_Ceric sulphate_, Ce(SO₄)₂, is obtained by the action of concentrated sulphuric acid on the dioxide. It is a deep yellow crystalline powder, dissolving readily in water to a brown solution, which has a strongly acid reaction; on warming or diluting, a basic sulphate separates. The solution slowly evolves oxygen, and therefore always contains cerous compounds. On evaporation, _a cero-ceric acid sulphate_ of the formula HCe^{iii}Ce^{iv}(SO₄)₄,12(13 ?)H₂O first separates; the hydrated sulphate Ce(SO₄)₂,4H₂O, being more soluble, separates on further concentration.[216] The relative amounts of the two compounds obtained depends on the temperature and the concentration of acid in the solution; if both these factors are kept low, the almost pure hydrated sulphate can be at once obtained. This separates in yellow crystals belonging to the rhombic system; it is readily soluble in water. The mixed acid salt is less soluble, and forms orange prisms and needles, which cling tenaciously to sulphuric acid. Other complex and double salts have also been obtained. When, for example, silver nitrate is added to a warm solution of the sulphate in concentrated sulphuric acid, a bright orange-yellow precipitate of the salt 10Ce(SO₄)₂,6Ag₂SO₄ is obtained.[217] [216] See Meyer and Aufrecht, _Ber._ 1904, ~37~, 140; Brauner, _Zeitsch. anorg. Chem._ 1904, ~39~, 261. [217] Pozzi-Escot, _Compt. rend._ 1913, ~156~, 1074. Neutral ceric nitrate is unknown. A _basic nitrate_, Ce(NO₃)₃OH,3H₂O, is obtained in red crystals by evaporation of a solution of ceric hydroxide in strong nitric acid. The solid is readily soluble in water, forming a yellow, acid solution, which becomes paler by hydrolysis, on warming or on standing. The course of the hydrolysis is also indicated by the action towards acids, and towards hydrogen peroxide.[218] A freshly prepared ceric salt, on addition of acid, becomes immediately much darker in colour, whereas the colour change is very slow, if considerable hydrolysis has occurred. Similarly, hydrogen peroxide at once reduces a freshly prepared solution, forming colourless cerous salts, whilst if much hydrolysis has occurred, deeply coloured higher oxidation products are at first formed, and these lose their colour only slowly. [218] Meyer and Jacoby, _Zeitsch. anorg. Chem._ 1901, ~27~, 359.