For concentrated nitric acid you can do the following reactions,
1) Put one drop of your soultion on clean Brass, it should give blue-green color
2)Put one drop of your soultion on clean Nickel, it should give pale green color
Neither of these tests will prove the concentration of HNO3. Even solutions graded as dilute or industrial would do the same. The way to test the concentration of HNO3 is to check the specific density. (25cc acid, weigh, divide by 25 to give grams per cubic centimeter, or specific gravity.) Check the standard SG chart for HNO3 and you have the absolute value.
1. When copper turnings react with conc. HNO3, reddish brown fumes of nitrogen dioxide gas evolves.
2. Nitric Acid satisfies the brown ring test.