40 VINEGAR, CIDER, AND FRUIT-WINES. 



To prepare pure aldehyde 3 parts of potassium clichromate in 

 small pieces are placed in a flask surrounded by a freezing mix- 

 ture and a well-cooled mixture of 2 parts of spirit of wine, 4 of 

 sulphuric acid, and 4 of water added. After connecting the flask 

 with a condenser the freezing mixture is removed ; a violent reac- 

 tion soon sets in and the liquid begins to boil. The vapors have 

 first to pass through an ascending tube surrounded by warm water 

 at about 122 F. Alcohol and different products are condensed 

 and flow back while the vapor of the aldehyde, after having 

 passed through a descending condenser, is absorbed in anhydrous 

 ether. 



Pure aldehyde thus obtained is a colorless liquid of the com- 

 position C 2 H 4 O. Its specific gravity is 0.800, and it boils at 

 about 71.5 F. It has a pungent and suffocating smell and is 

 readily soluble in water, alcohol, and acetic acid. Like all the 

 aldehydes it is very easily oxidized and acts, therefore, as a pow- 

 erful reducing agent. Thus, on heating it with a little ammonia 

 and nitrate of silver, metallic silver separates out, coating the 

 sides of the vessel with a bright mirror. It combines with ammo- 

 nia and forms a crystalline compound which has a peculiar smell 

 of mice. 



Though it is likely that in the fabrication of vinegar by the 

 quick process, besides aldehyde, acetic and formic ethers are 

 formed, they are of comparatively little importance for our pur- 

 poses. Of more importance, however, is acetal, the formation of 

 this combination affording an interesting insight into the compli- 

 cated processes accompanying the conversion of alcohol into acetic 

 acid. 



Acetal. 



This combination is best prepared by distributing pieces of 

 pumice, previously moistened with 25 per cent, alcohol over a 

 large glass plate, placing watch crystals containing platinum black 

 upon the pieces of pumice and covering the whole with a large 

 bell-glass. The alcohol absorbed by the pumice being converted 

 into acetic acid, 60 per cent, alcohol is poured upon the plate and 

 the air in the bell-glass from time to time renewed. In a few 



