PREPARATION OF PURE CONCENTRATED ACETIC ACID. 257 



Hence it is better to use 2 parts of sodium bisulphate and 1 part 

 of crystallized lead acetate, a mixture of lead sulphate and neutral 

 sodium sulphate then remaining in the retort, which can be 

 softened with water and readily removed. Instead of bisulphate 

 any desired quantity of Glauber's salt may be added to the lead 

 acetate and the whole distilled with the above-mentioned quantity 

 of sulphuric acid. An excess of the latter is to be avoided, the 

 acetic acid being decomposed at a high temperature by concen- 

 trated sulphuric acid. Distillation is carried on in a sand-bath. 

 For very concentrated acetic acid lead acetate dephlegmated 

 by gentle heating is used instead of the crystallized acetate and 

 decomposed with one-third of its weight of concentrated sulphuric 

 acid. 



The acetic acid is, however, not entirely pure in either case, as it 

 contains a small quantity of sulphurous acid formed by the action 

 of the sulphuric acid upon the acetic acid. This impurity can be 

 readily removed by rectification over brown lead oxide (Pbo 2 ) or 

 finely powdered peroxide of manganese (MnO 2 ), sulphate of lead 

 remaining in the retort in the first case, and in the latter a mix- 

 ture of manganous sulphate and hyposulphate. 



Bucholz gives the following direction which saves rectification, 

 the required quantity of peroxide of manganese being at once added 

 to the mixture of lead acetate and sulphuric acid : 192 parts of 

 lead acetate, 24 of Glauber's salt, 6 of peroxide of manganese, 56 

 of sulphuric acid, and 72 of water; the yield is 178 parts of 

 entirely pure acetic acid of 1.045 specific gravity. 



By decomposing solution of lead acetate or of barium acetate 

 with sulphuric acid, pure acetic acid which has, however, but 

 little strength, can be prepared without distillation, as it is only 

 necessary not to use an excess of the salts or of sulphuric acid. 

 Completely anhydrous barium acetate should be used, the crystal- 

 lized product being less suitable for the purpose as it readily loses 

 its water of crystallization. For 100 parts of barium acetate, 

 38.4 parts of concentrated sulphuric acid are required and for 

 100 parts of normal lead acetate 25.9 parts of sulphuric acid. The 

 solution of barium acetate should not be too concentrated, as other- 

 wise the barium sulphate does not appear in the ordinary form of 

 17 



