PREPARATION OF PURE CONCENTRATED ACETIC ACID. 261 



The purpose of the excess of lime is to expel the volatile basic 

 bodies, ammonia and methylamine, and to decompose the volatile 

 oils. The non-volatile bodies dissolved in the crude wood-vine- 

 gar separate partially in saturating with lime and partially in 

 boiling and evaporating. A portion of these foreign substances 

 remains, however, in solution, combined with the lime so that the 

 clear fluid obtained by decantation or filtration has a brown red 

 color. 



It is now slightly acidulated with crude hydrochloric acid, 4 

 pounds of the latter being at the utmost required for 22 impe- 

 rial gallons of wood-vinegir. A considerable quantity of tarry 

 substances is separated and after their removal the solution ap- 

 pears less highly colored. By now evaporating to dryness and 

 roasting in the previously described manner, or sharply drying 

 upon heated iron plates, the salt is obtained as a dirty gray- 

 brown mass. The acetic acid separated from it is, however, 

 scarcely more impure than that obtained from gray salt, and by 

 using somewhat more potassium bichromate, about 2 or 3 per 

 cent., in the rectification, there is no difference in the quality of 

 the acid. 



Reichenbach destroys the empyreumatic bodies in crude cal- 

 cium acetate by distilling with an excess of concentrated sulphuric 

 acid. According to his statements, a clear colorless acetic acid of 

 great strength and showing no empyreumatic odor is obtained. 

 The crude distillate, however, contains sulphurous acid, so that 

 it has to be rectified over pyrolusite and sulphuric acid or over 

 minium or potassium bichromate. 



According to Schnedermann, the wood-vinegar freed from 

 wood-spirit is exposed with an excess of quicklime to the air for 

 24 hours, whereby the separation of the tarry substances is claimed 

 to be promoted. The clear dark-brown solution of the calcium 

 salt is drawn off and after heating to boiling mixed with calcium 

 chloride solution as long as the latter produces a discoloring effect. 

 The now yellowish brown solution is evaporated and finally 

 decomposed with sulphuric acid (or hydrochloric acid). The 

 acetic acid obtained by distillation is claimed to possess only a 

 slightly yellow color and to be suitable for many technical pur- 



