The Chemistry of Powder and Explosives - Sciencemadness Dot Org

DETERMINATION OF NITROGEN 271
action vessel. In the usual form of the instrument as used in
Europe, the gas from the reaction is measured in cubic centimeters
at atmospheric pressure, the barometer and the thermometer
are read, and the weight of the nitrogen in the nitric oxide
and the percentage of nitrogen in the sample are calculated.
In the extremely ingenious DuPont nitrometer, a 1-gram
sample is "used for the analysis, and the gas is collected in a
measuring tube which has been graduated to read, at a certain
temperature and pressure, the correct percentage of nitrogen in
the 1-gram sample. By means of a compensating bulb and leveling
device, the gas in the measuring tube is brought to the volume
which it would occupy if it were confined at the temperature and
pressure at which the graduations are correct, and the percentage
of nitrogen is then read off directly. The DuPont nitrometer 103
was invented by Francis I. DuPont about 1896. It quickly came
into general use in the United States, and represents the form of
the nitrometer which is preferred and generally used in this country.
Lunge in 1901 claimed that it differs in no significant respect
from the "gasvolumeter" or "five-part nitrometer" 104 which he
had described in 1890.
Calibration and Use of the DuPont Nitrometer. The five essential
parts of the DuPont nitrometer are illustrated in Figure 68. The graduations
on the measuring bulb correspond to dry nitric oxide measured
at 20° and 760 mm., which nitric oxide contains the indicated number
of centigrams of nitrogen. Thus, the point marked 10 indicates the
volume which would be occupied under the standard conditions of temperature
and pressure by the quantity of dry nitric oxide which contains
0.10 gram of nitrogen, that is, by the nitric oxide produced in
the nitrometer reaction from a 1-gram sample of nitrate containing
10% nitrogen. The point marked 12 corresponds to 12/10 of this
volume, that marked 14 to 14/10, and so on, And the tube reads correctly
the per cent of nitrogen in a 1-gram sample provided the gas is
measured at 20° and 760 mm.
In setting up the instrument, dry air is introduced into the compensating
bulb and the outlet at the upper end of the bulb is sealed.
Dry air is introduced into the measuring bulb, the outlet is connected
to a sulfuric-acid manometer, and the mercury reservoir and the compensating
bulb are raised or lowered until the portions of air confined
10 3 Pitman, /. Sec. Chem. hid., 19, 982 (1900).
id., 9, 547 (1890); 20, 100 (1901).