IRON, NICKEL, COBALT 495 



^Cke ferrous salts are vale green and give colorless solutions, 

 containing ferrous-ion Fe^. The ferric salts, containing the ion 

 Fe 4 " 1 " 1 ", are usually yellow in solutioi 

 ide produced by hydrolysis. Q // 



? Ferrous Sulphate FeSO 4 . When the bath of dilute sul- 

 phuric acid, used in cleaning iron for making tin-plate (p. 508), 

 and galvanized iron (p. 449), is becoming exhausted, scrap iron is 

 thrown in to use up the rest of the acid. The solution gives, on 

 evaporation, pale green crystals of ferrous sulphate, FeS04,7H 2 O 

 (copperas or green vitriol^. The salt is used in making ink (see p. 

 499) and rouge (see p. 496), and in purifying water (p. 470). 



- Chlorides of Iron. Ferrous chloride FeCl 2 is obtained in 

 solution when iron displaces hydrogen from hydrochloric acid (p. 

 52), and is isolated by evaporation. The hydrate FeCl 2 ,4H 2 O is 

 pale green, the anhydrous salt colorless. When chlorine is dis- 

 solved in the solution, or when the latter, acidified with hydro- 

 chloric acid, is exposed to the air, ferric chloride FeCl 3 is produced : 



2FeCl 2 + C1 2 *+ 2FeCl 3 or 2Fe++ + C1 2 - 2Fe+++ + 2C1~ 

 4FeCl 2 + O 2 + 4HC1 -> 4FeCl 3 + 2H 2 O 



and is familiar in the form of a yellow hydrate FfiCl^^fiH^O ob- 

 tained by evaporation. Other oxidizing agents, such as nitric 

 acid, produce the same change. 



Ferric chloride, in solution, has an acid reaction, due to hydroly- 

 sis. It is reduced to ferrous chloride by shaking the solution, or 

 more quickly by boiling it, with iron filings : 



- Fe -> 3FeCl 2 or 2Fe+++ + Fe -> 3Fe++. 



'Hydroxides of Iron. Ferric hydroxide Fe(OH) 3 appears as 

 a brown precipitate when an equivalent amount of sodium hydrox- 

 ide is added to a solution of a ferric salt: 



FeCla + 3NaOH - Fe(OH) 3 j + 3NaCl. 



