FERTILIZERS 287

(6) Raw Materials.—Place an amount of material equivalent to 50 mg
of total water-insoluble organic nitrogen, determined as above, in a small
mortar. Add about 2 gm of powdered rock phosphate (to facilitate the
washing process) mix thoroughly by grinding, transfer to a filter paper and i
l\
When much oil or fat is present, it is well first to wash several times with
ether and to allow to stand until the odor of the latter has disappeared before
extracting with water.
Dry the residue from either class of materials at a temperature not exceed-
ing 80°- and transfer from the filter to a 500-cc Kjeldahl digestion flask.
Add 20 cc of water, about 1 gm of crushed porcelain to prevent bumping
and about 1 gm of paraffin to prevent frothing. Add 100 cc of the basic
permanganate solution and connect with the tin condenser, the lower end of
which dips into 50 cc of fifth-normal acid.
Digest slowly for at least 30 minutes, below the distillation point, with a
very low flame, using wire gauze and asbestos paper between the flask and
flame. Gradually raise the temperature and, after any danger of frothing has
passed, distill until 95 cc of the distillate (145 cc of distillate plus acid)
is obtained, then titrate as usual. If a tendency to froth is noticed lengthen
the digestion period. During the digestion gently rotate the flask occasion- 11
ally, particularly if the material shows a tendency to adhere to the sides of j.|
the flask.
The nitrogen thus obtained is the active water-insoluble organic nitrogen.
Potassium.—Most soils contain orthoclase (potassium alumin-
ium silicate) but the potassium of this is unavailable or so slowly
available that the supply from, this source is often not sufficient
to meet the needs of the rapidly growing plant. The need is
especially great in muck soils for plants such as potatoes or
sugar beets, which require a large amount of potassium.
Sodium compounds can take the place of potassium to only a
very slight extent, if at all." It has been noted that in places
where sodium nitrate has been used for some time to supply
nitrogen, much less than the usual response could be obtained
from potassium fertilizers. It is assumed therfore, that the
sodium of the fertilizer tended partly to perform the function of
potassium. The effect of potassium starvation is more definite I!
than that resulting from phosphorus deficiency and it is indicated
by the color of the plant becoming abnormal and dull, the ntcrn
weak and the ability to manufacture starch at the normal rate
lacking.
Preparation of Fertilizer Solution: (a) Mixed Fertilizers.—-Place 25 ^m of
the sample upon a 12.5-cm filter paper and wash with boiling wiitor unl.il the