PREPARATION OF PURE CONCENTRATED ACETIC ACID. 265 



Decomposition is complete in a few hours and the sodium sul- 

 phate crystallized out on the bottom, the supernatant acetic acid 

 being partially in a fluid and partially in a crystallized state. 

 The acid is then siphoned off and pure calcium acetate added as 

 above. The sodium sulphate is then regained and can be again 

 used in the fabrication. 



The acid thus obtained need only be reduced to the strength 

 desired by the consumer by diluting with water. 



Glacial Acetie Acid. 



Glacial acetic acid can be prepared by distilling 12 pounds ot 

 pure anhydrous sodium acetate with 11 pounds of concentrated 

 sulphuric acid. The last portion, which is frequently somewhat 

 empyreumatic, is collected by itself and the portion first passed 

 over rectified over sulphuric acid and pyrolusite to remove traces 

 of sulphurous acid. 



A better method published by Melsens is based upon the prop- 

 erty of neutral calcium acetate to absorb 1 equivalent of hydrated 

 acetic acid and to form a solid acid salt which decomposes only, 

 at 392 F., into hydrated acetic acid, which passes over, and into 

 neutral acetate which remains behind. Hence, by decomposing 

 sodium acetate with 2 equivalents of sulphuric acid and collecting 

 the strong acid first passing over as long as it shows from 10 to 

 8 B., it is only necessary to pour it into a copper still upon 

 fused potassium acetate coarsely powdered after cooling, and after 

 standing for several hours to distill over a free fire, the still 

 being provided with a silver neck and a worm of the same 

 material. When the temperature exceeds 248 F. all the weaker 

 acid has passed over and the receiver is changed. At 392 F. 

 glacial acetic acid passes over which is again rectified over fused 

 potassium acetate and then exposed to a low temperature to 

 freeze. 



Glacial acetic acid can also be prepared in the same manner 

 from acetic acid of 1.061 specific gravity obtained by VolckePs 

 method or by distilling it over anhydrous calcium chloride and 

 cooling the distillate, whereby one portion crystallizes. The por- 

 tion which remains liquid is poured off and again distilled over 



