262 VINEGAR, CIDEK, AND FRUIT-WINES. 



poses. The acid thus obtained, however, undoubtedly contains 

 hydrochloric acid and has to be rectified over sodium acetate. 



Acetic acid of a pure taste suitable for household use as well as 

 for technical purposes is, as previously mentioned, exclusively 

 obtained from sodium acetate either by distillation or without it. 



Sodium acetate is, to be sure, completely decomposed by 1 

 equivalent of sulphuric acid (36 Ibs. of acid to 100 Ibs. of crys- 

 tallized salt) and, on a small scale in glass retorts, it is effected 

 without difficulty, because a strong heat can finally be applied 

 without injury. On a large scale, however, where the distillation 

 is executed by means of steam* of two atmospheres, 1 equivalent 

 of sulphuric acid is not advantageous, because the remaining solid 

 neutral sodium sulphate retains much strong acetic acid. It is, 

 therefore, recommended to gradually pour 2 equivalents of sul- 

 phuric acid (72 Ibs. of acid to 100 Ibs. of the salt) upon the 

 crystallized salt in a copper still and introduce steam after allow- 

 ing the whole to rest several hours. The residue remaining in 

 this process is sodium bisulphate, which remains entirely fluid at 

 the distilling temperature and from which all the acetic acid can 

 be expelled. A further advantage of this method is that at first 

 very strong acetic acid passes over, which can be collected by 

 itself and worked into glacial acetic acid (see below). Later on 

 comes more dilute acid, because the water of crystallization of the 

 acetate, which was at first retained by the bisulphate, also passes 

 over. 



The bisulphate while still hot is poured into slightly conical 

 shallow copper pans in which it congeals on cooling. It might 

 thus be brought into commerce, but as the manufacturer would 

 have to compete with large chemical works producing mineral 

 acids, it is more advantageous to utilize it by distilling it with 

 crude sodium acetate in the proportion of 3 : 2, whereby 2.5 parts 

 of neutral anhydrous sodium sulphate remain behind, which, as 

 previously mentioned, can be again used for the preparation of 

 sodium acetate, while 2 parts of acetic acid with about 40 per 

 cent, of acetic anhydride, which is pure enough for many pur- 

 poses, pass over. 



* With the use of a free fire, the stills suffer very much. 



