2 BULLETIN 143, U. S. DEPARTMENT OF AGRICULTURE. 
recently devised in this laboratory for rendering the phosphoric acid 
and potash in a mixture of phosphatic limestone and feldspar " citric 
soluble." 
EARLIER METHODS. 
There are four * recorded processes for making a phosphoric acid- 
potash fertilizer from phosphate rock and feldspar. In chrono- 
logical order they are as follows: 
A method devised by Charles Bickell 2 in 1856, which consists in 
heating in a reverberatory furnace to a light redness for two hours 
an intimate mixture of 1 part feldspar, 0.5 part phosphate of lime, 
and 3 or 4 parts of air-slaked lime. Bickell claims that both phos- 
phoric acid and potash in available forms are obtained by this treat- 
ment. 
This experiment was repeated in this laboratory, using feldspar, 
Tennessee phosphatic limestone, and calcium carbonate in the fol- 
lowing proportions: 
Per cent. 
Feldspar (13.7 per cent K 2 0) 22.2 
Phosphatic limestone (23 per cent P 2 5 ) 11.1 
Calcium carbonate 66. 7 
Assuming that the carbon dioxide present in the calcium carbonate 
and phosphatic limestone was the only substance volatilized during 
the process, the product should have contained after ignition 4.38 
per cent potash (K 2 0) and 3.4 per cent phosphoric acid (P 2 5 ). 
Analysis of the residue, however, gave the following results : 
K 2 : Per cent. 
Total 1.94 
Water soluble .18 
P 2 5 : 
Total 3.62 
Citric soluble 1.40 
These results show that over 44 per cent of the potash present in 
the mixture was volatilized upon ignition, and of that which re- 
mained in the residue only 9 per cent was water soluble. While none 
of the phosphoric acid was volatilized, less than 39 per cent of the 
total amount present was soluble in a 2 per cent solution of citric 
acid (the method usually employed for determining the availability 
of phosphoric acid in basic slag). 
The second process for the manufacture of a phosphate-potash 
fertilizer from feldspar and phosphate rock was devised by Fred- 
erick Klett 3 in 1865. It consists of heating to redness for five hours 
an intimate mixture of one part feldspar, two parts carbonate of 
lime, one part phosphate rock, and adding for each part of K 2 in 
the feldspar two parts of calcium fluoride. It is claimed that a solu- 
1 Since transmitting, this manuscript several other processes have been devised. The 
author regrets that it is impracticable to consider these methods in the present paper. 
2 TJ. S. Patent No. 16111 (1856). 3 U. S. Patent No. 49891 (1865). 
