July i, 1918 Influence of Gypsum on Solubility of Potash in Soils 63 
Soil B was collected from near Spring Valley and is characteristic of 
the soils formed on the Kansan drift sheet. It was fairly well supplied 
with organic matter, but strongly acid in reaction owing to heavy 
precipitation and age of the drift sheet. 
Soil C was taken from the surface 6 inches of the Minnesota Experiment 
Station farm at St. Paul and is classified as Hempstead silt loam (8, p. 
26). This soil, overlying beds of sand and gravel, is to be regarded as of 
alluvial origin deposited from slowly running water issuing from the 
foot of the retreating ice sheet. It shows an acid reaction and is rela¬ 
tively low in total potash. 
Soil D, from near Worthington, would be classified as Barnes silt loam 
and is representative of a large area of well-drained soil developed on 
the late Wisconsin drift sheet. It is calcareous, as are all of the soils 
of this type, and being a prairie soil is relatively high in organic matter. 
Soil E is a silt loam from the loess near Caledonia in southeastern 
Minnesota, and would be classified as Knox silt loam. It is poorly 
supplied with organic matter, is of a strongly acid character, and is high 
in total potash. 
With the exception of sample C, the soils represent composites of 50 
individual samples from the surface foot, 10 taken from each of 5 different 
virgin fields. Soil C was collected from the surface 6 inches of a small 
field on University Farm that had been in forest plantation for about 
30 years. 
PREPARATION OF THE SAMPLES 
The air-dried soils were reduced with a rubber pestle so as to pass a 
2-mm. sieve. Two i,ooo-gm. portions of each were weighed out; 10 
gm. of pulverized gypsum were sifted over one, placed on a sheet of oil¬ 
cloth, and the whole was thoroughly mixed. Enough water was sprinkled 
over each portion to raise the moisture content to about two-thirds the 
moisture equivalent, after which they were again thoroughly mixed and 
finally transferred to glass jars of known weight, and enough water added 
to raise the moisture content to the moisture equivalent. The jars were 
kept loosely covered with glass plates to prevent excessive evaporation 
and allowed to remain in an attic storeroom from Febtuary 15 until May 
15, 1917. At the end of six weeks the jars were weighed and water added 
to each until the weight was equal to that at the time they were first 
put aside. The temperature of the storeroom during this period of 
exposure varied from 10.5 0 to 18 0 C. After this the soils were removed 
from the jars, spread out upon sheets of oilcloth and allowed to become 
air-dry when they were passed through a 2-mm. sieve and placed in 
ordinary Mason jars in which they were kept until the analyses could 
be begun in the following December. 
Four hundred gm. of the air-dried soil were weighed out and placed in 
a 7-liter bottle and treated with 4,000 c. c. of distilled water. At half-hour 
