Wk, SI LTS (jv A Mi('j{()s(.’()[’ir Sti'dv of Soml Soil Colloids. 
3 
In sain})loi? A 1351 mitl A 134-6 the ]jerfcc‘tion of the unifomiity of orienta- 
tion of the individual eoinponents irdo aggregates is amazing. It was not 
}K)ssible to identify infjre than one t>'pe of aggrt^gate. Tins indicated that 
such aggregates were characteristic of the Manptle as a wliole. 
'The refractive'- indict's W(U‘e doternuiu'd on aggr(>gates by hnnu'rsion in 
mixtures of clove oil and r(- -monoc]ilort)tuiphl lial^au'. 
Tlie main difftmaices between tlie two colloid se]iai'ations A I34(i ami 
xV 1351 is on(' of colour. Und('r the tnicros(*oj)e A 1346 is light brown ; A 1351 
is ('hocolate brown. All the mati'rial of both samples is doubly refracting ; 
A 1351 bemg the more l:>iriTringent. 'Fhe extinction of the aggregates is in 
all cases sharp. The indices in difteront din'ctions \\'('re easily d(‘tt‘rminal)le. 
44ie optical interference figure of aggrtgates of both samples is biaxial negativi^ 
and the axial angle is small. Tliese tigiires are similar in character to thos(' 
mentioned in the original woi-k of Hendricks and Fiy (3). The o])tical 
properti(‘s of aggregates of the' soil colloid fractions A 1351 and A 1346 ar(> 
suinmarisod in TabU' 2. 
Tablk 2. 
OPTICAL DATA KELATIXG 'I’O THE SOU. CObbOll) ERACTIOXS FROM 
a\t:stehx acstralia. 
()j)tical Properties. 
A 1346 (Water Dispersed). 
A 1351 (Water Dispersed). 
(( 
1 ■ 562 
1 • 555 
y • • « • . . 
I -572 
L570 

6- 010 
(0015 
’IV 
Small 
Small 
Optical character 
( - ) 
( - ) 
It may bt' seen from Table' 3 that these optieal properties are not those? 
of any cominon clay mineral. X-ray ewidemcc indic,ates that both the soil 
e?olloid samplers are composed of a mixture of two clay Toinorals, one be'longing 
to tlm micH group and the' otlier te) the' kaolinitc group. If the aggregate's 
under e?xaminat ion eu'e’ to bi' e-euiside'red roprese'atati\'o of the sam})li‘ as a 
whole, then these optical pi'ope'vties e'oulel re'sult from an aggregatieni ejf tlu' 
above two clay mineu'als. That twej clay mineu'als bHonging to different 
groups may closely intergrown iide) aggregate's which possess uniformity 
of crystallographie* orientation has alnmdy bc>en noted by Bray, Grim, and 
Kerr (4). Hence tlie optical ])ropcrtie's of aggregates of the soil colloid frac- 
tions A 1351 and A 1346 arc ce)nsistent with the? X-ray conclusions. 
Table 3. 
DPTTCAL PROPERTIES OF CLAY MINERALS. 
Kaolixite Grout. 
51ineraJ. 
7 
(( 
7 - « 
2V. 
Sign. 
Kaoliuite 
Nacrite 
Diekite 
Halloysite 
Hydrous Halloysite 
1-570— 1-560 
1 • 566— 1-563 
1-556 
Mean Index 
Mean Index 
1 -5(33— 1-553 
1 -560— 1 -557 
1 ■ 560 
i ■561—1-549 
1 -542—1 -526 
0-006 
0-006 
0-006 
Very slight 
\Yry slight 
40^—90° 
52°— 80° 
(--) 
( + ) or (— ) 
( + ) 
