CHROMIUM MOLYBDENUM, TUNGSTEN, URANIUM, ETC. 305 



nature, especially in those localities where iron occurs, whose ores 

 frequently contain compounds of manganous oxide, MnO, which presents 

 a resemblance to ferrous oxide, FeO, and to magnesia. In many minerals 

 magnesia and the oxides allied to it are replaced by manganous oxide; 

 calcspars and magnesites i.e. R"C0 3 in general are frequently met 

 with containing mauganous carbonate, which also occurs in a separate 

 state, although but rarely. The soil also and the ash of plants generally 

 contain a small quantity of manganese. In the analysis of minerals 

 it is generally found that manganese occurs together with magnesia, 

 because, like it, manganous oxide remains in solution in the presence of 

 ammoniacal salts, not being precipitated by reagents. The property of 

 this manganous oxido, MnO, of passing into the higher grades of oxida- 

 tion under the influence of heat, alkalis, and air, gives an easy means 

 not only of discovering the presence of manganese in admixture -with 

 magnesia, but also of separating these two analogous bases. Magnesia is 

 not able to give higher grades of oxidation, whilst manganese gives them 

 with great facility. Thus, for instance, an alkaline solution of sodium 

 hypochlorite produces a precipitate of manganese dioxide in a solution of 

 a manganous salt : MnCl 2 + NaClO + 2NaHO = Mn0 2 + H 2 + 3NaCl 

 whilst magnesia is not changed under these circumstances, and remains 

 in the form of MgCl 2 . If the magnesia be precipitated owing to the 

 ^presence of. alkali, it may be dissolved in acetic acid, in which manganese 

 tHoxicle is insoluble. The presence of small quantities of manganese 

 may also be recognised by th6 green coloration which alkalis acquire 

 when heated with manganese compounds in the air. This green colora- 

 tion depends on the property of manganese of giving a green alkaline 

 manganate : MnCl. 2 -f 4KHO + O 2 =K 2 Mn0 4 +2KC1 +-2H 2 O. Thus 

 the faculty of oxidising in the presence of alkalis forms an essential 

 character of manganese. The higher grades of oxidation containing 

 Mn 2 7 and Mn0 3 are quite unknown in nature, and even Mn0 2 is not 

 so widely spread in nature as the ores composed of manganous com- 

 pounds which are met with nearly everywhere. The most important 

 ore of manganese is its dioxide, or so-called peroxide, Mn0 2 , which is 

 known in mineralogy as pyrolusite. Manganese also occurs as an 

 oxide corresponding with magnetic iron ore, MnO,Mn 2 O 3 =Mn 3 4 , 

 forming the mineral known as hausmannite. The oxide .Mn 2 Q 3 also 

 occurs in nature as the anhydrous mineral braunite, and in a hydrated 

 form, Mn 2 O 3 ,H 2 0, called manganite. Both of these often occur as an 

 admixture in pyrolusite. Besides which, manganese is met with in 

 nature as a rose-coloured mineral, rhodonite, or silicate, MnSi0 3 . Very 

 fine and rich deposits of manganese ores have been found in. the 

 Caucasus, the Urals, and along the Dnieper. Those at the Sharapansky 



