Manganese

Manganous Salts.

The anhydrous chloride, is ob tained as a rose red crystalline solid by passing hydrochloric acid gas over manganese carbonate, first in the cold and afterwards at a moderate red heat. The hydrated chloride, is obtained in rose red crystal§ by dissolving the metal or its carbon ate in aqueous hydrochloric acid and concentrating the solution. It may be obtained in at least two different forms, one isomor phous with by concentrating the solution between 15° C and 2o° C; the other, isomorphous with FeC12.4H20, by slow evaporation of the mother liquors from the former. It forms double salts with the chlorides of the alkali metals. The bromide, iodide, and fluoride, are known.

Manganous sulphate, is prepared by strongly heating a paste of pyrolusite and concentrated sulphuric acid until acid fumes cease to be evolved. The ferric and aluminium sulphates present are thus converted into insoluble basic salts, and the resi due yields manganous sulphate when extracted with water. The salt crystallizes with varying quantities of water, according to the temperature at which crystallization is effected : between —4° C and +6° C with between 15° C and 20° C with and between 25° C and 31° C with 4H20. It crystallizes in large pink crystals and combines with the sulphates of the alkali metals to form double salts.

Manganous nitrate, obtained by dissolving the carbonate in nitric acid and concentrating the solution, crystallizes from nitric acid solutions in long colourless needles, which melt at 25.8° C.

Manganous carbonate, found native as manganese spar, may be prepared as an amorphous powder by heating manganese chloride with sodium carbonate in a sealed tube to 550° C, or in the hydrated form as a white flocculent precipitate by adding sodium carbonate to a manganous salt. In the moist condition it rapidly turns brown on exposure to air.

Manganous sulphide, MnS, found native as manganese glance, may be obtained by heating the monoxide or carbonate in a porce lain tube in a current of carbon disulphide vapour. R. Schneider obtained a crystalline variety by melting sulphur with anhydrous manganous sulphate and dry potassium carbonate, extracting the residue and drying it in a current of hydrogen. Ammonium sul phide alone gives incomplete precipitation of the sulphide. In the presence of ammonium salts the precipitate is dirty white in colour, whilst in the presence of free ammonia it is a buff colour. This form of the sulphide is readily oxidized when exposed in the moist condition, and is easily decomposed by dilute mineral acids.

Manganic Salts.

The sulphate, Mn2(SO4)3, is prepared by gt adually 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 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 sul phuric acid it forms K2SO4.Mn2(SO4)3.24H20, potassium man ganese alum. Manganic fluoride, a solid obtained by the action of fluorine on manganous chloride, is decomposed by heat into manganous fluoride and fluorine. It readily forms double fluorides such as Manganifluorides, are also known.

Manganese carbide, is prepared by heating manganous oxide with sugar charcoal in an electric furnace, or by fusing man ganese chloride and calcium carbide. Water decomposes it, giving methane and hydrogen, (H. Moissan).

Manganates.

These salts are derived from manganic acid, Those of the alkali metals are prepared by fusing man ganese dioxide with sodium or potassium hydroxide in the pres ence of air or of some oxidizing agent (nitre, potassium chlorate, etc.), In the absence of air the reaction proceeds slightly differently, some manganese sesqui oxide being formed, The fused mass has a dark olive green colour, and dissolves in a small quantity of cold water to a green solution, which is, how ever, 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 : 3K2Mn04+2CO2=2K2CO3+2KMnO4+Mn02.

Permanganates are the salts of permanganic acid, HMn04. The potassium salt, may be prepared by passing chlorine or carbon dioxide through an aqueous solution of potassium man ganate, or by the electrolytic oxidation of the manganate at the anode. It crystallizes in dark purple-red prisms, isomorphous with potassium perchlorate. It acts as a powerful oxidizing agent both in acid and alkaline solution ; in the first case two molecules yield five atoms of available oxygen and in the second, three atoms: It is used extensively in analytical work, especially in estimating ferrous salts and oxalic acid or oxalates, and also in organic chem istry for oxidations.