Manganese is one of the heavy metals of which iron may he taken as the representative. It is of a grayish white color, presents a metallic brilliancy, and is capable of a high degree of polish, is so hard as to scratch glass and steel, is non-magnetic, and is only fused at a white heat. As it oxidizes rapidly on exposure to the atmosphere, it should be preserved under naphtha.
It occurs in small quantity in association with iron in meteoric stones; with this exception it is not found native. The metal may be obtained by the reduction of its sesquioxide by carbon at an extreme heat.
Manganese forms no less than six different oxides--viz., protoxide, sesquioxide the red oxide, the binoxide or peroxide, manganic acid, and permanganic acid. The protoxide occurs as olive-green powder, and is obtained by igniting carbonate of manganese in a current of hydrogen. Its salts are colorless, or of a pale rose color, and have a strong tendency to form double salts with the salts of ammonia. The carbonate forms the mineral known as manganese spar. The sulphate is obtained by heating the peroxide with sulphuric acid till there is faint ignition, dissolving the residue in water and crystallizing. It is employed largely in calico printing. The silicate occurs in various minerals.
The sesquioxide is found crystallized in an anhydrous form in braunite, and hydrated in manganite. It is obtained artificially as a black powder by exposing the peroxide to a prolonged heat. When ignited it loses oxygen, and is converted into red oxide. Its salts are isomorphous with those of alumina and sesquioxide of iron. It imparts a violet color to glass, and gives the amethyst its characteristic tint. Its sulphate is a powerful oxidizing agent.
The red oxide corresponds to the black oxide of iron. It occurs native in hausmannite, and may be obtained artificially by igniting the sesquioxide or peroxide in the open air. It is a compound of the two preceding oxides.
The binoxide, or peroxide, is the black manganese of commerce, and the pyrolusite of mineralogists, and is by far the most abundant of the manganese ores. It occurs in a hydrated form in varvicite and wad. Its commercial value depends upon the proportion of chlorine which a given weight of it will liberate when it is heated with hydrochloric acid, the quantity of chlorine being proportional to the excess of oxygen which this oxide contains over that contained in the same weight of protoxide. When mixed with chloride of sodium and sulphuric acid it causes an evolution of chlorine, the other resulting products being sulphate of soda and sulphate of protoxide of manganese. When mixed with acids, it is a valuable oxidizing agent. It is much used for the preparation of oxygen, either by simply heating it, when it yields 12 per cent. of gas, or by heating it with sulphuric acid, when it yields 18 per cent. Besides its many uses in the laboratory, it is employed in the manufacture of glass, porcelain, and kindred wares.
Manganic acid is not known in a free state. Manganate of potash is formed by fusing together hydrated potash and binoxide of manganese. The black mass which results from this operation is soluble in water, to which it communicates a green color, due to the presence of the manganate. From this water the salt is obtained in vacuo in beautiful green crystals. On allowing the solution to stand exposed to the air, it rapidly becomes blue, violet, purple, and finally red, by the gradual conversion of the manganate into the permanganate of potash; and on account of these changes of color the black mass has received the name of mineral chameleon.
Permanganic acid is only known in solution or in a state of combination. Its solution is of a splendid red color, but appears of a dark violet tint when seen by transmitted light. It is obtained by treating a solution of permanganate of baryta with sulphuric acid, when sulphate of baryta falls, and the permanganic acid remains dissolved in the water. Permanganate of potash, which crystallizes in reddish purple prisms, is the most important of its salts. It is largely employed in analytical chemistry, and is the basis of Condy's Disinfectant Fluid.
Manganese is a constituent of many mineral waters, and is found in small quantities in the ash of most vegetables and animal substances. It is always associated with iron.
Various preparations of manganese have been employed in medicine. The sulphate of the protoxide in doses of one or two drachms produces purgative effects, and is supposed to increase the excretion of bile; and in small doses, both this salt and the carbonate have been given with the intention of improving the condition of the blood in cases of anaemia. Manganic acid and permanganate of potash are of great use when applied in lotions (as in Condy's Fluid diluted) to foul and fetid ulcers. In connection with the medicinal applications of manganese it may be mentioned that manganic acid is the agent employed in Dr. Angus Smith's celebrated test for the impurity of the air.
It is the glass maker's soap of glass manufacture, and is used to correct the green color of glass, which is owing to the presence of protoxide of iron. This it converts into the comparatively colorless peroxide.
It is also used in the Bessemer and similar processes, to decompose the oxide of iron. Spiegeleisen, an iron which contains a natural alloy of from 10 to 12 per cent. of manganese, is used for this purpose when conveniently attainable.--Glassware Reporter.