A Manual of the Chemistry of the Carbon Compounds

206 THE CHEMISTRY OF
water and silver oxide. Tlie latter reaotion takes place in two stages,
First monoddoroglycoUie add is formed:—
CHCL CHC() CHCl(OH)
| + HeO = [ + AgCl
CO.OAg CO.OH
and tills compound is by the further action of silver oxide converted
into glyoxylic acid. The free acid forms a sour, thick, syrupy
liquid.
Glyoxylic acid is easily oxidized to oxalic acid, and like other
aldehydes it combines with the sulphites of the alkali-metals forming
CHgO.SOjNa%
crystalline compounds as I When the acid is heated
CO.ONa
with an ammoniacal solution of silver nitrate, metallic silver separates
out as a brilliant mirror;—
C^O, +. Ag2O = CjH204 + H2O + Ag8
Glyoxal or Oxaldehyde C2H2O2.—This compound is isolated from
the crude calcium glyeollate by treating it with alcohol, which
dissolves the glyoxal whilst the calcium salts of glyoxylic and
glycollic acids are left behind. On shaking the alcoholic solution
with add sodium sulphite a crystalline precipitate of glyoxal-sodiuni
sulphite is formed, whioh with barium chloride yields the corresponding
sparingly soluble barium salt. By decomposing this compound
with dilute sulphuric acid, and evaporating the filtrate, glyoxal is left
behind as a crystalline, deliquescent mass. By the action of weak
nitric add it yields glyoxylic acid, whilst a stronger acid oxidizes it
to oxalio acid. Alkalis readily convert it into glycollic acid, even
more easily than the isomeric glycollide (page 198).
PROPENE COMPOUNDS.
Propene or Propylcm CaIL, a gas resembling ethene, is produced
by heating propyl alcohol with concentrated sulphuric acid, or by the
action of alcoholic potash p solution upon p secondary y propyl ppy iodide.
P Pure propene is i also l readily dil obtained bid by b bringing bii allyl llyl iodide iodid CUII ^
(see Allyl Compounds) in contact with zinc and dilute hydrochloric
acid. When the vapours of aniyl alcohol or isobutyl alcohol are
passed through a red-hot tube, or when valerianic acid is heated with
quicklime, the products of decomposition always contain a large proportion
of propene. It also occurs in coal gas,
Propene is a colourless gas condensible to a liquid by strong
pressure; it readily combines with hydriodic acid, forming secondary
propyl iodide:—