140 
PACIFIC SCIENCE, Vol. VI, April, 1952 
1 . The lowest cation exchange capacities were 
found in the soils belonging to the Honou- 
liuli family where the range was from 11.0 to 
21.3 milliequivalents per 100 grams. The 
cation exchange capacities of soils of the 
Kalihi and Kaloko families range from 24.3 
to 41.1 milliequivalents per 100 grams, which 
are much higher than capacities of the Ho- 
nouliuli soils. Likewise, the per cent mag- 
nesium saturation is the lowest in the soils of 
the Honouliuli family. The range for all soils 
was from 28.9 to 66.5 per cent. The ratio of 
exchangeable calcium to exchangeable mag- 
nesium was very variable in each soil family 
and showed little evidence of any real dif- 
ferences. 
The organic matter content of the gray 
hydromorphic soils varies greatly from soil to 
soil. These soils have the lowest organic 
matter content of the Hawaiian soils, as most 
zonal soils of the islands have an organic 
matter content higher than 3 per cent. In 
general, the greater the expression of hydro- 
morphic condition, the greater the organic 
matter content of the soil. 
The soil particles less than 5 microns in 
size make up the major portion of the par- 
ticles of these soils. Most of these soils have 
from 40 to 50 per cent clay-size particles. 
Thus, all of these soils are clays. The clay 
content was practically the same for the soils 
of each soil family. 
The plastic numbers of these soils ranged 
from 11.8 to 30.4. The highest values for the 
plastic number were found for the soils of the 
Kaloko family and the lowest for the soils of 
the Honouliuli family. This would indicate 
that the plastic properties were developed to 
the greatest extent in the soils having the 
greatest hydromorphic conditions. 
INTERRELATIONSHIP OF PROPERTIES TO 
PLASTIC NUMBER 
The data presented in Table 1 indicate that 
some of the chemical properties are related to 
the plastic number. Figure 1 shows the rela- 
tionship between the cation exchange capa- 
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h 
U 
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^ 30 
< 
O 
LU 
0 25 
Z 
< 
X 
o 
X 20 
LU 
z 
a- 
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10 
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n. = 0.6966 
1 
1 
1 
10 15 20 25 30 
PLASTIC NUMBER 
Fig. 1. The relation between cation exchange 
capacity in milliequivalents per 100 grams and plastic 
number of gray hydromorphic soils. 
city of the soil and the plastic number. This 
relationship is very significant. Statistical 
analysis of the data shows a correlation co- 
efficient of .697. 
The data presented in Figure 2 show the 
relationship between per cent magnesium 
saturation and plastic number. There appears 
to be no real relationship between these 
factors. Likewise, there is no relationship be- 
tween the ratio of exchangeable calcium to 
exchangeable magnesium and the plastic 
number. It is apparent that, since there is an 
observed relationship between per cent mag- 
nesium saturation and a dispersed condition 
of the soil, some other soil factor must play a 
major role in the development of the plastic 
properties of the clay. 
The relationship between the organic mat- 
ter content of the soil and the plastic number 
of the soil is shown in Figure 3. A correlation 
coefficient of .726 indicates a highly signifi- 
