PHOSPHATE ROCK: UTILIZATION AS FERTILIZER. ap 
Processes of this type, if practicable, would have an advantage over 
the one now generally employed in that they produce available phos- 
phoric acid from phosphate rock in a single operation, thus obviating 
the necessity of first manufacturing sulphuric acid. Experiments in 
the laboratories of the Bureau of Soils have shown, however, that 
phosphate rock is very resistant to the action of sulphurous acid or 
sulphur dioxide, and efforts to obtain complete decomposition of 
phosphate rock by such treatments were unsuccessful. Further work 
along these lines, however, seems desirable. 
The processes of Glaser ! have for their object the production of con- 
centrated phosphates by treating phosphate rock with sufficient dilute 
sulphuric acid to produce phosphoric acid and then using this phos- 
phoric acid as a solvent for more phosphate rock. 
They involve the well-known method of making double acid phos- 
phate, a method admirably suited for the treatment of low-grade 
phosphate rock containing but little iron and aluminum. ‘The equa- 
tions showing the reactions taking place in this process have already 
been shown on page 10. The product usually requires artificial 
drying, since it contains but little sulphate of lime. The patents of 
Glaser have now expired. 
In order to produce a dry pulverulent product, Memminger ? pro- 
poses to mix calcium fluoride or fluorite with phosphate rock and then 
treat the mixture with sulphuric acid. The generation of gaseous 
compounds of fluorine, he claims, renders the acid phosphate porous 
and thus facilitates the escape of moisture from the hot mass. 
While this procedure would no doubt produce a high-grade acid 
phosphate, the poisonous nature of the fumes evolved during the 
curing of the acid phosphate would make it objectionable to employ 
such a method either in the vicinity of towns or in a farming country. 
Moreover, it is questionable whether the extra quantity of acid 
required to act upon the fluorite would not offset the advantages 
gained. This patent expired in 1908. 
Hoyerman * devised a process to economize on the quantity of acid 
required to produce available phosphoric acid. His process consists 
in adding to phosphate rock a quantity of sulphuric acid sufficient 
only to convert it into dicalcium phosphate, a product which has 
practically the same trade value as monocalcium phosphate. 
Such a process, while theoretically possible, presents difficulties in 
actual practice. The quantity of ordinary sulphuric acid required is 
hardly sufficient to mix intimately with a large bulk of ground phos- 
phate, and, therefore, the resulting mass is apt to contain a con- 
siderable percentage of so-called unavailable phosphoric acid, owing 
to the fact that some of the phosphate rock has not been acted upon. 
1 United States Patents Nos. 389566 (1888), 417820 (1889), 459575 (1891). 
2 United States Patent No. 445567 (1891). 
3 United States Patent No. 736730 (1903). 
