hus
admitted, by three narrow slot-like openings, to the front of the furnace
between the tiles, a, b, and c, and under c and through the fire bars, e.
The air openings below are about three times the area of the openings in
the front of the furnace; but as the openings between the fire bars and the
tiles are always more or less covered by tar coke, it is impossible to say
what the effective openings are. This disposition answers admirably, and
requires little attention. Three minutes per hour per fire seems to be the
average, and the labor is of a very light kind, consisting of clearing the
passages between the tiles, and occasionally pushing back the coke on to
the fire bars. These latter are not interfered with, and will not require
cleaning unless any bricks in the furnace have been melted, when a bed of
slag will be found on them.

THE AMOUNT OF DRAUGHT

required for these fires is very small, and less than with coke firing. I
find that 0.08 in. vacuum is sufficient with tar fires, and 0.25 in. for
coke fires. The fires would require less attention with more draught and
larger tar supply, as the apertures do not so easily close with a sharp
draught, and the tar is better carried forward into the furnace. A regular
feed of tar is required, and considerable difficulty seems to have been
experienced in obtaining this. So long as we employed ordinary forms of
taps or valves, so long (even with filtration) did we experience
difficulties with the flow of viscous tar. But on the construction of
valves specially designed for the regulation of its flow, the difficulty
immediately disappeared, and there is no longer the slightest trouble on
this account. The labor connected with the feeding of furnaces with coke
and cleaning fires from clinker is of a very arduous and heavy nature.
Eight coke fires are normally considered to be work for one man. A lad
could work sixteen of these tar fires.

COMPOSITION OF FURNACE GASES.

Considerable attention has been paid to the composition of the furnace
gases from the tar fires. The slightest deficiency in the air supply, of
course, results in the immediate production of smoke, so that the damper
must be set to provide always a sufficient air supply. Under these
circumstances of damper, the following analyses of combustion gases from
tar fires have been obtained:

No Smoke.
CO_{2}. O. CO.
11.7 5.0 Not