THE FATTY ACIDS 95 



Reactions and Detection. 



A solution of formic acid must be exactly neutralised with soda 

 or ammonia before the tests can be carried out. Solid formates are 

 obtained by evaporating their solutions to dryness. 



(1) On boiling a solution of a formate with dilute sulphuric acid, 

 formic acid is evolved. Its pungent odour is only perceptible with 

 strong solutions. 



(2) On heating a solid formate with concentrated sulphuric acid, 

 carbon monoxide is evolved and it may be ignited at the mouth of 

 the test tube. 



(3) Ethyl formate is formed when solid formates are heated with 

 alcohol and concentrated sulphuric acid. 



(4) A red solution containing ferric formate is obtained when 

 ferric chloride or ferric nitrate is added to a solution of a formate. 

 On heating a reddish-brown precipitate of basic ferric formate is 

 produced. 



Formic acid differs from acetic acid in its reducing properties 

 which are due to the presence of the aldehyde group CHO in its 

 molecule. 



(5) In concentrated solution it forms with silver nitrate a white 

 crystalline precipitate of silver formate. This precipitate darkens on 

 standing owing to reduction to metallic silver. A precipitate is not 

 formed in dilute solution, but the solution is reduced on heating with 

 separation of metallic silver. The reduction is retarded in the pre- 

 sence of ammonia. 



(6) On adding mercuric chloride solution and heating a pre- 

 cipitate of mercurous chloride is produced, which, on further heating, 

 may be reduced to metallic mercury. 



