PREPARATION OF PURJE CONCENTRATED ACETIC ACID. 263 



From 100 Ibs. of crystallized sodium acetate 80 Ibs. of acetic 

 acid with 55 per cent, of acetic anhydride (1.065 specific gravity) 

 are obtained, or 100 Ibs. of acid with 44 per cent, of acetic 

 anhydride. Asa rule, the acid is, however, not entirely pure ; 

 it generally contains traces of hydrochloric acid, of sulphurous 

 acid and of copper. It is, therefore, again distilled in the same 

 apparatus, now provided, however, with a neck and worm of silver 

 or of stoneware, some sodium acetate, or, still better, minium or 

 potassium bichromate being added. In each case the hydrochloric 

 acid remains behind as metallic chloride (chloride of sodium, 

 lead, potassium and chromium). In the first case the first por- 

 tions passing over contain some sulphurous acid and may have a 

 slightly empyreumatic odor ; but the acid passing over later on is 

 pure. In the second and third case the sulphurous acid is con- 

 verted into sulphuric acid by the disposable oxygen of the 

 minium of the bichromate and retained as sulphate, the empy- 

 reumatic substances being also destroyed. 



The portion of acid of a pure taste, which passes over first in 

 rectifying, being weakest, is used for household purposes ; later on 

 comes a stronger acid up to 10 B. = 1.075 specific gravity. 



Although in thoroughly rectified acid no impurity can be 

 established by the most sensitive reagent, for instance, potassium 

 permanganate, its taste is not as pure as that of acid prepared with- 

 out distillation. This imperfection can, however, be concealed by 

 the addition of a small quantity of acetic ether or of alcohol 

 (about 1 quart to 22 imp. gallons), which is converted into acetic 

 ether. 



Mollerat's method renders, however, even this resort unneces- 

 sary. According to it, pure sodium acetate obtained in small 

 crystals by disturbing crystallization is decomposed with 1 equiv- 

 alent of concentrated sulphuric acid (65 Ibs. of acid to 100 Ibs. 

 of salt) in a large vat provided with a false bottom. The sub- 

 stances being thoroughly mixed by means of a stirring apparatus, 

 Fig. 62, the mixture is allowed to stand till the next day. De- 

 composition is completely effected in this time at an ordinary 

 temperature, the acetic acid being liberated and the greater portion 

 of the neutral sodium sulphate, which dissolves but little in the 

 acid, crystallized out. To prevent the perforations of the false 



