May 3917 Solubility of Certain Inorganic Soil Constituents 255 
method of analysis 
The soil extracts thus obtained contained large amounts of organic 
matter in solution, which it was necessary to remove before proceeding 
with the analysis. A number of methods were tested with solutions con¬ 
taining known amounts of the mineral elements under investigation, to¬ 
gether with large amounts of organic extracts known to be free from these 
mineral elements. Of these methods, the following gave the best results: 
The soil extracts obtained with the organic solvents were made and 
kept slightly ammoniacal, an excess of ammonium oxalate was added, and 
the extracts were evaporated to dryness. The residue was ignited just 
sufficiently to bum off the organic matter. The ignited mass was taken 
up with a measured 1 amount of nitro-hydrochloric acid, diluted some¬ 
what with distilled water, and heated on the water bath until everything 
except the free silica had gone into solution. This acid solution was 
made up to volume and analyzed. 
The phosphoric acid was determined volumetrically by Pemberton's 
molybdic method, The calcium was determined volumetrically by 
titrating the oxalate with potassium permanganate. The magnesium 
was determined volumetrically by the method of Meade. The detailed 
methods of determining the above-mentioned three elements are sub¬ 
stantially those given by Sutton. 2 The iron was determined colorimet- 
rically by comparing the red color developed on the addition of potassium 
thiocyanate to the unknown solution with a standard iron solution. The 
color in the standard solution was developed at the same time that the 
color in the unknown solutions was developed, and the readings were 
made at once. 
SOLUBILITY OF SOIL MINERALS IN EXTRACTS OF DECOMPOSING 
ORGANIC MATERIAL IN DIFFERENT STAGES OF DECOMPOSITION 
In the mulched basin under field conditions the products of decompo¬ 
sition are gradually leached into the soil. To approximate this action, 
the organic solvents were prepared by extracting the same samples of 
decomposing organic matter at intervals as shown in Table I. The 
amount of calcium, magnesium, phosphoric acid, and iron removed from 
two soils by such organic solutions prepared from cow manure, barley 
hay, alfalfa hay, and sweet-clover hay in various stages of decomposition 
is given in Table III. 
To determine the solvent action of these organic solvents in excess of 
that of pure water alone, a number of determinations were made of the 
solubility of the iron, calcium, magnesium, and phosphoric acid in the 
1 It was necessary to use a measured amount of add in taking up the ignited residue after evaporating 
the organic soil extracts to dryness, owing to the fact that the red solution formed by the addition of potas¬ 
sium thiocyanate to ferric iron is rendered colorless by an excess of hydrochloric or nitric acid. In working 
with a few parts per million of iron in the solution, it was found unsafe to have present in too c. c. of the 
solution under investigation more than 3 c. c. of concentrated nitric or hydrochloric add, or the same 
amount of a mixture of both acids. 
Sutton, Frands, A Systematic Handbook of Volumetric Analysis . . , ed. 10, 621 p., 121 fig. 1911. 
