42 VINEGAR, CIDER, AND FRUIT-WINES. 



Acetic Acid. 



Pure acetic acid, C 2 H 4 O 21 , cannot be directly obtained from 

 vinegar, but only from acetates by methods which will be described 

 later on. The strongest acetic acid which can be prepared is 

 known as glacial acetic acid, from its crystallizing in icy leaflets 

 at about 40 F. Above a temperature of about 60 F. the 

 crystals fuse to a thin, colorless liquid of an exceedingly pungent 

 and well r known odor. When diluted it has a pleasant acid taste 

 and agreeable odor. Pure acetic acid is a powerful restorative 

 when applied to the nostrils in impending fainting. It is the 

 strongest of the organic acids and nearly as acrimonious as sul- 

 phuric acid. When dropped on the skin it acts as an escharotic, 

 speedily raising a blister and producing much heat and rapid 

 inflammation ; when taken into the mouth or applied to any 

 mucous membrane it blackens like sulphuric acid. Highly con- 

 centrated acetic acid is a solvent of many volatile oils, resins, 

 albuminates, and glue; the ability to dissolve lemon oil is used in 

 the practice as a test for the high concentration of acetic acid, 

 since in the presence of only 2 per cent, of water in the acid 

 lemon oil is no longer dissolved by it. 



The specific gravity of pure acetic acid is at 59 F. : 



According to Onderaans 1.0553 



Roscoe 1.0564 



Kopp 1.0590 



Mendelejeff 1.0607 



Mohr 1.0600 



According to Mohr's determinations, the specific gravity of 

 pure acetic acid varies much at different temperatures, it being 



1.0630 at 54.5 F. 



1.0600 " 59.0 " 



1.0555 "i 68.0 " 

 1.0498 77.0 " 



1.0480 79.0 " 



Mixtures of acetic acid and water show a peculiar behavior in 

 regard to their specific gravity ; the latter rises steadily until the 

 content of water amounts to from 20 to 23 per cent. ; the density 

 of the liquid then diminishes so that a mixture containing 46 



