40 
BULLETIN 62, HAWAII EXPERIMENT STATION 
Tarle 18. — Comparison of the detailed hydrometer method and the pipette 
method of mechanical soil analysis 
Soil 
No. 
Method 
Hydrometer 
Pipette 
Hydrometer 
Pipette 
Hydrometer 
Pipette 
Hydrometer 
Pipette 
Hydrometer 
Pipette 
Hydrometer 
Pipette 
Mechanical analysis 
Colloids 
< (0.002 
millimeter) 
Per cent 
49.3 
51.5 
63.3 
66.6 
23.3 
23.1 
28.3 
32.5 
30.0 
30.1 
59.9 
59.6 
Very fine 
silt (0.005- 
0.002 milli- 
meter) 
Per cent 
8.0 
5.8 
12.0 
7.4 
12.0 
16.2 
18.0 
16.8 
18.0 
23 
Fine silt 
(0.01-0.005 
millimeter) 
Per cent 
7.0 
8.7 
6.0 
6.4 
10.0 
10.7 
10.0 
8.7 
17.0 
20.6 
Silt (0.02- 
0.01 milli- 
meter) 
Per cent 
7.0 
8.8 
5.0 
3.9 
8.0 
9.1 
6.0 
8.0 
23.0 
14.7 
Sand 
X0.02 
millimeter) 
Per 
cent 
28.7 
25.2 
13.7 
15.7 
46.7 
40.9 
37.7 
34.0 
12.0 
11.2 
The figures given in Table 18 show that the agreement in this case 
is much closer than in the case of the rapid hydrometer method. 
The over-all averages for the five soils, Nos. 2, 6, 37, 42, and 48, com- 
pare for the different fractions as follows : Colloids, 38.8 and 40.7 per 
cent; very fine silt, 13.6 and 13.9 per cent; fine silt, 10 and 11 per 
cent ; silt, 9.8 and 8.9 per cent ; and sand, 27.8 and 25.4 per cent. In 
each case the first figure given was by the hydrometer method and 
the second by the pipette method. 
SUMMARY 
Data relative to the origin, formation, and composition of tropical 
Hawaii soils are given. 
Physical characteristics of 21 soils which were selected for the 
investigation are described. 
Mechanical analyses of a few typical soils, with special reference 
to the fine fraction, are given. Variations in apparent and real spe- 
cific gravities are pointed out. Hygroscopic and capillary moisture, 
moisture-holding capacity, and moisture equivalent of these soils 
were determined and correlated with the texture and organic-matter 
content. The amount and distribution of organic matter is a 
determining factor in moisture relationships. 
A considerable portion of the organic material is often in the non- 
colloidal fraction. With soils the organic content of which is 
small, the textural conditions and the chemical composition are the 
determining factors. Sometimes large differences exist in the silica 
sesquioxide ratio of the different fractions in any one soil. 
Experimental results on the dispersing qualities of typical Ha- 
waii soils are given. For mechanical study the electrical stirrer 
was found to be far superior to either of the methods of shaking or 
rubbing. For chemical treatment prior to dispersion it was found 
that in most cases cold twentieth-normal hydrochloric acid is satis- 
factory for the removal of calcium, that the destruction of organic 
matter with hydrogen peroxide is not necessary, and that sodium 
carbonate is the best agent to aid deflocculation. 
