46 BULLETIN 1179, U. S. DEPARTMENT OF AGRICULTURE. 
seldom occurs in normal operation, and if so may often be remedied 
by a momentary reduction in the air pressure. 51 
In order to remedy the main difficulties encountered in the last 
experimental run of the furnace, arrangements have been made for 
the installation of a coil of pipe in the oil line to the burners. This 
coil will be immersed in a vessel which is kept constantly supplied with 
hot water from the furnace-cooling devices. Such a scheme should 
make it possible to deliver the oil to the furnace almost at its flash 
point and thus insure its thorough atomization and immediate com- 
bustion. 
A variable speed motor for driving the positive-pressure blower 
will also be installed, which will make it feasible to determine accu- 
rately the amount of air being delivered to the furnace, and thus 
adjust the oil accordingly. 
While it is expected that the above changes will largely remedy 
the mechanical difficulties heretofore experienced, it would be of 
considerable advantage to substitute a single large pipe stove in place 
of the four checker brick stoves now employed. In a pipe stove the 
air for the combustion of the fuel is passed through a series of pipes 
contained in a casing or chamber lined with fire brick and heated by 
the hot and burning gases from the furnace. Such an arrangement 
makes it possible to obtain air at a more constant and uniform tem- 
perature and obviates the necessity of shifting stoves. To shift these 
stoves quickly in the present plant requires two laborers and an 
experienced man to direct them, and since the scientific personnel 
available for the protracted runs of this furnace is very limited, every 
possible device should be employed for conserving the time and 
energies of those directing the work and collecting the necessary data. 
An investigation is now being conducted in these laboratories on the 
effect of mixtures of P 2 5 , water vapor, and other gases at high tem- 
peratures on the various metals from which the pipes of such stoves 
may be constructed. 
ESTIMATED COST OF PRODUCTION. 
Before data can be obtained which will show conclusively the 
commercial feasibility of producing phosphoric acid by this process, 
it will be necessary to eliminate certain of the mechanical difficulties 
which have so far interfered with the efficient working of the present 
plant during the more protracted tests. It is believed that these 
mechanical troubles can be overcome and that then a continuous run 
of several days will make it possible to obtain figures which will more 
nearly show the relation between the fuel consumed and the acid 
eliminated from the briquetted charge. While these figures will be 
much less favorable in a small furnace than in one of larger dimen- 
sions where heat losses through radiation are less serious, if the data 
so obtained show economies over the sulphuric acid process, even 
greater economies may be assumed where a plant of commercial size 
is employed. 
During the tests just described, however, there were periods of from 
three to five hours when the furnace appeared to operate quite effi- 
ciently and if the data taken at such times are considered indicative 
of normal working conditions, the cost of producing phosphoric acid 
i 
51 Johnson, J. E., jr. The Principles, Operation, and Products of the Blast Furnace, p. 348-349 (1918) : 
Wilcox, F. H. Bui. 1*30. Bureau of Mines, p. 188, 250-252 (1917). 
