the study of a large number of organic reactions. According to tliis, when one compound is trans- formed into another by some simple reaction, the molecule — at least the principal part of it — remains unchanged. Once, therefore, the con- stitution of a certain number of substances has been determined, say, by Kiirner's method, the constitution of any new substance derived from one of them by a simple reaction becomes evident by the very fact that it is derived from a substance of known constitution, or by the fact that it may be transformed into a sub- stance of known constitution: and it is in this manner that the constitution of a great majority of carbon eom])(mnds has been brought to light. Thus, if the di-chlorobenzene, CeHjCI., which is shown by KiJrner's method to be an oiifto-compound, were transformed into dioxy- benzene, CijHi(OH):, the latter, too, would be assumed to be an o;V/io-compound. It is easy to see that this principle is at the basis of Kiir- ner's method itself, and it may be considered as one of the fundamental principles of organic re- search.
Classification of Cakbon Compounds. The innumerable compounds that are said to be derived from benzene all resemble the latter in certain chemical properties — a fact which is in accordance with their formulas having in com- mon the benzene ring, or 'benzene nucleus,' con- sisting of six carbon atoms. It is therefore con- venient to treat the benzene derivatives, other- wise called 'aromatic compounds,' separately from the rest of the compounds of carbon; and hence the division of organic compounds into iatty (or aliphatic) and aromatic. Just as the aromatic compounds may be considered as de- rivatives of benzene, the fatty compounds may be considered as derivatives of methane, or marsli-gas, the simplest of the compounds of carbon; and while the aromatic compounds are characterized by having, in their formulas, a nucleus of carbon atoms arranged in a ring, or cloned chain, the fatty compounds have graphical formulas in which the carbon atoms are arranged along straight lines, or open chains. However, in spite of this constitutional distinction between fatty and aromatic compounds, it must be re- membered that the compounds of the two classes are more or less closely related, and that ctmi- pounds of one of these classes may, by suitable methods, be transformed into compounds of the other class. A classical example of such a trans- formation is Berthelot's celebrated synthesis of benzene itself from acetylene, effected by sinijjly passing the latter through red-hot tubes. Again, the subdivisions of the two great classes present a notable parallelism. Thus, corresponding to the falty acids, alcohols, aldehydes, ketones, etc., there are also aromatic acids, alcohols, aldehydes, ketones, etc.
Just as the division of organic compounds into fatty and aromatic is based on a dill'orence in their chemical constitution, so is the further classification of the compounds belonging to each of the two great classes based on constitutional similarities and dissimilarities.
The most important classes of carbon compounds, as well as a large number of individual compounds that are interesting because of the important rAle that they play in the bodies of animals and plants, or because of their useful applications in medicine and the arts, are de- scribed under their special names. See Hydro- carbons; Alcohols; Ethers; Aldehydes; ]ve- TONES; Acids; Ksteks; Amides; .mines; Organo-JIetali.ic Compoinds; Carbohydrates; Phenols; DiazoCompoinds; etc. Besides the derivatives of methane and of benzene, the deriva- tives of naphthalene, anthracene, pyridine, and quinoline (qq.v.) deserve mention here. I'or history and bibliography of organic chemistry, see Chemlstry.
CAR'BONDALE. A city in Jackson County,
111., 'J- miles southeast of Saint Louis, ilo.,
on the Illinois Central and other railroads
(Map: Illinois, C 6). It is the seat of the South-
ern Illinois Normal University, which has a
good library, museum, laboratories, and other
well-equipped buildings. The city has Hour-mills,
iron-works, and other industrial establishments,
is the centre of an agricultural and coal-mining
region, and s]ii])s coal, fruit. Hour, grain, etc.
Populatibn, in 1800, 2382; in 1900, 3318.
CARBONDALE. A city in Lackawanna
County, I'a., 1(1 miles northeast of Scranton;
near the head of the Lackawanna Kiver, and on
the Erie, the Delaware and Hudson, and the New
York, Ontario and Western railroads (Map:
Pennsylvania, F 2). It is in the centre of one
of the most important anthracite coal-mining
districts in the State, and has silk-mills,
foundries and machine-shops, car-shojis, etc. The
city has a public library, Emergency Ilospit^il,
and a small park in the heart of the city, con-
taining a soldiers' monument. Settled in 1824,
Carbondale was incorporated in 18.51, It is gov-
erned by a mayor, elected every three years, and a
bicameral city council. The mayor, with the con-
sent of the council, a|)|)oints policemen and the
health board; the council elects the city engineer,
clerk, and attorney; all other ollices are filled
by popular election. Population, in 1890, 10,833;
in 1000, 13,53ti.
CARBON DISUL'PHIDE, or Bisulphide
(carhuii -- disiiljjhidc, from Ok. dl-, di-, doul)le
-j- suijjhide, and bisulphide, from Lat. hi-, doulile
+ sulphide), CS,. An unstable compound of
carbon and sulphur, analogous to carbon dioxide,
whose formula is CO™. It may be prejiared by
passing the vapors of sulphur over charcoal kept
at a red heat. On a large scale it is prepared as
follows: A cast-iron cylinder containing char-
coal js placed in a furnace and heated to the re-
quired temperature. The cylinder is provided
with two tubes, through one of which sulphur
vapors or pieces of sulphur are introduced, while
the other serves as an exit for the vapors of car-
bon disulphide, which are liquefied in a suit-
able condenser. Pure carbon disil])hide is a
heavy colorless liquid of a rather pleasant etheric
odor; the ordinary prejiarations, however, have a
most sickening smell, owing to the presence of
impurities. The specific gravity of the purified
comiwund at 0° C. is 1.293. It has a high re-
fracting power and mixes in all proportions with
absolute alcohol, ether, hydrocarbons, and other
organic liquids. It is an excellent solvent for
many substances, such as sulphur, iihosphorus,
india-rubber, gutta-percha, the resins, fats, etc.
Water does not mix with it, and alcohol contain-
ing a considerable amount of water dissolves it
only to a limited extent. The boiling-point of
carbon disulphide is 40° C. .t high temperatures
it dissociates into its constituents, carbon and
