11 
the iron from 9.61 to 30.50, and the alumina from 26.52 to 39.05 per 
cent. As compared with silt and coarser particles, fine silt is higher 
in silica and alumina and lower in iron. 
Clay. — The smallest grains, 0.002 millimeter or less in diameter, in 
Hawaiian soils are referred to as clay only in so far as this term ap- 
plies to the size of the soil particles. Grains taken from a red clay 
soil showed diameters ranging from 0.00165 to 0.00065 millimeter. 
As regards the composition of Hawaiian clay, silica varies from 12.48 
to 47.75 per cent, ferric oxid from 10.01 to 25.16 per cent, and alumina 
from 27.53 to 48.42 per cent. With the exception of titanium, the 
other constituents do not vary greatly. 
The colors of the clay samples were red, yellow, and brown, the 
depth of each color varying considerably. The yellow clays were 
lowest in iron and contained the least combined water. This latter 
fact does not necessarily hold for yellow soils. The clay separated 
from soil No. 448, a yellow type, had a red color before ignition. All 
clays had the same depth of redness after ignition. 
The properties of these clays vary as widely as their composition. 
Soil Xo. 291, the highest in silica, was as hard and brittle as cement 
upon drying. The other clays all remained in the form of a fine 
powder on ignition. The most noticeable of the peculiar properties 
of these clays is the action toward coagulants. Analyses of the co- 
agulable and noncoagulable grains are submitted herewith. Four 
samples of soil were treated according to the official method for de- 
termining humus. Treatment with ammonium carbonate of the 
humus extract, which contained large amounts of clay, resulted in a 
partial coagulation. The results are given in the following table : 
Composition of clay coagulated and not coagulated from the humus extract by 
ammonium carbonate. 
Coagulated. 
Not coagulated. 
Constituents. 
Soil 
No. 99. 
Soil 
No. 101. 
Soil 
No. 106. 
Soil 
No. 108. 
Soil 
No. 99. 
Soil 
No. 101. 
Soil 
No. 106. 
Silica 
Per cent. 
29.00 
37.38 
33.12 
Pa cent. 
22.24 
34.93 
37.33 
Per cent. 
25.33 
34.91 
30.42 
Per cent. 
23.80 
37.84 
31.16 
Per cent. 
38.21 
23.40 
37.39 
Per cent. 
38.29 
18.14 
43.57 
Per cent. 
46.01 
Alumina 
21.42 
Ferric oxid 
32.57 
Some Hawaiian clays are almost completely coagulated by am- 
monium carbonate but it appears that the action of this salt is greatly 
inhibited in clays high in iron and silica, but low in alumina. The 
clay in soil Xo. 108 was entirely coagulated, hence only analysis of 
coagulated grains is tabulated. 
As regards the relation between the composition of the clay and 
coarser grains, silica and alumina vary between wider limits than in 
the silts. The clay also contains the highest silica content. 
