PHYSICAL PROPERTIES OF HAWAII SOILS 35 
Columns 2 and 3 give the water vapor adsorbed, expressed on a 
dry basis, by soils and colloids, respectively. Column 4 gives the 
ratio adsorption per gram of soil to adsorption per gram of colloid 
multiplied by 100, or the computed percentage of colloids. For the 
sake of comparison, the percentage of colloids as determined in the 
mechanical analysis is given in column 5. 
The magnitude of adsorption varied considerably, both in soils 
and in colloids. In soils the adsorption ranged between 10 and 30 
per cent in round numbers, with an average of 18.4 per cent; whereas 
the adsorption of the colloids ranged between 12 and 33 per cent, 
with an average of 21.7 per cent. In several cases the percentage of 
adsorption of soil was nearly equal to, or even greater than, the per- 
centage of adsorption of the corresponding colloid. On the whole, 
the average adsorption of the 14 soils given in Table 15 is less than 
the average adsorption of mainland soil colloids, which was found 
co be about 30 per cent in certain types of soil. One of the reasons 
for this difference, other than for the difference in chemical compo- 
sition, may be due to the fact that in this investigation everything 
failing to settle out from suspension at the 0.002-millimeter limit 
according to Stokes' law was considered to be colloid; whereas in 
the case of the soils of the mainland the upper limit of the colloidal 
particle was about 0.0003 millimeter. The average amount of col- 
loid extracted from the above-mentioned 14 soils was around 13 
grams per 100 grams of soil, comprising about 42 per cent of the 
total colloids present as determined by the mechanical analysis. 
Obviously, a constant " adsorption per gram of colloid " factor could 
not be applied in this case to all the soils since the fluctuations in 
value were rather considerable. The percentage of colloids com- 
puted from the adsorptivities gives excessive results, in two instances 
the figure being above 100. Only in two instances is there a sem- 
blance of agreement with the colloids estimated in the mechanical 
analysis. 
In discussing these Very divergent results, certain relationships 
which were brought out earlier in this bulletin (pp. 23, 25) are 
called to the reader's attention. It was pointed out that the amount 
and distribution of organic matter and the chemical composition of 
the inorganic phase in the various soil fractions seem to be of such 
nature in many Hawaii soils as to preclude the use of the water- 
vapor adsorption method for computing the percentage of colloids. 
The figures obtained indicate that the above-referred-to assumptions 
made in connection with this method are not permissible for many 
Hawaii soil types containing high percentages of organic matter. 
The figures given in Table 8 indicate that a large part of the organic 
matter may be present in the silt, and even in the sand fractions, 
either as separate particles or as aggregates resisting dispersion, ex- 
hibiting high adsorptive properties. Furthermore, it is an estab- 
lished fact that particles show colloidal properties, even to a lesser 
extent perhaps, long before the arbitrary limit made for colloids 
or clay is reached. 
Davis (H, V- ®?6) finds that the dispersion of soils in the course of 
mechanical analysis may be so incomplete that the silt fraction will 
contain 25 to 97 per cent colloids in the form of aggregates, and that 
even the sand fraction may contain 2 to 25 per cent colloids in the 
