262 
MANUFACTURE OF ACETIC ACID. 
self throughout every part of the vessel, its acid entering into com- 
bination with the base employed, and forming the acetate, which 
falls to the bottom of the vessel, and in its descent meets with the 
ascending streams of vapor, the acid of which renders it perfectly 
neutral; meanwhile the more aqueous parts of the vapor become 
liberated, and maintaining their temperature ascend, and in their 
passage through the successive layers of the base are thereby de- 
prived of their remaining acid. The vapor thus reduced to simple 
steam is allowed to escape through one or more pipes at the top 
of the vessel ; and as this steam still maintains a boiling tem- 
perature, it is conducted through a worm to evaporate the acetate, 
or the mother-liquor by its heat. The distillation of the acid is con- 
tinued until the acetate in the vessel is arrived at the proper degree of 
concentration for crystallization, which is easily ascertained by 
examining a small quantity drawn off by a cock at the bottom of 
the vessel, by which cock the whole contents are discarged when 
the operation is completed. 
As the operation draws to its close, by nearly all the base hav- 
ing combined with the acid, the vapor issues out of the vessel 
charged with a certain portion of acid ; and in order that no loss 
may be sustained by its escape into the atmosphere, it is conduct- 
ed into another vessel prepared like the first mentioned, but charg- 
ged superabundantly with the base, to take up every particle of 
the acid issuing out of the first vessel, until the operation in that 
first vessel is ended. As the temperature of the solution of the ace- 
tate can never exceed that of the vapor, the crystalline product is 
•)f fine quality. 
Manufacture of Acetic Acid. — In treating of the manufacture 
of acetic acid we shall not enter upon any other processes than 
those of the decomposition of the acetates, as effected either by 
heat or by sulphuric acid. 
Acetic Acid obtained by Decomposition of the Acetates by means 
of Heat — Aromatic Vinegar. — We have already mentioned, whilst 
speaking of the production of pyro-acetic spirit, that when the 
acetates are submitted to dry distillation, acetic acid is produced. 
The following is another extract from the table then quoted, show- 
ing the quantity of acetic acid obtained by the decomposition of the 
metallic acetates : — 
