14 
BULLETIN 1122, U. S. DEPAETMENT OE AGRICULTURE. 
of the colloidal particles separated from the particles above 1 micron 
in diameter by means of the centrifuge. This procedure was the 
same as that followed in separating colloids from soils, except that 
no ammonia was used with the mineral powders. 
Determinations of the absorptive capacities of each of the powdered 
minerals for malachite green, water, and ammonia are given in Table 4. 
Table 4. — Absorption of mineral particles less than 1 micron in diameter. 
Absorption per gram of 
mineral powder. 
Mineral powder. 
Mala- 
chite 
green. 
HoO. 
NHs. 
Muscovite.. . ...... 
Gram. 
0. 0829 
.0078 
.1168 
.0000 
.0242 
.0000 
Gram. 
0.3581 
.2289 
■.■1694' 
.1673 
.0870 
Gram. 
0141 
Limonite 
.0100 
Chlorite 
.0091 
Microcline 
.0067 
Orthoclase 
.0077 
Quartz 
,0049 
Average 
.0386 
.2021 
.0088 
The absorptive powers of these very fine mineral powders for 
malachite green present striking contrasts. Microcline and quartz 
did not absorb a detectable amount of dye. On the other hand, 
clilorite and muscovite had absorptive capacities which Avere as high 
as the least absorptive ultra clays found in 33 different soils. In 
no case was the absorption as high as the average for soil colloids. 
The different minerals varied less in their absorptive capacities for 
water vapor. The values for muscovite and limonite are not greatly 
different from the average for soil colloids; the others, however, are 
somewhat lower. 
None of the mineral colloids absorbed as much ammonia as the 
least absorptive ultra clay we have tested, and the average value for 
the mineral powders is only 22 per cent of the average value for the 
ultra clays. 
While the absorptive capacities of these mineral powders were, on 
the whole, much greater than those of the 1 to 50 micron powders, 
they were much lower than those of the ultra clays, particularly as 
regards absorption of the dye. 
The absorptive values obtained for these minerals doubtless did 
not represent accurately the true absorptive capacities of unaltered 
minerals of any particular size. In preparing these fine powders it 
was necessary to treat the material with 2 to 10 liters of distilled 
water for each gram of colloidal mineral extracted, in order to remove 
completely the coarser particles, and the material was in contact with 
water for three to five days. There was, therefore, opportunity for 
considerable alteration or breaking down of the minerals through 
hydrolysis. Hence, a considerable part of the absorptive capacities 
of these preparations may weU have been due to the presence of 
colloidal decomposition products of the minerals. 
It is well recognized that many silicate minerals are acted upon 
by distilled water, yielding an alkaline solution and doubtless insolu- 
