that are devoid of color, or which have certain special tints, are highly esteemed as gems.

Carbon has the chemical symbol C, and an atomic weight of 12.0 if 0=16, and 11.91 if H=1. The specific gravity of diamond is 3.51, that of graphite is from 2.11 to 2.26, and that of hard gas-coke is about 2.35. The linear coefficient of expansion of diamond (Fahrenheit scale) is 0.00000066 at ordinary temperatures, and that of graphite is 0.0000044. Graphite has an electrical conductivity of about one twelfth, and hard gas-coke about one one-hundredth, when the corresponding conductivity of mercury is taken as the unit. Diamond is practically a non-conductor. The specific heats of diamond and graphite are quite different at ordinary temperatures. Thus at 50° F. diamond has a specific heat of 0.113, graphite 0.160, and wood charcoal about 0.165. These values increase as the temperature rises, and at about 1,100° F. all three varieties have a common specific heat of about 0.44.

Carbon is infusible, and insoluble in any known liquid at ordinary temperatures. It dissolves to a limited extent in melted cast iron, and in melted platinum it dissolves freely, separating out again in the form of graphite upon cooling. It is unaltered by the action of acids, except when some powerful oxidizing agent like chlorate of potassium or bichromate of potassium is also present. Chemically it is tetravalent in nearly all of its compounds. It combines with oxygen in two different proportions, with the formation of a monoxide CO, and a dioxide CO2. It also forms, with hydrogen, a great number of compounds known as hydrocarbons (q.v.); and it combines with many of the metals to form carbides (q.v.). With hydrogen, oxygen, nitrogen, and small quantities of other elements, it constitutes the entire substance of animals and plants; and the coal beds that make our modern civilization possible are composed of vegetable remains from which the elements other than carbon have been mostly expelled by the combined action of heat and pres

sure.

For further information_concerning carbon, See AROMATIC COMPOUNDS; CARBON COMPOUNDS; CHARCOAL; COAL; DIAMOND; FATTY COMPOUNDS; GRAPHITE.

Carbon Black. This is the trade term given in this country to black made from gas. It was originally called hydrocarbon gas black, and a black of a similar nature to that now made was manufactured both in this country and in Europe from artificial gas. The industry did not, however, assume any importance before 1872, when the first patent was obtained for producing this black from natural gas. Since this date, innumerable patents have been taken out for the manufacture of this black from natural gas, and at the present time there are 10 distinctly different processes in operation.

The various methods of making the black from natural gas are fundamentally the same, the black in every case being produced by allowing the flame to strike a metal surface, upon which the carbon is deposited in the form of a black flocculent powder. Carbon black is of a similar nature to lampblack made from oil. It is an exceptionally pure form of carbon, varying from 98 per cent to 991⁄2 per cent pure. The color is absolutely permanent, and it is the

blackest and most brilliant permanent black produced.

The difference in the qualities are principally due to the amount of air supplied to the flame, and the shape of the plates or rollers upon which the black is collected. All of the works now operated are automatic, for the gas not only converts itself into the black, but also furnishes the power that scrapes it off the plates and collects and packs it in Larrels, ready for shipment, the black not being seen or touched until it is used by the consumer.

The principal use for the black is in the manufacture of printing inks, paints, rubber goods, oil cloth, blackings, etc.; the finest qualities are used in the manufacture of lithographic and half tone inks; the cheaper in news inks.

The abundance of natural gas in the United States, and the automatic method of making the black have enabled the manufacturers in this country to produce it at so much lower prices that little of this black is now made from artificial gas, and large quantities of the product are exported annually. The total production of carbon black in this country is (1905) 12,000,000 pounds per annum, of which one-fifth is exported. C. HAROLD SMITH,

Of the Binney & Smith Co., New York.

Carbon Compounds, in chemistry those compounds which contain the element carbon; and since carbon is an essential constituent of nearly all organic substances, the chemistry of its compounds is practically synonymous with "organic chemistry." Until within the past half-century it was thought by many authorities that the compounds that occur in animals and plants are essentially different in nature from those that are produced in the laboratory, and that they cannot be obtained without the action of the vital principle." This idea received its first blow in 1828, when Wöhler prepared urea sidered to be inorganic; yet as late as 1849 the from substances that had been previously conistry as "the chemistry of compounds formed great chemist, Berzelius, defined organic chemunder the influence of life." A vast number of have now been prepared in the laboratory, and substances that were formerly classed as organic the old classification of chemistry into organic organic division being now and inorganic branches has broken down, the called the "chemistry of carbon compounds." more correctly great complexity, and are apparently unlimited The carbon compounds form a in number. The reasons for this are that carbon is quadrivalent; that it forms multitudes of compounds with hydrogen alone, in many of which more or less of the hydrogen can be replaced by other elements, with the formation of new and altogether different substances; that its chemical bonds are apparently powerful; and that it unites with elements of the most widely different nature.

group of

In a general way, the better-known carbon compounds are mostly divided into two great classes, according to the type of the "graphical" or "structural" formula that must be used in order adequately to represent their chemical relations. The first class includes all those bodies whose structural formulæ are distinguished by the fact that the atoms (or radicals) that are present form "open" chains, which do not any

HC

HU

H-C-C- C-H,

H H H

is an illustration of this class. The "open chain" compounds are called fatty compounds, and are treated under that heading. The name was originally given because many of the substances that are included in the class have long been known in connection with fats and allied bodies; but it would be more logical to call them "methane derivatives," since they may be considered to be obtainable from the hydrocarbon methane, CH4, by a process of substitution. The second great class of carbon compounds is distinguished by the fact that the structural CH formula that are required in order to exhibit the chemical properties of its members return into themCH selves, so as to form "closed" chains or rings, which (at least in the fundamental forms) contain six carbon atoms. Benzene is a familiar example. From the fact that many of the first known representatives were balsams, oils, and resins, these substances are known collectively as aromatic compounds, and are described under that heading. A better name would be "benzene derivatives," since all the members of the class are derivable from benzene by substitution.

HC

CH

Н

In addition to the aromatic and fatty compounds, others are known which do not properly come under either heading. Thus the structural formula of furfuran contains a closed ring, formed by the union of four atoms of carbon and one of oxygen. Closed rings, consisting of three, four, and five atoms of carbon, are also known. The pronounced analogies and affinities that exist among the members of the aromatic and fatty groups, respectively, have forced those two groups upon the attention of chemists. Those compounds of carbon which are strictly included within either have not yet been classified upon a similarly broad basis.

not

The principal phenomena of the carbon compounds are given under special headings. In addition to those already given, see, particularly, ISOMERISM; and RADICAL.

For an excellent presentation of the whole subject, see Hjelt, Principles of General Organic Chemistry.'

Carbon Dioxide, Carbonic Acid Gas, or Carbonic Anhydride, CO,, is formed whenever carbon is burned in the presence of excess of oxygen or air. It is a colorless, odorless gas, soluble to a considerable extent in cold water, especially when subjected to pressure. Its solution possesses feebly acid properties, and has a peculiarly pungent taste, on account of which the aqueous solution of the acid is greatly used as a constituent of various beverages. The ef

fervescence accompanying the opening of a bottle of beer, soda-water, or champagne, is due to the escape of the carbon dioxide that was previously held in solution. Carbon dioxide occurs in great abundance in nature, both free and in combination with various elements, in the form of carbonates. Carbonate of lime, CaCO3, is one of the most common carbonates. It is formed when the gas is allowed to bubble up through a solution of lime water, and exists in nature in vast masses, as limestone and marble. (Other carbonates are described under the metals that constitute their bases.) Carbon dioxide is a constant constituent of the atmosphere (see AIR), occurring even at the tops of mountains and in the air collected from balloons. It is generated by the combustion of fuel, by respiration, by fermentation, and by the decay of animal and vegetable matter. In some localities, too, immense quantities of the gas are emitted from the ground, or from mineral springs and wells, as in the Grotto del Cane, the Cave of Montjoly in Auvergne, in the valley of Wehr, in the Eifel, and at many other places. It is being simultaneously abstracted from the air by plants, which in the sunlight decompose the gas, fixing the carbon that it contains, and setting the oxygen free. Carbon dioxide has but feeble affinity for the bases with which it combines, and is readily replaced by almost any other acid. In preparing the gas for experimental purposes the usual method is to add a dilute mineral acid to pulverized marble or other carbonate, the carbon dioxide then being liberated continuously and in large quantities. The gas is about 1.53 times as heavy as an equal bulk of air. Its critical temperature is about 90° F., and at any temperature lower than this it can be reduced to a liquid by the application of pressure.

Poisoning by this gas frequently results in closed rooms crowded with people. The symptoms may be very slight, consisting of a mild indisposition, or they may be severe- headache, nausea, vomiting, etc. In poisoning in the severer grades there is cyanosis, coma, and unconsciousness. Carbon dioxide alone is not a fatal poison; it is rendered so usually by the diminution of oxygen supply.

The

Carbon Disulphide, CS2, a liquid formed hot charcoal. Under normal conditions it is a when the vapor of sulphur is passed over redvery volatile, inflammable liquid, having a specific gravity of 1.29, and boiling at 115° F. commercial disulphide has an exceedingly disagreeable smell, but this is due to the presence ethereal smell. Carbon disulphide (or bisulof impurities. The pure liquid has a pleasant, phide) does not mix with water, but it dissolves sulphur, phosphorus, caoutchouc, and many other organic bodies that are difficultly soluble in other menstrua, and it is to this property that it owes its commercial value.

Poisoning by carbon disulphide is becoming very prevalent since the use of rubber goods has become so extensive. The symptoms of acute poisoning are due to a poisoning of the blood and a central paralysive action on the nervous system. The blood action is that of a breaking up of the red blood cells, hemolysis. This results in cyanosis, pains, headache, coma, vertigo, nausea, vomiting, weakness, unconsciousness, coma, and death. Such symptoms

are rare, the poisoning developing as a rule much less rapidly. In workers in rubber factories, in which there is much vapor of CS there develop disturbances of temper, pressure feelings on the head, heat, and the feeling as if the blood would burst through the skull, with headache. There may also be symptoms of irritation of the bronchi, coughing, and roughness of the voice, etc. Treatment is fresh air and symptomatic.

Carbon Monoxide, or Carbonic Oxide, CO, is produced, in addition to the dioxide, when carbon is burned with a limited supply of air or oxygen. It is also generated by passing carbon dioxide through a red-hot bed of carbon, in accordance with the equation CO2+ C=2CO. For experimental purposes the gas may be generated by decomposing oxalic acid by heating it with strong sulphuric acid, and passing the gases that are evolved through a solution of caustic soda to absorb the carbon dioxide that is present. Carbon monoxide is colorless, and has a density about 0.97 times that of air. It burns with a lambent, blue flame that is often seen in coal fires that have been freshly supplied

with fuel.

Carbon Oxychloride. See PHOSGENE.

Carbonado, or Carbon, a massive, black or dark-gray variety of diamond, also called "black diamond." Though possessing the adamantine or resinous luster of the crystallized variety, it is opaque and, therefore, of no value as a gem. It is the hardest substance known and this fact makes it the most desirable for use in diamond drills; it therefore sells for as high a price per carat as one carat rough gem diamonds (q.v.). Being without cleavage it is less brittle than the crystals, and owing to its somewhat porous structure, its specific gravity is less, 3.15 to 3.29. The commercial supply comes exclusively from the province of Bahia, Brazil, where it occurs in angular fragments which occasionally show a rough cubic outline.

Carbonari, kär-bo-nä'rē (colliers, or more strictly, charcoal-burners), the name of a large political secret society in Italy. According to Botta's Storia d'Italia' the Republicans fled, under the reign of Joachim (Murat), to the recesses of the Abruzzi, inspired with an equal hatred of the French and of Ferdinand. They formed a secret confederacy, and called themselves carbonari. Their chief, Capobianco, possessed great talents as an orator. Their warcry was "Revenge for the lamb mangled by the wolf!" When Murat ascended the throne of Naples he employed Maghella, a Genoese, in the department of police, and afterward as minister. All his efforts were directed to the union and independence of Italy, and for this purpose he made use of the society of the Carbonari. The ritual of the Carbonari was taken from the trade of the charcoal burner. Clearing the wood of wolves (opposition to tyranny) was the symbolic expression of their aim. By this they are said to have meant at first only deliverance from foreign dominion; but in later times democratic and anti-monarchical principles sprang up. They called one another good cousins. No general union of the order under a common head seems to have been effected. The separate societies in the small towns entered into a connection with each other, but this union extended

no farther than the province. The place of assembly was called the hut (barraca); the surrounding neighborhood was called the wood; the meeting itself was distinguished as the sale (vendita). The confederation of all the huts of the province was called the republic, generally bearing the ancient name of the province. The chief huts (alta vendita) at Naples and at Salerno endeavored to effect a general union of the order, at least for the kingdom; but the attempt appears to have been unsuccessful. The order, soon after its foundation, contained from 24.000 to 30,000 members, and increased so rapidly, that it spread through all Italy. In 1820, in the month of March alone, about 650,000 new members are said to have been admitted; whole cities joined it. The clergy and the military, in particular, seem to have thronged for admission. The religious character of the order appears from its statutes: "Every Carbonaro has the natural and inalienable right to worship the Almighty according to the dictates of his conscience." After the suppression of the Neapolitan and Piedmontese revolution in 1821, the Carbonari throughout Italy were declared guilty of high treason, and punished by the laws. Meantime societies of a similar kind had been formed in France, with which the Italian Carbonari amalgamated, and Paris became the headquarters of Carbonarism. The organization took on more of a French character, and gradually alienated the sympathies of the Italian members, in order to form the party of Young Italy. a number of whom dissolved connection with it,

Car'bonates. See CARBON DIOXIDE.

Carbondale, Pa., a city of Lackawanna County, situated on the Lackawanna River, 110 miles north-northwest of Philadelphia; and on the Erie, the Delaware & H., and the New York, O. & W. R.R.'s. It is the centre of an important anthracite coal-field, and the principal industry is mining. There are also machine-shops, foundries, etc. As it is in a monuntain region with fine scenery, it is also a summer resort. Pop. (1900) 13,536.

Carbonear, kär'bon-ēr, Newfoundland, a port of entry on the eastern side of the peninsula separating Trinity Bay from Conception Bay 25 miles in a northwesterly direction from St. John's. Pop. (1901) 3,703.

Carbonic Acid, or Carbonic Acid Gas. See CARBON DIOXIDE.

Carbonic Anhydrid. See CARBONIC DIOXIDE.
Carbonic Oxide. See CARBON MONOXIDE.

Carboniferous Limestone, or Mountain Limestone, certain limestones of Lower Carboniferous age, as named by Murchison and other English geologists. In the United States the silver-lead ores of Leadville and other Rocky Mountain camps, and the zinc and lead ores of southwestern Missouri, are in limestones of Carboniferous age. See CARBONIFEROUS SysTEM.

Carboniferous Period, the last of the great time divisions of the Paleozoic Epoch. During it were laid down vast beds of plantremains now turned to coal, whence the name. It is true that coal fields of later age than Carboniferous are known, particularly in North America, but the important coal fields of Europe and of eastern North America are of Carboniferous age. In North America, when the