CITRIC-SOLUBLE PHOSPHORIC ACID AND POTASH. 5 
substances were ignited at temperatures ranging from 1,200° to 
1,400° C, but only viscous fusions were obtained and the potash 
and phosphoric acid in none of these were soluble in 2 per cent 
citric acid, the solution conventionally employed to determine the 
availability of phosphoric acid in basic slag. 
The failure to obtain liquid fusions was at the time attributed to 
the absence of iron or manganese, or both, in the mixtures, since it is 
well known that these elements impart fluidity to slags in the manu- 
facture of iron and steel. Subsequent experiments have proved that 
such was the case, for on the addition of small quantities of these 
two elements to certain mixtures of feldspar and phosphatic lime- 
stone liquid fusions were obtained, and these were found to contain 
both phosphoric acid and potash in a citric soluble form. 
In Table I is given the composition of the materials used in the 
experiments. 
Table I. — Composition of feldspar and phosphatic limestone used. 
Material. 
Si0 2 . 
AI2O3. 
CaO. 
K 2 0. 
NasO. 
P 2 5 . 
C0 2 . 
Per cent. 
65.7 
32.4 
Per cent. 
18.4 
Per cent. 
Per cent. 
13.7 
Per cent. 
2.2 
Per cent. 
Per cent. 
Phosphatic limestone 
37.1 
20.0 
10.5 
The above materials were mixed in various proportions and small 
amounts of hematite and manganese dioxide were added. Each 
mixture was then placed in a graphite crucible and heated in a 
muffle furnace until fusion took place. The melts were then cooled, 
finely ground, and analyzed for phosphoric acid and potash (both 
total and citric soluble). 
It was found that while citric soluble potash can be readily ob- 
tained by heating various mixtures of feldspar and phosphatic lime- 
stone over a wide range of temperatures, the limits within which the 
maximum yields of citric soluble phosphoric acid are obtained are 
quite narrow, both in respect to the proportion of the ingredients in 
the mixture and the length of time of heating. 
The percentages of the ingredients used in the various mixtures 
before ignition and the composition of the melts are given in 
Table II. 
