4 
W. V. COLK. 
Montmorjij.onjtk Okoijp. 
M iiK'ral. 
y 
(( 
1 
y - 
2V. 
Higu. 
Meait morilloiiite' . . . 
1 ■5;!(i - 
1 - Mm 1 1 -505 
1 -47(1 
(>■035 - t)*()35 
r- 25° 
( — ) 
P>.'i(l('llit(‘ 
1 ■5()(l 
1 - .-.30- 
1 -5(10 
(1-935 — 9-935 
Small 
{— ) 
Xont remit 
1 -(>10 
l-5(i(» 1-575 
1 -530 
9-935- 9-()39 
Small 
{-) 
Sa|)e)nilc ... 
1 lulice's 
e>f re'fractioii 
similiir 
ti) .Monttiioriliemite* 
j 
Mjca (jRorr. 
Miru'ral. 
r 
i( 
y - a 
2V. 
Sign. 
niite' 
1 .(ior,— ! .51)5 
1 •579—1 -535 
9-035— 0-939 
Small 
{-) 
Xole : This Tahh* is based on that ])ul>!is]ied ))V (dim (5). 
SOIL ('OLI.OID KKACTIONS KKOM TASMANIA. 
Ill ^(‘iK'ral Mu' nMimiTs jiuulo in tlu^ pi'nvious section as r('pir(ls ag^rc'ga- 
tion of soil colloid mutt'i'ial aftta* drying apply also to tlio Tasnuuiian soil 
colloid fractions. W’luai \ic\\cd nndci' the inii'roscopc* all four sample's woi'o 
sc.<>n to !)(' in IIk' form of [lartTde^s up to and greater in diam<;t('r. In view 
of what ha-s hei'ii previously stated, tJies(> })art'ich‘s are eonsidt'iHMl to bo 
aggi*('gat('s of the soil colloid particles which Imvt^ a.n td’tV'ctive diamedcr (in 
tliis ('as(') td 1-4/^ and h'ss. Sample 222 is, howevea*, the only fraction whi(*h 
shows any deHlucihle uniformity of crystallographic orientation of individual 
compoiu'uts. d'he three samples, 551, Still, 4d9, and tlu^ grt'ater [lart of 222, 
ai'(^ dark helwe'eai (U'osst'd nicols. In siudi sample's a nuam ind(>x of I'efraction 
onl> A\as di'termined. N'ariations from I hi* nu'an \'alue are small. 
The soil colloid sample's 551, Slit), and 4tU) are' \ i'ry similar. Aggj-('gat('s 
(oi'ined from (>ach of llu'st' thre'i' sainph's art' cliaracti'rise'd by theii- t'olour, 
high indict's of refraction, a-nd a,ppar('ntly isotrtipic character. Tlu' colour 
of 4i)t) uiuh'r tile microscojH' is chocolate' brown, that of 551 and Still dark 
brown. 'The' high indice's of re-fraction are' probably due' to tlie high iron 
conte'iit ol the' seiil e'olloid sample's. This iron e'onte'iit elot>8 not ('liter th(> 
struedme eif the' clay inine'rais pre'se'ut in the* soil colloids (a cotu'lusion arrived 
at freiin the* X-ray analvsis) but jirobably coats tlu* colloid jiarticles in the. 
form t)f ii’on o\id(\s (.ir liyelroxidos. Such a pejssiliility has already bet'ii noted 
by Nagelselnnult (ti). These indice's eil refraction, tlua'C'fore*, eh'ai’ly do not 
r(>pivHent the* refracti\'(' inde^x of the clay mineral shown io be* pn^sent by 
X-ray examination. Ibaulrieks and Kry (M) have' note'd that a high iron 
contr*nt in a soil colloid frae*tion te'uds to mask the doubly re'fracting mat(''i'ial 
pre'sent. In N'ie'w ol tii(> X-ray i‘e.»nclusioii that the' elay miiu'ral ])rese’nt in 
those' tliree' eolloid fVaetieaxs is preHleaninantly kaeilinit.e', it is belit'\-eMl that, in 
the ahsenee of a liigli iron eonle*nl, aggre'gati's fornu'd from eaeli of these thre'C 
colloid fractions would still posse>ss only a \ery weak hin'fringonce. Hemce, 
generally speaking, the optica! data relating to aggregate's of the soil colloid 
fractions 551, 560, and 499 (which are summarised in Table 3) are consistent 
with the X-ray conclusions. 
