PHOSPHATE ROCK: 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 ard 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: 
Ca,(PO,).+2H.S0,+2H,0=CaH,(PO,).+2(CaSO,. 2H,O) . 
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,0;). The remaining 82 per cent consists of 
gypsum, siliceous material, and other impurities. It is obvious 
therefore, that it is poor economic policy to ship such material long 
6819°—Bull. 312—15——2 
