Chapter X: Part 10

3. GNAEUS PAPIRIUS CARBO (c. 130-82 B.C.), nephew of (1). He was a strong supporter of the Marian party, and took part in the blockade of Rome (87). In 85 he was chosen by Cinna as his colleague in the consulship, and extensive preparations were made for carrying on war in Greece against Sulla, who had announced his intention of returning to Italy. Cinna and Carbo declared themselves consuls for the following year, and large bodies of troops were transported across the Adriatic; but when Cinna was murdered by his own soldiers, who refused to engage in civil war, Carbo was obliged to bring them back. In 82 Carbo, then consul for the third time with the younger Marius, fought an indecisive engagement with Sulla near Clusium, but was defeated with great loss in an attack on the camp of Sulla's general, Q. Caecilius Metellus Pius [see under METELLUS (6)] near Faventia. Although he still had a large army and the Samnites remained faithful to him, Carbo was so disheartened by his failure to relieve Praeneste, where the younger Marius had taken refuge, that he decided to leave Italy. He first fled to Africa, thence to the island of Cossyra (Pentellaria), where he was arrested, taken in chains before Pompey at Lilybaeum and put to death.

See Appian, _Bell. Civ._ i. 67-98; Livy, _Epit._ 79, 84, 88, 89;
Plutarch, _Pompey_, 5, 6, 10, and _Sulla_, 28; Cicero, _ad Fam._ ix.
21; Eutropius, v. 8, 9; Orosius, v. 20; Valerius Maximus, v. 3. 5, ix.
13. 2; art. SULLA, L. CORNELIUS.

CARBOHYDRATE, in chemistry, the generic name for compounds empirically represented by the formula C_{x}(H2O)_{y}. They are essentially vegetable products, and include the sugars, starches, gums and celluloses (q.v.).

CARBOLIC ACID or PHENOL (hydroxy-benzene), C6H5OH, an acid found in the urine of the herbivorae, and in small quantity in _castoreum_ (F. Wohler, _Ann._, 1848, 67, p. 360). Its principal commercial source is the fraction of coal-tar which distils between 150 and 200 deg. C., in which it was discovered in 1834 by F. Runge. In order to obtain the phenol from this distillate, it is treated with caustic soda, which dissolves the phenol and its homologues together with a certain quantity of naphthalene and other hydrocarbons. The solution is diluted with water, and the hydrocarbons are thereby precipitated and separated. The solution is then acidified, and the phenols are liberated and form an oily layer on the surface of the acid. This layer is separated, and the phenol recovered by a process of fractional distillation. It may be synthetically prepared by fusing potassium benzene sulphonate with caustic alkalis (A. Kekule, A. Wurtz); by the action of nitrous acid on aniline; by passing oxygen into boiling benzene containing aluminium chloride (C. Friedel and J.M. Crafts, _Ann. Chim. Phys._, 1888 (6) 14, p. 435); by heating phenol carboxylic acids with baryta; and, in small quantities by the oxidation of benzene with hydrogen peroxide or nascent ozone (A.R. Leeds, _Ber._, 1881, 14, p. 976).

It crystallizes in rhombic needles, which melt at 42.5-43 deg. C., and boil at 182-183 deg. C.; its specific gravity is 1.0906 (0 deg. C.). It has a characteristic smell, and a biting taste; it is poisonous, and acts as a powerful antiseptic. It dissolves in water, 15 parts of water dissolving about one part of phenol at 16-17 deg. C., but it is miscible in all proportions at about 70 deg. C.; it is volatile in steam, and is readily soluble in alcohol, ether, benzene, carbon bisulphide, chloroform and glacial acetic acid. It is also readily soluble in solutions of the caustic alkalis, slightly soluble in aqueous ammonia solution, and almost insoluble in sodium carbonate solution. When exposed in the moist condition to the air it gradually acquires a red colour. With ferric chloride it gives a violet coloration, and with bromine water a white precipitate of tribrom-phenol.

When phenol is passed through a red-hot tube a complex decomposition
takes place, resulting in the formation of benzene, toluene,
naphthalene, &c. (J.G. Kramers, _Ann._, 1877, 189, p. 129). Chromium
oxychloride reacts violently on phenol, producing hydroquinone ether,
O(C6H4OH)2; chromic acid gives phenoquinone, and potassium
permanganate gives paradiphenol, oxalic acid, and some salicylic acid
(R. Henriques, _Ber._, 1888, 21, p. 1620). In alkaline solution,
potassium permanganate oxidizes it to inactive tartaric acid and
carbon dioxide (O. Doebner, _Ber._, 1891, 24, p. 1755). When distilled
over lead oxide, it forms diphenylene oxide, (C6H4)2O; and when
heated with oxalic acid and concentrated sulphuric acid, it forms
aurin, C19H14O3. It condenses with aceto-acetic ester, in the presence
of sulphuric acid, to [beta]-methyl coumarin (H. v. Pechmann and J.B.
Cohen, _Ber_., 1884, 17, p. 2188).

The hydrogen of the hydroxyl group in phenol can be replaced by
metals, by alkyl groups and by acid radicals. The metallic derivatives
(phenolates, phenates or carbolates) of the alkali metals are obtained
by dissolving phenol in a solution of a caustic alkali, in the absence
of air. Potassium phenolate, C6H5OK, crystallizes in fine needles, is
very hygroscopic and oxidizes rapidly on exposure. Other phenolates
may be obtained from potassium phenolate by precipitation. The alkyl
derivatives may be obtained by heating phenol with one molecular
proportion of a caustic alkali and of an alkyl iodide. They are
compounds which greatly resemble the mixed ethers of the aliphatic
series. They are not decomposed by boiling alkalis, but on heating
with hydriodic acid they split into their components. _Anisol_, phenyl
methyl ether, C6H5.O.CH3, is prepared either by the above method or by
the action of diazo-methane on phenol, C6H5OH+CH2N2 = N2+C6H5.O.CH3
(H. v. Pechmann, _Ber_., 1895, 28, p. 857); by distilling anisic acid
(para-methoxy benzoic acid) with baryta or by boiling phenyl diazonium
chloride with methyl alcohol. It is a colourless pleasant-smelling
liquid which boils at 154.3 deg. C. _Phenetol_, phenyl ethyl ether,
C6H5.O.C2H5, a liquid boiling at 172 deg. C., may be obtained by
similar methods. A. Hantzsch (_Ber._, 1901, 34, p. 3337) has shown
that in the action of alcohols on diazonium salts an increase in the
molecular weight of the alcohol and an accumulation of negative groups
in the aromatic nucleus lead to a diminution in the yield of the ether
produced and to the production of a secondary reaction, resulting in
the formation of a certain amount of an aromatic hydrocarbon.

The acid esters of phenol are best obtained by the action of acid
chlorides or anhydrides on phenol or its sodium or potassium salt, or
by digesting phenol with an acid in the presence of phosphorus
oxychloride (F. Rasinski, _Jour. f. prak. Chem._, 1882 [2], 26, p.
62). Phenyl acetate, C6H5.O.COCH3, a colourless liquid of boiling
point 193 deg. C., may be prepared by heating phenol with acetamide.
When heated with aniline it yields phenol and acetanilide. Phenyl
benzoate, C6H5.O.COC5H5, prepared from phenol and benzoyl chloride,
crystallizes in monoclinic prisms, which melt at 68-69 deg. C. and
boil at 314 deg. C.

Phenol is characterized by the readiness with which it forms
substitution products; chlorine and bromine, for example, react
readily with phenol, forming ortho- and para- chlor- and -bromphenol,
and, by further action, trichlor- and tribrom-phenol. Iodphenol is
obtained by the action of iodine and iodic acid on phenol dissolved in
a dilute solution of caustic potash. Nitro-phenols are readily
obtained by the action of nitric acid on phenol. By the action of
dilute nitric acid, ortho- and para-nitrophenols are obtained, the
ortho-compound being separated from the para-compound by distillation
in a current of steam. Ortho-nitrophenol, C6H4.OH.NO2(1.2),
crystallizes in yellow needles which melt at 45 deg. C. and boil at
214 deg.C. Para-nitrophenol, C6H4.OH.NO2(1.4), crystallizes in long
colourless needles which melt at 114 deg.C. Meta-nitrophenol,
C6H4.OH.NO2.(1.3), is prepared from meta-nitraniline by diazotizing
the base and boiling the resulting diazonium salt with water. By
nitrating phenol with concentrated nitric acid, no care being taken to
keep the temperature of reaction down, trinitrophenol (picric acid) is
obtained (see PICRIC ACID). By the reduction of nitro-phenols, the
corresponding aminophenols are obtained, and of these, the meta- and
para-derivatives are the most important. Para-aminophenol,
C6H4.OH.NH2(1.4) melts at 148 deg. C., with decomposition. Its most
important derivative is phenacetin. Meta-aminophenol,
C6H4.OH.NH2(1.3), and dimethyl meta-aminophenol, C6H4.OH.N(CH3)2(1.3),
are extensively employed in the manufacture of the important dyestuffs
known as the rhodamines. The aminophenols also find application as
developers in photography, the more important of these developers
being amidol, the hydrochloride of diaminophenol, ortol, the
hydrochloride of para-methylaminophenol, C6H4.OH.NHCH3.HCl(1.4),
rodinal, para-aminophenol, and metol, the sulphate of a
methylaminophenol sulphonic acid. Meta-aminophenol is prepared by
reducing meta-nitrophenol, or by heating resorcin with ammonium
chloride and ammonia to 200 deg. C. Dimethyl-meta-aminophenol is
prepared by heating meta-aminophenol with methyl alcohol and
hydrochloric acid in an autoclave; by sulphonation of dimethylaniline,
the sulphonic acid formed being finally fused with potash; or by
nitrating dimethylaniline, in the presence of sulphuric, acid at 0
deg. C. In the latter case a mixture of nitro-compounds is obtained
which can be separated by the addition of sodium carbonate. The
meta-nitro-compound, which is precipitated last, is then reduced, and
the amino group so formed is replaced by the hydroxyl group by means
of the Sandmeyer reaction. Dimethyl-meta-aminophenol crystallizes in
small prisms which melt at 87 deg. C. It condenses with phthalic
anhydride to form rhodamine, and with succinic anhydride to rhodamine
S.

Phenol dissolves readily in concentrated sulphuric acid, a mixture of
phenol-ortho- and -para-sulphonic acids being formed. These acids may
be separated by conversion into their potassium salts, which are then
fractionally crystallized, the potassium salt of the para-acid
separating first. The ortho-acid, in the form of its aqueous solution,
is sometimes used as an antiseptic, under the name of aseptol. A
_thiophenol_, C6H5SH, is known, and is prepared by the action of
phosphorus pentasulphide on phenol, or by distilling a mixture of
sodium benzene sulphonate and potassium sulphydrate. It is a
colourless liquid, which possesses a very disagreeable smell, and
boils at 168 deg. C.

Various methods have been devised for the quantitative determination
of phenol. J. Messinger and G. Vortmann (_Ber._, 1890, 23, p. 2753)
dissolve phenol in caustic alkali, make the solution up to known
volume, take an aliquot part, warm it to 60 deg. C., and add
decinormal iodine solution until the liquid is of a deep yellow
colour. The mixture is then cooled, acidified by means of sulphuric
acid, and titrated with decinormal sodium thiosulphate solution. S.B.
Schryver (_Jour, of Soc. Chem. Industry_, 1899, 18, p. 553) adds
excess of sodamide to a solution of the phenol in a suitable solvent,
absorbs the liberated ammonia in an excess of acid, and titrates the
excess of acid. See also C.E. Smith, _Amer. Jour. Pharm._, 1898, 369.

_Pharmacology and Therapeutics_.--Carbolic acid is an efficient parasiticide, and is largely used in destroying the fungus of ringworm and of the skin disease known as _pityriasis versicolor_. When a solution of the strength of about 1 in 20 is applied to the skin it produces a local anaesthesia which lasts for many hours. If concentrated, however, it acts as a caustic. It never produces vesication. The drug is absorbed through the unbroken skin--a very valuable property in the treatment of such conditions as an incipient whitlow. A piece of cotton wool soaked in strong carbolic acid will relieve the pain of dental caries, but is useless in other forms of toothache. Taken internally, in doses of from one to three grains, carbolic acid will often relieve obstinate cases of vomiting and has some value as a gastric antiseptic.

_Toxicology_.--Carbolic acid is distinguished from all other acids so-called--except oxalic acid and hydrocyanic acid--in that it is a neurotic poison, having a marked action directly upon the nervous system. In all cases of carbolic acid poisoning the nervous influence is seen. If it be absorbed from a surgical dressing there are no irritant symptoms, but when the acid is swallowed in concentrated form, symptoms of gastro-intestinal irritation occur. The patient becomes collapsed, and the skin is cold and clammy. The breathing becomes shallow, the drug killing, like nearly all neurotic poisons (alcohol, morphia, prussic acid, &c.), by paralysis of the respiratory centre, and the patient dying in a state of coma. The condition of the urine is of the utmost importance, as it is often a clue to the diagnosis, and in surgical cases may be the first warning that absorption is occurring to an undue degree. The urine becomes dark green in colour owing to the formation of various oxidation products such as pyrocatechin. Fifteen grains constitute an exceedingly dangerous dose for an adult male of average weight. Other symptoms of undue absorption are vertigo, deafness, sounds in the ears, stupefaction, a subnormal temperature, nausea, vomiting and a weak pulse (Sir Thomas Fraser).

The antidote in cases of carbolic acid poisoning is any soluble sulphate. Carbolic acid and sulphates combine in the blood to form sulpho-carbolates, which are innocuous. The symptoms of nerve-poisoning are due to the carbolic acid (or its salts) which circulate in the blood after all the sulphates in the blood have been used up in the formation of sulpho-carbolates (hence, during administration of carbolic acid, the urine should frequently be tested for the presence of free sulphates; as long as these occur in the urine, they are present in the blood and there is no danger). The treatment is therefore to administer an ounce of sodium sulphate in water by the mouth, or to inject a similar quantity of the salt in solution directly into a vein or into the subcutaneous tissues. Magnesium sulphate may be given by the mouth, but is poisonous if injected intravenously. If the acid has been swallowed, wash out the stomach and give chalk, the carbolate of calcium being insoluble. Alkalis which form soluble carbolates are useless. Give ether and brandy subcutaneously and apply hot water-bottles and blankets if there are signs of collapse.

CARBON (symbol C, atomic weight 12), one of the chemical non-metallic elements. It is found native as the diamond (q.v.), graphite (q.v.), as a constituent of all animal and vegetable tissues and of coal and petroleum. It also enters (as carbonates) into the composition of many minerals, such as chalk, dolomite, calcite, witherite, calamine and spathic iron ore. In combination with oxygen (as carbon dioxide) it is also found to a small extent in the atmosphere. It is a solid substance which occurs in several modifications, differing very much in their physical properties. _Amorphous carbon_ is obtained by the destructive distillation of many carbon compounds, the various kinds differing very greatly as regards physical characters and purity, according to the substance used for their preparation. The most common varieties met with are lampblack, gas carbon, wood charcoal, animal charcoal and coke. _Lampblack_ is prepared by burning tar, resin, turpentine and other substances rich in carbon, with a limited supply of air; the products of combustion being conducted into condensing chambers in which cloths are suspended, on which the carbon collects. It is further purified by heating in closed vessels, but even then it still contains a certain amount of mineral matter and more or less hydrocarbons. It is used in the manufacture of printer's ink, in the preparation of black paint and in calico printing. _Gas carbon_ is produced by the destructive distillation of coal in the manufacture of illuminating gas (see GAS: _Manufacture_), being probably formed by the decomposition of gaseous hydrocarbons. It is a very dense form of carbon, and is a good conductor of heat and electricity. It is used in the manufacture of carbon rods for arc lights, and for the negative element in the Bunsen battery.

_Charcoal_ is a porous form of carbon; several varieties exist. _Sugar charcoal_ is obtained by the carbonization of sugar. It is purified by boiling with acids, to remove any mineral matter, and is then ignited for a long time in a current of chlorine in order to remove the last traces of hydrogen. _Animal charcoal_ (bone black) is prepared by charring bones in iron retorts. It is a very impure form of carbon, containing on the average about 80% of calcium phosphate. It possesses a much greater decolorizing and absorbing power than wood charcoal. A variety of animal charcoal is sometimes prepared by calcining fresh blood with potassium carbonate in large cylinders, the mass being purified by boiling out with dilute hydrochloric acid and subsequent reheating. _Wood charcoal_ is a hard and brittle black substance, which retains the external structure of the wood from which it is made. It is prepared (where wood is plentiful) by stacking the wood in heaps, which are covered with earth or with brushwood and turf, and then burning the heap slowly in a limited supply of air. The combustion of the wood is conducted from the top downwards, and from the exterior towards the centre; great care has to be taken that the process is carried out slowly. The disadvantage in this process is that the by-products, such as pyroligneous acid, acetone, wood spirit, &c., are lost; as an alternative method, wood is frequently carbonized in ovens or retorts and the volatile products are condensed and utilized.

Charcoal varies considerably in its properties, depending upon the
particular variety of wood from which it is prepared, and also upon
the process used in its manufacture. It can be made at a temperature
as low as 300 deg. C., and is then a soft, very friable material
possessing a low ignition point. When made at higher temperatures it
is much more dense, and its ignition point is considerably higher.
Charcoal burns when heated in air, usually without the formation of
flame, although a flame is apparent if the temperature be raised. It
is characterized by its power of absorbing gases; thus, according to
J. Hunter [_Phil. Mag._, 1863 (4), 25, p. 363], one volume of charcoal
absorbs (at 0 deg. C. and 760 mm. pressure) 171.7 ccs. of ammonia,
86.3 ccs. of nitrous oxide, 67.7 ccs. of carbon monoxide, 21.2 ccs. of
carbon dioxide, 17.9 ccs. of oxygen, 15.2 ccs. of nitrogen, and 4.4
ccs. of hydrogen [see also J. Dewar, _Ann. Chim. Phys._, 1904 (8), 3,
p. 5]. It also has the power of absorbing colouring matters from
solution. Charcoal is used as a fuel and as a reducing agent in
metallurgical processes.

The element carbon unites directly with hydrogen to form acetylene
when an electric arc is passed between carbon poles in an atmosphere
of hydrogen (M. Berthelot); it also unites directly with fluorine,
producing, chiefly, carbon tetrafluoride CF4. It burns when heated in
an atmosphere of oxygen, forming carbon dioxide, and when heated in
sulphur vapour it forms carbon bisulphide (q.v.). When heated with
nitrogenous substances, in the presence of carbonated or caustic
alkali, it forms cyanides. It combines directly with silicon, at the
temperature of the electric furnace, yielding _carborundum_, SiC; and
H. Moissan has also shown that it will combine with many metals at
the temperature of the electric furnace, to form carbides (q.v.).

The specific heat of carbon varies with the temperature the following
values having been obtained by H.F. Weber (_Jahresberichte_, 1874, p.
63):--

+-----------------+-----------------+-------------------+
| Diamond. | Graphite. |Porous wood carbon.|
+-------+---------+-------+---------+--------+----------+
| t deg.| Sp. Ht. | t deg.| Sp. Ht. | t deg. | Sp. Ht. |
+-------+---------+-------+---------+--------+----------+
| -50.5 | 0.0635 | -50.3 | 0.1138 | 0-23 | 0.1653 |
| -10.6 | 0.0955 | -10.7 | 0.1437 | 0-99 | 0.1935 |
| +10.7 | 0.1128 | +10.8 | 0.1604 | 0-223 | 0-2385 |
| 85.5 | 0.1765 | 61.3 | 0.1990 | | |
| 206.1 | 0.2733 | 201.6 | 0.2966 | | |
| 606.7 | 0.4408 | 641.9 | 0.4454 | | |
| 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 potassium ferrocyanide with a large excess
of concentrated sulphuric acid, K4Fe(CN)6 + 6H2SO4 + 6H2O = 2K2SO4 +
FeSO4 + 3(NH4)2SO4 + 6CO. It is a colourless, odourless gas of
specific gravity 0.967 (air = 1). It is one of the most difficultly
liquefiable gases, its critical temperature being -139.5 deg. C., and
its critical pressure 35.5 atmos. The liquid boils at -190 deg. C.,
and solidifies at -211 deg.C. (L.P. Cailletet, _Comptes rendus_, 1884,
99, p. 706). It is only very slightly soluble in water. It burns with
a characteristic pale blue flame to form carbon dioxide. It is very
poisonous, uniting with the haemoglobin of the blood to form
carbonyl-haemoglobin. It is a powerful reducing agent, especially at
high temperatures. It is rapidly absorbed by an ammoniacal or acid
(hydrochloric acid) solution of cuprous chloride. It unites directly
with chlorine, forming carbonyl chloride or phosgene (see below), and
with nickel and iron to form nickel and iron carbonyls (see NICKEL and
IRON). It also combines directly with potassium hydride to form
potassium formate (see FORMIC ACID). The volume composition of carbon
monoxide is established by exploding a mixture of the gas with oxygen,
two volumes of the gas combining with one volume of oxygen to form two
volumes of carbon dioxide. This fact, coupled with the determination
of the vapour density of the gas, establishes the molecular formula
CO.

_Carbon dioxide_, CO2, is a gas first distinguished from air by van
Helmont (1577-1644), who observed that it was formed in fermentation
processes and during combustion, and gave to it the name _gas
sylvestre_. J. Black (_Edin. Phys. and Lit. Essays_, 1755) showed that
it was a constituent of the carbonated alkalis and called it "fixed
air." T.O. Bergman, in 1774, pointed out its acid character, and A.L.
Lavoisier (1781-1788) first proved it to be an oxide of carbon by
burning carbon in the oxygen obtained from the decomposition of
mercuric oxide. It is a regular constituent of the atmosphere, and is
found in many spring waters and in volcanic gases; it also occurs in
the uncombined condition at the Grotto del Cane (Naples) and in the
Poison Valley (Java). It is a constituent of the minerals cerussite,
malachite, azurite, spathic iron ore, calamine, strontianite,
witherite, calcite aragonite, limestone, &c. It may be prepared by
burning carbon in excess of air or oxygen, by the direct decomposition
of many carbonates by heat, and by the decomposition of carbonates
with mineral acids, M2CO8 + 2HCl = 2MCl + H2O + CO2. It is also
formed in ordinary fermentation processes, in the combustion of all
carbon compounds (oil, gas, candles, coal, &c.), and in the process of
respiration.

It is a colourless gas, possessing a faint pungent smell and a
slightly acid taste. It does not burn, and does not support ordinary
combustion, but the alkali metals and magnesium, if strongly heated,
will continue to burn in the gas with formation of oxides and
liberation of carbon. Its specific gravity is 1.529 (air = 1). It is
readily condensed, passing into the liquid condition at 0 deg. C.
under a pressure of 35 atmospheres. Its critical temperature is 31.35
deg. C., and its critical pressure is 72.9 atmos. The liquid boils at
-78.2 deg. C. (l atmo.), and by rapid evaporation can be made to
solidify to a snow-white solid which melts at -65 deg. C.(see LIQUID
GASES). Carbon dioxide is moderately soluble in water, its coefficient
of solubility at 0 deg. C. being 1.7977 (R. Bunsen). It is still more
soluble in alcohol. The solution of the gas in water shows a faintly
acid reaction and is supposed to contain _carbonic acid_, H2CO3. The
gas is rapidly absorbed by solutions of the caustic alkalis, with the
production of alkaline carbonates (q.v.), and it combines readily with
potassium hydride to form potassium formate. It unites directly with
ammonia gas to form ammonium carbamate, NH2COONH4. It may be readily
recognized by the white precipitate which it forms when passed through
lime or baryta water. Carbon dioxide dissociates, when strongly
heated, into carbon monoxide and oxygen, the reaction being a balanced
action; the extent of dissociation for varying temperatures and
pressures has been calculated by H. Le Chateller (_Zeit. Phys. Chem._,
1888, 2, p. 782; see H. Sainte-Claire Deville, _Comptes rendus_, 1863,
56, p. 195 et seq.). The volume composition of carbon dioxide is
determined by burning carbon in oxygen, when it is found that the
volume of carbon dioxide formed is the same as that of the oxygen
required for its production, hence carbon dioxide contains its own
volume of oxygen. Carbon dioxide finds industrial application in the
preparation of soda by the Solvay process, in the sugar industry, in
the manufacture of mineral waters, 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 + HCl = COS + KCl + C2H5OH. It is
a colourless, odourless gas, which burns with a blue flame and is
decomposed by heat. Its vapour density is 2.1046 (air = 1). The
liquefied gas boils at -47 deg. C. under atmospheric pressure. It is
soluble in water; the aqueous solution gradually decomposes on
standing, forming carbon dioxide and sulphuretted hydrogen. It is
easily soluble in solutions of the caustic alkalis, provided they are
not too concentrated, forming solutions of alkaline carbonates and
sulphides, COS + 4KHO = K2CO3 + K2S + 2H2O.

CARBONADO, a name given in Brazil to a dark massive form of impure diamond, known also as "carbonate" and in trade simply as carbon. It is sometimes called black diamond. Generally it is found in small masses of irregular polyhedral form, black, brown or dark-grey in colour, with a dull resinoid lustre; and breaking with a granular fracture, paler in colour, and in some cases much resembling that of fine-grained steel. Being slightly cellular, its specific gravity is rather less than that of crystallized diamond. It is found almost exclusively in the state of Bahia in Brazil, where it occurs in the _cascalho_ or diamond-bearing gravel. Borneo also yields it in small quantity. Formerly of little or no value, it came into use on the introduction of Leschot's diamond-drills, and is now extremely valuable for mounting in the steel crowns used for diamond-boring. Having no cleavage, the carbon is less liable to fracture on the rotation of the drill than is crystallized diamond. The largest piece of carbonado ever recorded was found in Bahia in 1895, and weighed 3150 carats. Pieces of large size are, however, relatively less valuable than those of moderate dimensions, since they require the expenditure of much labour in reducing them to fragments of a suitable size for mounting in the drill-heads. Ilmenite has sometimes been mistaken in the South African mines for carbonado. (F. W. R.*)

CARBONARI (an Italian word meaning "charcoal-burners"), the name of certain secret societies of a revolutionary tendency which played an active part in the history of Italy and France early in the 19th century. Societies of a similar nature had existed in other countries and epochs, but the stories of the derivation of the Carbonari from mysterious brotherhoods of the middle ages are purely fantastic. The Carbonari were probably an offshoot of the Freemasons, from whom they differed in important particulars, and first began to assume importance in southern Italy during the Napoleonic wars. In the reign (1808-1815) of Joachim Murat a number of secret societies arose in various parts of the country with the object of freeing it from foreign rule and obtaining constitutional liberties; they were ready to support the Neapolitan Bourbons or Murat, if either had fulfilled these aspirations. Their watch-words were freedom and independence, but they were not agreed as to any particular form of government to be afterwards established. Murat's minister of police was a certain Malghella (a Genoese), who favoured the Carbonari movement, and was indeed the instigator of all that was Italian in the king's policy. Murat himself had at first protected the sectarians, especially when he was quarrelling with Napoleon, but later, Lord William Bentinck entered into negotiations with them from Sicily, where he represented Great Britain, through their leader Vincenzo Federici (known as Capobianco), holding out promises of a constitution for Naples similar to that which had been established in Sicily under British auspices in 1812. Some Carbonarist disorders having broken out in Calabria, Murat sent General Manhes against the rebels; the movement was ruthlessly quelled and Capobianco hanged in September 1813 (see Greco, _Intorno al tentativo dei Carbonari di Citeriore Calabria nel 1813_). But Malghella continued secretly to protect the Carbonari and even to organize them, so that on the return of the Bourbons in 1815 King Ferdinand IV. found his kingdom swarming with them. The society comprised nobles, officers of the army, small landlords, government officials, peasants and even priests. Its organization was both curious and mysterious, and had a fantastic ritual full of symbols taken from the Christian religion, as well as from the trade of charcoal-burning, which was extensively practised in the mountains of the Abruzzi and Calabria. A lodge was called a _vendita_ (sale), members saluted each other as _buoni cugini_ (good cousins), God was the "Grand Master of the Universe," Christ the "Honorary Grand Master," also known as "the Lamb," and every Carbonaro was pledged to deliver the Lamb from the Wolf, i.e. tyranny. Its red, blue and black flag was the standard of revolution in Italy until substituted by the red, white and green in 1831.

When King Ferdinand felt himself securely re-established at Naples he determined to exterminate the Carbonari, and to this end his minister of police, the prince of Canosa, set up another secret society called the _Calderai del Contrappeso_ (braziers of the counterpoise), recruited from the brigands and the dregs of the people, who committed hideous excesses against supposed Liberals, but failed to exterminate the movement. On the contrary, Carbonarism flourished and spread to other parts of Italy, and countless lodges sprang up, their adherents comprising persons in all ranks of society, including, it is said, some of royal blood, who had patriotic sentiments and desired to see Italy free from foreigners. In Romagna the movement was taken up with enthusiasm, but it also led to a certain number of murders owing to the fiery character of the Romagnols, although its criminal record is on the whole a very small one. Among the foreigners who joined it for love of Italy was Lord Byron. The first rising actively promoted by the Carbonari was the Neapolitan revolution of 1820. Several regiments were composed entirely of persons affiliated to the society, and on the 1st of July a military mutiny broke out at Monteforte, led by two officers named Morelli and Silvati, to the cry of "God, the King and the Constitution." The troops sent against them, under General Pepe, himself a Carbonaro, sympathized with the mutineers, and the king, being powerless to resist, granted the constitution (13th of July), which he swore on the altar to observe. But the Carbonari were unable to carry on the government, and after the separatist revolt of Sicily had broken out the king went to the congress of Laibach, and obtained from the emperor of Austria the loan of an army with which to restore the autocracy. He returned to Naples early in 1821 with 50,000 Austrians, defeated the constitutionalists under Pepe, dismissed parliament, and set to work to persecute all who had been in any way connected with the movement.

A similar movement broke out in Piedmont in March 1821. Here as in Naples the Carbonari comprised many men of rank, such as Santorre di Santarosa, Count San Marzano, Giacinto di Collegno, and Count Moffa di Lisio, all officers in the army, and they were more or less encouraged by Charles Albert, the heir-presumptive to the throne. The rising was crushed, and a number of the leaders were condemned to death or long terms of imprisonment, but most of them escaped. At Milan there was only the vaguest attempt at conspiracy; but Silvio Pellico, Maroncelli and Count Confalonieri were implicated as having invited the Piedmontese to invade Lombardy, and were condemned to pass many years in the dungeons of the Spielberg.

The French revolution of 1830 had its echo in Italy, and Carbonarism raised its head in Parma, Modena and Romagna the following year. In the papal states a society called the Sanfedisti or Bande della Santa Fede had been formed to checkmate the Carbonari, and their behaviour and character resembled those of the Calderai of Naples. In 1831 Romagna and the Marches rose in rebellion and shook off the papal yoke with astonishing ease. At Parma the duchess, having rejected the demand for a constitution, left the city and returned under Austrian protection. At Modena, Duke Francis IV., the worst of all Italian tyrants, was expelled by a Carbonarist rising, and a dictatorship was established under Biagio Nardi on the 5th of February. Francis returned with an Austrian force and hanged the conspirators, including Ciro Menotti. The Austrians occupied Romagna and restored the province to the pope, but though many arrests of Carbonari were made there were no executions. Among those implicated in the Carbonarist movement was Louis Napoleon, who even in after years, when he was ruling France as Napoleon III., never quite forgot that he had once been a conspirator, a fact which influenced his Italian policy. The Austrians retired from Romagna and the Marches in July 1831, but Carbonarism and anarchy having broken out again, they returned, while the French occupied Ancona. The Carbonari after these events ceased to have much importance, their place being taken by the more energetic Giovane Italia Society presided over by Mazzini.

In France, Carbonarism began to take root about 1820, and was more thoroughly organized than in Italy. The example of the Spanish and Italian revolutions incited the French Carbonari, and risings occurred at Belfort, Thouars, La Rochelle and other towns in 1821, which though easily quelled revealed the nature and organization of the movement. The Carbonarist lodges proved active centres of discontent until 1830, when, after contributing to the July revolution of that year, most of their members adhered to Louis Philippe's government.

The Carbonarist movement undoubtedly played an important part in the Italian Risorgimento, and if it did not actively contribute to the wars and revolutions of 1848-49, 1859-60 and 1866, it prepared the way for those events. One of its chief merits was that it brought Italians of different classes and provinces together, and taught them to work in harmony for the overthrow of tyranny and foreign rule.

BIBLIOGRAPHY.--Much information on the Carbonari will be found in R.M.
Johnston's _Napoleonic Empire in Southern Italy_ (2 vols., London,
1904), which contains a full bibliography; D. Spadoni's _Sette,
cospirazioni, e cospiratori_ (Turin, 1904) is an excellent monograph;
_Memoirs of the Secret Societies of Southern Italy_, said to be by one
Bertoldi or Bartholdy (London, 1821, Ital. transl. by A.M. Cavallotti,
Rome, 1904); Saint-Edme, _Constitution et organisation des Carbonari_,
P. Colletta, _Storia del Reame di Napoli_ (Florence, 1848); B. King,
_A History of Italian Unity_ (London, 1899), with bibliography.
(L. V.*)

CARBONATES. (1) The metallic carbonates are the salts of carbonic acid, H2CO3. Many are found as minerals, the more important of such naturally occurring carbonates being cerussite (lead carbonate, PbCO3), malachite and azurite (both basic copper carbonates), calamine (zinc carbonate, ZnCO3), witherite (barium carbonate, BaCO3), strontianite (strontium carbonate, SrCO3), calcite (calcium carbonate, CaCO3), dolomite (calcium magnesium carbonate, CaCO3.MgCO3), and sodium carbonate, Na2CO3. Most metals form carbonates (aluminium and chromium are exceptions), the alkali metals yielding both acid and normal carbonates of the types MHCO3 and M2CO3 (M=one atom of a monovalent metal); whilst bismuth, copper and magnesium appear only to form basic carbonates. The acid carbonates of the alkali metals can be prepared by saturating an aqueous solution of the alkaline hydroxide with carbon dioxide, M.OH + CO2 = MHCO3, and from these acid salts the normal salts may be obtained by gentle heating, carbon dioxide and water being produced at the same time, 2MHCO3 = M2CO3 + HO2 + CO2. Most other carbonates are formed by precipitation of salts of the metals by means of alkaline carbonates. All carbonates, except those of the alkali metals and of thallium, are insoluble in water; and the majority decompose when heated strongly, carbon dioxide being liberated and a residue of an oxide of the metal left. The alkaline carbonates undergo only a very slight decomposition, even at a very bright red heat. The carbonates are decomposed by mineral acids, with formation of the 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
boils at 93.1 deg.C., and has a specific gravity of 1.144 (15 deg.
C.). When heated with ammonia it yields urethane. Sodium amalgam
converts it into formic acid; whilst with alcohol it yields the normal
carbonic ester. It is easily broken down by many substances (aluminium
chloride, zinc chloride, &c.) into ethyl chloride and carbon dioxide.

_Percarbonates._--Barium percarbonate, BaCO4, is obtained by passing
an excess of carbon dioxide into water containing barium peroxide in
suspension; it is fairly stable, and yields hydrogen peroxide when
treated with acids (E. Merck, _Abs. J.C.S._, 1907, ii. p. 859). Sodium
percarbonates of the formulae Na2CO4, Na2C2O6, Na2CO5, NaHCO4 (two
isomers) are obtained by the action of gaseous or solid carbon dioxide
on the peroxides Na2O2, Na2O3, NaHO2 (two isomers) in the presence of
water at a low temperature (R. Wolffenstein and E. Peltner, _Ber._,
1908, 41, pp. 275, 280). Potassium percarbonate, K2C2O6, is obtained
in the electrolysis of potassium carbonate at -10 to -15 deg.

CARBON BISULPHIDE, CS2, a chemical product first discovered in 1796 by W.A. Lampadius, who obtained it by heating a mixture of charcoal and pyrites. It may be more conveniently prepared by passing the vapour of sulphur over red hot charcoal, the uncondensed gases so produced being led into a tower containing plates over which a vegetable oil is allowed to flow in order to absorb any carbon bisulphide vapour, and then into a second tower containing lime, which absorbs any sulphuretted hydrogen. The crude product is very impure and possesses an offensive smell; it may be purified by forcing a fine spray of lime water through the liquid until the escaping water is quite clear, the washed bisulphide being then mixed with a little colourless oil and distilled at a low temperature. For further methods of purification see J. Singer (_Journ. of Soc. Chem. Ind._, 1889, p. 93), Th. Sidot (_Jahresb._, 1869, p. 243), E. Allary (_Bull. de la Soc. Chim._, 1881, 35, p. 491), E. Obach (_Jour. prak. Chem._, 1882 (2), 26, p. 282).

When perfectly pure, carbon bisulphide is a colourless, somewhat pleasant smelling, highly refractive liquid, of specific gravity 1.2661 (18 deg./4 deg.) (J.W. Bruhl) or 1.29215 (0 deg./4 deg.) (T.E. Thorpe). It boils at 46.04 deg. C. (T.E. Thorpe, _Journ. Chem. Soc._, 1880, 37, p. 364). Its critical temperature is 277.7 deg. C., and its critical pressure is 78.1 atmos. (J. Dewar, _Chem. News_, 1885, 51, p. 27). It solidifies at about -116 deg.C., and liquefies again at about -110 deg.C. (K. Olszewski, _Jahresb._, 1883, p. 75). It is a mono-molecular liquid (W. Ramsay and J. Shields, _Jour. Chem. Soc._, 1893, 63, p. 1089). It is very volatile, the vapour being heavy and very inflammable. It burns with a pale blue flame to form carbon dioxide and sulphur dioxide. It is almost insoluble in water, but mixes in all proportions with absolute alcohol, ether, benzene and various oils. It is a good solvent for sulphur, phosphorus, wax, iodine, &c. It dissociates when heated to a sufficiently high temperature. A mixture of carbon bisulphide vapour and nitric oxide burns with a very intense blue-coloured flame, which is very rich in the violet or actinic rays. When heated with water in a sealed tube to 150 deg. C. it yields carbon dioxide and sulphuretted hydrogen. Zinc and hydrochloric acid reduce it to tri-thioformaldehyde (CH2S)3 (A. Girard, _Comptes rendus_, 1856, 43, p. 396). When passed through a red-hot tube with chlorine it yields carbon tetrachloride and sulphur chloride (H. Kolbe). Potassium, when heated, burns in the vapour of carbon bisulphide, forming potassium sulphide and liberating carbon. In contact with chlorine monoxide it forms carbonyl chloride and thionyl chloride (P. Schutzenberger, _Ber._, 1869, 2, p. 219). When passed with carbon dioxide through a red-hot tube it yields carbon oxysulphide, COS (C. Winkler), and when passed over sodamide it yields ammonium thiocyanate. A mixture of carbon bisulphide vapour and sulphuretted hydrogen, when passed over heated copper, gives, amongst other products, some methane.

Carbon bisulphide slowly oxidizes on exposure to air, but by the
action of potassium permanganate or chromic acid it is readily
oxidized to carbon dioxide and sulphuric acid. By the action of
aqueous alkalis, carbon bisulphide is converted into a mixture of an
alkaline carbonate and an alkaline thiocarbonate (J. Berzelius,
_Pogg. Ann._, 1825, 6, p. 444), 6KHO + 3CS2 = K2CO3 + 2K2CS3 + 3H2O;
on the other hand, an alcoholic solution of a caustic alkali converts
it into a xanthate (A. Vogel, _Jahresb._, 1853, p. 643),

CS2 + KHO + R.OH = H2O + RO.CS.SK.

Aqueous and alcoholic solutions of ammonia convert carbon bisulphide
into ammonium dithiocarbamate, which readily breaks down into ammonium
thiocyanate and sulphuretted hydrogen (A.W. Hofmann),

CS2 + 2NH3 -> NH2.CSS.NH4 -> H2S + NH4CNS.

Carbon bisulphide combines with primary amines to form alkyl
dithiocarbamates, which when heated lose sulphuretted hydrogen and
leave a residue of a dialkyl thio-urea,

CS2+2R.NH2 -> R.NH.CSS.NH3R -> CS(NHR)2 + H2S;

or if the aqueous solution of the dithiocarbamate be boiled with
mercuric chloride or silver nitrate solution, a mustard oil (q.v.) is
formed,

R.NH.CSS.NH3R + HgCl2 -> Hg(R.NH.CSS)2 -> 2RNCS + HgS + H2S.

Carbon bisulphide is used as a solvent for caoutchouc, for extracting
essential oils, as a germicide, and as an insecticide.

_Carbon monosulphide_, CS, is formed when a silent electric discharge
is passed through a mixture of carbon bisulphide vapour and hydrogen
or carbon monoxide (S.M. Losanitsch and M.Z. Jovitschitsch, _Ber.,_
1897, 30. p. 135).

CARBONDALE, a city of Lackawanna county, Pennsylvania, U.S.A., on the Lackawanna river, 16 m. N.E. of Scranton. Pop. (1890) 10,833; (1900) 13,536, of whom 2553 were foreign-born; (1910 census) 17,040. Carbondale is served by the Erie, the Delaware & Hudson (which has machine shops here), and the New York, Ontario & Western railways. The city lies near the upper end of the Lackawanna valley, and the scenery of the surrounding mountains makes it a summer resort of some importance. It has a public library, a small park, an emergency hospital and the Carbondale city private hospital. Carbondale is situated in one of the richest anthracite coal regions of the state, and its principal interest is in coal. Among its manufactures are foundry and machine shop products, sheet-iron, silk, glass, thermometers and hydrometers, bobbins and refrigerating machines. The value of the city's factory products increased from $1,146,181 in 1900 to $2,315,695 in 1905, or 102%. The settlement of the place began in 1824 with the opening of the coal mines, and Carbondale was chartered as a city in 1851.

CARBONIC ACID, in chemistry, properly H2CO3, the acid assumed to be formed when carbon dioxide is dissolved in water; its salts are termed carbonates. The name is also given to the neutral carbon dioxide from its power of forming salts with oxides, and on account of the acid nature of its solution; and, although not systematic, this use is very common.

CARBONIFEROUS SYSTEM, in geology, the whole of the great series of stratified rocks and associated volcanic rocks which occur above the Devonian or Old Red Sandstone and below the Permian or Triassic systems, belonging to the Carboniferous period. The name was first applied by W.D. Conybeare in 1821 to the coal-bearing strata of England and Wales, including the related grits and limestones immediately beneath them. The term is a relic of that early period in the history of stratigraphy when each group of strata was supposed to be distinguished by some peculiar lithological character. In this case the carbonaceous beds--coal-seams--naturally appealed most strongly to the imagination, and the name is a good one, notwithstanding the fact that coal-seams occupy but a small fraction of the total thickness of the Carboniferous system; and although subsequent investigations have demonstrated the existence of coal in other geological formations, in none of these does it play so prominent a part. The stratified rocks of this system include marine limestones, shales and sandstones; estuarine, lagoonal and fresh-water shales, sandstones and marls with beds of coal, oil-bearing rocks, gypsum and salt.

In many parts of the world there is no sharp line of demarcation between the Devonian and the Carboniferous rocks; neither can the fossil faunas and floras be clearly separated at any well-defined line; this is true in Britain, Belgium, Russia, Westphalia and parts of North America. Again, at the summit of the Carboniferous series, both the rocks and their fossil contents merge gradually into those of the succeeding Permian system, as in Russia, Bohemia, the Saar region and Texas. This has led certain geologists to classify the Devonian, Carboniferous and Permian into one grand system; E. Renevier in 1874 proposed to include these three into a single "Carbonique" system, later he retained only the two latter groups. There seems to be sufficient reason, however, to maintain each of these groups as a separate system and limit the term Carboniferous (_carboniferien_) in the manner indicated above. At the same time it must be remembered that there is in India, South Africa, the Urals, in Australasia and parts of North America an important series of rocks, with a "Permo-Carboniferous" fauna, which constitutes a passage formation between the Carboniferous, _sensu stricto_, and Jurassic rocks.

_Stratigraphy._--No assemblage of stratified rocks has received such
careful and detailed examination as the Carboniferous system;
consequently our knowledge of the stratigraphical sequence in isolated
local areas, where the coals have been exploited, is very full.

In Europe, the system is very completely developed in the British
Isles, where was made the first successful attempt at a classification
of its various members, although at a somewhat earlier date Omalius
d'Halloy had recognized a _terrain bituminifere_ or coal-bearing
series in the Belgian region.

The area within which the Carboniferous rocks of Britain occur is
sufficiently extensive to contain more than one type of the system,
and thus to cast much light on the varied geographical conditions
under which these rocks were accumulated. In prosecuting the study of
this part of British geology it is soon discovered, and it is
essential to bear in mind, that, during the Carboniferous period, the
land whence the chief supplies of sediment were derived rose mainly to
the north and north-west, as it seems to have done from very early
geological time. While therefore the centre and south of England lay
under clear water of moderate depth, the north of the country and the
south of Scotland were covered by shallow water, which was continually
receiving sand and mud from the adjacent northern land. Hence vertical
sections of the Carboniferous formations of Britain differ greatly
according to the districts in which they are taken.

The Coal-Measures and Millstone Grit are usually grouped together in
the _Upper Carboniferous_, the Carboniferous Limestone series
constituting the _Lower Carboniferous_.