IKON. 297 



rent of dry hydrochloric acid gas. The solution and salt absorb 

 oxygen very readily : 



3FeCl 2 -f O = FeO + 2FeCl 3 . 



Ferric chloride, Perri chloridum, FeCl r 6H 2 O =268.32 (Chlo- 

 ride, sesqui-chloride, or perchloride of iron), is obtained by adding to 

 the solution of ferrous chloride (obtained as mentioned above) hydro- 

 chloric and nitric acids in sufficient quantities, and applying 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 dioxide being formed 

 also : 



3FeCl 2 + HNO 8 + 3HC1 = 3FeCl s + 2H 2 O + NO. 



By sufficient evaporation of the solution, ferric chloride is obtained 

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

 quescent, has an acid reaction, and a strongly styptic taste. The 

 water of crystallization cannot be expelled by heat, because heat 

 decomposes the salt, free hydrochloric acid and ferric oxide being 

 formed. 



Experiment 30. Dissolve by the aid of heat 1 gramme of fine iron wire in 

 about 4 c.c. of hydrochloric acid, previously diluted with 2 c.c. of water. 

 Filter the warm solution of ferrous chloride, mix it with 2 c.c. of hydrochloric 

 acid, and add to it slowly and gradually about 0.6 c.c. of nitric acid. Evap- 

 orate in a fume chamber as long as red vapors escape ; then test a few drops 

 with potassium ferricyanide, which should not give a blue precipitate ; if it 

 does, the solution has to be heated with a little more nitric acid until the con- 

 version into ferric chloride is complete and the potassium ferricyanide pro- 

 duces no precipitate. Ferric chloride thus obtained may be mixed with 4 c.c. 

 of hot water and set aside, when it forms a solid mass of FeCl 3 .6H 2 O. How 

 much FeCl 2 , how much FeCl 3 , and how much FeCl 3 .6H 2 O can be obtained 

 from 1 gramme of iron? 



Solution of ferric chloride, Liquor ferri chloridi. This is a 

 solution in water, containing 29 per cent, of the anhydrous ferric 

 chloride. It is a reddish-brown liquid of specific gravity 1.315, hav- 

 ing the taste and reaction of the dry salt. This solution, mixed with 

 alcohol in the proportion of 35 to 65 parts by volume, and left stand- 

 ing in a closed vessel for at least three months, forms the tincture of 

 ferric chloride, Tinctura ferri chloridi. By the action of the alcohol 

 on ferric chloride this is reduced to the ferrous state, while at the 

 same time a number of other compounds are formed, imparting to the 

 liquid an ethereal odor. 



Solutions of ferric salts usually have a brown color and show an acid reac- 

 tion. This is due to the partial hydrolysis of the salts, forming ferric hydroxide 



