FED-STD-791D
6.6 Carefully remove the glass fiber filter disc and dry it in oven at 110C for 15
min.
6.7 Remove the filter disc and cool it to 25 3C.
6.8 Add 3 drops of diphenylamine solution to the center of the disc and observe
whether a blue or blue-black color forms.
7. CALCULATIONS
7.1 This section is not applicable to the test procedure.
8. REPORTING
8.1 The presence of organic nitrate ester-type cetane improvers will be reported if
the formation of a blue color occurs. Reference samples of diesel fuels containing 0.5%
by volume of any one of the approved cetane improvers (amyl nitrate, cyclohexyl nitrate,
hexyl nitrate and isopropyl nitrate) give an intense blue to blue-black color throughout
the reagent spot whereas those samples containing only 0.1% by volume produce a blue
ring at the outer boundary of the reagent. If a positive reaction occurs (i.e., a blue or
blue-black coloration), the carbon residue determination (ASTM D524) must be
performed on a neat or base fuel blend.
9. PRECISION
9.1 Precision data have not been developed for this method.
Method Prepared by:
Army - ME - 1986
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