14 



BULLETIN 1122, XJ. S. DEPARTMENT OF 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. 



Gram. 



0. 0829 

 .0078 

 .1168 

 .0000 

 .0242 

 .0000 



HsO. 



NH3. 



Muscovite 



Gram. 



0. 3581 



.2289 



'."1694' 

 .1673 

 .0870 



Gram. 

 0. OUl 



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, 

 chlorite and muscovite had absorptive capacities which were 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 thi-ough 

 hydrolysis. Hence, a considerable part of the absorptive capacities 

 of these preparations may well 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- 



