An aqueous solution of an ammonio-complex of manganese, in which the manganese occurs predominantly in an anion, contains in equilibrium the three components Mn(OH)2, NH4OH and HX (where X is an anion forming a manganese salt at least as soluble as manganous sulphide), the manganese content as Mn(OH)2 being at least 10 grams per litre, the NH4OH content being at least 40 per cent by weight of the total of the three components and sufficient to prevent the formation of a permanent precipitate on addition of 1 cc. of saturated ammonium carbonate solution to 10 ccs. of the solution, and the solution containing a total of more than 100 grams per litre of the three p components and an amount of the anion X at least stoichiometrically equivalent to the manganese content. The solution may be prepared by extracting a material containing manganese in the metallic or manganous form with an aqueous ammoniacal solution of an ammonium salt of the acid HX, containing more than 50 grams NH3 per litre (see Group III). Solutions according to the invention may be formed containing radicals of the following acids: acetic, naphthenic, benzoic, cinnamic, alkane sulphonic, phenol sulphonic, lactic, and hydroxyacetic. By exposing the solutions to anhydrous calcium sulphate in a desiccator, crystals are obtained corresponding to the formula <FORM:0690134/IV (b)/1> where X is a univalent anion or half a divalent anion. An example describes the preparation of such crystals, where X is the acetate ion, from a solution obtained by dissolving manganese acetate in concentrated aqueous ammonia. On adding naphthenic acid to this solution and boiling to remove ammonia, a precipitate of manganese naphthenate is formed. A diagram illustrating the ternary system Mn(OH)2-NH4OH-CH3COOH is given, showing the range of composition in which the complex compound is formed.ALSO:An aqueous solutions of an ammonio-complex of manganese, in which the manganese occurs predominantly in an anion, contains in equilibrium the three components Mn (OH)2, NH4OH and HX (where X is an anion forming a manganese salt at least as soluble as manganous sulphide), the manganese content as Mu(OH)2 being at least 10 grams per litre, the NH4OH content being at least 40 per cent by weight of the total of the three components and sufficient to prevent the formation of a permanent precipitate on addition of 1 cc. of saturated ammonium carbonate solution to 10 ccs. of the solution, and the solution containing a total of more than 100 grams per litre of the three components and an amount of the anion X at least stoichiometrically equivalent to the manganese content. The solution may be prepared by extracting a material containing manganese in the metallic or manganous form with an aqueous ammoniacal solution of an ammonium salt of the acid HX, containing more than 50 grams NH3 per litre. Formation of the solutions is assisted by the presence of reducing agents, for example hydroxylamine acid sulphate or hydrochloride, thiourea, ferrous salts, sulphites, or sodium or ammonium sulphide or polysulphide. Extraction with an equilibrium mixture of ammonium carbonate and ammonium carbamate yields a solution from which manganese carbonate may be precipitated by heating with the addition of carbon dioxide and the removal of ammonia. In a cyclic process for obtaining manganese carbonate from ore, the manganese content of the ore is converted to MnO by heating in a reducing atmosphere or with charcoal, anthracite or oil, the product is agitated for a few minutes to one hour at 10 DEG -30 DEG C with an aqueous solution containing a minimum of 12 mols per litre of NH3 and 2.5 to 4 mols per litre of CO2, the solid residue is separated, carbon dioxide is added to the solution in an amount equivalent to the manganese present, ammonia is removed from the solution down to a concentration of less than 12 mols per litre, the solution is heated to at least 60 DEG C for at least 30 minutes to precipitate manganese carbonate which is separated, and ammonia is then added to the depleted solution to raise its NH3 content to the original value for reuse. Addition of carbon dioxide may be effected simultaneously by passing hot oxygen-free combustion gases through the manganese-containing solution. The solid residue from the extraction is washed with ammonia solution and then with water, the ammonia washings being combined with the manganese-containing solution. The precipitate of manganese carbonate is also washed with ammonia solution and then with water, and the ammonia washings are combined with the depleted solution. In each case ammonia is recovered from the water washings. Tables are given regarding this process showing the effect of various reducing agents, the temperature of extraction, and the concentrations of ammonia and carbon dioxide. Further tables relate to the precipitation of manganese carbonate and show the effect of time and temperature in pressure precipitation, and of the degre of reduction of the NH3 content: in this precipitation the ratio CO2:Mn in the solution is preferably maintained above 1.75. The manganese carbonate can be converted into manganese dioxide by heating in air or oxygen; the MnO2 content of the product may be increased by leaching with a dilute solution of an acid or ammonium salt, or by recarbonating and then re-heating; for battery oxide the crystal size of the manganese carbonate treated is preferably 0.25-6.0 microns diameter. Solutions according to the invention may also be formed containing radicals of the following acids: hydrochloric, sulphuric, nitric, acetic, dithionic, perchloric, boric, naphthenic, benzoic, cinnamic, hydrosulphuric, fluoboric, alkane sulphonic, phenol sulphonic, fluosilicic, succinic, lactic, hydroxyacetic, thiocyanic, and sulphamic. By exposing the solutions to anhydrous calcium sulphate in a desiccator, crystals are obtained corresponding to the formula <FORM:0690134/III/1> where X is a univalent anion or half a divalent anion. In examples of the preparation of the solutions by other methods, (1) ammonia is passed into a solution of manganese chloride; (2) manganese acetate is dissolved in concentrated aqueous ammonia; (3) electrolytic manganese is dissolved in a concentrated aqueous solution of ammonia containing ammonium sulphate or ammonium carbonate; (4) manganese hydroxide is dissolved in a concentrated aqueous thiocyanate; (5) manganous oxide is stirred with aqueous ammonia solution and carbon dioxide is passed in; (6) manganese ore is stirred in an atmosphere of nitrogen with a mixture of aqueous ammonia and ammonium carbonate which has been allowed to stand overnight to form an equilibrium mixture of ammonium carbonate and carbamate. Boiling solution (1) under vacuum precipitates manganese hydroxide. On adding naphthenic acid to solution (2) and boiling to remove ammonia, a precipitate of manganese naphthenate is formed. By passing carbon dioxide into solution (3) prepared using ammonium carbonate, a precipitate of manganese carbonate is obtained. A solution containing manganese hydroxide, ammonia, and carbonic acid yields a precipitate of manganous sulphide on treatment with hydrogen sulphide. A cyclic process for making manganese hydroxide is described in which manganous oxide is treated with an ammoniacal aqueous solution of ammonium chloride and the complex formed is decomposed. Diagrams illustrating ternary systems Mn(OH)2 -NH4OH-HX are given, showing the ranges of composition in which the complex compounds are formed.