Official test for identity of caffeine is
1
Substance + HCl + KCI \(\rm \xrightarrow{\Delta}\) NH3 vapours → Pink colour
2
Substance + HCl + KCIO3 \(\rm \xrightarrow{\Delta}\) NH3 vapours → Purple colour
3
Substance + HCl + KNO3 \(\rm \xrightarrow{\Delta}\) NH3 vapours → Green colous
4
Substance + HCl + KNO2 \(\rm \xrightarrow{\Delta}\) NH3 vapours → Blue colous