PREPARATION OF PURE CONCENTRATED ACETIC ACID. 253 



progress through the retort the materials are completely carbon- 

 ized and all the volatile products disengaged. Two pipes branch 

 off from the extremity of the retort, one of which passes down- 

 wards and dips into an air-tight vessel of cast-iron or a cistern of 

 water into which the carbonized substance falls ; the other is an 

 ascending pipe and carries off' the volatile products of the distil- 

 lation into the condenser, which consists of copper or iron pipes 

 immersed in or surrounded by water. 



According to statements by Hargreaves and others, saw-dust 

 from resinous woods gives as much wood-vinegar in 24 hours 

 with 8 or 10 retorts 14 inches in diameter, as with 16 retorts 3 

 feet in diameter. 



In another comparison of the two systems, 8 Halliday retorts 

 consuming 22 tons of saw-dust weekly produce : 



Wood-vinegar of specific gravity 1.05 . . 2494 gallons. 

 Tar 240 



While a ton of oak (2240 Ibs.) carbonized in large retorts 

 gives : 



Wood-vinegar of specific gravity 1.03 . . 1277 pounds. 

 Charcoal 600 " 



To make the comparison more satisfactory it would have been 

 necessary to state the kind of gallon employed and the percentage 

 of real acid in the wood- vinegar, since hydrometers and specific 

 gravities give indications of very little value in this case. 



CHAPTER XXII. 



PREPARATION OF PURE CONCENTRATED ACETIC ACID. 



THE strongest vinegar which can be prepared by the process 

 of fermentation contains somewhat above 13 per cent, of acetic 

 acid, and it is difficult, even with the greatest care, to continu- 

 ously obtain a product of this strength. The difficulties encoun- 

 tered are due to the fact that the vinegar ferment is incapable of 

 vigorous vegetation in a fluid containing, besides 10 per cent, of 



