11 
coagulant. Not having the apparatus to effect a rapid filtration 
through clay filters, small amounts of ammonium chlorid were used 
to bring about coagulation of the clay and make filtration through 
filter paper possible. In addition to using distilled water as a solvent, 
fifth-normal nitric acid was chosen in order to gain additional infor- 
mation concerning the action of different solvents. The means 
chosen for drying the soils were in an air bath at 100° C, and 250° C, 
over a Bunsen burner. It being practically impossible to obtain 
ignition all the samples fresh, extraction upon the soils in this state 
was not attempted. 
METHOD OF PREPARING EXTRACTS. 
The soils were prepared as follows: Upon receipt in the labora- 
tory they were spread out to dry. After reaching an approximately 
stable moisture content portions were weighed into porcelain dishes. 
One series was dried in an oven at 100° C. for 8 hours continuously, 
another treated likewise at 250° C, while the last series was heated 
over a Bunsen burner, at first carefully on a wire gauze for 2 hours to 
prevent dusting and then over the direct flame for 2 hours, thus 
destroying practically all the organic matter. 
Water extract. — This extraction was made by treating 200 gram 
portions of the soils with 1 liter distilled water, shaking occasionally 
for 1 hour, as previously mentioned, and then allowing to settle 24 
hours, adding small amounts of ammonium chlorid as a coagulant 
when necessary. Particular attention was given to these extrac- 
tions in order that all the samples in each series of the same soil 
should receive similar treatment as regards the number of times of 
shaking, thus making the results more directly comparable. Like- 
wise, all distilled water for a series was taken from the same lot in 
order to eliminate any slight influence which varying amounts of car- 
bon dioxid in the distilled water would have upon the solubility of 
the minerals. After settling 24 hours the solution was filtered 
through double filter papers and from this solution 500 cubic centi- 
meters was evaporated to a small volume and used for analysis. 
All determinations were made gravimetrically except phosphoric 
acid, iron, and bicarbonate. The former was made colorimetrically 
in 50 cubic centimeters of the original solution. 1 Iron was deter- 
mined colorimetrically 2 in a solution of the ammonia precipitate 
from the 500 cubic centimeters portion, and bicarbonate was de- 
termined by titrating 50 cubic centimeters of the original solution 
with twentieth-normal acid potassium sulphate, using methyl orange 
as indicator. 
Nitric acid extract. — The soils for this phase of the work were pre- 
pared in the same manner as above described as regards tempera- 
'U. S. Dept. Agr., Bur. Soils Bui. 31, p. 45. 
«U. S. Dept. Agr., Bur. Soils Bui. 31, p. 38. 
