MANUFACTURE OF PHOSPHORIC ACID. 39 
pounds per hour. The oil consumption toward the last of the test 
was reduced to 8.3 gallons per hour, yet the temperature of the 
furnace seemed to be efficiently maintained, so on this basis a 
volatilization of 5.6 pounds of P 2 t) 5 per gallon of fuel oil was obtained. 
The old electrical treater (previously described) was used in this test, 
and since the precipitator pipes not only had too small a capacity 
but were also badly out of line, only a small proportion of the acid 
evolved was collected. The concentration of this acid varied from 
21.5 per cent to 64 per cent H 3 P0 4 , the stronger acid being collected 
toward the last of the run, when the temperature of the system 
had risen to the point where much less moisture condensed. 
PRESENT FURNACE EQUIPMENT AND LATEST RESULTS. 
After the completion of the experiments just described it was found 
that the fire-brick linings of the shaft and in the central portion of 
the crucible arch were in such bad condition that it was desirable to 
rebuild the furnace. In this later furnace the crucible and lower part 
of the furnace shaft were lined entirely with carborundum brick, fire 
brick being used only in the outer layers of the furnace walls and in 
the upper part of the charge chamber (above the bosh) . The old 
stoves (having a common wall) were also torn down and replaced by 
four individual steel shells 4 feet in diameter and 10 feet high. Each 
of these shells was lined with fire brick and divided into two 
chambers — one for burning the combustible gases and the other filled 
with checker brick to act as a heat reservoir for preheating the air 
delivered to the oil burners. Suitable inlets and outlets (controlled 
by valves) were^ provided for the air and gas. An exhaust fan placed 
between the stoves and the electric precipitator served to draw the 
gases from the furnace through the stoves and introduce them into 
the collector, the temperature of these gases being reduced when 
necessary by a cooler surrounding the ga's main. A "Roots " positive- 
pressure blower capable of delivery of 1,000 cubic feet of free air per 
minute under a maximum pressure of 4 pounds per square inch re- 
placed the three small blowers previously used, and the air main to 
the oil burners was increased from 4 inches to 6 inches in diameter. 
There were also installed a recording gauge to show this air pressure 
and an instrument (Tapalog) connected with two pyrometers, which 
recorded the temperature of the gases from the stoves to the 
precipitator and that of the air delivered to the burners. 
By means of a small pipe (a bleeder) inserted in the furnace flue 
samples of the gases were withdrawn from time to time and analyzed. 
After considerable experimentation with this equipment the old 
fire-brick dust catcher also was removed and a steel cylinder lined 
with fire brick and provided with two baffle walls was used in its 
place. 
A number of experiments lasting from 10 to 20 hours were conducted 
in this furnace, but it became evident that water-cooling devices must 
be employed in order to maintain unaltered the interior dimensions 
of the furnace shaft, since in protracted tests the combined effects of 
the high temperature and the erosive action of the slag gradually 
wore away the linings. Accordingly the furnace shaft was again 
torn down and replaced by a steel shell lined in the lower portion 
with carborundum brick and in the upper portion with fire brick. 
This shell was bolted to a bronze basin which fitted over the carbo- 
