Chromium(III) oxide contains $\ce{Cr^3+}$ which can be detected through salt analysis. Only specific test for $\ce{Cr^3+}$ is mentioned.
- Source 1*
$$\ce{Cr^3+(aq) + 3OH^{–}(aq) -> Cr(OH)3(s)}$$
Chromium(III) hydroxide is formed when $\ce{Cr^3+}$ is treated with
ammonia or sodium hydroxide, which is soluble in excess alkaline
solution (amphoteric, dissolves in acids too) but not soluble in
excess ammonia . With sodium hydroxide, a dark green soluble
hexahydroxo–complex ion is formed.
$$\ce{Cr(OH)3(s) + 3NaOH(aq) -> [Cr(OH)6]^{3–}(aq)}$$
- Source 2**
Chromium can be taken through a series of colored tests which leaves
no doubt as to its identity. Chromium(III) forms a steel green
hydroxide which dissolves in excess strong base to give a deeply green
colored solution of the hydroxy complex. Treating this complex with 3%
hydrogen peroxide gives the yellow solution of the chromate ion, which
upon acidification with dilute nitric acid gives the orange color of
dichromate. Treatment of the cold solution of dichromate with 3%
hydrogen peroxide gives the intense blue color of a peroxide of
chromium. (The actual composition of this peroxide is not known, but
it is believed to have the empirical formula $\ce{CrO5}$). This
peroxide readily decomposes to the pale violet color of the original
hydrated chromium(III) ion. In low concentrations of dichromate the
blue color is fleeting, and attention must be focused on the test tube
during the addition of the hydrogen peroxide to avoid missing the
color change.
$$\ce{Cr(OH)^{4-} (green) + H2O2 + OH^{-}→ CrO4^{2-}(yellow)}$$
$$\ce{CrO4^{2-} + H+→ Cr2O7^{2-} (orange)}$$ $$\ce{Cr2O7^{2-} + H2O2 +
HNO3→ CrO5 (blue)→ [Cr(H2O)6]^3+ (violet)}$$
The following color changes are all indicative of $\ce{Cr^3+}$. Add an
excess of 6 M $\ce{NaOH}$ to about one mL of test solution. To this
green solution add 10 drops of 3% $\ce{H2O2}$. Heat the test tube in
the water bath until the excess $\ce{H2O2}$ is destroyed as indicated
by the cessation of bubbles. Acidify the yellow solution with 3 M
$\ce{HNO3}$. Cool the resulting orange solution in an ice bath. To the
cooled solution add a drop or two of 3% $\ce{H2O2}$ and observe the
immediate fleeting blue color.
Reference
*http://www.docbrown.info/page13/ChemicalTests/ChemicalTestsc.htm
**http://www.wiredchemist.com/chemistry/instructional/laboratory-tutorials/qualitative-analysis