FERTILIZERS 285
Nitrate and Ammonia Nitrogen.—These two forms of nitrogen
may be determined together by first reducing the nitrate to
ammonia by nascent hydrogen, then distilling the solution made
basic by magnesium hydroxide.
Determination of Nitrate and Ammonia Nitrogen: Iron Reduction
Method.—Place 1 gm of the sample in a 500-cc flask, add about 30 cc of
water and 3 gm of iron reduced by hydrogen. After standing long enough
to insure solution of nitrates and ammonium salts, add 10 cc of a mixture of
equal volumes of concentrated sulphuric acid and water; shake thoroughly,
place a funnel in the neck of the flask to prevent mechanical loss and allow to
stand until the reaction has moderated. Heat the solution slowly, then boil
for 5 minutes and cool. Add about 100 cc of water, a little paraffin to
prevent foaming and 10 gm of magnesium oxide, made free from carbonates
by previous strong ignition. Connect with the tin condenser and boil for
40 minutes, or nearly to dryness, collecting the distillate in 50 cc of fifth-
normal acid. Titrate the excess of acid with fifth-normal base, using methyl
red, and calculate nitrogen of nitrates and ammonia.
If the sample is known to consist of nitrates alone, proceed as above except
that 0.25 gm of the sample, is used, together with 5 gm of reduced iron.
After the boiling, add 75 cc of water and an excess of saturated sodium
hydroxide solution (instead of magnesium oxide), and distill as above
directed.
Availability of Nitrogen.—Mention has already been made of
the low fertilizing value of certain nitrogenous materials, due to
slowness of decomposition occurring when the fertilizer is added
to the soil. Nitrogen is probably directly assimilated by plants
only in the most highly oxidized form, i.e., that of nitrates.
Ammonium salts and certain organic materials, such as dried
blood, have almost as great value because they readily decompose
and oxidize in the soil, forming nitrates. Hoof, hair, leather
and hide are rich in nitrogen but they do not so decompose,
except very slowly, and a method for differentiating between
available and non-available forms of nitrogen is desirable. The
microscope will detect ground hair and other similar materials
but it can give only qualitative results. Fortunately qualita-
tive results are all that are necessary where the addition of such
materials is contrary to law, but for scientific purposes a quantita-
tive distinction between available and non-available nitrogen
may be of great practical use. An exact analytical method for
such a purpose seems to be impossible because there is no sharp
distinction to be made between the classes of fertilizer materials.