ACETIC ACID 



9 



by means of the swing crane, then the cylinder itself is lifted out and replaced imme- 

 diately by another one previously charged. When the cylinder which has been 

 taken out of the furnace is entirely cooled, its cover is removed, and the charcoal 

 is emptied. Five cubic meters of wood furnish about 7 chaldrons and a half of 

 charcoal. 



The carbonisers of Reichenbach and Schwartz are usually employed with special 

 reference to the manufacture of wood-charcoal, the condensation of the volatile 

 products being only a secondary consideration. 



In England the distillation of wood, with especial reference to the manufacture 

 of pyroligneous acid, is generally carried out in large iron retorts, placed hori- 

 zontally in the furnace ; the process, in fact, closely resembling' the distillation of 

 coal in the manufacture of coal gas, excepting that the retorts are generally larger, 

 being sometimes 4 feet in diameter, and 6 or 8 feet long. Generally two, or even 

 three, are placed in each furnace, as shown in fig. 3, so that the fire of the single 

 furnace, a, plays all round them. The doors for charging the retorts are at one end, b 

 (fig. 4), and the pipe for carrying off the volatile products at the other, c, by which 

 they are conducted, first to the tar-condenser, d, and finally through a worm in a 

 large tub, e, whero the crude acetic acid is collected. 



Of course, in different localities an endless variety of modifications of the process 

 are employed. 



In the Forest of Dean, instead of cylindrical retorts, square sheet-iron boxes are 

 used, 4 ft. 6 in. by 2 ft. 9 in., which are heated in large square ovens. 



Dr. Ure gives the following description of special works in Glasgow : 



The cylinders here employed are 6 feet long, and both ends project a little beyond 

 the brickwork. One end has a disk, or round plate of cast-iron, well fitted and 



firmly bolted to it, from the centre of which an iron tube, about 6 inches in diameter, 

 proceeds, and enters at a right angle the main tube of refrigeration. The diameter 

 of this tube may be from 9 to 14 inches, according to the number of cylinders. The 

 other end of the cylinder is called the mouth of the retort ; this is closed by a disc of 

 iron, smeared round its edge with clay-lute, and secured in its place by iron wedges. 

 The charge of wood for such a cylinder is about 8 cwt. The hard woods oak, 

 ash, birch, and beech are alone used in this manufactory fir not being found to 

 answer. The heat is kept up during the day, and the furnace allowed to cool during 

 the night. Next morning the door is opened, the charcoal removed, and a new 

 charge of wood introduced. The average product of crude vinegar is 35 gallons. 

 It is much contaminated with tar, is of a deep brown colour, and has a specific gra- 

 vity of 1'025. Its total weight is therefore about 300 Ibs. ; but the residuary charcoal 

 is found to weigh no more than one-fifth of the wood employed ; hence nearly one- 

 half of the ponderable matter of the wood is dissipated in incondensable gases. 



With regard to the relative advantages of cylindrical retorts or square boxes, 

 it should be remarked, that the cylinders are more adapted for the distillation of the 

 large billets of Gloucestershire and the refuse ship timber of Glasgow, Newcastle, 



