mass of coke in the gas producer. The atmospheric air admitted at the
several openings previously spoken of ascends through the lower layers
of the incandescent coke, the carbon of which burns to carbonic acid
gas at the expense of the oxygen of the air. Among the middle and upper
layers of the incandescent coke the carbonic acid gas takes up a further
quantity of the fixed carbon, and becomes transformed into carbonic
oxide gas (CO_{2}+C=2CO), which is an inflammable body, and possesses
considerable calorific power. Unless the carbonic acid gas is very
completely "baffled" in its ascent through the coke in the producer, a
quantity of it passes into the furnace along with the carbonic oxide,
the efficiency of which is diminished in proportion as the former
increases in quantity. Of course, also, the nitrogen associated with
the oxygen in the air admitted to the gas generator passes on with the
carbonic oxide gas, this nitrogen acting as a dilutant and being of
course absolutely useless as a generator of heat. The steam which
we previously spoke of serves two good purposes. In contact with
incandescent coke it suffers decomposition, its oxygen uniting with some
of the fixed carbon to form carbonic oxide, while the hydrogen which
is set free passes onward, and mixes with the other gases to be
subsequently consumed with them. The admission of the steam thus causes
the absorption of heat in the gas generator where the decomposition
takes place, this heat being again evolved on the subsequent combustion
of the hydrogen. Then, again, as the steam is delivered in among the
coke in a jet, or a series of jets, it has the effect of almost entirely
preventing any clinkering or slagging of the earthy and silicious
materials, which form such a large portion of the substance of the coke
obtained from Scotch cannels, sometimes as much as from 15 to 20 per
cent. It is scarcely necessary for the stokers to go down below to the
bottom of the producers to remove the ash above once in every six hours.
Referring to the composition of the gaseous fuel obtained from cannel