tungsten reacts slowly to form a brown-colored liquid
inexperienced person confused aluminum and
with a yellow sediment.
stainless steels. Remember that ferrous metals, being
iron-based alloys, are magnetic whereas nonferrous
Instead of the brown-black colors that usually
metals are nonmagnetic.
appear when ferrous metals are tested, various shades
of green and blue appear as the material dissolves
Nitric Acid Test
when nonferrous metals and alloys are subjected to the
nitric acid test. Except with nickel and Monel, the
reaction is vigorous. The reaction of nitric acid on
The nitric acid test is one of the easiest tests to
nickel proceeds slowly, developing a pale green color.
distinguish between stainless steel, Monel, copper
On Monel, the reaction takes place at about the same
nickel, carbon steels, and various other metals. You
rate as on ferrous metals, but the characteristic color
need no special training in chemistry to perform this
of the liquid is greenish-blue. Brass reacts vigorously,
test. However, you must observe the following safety
with the test material turning to a green color. Tin
precautions when using or handling acids of any type:
bronze, aluminum bronze, and copper all react
-- Never open more than one container of acid at
vigorously in the nitric acid test, with the liquid
changing to a blue-green color. Aluminum and
magnesium alloys, lead, lead-silver, and lead-tin
-- Use only glass containers when mixing or
alloys are soluble in nitric acid, but the blue or green
color is lacking.
-- In mixing, always pour acid slowly into water.
From the information given thus far, it is easy to
NEVER pour water into acid, because an
see that it will require considerable visual skills to
explosion is likely to occur.
identify the many different reactions of metals to nitric
acid. As an HT, you will be mostly concerned with the
-- If any acid is spilled, dilute it with plenty of
identification of stainless steel, Monel, and carbon
water to weaken it so that it can safely be
-- If an acid is spilled on the skin, wash
File Hardness Test
immediately with large quantities of water.
Then wash with a solution of borax and water.
Hardness tests are commonly used to determine
the ability of a material under test to resist abrasion or
-- Wear safety goggles. Clear-lens goggles will
penetration by another material. Many methods have
make it easier to detect the reaction of a metal
evolved for measuring the hardness of metal. The
to an acid test, which may be evidenced by a
simplest method is the file hardness test. This test
color change, the formation of a deposit, or the
cannot be used to make positive identification of
development of a spot.
metals but can be used to get a general idea of the type
-- Conduct tests in a well-ventilated area.
of metal being tested and to compare the hardness of
various metals on hand. Thus, when identification of
To perform the nitric acid test, place one or two
metal by other means is not possible, you might use a
drops of concentrated (full strength) nitric acid on a
file to determine the relative hardness of various
metal surface that has been cleaned by grinding or
metals. The results of such a test may enable you to
filing. Observe the resulting reaction (if any) for about
select a metal more suitable for the job being
2 minutes. Then add three or four drops of water, one
drop at a time, and continue observing the reaction. If
there is no reaction at all, the test material may be one
The file hardness test is simple to perform. The
of the stainless steels.
metal being tested may be held by hand and rested on
a bench, or held in a vise. Grasp the file, with the index
The reaction that results in a brown-colored liquid
finger extended along the file, and apply the file
indicates a plain carbon steel. A reaction producing a
slowly but firmly to the surface being tested.
brown to black color indicates a gray cast iron or one
of the alloy steels containing as its principal element
If the material is cut by the file with extreme
either chromium, molybdenum, or vanadium. Nickel
ease and tends to clog the spaces between the file
steel reacts to the nitric acid test by forming a brown
teeth, it is VERY SOFT. If the material offers some
to greenish-black liquid, while a steel containing
resistance to the cutting action of the file and tends to