8 
The experience of the writers, however, as well as that of a number 
of other investigators, has been that in the absence of a reducing 
agent very much higher temperatures must be employed to break 
the bond between the lime and phosphoric acid in the phosphate 
rock, and therefore it is poor economic practice to produce phos- 
phoric acid without the addition of carbon or coke when such material 
can be obtained so cheaply. 
Machalske 30 suggests that coke and an alkali metal chloride (sodium 
chloride) be mixed with the phosphate rock in the electric furnace, 
claiming that phosphorus chloride or hydrochloric and phosphoric 
acids are volatilized and sodium carbide is produced. He further 
claims that by introducing nitrogen sodium cyanide or cyanamid is 
obtained. 
Haff 31 and Wilson and Haff 32 propose to heat feldspar and phos- 
phate rock in an electric furnace to 2,000° C. without the addition of 
a reducing agent, claiming that phosphoric acid and potash are 
simultaneously evolved with the production of potassium phosphate 
according to the following equation : 
3Al 2 3 .K 2 O.Si0 2 +Ca 3 (P0 4 ) 2 = 3Al 2 3 .CaO.Si0 2 4- 2K 3 P0 4 . 
These processes are open to the same objection as those of May- 
wald, Levi, and certain other processes proposed by Wilson and Haff 
in which no reducing agent is employed, and consequently very high 
temperatures are required. 
Hechenbleikner 33 employs carbon or coke in addition to feldspar 
in smelting the phosphate charge, but it would seem to the writers 
that even under these conditions greater energy would be required 
to effect the chemical change indicated above, since potash is more 
readily volatilized from a basic and phosphoric acid from an acid 
slag. The economic possibility of employing silica in the form of 
greensand, potash shales, feldspar, or other potash-bearing silicates 
in the furnace process is very attractive, however, and this problem 
is now under investigation in this bureau. 
With a view to producing compounds containing both phosphorus 
and nitrogen, Peacock 34 heats mixtures of phosphate rock and car- 
bon in an atmosphere of nitrogen, claiming that phosphorus and 
carbonitrides are produced which can be converted into ammonia 
and ammonium phosphate by treatment with steam. No particular 
type of furnace is specified by this inventor. As far as known, how- 
ever, there has been no commercial application of this process. 
With a view to the simultaneous production of ferrophosphorus 
and phosphoric acid or other phosphorus compounds, J. J. Gray 36 
proposes to smelt a mixture of phosphate rock, silica, coke, and iron 
ore in an ordinary blast furnace. The ingredients in the charge are 
so proportioned that while the maximum displacement of phosphorus 
from the phosphate rock is sought the amount of iron added in the^ 
form of ore is insufficient to take up all of the phosphorus thus 
evolved. Two blast furnaces for the production of ferrophosphorus 
are in operation in Tennessee, but in neither case is any elemental 
phosphorus or phosphoric acid recovered. 
so U. S. Patents Nos. 789438, 789439, 7S9440 (1905). 33 u. S. Patent No. 1299337 (1919). 
3i U. S. Patent No. 10181S6 (1912). ™ U. B. Patents Nos. 1129514, 1129722 (1915). 
32 U. S. Patent No. 1103910 (1914). 3s u. S- Patent No. 1168495 (1916). 
