MANUFACTURE OF PHOSPHORIC ACID. 37 
LARGER SCALE EXPERIMENTS. 
With the exception of a few experiments conducted in the furnace 
shown in Figure 9, A, practically all of the larger scale work on the 
volatilization of phosphoric acid from briquetted charges of phosphate 
rock. sand, and coke have been conducted in furnaces having certain 
features of both the open-hearth and blast-furnace types. While the 
dimensions of the furnace proper, the materials used for linings, and 
the character of the outer shell have been altered from time to time, 
the present furnace plan is in a general way the same as that 
employed in the earlier experiments. Briefly, this furnace consists 
of an elongated arched crucible, 12 feet in length. 2 feet in diameter, 
and 2 feet in height at the crown of the arch. In the center of the 
arched roof of this chamber is a circular opening leading up into a 
shaft or charge chamber 7 feet 6 inches in height and having the 
shape of the usual type of blast furnace. The throat of the chamber 
where it discharges onto the furnace hearth was originally 12 inches 
in diameter, but this was later reduced to 10 inches. This charge 
chamber widens out gradually until at the top of the bosh the 
internal diameter is 2 feet. From here on the walls of the chamber 
taper inwardly until at the top of the shaft the opening is only 14 
inches in diameter. This chamber holds approximately 700 pounds 
of briquetted charge. One foot from the top of the furnace shaft is a 
flue leading into a dust chamber. The furnace was originally con- 
structed entirely of fire brick, but after a number of experiments it 
was found that the temperatures attained were so high (1,500° to 
1,700° C.) that it was desirable to replace them in part by carborun- 
dum brick, particularly since in the earlier work neither the crucible 
nor furnace shaft were steel jacketed and therefore no water-cooling 
devices could be employed. 
Both the dust catcher and the stoves for burning any combustible 
gases evolved from the furnace and regenerating the heat in the 
effluent gases were originally constructed of fire brick without any 
outer steel casing. These stoyes were built together with a yiew to 
reducing radiation losses, but this plan also was found to be imprac- 
tical, since it was impossible to render the common walls of these 
stoves sufficiently tight to prevent the gases from one stoye mixing 
with the air passing through the adjoining one. The likelihood of 
thus causing an explosion made it necessary to abandon them as a 
means for heating the air to the oil burners, so they were used only 
to burn the combustible gases evolved from the furnace. In order 
to obtain the preheated air which should have been furnished by the 
stoves, a fire-brick chamber was built containing a coil of 60 feet of 
4-inch steel pipe heated by means of a small oil burner. The air 
required for the furnace in these earlier experiments was furnished 
by three Leiman positive-pressure blowers, two having a capacity of 
160 cubic feet of free air per minute each and the third a capacity 
of 360 cubic feet. When the furnace was well heated the large ancl 
one small blower were employed to supply the air. These discharged 
into a 4-inch main which was constricted at each burner to 3 inches 
in diameter. Views of the furnace plant used in this earlier work 
are shown in Plate V, Figures 1 and 2. 
The oil burners finally adopted for the furnace and the ones which 
are still being employed operate with high-pressure oil (from 50 to 
200 pounds per square inch) but with air at relatively low pressure 
