BUREAU OF SOILS. 297 



fed furnace. Had investigations been conducted no further it is 

 considered that the proof of this one point, which was never estab- 

 lishti] before, would have justified the money expended on this prob- 

 lem. The experiments, however, are now being conducted on a much 

 larger scale with a view to showing the commercial practicability of 

 the process. A furnace of semicommercial size (capable of handling 

 over 1,000 pounds of material per day) has been constructed at Ar- 

 lington Farm, Virginia, and the auxiliary equipment necessary for 

 collecting the dust and burning the combustible gases evolved, and 

 for the recovering and collecting of the phosphoric acid produced 

 has also been erected. With this furnace the bureau has already 

 made a number of tests which have yielded interesting and valuable 

 data and enabled it to solve many of the mechanical difficulties and 

 details of operation. The results obtained make it possible to plan 

 intelligently the form of a larger installation which it is believed 

 will definitely prove the commercial feasibility of this new process. 

 The work, however, has reached a stage where a statement can be 

 made, partly on experimental evidence, and partly on theoretical 

 considerations, Avhicli will give a rough approximation of what may 

 be expected of this new process. 



In the first place the utilization of "mine-run" material will not 

 only eliminate largely the tremendous losses of phosphate and thus 

 prolong the life of our phosphate deposits, but will also render un- 

 necessary many of the elaborate and costly plants for cleaning and 

 preparing the phosphate rock for treatment with sulphuric acid in 

 the manufacture of acid phosphate. These points, when taken in 

 conjunction with the fact that a concentrated product can be ob- 

 tained capable of standing the expense of long shipments and the 

 great increase in handling charges, should more than offset the added 

 expense, if any, of using fuel as a reagent in place of sulphuric acid. 

 It is evident from the results so far obtained that the operation of 

 smelting the phosphatic charge used for the production of phos- 

 phoric acid is similar to that of smelting the charge usually eni- 

 ployed in a blast furnace for the production of pig iron, and on this 

 basis the process appears most promising. While in the production 

 of phosphoric acid by the furnace treatment nearly twice as much 

 material must be heated to a smelting temperature in order to pro- 

 duce a ton of phosphoric acid as is required in the production of 1 

 ton of pig iron, nearly all of the heat units except those lost in the 

 slag and from radiation through the furnace walls can be recovered 

 and returned to the system. In the production of pig iron, on the 

 other hand, much heat is consumed in reducing the iron to the 

 metallic or marketable condition, and the heat thus consumed is 

 not recovered. Moreover, the value of phosphoric acid per ton for 

 fertilizer purposes is over four times as great as the value of pig 

 iron per ton. 



The final proof of tlie commercial practicability of these furnace 

 processes, however, must rest in a plant of commercial size. The 

 construction of such a plant is quite costly and a relatively large 

 force is required to operate it. While a number of outside interests 

 have signified their willingness to assume in part the expense of 

 this larger installation as soon as the experiments have reached 

 the stage where such an expenditure is warranted, it is not possible 



24435— AGR 11120 20 



