38 BULLETIN 1179, U. S. DEPARTMENT OF AGRICULTURE. 
(4 to 8 ounces). The consumption of oil by these burners is con- 
trolled by the pressure and also by the size of the openings in the 
tips used. These burners work exceedingly well as long as the oil 
fed to them is thoroughly strained, but clog very readily if all 
sediment is not completely removed. The ends of these burners are 
surrounded by steel water jackets which in turn are set into the ends 
of the furnace at an angle of about 60° from the horizontal, so that 
the oil flame plays directly upon the hearth. A steel tank holding 
500 gallons is used as the main reservoir for the fuel oil, this tank 
being connected with a small 80-gallon tank provided with a gauge 
to measure the oil consumption. The oil is fed by gravity to a pump 
which forces it to the burners under a pressure of from 30 to 200 
pounds per square inch. 
The phosphate used in the experiments with this first equipment 
was from hard-rock phosphate mines near Newberry, Fla. This 
material was run-of-mine phosphate, containing sufficient natural 
binder to make a good grade of briquets, which stood up well under 
preliminary shatter tests and exhibited no tendency to disintegrate 
upon being suddenly heated to a high temperature. The phosphoric 
acid content of this briquetted charge, exclusive of moisture and 
carbon (both of which are finally eliminated), was 19.99 per cent. 
A number of tests were made in this furnace before the auxiliary 
equipment was changed and the results of the last two experiments 
have already been described in detail, 47 but brief summaries are given 
below. 
The first of these latter tests was conducted for a period of only 
10 hours, during which time 2,200 pounds of briquetted charge were 
smelted. The rapid rate, however, at which this material melted in 
the shaft and discharged onto the furnace hearth allowed the lower 
strata of slag to cool to the point where phosphoric acid was not 
readily evolved, and also resulted (toward the latter part of the run) 
in the material freezing in the cinder notches, so that the furnace 
could not be tapped and had to be closed down. The average tem- 
perature of the preheated air delivered to the oil burners during the 
greater part of this run was 250° C. and the highest temperature 
recorded on the hearth was 1,500° C. The volatilization of phos- 
phoric acid ranged between 38 and 63.5 per cent, or an average of 52 
per cent, the rate of evolution being about 80.5 pounds P 2 5 per hour. 
Since the oil consumption toward the last of the test was 9-j gallons 
per hour, the yield (figured on this basis) was approximately 8.5 
pounds of P 2 5 per gallon of fuel oil. 
The next test was continued for a period of 20 hours, during which 
time 3,500 pounds of briquetted charge were smelted and run out of 
the furnace in a molten condition. In the earlier stages of this run 
numerous mechanical difficulties were encountered, but in the last 3£ 
hours of the test the furnace appeared to operate quite efficiently and 
an average volatilization of 97 per cent P 2 5 was obtained. The 
preheated air was delivered to the burners at temperatures ranging 
from 325° to 350° C. and the hearth temperature was between 1,500° 
and 1,600° C. The final slag tapped had an average content of 0.77 
per cent P 2 5 , which corresponds to a volatilization of 97 per cent of 
that present in the original charge. The rate of evolution was 46.3 
< 7 Investigations on Pyrolytic Production of Phosphoric Acid. Jour. Chem. and Met. Eng. 23, p. 1057 
(1920). 
