CH,.CO.H -I- 0= CEILCOOH.
Acetic aldehyde Acetic acid.
Acetic Aldehyde or Acetaldehyde.— When not qualified in any way the term aldehyde is understood to mean acetic aldehyde, the sub stance whose formation from ethyl alcohol has just been described. It is found among the products of the dry distillation of sugar, in wines during the ageing process, in crude wood alcohol and in crude petroleum. Aldehyde in this sense) is a colorless liquid with a suffo cating smell, miscible in all proportions with water, alcohol and ether, boiling at 70° F. and having a specific gravity of 0.800 at 32° F. It is highly inflammable and burns with an almost non-luminous flame. It is capable of existing in several polymeric states, each having the same chemical composition as aldehyde, but differing from it in appearance and behavior. Thus al though aldehyde may be preserved for a long time if kept in contact with excess of acid, in its pure state it soon deposits a solid substance in needle-like crystals known as metaldehyde, which sublimes at 240° F. without decomposi
tion, and is reconverted into aldehyde when confined and heated to F. By treatment with sulphuric or hydrochloric acid, aldehyde may be converted into a liquid known as par aldehyde, a colorless liquid which boils at Z55° F., has a vapor density indicating the formula 3(Cski.0) and crystallizes in large transparent prisms at about 50° F.
Aldehyde is used for silvering mirrors and other objects, on account of the property that it possesses (in common with other aldehydes) of throwing down a deposit of metallic silver when heated with a concentrated am moniacal solution of silver nitrate containing a little caustic soda.