ABSORPTION BY SOIL CONSTITUENTS. 
11 
Table 3 shows, for the four soils studied, that part of the total 
absorption of the soil which must have been due to the unaltered 
minerals present. In compiling this table the absorption of each fine 
fraction was calculated from the mineralogical composition given 
above and from the absorption data for particles of this size given 
in Table 2. The absorption of each coarse fraction was calculated 
from that of the corresponding fine one, assuming that the two frac- 
tions were of the same mineralogical composition and that the 
absorptive values were therefore inversely proportional to the size 
of the particles. 
Table 3. — Part of soil absorption due to unaltered miverals. 
Absorption of the unal- 
tered minerals present 
in 1 gram of soil. 
Absorption of 1 gram 
of soil.i 
Part of soil absorption due 
to unaltered minerals, in 
case of— 
Type of soil. 
Mala- 
chite 
green. 
HoO. 
NHj. 
Mala- 
chite 
green. 
H2O. 
NH3. 
Mala- 
chite 
green. 
1 
H,0. NHj. 
Huntington loam, 
soil 
Gram. 
0.0002 
Trace. 
.0005 
Gram. 
0.0002 
Gram. 
Trapft. 
Gram. 
0.0234 
.0193 
.0286 
Gram. 
0. 0508 
.0712 
.0530 
Gram. 
0.0089 
.0064 
.0060 
.0312 
Per cent. 
0.8 
Trace. 
1.7 
.4 
Per cent. Per cent. 
0. 4 Traofi- 
Huntington loam, 
subsoil 
Sassafras silt loam, 
subsoil . . 
Trace. 1 Trace. 
.0006 Trarfi. 
Trace. 
1.1 
.5 
Trace. 
Trace. 
Sharkey clay, soil... 
.0007 
.0009 
Trace. 
.1880 
.1712 
Trace. 
1 Calculated from the absorption given for fractions in Table 1. 
It is evident from Table 3 that the absorption of the noncolloidal 
minerals is less than 2 per cent of the total soil absorption in each of 
the four soils described and is therefore negligible as compared with 
the absorption of the colloid. This value for the noncolloidal absorp- 
tion is very much lower than that sho^\Ti by the first method of 
investigation and is, we believe, much more accurate. 
The preceding calculations show the relative absorptions of the 
colloids and noncolloids in four soils only, but a rough estimate can 
be made for soils in general. The average absorptions per gram of 
the unaltered common soil minerals of silt and clay size for malachite 
green, water, and ammonia, as shown in Table 2, are, respectively, 
0.0088, 0.0095, and 0.0008, while the averages for ultra clays ex- 
tracted from some 40 different soils are respectively 0.200, 0.298, 
and 0.040.^ The average absorptions per gram of unaltered minerals 
just above the colloidal size are thus only 4 per cent, 3 per cent, and 
2 per cent as high as those of the colloids for malachite green, water, 
and ammonia. 
Since there are such wide variations in the absorptions of the 
different minerals, a proper estimate can not be made of the relative 
absorptions of the colloidal and noncolloidal parts of the soil unless 
consideration is given to the relative quantities in which the different 
minerals are present. In a former bulletin of the Bureau of Soils (19) 
mineralogical analyses are given of the finer sand and silt groups in 
26 representative American soils. The average mineralogical com- 
position of the silt group in these 26 soils is as follows: Quartz 51 pep 
» The extreme variations in the absorptions per gram of the different ultra clays are: 0.431 and 0.070 gram 
of malachite green, 0.348 and 0.240 gram of water, and 0.076 and 0.019 gram of ammonia. 
