572 GEOLOGY OF OHIO. 
A form of the round oyen is used in great numbers in France in 
the Loire basin, in Belgium and in the Soar basin, and is known as the 
French furnace. The furnace is similar to the bee-hive oven, excepting 
that it has an encircling canal in the walls, which communicates 
with the interior of the furnace by small conduits, which are highly 
inclined, converging toward a point near the center of the roof. 
These canals open to the air by openings on each side of the door, 
where the admission of air may be readily regulated. The charge 
is made through the opening in the roof, and the door is then tightly 
closed, air being only admitted through certain channels. The air is 
thus supplied regularly in equal portions to all parts of the oven. 
Though the expense of their construction is somewhat greater than of 
the ordinary round oven, it is claimed in France that the yield of the 
coal is increased 6 per cent. 
Cox’s oven. A form of oven similar to the latter, in so far as air is 
admitted to the coking chamber through certain canals in the walls of 
the furnace, is known as Cox’s oven. This oven was patented by Cox 
in 1840, and has been used somewhat in South Wales. 
The oven is rectangular in plan, tapering a little toward the door 
in front, which has the full width of the oven. Ata height of 53 feet 
the oven is covered by an arch, and a small distance above this is a 
second arch. The space between these arches communicates in_ front 
with the interior of the oven, and at the back with the chimney. Two 
ovens being placed back to back, they open into the same chimney, 
which is separated into two flues, one for each furnace. The space 
above the upper arch and between the ovens is filled with sand, which 
concentrates much of the heat evolved during the working operation. 
On one side of the front of each oven an opening communicates with a 
flue, passing horizontally in the wall to the back of the furnace, where 
it communicates with the interior by the canals. The charge is made 
by shoveling the coal in from the front, and then the door is lowered 
and fastened by an iron bar. The door is formed of an iron frame, 
which is lined with fire-brick, and when in place is tightly luted to 
prevent access of air. 
The air for the combustion of the gases enters through the canals 
into the inside of the furnace, when the gases burn and escape into the 
vault above, and into the chimney. A valve being placed in the 
chimney flue of each furnace, the draught may be regulated at will 
