782 ACETYL. 



Aldehyde is capable of combining directly with ammonia and 

 potash, thus evincing an approach to the acid character. 



Ammonia-aldehyde, C 4 H 3 O,NH 3 4-HO, crystallizes in acute 

 rhombohedrons, which are transparent, and of great lustre. 

 These crystals fuse between 70 and 80 cent, and distil without 

 alteration at 100 cent. 



Acetaly or compound of aldehyde with ether, AcO,EO + HO= 

 C 8 H 9 O 3 , was discovered by Dobereiner, and is formed by the 

 action of platinum black on the vapour of alcohol with the pre- 

 sence of oxygen. Acetal is a colourless very fluid liquid, having 

 a peculiar odour, suggesting that of Hungary wines. It boils at 

 95.2 cent., its density is 0.823 at 20 cent. It is soluble in 6 

 or 7 parts of water, and mixes with alcohol in all propor- 

 tions. 



Resin of aldehyde is a product of the decomposition of alde- 

 hyde by alkalies, with the assistance of air. 



ACETOUS OR ALDEHYDIC ACID. 



Formula of the hydrated acid, C 4 H 3 O 2 + HO=AcO 2 -f HO. 

 This acid is formed when aldehyde is heated in contact with 

 oxide of silver, one half of the oxide being reduced to the me- 

 tallic state, while the other half unites with the aldehydic acid 

 formed. If to water in a test-tube containing a few drops of 

 aldehyde, a little nitrate of silver be added, and ammonia so as 

 to precipitate the oxide of silver, and then the tube be rapidly 

 heated by the flame of a spirit-lamp, the silver is deposited on 

 the tube with a bright surface, like a mirror, and forms a 

 beautiful experiment. When the salts of this acid are evapo- 

 rated, they become brown, and undergo decomposition. 



ACETIC ACID. 



Formula of the hydrated acid HO + C 4 H 3 O 3 =HO+AcO 3 . 



Vinegar has long been derived by the action of air upon alco- 

 holic liquors, such as wine and beer, but the remarkable disco- 

 very of Dr. J. Davy, that platinum black in contact with alcohol 

 became incandescent, and gave rise to acetic acid, first led Dobe- 

 reiner to the discovery that alcohol by absorbing oxygen, gives 

 rise to water and acetic acid, without disengaging carbonic acid. 

 He found that the elements of 1 atom of alcohol absorb 4 atoms 



