ABSOEPTION BY SOIL CONSTITUENTS. 



If' 



very few particles larger than 0.050 millimeter or smaller than 0.001' 

 millimeter in any of the samples. However, the different sample&= 

 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 sm-face represent only a minimum vnlue, 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. 



'Apatite, CaFCa4(P04)3 



Biotite, K2O.4(Mg,Fe)0.2(Al, Fe)208.6SiO.H20 



1 Calcite, CaCOs 



3 aarnpt ;Ca3Al2(Si04)3 ■ 



^^™^^ IFesAlKSiOi):). 



Chlorite, H8(Mg,Fe)oAl2Si30i8 



Cyanite, AUSiOs . 



y- 



, Enidote fCa2 A10H)Al2(Si04 3 



siipldote \Ca2(FeOH)Fe2(Si04)3 



(Ca(Mg,Fe)2(Si03)3-- 

 Hornblende ■^Na2/Vl2(Si03)4 



l(Mg,Fe4)(AlFe2)Si06. 



Limonite, Fe2(OH)6Fe203 



4 Magnetite, FesOi 



MicrocUne, I^AlSiaOg 



Muscovite, K2O.3Al2O3.6SiO2.2H2O 



Orthoclase, IvAlSisOg 



I'l-^o^i-e «iiS^ 



Quartz, Si02- 



Rutile, Ti02 



SiUmanite, A^SiOj 



3 Titanite, CaU .Ti02.Si02 



TourmaUne, Na20,(Fe,Mg,Cr)0,Al203,ei02.EsCs H2O 



Zircon, ZrSiOi ' 



, 7oi,itp /Ca2( A10H)Al2(Si04)3 x . . 



■^"'^"^ \Ca2(FeOH)Fe2(Si04)3 J/. 



Average values 



Square 



ceniimeter. 



2,813 



3 1, 764 



1,225 



1,687 



2,241 

 2,619 



1,131 



1,165 



753 



674 



3,104 



2 2,025 



3,449 



3,229 



3,179 

 694 

 1,609 

 2,694 

 1,386 

 977 



1 1, 166 



Gram. 



' '6.' 6376' 



.0192 

 .0060 



.0001 

 .0390 

 .0005 



.0000 



.0000 

 .0000 

 .0105 

 .0059 

 .0130 

 .0048 



.0000 



Gram. 

 0. 0015 

 .0223 

 .0012 



.0093 



.0148 

 .0067 



.0016 



.0018 



.0308 

 .0006 

 .0008 

 .0509 

 .0016 



.0028 



.0005 

 .0240 

 .0022 

 .0039 

 .0007 

 .0055 



.0078 



.0095 



Gram. 

 0. 0000 

 .0012 

 .0000 



.0008 



.0012 

 .0006 



.0008 



.0000 



.0052 

 .0000 

 .0000 

 .0023 

 .0000 



.0000 



.0002 

 .0012 

 .0008 

 .0010 

 .0000 

 .0012 



.0007 



.000& 



1 Calcite, and probably apatite, in the absence of colloidal soil material develops an alkalhie reaction 

 In the process of the dye determination, and thus decolorizes the malachite green oxalate. This decolori~ 

 zation, however, does not take place when soil material is present to act as a buffer. 



2 Owing to plate- like form of particles, 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 



