COAL-TAR AND WATER-GAS TAR CREOSOTES. 9 
Table 2. — Hydrocarbons found in the primary-reaction products of the distillation of coal. 
Saturated hydrocarbons. 
Methane CHt 
Ethane C 2 H R 
Propane CWg 
Butane C4H10 
Pentane C 6 Hi 2 
Hexane C 6 Hi4 
Heptane C 7 His 
Octane C 8 Hi 8 . . . . 
Monane CjHso 
Decane C10H22... 
Possibly paraffins. 
Unsaturated 
hydrocarbons. 
Naphthenes. 
Ethylene C2IT6 . 
Propylene C 6 H 6 . 
Butylene C 4 H 8 . 
Amyiene C B Hi . 
Hexylene C fi Hi 2 . 
Heptylene C 7 Hn. 
Hexahydrobenzene C 6 Hi 
All these hydrocarbons, both gaseous and liquid, are similar to 
what we obtain from crude petroleum. In addition to the above, 
the oxygen in the coal is probably in a large measure converted into 
oxides of carbon and phenols, as we find these materials in great 
abundance in low- temperature tars. All of the products of the 
primary reaction, with the exception of the gaseous carbon monoxide, 
carbon dioxide, methane, and ethane, will undergo decomposition at 
somewhat higher temperatures into more simple hydrocarbons 
with a production of the permanent gases, methane, ethane, ethylene, 
acetylene, and hydrogen. This is the secondary reaction. The 
products of the secondary reaction probably contain compounds 
having three carbon atoms or less, with the exception of possibly 
small amounts of benzene and xylene, which result from the decom- 
position of the naphthenes. We should expect that this phase of 
the reaction would produce chiefly hydrogen; the saturated hydro- 
carbons — methane, ethane, and possibly propane; and the unsatu- 
rated hydrocarbons — ethylene, propylene, acetylene, and amyiene. 
All of these, as well as different members of the acetylene series, have 
been identified as products of the distillation of coal. If the gas 
maker could so arrange his distillation that only the first and second 
reactions would take place, it would probably be a very satisfactory 
arrangement for him. In order, however, to heat the coal hot 
enough all the way through to induce a secondary reaction as nearly 
complete as possible, it is necessary to superheat the retorts or ovens, 
and, as a result, a third reaction may and does take place. 
The tertiary reaction consists in building up more complex but 
more stable compounds from the more simple ones. This reaction 
is often accompanied by the elimination of hydrogen. The hydro- 
carbons formed are those classed by the chemist as aromatic hydro- 
carbons, and they differ from the paraffin hydrocarbons in containing 
less hydrogen per carbon atom, in the arrangement of the carbon 
atoms themselves, in their chemical reactions, and in their resistance 
to heat. The aromatic hydrocarbons may be subdivided into a 
