FERTILIZERS 283
Because of the differences in cost and availability of different
forms of nitrogen, it is often desirable to know the relative
amounts existing as nitrates, ammonia or organic forms in the
fertilizer. The following methods will give information of this
character.
Detection of Nitrates.—If sulphuric acid is added to a nitrate,
nitric acid will be set free. This will be reduced to nitric oxide
in the presence of ferrous sulphate, forming a brown ring ( |
(FeSOrN202 or FeS04-NO). jjf
! i'
Treat 5 gm of fertilizer with 25 cc of hot water, then filter. Mix about
3 cc of this solution with an equal volume of concentrated sulphuric acid
(free from nitrates) in a test tube and cool, then pour 2 or 3 cc of concen-
trated ferrous sulphate solution carefully down the side of the tube so that
the two liquids do not mix. In the presence of nitrates a brown or reddish
brown ring will form at the junction between the two solutions. If no color
forms immediately let stand 2 or 3 minutes.
Nitrogen of Ammonium Salts.—If a material containing
nitrogen in various forms is placed in water and heated with
magnesium oxide, ammonia is distilled and both nitrates and
protein nitrogen remain behind. Magnesium hydroxide is the
active agent:
MgO + H20 -> Mg(OH)2, (1)
Mg(OH)2 + 2NH4N03 -* Mg(N08)s + 2NH3 + H2O. (2)
The ammonia is absorbed in standard acid and the titration
finished as usual.
Determination of Ammonia Nitrogen: Magnesium Oxide Method.—Place
2 gm of sample in a Kjeldahl digestion flask with about 200 cc of water
and 5 gm or more of magnesium oxide which has been rendered free from
carbonates by a previous strong ignition. Connect the flask with a
condenser and distill 100 cc of the liquid into 50 cc of fifth-normal acid.
Titrate the excess with fifth-normal base solution, using methyl red. Calcu-
late the per cent of ammonia nitrogen.
Determination of Organic and Ammonia Nitrogen: Kjeldahl Method.—
The method described for organic nitrogen in feeds, page 151, includes also
nitrogen of ammonium salts if present, as they may be in fertilizers. Deter-
mine as there directed, using accurately weighed samples of about 2 gm.
Determination of Organic and Ammonia Nitrogen: Gunning Method.—
Determine as for organic nitrogen in feeds, page 154.
Nitrate Nitrogen.—When nitrogen is determined by these
methods most of the nitrate nitrogen is volatilized and lost upon