254 VINEGAR, CIDER, AND FRUIT-WINES. 



acetic acid, a sufficient quantity of alcohol for the further forma- 

 tion of 3 per cent, of acetic acid, and it requires the greatest vigi- 

 lance and utmost care as regards the maintenance of the correct 

 temperature and ventilation in the factory to convert, under these 

 conditions, alcohol into acetic acid. 



It has frequently been asked whether it is advisable to increase 

 the content of acetic acid in vinegar prepared from alcohol, which 

 contains only 7 or 8 per cent., to 12 or 14 per cent, by the addi- 

 tion of concentrated acetic acid obtained from wood. This ques- 

 tion may be answered in the affirmative, provided absolutely pure 

 acetic acid, free from all empyreumatic substances, be used, and it 

 is advisable in all cases to test the acetic acid as to a content of 

 these substances as well as to the presence of sulphurous acid and 

 of metals (copper, tin, etc.). 



To establish the presence of empyreumatic substances, dilute 

 the concentrated acetic acid with twice or three times its volume 

 of distilled water, and add a few drops of a solution of potassium 

 permanganate. In the presence of empyreumatic substances or 

 sulphurous acid the red coloration of the fluid disappears at once. 

 The manner of detecting the presence of sulphurous acid and of 

 copper and other metals has already been given on p. 211. 



Acetic acid which gives negative results with these tests may 

 be considered as chemically pure, and can without hesitation be 

 used for increasing the strength of vinegar prepared from alcohol ; 

 in fact, the employment of the so-called vinegar essence for this 

 purpose is constantly increasing. The fluid occurring in com- 

 merce under this name is highly concentrated acetic acid with a 

 content of acid varying between 60 and 80 per cent. By diluting 

 this fluid with water so that its content of acetic acid is equal to 

 that of ordinary table vinegar, a product is obtained which, as re- 

 gards taste, can be scarcely distinguished from ordinary vinegar 

 prepared from alcohol. Chemically there is also but little differ- 

 ence, the vinegar prepared from alcohol containing a small quan- 

 tity of acetic ether and of extractive substances which do not 

 occur in vinegar essence obtained by distillation. 



For the preservation of fruit, cucumbers, and the so-called 

 mixed pickles, and, in fact, for all purposes where only a fluid 

 containing acetic acid and water is required, acetic acid obtained 



