40 
PACIFIC SCIENCE, January, 1947 
by titration with a standard acid. A blank 
determination was made by the same method, 
using only the chemical reagents. 
To determine the composition of the carbo¬ 
nates, another sample of soil was extracted 
with the amount of half-normal hydrochloric 
acid calculated as necessary to decompose the 
determined quantity of carbonates in the soil, 
this amount being based on carbonate-carbon 
dioxide determinations. To insure a slight ex¬ 
cess of the acid, 0.1 ml. was added. Previous 
work has shown that only the carbonates are 
attacked by this quantity of acid (Sherman, 
1937). The mixture w 7 as diluted with distilled 
water and then heated to boiling to insure the 
complete digestion of the carbonates. The mix¬ 
ture was filtered and the soil washed free of 
chloride with hot distilled water. Calcium and 
magnesium were determined in the filtrate by 
using the usual standard methods for these 
elements. 
EXPERIMENTAL RESULTS 
Samples of surface soils were collected 
from various parts of Lualualei Valley, Wai- 
anae Valley, and Makaha Valley on the island 
of Oahu, and in Table 1 is given the content 
of exchangeable calcium and magnesium in 
these soils. In every soil, magnesium consti¬ 
tuted a very appreciable part of the cations, 
accounting for 20 to 45 per cent of the total 
exchangeable cations present in the soil. 
Samples from a soil profile representing 
a typical area which showed indications of 
dolomitization were analyzed for composi¬ 
tion of the water-soluble salts, quantity of 
each exchangeable cation, and composition 
TABLE 1 
The Content of Exchangeable Calcium and Magnesium in Surface Soils from Makaha Valley, 
Waianae Valley, and Lualualei Valley on the Island of Oahu 
LOCATION OF SOIL 
pH 
EXCHANGEABLE 
Ca 
EXCHANGEABLE 
Mg 
RATIO 
Ca:Mg 
m.e./100 gm. 
m.e./lOO gm. 
Makaha Valley. 
7.3 
22.12 
16.06 
1.38 
Waianae Valley. 
7.1 
24.15 
19.69 
1.23 
7.4 
39.36 
13.62 
2.90 
6.3 
27.40 
14.21 
1.93 
6.9 
27.38 
19.05 
1.44 
7.3 
36.80 
14.69 
2.50 
7.3 
40.00 
14.79 
2.70 
Lualualei Valley ...... 
7.1 
56.80 
16.15 
3.49 
6.4 
29.40 
18.62 
1.58 
6.9 
31.98 
19.16 
1.67 
7.0 
26.10 
17.77 
1.47 
7.8 
33.89 
9.89 
3.43 
7.6 
37.42 
9.64 
3.88 
TABLE 2 
The Composition of the Water-soluble Salts of a Lualualei Valley Soil Which Contains 
Dolomitic Carbonates 
pH 
WATER-SOLUBLE SALTS M.E. PER 100 GM. SOIL 
RATIO 
DEPTH OF SOIL SAMPLES 
Ca 
Mg 
SO* 
Ca:Mg 
inches 
0 6. 
7.8 
0.84 
0.43 
0.52 
1.95 
6-12. 
7.7 
0.76 
0.43 
0.36 
1.77 
12 18. 
7.5 
0.72 
0.48 
0.40 
1.50 
18-24 . 
7.5 
0.80 
0.41 
0.41 
1.95 
24-30 . 
7.2 
8.48 
2.18 
10.10 
3.89 
30-36 . 
7.3 
26.60 
3.63 
30.12 
7.33 
36-42 . 
7.3 
26.78 
4.36 
31.08 
6.14 
