkali sulphates.
The diminution in the solubility of cerous sulphate in water, caused by the presence of various alkali sulphates, is as follows (data represent grams of anhydrous salt present in solution per 100 grams of water): 
Temp. 16° C.  Temp. 19° C.  Temp. 16° C.  K_{2}SO_{4}.  Ce_{2}(SO_{4})_{3}.  Na_{2}SO_{4}.  Ce_{2}(SO_{4})_{3}.  (NH_{4})_{2}SO_{4}.  Ce_{2}(SO_{4})_{3}.  0.00  10.75  0.00  9.65  0.00  10 75  0.18  0.96  0.33  0.64  3.46  1.03  0.51  0.43  1.09  0.09  9.32  0.78  0.73  0.25  1.39  0.06  19.24  0.75  1.29  0.04  1.70  0.03  45.62  0.50  2.50  0.00  3.59  0.01  72.84  0.04  
Cerous ammonium sulphate, Ce_{2}(SO_{4})_{3},(NH_{4})_{2}SO_{4}Cerous ammonium sulphate, Ce_{2}(SO_{4})_{3}.(NH_{4})_{2}SO_{4}.8H_{2}O, is a monoclinic salt of density 2.523. It loses 6H_{2}O at 100°, and the remaining 2H_{2}O at 150°. The solubility, in grams of Ce_{2}(SO_{4})_{3}.(NH_{4})_{2}SO_{4} per 100 grams of water, is as follows (Wolff): 
Temp. °C  22.3°  35.1°  45.2°  Grains of Ce_{2}(SO_{4})_{3}.(NH_{4})_{2}SO_{4}  5.33  5.18  4.99 
Above 45° the anhydrous double salt is the stable phase in contact with the solution, and its solubility is as follows (Wolff): 
Temp. °C  45°  55.3°  75.4°  82.2°  Grams of Ce_{2}(SO_{4})_{3}.(NH_{4})_{2}SO_{4}.  2.99  2.24  1.48  1.18 
The sulphates of hydrazine and hydroxylamine combine with cerous sulphate. 
Cerous thallous sulphate, Ce_{2}(SO_{4})_{3},Tl_{2}SO_{4}Cerous thallous sulphate, Ce_{2}(SO_{4})_{3}.Tl_{2}SO_{4}.4H_{2}O, crystallises in monoclinic prisms (a:b:c = 1.1309:1:0.7059, β = 91°53'). The salt Ce_{2}(SO_{4})_{3}.3Tl_{2}SO_{4}. H_{2}O has also been described. 
Cerous cadmium sulphate, Ce_{2}(SO_{4})_{3},CdSO_{4}Cerous cadmium sulphate, Ce_{2}(SO_{4})_{3}.CdSO_{4}.6H_{2}O, crystallises in the orthorhombic system (a:b:c = 1.1336:1:0.7535). 
Cerous nitratosulphate, Ce(NO_{3})(SO_{4})Cerous nitratosulphate, Ce(NO_{3})(SO_{4}).H_{2}O, crystallises out when a solution of cerous sulphate in concentrated nitric acid is evaporated on the steambath. 


