240 CHEMISTRY. 



CHAPTER XVIII. 



GROUP V. MANGANESE, IRON, COBALT, NICKEL, CHROMIUM. 



335. Manganese. This metal is never found in nature, and 

 it is rather difficult to obtain it from its ores on account 

 of the great stability of its oxides and its high melting- 

 point. It is remarkable for the number of the compounds 

 which it forms with oxygen. There are six of them. Here 

 follow their names and formulae : 



1. Manganous oxide MnO. 



2. Manganese sesquioxide Mn 2 O 3 . 



3. Manganous manganic oxide Mrt^O 4 . 



4. Manganese dioxide MnO 2 . 



5. Manganous anhydride MnO.,. 



6. Permanganic anhydride Mn 3 O 7 . 



The first two form numerous compounds. Number 4 we 

 have already used for preparing oxygen. Numbers 5 and 

 6 are not known in the free state, but their compounds are 

 important; they combine with bases forming manganates 

 and permanganates respectively. Potassium permanganate 

 is used in dilute solution as a tooth- wash. Its solution 

 has a magnificent purple color. It is a powerful oxidizing 

 agent. 



336. Iron. Iron when pure is almost white, and is rather 

 soft, but very tenacious. It is quite malleable. It can be 

 made into leaves so thin that it would take over three hun- 

 dred of them to make half an inch in thickness. But even 

 the best of iron found in the market is far from being pure. 

 It contains small amounts of carbon and other substances. 

 Perfectly pure iron is never obtained except in small quan- 



