ACETIC ACID. 



413 



tar, and several other ingredients, among which may be named creosote ; 

 it is from this source all the creosote, for the cure of toothache, is obtained. 

 To purify this liquid it is first distilled, and 

 this separates much of the tar ; it is then 

 mixed with lime, evaporated to dryness, and 

 heated to expel the remaining tar and other 

 impurities ; it is next mixed with sulphate 

 of soda and water, and the whole stirred to- 

 gether ; the soda, now in union with the 

 acetic acid, is washed out from the lime 

 and strained quite clear ; it is afterwards 

 evaporated till it crystallises, and vitriol 

 (sulphuric acid) then added; finally the 

 acetic acid is distilled over, and the sulphuric acid left in union with the 

 soda, forming sulphate of soda, to be used in a similar process for the next 

 batch of acid. The acetic acid is now quite colourless, transparent, and very 

 sour, possessing a fragrant smell. This is not pure acetic acid, but contains 

 a considerable quantity of water. The acetic acid of commerce, mixed with 

 seven times its bulk of water, forms an acid of about the strength of malt 

 vinegar, perfectly wholesome, and agreeable as a condiment. 



Fig. 422. Vinegar-cooling process. 



Fig. 423. Tan-yard and pits. 



Pure acetic acid may be made by mixing dry acetate of potash with oil 

 of vitriol in a retort, and distilling the acetic acid into a very cold receiver ; 

 this, when flavoured with various volatile oils, forms the aromatic vinegar 

 sold by druggists. It is a very strong acid, and if applied to the skin will 

 quickly blister it. 



Acetate of lead, or sugar of lead, is obtained by dissolving oxide of 



