| 985.0 | 0.4589 | 977.0 | 0.4670 | | |
+-------+---------+-------+---------+--------+----------+

The atomic weight of carbon has been determined by J.B.A. Dumas and by
J.S. Stas [_Ann. Chim. Phys._, 1841 (3), 1, p. 1: _Jahresb._, 1849,
223] by estimating the amount of carbon dioxide formed on burning
graphite or diamond in a current of oxygen, the value obtained being
12.0 (O = 16). Confirmatory evidence has also been obtained by O.L.
Erdmann and R.F. Marchand (_Jour. Prak. Chem._, 1841, 23, p. 159; see
also F.W. Clarke, _Jahresb._, 1881, p. 7).

_Compounds_.--Three oxides of carbon are known, namely, carbon
suboxide, C3O2, carbon monoxide, CO, and carbon dioxide, CO2. _Carbon
suboxide_, C3O2, is formed by the action of phosphorus pentoxide on
ethyl malonate (O. Diels and B. Wolf, _Ber._, 1906, 39, p. 689),
CH2(COOC2H5)2 = 2C2H4 + 2H2O + C3O2. At ordinary temperatures it is a
colourless gas, possessing a penetrating and suffocating smell. It
liquefies at 7 deg. C. It is an exceedingly reactive compound,
combining with water to form malonic acid, with hydrogen chloride to
form malonyl chloride, and with ammonia to form malonamide. When kept
for some time in sealed tubes it changes to a yellowish liquid, from
which a yellow flocculent substance gradually separates, and finally
it suddenly solidifies to a dark red mass, which appears to be a
polymeric form. Its vapour density agrees with the molecular formula
C3O2, and this formula is also confirmed by exploding the gas with
oxygen and measuring the amount of carbon dioxide produced (see
KETENES).

_Carbon monoxide_, CO, is found to some extent in volcanic gases. It
was first prepared in 1776 by J.M.F. Lassone (_Mem. Acad. Paris_) by
heating zinc oxide with carbon, and was for some time considered to be
identical with hydrogen. Cruikshank concluded that it was an oxide of
carbon, a fact which was confirmed by Clement and J.B. Desormes (_Ann.
Chim. Phys._, 1801, 38, p. 285). It may be prepared by passing carbon
dioxide over red-hot carbon, or red-hot iron; by heating carbonates
(magnesite, chalk, &c.) with zinc dust or iron; or by heating many
metallic oxides with carbon. It may also be prepared by heating formic
and oxalic acids (or their salts) with concentrated sulphuric acid (in
the case of oxalic acid, an equal volume of carbon dioxide is
produced); and by heating pota