122 PREPARATION OF ACETIC ACID. 



When perfectly free from water, acetic acid consists of — 

 Carbon . . . 47-5 per cent., or 4 atoms 

 Hydrogen . . 5-8 " or 3 " 

 Oxygen. . . 46-7 " or 3 " 



'4 



100 



It is therefore represented by the formula C, 

 those given in the preceding sections for starch, sugar, dec, tlie numbers 

 representing the atoms of hydrogen and oxygen are equal, and conse- 

 quently these elements are in the proportion to form water. Hence, 

 vinegar, like sugar, may be represented by carbon and water. 



Let us consider for a moment the several processes by which this acid 

 IS usually formed. 



1°. By the distillation of wood. — This a method by which wood 

 vinegar — often caW^d pyroligneous acid — is prepared in large quantity. 

 "Wood which has been dried in the air is put into an iron retort and distil- 

 led. The principal products are vinegar, water, and tarry matter. 

 The decomposition is of a complicated description, but by comparing 

 the constitution of woody fibre with that of vinegar, we can readily see 

 the nature of the changes by which the latter is produced. 

 Woody Fibre is = C^a Hg Og 

 3 of Vinegar are =0,2 Hg Og 



Difference = H^ O^ ; or the elements 



of one atom of water. One portion of the woody fibre, therefore, com- 

 bines with the elements of an atom of water, obtained by the decompo- 

 sition of another portion, and thus vinegar is produced. *" 



2°. Manufacture of Vinegar from Cane Sugar. — It is a well known 

 fact in domestic economy, that if cane sugar be dissolved in water, a 

 little vinegar added to it, and the solution kept for a length of time at a 

 moderate temperature, the whole will be converted into vinegar without 

 any sensible fermentation. This process is frequently followed in the 

 preparation of household vinegar, and was formerly adopted to some ex- 

 tent in our chemical manufactories. It will be recollected that we re- 

 presented Cane Sugar by C12 ^\o Oio, while 

 3 of Vinegar = C12 Hg O3 



Difference Hi O^ ; or the elements 



of an atom of water, which cane sugar must lose in order to be convert- 

 ed into vinegar. Whether the change in this instance takes place by 

 the direct conversion of cane sugar into vinegar, or whetlier the former 

 is previously transformed into grape sugar, has not been satisfactorily de- 

 termined. 



3°. Manufacture of Vinegar from Alcohol. — In Germany, where 

 common brandy is cheaper than vinegar, it is found profitable to manu- 

 facture this acid from weak spirit. For this purpose it is mixed with a 

 little yeast, and then allowed to trickle over wood shavings moistened 

 with vinegar, and contained in a cask, the sides of which are perforated 

 with holes for the admission of a current of air. By this method oxy- 

 gen is absorbed from the air, and in 24 hours the alcohol in the spirit is 

 converted into vinegar and -.^-ster. 



