MANUFACTURE OF PHOSPHORIC ACID. 9 
Washburn 38 and Hechenbleikner 37 have each taken out a great 
number of patents dealing with processes for the volatilization of 
phosphoric acid and with types of furnaces in which the reactions 
mav be brought about. Space forbids detailed discussions of all 
these methods and apparatus, but several which appear to have par- 
ticularlv interesting features are given below. 
In Patent No. 1100639 (1914; Washburn proposes to charge a 
mixture of phosphate rock, silica, and carbonaceous material into 
the shaft of a blast furnace, where the combustion of the fuel is 
effected and the mass brought to a state of fusion. The molten 
material is then run into the" crucible of an electric furnace, where 
the final smelting of the charge and complete volatilization of the 
phosphoric and m accomplished. In Patent Xo. 1314229 (1919) he 
describes an apparatus in which are combined certain features of 
both the blast and electric furnace, and suggests a briquet ted mix- 
ture of phosphate rock and silica in order to insure a free passage of 
the gaseous products through the charge in the shaft. Air is intro- 
duced into the shaft to burn the combustible gases and evolved 
phosphorus and thus preheat the green charge. 
Both Hechenbleikner and Washburn describe furnaces 38 in which 
the charge is led through a rotary kiln and the preheated or partially 
smelted mass then run into the crucible of an electric furnace, where 
coke or some other carbonaceous material is added and the remain- 
ing phosphoric acid is driven off. By leading the hot and burning 
eases through the kihi countercurrent t:o the phosphate charge, heat 
economies are effected which cut down the energy required in smelt- 
ing the material in the electric furnace. 
Other processes related to the volatilization of phosphorus and 
phosphoric acid are described in the public service patents taken out 
by Ross. Carothers, and Merz 39 . Waggaman, and others 40 . 
THE LSE OF THE ELECTRIC FURNACE IN THE VOLATILIZATION OF PHOSPHORIC ACID. 
The first experimental work conducted in this bureau on the pro- 
duction of phosphoric acid by the volatilization process was carried 
on by Ross. Carothers. and Merz 41 in an electric furnace. A fair 
grade of sand and coke and a medium grade of Florida pebble phos- 
phate were employed, these ingredients being mixed in such propor- 
tions as to react according to the first equation given on page 4 except 
that an excess of 20 per cent of both coke and sand were added over 
that theoretically required. 
A furnace of very simple design was used in these early experi- 
ments. It consisted of an iron cylinder. 4 feet in diameter and 4^ 
feet high, lined with 9 inches of fire brick, and provided with a tap 
hole near the bottom for the removal of the slag. A three-phase 
alternating current was used, and this was stepped down from 220 volts 
by two single-phase 75 kilovolt ampere transformers. Each trans- 
former was provided with a split primary, and by joining in different 
combinations in series and in parallel the coils in the secondary, Volt- 
s' U. S. Patents No?. 1000311 (1911); 1044957, 1047S64 (1912); 1100639 (1914); 1149233 (1915); 1314229 
(1919): 1359211 (1920): 1373471 (1921). 
"U- S. Patents Xos. 1112211 (1914); 1167755, 1173960, 1202837 (1916), 1217306 (1917); 1299336, 1299337 
(1919). 
'. S. Patents Xos. 1167755 (1916): 1299336, 1299337 (1919): 1339211 (1920). 
8. Patents Xos. 1283398 (1918); 12^,4200 (1918): 1329273 (1920). 
«°U. S. Patents Nos. 1241971 (1917): 12S2994 (1918): 1334474 (1920;: 13S7^17 (1921). 
« Jour, of Ind. and Eng. Chem. 9, Xo. 1, p. 26 (1917). 
52670—23 2 
