380 THE POPULAR SCIENCE MONTHLY. 



Sugar. Alcohol. Carbonic dioxide. 



C G H 12 6 = 2C 2 H c O + 2C0 3 



The bubbles which appear when cider is " working " are carbonic 

 dioxide. In the conversion of alcohol to acetic acid, a subtance called 

 aldehyde is first formed. The oxygen for these changes is taken from 

 the air : 



Alcohol. Oxvgen. Aldehyde. Water. 



C 3 H 6 + O = C 2 H 4 + H 2 0. 



Acetic acid. 



C 2 H 4 + O = C 2 II 4 2 



By substantially the same slow process as that still employed in 

 the household was all vinegar obtained from the time of Moses, or 

 earlier, down to 1822. In 1814 Berzelius had found out the chemical 

 composition of acetic acid, and De Saussure that of alcohol ; so that, 

 after Doebereiner had discovered that a weak solution of alcohol ex- 

 posed to the air in contact with platinum-black was converted to acetic 

 acid, he was enabled to set forth the theory on which depends the 

 modern "quick process" of vinegar making — the method now regu- 

 larly employed in the vinegar-factories of EurojDe and America. The 

 essential feature of this process consists in bringing the alcoholic solu- 

 tion into intimate contact with the air by causing it to trickle through 

 a mass of loose material, which effects the acetification in from twenty- 

 four to forty-eight hours. The operation is carried on in wooden tubs, 

 six to ten or more feet high, called generators. Around the sides of 

 the generator, a few inches above the bottom, is a ring of air-holes. 

 Just above the air-holes is a perforated false bottom, and from this 

 nearly to the top the generator is filled with beech-wood shavings, 

 which are closely curled so that they will not crush and prevent the 

 air circulating freely through them. A few inches above the shavings 

 is a wooden head or sieve, perforated with small holes, which serves 

 to distribute the alcoholic liquid, or " wash," evenly over the shavings. 

 Several air-pipes are inserted in the sieve, extending a few inches above 

 and below it. The generator has a cover with a hole in the middle 

 through which the wash is poured in, and the ascending current of air 

 passes out. The vinegar-room is kept at a temperature between 70° 

 and 90° Fahr. A high temperature and large supply of air hasten the 

 operation, but cause loss by the evaporation of the alcohol. If the 

 temperature falls much below 60°, the acetification stops, and putrefac- 

 tion sets in ; while if too little fresh air is supplied, aldehyde, the half- 

 way product mentioned above, instead of being promptly converted to 

 acetic acid, is evaporated and lost. The presence of aldehyde in the 

 air may be detected by its penetrating aroma and by the eyes smart- 

 ing. The wash must be passed several times through the shavings, 

 in order to effect its complete acetification. 



Two kinds of vinegar are sold by grocers in the United States for 

 domestic use — cider-vinegar and white-wine vinegar. Both kinds are 



