MANUFACTURE OF PHOSPHORIC ACID. 11 
The capacity of the fail used in drawing off the fumes from the furnace was 450 
cubic feet per minute. As shown later, this flow of air was much in excess of that 
necessary to oxidize the phosphorus evolved from the furnace. Using a fan of this 
-capacity it was found neccessary to use six pipes to bring about complete precipitation 
of the fumes. * * * 
Since the phosphorus passes off from the furnace for the most part in the form of 
phosphorus pentoxide it mieht be expected at first thought that it would be collected 
as such in the precipitator. A simple calculation will show, however, that this is 
not practical, for there will always be enousrh moisture in the charge used and in the 
air required to oxidize the phosphorus evolved to convert the phosphorus pentoxide 
either in whole or in part into phosphoric acid. * * * 
When the fumes were passed through the tower and precipitation thus made at a 
temperature but little above normal, the concentration of the acid first collected 
was in the neighborhood of 60 per cent phosphoric acid. * * * On cutting down 
the flow of air somewhat the concentration of the acid was increased to about 80 per 
cent, and it is quite evident that with the humidity of the air remaining the same a 
still more concentrated acid misht be obtained by further limiting the flow of air 
through the furnace. 
After the precipitator tower just described had been used inter- 
mittently for over two years it was found necessary to have one with 
a greater capacity, better suited to handle the gases (at a high velocity) 
evolved from a fuel-fired furnace. Accordingly the old treater of six 
(6-inch) terra-cot t a pipes 14 feet long was torn down and a new one 
built containing nine pipes of the same dimensions; thus the capacity 
of the collector was increased approximately 50 per cent. In order 
to prevent the wires in the pipes from swinging in unison (a condition 
which at times caused considerable trouble in the old precipitator) 
the weights were not only fastened together with a grid but this grid 
was connected with a rigid horizontal bar (pipe) which passed through 
the center of a 6-inch terra-cotta pipe cemented into the side of the 
precipitator chamber. This bar in turn was anchored to an insulator 
outside of the tower. Such an arrangement did away with the 
frequent arcking encountered in the earlier experiments due to the 
swinging of the wires. 
LARGER SCALE EXPERIMENTS. 
The results obtained in the preliminary experiments with the elec- 
tric furnace were so encouraging that it was deemed wise to continue 
the investigation on a larger scale in order to determine the commer- 
cial possibilities of the process. Accordingly a cooperative arrange- 
ment was entered into with several firms interested in this line of 
work and a plant of considerably larger capacity and much better 
suited for the purpose than that at Arlington Experimental Farm was 
erected at Hoboken, N. J. Protracted tests were made over a period 
of several days and weeks, and data obtained from which the cost of 
producing phosphoric acid by this method was estimated. This 
work was conducted under the direct supervision of J. N. Carothers, 
and a quotation from his article 44 describing the equipment is given 
l>elow: 
From the transformer ratines, the plant was a 200-kilowatt installation. The 
incoming power was quarter phase, 2.400 volts, which was transformed to 3 phase, 
220 volts, by a bank of Scott connected tranformers. A second bank of transformers 
and aset of double-throw switches made it possible to have either 220 volts or 110 
volts in the furnace. This arrangement was adopted so as to use the higher voltage 
for starting and the low voltaee for operating. For the best operating conditions 110 
volts were found satisfactory. 
«.Iour. Ind. and Eng. Chen 10, Xo L, n. 35 '1918; . 
