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 Gait 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 2 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 3 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. Fertiliser Handbook, pp. 62-64 (1914). 



2 United States Patent No. 301407 (1884). 



s United States Patents Nos. 412792; 412793 (1889); 714331 (1902). 



