132 Biological Chemistry. 



analogous to the formation of chlorides and hypochlorites 

 when chlorine is passed into alkalis 



(CN) 2 + 2KOH = KCN + KCNO + H 2 

 C1 2 + 2KOH = KC1 + KC10 + H 2 



On hydrolysis with acids, the (CN) group undergoes the 

 usual transformation into the carboxyl group, yielding 

 oxalic acid 



(CN) 2 + 4H 2 = HOOC-COOH + 2NH 3 



Hydrocyanic acid, HCN, which bears a similar rela- 

 tionship to cyanogen that chlorine does to hydrochloric 

 acid, can be prepared by the method already mentioned 

 of treating potassium ferrocyanide with sulphuric acid 



2K 4 Fe(CN) 6 + 3H 2 S0 4 = 6HCN + K 2 FeFe(CN) 6 + 3K 2 S0 4 



For this reaction dilute sulphuric acid is used. When 

 concentrated sulphuric acid is employed, the following 

 reaction takes place : 



K 4 Fe(CN) 6 + 6H 2 (from the water of crystallization of the ferro- 

 cyanide) + 6H 2 S0 4 = 600 + 2K 2 S0 4 + FeS0 4 + 3(NH 4 ) 2 S0 4 



It can also be obtained from potassium cyanide (a salt 

 which is made on a large scale for certain industrial pro- 

 cesses, such as extraction of gold from tailings) by treat- 

 ment with sulphuric acid 



2KCN + H 2 S0 4 = K 2 S0 4 + 2HCN 



Hydrocyanic acid, when obtained anhydrous, is a colour- 

 less intensely poisonous liquid, of boiling point 25. Two 

 reactions are of interest. Its aqueous solution on keeping 

 undergoes decomposition, forming, amongst other products, 

 ammonium formate 



and on reduction it yields methylainine 



2 ==CH 3 NH a 



