A Manual of the Chemistry of the Carbon Compounds

THE CARBON COMPOUNDS. 65
rapidly nets on it, carbon dioxide and hydrochloric acid being
formed :—
COClj + H2O = CO2 4- 2HC1
Carbonyl chloride is also formed by heathig chloroform with potassium
dichromate and an excess of sulphuric acid:—
2CHC13 + 2CrO8 = 2COC13 + C^ + H2O + Cr2Os
By exposing a mixture of bromine vapour and carbon monoxide,
to the sunlight carbonyl dibromide COBr2 is formed, a compound
which is very little known.
Carbamic Acid CO j Q,, 2 is not known in the free state; its
ammonium salt CO j QN^ is obtained by mixing dry carton dioxide
with dry ammonia. It is a white solid, which is very volatile,
being decomposed at a gentle heat into its constituents. It dissolves
in water, forming ammonium carbonate. Other metallic carbamates
have not yet been obtained, bitt.there exists a series of ethers of this
acid or compounds containing alcohol radicals in the place of the
hydrogen of the hydroxyl.
Carbamide or Urea CO-J >JTI S -—This body is formed when carbonyl
chloride is acted upon by dry ammonia :—
CO I £| + 4NH8 m CO I ^y 2 + 2NH4C1
It is also produced whnn ammonium carbonate or the commercial
sesqnicarbonate are boated to 130° to 140° in closed tubes:—
Carbamide ocenrs in the virine of mammals, birds, and reptiles, and
is also found in other animal liquids; it was known for a long time
before its constitution was determined, by the name of urea. 3b may
be obtained from urine by evaporating it to the consistency of a
syrup, and adding to the cold residue strong, pure nitric acid, which
precipitates urea nitrate, a salt easily purified by recrystalliiiatiQn.
Urea ia, however, most conveniently prepared from ammonium
cyanate, a compound which, as has already been mentioned, undergoes
on heating a remarkable molecular change, being transformed
into urea.
To obtain it by this method eight parts of anhydrous potassium
ferrocyanide are fused with three parts of potassium carbonate, and
fifteen parts of red lead are gradually added. The cooled mass is
exhausted with water, and the solution of potassium cyanate is
evaporated with eight parts of ammonimn sulphate, The dry residue,
G v