MANUFACTURE OF PHOSPHORIC ACID. 13 
on a 24-hour basis 300 days of the year at 0.22 pound per kilowatt 
hour. Assuming that power was available at $25 per horsepower 
year he estimated the cost of production, exclusive of interest charges, 
maintenance, and depreciation, at 3.37 cents per pound of P 2 5 . 
While this cost compared rather favorably with that of the P 2 5 
in acid phosphate during the war. when the price of sulphuric 
acid was exceptionally high, the figures indicated that this process 
could hardly compete with the older method under normal conditions 
unless cheaper power or higher efficiency were obtained. But as 
Carothers has pointed out, there is little doubt that with a furnace 
of different design provided with means of recovering the heat in the 
effluent gases and utilizing the heat regenerated when the phos- 
phorus is burned to P 2 5 and the CO to CO,, a considerably greater 
efficiency should be attained. Furthermore, the volatilized acid 
collected by the Cottrell precipitator can be used directly (without 
involving the expense of concentration) for treating high-grade phos- 
phate rock in the production of double superphosphate, and thus the 
final cost of the unit of soluble P 2 5 materially reduced. 
Since these experiments were conducted, electric furnaces of com- 
mercial size for the simultaneous production of ferrophosphorus and 
phosphoric acid have been erected at Anniston, Ala., and are oper- 
ating quite successfully. While most of the phosphoric acid produced 
at this plant is purified and sold for the purpose of manufacturing 
baking powder, and to the pure chemical trade, the president 45 of the 
company states that the experience gained during the last three 
years "clearly indicates that with cheap hydroelectric power and 
proper plant location phosphate rock can be smelted in the electric 
furnace for the production of fertilizer material at a cost comparing 
very favorably with the present method." 
ELECTRIC SMELTING OF MINE-RUN PHOSPHATES. 
But there is another factor equally if not more important than those 
just mentioned which has a direct bearing on the cost of the unit of 
P 2 5 manufactured by the furnace process. This is the great saving 
which can be effected by employing low-grade and run-of-mine 
phosphates which are either unfit for treatment with sulphuric acid 
because of the inherent nature of the rock itself, or must be 
treated by some mechanical means to separate the phosphate from 
the impurities with which it is associated. With these facts in mind, 
the senior author undertook a number of experiments with the smaller 
electric furnace at Arlington Experimental Farm, Va., and while 
these tests were not conducted over any long period of time, they 
show that impure phosphates which can be readily and cheaply 
mined may be advantageously smelted in the electric furnace and 
the final product not only obtained more cheaply but a great con- 
servation of our phosphate resources effected. 
For this work samples of phosphate materials were obtained from 
each of the following three localities: (1) Mine-run phosphate from 
the hard-rock regions near Newberry, Fla. ; (2) mine-run phosphate 
from the pebble fields near Fort Meade, Fla.; (3) Tennessee brown- 
rock phosphate from old dumps near Mount Pleasant, Tenn. The 
analyses of these samples of phosphatic material are given in Table 1 . 
"Jour. Ind. and Eng. Chem. 14, p. 630, (1922). 
