FED-STD-228A
4.2.2 Polyisobutylene spot test. This test shall be conducted as described for chloroprene-nitrile test in
4.2.1, using filter paper that has been moistened with the mercuric oxide sulfuric acid wetting solution.
4.2.3 Rubber-styrene spot test. The rubber-styrene spot test shall be conducted as described in 4.2.1,
using the p-dimethylaminebenzaldehyde-hydroquinone test paper moistened with the trichloroacetic acid-
isopropanol wetting solution.
4.2.4 The material tested in accordance with 4.2.1, 4.2.2, and 4.2.3, shall be classified by reference to
the colors listed in table II. The chloroprene-nitrile test shall be carried out first. If both of these
compounds are absent the other tests will be successful.
TABLE II
Material
Chloroprene-nitrile test Polyisobutylene test
Rubber-styrene test
Chloroprene
Red
Blank 1
Green
Nitrile
Green
Pale brown
Yellow green
Chloroprene-nitrile mixture Red/green
Do.
Green
Polyisobutylene
Blank 1
Yellow
Pale lavender
Natural rubber
Do. 1
Brown
Blue
Styrene
Do. 1
Do.
Blue green
1/ Blank color tests may be pale brown rather than colorless.
4.2.5 Mixtures of rubber compounds. Chloroprene-nitrile mixtures containing more than 30 percent of
chloroprene rubber give a green color on the wet portion and a red color on the dry portion of the spot test
paper when tested as described in 4.2.1 Chloroprene in quantities less than 30 percent cannot usually be
detected in this mixture. Chloroprene polymer will not normally mask natural or polyisobutylene
elastomers, but may mask a styrene polymer. Nitrile polymer will mask styrene and may also cause
some difficulty in detecting natural rubber. Polyisobutylene polymers normally can be detected in the
presence of moderate amounts of the other four elastomers. The chloroprene-nitrile test is not masked
by the presence of the other three materials. Styrene rubber is quite difficult to detect unless alone or
with only small amounts of other rubber compounds. Styrene elastomers and natural rubber together can
only be identified in the range of 50-50 mixtures. These spot tests are not always sufficient for detecting
all rubber compounds. However, a combination of these and the confirmatory tests, 4.3, are usually
satisfactory for identifying most all mixtures of elastomers.
4.3 Confirmatory tests. These tests may be used to conform the tests made in 4.1 and 4.2.
4.3.1 Chloroprene polymers.
4.3.1.1 Iodine test. Chloroprene polymers may be distinguished from the saturated poly-vinyl type by the
iodine test. A specimen of the elastomer compound shall be shaken with 2 ml. of iodine solution (0.2
gram of iodine per liter of carbon tetrachloride). The formation of a violet color which fades noticeably in 2
or 3 minutes indicates the presence of chloroprene.
4.3.1.2 Flame test. A specimen shall be burned in contact with a clean copper wire. A persistent green
flame indicates the presence of chlorine-containing polymers. This test is particularly applicable for
testing chlorine containing polymers in the presence of much nitrile polymer.
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