ACETATES AND THEIR MANUFACTURE. 267 



hydrogen which can be replaced by a metal : C 2 H 4 O 2 = C 2 H 3 O 21 H. 

 If this hydrogen is replaced by a univalent metal (for instance, K 

 or Xa), a salt of the formula C 2 H 3 O 2 Xa or C 2 H 3 NaO 2 is formed. 

 If, however, 2 atoms of hydrogen in 2 molecules of acetic acid 

 be replaced by a bivalent metal, (C 2 H. s O 2 ) 2 Ba, etc., is formed, and 

 finally with a trivalent metal, (Al) (C 2 H 3 O 2 ) 3 A1. 



Most of the acetates are readily soluble in water; the acetates 

 of molybdenum are insoluble ; and those of argentic monoxide 

 and of mercurous oxide dissolve with great difficulty. 



The preparation of the acetates is effected partially by dis- 

 solving the oxides or carbonates in acetic acid, which must, how- 

 ever, not be too concentrated for the barium and calcium salts, 

 and partially by double decomposition, generally by means of 

 the lead salt and a sulphate of another metal. 



The acetates of potassium, sodium, and ammonium show a 

 slightly alkaline reaction and the readily soluble basic lead ace- 

 tates .a strong alkaline one ; the remaining lead acetates react neu- 

 tral or slightly acid. 



The acetates of the fixed alkalies and alkaline earths, submit- 

 ted to dry distillation, yield water and acetone, while the oxide, 

 and sometimes the reduced metal, remain in the distilling appa- 

 ratus. The solutions of alkaline acetates become mouldy after a 

 time. 



The acetic acid may be set free from its combinations by sul- 

 phuric acid, and is easily recognized by its characteristic odor ; 

 its salts, in common with those of organic acids, become black by 

 the action of heat. 



Potassium neutral acetate, KC 2 H 3 O 2 . Acetic acid is present 

 in the sap of many plants, and is generally combined with po- 

 tassium, forming neutral potassium acetate. When wood is cal- 

 cined the potassium acetate is decomposed, the acetic acid being 

 replaced by carbonic acid. It is by this interchange that the 

 carbonate of potassium found in wood ashes is formed. 



It is prepared by dissolving pure carbonate of potassium in a 

 slight excess of acetic acid, evaporating and fusing. The excess 

 of acid is necessary to replace that which is lost during evapora- 

 tion ; without it the salt turns yellow or brown. 



Another method of obtaining it is by decomposing normal 



