PHOSPHATE ROCK: UTILIZATION AS FERTILIZER. 15 
practicable to manufacture the product by mixing the phosphate 
rock with the molten slag as the latter flows from the furnace. The 
heat of the slag could thus be utilized. 
The fertilizer value of basic (phosphatic) slag is unquestioned, 
and it would be practicable to produce large quantities of this 
material by using phosphatic limestone to smelt siliceous iron ores, 
but it would be very difficult to overcome the prejudice against using 
a phosphorus-bearing substance in smelting operations when the 
chief aim is to eliminate phosphorus from the metal product. 
PROCESSES IN WHICH THE PHOSPHORUS OR PHOSPHORIC ACID IS 
VOLATILIZED. 
Processes under this head have been exciting considerable interest 
in recent years. They are all based on the method long in use for 
the manufacture of phosphorus and require a high temperature and 
a furnace which will resist both the temperature and the corrosive 
effect of the volatile products formed. The main advantage of the 
processes listed in Table VII is that comparatively pure concentrated 
phosphoric acid can be obtained from rather impure raw materials. 
The first recorded American process for obtaming phosphoric 
acid in this way is that of Giles and Shearer.’ Their process of 
separating phosphoric acid from its impurities consists in passing a 
current of steam over the acid heated to redness. The distillate 
condensed and collected in some suitable vessel consists of relatively 
pure phosphoric acid. 
In 1907 Landis? described a process for producing phosphoric 
acid and phosphorus from phosphate rock, which consists in mixing 
phosphate rock, sand, or a silicate and coke with some binding 
material, and molding the mixture into briquettes. The briquettes 
are subsequently placed in an electric furnace and heated. The 
inventor claims that by this method a more even distribution of the 
heat is obtained, excessive temperatures can be avoided, and less 
dust and impurities are carried over with the volatilized phosphoric 
acid. 
The methods of Levi,? Washburn,‘ and Haff ® are three of the more 
recent processes for the production of phosphoric acid by volatiliza- 
tion. Described in brief, they are as follows: 
Levi heats a mixture of phosphate rock and silica or silicate in an 
electric furnace, claiming that the following reaction takes place: 
Ca;(PO,).+3S810,=P,0;+3CaSi103. 
The phosphoric anhydride which is volatilized is then absorbed in 
water, producing phosphoric acid (H,PO,), and the fused calcium 
1 United States Patent No. 393428 (1888). 4 United States Patents Nos. 1047864 (1912); 1100639 (1914). 
2 United States Patent No. 859086 (1907). 5 United States Patent No. 1084856 (1914). 
_ 3 United States Patent No. 984769 (1912). 
