28(>

QVANTITA TIVK AGRICULTURAL A

Great reliance is placed upon culture experiments, comparing
the effect of using different fertilizers with plants under otherwise*,
identical conditions. However, such experiments are slow and
they have no value whatever for analytical purposes. An
approximate distinction can be made by the use of potassium
permanganate in either neutral or basic solution. Readily
decomposable materials are oxidized and the nitrogen is con-
verted into ammonia. It is not yet entirely clear as to how much
reliance is to be placed upon these methods but they have been
adopted by the Association of Official Agricultural Chemists.
Determination of Total Water-insoluble Organic Nitrogen.—Place 1 gm
of the material upon an 11-cm filter paper and wash with recently boiled
water at room temperature until the filtrate measures 250 cc. Dry and
determine nitrogen in the residue by the Kjeldahl method, making a blank
determination to correct for the nitrogen of the filter paper.
Determination of Water-insoluble Organic Nitrogen, Soluble in Potas-
sium Permanganate.—-Place a weighed quantity of the fertilizer, equivalent
to 50 ing of the water-insoluble organic nitrogen as determined above, on a
moistened 11-crn filter paper and wash with recently boiled water at room
temperature until the filtrate measures 250 cc. Transfer the insoluble
residue with 25 cc of water (at about 30°) to a 400-ce low-form heakcr, add
1 gm of sodium carbonate, mix arid add 100 cc of 2-per cent potoHStum
permanganate solution. Cover with a glass and immerse for .'$0 minutes
in a water or steam bath so that the level of the liquid in the }maker is below
that of the heating medium. Keep at 100°, stirring twice at intervals of
10 minutes each. At the end of this time remove from the bath, acid imme-
diately 100 cc of cold water and filter through a heavy 15-crn folded filter.
Wash with small quantities of cold water until the filtrate nieamireH about
400 cc. Determine total nitrogen, in the residue and filter by either of the
methods already described (not modified for nitrates) making a blank deter-
mination to correct for the nitrogen contained in the filter. The nitrogen
thus obtained is the inactive watcr^inxoluhle organic nitrogen. Subtract this
per cent from the total water-insoluble organic nitrogen. The remainder is
the per cent of organic, nitrogen soluble in neutral permanganate. AH already
explained, this is an approximate measure of organic nitrogen easily avail-
able for plant food.
Determination of Organic Nitrogen Soluble in Basic Permanganate.—
Prepare a solution of potassium permanganate by dissolving 25 gm in about
100 cc of water; dissolve 150 gm of sodium hydroxide in 500 cc of water and,
after thin has cooled, mix with the potassium permanganate solution and
dilute the whole to 1000 cc.
(a) Mixed Fertilizers.—Place an amount of material equivalent to 50 ing
of total water-insoluble organic nitrogen, determined as above, on a filter
paper and wash with water at room temperature until the filtrate measures
about 250 cc.