30 
BULLETIN 1311, U. S. DEPARTMENT OF AGRICULTURE 
The table shows that silica, iron, and alumina were dialyzed 
through the parchment membrane, as well as lime, magnesia, soda, 
potash, and sulphur. There were only small quantities of lime, soda, 
and sulphur in the colloid, and practically the total quantities of 
these constituents were extracted by the dialysis. The quantities 
of these elements found in the diffusate are doubtless limited by the 
quantities present in the colloids, and colloids containing more 
lime, soda, and sulphur probably would yield a greater concentra- 
tion of these constituents. The data indicate that the magnesia and 
potash are retained with considerable tenacity, although they are 
removed by dialysis more readily than the silica, alumina, and iron. 
Undoubtedly more material could be removed by a longer dialysis, 
and under this condition the dialyzed residue would contain little 
else than silica, alumina, and iron. The colloid and water used in 
this experiment were not sterile. Therefore the quantities of the 
various constituents found in the diffusate may differ from what 
would be found if bacterial action were eliminated. 
The property of the colloidal matter of retaining the monovalent 
and divalent bases with considerable tenacity is further brought out 
by the analyses of successive fractions of colloids from the same 
soil. (See Table 5 and footnote 21.) Particularly large volumes of 
distilled water were used in extracting these colloids. 
Oxalic acid. — The very pronounced red and yellow colors of some 
of the colloidal materials isolated suggests that some form of 
uncombined iron oxide might be present. It is well known that 
oxalic acid is one of the best solvents for iron rust, and it possesses 
a further advantage for diagnosing free iron oxide in soil colloids in 
that it is, in comparison with the common mineral acids, a weak acid 
and would probably have less solvent effect on the other constituents 
of the colloidal matter. For these reasons various soil colloids were 
tested with a dilute solution of oxalic acid. An amount of air- 
dried colloid equivalent to 2 grams of moisture-free material was 
shaken with distilled water till the mass appeared homogeneous. 
It was allowed to stand over night, and the following morning 2 
grams of oxalic acid were added in solution and the volume made up 
to 200 cubic centimeters. After digesting on the steam bath for 1 hour 
the flask being shaken every 5 to 10 minutes, the solution was filtered 
through an acid-washed Pasteur-Chamberland filter. The silica, 
alumina, and iron present in the filtrate are shown in Table 8. 
Table 8. — Solubility of the colloidal material in 1 per cent oxalic acid 
Description of colloidal material 
Fe20.3 dissolved | AI2O3 dissolved 
I 
Si02 dissolved 
No. 
Name 
Color 
Part of 
whole 
colloidal 
material 
Part of p , of ; Part of 
total : whole total 
quantity, JSJJELi quantity 
Fe 2 3 JSEKX A1 *°3 
present matenaI present 
Part of 
whole 
colloidal 
material 
Part of 
total 
quantitv 
Si0 2 
present 
1 
5 
Carrington loam 
Cecil clay loam 
Lufkin clay 
Black 
Red .. 
Per cent 
3.81 
6.48 
2.43 
5.70 
9.00 
7.60 
7.59 
3.99 
Per cent i Per cent 
49. 2 1 5. 47 
64.7 9.60 
27.0 1 8.S4 
50.1 i 6.31 
58. 2 ! 7. 60 
75. 2 7. 89 
73. 10. 40 
41. 7 6. 24 
Per cent 
24.3 
24.6 
38.5 
20.2 
30.3 
25.2 
Per cent 
5.34 
2.80 
6.79 
3.32 
4.38 
4.49 
Per cent 
11.9 
8.8 
?0 
Cream ... . 
12.3 
27 
30 
Norfolk fine sandy loam 
Ontario loam ... 
Yellowish brown . . 
Dark reddish brown 
Red... 
8.7 
10.2 
32 
Orangeburg fine sandy 
loam. 
Susquehanna clay 
Wabash silt loam 
11. 1 
40 
44 
Brilliant red 
Black 
27. 6 3. 46 
29. 9 5. 03 
9.4 
9.9 
