18 BULLETIN 6 2, HAWAII EXPERIMENT STATION 
they have developed high moisture-holding power no doubt due to 
excessive hydration and probably to the structure of the colloidal 
complexes in which their high organic matter plays no small role. 
Some of these soils hold as much as 500 per cent of water figured on 
the dry basis (33, p. J$3). Upon being air dried, however, they do 
not return to their former physical condition when moistened with 
water — a fact indicating the irreversible nature of the reactions tak- 
ing place in the colloidal phase. This fact also indicates that these 
soils in situ have never been deprived of their moisture to any 
appreciable degree. 
The hygroscopic-moisture content was determined by exposing the 
powdered soil to an atmosphere saturated with water vapor over 
3.3 per cent sulphuric acid at 30° C. for six days, when the gain 
in weight was determined by drying to constant weight. The va- 
rious factors entering into this determination, such as effect of time, 
vapor pressure, temperature, degree of vacuum, and size of particles, 
have been thoroughly investigated by Middleton (26, p. Jf55), whose 
findings were observed in these determinations. The amount of 
hygroscopic water which the soil holds under ordinary air-dry con- 
ditions was also determined. The soil was brought to a constant 
weight by drying it at room temperature, 28° to 32° C, at a relative 
humidity of approximately 50 per cent, and the moisture content was 
determined by drying in the oven at 110° for 18 hours or longer. 
The percentage of moisture was calculated on an oven-dry basis, 
both in this and in the other moisture-constant determinations. 
The capillary moisture was determined by filling a tared glass 
tube, 1 inch in diameter by 15 inches in length and fitted with a 
copper-gauze bottom, with air-dried soil to the 12-inch mark, and 
dropping the tube repeatedly 4 to 6 inches until compacting was 
no longer noticeable, when the weight was recorded. The base of the 
tube was then placed in a pan of water, until the water rose to the 
surface of the soil. Then the tube was removed from the water, 
placed on a blotting pad to remove excess moisture, and weighed. 
The time required for the surface to become moist was also recorded. 
The moisture-holding capacity was determined on the same sample 
on which capillary moisture was determined. The tube holding the 
soil plus capillary moisture was placed in a cylinder of water the 
level of which was the same as that of the soil, and was allowed to 
remain until the soil had become thoroughly saturated. At this 
point the tube was removed, drained of excess water, and weighed. 
The moisture equivalent was determined according to the specifi- 
cations of Briggs and McLane (8, p. lJfi). Approximately 30 grams 
of soil on an oven-dried basis was placed in the centrifuge cups the 
wire-gauze bottom of which was first covered with a sheet of filter 
paper. The cups of soil were then thoroughly moistened by placing 
them in a shallow pan containing water to a depth of one-fourth to 
one-half of an inch. The cups were allowed to stand overnight in 
the pan during which time they were suitably covered to protect 
against evaporation. 
The time of centrif uging was 30 minutes at a rate of 2,440 revolu- 
tions per minute at the end of which the moisture retained was 
determined by drying to constant weight at 110° C. 
The various moisture constants obtained are given in Table 5 and 
are shown graphically in Figure 8. 
