396 
Journal of Agricultural Research 
Vol. XXII [, No. 6 
It is known that the presence of considerable phosphorus affects the 
accuracy of the colorimetric thiocyanate method for the estimation of 
iron. The following experiment was performed to determine whether 
the amount of phosphorus contained in seeds was enough to affect the 
estimation of iron by the thiocyanate method. Graduated portions of 
a standard solution made by dissolving 5 gm. of potassium phosphate 
(KH 2 P 0 4 ) in 100 cc. of water were measured out into a series of test 
tubes. The phosphorus contained in the different tubes varied from an 
amount much less than that found in seeds and gradually increased 
until the phosphorus content was several times this amount. To the 
tubes containing the different concentrations of phosphorus were added 
equal amounts of the necessary reagents including 2 cc. of a standard 
ferric iron solution, and the red color produced compared with the color 
developed in a tube containing an equal amount of all of the reagents 
used in the experiment except phosphorus. 
No observable effect on the color of the solution could be detected 
until the phosphorus content was approximately .05 gm., an amount 
which is much in excess of that contained in an aliquot necessary for 
the estimation of iron in seeds. The color produced with thiocyanate 
in the presence of greater concentrations than .05 gm. of phosphorus 
was yellowish red instead of blood red as was produced with lower con¬ 
centrations of phosphorus. 
The results obtained represent the amounts of iron and manganese 
contained in the moisture-free seeds. 
Table I .—Percentages of iron and manganese found in the different species of seeds 
WHEAT 
Variety. 
Fe. 
Mo. 
Big Flame . 
Per cent . 
O. OO31 
. 0036 
. OO3 2 
.0051 
.0043 
.0032 
.0039 
. OO41 
. 0040 
. 0042 
Per cent . 
0. 0043 
.0049 
. 0043 
.0049 
.0038 
. 0061 
. 0036 
.0037 
.OO73 
.0043 
Dawson. 
Gold Coin. 
Gypsy . 
Deitz. 
Nebraska No. 60. 
Kanred. 
Red Wave. 
Ghirka. 
Mutant (Nebr. No. 28). 
Average. 
.0039 
.0047 
SPRING OATS 
White. 
0. 0046 
. 0049 
. 0078 
. 0062 
.0034 
. 0052 
.0034 
. 0042 
0.0058 
. 0048 
.0035 
.0038 
. 0048 
. 0060 
. 0052 
.0052 
Do. 
Do. 
Black. 
Burt. 
Rust proof. 
Mixed. 
Victory. 
Average. 
. 0050 
. 0049 
