PHYSICAL PROPERTIES OF HAWAII SOILS 15 
and enabling the reader to interpret one method of analysis in terms 
of another. These curves represent six typical Hawaii soil types. 
Curves Nos. 2 and 31 represent certain heavy types, and curve No. 
15 represents certain light types of soil. 
SPECIFIC GRAVITY 
In view of the fact that the true specific gravity of soils had to be 
used in several phases of the investigation, especially those involving 
the use of Stokes' formula of settling particles, it became desirable 
to determine the magnitude of variations in the specific gravity of 
Hawaii soils. 
In soils formed from siliceous rocks under arid or semiarid condi- 
tions, such as are most of the mainland soils, containing large 
amounts of quartz and feldspar and only a small amount of iron- 
bearing minerals and a small percentage of organic matter, the 
specific gravity varies between the narrow range of 2.6 and 2.7. 
This is due to the fact that the quartz and the feldspar making up 
the larger part of the mineral portion have a specific gravity of 2.65 
and 2.57, respectively. Compounds causing a deviation in specific 
gravity from these figures are manganese, iron, and aluminum com- 
pounds, and organic matter. Table 1 shows the modifying effect 
upon the specific gravity of soils of these compounds when they are 
present in larger amounts. 
In view of the above-mentioned facts, it is natural to expect main- 
land soils and tropical volcanic soils to exhibit considerable difference 
in specific gravity. It has been shown that with submicroscopically 
porous materials varying results are obtained when different liquids 
are used in the determinations of true specific gravity. In these 
determinations water and toluol were used, but in applying the fig- 
ures to Stokes' law the specific gravity as determined in water was 
used. The determinations were made as follows : 
The soil material was ground to pass a 60-mesh sieve and was 
dried in an electric oven at 110° C. for at least 18 hours. A 50 cubic 
centimeter soil pycnometer was half filled with recently boiled dis- 
tilled water and weighed. From 6 to 8 grams of the oven-dried soil 
was added, the whole weighed and then boiled for five minutes to 
expel any air occluded in the interstices of the soil particles. When 
the pycnometer had cooled and the soil particles had settled, leaving 
the supernatant liquid clear, it was filled with water to the point 
of overflow. The pycnometer and contents were brought to the 
temperature at which the determinations were made (30° ) , the ground- 
glass stopper was inserted, the liquid which had overflowed was 
removed, and weighing was quickly done. Duplicate determina- 
tions made in this manner usually checked within 0.05. 
In several instances the true specific gravity was determined, 
toluol being used. In most cases the agreement was good, the aver- 
age being 2.88 in toluol as compared with 2.8 in water, where both 
determinations were made. In determining the apparent specific 
gravity or volume weight, the same soil material was used as in the 
true specific gravity determinations. A tared glass cylinder grad- 
uated to 50 cubic centimeters was filled with the soil to the upper 
mark, dropped 4 to 6 inches a number of times until compacting 
was no longer noticeable, when the volume was noted and the soil 
with the cylinder weighed to 0.1 gram. 
