27 
of salts is very similar and also tends to increase this property to a 
slight extent. 
The two physical properties of soils known as cohesion and ap- 
parent specific gravity are more or less dependent upon and governed 
by the same factors, and it is shown in the table that the effect of 
varying moisture contents and addition of salts is similar. Both 
reach a minimum at the point known as that of optimum moisture 
content, which is conceded to be the stage most favorable to plant 
growth. Hence these properties are of special significance in soil 
investigations. 
/O /3 20 
MO/STUP£: CONTENT 
Fig. 3.— Relation between cohesion, apparent specific gravity, and moisture content of soils. 
In classifying the Hawaiian types of soil according to these prop- 
erties, the clay soil possesses the highest cohesive properties, the man- 
ganese silt next, the sandy soil third, while the lowest and hence the 
most easily cultivated is the silty soil, No. 573. The same relation 
applies also to the apparent specific gravity and is true not only at 
the optimum moisture content but also on the air-dry soils. The 
curve shown in figure 3 well illustrates the relationship existing 
between these two properties of Hawaiian soils. At the lower 
moisture contents the curves diverge considerably while above a given 
point they again foUow similar lines. 
