298 
Journal of A gricultural Research voi. xi v, No. 8 
Hartwell and Pember (1908) conducted experiments with feldspar 
(variety not given) as the source of potash for plants. Their results 
led to the conclusion that little could be expected from this material as a 
source of available potash. 
Prianischnikow (1912) experimented with a number of crops, using 
various minerals as the source of potash. From his work conclusions 
are drawn that biotite and muscovite are superior to feldspar (orthoclase 
and microcline) as carriers of potash. 
Fraps ( 1912 ) found that all potash is extracted from biotite with 
strong hydrochloric acid, about one-third from muscovite, and only a 
small percentage from orthoclase and microcline. Fraps also found that 
practically no potash is removed from orthoclase and microcline by JV/5 
nitric acid, less than 10 per cent from biotite, and 15 per cent from 
muscovite. 
McCaughey and Fry ( 1913 ) conclude from observations of the optical 
properties of the potash-bearing soil-forming minerals that biotite must 
give up its potash to solution faster than muscovite and orthoclase 
faster than microcline. 
Curry and Smith ( 1914 ) found from fertilizer experimentation for hay 
that calcium carbonate and lime have practically no effect on the solu¬ 
bility of soil potash. 
Plummer {1915) found indications from field experiments that soils 
with high content of the micas respond less to potash fertilization than 
do those in which the feldspars predominate. 
Clark (zpzd, p . 395) says: 
Muscovite under ordinary circumstances is one of the least alterable of minerals. 
The feldspar of a granite may be completely kaolinized, while the imbedded plates 
of mica retain their brilliancy unchanged. 
Lyon and Bizzell ( 1916 ) say, as a result of lysimeter experiments: 
So far as could be ascertained from the potassium in the drainage water and the 
crop raised on the soil treated with lime and the soil not so treated, there was no lib¬ 
eration of potassium effected by the lime treatment. 
Fraps (1916) finds only slight gains of potash due to additions of car¬ 
bonate of lime on the insoluble potash of the soil. 
Briggs and Breazeale (1917) find that calcium-hydrate solutions do 
not modify the solubility of potash in orthoclase or orthoclase-bearing 
soils. 
In view of the variance of results set forth in the foregoing discussions, 
it would seem desirable that experimentation be carried out to deter¬ 
mine the relative availability of potash in the minerals which supply 
the soil with this constituent. 
EXPERIMENTAL WORK 
The minerals used were as representative and free from impurities as 
could be obtained. Each specimen was ground to an impalpable powder 
and sifted through the finest grade of bolting cloth. 
