Kkstlts or A Mk'koscopio Studv or So.mk Soil ('oi.loids. 
vSaiopk' 222 is (lifiVront froTii the oIIk'v 'I'asitianian sain]iU>s in tliat th(' colour 
Ixaioatii tlie iniorosropo is ^royish-x cllow, tho itidicc^s of i'(>fi*ac'tinn art' lowof, 
and tlio ajjcu;rt'^atos a>'i> nu)l't^ hirofringtait. Many a^^iu'^att's art* dai'k Ix'twci'ii 
arossod tiicols but soino. slunv fairly unifonn orystallograpliir oricntalion oi 
indix idual aoinpononts and for tliosf^ y n ^ ()*005. Such aggr('jiatos iailod 
to show int(M'f(M-('n('o liguros suiliaiiaitly satisfaaior\ Ibr tho <lot(‘rniinal ion of 
llio o])tioa! oharaotoi'. X-j'ay o\idoncf' indioato.s that kaolinilo and inonl 
inorilloniU' ari' tln' olav' ininorals prt^sont in this soil colloid fraction. In 
\ ii'w of t he fact that the tlii’ci’ colloal fractions aol. . >(>(►, and 491), containing 
kaolinit(‘ as t hi' only clay initu'ral art' nou-bireli'ingent , the slight ly biri'fringent 
character of 222 ('fable 4) is consist I'nt with the al)o\(' X -I'ay i-onchision. 'fliat 
is, if the aggregates under ('xainination are to be I'onsidered re|)resentati\ e of 
till! sanipk' as a wholes tlu'u thesis two minerals (kaolinite and montmorillonite) 
are occasionally closely iiitergi-own into aggri^gatos which possi'ss unit'ormit\' 
of crystallographic oruaitatiou. 
Tarlk 4. 
OPTK'AL DATA liK.LATTXtJ TO TIIK SOIL C(.)Lb01l) FKACTTOXS FROM 
TASMANIA. 
Sample. 
(( 
Mean 
Refractive iiide.v. 
y - c 
9a»> 
1 • 507 
1 • 572 
0-0( 15 
AM 
1 • 00.7 
-MiO 
! -OLS 
499 
1 ■ 05,7 
RK-DISPF.RSION AND 
RF-ACKiRFOATlON 
OK THK SOIL COLLOIDS. 
In view of criticism of the o]‘)S(‘rvations made in this study that fii'stly 
the particles examined wi'n* aggregati's (of a size ii]) to and greatei- in 
diameder) of soil colloid partii'les rathi'r than original single crystals wiiiedi 
had not been broken down in the |)re])arat ion, and that sec'ondly two clay 
minerals bi'longing to diftei'iait groups nia\' l)e closidy intt'rgre)wn into aggre- 
gates whicli possi’ss uniformity of crystallographic oi-icnt ation, it ^^’as of 
inte'rest to restori' tlu' particles to their original sus]>ended stati' where they 
liad an effective diana-ter of 2^ aiul to re|-)roduce tla^ aggri'gafes by remox'ing 
the ])artiid<;s from suspension. 'This applii'd ])articularly to tlui soil colloid 
fractions from Western Australia \\-hicli exhibit well marked crystallinity. 
Hv-disijcr-sion.^-'Vhv re-dispiM’sion of one of these samj)les (A Dial) was 
undertaken ])y Mr. I>ur\ ill, of llie State Department of Agriculture, who was 
n^sponsiblo for the original si'paration of the West Australian soil i-olloids. 
By repeating ]a'ecisely the procedure adopted in the prepai-at ion, Mi‘. Uur\ iil 
was able to re-disperse the greater t>art of the soil colloid sajupk' A Biol. 'Vlu' 
individual partick's of this susiiended mati'rial wi're not \'isihle under liigh 
power magnitieation. 'riial sonu' matei'ial was not i-e-dispersi'd is ol little eon- 
set[uence when it is realised that, as a result of the grinding a sample- i'eeei\es 
in a mi'elianieal analysis, the amount of clay recorded is rather arbitrary. 
Re-iiggrcgatioa . — By removing the clay particles from suspension in the 
same maiau'r as oiiginally carried out by Mi*. Ihir\ill, the author was able to 
reproduce the state of large-sized crystal aggregates in wtiich tlie sample 
originally existed. These aggregates again exhibited a well marked uni- 
formity of crystallographic orientation. 
