ACETIC ACID 5 



being a very volatile body, it is desirable always to effect the oxidation as completely 

 and rapidly as possible, to avoid the loss of alcohol by the evaporation of this 

 aldehyde. 



Alcohol contains C'lFO 2 (CWC) 



Aldehyde C 4 H 4 0* (CfH'O) 



Acetic acid C 4 H 4 4 (C 2 H 4 O 2 ) 



The process, therefore, consists first in the removal of two atoms of hydrogen from 

 alcohol, which are converted into water aldehyde being produced and then the 

 further union of this aldehyde with two atoms of oxygen to convert it into acetic acid. 

 See ALDEHYDE. 



By the oxidation of alcohol, pure acetic acid is obtained : but the vinegars of com- 

 merce are mixtures of the pure acetic acid with water ; with saccharine, gummy, and 

 colouring matters ; with certain ethers (especially the acetic ether), upon which their 

 agreeable aromatic flavour depends ; with empyreumatic oils, &c. 



The pure acetic acid (free from water and other impurities) may be obtained most 

 advantageously, according to Melsens, 1 by distilling pure acetate of potash with an 

 excess of acetic acid (which has been obtained by the redistillation of ordinary acetic 

 acid, procured either by oxidising alcohol, or by the destructive distillation of wood) : 

 the acid which first passes over contains water ; but finally it is obtained free. 



Properties of pure Acetic Acid. When absolutely pure, acetic acid is a colourless 

 liquid of specific gravity 1-064, which at temperatures below 62 F. (17 C.) 

 solidifies into a colourless crystalline mass. It has strongly acid properties, being as 

 powerfully corrosive as many mineral acids, causing vesication when applied to the 

 skin ; and it possesses a peculiarly pungent, though not a disagreeable smell. 



The vapour of the boiling acid is highly combustible, and burns with a blue flame. 

 Hydrated acetic acid dissolves camphor, gliadine, resins, the fibrine of blood, and 

 several organic compounds. When its vapour is conducted through a slightly 

 ignited porcelain tube, it is converted entirely into carbonic acid and acetone, an atom 

 of the acid being resolved into an atom of each of the resultants. A a white heat 

 the acid vapour is converted into carbonic acid, carburetted hydrogen, and water. 



It attracts water with great avidity, mixing with it in all proportions. Its solution 

 in water increases in density with the increase of acetic acid up to a certain point ; 

 but beyond this point its density again diminishes. Its maximum density being 

 1-073, and corresponding to an acid containing C 4 H 4 4 + 2Aq, which may be ex- 

 temporaneously produced by mixing 77'2 parts of crystallised acetic acid with 22'8 

 parts of water. This hydrate boils at 104 C. (219 F.), whilst the crystallised acid 

 boils only at 120 C. (248 F.) * 



The proportion of acetic acid in aqueous mixtures may therefore be ascertained, 

 within certain limits, by determination of the specific gravity. See AOETIMETRY. 



The following Table, by Mohr, indicates the per-centage of acetic acid in mixtures 

 of different specific gravities ; but of course this is only applicable in cases where no 

 sugar or other bodies are present which increase the specific gravity : 



Abstract of Mohr 1 s Table of the Specific Gravity of Mixtures of Acetic AM and 



Water. 3 



1 Comptes Eendus, xix. 611. * Gerhardt, Chimie Organlque, i. 718. 



3 Mohr, Ann. der Cbem. nnd Phar. xx.xi. 227. 



