CHROMIUM, MOLYBDENUM, TUNGSTEN, UBANIUM, ETC. 307 



As the salts of manganous oxide MnX 2 closely resemble (and are 

 isomorphous with) the salts of magnesia MgX 2 in many respects (with 



<from the native MnO.J, from which it cannot be freed by crystallisation. Their 

 removal may, however, ba effected by mixing a portion of the liquid with a solution of 

 sodium carbonate ; a precipitate of manganous carbonate is then formed. This pre- 

 cipitate is collected and washed, and then added to the remaining mass of the impure 

 solution of manganous sulphate; on heating the solution with this precipitate, the 

 whole of the iron is precipitated as oxide. This is due to the fact that in the solution of 

 the manganese dioxide in sulphuric acid the whole of the iron is converted- into the 

 ferric state (because the dioxide acts as an oxidising agent), which, as an exceedingly 

 feeble base precipitated by calcium carbonate and other kindred salts, is also precipitated 

 by manganous carbonate. After being treated in this manner, the solution of manganous 

 sulphate is further purified by crystallisation. If it be a bright red colour, it is due to 

 the presence of higher grades of oxidation of manganese ; they may be destroyed by 

 boiling the solution, when the oxygen from the oxides of manganese is evolved and a 

 very faintly coloured solution of manganous sulphate is obtained. This salt is remarkable 

 for the facility with which it gives various combinations with water. By evaporating 

 the almost colourless solution of manganous sulphate at very low temperatures, and by 

 cooling the saturated solution at about 0, crystals are obtained containing 7 atoms of 

 water of crystallisation, MnSO.^TH.jO, which ara isomorphous with cobaltous and ferrous 

 sulphates. These crystals, even at 10, lose 5 p.c. of water, and completely effloresce at 

 15-", losing about 20 p.c. of water. By evaporating a solution of the salt at the ordinary 

 temperature, but not above 20, crystals are obtained containing 5 mol. H 2 O, which 

 are isomorphous with copper sulphate ; whilst if the crystallisation be carried on between 

 20 J and 30, large transparent prismatic crystals are formed containing 4 mol. H 2 O (see 

 Nickel). A boiling solution also deposits these crystals together with crystals containing 

 8 mol. H 2 O, whilst the first salt, when fused and boiled with alcohol, gives crystals 

 containing 2 mol. H.^O. Graham obtained a monohydrated salt by drying the salt at 

 about 200 ^ The last atom of water is eliminated with difficulty, as is the case with all 

 salts like MgSO^iH^O. The crystals containing a considerable amount of water are 

 rose-coloured, and the anhydrous crystals are colourless. The solubility of MnSO 4 ,4H 2 Q 

 (Chapter I., Note 24) per 100 parts of water is : at 10, 127 parts; at 87 '5, 149 parts ; at 

 75, 145 parts ; and at 101, 92 parts. Whence it is seen that at the boiling-point this salt 

 is less soluble than at lower temperatures, and therefore a solution saturated at the 

 ordinary temperature becomes turbid when boiled. Manganous sulphate, being analogous 

 to magnesium sulphate, is decomposed, like the latter, when ignited, but it does not then 

 leave manganous oxide, but the intermediate oxide, Mn 3 O 4 . It gives double salts with 

 the alkali sulphates. With aluminium sulphate it forms fine radiated crystals, whose 

 composition resembles that of- the alums namely, MiiA^SC.^.,, 24HjO. This salt is 

 easily' soluble in water, and occurs in nature. 



Manganous chloride, MC1 2 , crystallises with 4 mol. HoO, like the ferrous salt, and 

 not with 6 mol. H. 2 O like many kindred salts for example, those of cobalt, calcium, and 

 magnesium ; 100 parts of water dissolve 88 parts of the anhydrous salt at 10 and 55. 

 parts at 62. Alcohol also dissolves manganous chloride, and the alcoholic solution 

 burns with a red flame. This salt, like magnesium chloride, readily forms double salts. 

 A solution of borax gives a dirty rose-coloured precipitate having the composition 

 MnH^BOj^H.O, which is used as a drier in paint-making. Potassium cyanide pro- 

 duces a yellowish-grey precipitate, MnC.^No, with manganous salts, soluble in n excess of 

 the reagent, a double salt, K 4 MnC (< N e , corresponding with potassium ferrocyanide, 

 being formed. On evaporation of this solution, a portion of the manganese is oxidised 

 And precipitated, whilst a salt corresponding to Gmelin's red salt, K^MnC B N 6 (see 

 Chapter .XXII.), remains in solution. Sulphuretted hydrogen does not precipitate 

 salts of manganese, not even the acetate, but ammonium sulphide gives a flesh-coloured 

 precipitate, MnS ; at 320 this sulphide of manganese passes into a green variety (Antony). 

 Oxalic acid in strong solutions of manganous salts gives a white precipitate of the 



