14 
The results of the silica determinations in the water extract are 
rather inconsistent, but the average shows the highest solubility at 
ignition. It will be observed that the data obtained with fifth-normal 
nitric acid disclose some very interesting facts which show that an 
increase in solubility of silica in dilute nitric acid in Hawaiian soils 
is produced upon heating to ignition. Furthermore, the tendency 
points toward a general increase in solubility with increase in tempera- 
ture. Attention is called to the fact that the soils high in magnesia 
show the greatest solubility of silica in dilute nitric acid. An excep- 
tion in this particular is found in sample No. 164, a soil almost devoid 
of organic matter and containing a very high titanium, iron, and 
silica content. A further discussion of these results will be taken up 
following the table of alumina determinations in consideration of the 
relation of these two elements in the soil. 
ALUMINA. 
The following table shows the results obtained in the determinations 
of alumina in heated and unheated soils: 
Solubility of alumina in water and fifth-normal nitric acid. 
[Calculated on basis of dry soil.] 
' 
Soluble in water (parts per million). 
Soluble in fifth normal nitric acid (per 
cent). 
Soil No. 
Air dry. 
Dried at 
100° c. 
Dried at 
250° C 
Ignited. 
Air dry. 
Dried at 
100° C. 
Dried at 
250° C 
Ignited. 
74 
11.1 
7.5 
4.8 
16.6 
19.1 
7.6 
17.6 
15.3 
10.3 
4.4 
2.9 
4.9 
3.2 
9.5 
1.1 
17.6 
12.7 
13.8 
12.8 
9.0 
19.6 
6.3 
6.6 
.7 
10.3 
9.5 
9.5 
14.5 
12.8 
17.6 
16.1 
4.8 
28.5 
11.9 
1.7 
5.8 
22.3 
5.0 
3.7 
17.1 
17.7 
12.2 
20.9 
28.9 
38.0 
8.8 
2.1 
2.6 
0.291 
.060 
.583 
.874 
.266 
.169 
.420 
.679 
.295 
2.261 
.308 
.979 
0.292 
.048 
.675 
.598 
.292 
.133 
.509 
.661 
.314 
2.031 
.347 
1.757 
0.318 
.139 
.676 
.584 
.691 
.444 
1.057 
1.413 
.882 
2.208 
1.192 
1.966 
0.9.56 
164... 
.288 
9 
1.034 
292 
1.055 
290... 
.749 
405 
.897 
416 
1.515 
417 
1.495 
406 
1.425 
428 
2.244 
426 
1.571 
448 
2.757 
It will be observed from this table that the alumina is affected in 
very much the same way as the silica. The results, while somewhat 
inconsistent, show an increase in water-soluble alumina in the heated 
soils, the number showing increase of alumina by heating from 100 to 
250° C, being about the same as in passing to ignition. The effect of 
heat upon the solubility of this element in dilute nitric acid is very 
marked and increases regularly with increase in temperature. There 
is scarcely any correlation between the solubility of the alumina and 
the total amount of silica present. However, it is worthy of note 
that there seems to be a relation between the solubility of the alumina 
in dilute nitric acid and the volatile matter (organic matter and 
combined water) existing in the soil, as will be readily seen from the 
