(2) Hydrochloric-acid testing. Aqua regia (nitrohydrochloric) acid consists of one part nitric
acid mixed with three parts of hydrochloric acid. Since this mixture breaks down after 24 hours,
perform the test by placing one drop of nitric acid and three drops of hydrochloric acid directly on the
spot being tested. This solution should turn blue-green for cobalt-based alloys and green for nickel-
(3) Potassium-ferricyanide testing. Use potassium ferricyanide (10 percent solution) to
determine the iron content of nickel-based alloys since there is no simple spot-testing for determining
the percent of nickel content. Perform this test by adding a drop of potassium ferricyanide to the spot
tested by aqua regia. The color reaction will be very dark blue-black for high iron content and light blue
for low iron content.
d. Complex Testing. Complex tests are qualitative tests consisting of a spectrographic or
chemical analysis. Use them only when a specimen cannot be identified by other tests or when the
quantity involved warrants it.