he corresponding salt of the acid, and
liberation of carbon dioxide. Many carbonates which are insoluble in
water dissolve in water containing carbon dioxide. The individual
carbonates are described under the various metals.

(2) The organic carbonates are the esters of carbonic acid, H2CO3, and
of the unknown ortho-carbonic acid, C(OH)4. The acid esters of carbonic
acid of the type HO.CO.OR are not known in the free state, but J.B.
Dumas obtained barium methyl carbonate by the action of carbon dioxide
on baryta dissolved in methyl alcohol (_Ann._, 1840, 35, p. 283).

Potassium ethyl carbonate, KO.CO.OC2H5, is obtained in the form of
pearly scales when carbon dioxide is passed into an alcoholic solution
of potassium ethylate, CO2 + KOC2H5 = KO.CO.OC2H5. It is not very
stable, water decomposing it into alcohol and the alkaline carbonate.
The normal esters may be prepared by the action of silver carbonate on
the alkyl iodides, or by the action of alcohols on the chlorcarbonic
esters. These normal esters are colourless, pleasant-smelling liquids,
which are readily soluble in water. They show all the reactions of
esters, being readily hydrolysed by caustic alkalis, and reacting with
ammonia to produce carbamic esters and urea. By heating with
phosphorus pentachloride an alkyl group is eliminated and a
chlorcarbonic ester formed. Dimethylcarbonate, CO(OCH3)2, is a
colourless liquid, which boils at 90.6 deg. C., and is prepared by
heating the methyl ester of chlorcarbonic acid with lead oxide.
Diethylcarbonate, CO(OC2H5)2, is a colourless liquid, which boils at
125.8 deg. C.; its specific gravity is 0.978 (20 deg.) [H. Kopp]. When
it is heated to 120 deg. C. with sodium ethylate it decomposes into
ethyl ether and sodium ethyl carbonate (A. Geuther, _Zeit. f. Chemie_,
1868).

Ortho-carbonic ester, C(OC2H5)4 is formed by the action of sodium
ethylate on chlorpicrin (H. Bassett, _Ann._, 1864, 132, p. 54),
CCl3NO2 + 4C2H5ONa = C(OC2H5)4 + NaNO2 + 3NaCl. It is an
ethereal-smelling liquid, which boils at 158-159 deg. C., and has a
specific gravity of 0.925. When heated with ammonia it yields
guanidine, and on boiling with alcoholic potash it yields potassium
carbonate.

Chlorcarbonic ester, Cl.CO.OC2H5, is formed by the addition of
well-cooled absolute alcohol to phosgene (carbonyl chloride). It is a
pungent-smelling liquid, which fumes strongly on exposure to air. It