MIL-PRF-26539F
4.3.2.1.3 Calculation. The percent NO shall be calculated by the following formulas:
x = B-A
y =C-B
⎡
x + y ⎞⎤
⎛
y - 0.003857⎜ z -
⎟ 187.5
⎢
1.49 ⎠⎥
⎝
NO, percent by wt = ⎣
⎦
- 0.15
x
where:
x = sample weight in grams.
y = O2 weight in grams.
z = volume of sample bomb in mL. Determined by difference in weight from evacuated and water
filled.
A = weight of empty sample bomb in grams.
B = weight of sample bomb plus sample in grams.
C = weight of sample bomb plus sample and O2 in grams.
4.3.2.2 Alternate procedure.
4.3.2.2.1 Preparation. Clamp the sampler specified in 4.3.2.1 to a stand as shown in Figure 1.
Attach a 1/16 inch ID length of polytetrafluoroethylene tubing to the outlet valve. Place another length of
1
/16 inch ID polytetrafluoroethylene tubing in a beaker containing a strong NaOH solution. Set this
apparatus up in a fume hood in which low pressure gaseous nitrogen, conforming to MIL-PRF-27401, is
available for purging excess N2O4 from the 1/16 inch ID polytetrafluoroethylene tubing. The flow-through
spectrophotometric cell depicted shall conform to the following:
a.
2.00 ± 0.02 mm sample path length.
b.
Coolant jacket for sample temperature control.
Constructed of material compatible with N2O4.
c.
d.
Constructed to fit instrument cell compartment.
Figure 2 and 3 show suggested designs. Maintain the temperature of the flow-through cell at 32 ± 1.8°F
(0 ± 1°C) by connecting the cell to a circulating ice-water glycol (20:1) bath located at the apparatus in the
fume hood and/or at the spectrophotometer. Maintain a purge of low pressure gaseous nitrogen,
conforming to MIL-PRF-27401, in the spectrophotometer cell compartment or on the cell assembly to
prevent condensation of moisture on the cell windows when the cell is in the spectrophotometer.
4.3.2.2.2 Procedure. Clamp a cylinder containing red-brown dinitrogen tetroxide (NTO) in the
apparatus according to Figure 1. Connect the spectrophotometric cell to the cylinder by means of 1/16
inch ID polytetrafluoroethylene tubing. Purge the cell with dry nitrogen for several minutes. Close the
inlet and outlet valves. Connect the cold bath to the cell and precool by pumping coolant for several
minutes. Open the lower valve on the N2O4 cylinder slightly and control the sample flow with the cell
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