412 



SCIENTIFIC RECREATIONS. 



Vinegar contains acetic acid, which is distilled from wood, as we shall see 

 presently. Vinegar is made abroad by merely permitting wine to get sour ; 

 hence the term Vin-aigre. In England vinegar is made from " wort," of 

 malt which is fermented for a few days, and then put into casks, the bung- 

 holes of which are left open for several weeks, until the contents have become 

 quite sour. The liquid is then cleared by isinglass. The vinegar of com- 

 merce contains about 6 per cent, of pure acetic acid, and some spirit, some 

 colouring matter, and, of course, water. Wood vinegar (pyroligneous acid) 



Fig. 420. Vinegar ground. 



is used for pickles. The ordinary vinegar when distilled is called white 

 vinegar, and it may also be obtained from fruits, such as gooseberries or 

 raspberries. 



Acetic acid, or "wood vinegar," is prepared 

 as follows : There are some large iron cylinders 

 set in brickwork over furnaces, and these cylinders 

 have each a tube leading to a main pipe in which 

 the liquid is received for condensation. The 

 cylinders, which contain about seven or eight 

 hundredweight, are filled with logs of wood, either 

 oak, beech, birch, or ash, the door is closely fastened, 

 and the joints smeared with clay ; the fires are 

 now lighted and kept up all day, till the cylinders 

 are red-hot ; at night they are allowed to cool. In 

 the morning, the charcoal, into which the wood is 

 now converted, is withdrawn, and a fresh charge 

 supplied ; it is then found that about thirty or 

 forty gallons of liquid has condensed in the main 

 tube from each cylinder, the remainder being charcoal and gases which pass 

 off; the liquid is acid, brown, and very offensive, and contains acetic acid, 



Fig. 421. Boiler or copper. 



