Aug. 1, 1925 
Colloidal Silica and Efficiency of Phosphates 
253 
cultures was recently offered by Lemmermann and Wiessmann {20 ). 
They suggested that the beneficial effect of certain forms of silica 
is due, not to its action on the soil, but to a direct action on the plant. 
This view will be discussed later. 
Analyses were made of the plants where sufficient material was 
available, by the methods of the Association of Official Agricultural 
Chemists ( 1 ). The results are given in Table II. 
Table II. — Assimilation of silica and phosphoric add by millet grown with acid 
phosphate or rock phosphate with and without silica gel 
In the oven-dry 
substance of 
the plants 
In the 
pure ash 
Present in 7 
plants (from 
1 pot) 
'O.S'O 
a 
ill 
W 0 . ® 
Pot 
Nos. 
Differential treatment of pots 
Pure ash, C, 
CO 2 , and 
sand free 
5 
02 
s-/ 
s 
3 
GO 
Phosphoric 
acid (P 2 O 5 ) 
O 
02 
v-x 
1 
02 
Phosphoric 
acid (P 2 O 6 ) 
O 
m 
CS 
.2 
02 
0 
ftw 
W_. 
©!2 
0 
* 
« {> 
all 
3S.S 
«« P.P. 
O 
7,8,9____ 
0.06 gram P 2 O 5 , acid phosphate... 
P.ct. 
9.27 
P.ct. 
0.96 
P. ct. 
0.40 
P.ct. 
10.33 
P.ct. 
4.07 
Gm. 
0.0426 
Gm. 
0.0177 
P.ct. 
29.5 
10,11,12_ 
0.12 gram P 20 s f acid phosphate.. 
6.48 
.59 
.47 
9.14 
7.34 
.0536 
.0427 
35.7 
13,14,15. 
0.24 gram P 2 O 5 , rock phosphate.. 
15.09 
4.39 
.59 
29.05 
4.02 
.1681 
.0226 
9.4 
19,20,21. 
0.06 gram P 2 O 5 , acid phosphate, 50 grams 
silica gel ..... 
9.66 
2.54 
.43 
26.34 
4.49 
.1361 
.0230 
38.3 
22, 23,24. 
0.24 gram P 2 O 5 , rock phosphate, 50 grams 
silica gel..... 
8.78 
3.08 
.54 
35.10 
6.02 
.2914 
.0511 
21.3 
25.. 
0.24 gram P 2 O 5 , rock phosphate, 150 
grams silica gel.... 
8.40 
2.74 
.57 
32.47 
6. 55 
.2493 
.0519 
21.6 
The percentages of phosphoric acid in the dry substance generally 
increased with the growth. However, the plants grown with rock 
phosphate contained a somewhat higher percentage of phosphoric 
acid in the dry substance than the plants grown with acid phosphate, 
although they contained approximately the same percentage of 
phosphoric acid in the ash as tne acid-phosphate plants of equivalent 
growth. The percentage of phosphoric acid in the plant is doubtless 
influenced to some extent by the rates at which the plants grew 
during different stages of their development, or by slightly different 
stages of maturity at the time of harvesting. 
During the latter part of the growing period the rock-phosphate 
plants appeared to be picking up slightly on the acid-phosphate 
plants; owing to increased excretion of carbon dioxide or to some 
other cause, they doubtless obtained phosphorus at a somewhat 
faster rate toward the end of the growing period than at the start. 
The assimilability of the phosphorus of acid phosphate, on the 
other hapd, might have been more constant. Such differences 
would account for the different percentages of P 2 0 5 in the dry sub¬ 
stance of the plant. 
Addition of silica gel increased the percentage of silica in the 
acid-phosphate plants by more than one and a half times. In the 
case of the rock-phosphate plants, however, the silica gel diminished 
the percentage of silica in the dry substance and raised the silica in 
the ash relatively little. 
The quantities of phosphoric acid and silica present in seven 
plants (the yield from one pot) are significant in indicating how 
silica gel increased the yield. It will be noted that the quantities 
