16 
Denrtrification refers, of course, to any transformation which nitrates 
may undergo, such as its conversion into nitrate, ammonia, free nitro- 
gen, or protein. 
ABSORPTION OF FERTILIZER SALTS BY FRESH AND AIR-DRIED 
SOILS. 
The type of soil occurring in greatest abundance on the islands is a 
highly ferruginous red clay (No. 517). For this reason it was de- 
cided to make a series of percolations using both soil and subsoil of 
this type in the fresh and air-dry condition, using sodium nitrate, 
ammonium sulphate, potassium phosphate, and calcium phosphate. 
The fresh soil contained 19.7 per cent moisture; the fresh subsoil, 
24.4 per cent moisture. 
The method employed was essentially the same as that used in the 
previous series except that it was found to be necessary to use only 50 
grams of soil with the phosphates in order to effect a passage of the 
solution through the soil column. Also the concentration of the solu- 
tion was increased in an attempt to saturate the soil with phosphates. 
Determinations were made of the solubility in distilled water of the 
phosphate in the saturated soil, and it was found to be negligible. 
On passing distilled water through a column of 50 grams of soil and 
determining the percentage of phosphoric acid in each 100 cubic 
centimeters passing through, only a faint trace was detected. 
ABSORPTION OF PHOSPHORIC ACID. 
The following table shows the absorbing power of the red clay soil 
for phosphoric acid when applied as monopotassium phosphate: 
Absorption of phosphoric acid from a solution of KH 2 PO^. 
[Expressed in parts per million of PO4 in the percolate.] 
P0 4 IN SOLUTION, 800 PARTS PER MILLION. 
Percolates of 
100 cc. each. 
Fresh 
soil. 
Fresh 
subsoil. 
Air-dry 
soil. 
Air-dry 
subsoil. 
Percolates of 
100 cc. each. 
Fresh 
soil. 
Fresh 
subsoil. 
Air-dry 
soil. 
Air-dry 
subsoil. 
100 
44 
38 
124 
72 
128 
165 
Trace. 
21 
22 
Trace. 
27 
29 
400 
180 
220 
290 
260 
340 
340 
24 
32 
200 
500 
300 
600 
P0 4 IN SOLUTION, 1,400 PARTS PER MILLION. 
500.. 
600.. 
700.. 
800.. 
900.. 
1,000. 
1,100. 
1,200. 
410 
390 
400 
430 
530 
620 
460 
460 
500 
500 
400 
560 
150 
325 
350 
560 
675 
825 
290 
325 
360 
665 
675 
825 
1,300. 
1,400. 
1,500. 
1,600. 
1,700. 
1,800. 
1,900. 
2,000. 
950 
900 
750 
750 
725 
875 
675 
875 
850 
825 
750 
750 
600 
850 
675 
825 
P0 4 IN SOLUTION, 1,025 PARTS PER MILLION. 
1,500 
700 
675 
600 
700 
675 
600 
2,800 
950 
950 
1,750 
3,250.... 
600 
600 
2,250 
3,300... 
1,025 
1,025 
2.500 
750 
675 
675 
675 
3,800 
4,300 
950 
1,025 
950 
1,025 
2,725 
