148 METALS AND THEIR COMBINATIONS. 



heat until complete oxidation has taken place. The nitric acid 

 oxidizes the hydrogen of the hydrochloric acid to water, while 

 the chlorine combines with the ferrous chloride, nitrogen di- 

 oxide being also formed : 



6FeC) 2 + 2HNO 3 + 6HC1 = 3Fe 2 Cl 6 + 4H 2 O + 2NO. 



By sufficient evaporation of the solution, ferric chloride is 

 obtained as a crystalline mass of an orange-yellow color ; it is 

 very deliquescent, has an acid reaction, and a strongly styptic 

 taste. The water of crystallization cannot be expelled by heat, 

 as decomposition of the salt takes place, free hydrochloric acid 

 and ferric oxide being formed. 



Solution of chloride of iron, Liquor ferri chloridi, U. S. P. This 

 is a solution in water, containing 37.8 per cent, of the anhydrous 

 ferric chloride. It is a reddish-brown liquid of specific gravity 

 1.405, having the taste and reaction of the dry salt. This solu- 

 tion, mixed with about 2 parts of alcohol and left standing in a 

 closed vessel for several months, forms the tincture of chloride of 

 iron, Tinctura ferri chloridi. U. S. P. 



Dialyzed iron is an aqueous solution of about 5 per cent, of 

 ferric hydrate with some ferric chloride. It is made by slowly 

 adding to a solution of ferric chloride, ammonium hydrate as 

 long as the precipitate of ferric hydrate formed is redissolved 

 in the ferric chloride solution on shaking violently. The clear 

 solution thus obtained is placed in a dialyzer, floating in water, 

 which latter is renewed every day until it shows no reaction 

 with silver nitrate. The ammonium chloride passes through 

 the membrane of the dialyzer into the water, while all iron as 

 hydrate with some chloride is left in solution. 



The combination of an oxide or hydrate with a neutral salt is 

 usually called a basic salt or oxy-salt ; dialyzed iron is a highly 

 basic oxychloride of iron. 



Ferrous iodide, FeI 2 . When water is poured upon a mixture 

 of metallic iron (fine wire is best) and iodine, the two elements 

 combine directly, forming a pale green solution of the ferrous 

 iodide, from which the salt may be obtained by evaporation. 



