528 SMITH'S INTERMEDIATE CHEMISTRY 



scribed. Traces of manganese seem to be essential to the growth 

 of plants. 



The Chemical Relations of the Element. Manganese 

 stands, at present, alone on the left side of the eighth column of 

 the periodic table. The right side is occupied by the halogens. 

 It is never univalent, as are the halogens, but its heptoxide Mn 2 O 7 

 and the corresponding acid, permanganic acid HMn0 4 , are in 

 many ways closely related to the heptoxide of chlorine and per- 

 chloric acid HC104. Of the lower oxides of manganese, MnO 

 is basic, and Mn 2 3 feebly basic. Mn0 2 is feebly acidic, Mn0 3 

 more strongly so, and permanganic acid (from Mn 2 7 ) is a very 

 active acid. Contrary to the habit of feebly acidic and feebly 

 basic oxides, such as those of zinc, aluminium, and tin, the basic 

 oxides of manganese are not at all acidic, and the acidic oxides, 

 with the exception of Mn0 2 , are not also basic. There are thus the 

 five following, rather well-defined sets of compounds, showing 

 five different valences of the element. Of these the first, fourth, 

 and fifth are the most stable and the most important. 



1. Manganous compounds, MnO, Mn(OH) 2 , MnS0 4 etc. These 

 compounds resemble those of the magnesium family (and those of 

 Fe++). The salts of weak acids, such as the carbonate and sul- 

 phide, are easily made, and there is little hydrolysis of the halides. 

 The salts are pale-pink in color. 



2. Manganic compounds, Mn 2 3 , Mn(OH) 3 , Mn 2 (S0 4 ) 3 , [MnClJ. 

 The salts resemble aluminium salts in behavior, but are very 

 unstable (see p. 142) and are completely hydrolyzed by water. 

 The salts are violet in color. 



3. Manganites, Mn0 2 , H 2 Mn0 3 , CaMn0 3 . The alkali man- 

 ganites are strongly hydrolyzed, like the silicates. 



4. Manganates, Mn0 3 , H 2 Mn0 4 , K 2 Mn0 4 . The salts resemble 

 the sulphates and chromates, but are much more easily hy- 

 drolyzed. They are green in color. 



