CYANOGEN AND ITS COMPOUNDS. 337 



tions with sulphur, when either oxygen or sulphur is taken up 

 by the alkaline cyanide : 



KCy + O = KCyO = Potassium cyanate. 



KCy -(- S = KCyS = Potassium sulphocyanate. 



The acids themselves may be liberated from their salts by 

 diluted mineral acids. Sulphocyanates give with ferric salts a 

 deep red color, which is not affected by hydrochloric acid, but 

 disappears on the addition of mercuric chloride. 



Metallocyanid.es. Cyanogen not only combines with metals to 

 form the true cyanides, which may be looked upon as deriva- 

 tives of hydrocyanic acid, but cyanogen also enters into combi- 

 nation with certain metals (chiefly iron), forming a number of 

 complex radicals, which upon combining with hydrogen form 

 acids or with basic elements form salts. It is a characteristic 

 feature of the compound cyanogen radicals thus formed that 

 the analytical characters of the metals (iron, etc.) entering 

 into the radical are completely hidden. Thus, the iron in ferro- 

 or ferricyanides is not precipitated by either alkalies, soluble 

 carbonates, ammonium sulphide, or any of the common reagents 

 for iron, and its presence can only be demonstrated by these 

 reagents after the organic nature of the compound has been 

 destroyed by burning it (or otherwise), when ferric oxide is left, 

 which may be dissolved in hydrochloric acid and tested for in 

 the usual manner. 



The principal iron-cyanogen radicals are ferrocyanogen 



These two radicals contain iron in the ferrous and ferric state 

 respectively, and form, upon combining with hydrogen, acids 

 which are known as hydroferrocyanic acid, H 4 FeCy 6 (tetrabasic), 

 and hydroferricyanic acid, H 6 Fe 2 CN 12 , or IlgFejCy^ (hexabasic) ; 

 the salts of these acids are termed ferrocyanides and ferri- 

 cyanides. 



Potassium ferrocyanide, Potassii ferrocyanidum, K 4 Fe(CN) 6 .3H.,0 

 421.9 (Ferrocyanide of potassium, Yellow prussiate of potash). This 

 salt is manufactured on a large scale by heating refuse animal 

 matter (scrapings of horns, hoofs, hides, etc.) with potassium 

 carbonate and waste iron (filings, etc.). The fused mass is 



22 



