AMINES AND AMIDES. CYANOGEN COMPOUNDS. 363 



Potasssium ferrocyanide, Potassii ferrocyanidum, K 4 Pe(CN) 6 . 

 3H 2 O = 421.9 (Yellow prussiate of potash). This salt is manu- 

 factured on a large scale by heating refuse animal matter (waste 

 leather, horns, hoofs, etc.) with potassium carbonate and iron (filings, 

 etc.). The fused mass is boiled with water, and from the solution 

 thus formed the crystals separate on cooling. 



The nitrogen and carbon of the organic matter (heated as above 

 stated) combine, forming cyanogen, which enters into combination 

 first with potassium and afterward with iron. 



Potassium ferrocyanide forms large, translucent, pale lemon-yellow, 

 soft, odorless, non-poisonous, neutral crystals, easily dissolving in 

 water, but insoluble in alcohol. 



Analytical reactions : 



1. Ferrocyanides heated on platinum foil burn and leave a residue 

 of (or containing) ferric oxide. 



2. Ferrocyanides heated with concentrated sulphuric acid evolve 

 carbonic oxide ; with dilute sulphuric acid liberate hydrocyanic acid ; 

 with concentrated hydrochloric acid liberate hydroferrocyanic acid. 



3. Soluble ferrocyanides give a blue precipitate with ferric salts 

 (Plate L, 5) : 



3K 4 Fe(CN) 6 + 2Fe 2 Cl 6 = 12KC1 -f Fe 4 (FeC 6 N 6 ) 3 . 



Potassium Ferric Potassium Ferric ferro 



ferrocyanide. chloride. chloride. cyanide. 



The blue precipitate of ferric ferrocyanide, or Prussian blue, is 

 insoluble in water and diluted acids, soluble in oxalic acid (blue 

 ink), and is decomposed by alkalies with separation of brown ferric 

 hydroxide and formation of potassium ferrocyanide. The addition 

 of an acid restores the blue precipitate. 



4. Soluble ferrocyanides give with cupric solutions a brownish-red 

 precipitate of cupric ferrocyanide. (Plate III., 5.) 



5. Soluble ferrocyanides produce, with solutions of silver, lead, and 

 zinc, white precipitates of the respective ferrocyanides. 



6. Ferrocyanides give with ferrous salts a white precipitate of 

 ferrous ferrocyanide, soon turning blue by absorption 6f oxygen. 

 (Plate I., 4.) 



Potassium ferricyanide, K c Pe 2 (CN) 12 (Red prussiate of potash). 

 Obtained by passing chlorine through solution of potassium ferro- 

 cyanide : 



2K 4 Fe(CN) 6 + 2C1 = 2KC1 + K 6 Fe 2 (CN) 12 . 



Potassium Chlorine. Potassium Potassium 



ferrocyanide. chloride. ferricyanide. 



