32 



AQUEOUS DISTILLATE OF CRUDE PYROLIGNEOUS ACID. 



GENERAL TREATMENT FOR THE SEPARATION OF ACETIC ACID AND METHYL ALCOHOL. 



This distillate, comprising from 30 to 50 per cent of the weight of 

 the wood, contains as its chief constituents, methyl alcohol (4 to 6 

 per cent), acetic acid (8 to 14 per cent), acetone (0.2 per cent), and 

 tar held in solution by the acids and alcohol present, the balance 

 being practically all water contained in the wood and resulting from 

 its decomposition. The distillate is a dark red liquid having a strong 

 acid reaction and an empyreumatic odor. Its specific gravity varies 

 with the amount of water in the wood and the character of wood 

 used, but usually falls between 1.020 and 1.050. This crude liquor 

 is used to a limited extent in making "pyrolignite of iron," or " black 

 iron liquor," an impure acetate of iron used in dyeing and calico print- 

 ing. There are a number of different methods followed for separating 

 the tar from this aqueous distillate and the several valuable con- 

 stituents of the latter from each other. As has been said, raw tar is 

 usually separated by settling all the liquors in large wooden vats, 

 but even under the most favorable conditions the crude liquor still 

 contains, dissolved in it, considerable quantities of tar, which inter- 

 fere seriously with the purification of acetate of lime and alcohol 

 prepared therefrom. In practice one of two general methods is used 

 in handling the settled crude liquor: 



(1) It is neutralized directly with lime and the alcohol distilled. 

 The resulting calcium acetate is much contaminated with tar,, and 

 when evaporated and dried at about 125 C. forms the commercial 

 " brown acetate of lime," containing from 65 to 75 per cent of real 

 acetate of lime (C 2 H 3 O 2 ) 2 Ca, the balance being tarry matter, calcium 

 carbonate, and water. 



(2) The crude pyroligneous acid without previous neutralization 

 is distilled from the tar it contains. This is the better practice, and 

 here again one of two procedures may be followed: 



(a) Distil the alcohol, acid, and other volatile constituents, leaving 

 only tar (boiled tar) in the still. Then carefully neutralize this dis- 

 tillate with milk of lime, force it to a still (lime-lee still, fig. 15) and 

 redistil. Alcohol, aldehyde, and ketones pass over, while the acetic 

 acid remains in the still in combination with lime. The most perfect 

 separation and highest yields are obtained by this method. 



(&) In the second procedure the alcohols, aldehydes, and ketones 

 are separated from the acids by fractionation, using a column still 

 (fig. 12). The first fractional portion, containing alcohol, acetone, 

 and other compounds having low boiling points, but not the acids, is 

 received in the alcohol vat until its density reaches 1.000. The 

 second fraction or portion contains the acids and is received in the 



[Cir. 86] 



