IRON. 



165 



Summary of analytical characters of the earth-metals and 



chromium. 



25. IRON. (Ferrum.) 

 Feii = 55.9 (55.88). 



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

 six metals (Fe, Co, M, 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 

 hydrosulphuric acid, 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. 



With the exception of zinc, which is bivalent, the metals of the 

 iron group are bivalent in some compounds, trivalent in others, and 

 form a number of oxides, the higher of which show, in some cases, 

 decidedly acid properties, as, for instance, chromic or manganic 

 oxides. 



The trivalence of the elements mentioned is now assumed to be 

 due to the combining of two quadrivalent atoms of these elements. 

 It is for this reason that we find in ferric, manganic, or chromic 

 compounds always a double atom of these elements exerting a valence 

 of six. The constitution of ferric chloride, Fe 2 Cl 6 , and ferric oxide, 

 Fe 2 O 3 , may be graphically represented thus : 



