Dec. 18, 1916 
519 
Assimilation of Iron by Rice 
showed that practically all the iron added to this solution was precipitated. 
As this solution evidently had less precipitate than some others, the 
character of the precipitate probably varied somewhat in the different 
solutions. The amount of iron present in the filtered solutions in which 
plants had grown also failed to correspond to the growth of plants. 
Table XII.— Quantity of iron (in grams) in filtered solutions at different times after 
addition of iron to solution, with and without growth of plants in the solution 
Quantity of iron in 1,000 liters of filtered 
solution. 
Nutrient 
solution. 
Source of iron. 
8 
1 
No plants in solu¬ 
tions. 
Plants grown in solutions. 
1 
2 
3 
4 
5 
6 
7 
8 
9 
Acid.... 
.do.. 
.do.. 
Neutral. 
.do.. 
.do.. 
Alkaline 
.do.. 
.do.. 
Ferrous sulphate. . . 
_do. 
Ferric citrate. 
Ferrous sulphate. . . 
_do. 
Ferric citrate. 
Ferrous sulphate. . . 
....do. 
Ferric citrate. 
< 
o. 07 
•30 
•03 
•49 
•03 
.87 
. 40 
•05 
• 57 
o. 05 
•43 
.07 
1. 27 
• 17 
1. 63 
i- 33 
. 18 
1. 00 
o. 05 
• 23 
•05 
i- i 3 
. 10 
i- 33 
.86 
93 
0.03 
.07 
•03 
.80 
.07 
.80 
. 60 
• 53 
The growth of plants did not agree with the quantity of iron found in 
the filtered solutions because, without doubt, colloidal iron, as well as 
truly soluble iron, was present. Previous work having shown that 
colloidal iron was not available for rice (6), the determinations in Table XII 
did not represent the available iron. At this great dilution it was, of 
course, impossible to distinguish analytically between colloidal and soluble 
iron or between ferrous and ferric iron. While the existence of colloidal 
iron could not be definitely demonstrated in these solutions, it is well 
known that most ferric salts in dilute solutions are more or less com¬ 
pletely hydrolytically dissociated into colloidal ferric hydroxid and the 
acid. Moreover, a test showed that dialyzed iron could not be distin¬ 
guished from distilled water with regard to color or filtration when used 
in somewhat greater concentration than iron was present in the above 
filtrates. 
In solutions where ferric iron was used iron was probably present in the 
following forms: (i) As precipitated ferric phosphate and hydroxid, (2) 
66848 °— 16-—2 
