292 



METALS AND THEIR COMBINATIONS. 



Summary of analytical characters of the earth-metals and 



chromium. 



27. IRON. (Ferrum.) 

 Fe = 55.5. 



General remarks regarding- the metals of the iron group. The 

 six metals (Fe, Co, Ni, Mn, Cr, Zn) belonging to this group are distin- 

 guished by forming sulphides (chromium excepted) which are insolu- 

 ble in water, but soluble in dilute mineral acids; they are, conse- 

 quently, not precipitated from their neutral or acid solutions by 

 hydrogen sulphide, but by ammonium sulphide as sulphides 

 (chromium as hydroxide); their oxides, hydroxides, carbonates, 

 phosphates, and sulphides are insoluble; their chlorides, iodides, 

 bromides, sulphates, and nitrates are soluble in water. 



With the exception of zinc, these metals are magnetic ; they de- 

 compose water at a red heat, the oxide being formed and hydrogen 

 liberated; in dilute hydrochloric or sulphuric acid they dissolve 

 with formation of chlorides or sulphates respectively, and liberation 

 of hydrogen. 



Zinc is constantly bivalent, nickel is usually bivalent, but trivalent 

 in a few compounds, cobalt is bi- and trivalent, iron and chromium 

 are bi-, tri-, and sexivalent, manganese is bi-, tri-, sexi-, and septiva- 

 lenf. All the metals, except zinc, form several oxides, the higher 

 ones of which have acid character, as iron trioxide, chromium tri- 

 oxide, manganese trioxide and heptoxide. 



Occurrence in nature. Among all the heavy metals, iron is both 

 the most useful and the most widely and abundantly diffused in 

 nature. It is found, though usually in but small quantities, in nearly 

 all forms of rock, clay, sand, and earth ; its presence in these being 



