ters, and in the artificial production of
ice.

_Carbonyl chloride_ (phosgene), COCl2, was first obtained by John Davy
(_Phil. Trans._, 1812, 40, p. 220). It may be prepared by the direct
union of carbon monoxide and chlorine in sunlight (Th. Wilm and G.
Wischin, _Ann_., 1868, 14, p. 150); by the action of phosphorus
pentoxide on carbon tetrachloride at 200-210 deg. C. (G. Gustavson,
_Ber_., 1872, 5, p. 30), 4CCl4 + P4O10 = 2CO2 + 4POCl3 + 2COCl2; by
the oxidation of chloroform with chromic acid mixture (A. Emmerling
and B. Lengyel, _Ber_., 1869, 2, p. 54), 4CHCl3 + 3O2 = 4COCl2 + 2H2O
+ 2Cl2; or most conveniently by heating carbon tetrachloride with
fuming sulphuric acid (H. Erdmann, _Ber_., 1893, 26, p. 1993), 2SO3 +
CCl4 = S2O5Cl2 + COCl2.

It is a colourless gas, possessing an unpleasant pungent smell. Its
vapour density is 3.46 (air = 1). It may be condensed to a liquid,
which boils at 8 deg. C. It is readily soluble in benzene, glacial
acetic acid, and in many hydrocarbons. Water decomposes it violently,
with formation of carbon dioxide and hydrochloric acid. It reacts with
alcohol to form chlorcarbonic ester and ultimately diethyl carbonate
(see CARBONATES), and with ammonia it yields urea (q.v.). It is
employed commercially in the production of colouring matters (see
BENZOPHENONE), and for various synthetic processes.

_Carbon oxysulphide_, COS, was first prepared by C. Than in 1867
(_Ann. Suppl._, 5, p. 236) by passing carbon monoxide and sulphur
vapour through a tube at a moderate heat. It is also formed by the
action of sulphuretted hydrogen on the isocyanic esters, 2CONC2H5 +
H2S = COS + CO(NHC2H5)2, by the action of concentrated sulphuric acid
on the isothiocyanic esters, RNCS + H2O = COS + RNH2, or of dilute
sulphuric acid on the thiocyanates. In the latter reaction various
other compounds, such as carbon dioxide, carbon bisulphide and
hydrocyanic acid, are produced. They are removed by passing the
vapours in succession through concentrated solutions of the caustic
alkalis, concentrated sulphuric acid, and triethyl phosphine; the
residual gas is then purified by liquefaction (W. Hempel, _Zeit.
angew. Chemie_, 1901, 14, p. 865). It is also formed when sulphur
trioxide reacts with carbon bisulphide at 100 deg. C., CS2 + 3SO3 =
COS + 4SO2, and by the decomposition of ethyl potassium thiocarbonate
with hydrochloric acid, CO(OC2H5)SK +