THE FATTY ACIDS 97 



It is miscible in all proportions with water, alcohol and ether. 

 Heat is evolved on adding water to acetic acid and there is a con- 

 traction in volume. 



The liquid is not inflammable, but its vapour burns with a blue 

 flame. 



Acetic acid is a very corrosive liquid and dissolves oils, resins, 

 camphor, gelatin and many metallic salts which are insoluble in 

 water. It is a very stable compound and is attacked only with 

 difficulty by the most powerful oxidising agents. It is not affected 

 by nitric acid or chromic acid. A solution of chromic acid in acetic 

 acid is employed for oxidising hydrocarbons. Chlorine converts it 

 into chbracetic acids (p. loo). 



As an acid, acetic acid forms salts. Most of the salts are soluble 

 in water ; the silver and mercurous salts are sparingly soluble ; the 

 sodium and potassium salts are soluble in alcohol. Some of the basic 

 salts are insoluble. 



The salts are prepared by boiling the acid with the oxide or 

 carbonate of the metal until the solution is neutral, filtering and 

 evaporating the solution until crystallisation begins. The metallic 

 acetates on being subjected to dry distillation yield acetone. 



Reactions and Detection. 



Free acetic acid may be recognised by its odour. The acid solution 

 is exactly neutralised with sodium hydroxide and then tested. Neutral 

 solutions of acetates maybe tested directly. Insoluble (basic) acetates 

 are converted into sodium acetate by boiling with sodium carbonate, 

 filtering off the insoluble carbonate, neutralising and testing the 

 filtrate: 



(1) On warming the solution with dilute sulphuric acid the pungent 

 odour of acetic acid is evolved. 



(2) On adding ferric nitrate or ferric chloride, the neutral solution 

 gives a deep red liquid, which contains ferric acetate. An excess must 

 be avoided. On boiling, the liquid becomes colourless and a brownish- 

 red precipitate of basic ferric acetate is produced. 



The cold red liquid is decolourised by adding dilute hydrochloric 

 or sulphuric acid, but not by mercuric chloride solution. 



(3) Concentrated solutions and dry acetates give the smell of ethyl 

 acetate on heating with alcohol and concentrated sulphuric acid. 



(4) On mixing a solid acetate with arsenious oxide and heating, 

 cacodyl oxide, which has a garlic-like smell, is evolved Only minute 

 quantities should be used as the product is very poisonous. 



4 CH 3 . COONa + As 2 3 = (CH 3 ) 2 As . O . As(CH 3 ) 2 + 2CO 2 + 2 Na 2 CO 3 . 



4 



