784 ACETYL. 



scale by the distillation of wood, generally that of oak coppice 

 deprived of the bark, which is used in tanning. The watery 

 fluid containing the acid, and tarry matter which distil over 

 together, are separated, mechanically, in a great measure, by 

 subsidence. The acid may be freed from a portion of the em- 

 pyreumatic oils it holds in solution, by a single distillation. It 

 is purified completely by neutralising it with lime, crystallizing 

 the acetate of lime repeatedly, decomposing the latter by sul- 

 phate of soda, and fusing the acetate of soda by a high tempera- 

 ture, at which the empyreumatic matters are volatilised or 

 destroyed. By distilling 3 parts of the acetate of soda, well 

 dried and in powder, with 9.7 parts of sulphuric acid, a highly 

 concentrated and pure acetic acid is obtained. 



The proportions last mentioned give 2 parts of a hydrated 

 acetic acid, which is distilled again, and the two last thirds of 

 distilled liquid exposed to 24 or 25, for the protohydrate of 

 acetic acid, which crystallizes. The crystals may be drained, 

 fused, and crystallized again, to obtain the hydrate of acetic 

 acid in a state of purity. Below 63, the hydrate crystallizes in 

 shining transparent plates or tables, which fuse above 63 into a 

 limpid liquid, of density 1.063 ; it boils at 248. The odour of 

 this acid is penetrating and characteristic ; it forms blisters on 

 the skin, like a mineral acid. The liquid acid mixes with water, 

 alcohol, ether, and several essential oils in all proportions. It 

 dissolves camphor and some resins. The vapour of the acid in a 

 state of ebullition may be kindled, and burns with a pale blue 

 flame, producing water and carbonic acid. Nitric acid has no 

 action on acetic acid ; sulphuric acid with heat blackens acetic 

 acid, with an evolution of sulphurous acid. 



Acetic acid increases somewhat in density by a slight dilu- 

 tion ; the greatest condensation occurring in the hydrate con- 

 sisting of 1 atom of anhydrous acid and 3 atoms of water, of 

 which the density is 1.07. The strength of a dilute acetic acid 

 is best ascertained by the quantity of marble it dissolves. 



Acetic acid forms neutral salts, and with many metallic ox- 

 ides sub-salts containing 2 and 3 atoms of base to 1 atom of 

 acid. Most of its neutral salts are soluble. It is recog- 

 nised in combination by the peculiar odour of acetic acid evolved 

 when concentrated sulphuric acid is added. M. Liebig recom- 

 mends as the most certain means of discovering the presence of 

 acetic acid, or of an acetate in any substance, to distil it with 



