10 
No attempt was made to separate iron oxid and alumina, but the de- 
termination seems to vary considerably in the different soils. No. 313 
apparently increased in solubility with increase in time of extraction. 
If the abnormal figure, 53.5, be disregarded, the difference between the 
fresh, air-dried, and oven-dried soil is very slight. In the subsoil air 
drying produced a decrease in solubility, but the oven-dried were 
more soluble than the air-dried samples. The results from No. 319 
are discordant, but indicate the air-dried form to be the most soluble. 
Phosphoric acid. — This series is remarkably concordant and indi- 
cates an increase in solubility of this constituent upon drying in the 
oven and at the same time, without exception, shows an increase in 
solubility with increase in time of extraction. 
Manganese. — These results indicate an increase in solubility of 
manganese with increase in time of extraction and also an increase in 
solubility upon drying. Unfortunately the whole series of manganese 
determinations on the oven-dried samples was lost through accident. 
Lime. — While the results from the lime determinations are very 
inconsistent, the general average tends to show an increase in solu- 
bility upon heating in the oven and a maximum solubility in the one- 
hour period of extraction. This latter may be due, however, to sub- 
sequent precipitation in the longer extractions. 
Magnesia. — The table shows a marked consistency, especially with 
reference to the rate of increase in solubility of magnesia, due to 
drying. The concentration of the extracts from the fresh soils was 
least, with only one exception, while that from the oven-dried soils 
was greatest in most instances. While there is considerable varia- 
tion, the data indicate the most complete extraction in that of seven 
days' duration. 
Sulphuric acid. — The relative amounts of this constituent extracted 
show it to be slightly more soluble in the fresh soil, judging from the 
average of the series, although only slightly more so than in the 
oven-dried soil, and that the concentration is practically the same 
for the several periods of extraction. 
Potash. — The potash series shows this element to be much more 
soluble in the air-dry and fresh soils than in the oven-dried soils, 
while there is scarcely any difference in the solubility as induced by 
increasing the time of extraction from 24 hours to 7 days. 
The above results tended to establish the advisability of an arbi- 
trary extraction of not over 24 hours, and partly for this reason it was 
decided that the method at present in general use, namely, shaking 
for a period of 1 hour and allowing to settle for 24 hours would be 
suitable to our conditions. Owing to the mechanical texture of 
Hawaiian soils, caused by the presence in them of highly ferruginous 
clays, which assume a colloidal form if worked when too wet, it was 
found necessary to allow the extracts to settle and in every instance, 
except when heated to 250° C. or ignited, it was necessary to add a 
