_Manganese Disulphide_, MnS2, found native as hauerite, is formed as a red coloured powder by heating manganous sulphate with potassium polysulphide in a sealed tube at 160°-170° C. (H. v. Senarmont, _Jour. prak. Chem._, 1850, 51, p. 385).
_Manganic Salts._--The sulphate, Mn2(SO4)3, is prepared by gradually heating at 138° C. a mixture of concentrated sulphuric and manganese dioxide until the whole becomes of a dark green colour. The excess of acid is removed by spreading the mass on a porous plate, the residue stirred for some hours with nitric acid, again spread on a porous plate, and finally dried quickly at about 130° C. It is a dark green deliquescent powder which decomposes on heating or on exposure to moist air. It is readily decomposed by dilute acids. With potassium sulphate in the presence of sulphuric acid it forms potassium manganese alum, K2SO4·Mn2(SO4)2·24H2O. A. Piccini (_Zeit. anorg. Chem._ 1898, 17, p. 355) has also obtained a manganese caesium alum. _Manganic Fluoride_, MnF3, a solid obtained by the action of fluorine on manganous chloride, is decomposed by heat into manganous fluoride and fluorine. By suspending the dioxide in carbon tetrachloride and passing in hydrochloric acid gas, W. B. Holmes (_Abst. J.C.S._, 1907, ii., p. 873) obtained a black trichloride and a reddish-brown tetrachloride.
_Manganese Carbide_, Mn3C, is prepared by heating manganous oxide with sugar charcoal in an electric furnace, or by fusing manganese chloride and calcium carbide. Water decomposes it, giving methane and hydrogen (H. Moissan); Mn3C + 6H2O = 3Mn(OH)2 + CH4 + H2.
_Manganates._--These salts are derived from manganic acid H2MnO4. Those of the alkali metals are prepared by fusing manganese dioxide with sodium or potassium hydroxide in the presence of air or of some oxidizing agent (nitre, potassium chlorate, &c.); MnO2 + 2KHO + O = K2MnO4 + H2O. In the absence of air the reaction proceeds slightly differently, some manganese sesquioxide being formed; 3MnO2 + 2KHO = K2MnO4 + Mn2O3 + H2O. The fused mass has a dark olive-green colour, and dissolves in a small quantity of cold water to a green solution, which is, however, only stable in the presence of an excess of alkali. The green solution is readily converted into a pink one of permanganate by a large dilution with water, or by passing carbon dioxide through it: 3K2MnO4 + 2CO2 = 2K2CO3 + 2KMnO4 + MnO2.