HIGH TEMPERATURE CARBONIZATION OF COAL 399
THE HYDROCARBONS
Before the Chemical phenomena associated with the process of carbonization can be followed it is essential that some knowledge of the chemistry of the hydro-carbons should be obtained. The author feels that in a technical volume he will not be expected to retread the ground covered in elementary textbooks on chemistry. He proposes, therefore, to confine himself to a brief resumé of the composition and behaviour of the chief hydrogen and carbon compounds met with.
Carbon differs from other elements in forming an abnormally large numbei of compounds with hydrogen—called hydrocarbons. Tlie simplest is methane (CH4). The various compounds are classified as “ saturated ” and “ unsaturated,” according as to whether the carbon atoms are (owing to their tetravalent nature) fully saturated or not. When hydrocarbons are arranged in order of molecular weights, they com-prise a series, each member of which. contains so many atoms of carbon and hydrogen more than the preceding member. The more important series of hydrocarbons may be summarized as follows:—
1. The Paraffins
General formula Methane Ethane Propane Butane Pentane
Etc.
General formula Ethylene Propylene . Butylene Amylene
Etc.
CnH2n+2
CH4 \
c2h6
C3Hs - Saturated hydrocarbons. c4h10
C6H127
11. The Olefines
• CnH2n
C2H4 \
C H
3„6 ■ Unsaturated hydrocarbons.
Ci-Hg
. c5h10J
III. Thb Acetylenes
General formula ..... CnH2n_2
Acetylene . . ' . - ■ • C2H2 'j
Allylene (methyl-acetylene) . . • C3H4 Unsaturated hydrocarbons.
Crotonylene ..... C4H6 J
Etc.
IV. The Aromatic Series
General formula ..... C„H2„__6
Benzene ...... C(iH6
Toluene (methyl-benzene) . . • C7H8
Xylene (three isomers) . ■ ■ C8H10
The general formula of the aromatics gives the appearance of a high degree of unsaturation. In practice, however, it has been found that benzene possesses no