CITRIC-SOLUBLE PHOSPHOEIC ACID AND POTASH. 3 



ble silicate of lime and potassium phosphate are thus obtained. In 

 view of the fact that the percentage of potash in the mixture is rela- 

 tively small and that the time of heating is very long, it is hardly 

 likely that the value of the product would cover the cost of manufac- 

 ture. Moreover, the claim that phosphate of potash is formed in the 

 operation is apparently not justifiable. It was thought advisable, 

 however, to test this process also. A mixture of the following com- 

 position was made up and ignited in a muffle furnace for five hours 

 at red heat: 



Per cent. 

 Feldspar (13 per cent K 2 0) 24.21 



Phosphate rock (32.8 per cent P=0 5 ) 24.21 



Calcium carbonate 48. 42 



Calcium fluoride 3. 15 



The slightly sintered product of this mixture was finely ground and 

 analyzed both for potash and phosphoric acid. If carbon dioxide 

 were the only volatile substance formed by heating the above mixture 

 the final product should have contained 4 per cent of K 2 and 10.09 

 per cent of P 2 5 . Actual analysis of the material, however, gave the 

 following results: 



K 2 : Per cent. 

 Total 0.60 



P2O5 : 



Total 10.51 



Citric soluble 4. 15 



Here again, as in Bickell's process, the potash nearly all vola- 

 tilized, while less than one-half of the phosphoric acid present in the 

 residue is citric soluble. 



The third process for rendering the phosphoric acid and potash 

 of rocks available for fertilizer purposes is that of Coates, 1 which 

 consists in adding to the sterlized rock mixture certain microorgan- 

 isms that effect the breaking down of the rock minerals. It is 

 understood that the material thus prepared is being tried out ex- 

 perimentally by actual field tests, the results not yet having been 

 reported. 



In 1912 Haff 2 devised a process for making potassium phosphate 

 from a mixture of feldspar and phosphate rock. The method is based 

 on the fact that at high temperatures and in the presence of silica and 

 a nonvolatile base, both potash and phosphoric acid are volatilized. 

 Haff claims that 95 per cent of the potash and phosphoric acid of 

 natural rocks can be driven off at a temperature of 2,000° C. and 

 collected by passing the fumes through scrubbing towers. While 

 this method has not been tried out in this laboratory, the cost of 

 maintaining the high temperature necessary for the decomposition 



'U. S. Patent No. 947795 (1910). 2 U. S. Patent No. 1018186 (1912). 



