256 VINEGAR, CIDER, AND FRUIT-WINES. 



by these means, the amount is considerably larger than without 

 such an addition. The rock salt remaining unchanged, the resi- 

 due can be repeatedly used. Comparatively weak acetic acid 

 can, however, only be obtained by this method. For a stronger 

 product it is necessary to use an acetate and decompose it by a 

 mineral acid. 



The cheapest way is to fix the acetic acid on lime and to distill 

 the calcium acetate with crude hydrochloric acid. After neutra- 

 lizing the vinegar with milk of lime and bringing the solution of 

 the acetate to dryness, 100 Ibs. of the salt are dissolved in 110 to 

 120 Ibs. of crude hydrochloric acid of 1.16 specific gravity and 

 the whole is subjected to distillation. The acetic acid obtained 

 by this method is not entirely free from hydrochloric acid, but 

 can be readily purified by rectification over acetate of sodium or 

 of calcium. 



Preparation of Acetic Acid from Commercial Acetates and 

 from those obtained from Wood- Vinegar. - 



The most highly concentrated acetic acid, known as glacial 

 acetic acid, was formerly exclusively obtained by the dry distilla- 

 tion of crystallized verdigris (normal cupric acetate). By drying 

 this salt at between 320 and 356 F. and heating, a mixture of 

 acetone and glacial acetic acid is obtained which only requires 

 rectification. The yield of acetic acid amounts to J of the verdi- 

 gris used (see Acetates). This process has, however, been almost 

 entirely abandoned, cheaper methods having been introduced. 



The principal acetates now used for the purpose are those of 

 lead, barium, calcium, and sodium ; the latter two, being the 

 cheapest, are exclusively used for the manufacture on a large scale, 

 though the former are very suitable for the production on a small 

 scale. 



By decomposing normal lead acetate, frequently called sugar of 

 lead, with one equivalent of sulphuric acid (4.9 Ibs. of sulphuric 

 acid to 1 9 Ibs. of the salt) sulphate of lead remains in the retort 

 while acetic acid distills over. The sulphate of lead adheres, 

 however, very tightly to the retort, and, being insoluble in water, 

 it can, as a rule, not be removed without injury to the retort, 



