Manganese

Manganese (sym. Mn; atomic weight, 55) is one of the iron group of heavy metals. It is darker than wrought iron, is capable of a high degree of polish, and is so hard as to scratch glass and steel. It is only feebly attracted by the magnet, and oxidises readily on exposure to the air. The metal occurs in nature in small quantity along with iron in meteoric stones, but may be obtained in large amount by the reduction of its sesquioxide or carbonate by charcoal at an extreme heat.

With oxygen it forms six compounds: manganous oxide, $MnO$; manganic oxide, $Mn\_2O\_3$; manganoso-manganic oxide, $Mn\_3O\_4$; manganese dioxide, $MnO\_2$; manganic anhydride, $MnO\_3$; and permanganic anhydride, $Mn\_2O\_7$. Like iron it forms protosalts, $MnCl\_2$, and persalts, $Mn\_2Cl\_6$. It also forms salts derived from an acid, $H\_2MnO\_4$, such as potassium manganate, $K\_2MnO\_4$, and from an acid, $HMnO\_4$, as potassium permanganate, $KMnO\_4$. The binoxide, $MnO\_2$, is the chief form in which manganese is found in nature, and is the general source of the other compounds. It is known to mineralogists as pyrolusite, and in commerce as black manganese or manganese simply. When heated alone or with sulphuric acid it gives off oxygen, and when heated with hydrochloric acid chlorine is evolved. It is largely used in the manufacture of glass, to which it imparts a purple colour. It is also supposed to colour the amethyst.

Manganous oxide, $MnO$, is an olive-green powder. Its salts are colourless, or of a pale rose colour. The sulphate, $MnSO\_4$, in pink crystals, is largely used by the calico-printer for the production of black and brown colours, by decomposing it with bleaching powder or an alkali.

Manganic oxide, $Mn\_2O\_3$, in octahedral crystals, forms the mineral braunite, and in the hydrated form, $Mn\_2O\_3\; \backslash cdot\; H\_2O$, the mineral manganite.

Red oxide of manganese, $Mn\_3O\_4$, is formed when any of the other oxides are heated in the air. It is found in nature as the mineral hausmannite.

Manganic anhydride, $MnO\_3$, is not known in the free state. It forms a hydrated acid, $H\_2MnO\_4$, which forms salts. Manganate of potassium, $K\_2MnO\_4$, is the best known of these. It is in green crystals, and on allowing its 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; on this account it is sometimes called chameleon mineral.

Permanganic anhydride, $Mn\_2O\_7$, is only known in solution or in a state of combination. Its solution is of a splendid red colour, but appears of a dark violet tint when seen by transmitted light. Permanganate of potash, $KMnO\_4$, which crystallises 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 quantity in the ash of most vegetable and animal substances. It is almost always associated with iron. Various preparations of manganese have been employed in medicine. The binoxide has been used as a substitute for bismuth in dyspeptic affections, while various preparations have been tried as substitutes for iron in anaemia, but with disappointing results. The manganate and permanganate of potash readily part with their oxygen, and in weak solution are used as disinfecting and astringent lotions.