18 BULLETIN 312, TJ. S. DEPARTMENT OF AGRICULTURE. 



processes correct the acidity of the superphosphate which some 

 farmers consider so objectionable, and at the same time enhance the 

 value of the product. 



The process of Collett 1 consists in dissolving phosphate rock in 

 dilute nitric acid, and then adding ammonium sulphate to the solu- 

 tion, with the result that lime is precipitated as sulphate, and ammo- 

 nium phosphate and ammonium nitrate remain in solution. After 

 separating the gypsum, the ammonium salts may be crystallized out by 

 concentration of the solution. The reactions may be represented 

 thus: 



(1) Ca 3 (P0 4 ) 2 +4HN03=CaH 4 (P0 4 ) 2 +2Ca(N03) 2 . 



(2) CaH 4 (P0 4 ) 2 +2Ca(N0 3 ) 2 +3(NH 4 ) 2 S0 4 =3CaS0 4 +4NH 4 N0 3 +2NH 4 H 2 P0 4 . 



This last process is particularly interesting from a commercial 

 standpoint, since it has for its object the production of a high-grade 

 fertilizer containing both phosphoric acid and nitrogen in readily 

 available forms. Where phosphate rock occurs in regions far from the 

 fertilizer markets, the production of a highly concentrated product 

 which will admit of long shipment is essential to the successful develop- 

 ment of the mining part of the phosphate industry. 



The evaporation of the solutions, however, to the point where the 

 ammonium salts begin to crystallize out would entail considerable 

 expense. 



PROCESSES DEALING WITH THE PRODUCTION OF AVAILABLE 

 PHOSPHATES BY ELECTROLYSIS. 



Processes under this head are of two types : (1) Those in which the 

 phosphate rock is fused and the electric current passed through the 

 melt; and (2) those hi which some water-soluble salt or acid is used 

 as an electrolyte and the ground phosphate rock suspended or dis- 

 solved in the solution and the electrolysis performed in the wet way. 

 A list of the patents on this subject is given in Table IX, Appendix. 



The process of Palmaer and Wiborgh 2 for the production of dical- 

 cium phosphate is said to have been successfully practiced in Norway 

 where cheap water power is available. The process is as follows: 



Perchloric acid and sodium hydrate are produced by electrolizing a 

 solution of sodium perchlorate in a diaphragm cell. Phosphate rock 

 is then treated with the anode solution (perchloric acid) and the 

 resulting solution of phosphate filtered. One half of the cathode 

 solution (sodium hydrate) is then added to this filtrate, resulting in 

 the precipitation of dicalcium phosphate and the formation of sodium 

 perchlorate again. The other half of the cathode solution is treated 

 with carbon dioxide and added to the solution decanted from the 

 dicalcium phosphate precipitate, thus precipitating the lime as carbon- 

 ate and completely regenerating sodium perchlorate. 



i United States Patent No. 1058145 (1913). 2 United States Patents Nos. 707886 (1902); 748523 (1903). 



