Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

DETEKMINATION OF NITKOGEN 47
rapid-weighing balance, or a similar " half-micro " balance with a
limit of accuracy of 0-01 mg. is used. 1
I. DETERMINATION OF NITROGEN BY DUMAS' METHOD
A weighed quantity of substance is ignited with copper oxide in
an atmosphere of carbon dioxide. The carbon is thus oxidised to
carbon dioxide and the hydrogen to water, whilst the nitrogen is
liberated as such and is determined volumetrically after collection
over potassium hydroxide solution. Any oxides of nitrogen which
may be formed are reduced to nitrogen by means of a glowing copper
spiral. For the determination of nitrogen the following are required
:
A combustion tube of heat-resistant glass having a constriction at
one end (length, without the constricted part 55 cm., external
diameter 12 mm., length of the constricted part 3 cm., external
diameter 3-3-5 mm., internal diameter 2 mm.).
A one-holed rubber stopper. This stopper should be as nearly
cylindrical as possible, should fit the wider opening of the tube,
and must sit close to the wall of the tube.
Wire-form copper oxide (" for analysis ").
Long-fibre asbestos wool.
Some silver wool.
Two asbestos plates and a roll of iron-wire gauze (length 5 cm.;.
Kipp apparatus, electric combustion furnace, 2 nitrometer, nickel
dish, sieve of wire gauze, weighing bottle, and mixing tube are
supplied by the laboratory.
PREPARING THE APPARATUS
Air-free Kipp fox Carbon Dioxide.—Cover small pieces of marble in
a porcelain basin with dilute hydrochloric acid (1 vol. of HC1, d. 1-18 +
1 vol. of water). After the first vigorous reaction has subsided pour
off the scum which collects on the surface and wash the chips with water.
Now more than half-fill the middle globe of the Kipp with the chips, the
opening from the lower globe being packed with chips of glass or closed
with two semicircular glass rods. When the gas is being delivered
from the apparatus it is taken from the highest point in the middle
1 Details of the technique of weighing will be found in the Introduction by F.
Holscher, Munich, 1934, State Chemical Laboratory. This book is privately
published.
a A suitable furnace is supplied by Griffin and Tatlock, London. The tube has
two'supports, nob one as in Fig. 32. The resistance is mounted on the base-plate.