306 METALS AND THEIR COMBINATIONS. 



ysis of potassium permanganate. It has the color of the potassium salt, is 

 stable, and from it the permanganates of other metals may be made. 



Tests for manganese. 

 (A 5 per cent, solution of manganous sulphate may be used.) 



1. Ammonium sulphide produces a yellowish-pink or flesh-colored 

 precipitate of hydrated inanganous sulphide, MnS.H 2 O, soluble in 

 acetic and in mineral acids (Plate II., 2). 



2. Ammonium (or sodium) hydroxide produces a white precipi- 

 tate of manganous hydroxide, which soon darkens by absorption 

 of oxygen (Plate II., 3) and dissolves in oxalic acid with a rose-red 

 color. The presence of ammonium salts prevents the precipitation of 

 manganous hydroxide by ammonia-water (see test 2 for magnesium). 



3. Sodium (or potassium) carbonate produces a nearly white pre- 

 cipitate of manganous carbonate, which oxidizes to brown manganic 

 hydroxide. 



4. Any compound of manganese heated on platinum foil with a 

 mixture of sodium carbonate and nitrate forms a bluish-green mass, 

 giving a green solution in water, which turns red on addition of an 

 acid. (See explanation above.) 



5. Manganese compounds fused with borax on a platinum wire 

 give a violet color to the borax bead. Only a very small quantity of 

 the manganese compound should be used. 



6. Heat a trace of manganese compound (not the dioxide) with about 

 5 c.c. of dilute nitric acid and a small knife-pointful of red oxide of 

 lead (minium) to boiling, dilute with water, and let stand to settle. 

 A reddish-purple color of permanganic acid will be seen. This is a 

 very delicate test. 



Tests 4, 5, and 6 are the most decisive for manganese compounds. 

 Test 2 is also characteristic. Permanganate is usually recognized by 

 its color and action on reducing agents. Manganese salts are neu- 

 tral and colorless, or light red to pink. 



The most common ions of manganese are the divalent Mn' ions of the man- 

 ganous salts, and the univalent permanganate ions MnO/, which are purple 

 (see page 200). The divalent manganate ions MnO/ x , which are green, exist 

 only in neutral or alkaline solutions. In acid solutions they pass into MnO/ 

 ions. The ionic equations in the tests above for manganous ions, Mn' * are 

 similar to those given under the tests for calcium. 



Chromium, Cr = 51.7. Found in nature almost exclusively as 

 chromite, or chrome-iron ore, FeO.Cr 2 O 3 , a mineral analogous in 

 composition to magnetic iron ore, FeO.Fe ? O ? . The name chromium. 



