MIL-DTL-757C
4.4.10 Lead. Transfer approximately 0.45 to 0.55 g of the dry sample weighed to the
nearest 0.1 mg to a 250 mL beaker. Add 10 mL of concentrated nitric acid and 10 mL of
concentrated sulfuric acid. Cover the beaker with a watch glass and heat at moderate
temperature on a hot plate until dense fumes of sulfur trioxide are evolved. (Oxides of sulfur and
nitrogen are toxic; precautions shall be taken to assure personnel are not exposed to these fumes.)
Allow the beaker to cool for about 2 minutes, add 5 mL of concentrated nitric acid, and heat
again until dense fumes of sulfur trioxide are evolved. Repeat the addition of nitric acid and
heating to fumes until all the organic matter is destroyed and the solution is practically colorless.
Remove the beaker from the hot plate and allow it to cool. Wash down the watch glass and side
walls of the beaker with about 10 mL of distilled water. Place the uncovered beaker on the hot
plate and again heat until dense fumes of sulfuric acid are evolved. Allow to cool, then
cautiously dilute to about 100 mL with distilled water and again allow to cool. Add 25 mL of 95
percent ethyl alcohol and let it stand for at least 2 hours. Filter through tared sintered porcelain
crucible of fine porosity. Transfer the precipitate to the crucible with 5 percent sulfuric acid and
twice with 95 percent ethyl alcohol. Dry in an oven at 100°C to 105°C for 1/2 hour and then
ignite in a muffle furnace at 550°C to 600°C for 15 minutes. Cool in a desiccator and weigh to
the nearest 0.1 mg. Calculate the percent lead in the sample as follows:
68.32 A
Percent lead =
W
where: A = weight of ignited residue, g
W = weight of sample, g
4.4.11 Nitrogen.
4.4.11.1 Apparatus. Storage and titration system are as shown in Figures 1 and 2.
4.4.11.2 Reagents.
4.4.11.2.1 Potassium dichromate solution (0.200 N). Dry standard potassium dichromate
(National Institute of Standards and Technology [NIST] reference material 136) in an oven at
110°C for 2 hours, cool, dissolve 9.8070 g in distilled water, and dilute to 1 liter in a volumetric
flask. This is a primary standard.
4.4.11.2.2 Acetic acid solution (25 percent). Add 250 mL of glacial acetic acid to 750
mL of distilled water.
4.4.11.2.3 Titanous chloride solution (0.2N). This solution can be prepared from either
20 percent titanous chloride solution or from titanium hydride.
4.4.11.2.3.1 Preparation from 20 percent titanous chloride solution. Filter about 150 mL
of 20 percent titanous chloride solution through a glass filtering crucible. Add 100 mL of
concentrated hydrochloric acid and mix by means of a current of inert gas (oxygen-free carbon
dioxide or nitrogen). Add 750 mL of oxygen-free distilled water and again mix by means of a
current of inert gas. Store in an amber bottle under carbon dioxide supplied by a Kipp generator
10
For Parts Inquires submit RFQ to Parts Hangar, Inc.
© Copyright 2015 Integrated Publishing, Inc.
A Service Disabled Veteran Owned Small Business