ACETATES AND THEIR MANUFACTURE. 



289 



and the volume of the fluid containing the litharge increases, but, 

 when the boiling point is reached, in the condensing vessels, only 

 the acetic acid is retained, while the litharge is first converted 

 into sexbasic and then into tribasic acetate. To obtain, however, 

 neutral salt, either the vapors must be somewhat expanded or 

 several condensing vessels placed one after the other. 



Fig. 63 shows the distilling apparatus, consisting of a boiler, a, 

 of strong sheet-copper. The vapors pass through a copper-pi pe, 

 6, into the wooden vat c, lined with lead, and about 35 inches in 

 diameter and 67 inches deep. In this vat are four bottoms, <7, 

 of thick lead provided with fine perforations. Short lead pipes, 

 soldered into these bottoms and arranged as shown in the figure, 

 serve to conduct the vinegar vapors in the vat to and fro in the 

 interspaces between the lead bottoms. For each still at least 

 three of such vats are connected with each other. Upon the 

 lead bottoms is first placed a layer of linen or of flannel, and 

 next a layer of litharge 2 to 4 inches deep. To prevent the 

 litharge from packing, it is mixed with an equal volume of 



Fig. 63. 



pebbles about the size of a pea. The vats are provided with 

 lids of sheet-copper coated with lead. From the lid of the last 

 vat a pipe leads to a worm surrounded with cold water. The 

 stop-cocks on the bottoms of the vats permit the discharge of the 

 19 



