4 BULLETIN 143, U. S. DEPARTMENT OF AGRICULTURE. 
of the minerals and the expense of collecting and recovering the 
potash and phosphoric acid thus violatilized make it very doubtful 
if this process is commercially practicable. 
THE FUSION OF FELDSPAR AND PHOSPHATE ROCK. 
The solubility of phosphates in certain organic solutions has for a 
long time been regarded as a test of their agricultural availability. 
The nature and strength of the organic solvent used differs in various 
countries, and since each process is based on an arbitrary standard, 
it can only give corresponding results when conditions are the same. 
But in spite of the fact that none of these methods is founded upon 
a strictly scientific basis, it is generally thought that phosphates 
soluble in such solutions are under soil conditions more active than 
those which do not dissolve in the same mediums. 
The beneficial effect of the phosphoric acid in finely ground 
steamed bone is unquestioned, and although little of it is water 
soluble, a neutral solution of ammonium citrate will dissolve from 
12 to 31 per cent of the acid, depending on the temperature of the 
solution and the time of contact. 1 It is also an indisputable fact 
that excellent results have been obtained by the use of basic slag as 
a fertilizer, and it is claimed that these results are commensurable 
with the amount of citric soluble phosphoric acid present in the 
material. 
It has therefore become customary to regard citrate or citric 
soluble phosphoric acid as having a commercial value nearly equal 
to that of water soluble phosphate. 2 While this is true of phos- 
phates, the same view is not taken of potash-bearing substances, 
since practically all of the potash carriers used in agriculture are 
water soluble. The potash -in the ordinary soil minerals is almost 
entirely insoluble in water,' and but slightly soluble in the mineral 
acids, but if the potash present could be converted into a citric 
soluble form there seems to be no reason why it should not be con- 
sidered as available to crops as citric soluble phosphoric acid. 
During some investigations carried on in this laboratory on the 
possibilities of rendering the slags from the iron and steel industries 
available for fertilizer purposes, 3 attempts were made to fuse to- 
gether mixtures of feldspar and phosphatic limestone with a view to 
obtaining both the potash and phosphoric acid present in an " avail- 
able" form. Mixtures containing various proportions of these two 
1 Huston, H. A., 32d Annual Report Indiana State Board of Agriculture, p. 230 (1883) ; 
Wiley, H. W., Principles and Practice of Agricultural Analysis, vol. 2, p. 47 : Wheeler, 
H. J., Manures and Fertilizers, p. 172 (1913). 
2 A report of a conference of the experiment stations of New York, New Jersey, and 
New England, Mar. 1, 1911, indicates that citrate soluble phosphoric acid has about 
nine-tenths of the fertilizer value of water soluble phosphoric acid. 
3 Bui. 95, Bureau of Soils, U. S. Dept. of Agr., 1912. 
