290 VEGETABLE SUBSTANCES. 



a violent poison when swallowed in the quantity of 

 two or three drams. 



A crude kind of vinegar is prepared for calico-printers 

 by the distillation of wood : this is called Pyroligneous 

 acid. The process used to obtain this product con- 

 sists in subjecting wood enclosed in iron retorts to a 

 strong red heat, by which means vapour is given off, 

 which is conducted to, and condensed in a suitable ap- 

 paratus. A series of these retorts, having a cylindrical 

 form, each being about six feet long, and of four feet 

 diameter, is built horizontally in brick-work, so that the 

 flame of one furnace may play around two retorts. 

 Both ends of each cylinder project somewhat beyond 

 the brick-work ; one end is effectually closed by a disc 

 of cast iron, well fitted and firmly bolted. From the 

 centre of this an iron tube, about six inches in diameter, 

 proceeds, and enters at right angles the main tube of 

 refrigeration, through which, when the apparatus is in 

 operation, the vapour of the wood finds its way to a 

 condenser, whence it flows in a liquid form into a re- 

 ceiver. The diameter of this tube varies from nine to 

 fourteen inches, according to the number of cylinders 

 used. The other end of the retort is open to receive 

 the charge of wood, which, for a cylinder of the above 

 dimensions, is about eight cwt. It is then closed by 

 a disc of iron, luted round its edge, and secured in 

 its place by wedges. The hard woods, such as oak, 

 ash, birch, and beech, are alone used; fir is not consi- 

 dered to answer the purpose. When the cylinders 

 are charged the furnaces are put into action, and an 

 intense heat is kept up during the whole of the day : 

 towards night the fire is extinguished, and the retorts 

 are allowed to cool. Next morning the mouth of 

 each retort is opened, the wood now reduced to char- 

 coal is removed, and a new charge of wood is intro- 

 duced. The average product of acid from eight cwt. 



