14 BULLETIN 312, U. S. DEPARTMENT OF AGRICULTURE. 
bonate and the mixture heated in a suitable furnace to a bright-red 
or yellow heat. Newberry also employs lime or limestone in his mix, 
and Galt uses ‘‘lime mud” (a mixture of calcium carbonate and 
sodium hydroxide), a by-product of the soda industry. 
While these processes have not been thoroughly tested in this 
laboratory a conversion of at least a portion of the phosphate into 
a citrate-soluble form can undoubtedly be effected by such treat- 
ments. The proportions of alkali, lime, and phosphate rock required 
are such that the resulting product contains a much higher percentage 
of phosphoric acid than ordinary acid phosphate. For the commer- 
cial success of such processes, however, it must be borne in mind 
that the cost of heating plus the price of the reagents used in the pro- 
duction of a unit of phosphoric acid must not exceed the cost of the 
sulphuric acid required to produce a unit of phosphoric acid in super- 
phosphates. Payne,’ in discussing calcination processes, places the 
cost of available phosphoric acid produced by such processes at 
about 24 cents per unit. 
PROCESSES TO BE USED IN CONNECTION WITH THE IRON AND STEEL 
INDUSTRIES. 
Processes under this head have to do chiefly with the production 
of tetracalcium phosphate or some other basic phosphate soluble in 
a 2 per cent solution of citric acid. Because of the high temperature 
required, these processes can hardly be employed economically 
except in connection with the smelting industry. A list of the 
patents dealing with the production of available phosphoric acid 
along these lines is given in Table VI, Appendix. 
In 1884 Thomas? devised a process for producing an alkaline 
phosphate from pig iron high in phosphorus. His plan consists in 
pouring the molten metal upon an alkali carbonate in a basic Besse- 
mer converter. The resulting slag contains, according to his claim, 
phosphates of soda which can be separated by lixiviating the mass 
with water. This patent expired in 1901. 
The processes of Reese * are also worthy of consideration. 
One of his processes consists in adding to the usual furnace charge 
a certain quantity of phosphate rock to enhance the value of the 
resulting slag. Another of his processes consists in dephosphatizing 
the iron or iron ore in two stages. In this way the first slag run-off 
contains a high percentage of available phosphate. In a third 
process phosphate rock and basic open-hearth slag are fused together, 
resulting in the production of available phosphoric acid. If this 
claim is borne out in actual practice it should be economically 
1 Available phosphates by furnace treatment. Amer. Fertilizer Handbook, pp. 62-64 (1914). 
2 United States Patent No. 301407 (1884). 
3 United States Patents Nos. 412792; 412793 (1889); 714331 (1902). 
