362 CONSIDERATION OF CARBON COMPOUNDS. 



the above reaction 3, the object being to convert the soluble cyanide into an 

 insoluble ferrocyanide of iron. In most cases of poisoning by hydrocyanic 

 acid there is, however, no time for the action of such an antidote, in conse- 

 quence of the rapidity of the action of the poison, and the treatment is chiefly 

 directed to the maintenance of respiration by artificial means. 



Cyanic acid, HCNO, and Sulphocyanic acid, HCNS, are both 

 colorless acid liquids, the salts of which are known as cyanates and 

 sulpho-cyanates. These salts are obtained from alkali cyanides by 

 treating them with oxidizing agents or by boiling their solutions with 

 sulphur, when either oxygen or sulphur is taken up by the alkali 

 cyanide : 



KCN + O = KCNO = Potassium cyanate. 

 KCN + S = KCNS : Potassium sulphocyanate. 



The acids themselves may be liberated from their salts by dilute 

 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. 



Me tallo cyanides. Cyanogen not only combines with metals to 

 form the true cyanides, which may be looked upon as derivatives of 

 hydrocyanic acid, but cyanogen also enters into combination 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 com- 

 mon 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-cynogen radicals are ferrocyanogen [Fe u 

 (CNy]^, smdferricyanogen [Fe/^CN")^ 1 ]. These two radicals con- 

 tain iron in the ferrous and ferric state respectively, and form, upon 

 combining with hydrogen, acids which are known as hydroferrocyanic 

 add, H 4 Fe(CN) 6 (tetrabasic), and hydroferricyanic acid, H 6 Fe 2 (C!N") 12 

 (hexabasic) ; the salts of these acids are termed ferrocyanides and 

 ferricvanides. 



