CITRIC-SOLUBLE PHOSPHORIC 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.S per cent P,O ) 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.-O : Per cent. 
Total 0.60 
P,0 5 : 
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. Tatent No. 947795 (1910). 2 U. S. Patent No. 1018186 (1912). 
