ABSOBPTION BY SOIL CONSTITUENTS. 
9 
very few particles larger than 0.050 millimeter or smaller than O.OOl 
millimeter in any of the samples. However, the different sampled 
varied considerably in the distribution of the particles between these 
limits. The approximate surface exposed by 1 gram of each of the 
mineral powders was calculated. In this estimation account was 
taken of the specific gravity of the mineral; the mean diameter of 
each group of particles was taken as the diameter of all particles 
within the group, and all the particles were assumed to be spheres. 
No great accuracy can be claimed for these estimates of surfaces, since 
microscopical counts of particles of the different sizes are probably 
only accurate to about 10 per cent and certain of the minerals were 
far from spherical in shape. In the case of muscovite and biotite, 
the figures for surface represent only a minimum Vi^lue, since the 
particles doubtless approximated thin plates rather than spheres. 
The true surfaces of these powders were probably, therefore, several 
times the values given in Table 2. 
ABSORPTION BY THE DIFFERENT SOIL MINERALS. 
In Table 2 are given the amounts of malachite green, water, and 
ammonia absorbed by 1 gram of each of the mineral powders and the 
approximate surface exposed in each case. 
Table 2. — Absorption of mineral particles 1 to 50 microns in diameter. 
Mineral. 
Approxi- 
mate 
surface 
per gram 
of pow- 
dered 
mineral. 
Absorption per gram of 
mineral. 
Dye. 
H2O. 
NH3. 
1 Apatite, CaFCa<(P04)3 
Biotite, K2O.4(Mg,Fe)0.2(Al, Fe)a03.6SiO.H20 
1 Calcite, CaCOs 
3 Garnet fCa3Al2(Si04)3 -- 
^^™^^ tFe3Al;(SiOi)3.. 
Chlorite, H8(Mg,Fe)5Al2Si30i8 
Cyanite, Al2Si05 
3 Enidote fCa2(A10H)Al2(Si04)3 x.. 
3 ispiaote \Ca2(reOH)Fe2(Si04)3y.. 
Ca(Mg,Fe)2(Si03)3.- 
Hornblende <Na2Al2(Si03)4 
((Mg,Fe4)(AlFe2)SiO«. 
Limonite, Fe2(OH)6Fe203 
< Magnetite, Fe304 
Microcline, KAlSisOs 
Muscovite, K2O .3Al2O3.6SiO2.2H2O 
Orthoclase, KAlSi308 
Plamoolasp fNaAlSisOs x . . 
riagiociase \CaAl2SiLO8 y.. 
Quartz, SiOz 
Rutile, Ti02 
Sillmanite, AhSiOs 
3 Titanite, CaO.TiO2.SiO2 
Tourmaline, Na20,(Fe,Mg,Cr)0,Al203,fei02.BiC3 B2O 
Zircon, ZrSi04 
3 Zoisite /Ca2(A10H)Al3(Si04)3 l . . 
^^'^'^^ \Ca2(Fe0H)Fe2(Si04)3 y. 
Square 
cendmeter . 
2,813 
2 1, 764 
1,225 
1,687 
2,241 
2,619. 
1,131 
1,165 I 
753 I 
674 . 
3,104 ' 
2 2,025 
3,449 i 
3,229 
3,179 
694 
1,609 
2,694 
1,386 
977 
1.166 
Gram. 
' '6." 0376' 
.0078 
.0192 
.0060 
.0001 
.0089 I 
.0053 I 
'"'.'666i'[ 
.0390 ! 
.0005 : 
.0000 j 
.0000 ! 
.0000 
.0105 
.0059 
.0130 
.0048 
.0000 
Average values. 
1,885 
0088 
Gram. 
0. 0015 
.0223 
.0012 
.0093 
.0148 
.0067 
.0016 
,0018 
.0308 
,0006 
,0008 
,0509 
,0016 
,0028 
,0005 
,0240 
,0022 
.0039 
.0007 
.0055 
.007 
0095 
Gram. 
0.0000 
.0012 
.0000 
.0008 
.0012 
.0006 
.0008 
.0000 
.0052 
.0000 
.0000 
.0023 
.0000 
.0000 
.0002 
.0012 
.0008 
.0010 
.0000 
,0012 
.0007 
,0008 
1 Calcite, and probably apatite, in the absence of colloidal soil material develops an alkaline reaction 
in the process of the dye determination, and thus decolorizes the malachite green oxalate. This decolori- 
zation, however, does not take place when soQ material is present to act as a buffer. 
2 Owing to plate-like form of particies, this represents minimum surface. 
3 Trace of calcite present which was removed by 4 per cent HCl before making the dye determination. 
< Trace of calcite present. 
8107— 22— Bull. 1122 2 
