CYANOGEN COMPOUNDS. 



CN 

 (i) Cyanogen. 



CN 



Cyanogen, as it contains only the two elements carbon and nitro- 

 gen, is the simplest carbon compound containing nitrogen. It is 

 present in the gases of the blast furnace and is formed on passing 

 electric sparks between carbon poles in an atmosphere of nitrogen, 

 and on treating ammonium oxalate or oxamide (p. 1 30) with dehy- 

 drating agents, e.g. phosphorus pentoxide : 



COONH 4 CONH 2 CN 



| -> | = 2 H 2 0+ | 



COONH 4 CONH 2 CN. 



Preparation. 



Cyanogen is most readily prepared by heating mercuric cyanide : 



CN 



Hg(CN) 2 =| + Hg. 

 CN 



On heating a sntall quantity of mercuric cyanide in a dry test 

 tube, white fumes are given off which condense on the cooler parts 

 of the tube. On igniting the gas at the open end it will be observed 

 to burn with its characteristic pink flame. 



Cyanogen is also prepared by heating a concentrated solution of 

 I part of potassium cyanide with 2 parts of copper sulphate dissolved 

 in 4 parts of water. A yellow precipitate of cupric cyanide, Cu(CN) 2 , 

 is first formed and this decomposes into cyanogen and cuprous 

 cyanide, CuCN : 



4 KCN + 2CuSO 4 = Cu 2 (CN) 2 + (CN) 2 + 2K 2 SO 4 . 



Properties. 



Cyanogen is a colourless gas with a peculiar pungent smell and 

 has been condensed to a liquid. It burns with a pink flame forming 

 carbon dioxide and nitrogen. It is easily soluble in water and 

 alcohol and is intensely poisonous. 



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