PHOSPHATE BOCK: UTILIZATION AS FERTILIZER. 9 



of the processes devised for the manufacture of phosphatic fertilizers 

 arranged in chronological order, 'and giving short abstracts of the 

 processes or apparatus employed, the treatment proposed, and the 

 results or new features claimed by the inventors, will aid materially 

 those engaged in researches of this character. 



It is impossible in an article of this kind to give more than the 

 briefest abstracts or mention of most of the numerous processes on 

 this subject, but those are described more fully which appear to 

 possess features particularly interesting from either a commercial or 

 scientific standpoint. 



For convenience these various methods for treating phosphate rock 

 may be classified as follows: 



(1) Acid treatment, which includes the manufacture of superphos- 

 phate and phosphoric acid; (2) combined heating and acid treat- 

 ment; (3) double decomposition by means of a silicate or an alkali; 

 (4) processes used in connection with the steel industry; (5) processes 

 in which the phosphorus or phosphoric acid is volatilized; (6) treat- 

 ment dealing with the production of two or more fertilizer elements; 

 (7) electrolysis; (8) enrichment or concentration of phosphates; (9) 

 processes and apparatus for the mechanical treatment of phosphates; 

 (10) miscellaneous processes. 



ACID TREATMENT. 



The production of water-soluble phosphates by the treatment of 

 phosphate rock or bones with sulphuric acid is the oldest and most 

 widely used process. Nitric acid and hydrochloric acid have been 

 tried in place of sulphuric, but the latter has proved itself the most 

 satisfactory, because the calcium sulphate formed is not only a 

 dehydrating agent, but is also only sparingly soluble in dilute solu- 

 tions of phosphoric acid. 



In making superphosphate, ordinary chamber acid (50° B.) and 

 ground phosphate rock are thoroughly mixed in equal proportions by 

 weight and the mass allowed to cure for 24 to 36 hours. The equation 

 showing the reactions in simplest form may be represented thus : 



Ca3(P0 4 ) 2 +2H 2 S0 4 +2H 2 0=CaH 4 (P0 4 ) 2 +2(CaS0 4 .2H 2 0). 



In this case the gypsum formed renders the material dry and 

 pulverulent, and in excellent mechanical condition for mixing with 

 other ingredients in making a complete fertilizer. 



The richest superphosphate which can be made, however, by a 

 single acid treatment of the highest grade phosphate mined in the 

 United States (Florida hard rock) contains about 18 per cent of 

 phosphoric acid (P 2 6 ). The remaining 82 per cent consists of 

 gypsum, siliceous material, and other impurities. It is obvious 

 therefore, that il is poor economic policy to ship such materia] long 



6819°— Bull. 312—15 2 



